The indigenous helium refrigerator-cum-liquefier (HRL) plant of capacity 200 W at 4.5 K has been developed, operated and tested successfully in Mar-2023. The indigenously developed cold box of this plant has three helium turbines, seven plate-fin heat exchangers and one helium purifier at 80 K. It uses LN2-precooling. Turbines are normally designed for a particular nominal flow parameters to get the best efficiency at the design state point of operation. Three turbines of this indigenous helium plant have nominal operating inlet temperatures of helium as 33, 15, and 7 K, respectively. As per design, these turbines can also be operated safely with a room-temperature helium gas flow, provided a controlled flow is maintained. During start-ups of the plant and turbines, it becomes unavoidable to operate these turbines with room temperature helium flow. Later, gradually, it cools down to low temperature flow. In the past, there have been many events, where helium turbines failed during start-ups of the plant possibly due to operation at a speed beyond the safe limit. Hence it was necessary to understand what should be the controlled flow rate at different off-nominal temperature and pressures for safe operation of turbines. It is required to find, how much, the inlet control valve for the turbine should be opened with respect to inlet pressure and temperature, so that, flow through turbine will not lead to over-speed and damage of turbine. The details of this analysis and control strategies including a cooldown sequence used for safe operations will be discussed in this paper.

In recent years, the Experimental Advanced Superconducting Tokamak (EAST) has made a series of significant physical advances. As one of its critical subsystems, the 2kW/4.5K helium cryogenic system provides the cooling power for the superconducting magnets and other cold components of the EAST Tokamak. It has been operated over 3000 days since the first cool-down commissioning in 2006. Since 2021 till now, the annual cumulative operation time of the EAST cryogenic system has exceeded 250 days, during which there were no faults caused by the cryogenic system affecting the physical experiment occurred. And the longest continuous operation time of a single experiment campaign for the cryogenic system even reached 268 days. The EAST cryogenic system has completed a series of reconstruction and upgrades, which played a crucial role in improving system reliability and availability. This paper will present the main cryogenic engineering progress in recent five years, including the remote control and mobile supervision, the vibration monitoring and fault prognosis in helium warm compressors, and the design and testing of redundant helium recovery compressors and redundant turbine systems in helium refrigerator. The operational present status of the EAST cryogenic system will be analyzed, and also its operation and maintenance experience will be summarized in the end.

This study investigates steady-state and dynamic simulations of the SPARC Cryoplant (CRYP) to characterize its nominal and transient behavior. The simulation scope encompasses the warm compressor skid (WCS), oil removal system, gas management panel (GMP), and the Cold Box (CBX) designed by Linde Kryotechnik AG. The CBX supplies helium to the tokamak at three temperature levels: 80 K, 15 K, and 8 K. The 80 K stream, chilled by liquid nitrogen, cools the copper magnets and thermal shields. Simultaneously, three strings of turbo-expanders cool the helium to 15 K and 8 K to maintain the superconducting magnets and feeder cables at design temperatures. While the EcosimPro model excludes the full external cryogenic distribution loops, loop flow rates and heat loads are replicated using bypass valves paired with ambient heaters (for the 80 K level) or electrical heaters (for the 15 K and 8 K levels). Model validation is performed by comparing steady-state results against design T-S diagrams provided by the manufacturer and Site Acceptance Test (SAT) data obtained during CBX cooldown. Transient validation focuses on two methods of CBX cooldown from 300 K to 80 K, followed by the introduction of LN2 and further cooling to lower temperatures. Finally, the model validates various steady-state operational modes-including TF-ON, TF-OFF, DT/DD pulse and recovery, and high-temperature bake - by applying specific heat loads for each loop. Results indicate excellent agreement with SAT data during the 300 K to 80 K cooldown phase, while steady-state simulations for TF-ON and DT/DD pulse modes reproduced design T-S diagrams with a deviation within ±6.5%.

With the increasing integration of renewable energy into the power grid, energy storage technologies capable of addressing the intermittency and volatility of renewable sources are attracting growing attention. Liquid air energy storage (LAES) is a promising large-scale energy storage technology due to its minimal geographical constraints and operational flexibility. However, the round-trip efficiency (RTE) of standalone LAES systems remains relatively low. Concurrently, the rapid development of the hydrogen economy has driven a rising demand for liquid hydrogen (LH₂). However, the high-grade cold energy released during liquid hydrogen gasification is often underutilized, resulting in significant energy waste. To address these challenges synergistically, this paper proposes a novel integrated system that deeply integrates liquid hydrogen cold energy recovery with LAES (LH₂-LAES). Targeting scenarios requiring continuous hydrogen regasification, the system aims to enhance overall energy efficiency. A thermodynamic model of the LH₂-LAES system is established and analyzed based on relevant parameters. The study demonstrates that the coupled system achieves a higher RTE compared to standalone LAES systems, offering an efficient and low-carbon innovative pathway for the integrated development of hydrogen infrastructure and large-scale energy storage technologies.

The Electron-Ion Collider (EIC), a next-generation nuclear physics research facility under development at Brookhaven National Laboratory (BNL), represents a unique scientific endeavor that builds upon the existing Relativistic Heavy Ion Collider (RHIC) infrastructure. The EIC will incorporate a new electron injector and storage ring while leveraging RHIC’s cryogenic and accelerator systems to enable precision studies of the internal structure of protons and nuclei. Cryogenics play a vital role in the EIC’s operation, supporting key superconducting components such as magnets, radiofrequency (RF) cavities, current leads, and power couplers, all of which require cooling at multiple temperature levels. In order the handle temperatures below 4.5K, supplemental satellites systems will be located at specific locations around the collider to locally generate 1.9K and 2K cooling for the lower operating temperature required for certain devices. The original central plant was designed for a different project and was adapted to handle the smaller RHIC loads more efficiently. The central plant will again be adapted from its RHIC configuration to handle the various loads imposed by the EIC cryogenic elements and the new cryogenic satellites producing local 1.9K cooling. The final EIC loading on the central plant, which is higher than the RHIC loading, consists of isothermal loads, various non-isothermal loads returning at different temperatures and full liquefaction loads. While the current cryogenic infrastructure can accommodate the EIC’s additional thermal loads, this integration introduces several engineering challenges but also opportunities, to improve efficiency, to improve operation costs, and to minimize the increased compressor power demand. To achieve optimal performance and energy efficiency, significant upgrades to the cold ends comprising cold end expanders, with their associated heat exchangers, and tie-in of new return streams at different temperatures into the heat exchanger stack are under evaluation. This paper presents a summary of the updated EIC cryogenic load profile and explores several configurations of cold end expander arrangements with corresponding operational points. Comparative analysis of these configurations is conducted to identify optimal solutions that balance operational efficiency, reliability, and flexibility, ensuring robust cryogenic support for the EIC’s advanced scientific mission.

Liquid air energy storage (LAES) is a promising cryogenic energy storage technology involving air compression, liquefaction, and power generation through expansion. During operation, the compression stage requires effective heat absorption, while the expansion process depends on a continuous supply of heat. Under independent operation, these thermal requirements are mainly satisfied through internal thermal coupling and environmental heat exchange. However, such approaches are constrained by mismatches in temperature level and time scale, resulting in significant irreversibilities. An integrated LAES–thermal power plant scheme is proposed, and a corresponding thermodynamic model is developed. Steam extraction, condensate water, and feedwater from the power plant are incorporated as multi-level heat sources and heat sinks to analyze the operating characteristics and thermodynamic performance of the coupled system under integrated conditions. The study provides insights into cryogenic process optimization of LAES systems and their coordinated operation with conventional power generation systems.

The Rare isotope Accelerator complex for ON-line experiments (RAON) is a heavy-ion accelerator facility constructed at the Institute for Rare Isotope Science (IRIS) in South Korea. The superconducting linear accelerator SCL3, designed for low-energy experiments, is connected to the SCL3 cryogenic plant, which provides cooling capacity at 2.05 K, 4.5 K, and 35-55 K for the superconducting cavities and thermal shields. SCL3 has successfully completed three cooldown operations since 2022, utilizing subcooled liquid helium supplied by the SCL3 cryogenic plant. In 2022, the plant demonstrated 4.2 kW of the equivalent power at 4.5 K during a 24-hour continuous performance test, enabling stable operation of the whole superconducting system. Following two cooling operation periods from 2022 to 2024, a major overhaul was carried out from October 2024 to March 2025 to maintain cooling performance and operational availability. After the overhaul, the third cooldown process was conducted, and continuous cooling operation for more than 20 months is currently planned. During operation of the cryogenic system, several minor issues were identified, leading to unexpected downtime at 2.05 K. This paper analyzes the operational results before and after the three-year overhaul and presents an approach to enhance 2.05 K availability.

The Crab Cavity Project (beam deflecting RF system) takes part in the High Luminosity LHC (HL-LHC) Project, which is a major upgrade of the LHC accelerator at CERN. The Crab Cavities system will be installed on both sides of the ATLAS and CMS detectors. Two types of cavities were designed for the system: Double-Quarter Wave (DQW) and Radio Frequency Dipole (RFD). The first module, as demonstrator of the proton beam deflection capability, was built with DQW cavities and successfully tested between 2018 and 2023. The second prototype module, containing RFD cavities, was constructed as compatible for the HL-LHC in terms of the process, geometry and interfaces. Extensive campaign for the operational testing of the RFD module was handled in 2025 in the SPS BA6 RF testing facility. This paper will describe cryogenic design solutions adopted for the RFD module and will summarize thermal response of the module during different phases of testing. The test successes and unexpected findings leading to design adjustments will be discussed.

For several years now, hydrogen contaminations in liquid helium have been recognized as a problem. A number of industrial helium extraction plants in the Mediterranean region have been pinpointed by the authors as possible sources. Hydrogen contaminations, meanwhile, are found in a large number of local helium liquefaction plants. These impurities were brought in with the helium deliveries and continue to accumulate. This often results in significant operational disruptions at the universities or research institutes affected: for example, blockages in helium flow cryostats or in throttle sections of pumped systems are frequently observed. Therefore, the HyLiqHe research project aims to investigate this issue in more detail. The project is funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation). The solubility of hydrogen in liquid helium is very low and the exact value remains unknown. Preliminary results indicate a solubility limit slightly below 100 volumetric parts per billion (ppb v ); however, dispersion of solid hydrogen in the cold gas and in the liquid phase seem to play a role as well. At TUD, appropriate measurements on that are underway. In addition to reliably quantifying hydrogen in the ppb range, it is particularly challenging to distinguish between dispersion and solution within the liquid. However, it is not only the cryogenic liquid phase that is of interest. Understanding the distribution of concentrations in cryogenic systems also provides insight into the characteristics of such contaminations. A large number of measurement series were performed exemplarily at the TUD helium facilities, to track the hydrogen path through the plant. The results are discussed; they support existing hypotheses on the con-tamination behavior within cryogenic facilities.

The Shenzhen Superconducting Soft X-ray Free Electron Laser (S 3 FEL) is a major facility under development in Guangdong, China, designed to generate ultra-bright, ultrafast X-ray pulses for advanced scientific research. The project, approved for construction in 2023, was officially launched in December 2025 and is managed and constructed by the Institute of Advanced Light Source Facilities, Shenzhen (IASF). The S3FEL accelerator is based on superconducting radio-frequency (SRF) cavity technology, and its cryomodules (CMs) of the linear accelerator are designed to operate at 2 K, with additional cooling at 5 K for thermal intercepts and 40 K for thermal shielding. To meet the facility’s cryogenic requirements, three cryoplants will be built: a Test Facility Cryo-Plant (TFCP), a LINAC Test Facility Cryo-Plant (LTCP), and an Accelerator Cryo-Plant (ACCP). This paper presents a comprehensive overview of the three cryoplants, cryogenic distribution system, utility system, helium management system, etc.. Emphasis is placed on the design choices, update of the cryogenic processes, and heat load related to the modifications of the accelerator general physical layout, as well as on helium inventory and energy consumption. A preliminary installation and commissioning timeline has been established, with cryoplant procurement scheduled for completion in 2026. The TFCP and LTCP are planned to be commissioned by 2028, followed by the completion of the ACCP construction and commissioning by 2031, paving the way for integrated accelerator commissioning.

Shenzhen Superconducting Soft X-ray Free Electron Laser (S 3 FEL), located at Shenzhen, China, aims to construct a new light source that can generate high brightness X-Ray pulses. S 3 FEL, which consists of 25 cryomodules, based on the Superconducting Radio Frequency (SRF) technology for the linear accelerator operating in continuous wave. Before the construction of the S 3 FEL, the Superconducting Cryogenics Test Facility (SCTF) will be built to test the key SRF components and cryomodules. A Test Facility Cryo-Plant (TFCP) with an equivalent cooling capacity of 370 W@2 K has been built to provide the cryogens for the test facilities. The cold box of TFCP was designed to provide 4000 W cooling capacity at the temperature range 40-80 K, and a total mass flow of 30.4 g/s helium at a pressure of 3.5 bara and a temperature of 4.6 K. The refrigerator will be able to cope with simultaneous cooling loads for each of the steady-state operation modes including nominal design mode, turn-down mode and liquefaction mode. In this paper, the basic flowchart of the refrigerator and the thermodynamic analysis of the refrigeration cycle are presented. The exergy analysis of refrigerator on different operation modes are conducted to provide a theoretical basis for optimizing its future performance in terms of both efficiency and economy.

Demaco will present the design and progress of the Cryogenic Distribution System for the LCLS-II-HE. The project is built at SLAC, Stanford University on top of the San Andreas fault. Demaco has built, manufacured and installed the Inteface Box, Surface Transfer Lines, Feedcap and Endcap. The prestentation will contain the more details of the Scope of the project, Technical challenges, Lessons Learned and schedule challenges.

The High Luminosity LHC (HL-LHC) project is aiming to upgrade of the Large Hadron Collider (LHC) at CERN will increase peak luminosity by a factor of five with respect to its nominal value. This upgrade will include the replacement of the final focusing superconducting magnets and additional superconducting radiofrequency crab cavities in the long straight sections of the interaction points 1 and 5 of LHC. The increased luminosity will significantly increase the cryogenic heat loads in points 1 and 5 of the LHC accelerator. Therefore, two new refrigerators will be required in points 1 and 5, with each an equivalent capacity of 14 kW@4.5 K, including 3.25 kW@1.9 K. This paper presents the architecture and final design of the HL-LHC Refrigerators under commissioning at CERN. It provides the cryoplant characteristics, the layout and the necessary infrastructure requested to support the refrigerators as well as the main challenges of the installation.

Modeling and simulation methods for helium liquefaction and refrigeration cycles under cryogenic conditions have received limited attention. In commercial process simulators, the sequential modular approach is widely used; however, for complex helium cycles with multiple recycle loops, this approach requires extensive manual definition of tear streams and iteration logic. As process configurations frequently change during design, convergence control becomes increasingly difficult, resulting in low efficiency and limited suitability for system-level optimization. To address these issues, this study proposes a modeling and simulation method for helium liquefaction cycles based on the simultaneous solution of nonlinear equation systems using a trust-region dogleg algorithm. In contrast to the sequential modular approach, all governing equations describing the cycle are solved concurrently, provided that the number of equations equals the number of unknown variables. Component input parameters, output parameters, and design variables can be flexibly defined as known or unknown according to modeling objectives, eliminating the need for artificial tear-stream specification and simplifying the solution strategy. A typical large-scale helium liquefaction system consisting of a compressor station and a cold box is modeled. The cold box includes multiple reverse Brayton refrigeration stages and a final liquefaction stage. When the number of refrigeration stages equals two, the system reduces to the classical Collins helium liquefaction cycle. The model is implemented in a MATLAB environment, and helium thermophysical properties are obtained from the HEPAK database. To validate the proposed method, a Collins cycle with two turbines reported in the literature is analyzed. Key node temperatures and liquefaction performance are compared with published results. The relative deviations of calculated temperatures are within 1.5% under different initial value selections. In addition, the evolution of variables with respect to pseudo-time demonstrates stable and robust convergence behavior, confirming the numerical reliability of the trust-region dogleg–based solution strategy. The proposed simultaneous-equation modeling method provides a clear, stable, and extensible framework for the simulation of large-scale helium liquefaction systems, offering a solid foundation for subsequent system-level analysis and optimization of complex cryogenic processes.

The process control of cold compressor operation was investigated using a dynamic simulation model of the 2 K Cold Box (2K-CB) of the Central Helium Liquefier (CHL) at Oak Ridge National Laboratory. The 2K-CB consists of four cold compressors connected in series and is used to reduce the LINAC pressure from atmospheric conditions to its nominal operating level of 0.04 bar, producing 2.4 kW at 2 K operation. Several control strategies were evaluated, providing insights into cold compressor operational behavior and stability. In parallel, the effect of return flow variations from the 2K-CB on the 4K-CB were analyzed. The paper presents a detailed discussion of the transient operating behavior of CHL under these conditions.

The Steady State Superconducting Tokamak (SST-1) has Toroidal Field (TF) and Poloidal field (PF) Superconducting Magnet Systems (SCMS). There are total sixteen TF coils and nine PF coils. IPR has dedicated Helium Refrigerator and Liquefier (HRL) system of 1.3 kW at 4.5K to cool the SCMS of SST-1 either in two-phase Helium cooling or single phase Helium cooling using a cold circulator. The HRL system is integrated with other subsystems such as Integrated Flow Distribution and Control System (IFDCS), Current Feeder System (CFS), Warm Gas Management (WGM) system and LN 2 Management system with 80K Valve Box. Recently, we carried out dedicated SST-1 campaign for its cryogenic thermal load assessment. Detailed maintenance activities were planned for trouble-free operation of all cryogenic subsystems prior to carrying out a month long SST-1 campaign. The major activities were overhauling of Helium screw compressor for reliable long term operation, installation of new electrical motor for this overhauled compressor, upgradation of safety elements of Main Control Dewar (MCD), installation of additional temperature sensors on 4.5K and 80K surfaces of IFDCS/ CFS to understand thermal behaviour, in-house repairing of obsoleted IO modules of cold box PC3000 PLC and replacement of faulty positioner for electro-pneumatic control valves etc. Standard Operating Procedure (SOP) was implemented to remove impurities from Helium gas. The SOP covers a protocol of long regeneration of charcoal bed of Oil Removal System by dry nitrogen gas, extended regeneration of 80K heat exchanger and charcoal bed of on-line purifier and preconditioning activities of cold box and SST-1 SCMS. After above maintenance activities, we successfully operated all cryogenic subsystems for a month long SST-1 campaign. During the SST-1 campaign, TF SCMS was charged with its near nominal current and magnetic field for several hours. The paper describes the detail of maintenance activities with some technical challenges and engineering practices followed for such large cryogenic plant system and cryo distribution system. The maintenance activities and related technical experience discussed in this paper will be very helpful for cryogenics systems of future fusion devices.

SLAC National Accelerator Laboratory (SLAC) is installing a string of 23 superconducting radio frequency (SRF) Cryomodules (CM) on their existing LCLS-II X-Ray Free Electron Laser (XFEL) as part of their High Energy (LCLSII-HE) upgrade to achieve 8.0 GeV. The supply of cryogenic helium to these CMs is provided by the existing LCLSII helium refrigeration system with 4000 W @ 2.0 K capacity, and by a new cryogenic distribution system (installation target completion by September 2026). The new cryogenic distribution system consists of 3 cryogenic circuits flowing through an interface box, 300 m of multi-pipe transferlines, a distribution box with a 2K-4K heat exchanger and feed and end caps. The design and installation of these components was a multi-year collaboration between SLAC and Fermilab engineering teams. This paper details the functionality, design evolution, and challenges faced during the development of the new distribution system.

The LCLS-II X-ray light source, powered by a 700 m superconducting LINAC, is supported by two 4 kW @ 2.0 K cryoplants. The first cryoplant was commissioned in 2021 and cooled the LINAC to operating temperature in March 2022. This paper presents an analysis of the cryoplant’s operational performance and reliability over past four years of operation. Analysis includes reporting of key metrics, including Mean Time Between Failures (MTBF) and Mean Time to Recovery (MTTR). The paper summarizes the intrinsic and extrinsic factors that contributed to downtime and the mitigation strategies implemented to improve availability. Lessons learned are discussed with the objective of informing the design and operation of future large-scale 2 K cryogenic systems, with emphasis on reliability, maintainability, and sustained high-availability operation.

The European XFEL's planned High Duty Cycle (HDC) upgrade necessitates enhanced thermal management of cryomodules while maintaining stable cryogenic operation. Previous investigations established maximum heat-load limits for EuXFEL cryomodules using the Taitel-Dukler criteria to delineate stratified smooth-to-wavy (SS-SW) and stratified-to-non-stratified (S‑NS) flow transitions in the two-phase pipe (2PP). The present work extends this foundational framework through complementary investigations of two-phase helium II flow stability in L3 string configurations for HDC XTL. Due to the fact that each cryomodule (CM) in L3 has two connections available between the 2PP and the gas return pipe (GRP) placed at opposite sides of the GRP, the flow map of the boil-off gas in the 2PP will depend on the position of the CM relatively to the cold compressors (CCs). This causes the appearance of a bypass effect: the closer a CM to CCs, the more asymmetrical the flow map of the boil-off gas, the smaller the limiting heat load for this CM. The study derives analytical expressions for limiting heat loads in L3 strings affected and not affected by the bypass problem using both SS-SW and S-NS criteria, explicitly accounting for separate contributions from flash gas and boil-off gas. The SS-SW analysis reveals a crucial influence of the flash gas, where downstream strings exhibit much smaller limiting heat loads than the upstream ones. This results in the total L3 limiting heat load much below that required for the HDC operation. The flash gas influence can be eliminated by relocation of an additional JT valve to the middle of each string with outlet flow split symmetrically about central 2PP-GRP connections so that the flash-gas flow appears in zero-liquid-velocity sections. The solution also reduces the maximal LHe II velocity and thus the bypass problem. With optimized 2PP filling grades and strategically positioned additional valves, the L3 section can achieve the required 4 W per cavity design specification across all strings. In turn, the S-NS analysis shows that the required L3 limiting heat load can be achieved with the current L3 design. This reveals a wide "grey zone" between the two criteria, with SS-SW limits defining a conservative safe operating region and S-NS limits establishing an optimistic threshold. The findings of the study quantify the combined effects of helium quality, filling level, JT-valve placement, and string design on thermal performance while effectively avoiding flow instabilities. This information directly supports the HDC upgrade and provides a methodology that can be applied to future XFEL-class accelerators.

LCLS-II will be the first XFEL to be based on continuous-wave superconducting accelerator technology (CW-SCRF), with a linac energy of 4 GeV and two tunable-gap undulators (SXU, HXU), to generate X-ray pulses from 0.25 to 5 keV (2.5 Å) at repetition rates up to 1 MHz. In parallel, the existing LCLS normal conducting linac will generate very high peak power pulses at 120 Hz at photon energies up to 25 keV. The LCLS-II-HE project will increase the energy of the CW-SCRF linac to 8 GeV, enabling the photon energy range to be extended to at least 13 keV and potentially up to 20 keV at 1 MHz repetition rates. LCLS-II-HE’s Cryogenic Distribution System (CDS) will connect existing Cryoplant 1&2 to the new HE cryomodules. Reference designs have been completed for all components. Demaco has been contracted is working on detailed designs and fabrication, and eventually on-site installation as well.

With 15 years at the forefront of Turbo-Brayton commercialization, Air Liquide continues to adapt this robust technology for the world’s most demanding cryogenic challenges. The Turbo-Brayton cycle has established itself as an industry standard for onboard LNG reliquefaction and biogas liquefaction, prized for its operational simplicity, high reliability, and multi-megawatt scalability. Today, the technology is crossing a new frontier: reaching sub-20 K temperature regimes. Driven by the emerging requirements of HTS magnets for nuclear fusion and large-scale scientific research, the system continues to push the boundaries of cryogenic power. This paper examines the historical trajectory and the future scaling of Turbo-Brayton systems as they transition toward high-capacity & low temperature applications.

The High‑Luminosity upgrade of the Large Hadron Collider (HL‑LHC) at CERN is a major project designed to increase its levelled instantaneous luminosity by a factor of five with respect to the LHC design value. This upgrade requires, among other changes, the replacement of the final focusing superconducting magnets and the implementation of superconducting radiofrequency crab cavities in the long straight sections of interaction points 1 (ATLAS) and 5 (CMS). The cryogenic scope of the HL‑LHC upgrade encompasses the design, specification, procurement, installation, commissioning, and handover to operation of two new cryogenic plants and distribution systems at the high-luminosity interaction points 1 and 5. Each cryogenic plant, with an equivalent capacity of 14 kW at 4.5 K, including 3.25 kW at 1.9 K, has been designed to meet the expected heat loads of the new superconducting magnets, crab cavities, cold powering systems, and distribution elements. This paper provides an overview of the HL‑LHC cryogenic architecture, outlines the operating modes to be addressed during the commissioning and test phases, and presents the general status of the project, with a particular emphasis on the installation and commissioning activities.

Conventional helium purification systems primarily rely on adsorption-based technologies using molecular sieves or similar porous media. While effective at moderate contamination levels, adsorption systems face limitations in achieving sustained sub-ppmv moisture removal due to gradual loss of adsorbent capacity and the need for complex and carefully controlled regeneration procedures. These challenges motivate the development of alternative purification approaches capable of robust and continuous removal of trace moisture at cryogenic temperatures. Freeze-out purification offers an attractive alternative by exploiting the strong exponential dependence of saturated vapor pressure on temperature. At sufficiently low temperatures, water vapor can be removed from helium through controlled condensation and solidification on cold surfaces, eliminating reliance on adsorption media. This work presents an experimental characterization of a novel freeze-out heat exchanger based helium purification system developed at the Facility for Rare Isotope Beams (FRIB). The purifier employs a compact cross-counterflow, coiled finned-tube heat exchanger designed to promote controlled moisture freeze-out while maintaining acceptable thermal performance and pressure drop. A dedicated experimental test bench was constructed to evaluate purifier performance under well-defined operating conditions. The facility integrates the freeze-out heat exchanger with a calibrated moisture injection system capable of introducing controlled water vapor concentrations between 5 and 100 ppm v into a helium stream. Time-resolved measurements of thermal effectiveness, pressure drop evolution, and accumulated frost mass were obtained to characterize freeze-out dynamics and their impact on system performance. These results are benchmarked against those of a commercial helium purification system operating under comparable conditions. The moisture collection capacity of the developed purifier was found to be at least 3 times higher than a commercially available helium purification system of similar size. The experimental data provide new insight into the coupled heat transfer, mass transfer, and flow phenomena governing freeze-out purification in cryogenic helium systems, supporting its application as a viable alternative to adsorption-based systems in large-scale helium refrigeration plants.

Based on the requirements of SHINE (Shanghai High‑repetition‑rate XFEL and Extreme light facility) for the superfluid helium temperature regime, this paper conducts an in‑depth analysis and comparison of three mainstream pressure‑reduction cooling technical approaches. Accordingly, a large‑scale 1.8 K/2 K superfluid helium cryogenic system has been developed and realized. The core of the system integrates a 4.5 K helium refrigerator, multi‑stage heat exchangers, and a pressure‑reduction unit that couples a four‑stage cold compressor with a negative‑pressure screw compressor, thereby establishing an efficient and stable cryogenic thermodynamic cycle. Commissioning results demonstrate that the system successfully achieves stable production of 4 kW@2 K superfluid helium and performance boundary testing in the 1.8 K range, with all key performance parameters meeting or exceeding design expectations. The system has been connected to the first cryomodule of the facility for integrated commissioning and operation, achieving a one‑time pressure‑reduction success rate exceeding 73% under 2 K conditions. The successful operation of this system provides a reliable technical route and valuable engineering experience for the realization of ultra‑low‑temperature environments in future large‑scale scientific projects in China.

The Sanford Underground Research Facility (SURF) will host the Far Detectors of the Deep Underground Neutrino Experiment (DUNE), an international multi-kiloton long-baseline neutrino experiment located 1.5 km underground in Lead, South Dakota. The experiment relies on four massive cryostats containing approximately 70,000 metric tons of ultrapure liquid argon (LAr). To maintain a required impurity level of less than 100 parts per trillion (ppt) oxygen equivalent, the Long-Baseline Neutrino Facility (LBNF) has engineered a massive and highly integrated cryogenic infrastructure. This contribution details the operational modes, layout, and technical specifications of the LBNF Far Detector cryogenics. The system architecture is divided into several critical subsystems: - Argon Receiving and Surface Facilities: Includes liquid argon reception, automated purity screening via gas analysis, and vaporization systems for gas-phase transfer to the underground caverns. - Nitrogen Refrigeration System: Provides the primary cooling power for the experiment, utilizing a high-capacity refrigeration cycle, buffer storage, and a distribution network serving the argon condensers. - Purification and Regeneration: Employs molecular sieves and copper beds to achieve and maintain cryogenic purity. This system includes specialized protocols for the activation and periodic regeneration of media to ensure long-term impurity trapping. - Circulation and Condensation: Features redundant pump sets for bulk liquid circulation and a condenser system that utilizes nitrogen-cooled condensers to recondense and return argon boil-off to the cryostats via argon phase separators. - Argon Distribution and Internal Cryogenics: Manages the cryogenic distribution across the caverns and within the cryostats for commissioning, controlled cool-down, and steady-state operations. - Process Controls: A robust PLC-based control system with HMI integration ensures precise operation and strict Oxygen Deficiency Hazard (ODH) safety compliance. Managed by an international engineering collaboration, these systems are currently in an advanced stage of development. While several subsystems are in the final design phase, others have reached design finalization and are well into the manufacturing stage. This presentation provides an overview of the system’s functional requirements and technical performance, alongside a status report on current manufacturing and qualification milestones.

Isothermal helium cooling below 2K is essential for the development of future technologies and scientific advances, such as quantum computing and particle accelerators, which rely on superconducting magnets. The main challenge at these temperatures is the extremely low absolute pressure (15–35 mbar.a), which results in a very low return-flow density. This significantly impacts the capacity of warm helium compressors or process vacuum pumps, and it is not possible to process this flow in heat exchangers due to the limited available pressure drop. For small 2K loads ( In order to handle larger loads (> 500 W) and improve overall efficiency, the 2K return flow must be processed through the coldbox heat exchangers. Cold compressors enable the return flow to be compressed directly to above 500 mbar.a, or even to above 1 bar.a, achieving discharge temperatures of 20K – 30K. This reduces the required capacity of the vacuum pumps and enables efficient heat exchange with the high-pressure supply flow. Hybrid compression concepts, as implemented at ESS LUND and CERN HiLumi, exemplify this approach. Different approaches to achieving 2K cooling are illustrated. A design study has been conducted for the planned upgrade of the DESY XFEL facility. This study has developed a possible design for a new cold compressor coldbox, which can be used alongside two existing 4.5K plants to deliver a 2K load. Unlike new installations, this retrofit introduces unique challenges. For instance, integrating a new cold compressor box with two older 4.5K plants necessitates compressing the return flow to over 1 bar.a by a cold compressor string. The pressure ratio of the cold compressor string remains constant, even under varying loads, resulting in the generation of make-up flow during turndown conditions. Additional constraints, such as the limited size of the cold compressor coldbox to allow it to be transported into the building, further complicate implementation.

The superconducting accelerator of the Shanghai High Repetition rate XFEL and Extreme light facility (SHINE) operates at cryogenic temperatures to ensure its stability. To this end, the developed cryogenic system must provide cooling at temperature levels of 2K, 5K, and 40K for the superconducting cavities, cold interceptions, and thermal shields, respectively. Considering safety margins, three large-scale superfluid helium cryogenic systems have been designed and developed at both ends of the SHINE linear accelerator, each capable of providing 4 kW of cooling capacity at the 2K temperature level. This paper details the key components of the SHINE cryogenic system, covering the helium refrigerators that generate the cooling power, the cryogenic distribution system that delivers the cryogens to the superconducting accelerator, and the auxiliary systems handling liquid nitrogen and helium gas. To date, all equipment for the three cryogenic systems has been installed. Among them, the first cryogenic system has passed its performance acceptance tests, completed integrated commissioning with the injector, and is currently supporting the cryogenic operation of the first superconducting cryomodule. This progress provides a solid technical foundation for the stable operation and high-efficiency lasing of the SHINE facility's superconducting accelerator, while also offering valuable experience for cryogenic system research in similar large-scale scientific facilities.

The High Intensity Heavy-ion Accelerator Facility (HIAF) is located in Huizhou City in south China. The linear accelerator is cool-down with a new customized cryoplant able to provide the 2 kW @2K required by the superconducting cavities. In addition to this, the cryoplant provides 2kW@4.5K for the couplers and ~11 kW fo the thermal shields of the installation. The presentation will describe the solution developped to support this large project with budgetary constraints. The results of the commissioning will then be exposed as well as the main lessons learnt.

At the European Spallation Source (ESS), a 5MW beam of 2 GeV proton with a normal current of 62.5 mA driven by a linear accelerator impacts a rotating tungsten target at a repetition of 14 Hz and a pulse length of 2.86 ms. High-energy spallation neutrons are moderated to cold and thermal neutrons using a combination of two hydrogen moderator and a water premoderator. The nuclear heating is estimated to be 6.7 kW at the proton beam power of 5 MW for the two -moderator configuration. A cryogenic moderator system (CMS) was designed to continuously supply subcooled liquid hydrogen at a temperature of 17.5 K and 1.05 MPa with a parahydrogen fraction greater than 99.5% to each moderator. A flow rate delivered to each moderator is 240 g/s to limit an average temperature rise across the moderator within 3 K, caused by the nuclear heating. A static and dynamic heat loads will be removed via a plate-fin type heat exchanger by a large-scale 20 K helium refrigeration plant, the Target Moderator Cryoplant (TMCP), with a cooling power of 30.3 kW at 15 K. The TMCP commissioning was completed independently, without connection to the CMS, in December 2022. Operational procedures, including cooldown, warm-up and beam injection modes, were systematically investigated to establish an automatic TMCP-CMS control system. Concurrently, the CMS cold box, distribution box and transfer lines were installed, along with the connections between the TMCP valve box and the CMS cold box. Beginning in 2024, preliminary CMS commissioning integrated with the TMCP was conducted without the moderators, using nitrogen and helium, prior to hydrogen operation. This preliminary configuration was completed in February 2025, and the operational parameters of the CMS and TMCP during the cooldown and warm-up processes were investigated. In March 2025, for the first time, the first cooldown of the CMS without the moderators was succeeded using hydrogen. Subsequently, the moderators were integrated using bayonet transfer lines. The first hydrogen commissioning of the fully integrated CMS was successfully completed via semi-automatic operation and verified no harmful leakage at cryogenic environment in July 2025. This paper presents the first hydrogen commissioning results for the preliminary (without moderators) and fully integrated (with moderators) configurations.

Small-scale helium liquefaction systems based on 4 K Gifford–McMahon (GM) cryocoolers are widely used but currently suffer from limited performance. For a typical 1.5 W @ 4.2 K GM cryocooler, the long-term liquefaction rate remains around 20 L/day, which is less than 40% of its theoretical capacity due to severe cold-end helium superheating caused by the high wall thermal resistance induces severe cold‑end helium superheating. To overcome this limitation, this study proposes and experimentally validates a gas–thermal coupled hybrid liquefaction scheme. In this new mode, low-temperature helium is extracted from the cold end via a throttling orifice and mixed with the external flow. This configuration effectively reduces the initial temperature of the helium prior to condensation. Experimental results show that this configuration reduces the helium superheat by approximately 0.9-1 K. Consequently, the liquefaction rate is increased by over 36%, achieving a maximum capacity of 29.33 L/day. This performance surpasses state-of-the-art commercial liquefiers, offering a significant reduction in time and energy costs for liquid helium production.

Liquid hydrogen (LH2) fueled electric propulsion systems utilizing high-temperature superconducting (HTS) power devices are emerging as a promising solution for eco-friendly aviation. LH2 serves a dual purpose in the system: as the energy carrier for power generation with fuel cells and gas turbines, and as a cryogenic heat sink for thermal management systems (TMS). The TMS employs secondary cooling loops to enable integration, versatility, and safe operations. The secondary cooling loops use closed-loop gaseous helium (GHe) to transfer heat from the loads to LH2, maintaining the various electrical components at 30–350 K. We developed the graded heat exchanger concept to address stringent aircraft mass and size constraints and to maximize overall efficiency. The graded heat exchanger consists of several segmented heat exchanger blocks that produce multiple secondary loops, all of which transfer heat to the central core of the primary LH2 loop. A high-efficiency heat exchanger reduces the required helium mass flow rate, thereby reducing the cryogenic fan size and improving the TMS efficiency. In this study, the primary heat sink was simulated using a cryocooler to experimentally evaluate the cooling performance and effectiveness of the graded heat exchanger. Additionally, a prototype graded heat exchanger fabricated by metal 3D printing is designed to further enhance effectiveness. Computational Fluid Dynamics (CFD) analysis was conducted to investigate the thermal performance of the design. This work contributes to the development of efficient and lightweight thermal management systems for liquid hydrogen-powered electric aircraft.

The development of geothermal resources at great depths requires advanced drilling technologies capable of operating under extreme thermo-mechanical conditions. To enable faster and more efficient deep drilling in heterogeneous and hard rock formations, novel non-contact and hybrid drilling approaches are being explored. Within this context, the DeepU project investigated a laser-assisted drilling concept supported by cryogenic technologies, using supercritical nitrogen as a flushing and cooling medium. The proposed system aims at drilling ultra-deep wells (>4 km) for the creation of a U-shaped closed-loop geothermal heat exchanger. The drilling concept integrates a high-power laser source with downhole optical delivery, a drill string and drill head assembly, a cryogenic flushing system, and auxiliary subsystems required for controlled and efficient rock penetration. Supercritical nitrogen is transported downhole and undergoes isenthalpic expansion at the drill head, resulting in rapid cooling of the rock surface. This process induces thermal shock and vitrification of the rock material, while simultaneously removing drilling debris and protecting downhole components from excessive thermal loads. A mathematical model was developed to estimate the required mass flow rate of nitrogen during laser drilling operations, accounting for thermo-fluid and process parameters. The model was validated using experiments conducted on a dedicated laboratory-scale test rig. To ensure low temperature and high density of supercritical nitrogen over multi-kilometre well depths, a vacuum-insulated cryogenic transfer system with high thermodynamic efficiency is required. A comprehensive survey of commercially available cryogenic couplings and vacuum-insulated piping systems demonstrated that no off-the-shelf solutions meet the stringent diameter, pressure, and temperature requirements of the DeepU downhole application. As a result, an innovative coupling concept for a vacuum-insulated drill string was developed, designed to ensure leak-tightness, mechanical robustness, and ease of assembly. The coupling was experimentally tested under the most critical thermal and mechanical loading conditions, confirming its suitability for geothermal laser-driven drilling systems. In addition, a dedicated risk analysis of the cryogenic subsystem was performed, focusing on hazards related to supercritical nitrogen flow within vacuum-jacketed process lines. Based on this analysis, a set of risk mitigation measures applicable to both design and manufacturing stages was proposed. The results demonstrate the technical feasibility of integrating cryogenic systems with laser-based drilling concepts, providing a viable pathway toward next-generation ultra-deep geothermal drilling technologies. This research is funded by the European Union (G.A. 101046937). However, the views and opinions expressed are those of the author(s) only and do not necessarily reflect those of the European Union or EISMEA. Neither the European Union nor the granting authority can be held responsible for them.

Several gases are liquified for ease of storage and transportation. The liquefaction of natural gas, for example, reduces the volume of natural gas by more than a factor of 600. Cryogenic tanks have been designed to reduce boil off losses of the cryogenic liquid, and the designs have been customized for applications from lab scale dewars to trailer/tanker trucks to large stationary storage vessels. The effectiveness of the tank is dependent on its sustained ability to reduce heat transfer between the ambient atmosphere and the cryogenic liquid. This includes conduction of heat through mechanical, radiative and convective pathways. The mechanical and radiative conduction are in large part determined by the construction design and materials and are relatively constant throughout the lifetime of the vessel. The conductive heat transfer is minimized by pulling a very high vacuum between the inner and outer walls of the vessel and sealing shut. In time, the vacuum between the vessel walls degrades, in part due to the outgassing of hydrogen from the materials of construction. To account for this, it is common to include hydrogen getters specifically designed to capture this hydrogen and maintain the high vacuum needed for high efficiency cryogenic tanks. There are a number of commercially available hydrogen getters available. Some of these getters contain precious metals. Recent increases in metal prices is driving innovation in getter design. This presentation will provide a review of these currently used getters in terms of performance, cost and safety, as well as discuss efforts to make improved hydrogen getters.

This paper presents the development and experimental characterisation of a piezoelectric cryogenic heat switch based on mechanical contact. The switch is designed for applications requiring dynamic thermal control in the temperature range of 60-180 K, where low parasitic heat loads, compactness, and long-term stability are essential. Unlike conventional mechanical or gas-gap heat switches that require continuous actuation energy to maintain the conducting state, the proposed design passively maintains thermal contact using a disc spring preload and requires actuation energy only during switching to the non-conducting state. A multilayer piezoelectric actuator is used to separate the thermal interface, enabling reversible transitions between conducting and non-conducting configurations. The performance of the switch was evaluated using a guarded heater method. The measured thermal contact conductance in the conducting state reaches approximately 1.01×10 4 W m −2 K −1 at 60 K , while the non-conducting state conductance is approximately 7.95 × 10 1 W m −2 K −1 , yielding switching ratios in the range of 127-165. In addition to high thermal performance, the switch offers advantages in system integration due to its compact design and simple electrical actuation. A comparison with a previously developed gas-gap heat switch demonstrates significantly higher conductance and improved switching efficiency. These results demonstrate that the proposed design provides a high-performance, energy-efficient alternative to conventional cryogenic heat switch technologies.

In magnetically confined fusion devices, hydrogen isotopes undergo fusion reactions that release large amounts of energy in the form of helium nuclei and neutrons. To compensate for particle losses due to outward transport and fusion reactions, hydrogen isotopes must be supplied continuously to maintain a steady plasma density. Three established techniques exist for this purpose: gas puffing, supersonic molecular beam injection, and pellet injection. Among these, pellet injection offers superior performance due to its high penetration depth, achieved by injecting frozen hydrogen pellets into the plasma at high velocity. Since the complex nature of pellet-plasma interaction – similar to the Leidenfrost effect – prolongs the pellet’s lifetime in the plasma, the penetration depth can reach several tens of centimetres, increasing the fuelling efficiency. At present, the pellet injection technique is a proven, leading technology for fuelling and controlling the plasma density of magnetically confined fusion devices. Fuelling pellets are typically a few mm in diameter and length to minimise plasma perturbations upon injection. In return, the injection frequency is relatively fast, in the range of 10-20 Hz and quasi-continuous operation is required. Fuelling pellet injection systems consist of three main components: an ice extruder, a pellet cutter, and an accelerator. At the outlet of the extruder, a solid hydrogen rod is produced, which is cut to predefined lengths by a puncher or cutter mechanism. The pellets are then launched by gas propulsion or a centrifuge. In the Fusion Plasma Physics Department of HUN-REN Centre for Energy Research, a new pellet puncher for the EU DEMOnstration Power Plant (DEMO) was developed, along with a batch-type cryogenic extruder that would be used to test the pellet puncher in operation. The batch extruder has a theoretical ice capacity of >5,000 mm 3 and is designed for an extrusion duration of 10 seconds. The solid hydrogen rod produced by the extruder is 3.2 mm in diameter, and the target flow rate is 386 mm 3 /s, which is required for the 10 Hz operation of the pellet puncher when the pellet length is 3.2 mm. The extruder is installed in a custom-made large flexible cryostat and is cooled by a two-stage cryocooler. The second stage of the cryocooler is connected to the extruder, while the first stage is used for feed gas pre-cooling and cooling the support structure. The heat shield covering the extruder is cooled by liquid nitrogen to reduce the thermal load on the cryocooler. During the extrusion process, temperatures at multiple points, heating power, extrusion force, and piston position are all measured. At the conference, the design of the batch extruder and its integration with the DEMO pellet puncher will be presented, along with thermal calculations and simulations, experimental measurement results, and analyses. Keywords: Solid Hydrogen, Extrusion, Cryogenic Extruder, Plasma Fuelling

The Levitated Dipole reactor concept describes a superconducting high-field magnet levitating inside a vacuum chamber, confining high-density fusion plasmas in a similar fashion to planetary magnetospheres. OpenStar Technologies have recently confined plasma on a levitating dipole for the first time using Junior; the first of a four-reactor pathway to commercially viable fusion. The Junior magnet is cooled to 30 K by helium gas, then evacuated prior to levitation. The cold thermal mass of the magnet acts as a thermal sink for resistive heating while levitating, raising the temperature of the magnet to ~45 K when it is re-docked, and requiring several hours to re-cool to 30 K. To prevent thermal cycling and improve reactor duty-cycle, OpenStar are developing the second-generation reactor, Tahi, with an onboard isothermal reservoir containing slush cryogen. The slush reservoir will melt over the duration of levitation, using the enthalpy of melting to maintain stable temperature of coils and onboard power supply. Mostly liquid at the end of each levitation, the cryogen will be periodically recharged during a ‘docking cycle’, when the magnet descends from levitation to allow engagement of transfer lines and exchange of cryogen. What little work has been conducted on slush cryogen has been dominated by NASA research, and was not implemented at industrial scale. Deciding the production method to employ requires consideration of slush homogeneity and crystal size, but also efficiency of production. Early models of Tahi require 200 W of cooling over a two-hour levitation, contained within a reservoir of 110 L and recharged within eight minutes. Several production vessels may be required to ensure a batch of cryogen is always available. OpenStar has proven, at small scale, production of slush by freeze-thaw process, using evacuation to reduce liquid pressure below triple point. In an alternative method, cryogenic auger production uses a cryocooler to cool a drum immersed in liquid, forming solid crystals on the surface which are swept away by rotating auger blades. To initiate and maintain conveyance of slush through delivery, pumping will be essential, however the range of pumps specific to slush cryogen application is limited. This work will cover various pumping technologies, such as centrifugal, piston or progressive cavity pumping, while comparing their efficiency, reliability and preservation of solid composition. OpenStar have a functioning docking and transfer system for gaseous helium, however liquid/slush presents additional process challenges. The transfer of slush will be intermittent, necessitating active management of stagnant transfer lines. The onboard reservoir requires flow isolation during levitation. Design of these components must minimise flow disturbance during transfer but must have very low leak during connection/disconnection, as leaks will impact duty cycle and plasma quality. Transfer of a two-phase flow over long distance may result in settling between the solid and liquid phases. Separation would reduce transfer of the solid portion and thus reduce the cooling capacity of the reservoir. This work will cover modelling, testing and hardware selection to optimise solid fraction and minimise separation. Also covered by this work are several design problems adjacent to slush production and delivery; designing the thermal interface between the reservoir and the magnet and power supply; automation of slush plant to be controlled by a human operator; and mechanical and automation design of docking hardware.

The magnet test platform of the Comprehensive Research Facility for Fusion Technology (CRAFT) is a major scientific engineering project in China for verifying the cryogenic performance of full-size superconducting magnets. To meet the stringent hydraulic and thermal requirements of the Cable-in-Conduit Conductors (CICC), an Auxiliary Cold Box (ACB) has been constructed to provide stable supercritical helium forced-flow cooling. The ACB is located between the upstream helium refrigerator and the downstream magnet users, functioning to convert cooling capacity into 4.5 K supercritical helium, 3.8 K or 3 K subcooled supercritical helium. In this paper, the overall system configuration and engineering implementation of the ACB are presented. The integration of critical components, including heat exchangers, cold compressors, circulating pumps, and liquid helium tanks, is described in detail. The interface management between the upstream cryoplant and downstream targets is also discussed to illustrate the system topology. Finally, the manufacturing progress and the on-site physical assembly status of the cold box are introduced.

The ITER disruption mitigation system (DMS) to protect the tokamak from damage is currently under design in different laboratories over the world. The CEA/DSBT was in charge of the design assessment of the cryogenic system using supercritical helium (SHe) forced flow to produce and store the large DMS cryogenic pellets (neon and/or hydrogen) to be injected into the ITER high-energy plasma when an impending disruption is detected. This paper presents the numerical work carried out to assess the ITER/DMS cryogenic system and operating conditions required to ensure stable and reliable formation and storage of the cryogenic pellets within the ITER requirements. The work was performed using the Simcryogenics MATLAB/Simulink‑based 0D/1D cryogenic simulation tool, developed by CEA/DSBT and validated by a large experimental database. First, the cryogenic system supplying the pellet formation cells, as well as the cold cells themselves are described from a thermal-hydraulic perspective and process control. Then the identified issues are presented. Among them, return pressure variations at the DMS cryogenic interfaces, imposed by another cryogenic cooling users (cryopumps), led to significant backflows impacting the liquid helium bath and causing unwanted helium consumption. In addition, uneven cooling flow distribution in parallel cold cell circuits producing large pellets (28.5 mm in diameter) of different compositions (H vs. Ne), was also anticipated and numerically confirmed, resulting in solid formation limitations. Finally, temperature transients occurring during the pellet formation cycle induced abrupt cooling flow rate variations in the cryogenic circuit, sometimes accompanied by backflow. To overcome the identified issues, mitigation solutions in the cooling design and control are detailed with the introduction of a control valve at the liquid helium bath outlet, flow orifices at the cold cell inlets and heater controls at the precooling stages. This work has been funded by ITER Organization under the contract IO/23/CT/4300002847 and by CEA funding. The views and opinions expressed herein do not necessarily reflect those of the ITER Organization.

The SST1 (Steady State Superconducting Tokamak) at IPR, Gandhinagar, Gujarat, India has been established for doing plasma experiments, which can be helpful towards nuclear fusion energy production. It’s superconducting magnet system (SCMS) is based on NbTi material and all 9 PF (Poloidal Field) coils and 16 TF (Toroidal Field) coils are designed to be cooled at ~5 K using either supercritical helium or 2-phase helium for its nominal operation. The whole SCMS including support structures, superconducting bus bars, current feeder system, cryogenic piping layout has cold mass about 35 tons, which need to be cooled down to about 5 K from room temperature and maintain at this low temperature for few weeks for different plasma experiments. To achieve this, a helium refrigerator-cum-liquefier (HRL) plant having equivalent refrigeration power of 1.3 kW at 4.5 K has been installed and operated successfully since 2003. Liquid nitrogen (LN2) cooled thermal radiation shields and thermal anchors have been used to reduce thermal radiation and conduction heat loads on 4.5 K helium cooling system. These involves many parallel paths with 2-phase nitrogen flow, which can lead to ill-cooled paths if this parallel flow system is not properly designed and not properly operated due to 2-phase nature. During assessment it is found that, there are areas, where 4.5 K components are facing room temperature thermal radiations leading to large cryogenic heat loads. As the superconducting tokamak experimental machines are compact and complex, cryogenic heat load, practically happens to be higher than design values. For the SST1 also, cryogenic heat loads are found to be high compared to the designed value. Due to high heat loads, achieving superconducting state for all PF coils and TF coils of SCMS simultaneously has been difficult so far. Only TF coils with stable current up to about 5 kA continuously for few hours had been possible in previous campaigns up to 2023. Various aspects and components have been considered to assess the cryogenic heat loads and root causes of these. Considering significant complexity of SST1 machine, it is not easy to assess exact cryogenic heat load values. But, sometimes, it is easy to find the root reasons of heat loads through visual inspection, analysis and operational results. Such assessments have been done and heat load mitigation have been planned. After certain modifications in the system and improvements in the operation procedure of LN2 cooling system and HRL plant, a significant improvement was observed with stable TF coil current charging ~9 kA for more than 8 hrs continuously without any quench. This paper will give details of these including future plan to reduce external heat loads further for better cooling of SCMS, maintenance and operational strategy which can allow trouble free operation of plant for more than a month. This can be useful for many other superconducting tokamak machines.

The Divertor Tokamak Test (DTT) is a superconducting tokamak under construction at the ENEA Research Center in Frascati, Italy. Its objective is to implement critical technological issues associated with power exhaust in magnetic confinement fusion devices. A key requirement for reliable DTT operation is the robustness of its superconducting magnet system, which must undergo thorough qualification under realistic cryogenic and electrical operating conditions. To support this need, ENEA is developing the Frascati Coil Cold Test Facility (FCCTF), a dedicated infrastructure designed for high-current superconducting coil testing. The facility is currently in the installation phase and is scheduled to be operational by the end of 2026, in alignment with the DTT construction timeline. FCCTF will be capable of hosting full-scale superconducting coils and reproducing conditions closely matching those expected during tokamak operation. The facility will carry out the qualification of all DTT superconducting magnets prior to their final installation, including 18 toroidal field (TF) coils, 7 central solenoid (CS) modules, and 2 poloidal field (PF1/6) coils. Beyond coil qualification, FCCTF will also support testing and validation of the TF coil power supply system, as well as the associated quench detection and protection systems. This work outlines the main technical characteristics of the FCCTF and provides an update on the installation progress of its principal subsystems, with particular attention to the cryogenic plant. Simulations have been conducted to investigate the cooldown procedure of a superconducting TF coil, confirming that the FCCTF cryogenic system can ensure a safe and well-controlled cooling process.

Boil-off gas (BOG) management in liquefied natural gas (LNG) systems is critical for energy efficiency and environmental sustainability. Traditional pure nitrogen reverse Brayton cycles often exhibit performance limitations due to the restricted expansion temperature drop caused by its low specific heat ratio (γ=1.40). To address these limitations, this study presents a comprehensive design and optimization of an integrated turbo-expander-compressor employing a helium-nitrogen (He-N 2 ) mixed refrigerant (4:1 molar ratio). A systematic design methodology is developed, combining thermodynamic cycle modeling, one-dimensional aerodynamic design based on velocity triangle theory, and three-dimensional computational fluid dynamics (CFD) simulation. The real gas properties (RGP) model and shear stress transport (SST) k-ω turbulence model are employed to capture the complex flow physics of the mixed refrigerant at cryogenic conditions (95-290 K). Operating at a refrigeration capacity of 86 kW, the system achieves a coefficient of performance (COP) of 0.216, representing a 14.3% improvement over conventional pure-nitrogen cycles. The compressor stage achieves 84.11% isentropic efficiency with a pressure ratio of 1.38, while the turbine stage delivers 89.03% efficiency with an expansion ratio of 1.70. Comprehensive off-design performance analysis demonstrates robust operational characteristics, with high-efficiency operation maintained across a broad range of 80-105% of design speed and 70-130% of design flow rate. A critical innovation is the axial thrust optimization strategy achieved through systematic modification of the impeller back cavity structure. By optimizing the seal diameter and back cavity pressure distribution, the compressor-end axial thrust is reduced from 2726 N to 1017 N (a 63% reduction). Combined with precise cavity pressure regulation (1.0-1.27 MPa), the total axial thrust of the integrated unit is successfully controlled within 167-723 N, which is well within the ±1000 N load capacity of magnetic bearings, thus ensuring rotor stability. The validated design demonstrates the technical and economic viability of He-N 2 mixed refrigerant configurations for compact, high-efficiency LNG BOG re-liquefaction systems, providing a foundation for industrial deployment. Keywords: Reverse Brayton cycle; Turbo-expander-compressor; He-N 2 mixed refrigerant; Axial thrust optimization; LNG BOG re-liquefaction

Pulse tube cryocoolers driven by linear compressors have gradually become popular cryogenic refrigeration devices for space exploration in recent decades. Friction and wear caused by moving components in the linear compressor are critical factors affecting the lifetime and reliability of the pulse tube cryocooler. Compared with flexure springs, gas bearings have advantages such as low friction, no pollution, compact structure, and wide range of temperature adaptability. They are key to achieving oil-free lubrication and extending service life of linear compressors. This study focuses on the slit gas bearings used in linear compressors and uses CFD software to analyze the bearing characteristics of the gas bearing. A three-dimensional model of the bearing flow field is established and meshed. The flow of the working medium in the bearing is numerically simulated to obtain the static and dynamic flow field characteristics. Furthermore, the influences of the structural parameters of the gas bearing and the operating parameters of the pulse tube cryocooler on the bearing characteristics are analyzed. The results show that the eccentricity ratio, gas film thickness, size of the throttling groove, number of throttling holes, charging pressure, and pressure ratio have a significant impact on the performance of the gas bearing, while the diameter of the throttling hole, the spacing of the throttling hole, and the frequency have a relatively small impact. Specifically, the bearing capacity reaches the maximum when the number of throttling holes is 6, and decreases exponentially with the increase of the average gas film thickness, and increases linearly with other parameters. The gas consumption of the bearing increases quadratically with the eccentricity ratio, average gas film thickness, and diameter of the throttling hole, while it increases linearly with other parameters. This study will provide a theoretical basis for optimizing the structural design of gas bearings and operating parameters.

There is an increasing demand for cryogenic cooling for stationary and mobile applications at 20 K with medium cooling capacities at around 500 W where reverse turbo Brayton cryocoolers have advantages over (paralleling) Gifford-McMahon or pulse-tube cryocoolers. Applications range from liquid hydrogen storage shield cooling, small scale liquefaction to quantum computing and superconducting cables, sensors and electrical machines. Besides high efficiency and reliability some of these applications demand also low micro-vibration emission in order not to disturb sensitive sensors and equipment. Gas bearing turbo expanders fulfill these requirements, they emit very low micro-vibration due to the high-speed rotation above 180 krpm / 3 kHz and the continuous gas flow and they are by design oil and maintenance free. This paper outlines the design of a gas bearing turbo expander for a 20 K, 500 W reverse turbo Brayton cryocooler. For this, a reverse turbo Brayton cycle design is depicted and the requirements for the turbo expander such as mass flows, pressure ratios and temperatures are derived. The gas bearing turbo expander concept and technology are described and the specific gas bearing turbo expander design results including turbine map, rotational speed, generator power and dimensions are presented.

Bladeless turbines have emerged as potential expansion devices for compact LNG cryogenic systems due to their simplified rotor assembly, absence of blade-induced erosion, and compatibility with multiphase operating conditions. Classical Tesla-type parallel-disk configurations, however, exhibit poor radial momentum transfer, limited torque generation, and pronounced viscous dissipation, with boundary-layer shear acting primarily as a momentum loss rather than a viable mechanism for work extraction. This produces strong dissipative losses and contributes little to useful work, leading to low system-level efficiencies, significant entrance and nozzle losses, and reduced performance at small scales. Their practical application has therefore remained limited, despite demonstrations of high rotor efficiency. To address these limitations, the present work examines a helicoidal bladeless turbine architecture in which the working fluid is admitted into a continuous conical helical channel machined within the rotor body. The three-dimensional curvature, torsion, and streamwise rotation inherent to this geometry induce strong secondary flow structures, namely Dean vortices and Coriolis-modified circulations that exchange momentum and static pressure within the rotating conduit. These secondary flows are hypothesized to constitute the principal mechanism for useful work transfer in the helicoidal configuration, whereas viscosity contributes predominantly to dissipative losses. In this work, a computational fluid dynamics (CFD) model is developed to evaluate the fluid dynamic behavior of the helicoidal bladeless turbine under cryogenic expansion. The simulations are performed on a three-dimensional representation of the conical helicoidal channel considering multiphase, compressible, and turbulent flow effects consistent with LNG operating conditions. Real-gas thermophysical properties are employed, and a RANS formulation with a curvature-sensitive turbulence model, k–ω SST is used to capture secondary vortex structures and cross-stream circulation. The objective of the CFD framework is to identify the dominant loss mechanisms within the channel and quantify their influence on work transfer capability. The CFD solver provides detailed flow-field information including velocity distributions, vorticity fields, pressure gradients, and entropy generation. These quantities are used to evaluate contributions from viscous dissipation, multiphase effects, and turbulence to the overall losses in the turbine. Beyond flow characterization, the CFD model is used to estimate the pressure drop and friction factor within the helicoidal conduit, which serve as practical engineering metrics for hydrodynamic performance and for comparison with conventional turboexpanders. The thermodynamic performance of the turbine is evaluated through estimation of the isentropic efficiency associated with an idealized isentropic expansion between the prescribed inlet and outlet states. This enables assessment of the work extraction potential and the relationship between hydrodynamic losses and thermodynamic efficiency. A nondimensional analysis is carried by simulating for varying parameters to express friction factor, pressure drop, and loss coefficients in terms of geometric and operating parameters using the non-dimensional numbers. In this formulation, nondimensional groups serve as post-processing tools for interpreting CFD results and for identifying scaling relationships. Together, the CFD modeling and nondimensional analysis provide a basis for evaluating losses, assessing feasibility, and guiding optimization of helicoidal bladeless turbines for LNG cryogenic expansion.

The Long-Baseline Neutrino Facility (LBNF) at the Sanford Underground Research Facility (SURF) in Lead, South Dakota, hosts the Deep Underground Neutrino Experiment (DUNE), which operates cryostats containing nearly 70,000 metric tons of ultra-pure liquid argon (LAr). Maintaining stringent LAr purity is essential to achieving the target electron lifetimes that directly determine the experiment’s signal-to-noise ratio. The Horizontal Drift (HD) Far Detector requires an electron lifetime above 3 ms across its 3.5 m drift, corresponding to less than 100 parts-per-trillion (ppt) oxygen-equivalent contamination, while the Vertical Drift (VD) Far Detector demands a lifetime above 6 ms across its 6.0 m drift, equating to below 50 ppt oxygen-equivalent contamination. Additionally, minimizing nitrogen (N 2 ) levels is critical to reduce quenching of LAr scintillation light; N 2 concentrations must remain below 1 ppm, as higher concentrations can reduce detected light by up to 20%, adversely affecting energy reconstruction and overall detector performance. As part of Brazil’s in-kind contribution to the LBNF Far Detector Cryogenics, the State University of Campinas (UNICAMP) leads research and development on argon purification and regeneration technologies for the HD and VD systems. To support this effort, UNICAMP designed and constructed the Purification Liquid Argon Cryostat (PuLArC), a small-scale facility for evaluating purification media. Tests using PuLArC identified Li‑FAU zeolite as an effective material for mitigating nitrogen contamination in LAr. Subsequent experiments at Fermilab validated its scalability and performance, demonstrating its potential applicability to large-scale cryogenic systems such as ProtoDUNE. This work presents the research approach, experimental setups, and key findings, highlighting Li-FAU’s potential as an alternative to Molecular Sieve 4A for liquid argon cryogenic systems. The study also summarizes the current design progress for the argon purification and regeneration systems of the HD and VD detectors. These advancements contribute to enhancing DUNE's measurement precision and exemplify the strength of international collaboration in advancing cryogenic technology for next-generation neutrino experiments.

With the rapid development of nuclear fusion technology, large-scale superconducting magnets require reliable forced-flow cooling using supercritical helium (SHe). To support the operation of superconducting magnets in the Comprehensive Research Facility for Fusion Technology (CRAFT), a high-speed centrifugal SHe circulation pump was developed. However, direct performance testing under SHe conditions is limited by the high cost and complexity of large cryogenic refrigeration systems.To overcome these limitations, a cost-effective experimental validation method using liquid nitrogen (LN₂) as a substitute working fluid was proposed based on hydrodynamic similarity theory. A dedicated cryogenic test rig was constructed to evaluate the hydraulic performance of the pump. According to similarity scaling, the rated SHe operating speed of 12,000 rpm was converted to an equivalent LN₂ test speed of 6,600 rpm, with a corresponding theoretical flow rate of 192.5 g/s and head of 27.36 m.Numerical simulations under LN₂ conditions showed good agreement with theoretical predictions, yielding a flow rate of 200 g/s and a head of 27.04 m. Cryogenic experiments produced a measured flow rate of 186 g/s and a head of 20.95 m. The close agreement in flow rate among theoretical, numerical, and experimental results confirms the validity of the hydraulic design and the similarity-based scaling approach. The lower experimental head is mainly attributed to internal leakage, increased hydraulic losses, and manufacturing tolerances, while the overall performance trends remain consistent with theoretical expectations.These results demonstrate that LN₂-based substitution testing provides an efficient and reliable method for validating the hydraulic characteristics of SHe centrifugal pumps, significantly reducing experimental complexity and cost. The proposed approach offers valuable engineering support for the optimization of forced-flow cooling systems in fusion applications and can be extended to other cryogenic fluid machinery.

The cryogenic moderator system (CMS) at Japan Proton Accelerator Research Complex (J-PARC) forms a closed-circulation loop that supplies cryogenic hydrogen at a temperature of 18 K at a pressure of 1.5 MPa (above the critical pressure of 1.29 MPa) to three moderator vessels. In those vessels, fast neutrons generated by spallation reaction between mercury target and a high-power proton beam (1 MW at a repetition of 25 Hz) are moderated by collisions between the neutrons and the hydrogen molecules, resulting in production of cold neutron beams for neutron scattering experiments. The nuclear heat generated during the moderation process is estimated to be 3.75 kW under 1 MW proton beam operation. The cryogenic hydrogen must be circulated at a flow rate greater than 162 g/s, to maintain average temperature rise across each moderator below 3 K. The resulting static and dynamic heat loads are removed via a heat exchanger by a helium (He) refrigeration system with a cooling power of 6 kW at 17 K. Two dynamic gas-bearing hydrogen pumps, developed based on the supercritical helium pump used in the International Thermonuclear Experimental Reactor (ITER) project, are arranged in parallel. A foil-type self-acting gas bearing is adopted as the journal bearing. Teflon is coated on the foil of the journal bearing and on the thrust bearing to reduce the friction coefficient. A closed impeller with a diameter of 26 mm, which is exposed to liquid hydrogen, is located 30 mm from the thrust bearing. The thrust bearing is mounted on the pump cartridge flange and maintained at ambient temperature. The rotor and bearings remain non-contacting during normal operation due to the gas-bearing support. However, contact occurs during start-up and shutdown, which gradually damages the bearing coating. Consequently, the bearings are replaced annually. A space between the impeller and the thrust bearing is filled with a G10 block to reduce heat leakage. The resulting gap between the pump casing and G10 block is 0.2 mm. Two pumps are operated simultaneously to provide redundancy. The allowable minimum and maximum pump speeds are 30,000 rpm and 60,000 rpm, respectively. The maximum allowable pump head is 120 kPa. Even if one of the pumps is accidentally stopped, the speed of the other increased to continue the proton beam operation. During the commissioning in 2008, the pump flange temperature dropped excessively down to 250 K when passing through critical temperature during the first cooldown. To mitigate this, a water-radiator, through which the cooling water for the induction motor flows, was installed to maintain the O-ring seal and surrounding flange area at ambient temperature. The European Spallation Source (ESS), where ball-bearing hydrogen pumps are operated in series, reported that the flange temperature phenomena were also observed during their commissioning using helium at 17 K, prior to hydrogen operation, with a temperature distribution along the circumference of the pump flange. In this study, the performances of the hydrogen pumps were measured under nominal operating conditions of 1.5 MPa and 20 K, with the pump speeds varied from 34,000 to 55,000 rpm, while monitoring six thermo-coupe temperature sensors mounted circumferentially on the flange and a Si-diode temperature sensor on the casing between the impeller and thrust bearing, and compared with the design curve. The maximum efficiency occurred at the same flow coefficient, which is a non-dimensional expression of a flow rate using the flow density and the wheel speed, independent of the pump speeds. Away from this flow coefficient, temperature drops of the flange and casing were observed. However, it was confirmed that the flange temperature remained above 15 at nominal operation of the CMS. This paper presents pump performance test results in detail and discusses the stable operating conditions for the hydrogen pump, not only for the current 1-MW proton beam but also for the planned future 1.5 MW operation.

Superleaks composed of micro- or nano-porous media are critical components in superfluid 4 He based cryogenic systems, often utilized in fountain effect pumps, special dilution refrigerators, and helium isotope separation units. Powder compaction remains the predominant method for fabricating these porous structures. In this study, we fabricated superleaks using aluminum oxide (Al 2 O 3 ) powders and systematically investigated the influence of particle size on their transport properties. We measured the gas permeability at room temperature to characterize the pore structure and hydraulic resistance. Furthermore, the thermal conductivity of the superleaks was experimentally determined in the temperature range below 2K. A comparative analysis was conducted between the thermal conductivity in a vacuum environment and that in a superfluid helium (He-II) saturated state. The results provide insights into the relationship between powder particle size, permeability, and thermal conductivity of superleaks, providing essential data for the optimization of cryogenic fluid devices.

Reverse Brayton cryocoolers, recognized as the key technology for large-capacity space cryocoolers, require high efficiency and compact design. The recuperators serve as critical components in these systems, where even slight effectiveness degradation directly results in significant cooling capacity loss while accounting for most of the system's weight and volume. Printed circuit heat exchangers (PCHEs) offer a promising solution through their compact structure and superior performance, manufactured via chemical etching and diffusion bonding processes. However, etching effects directly influence flow passage geometry and consequently impact PCHE hydraulic and thermal performance, necessitating a comprehensive investigation. Furthermore, high-effectiveness PCHEs lack sufficient cryogenic experimental validation. This study quantifies etching impacts on high-effectiveness pin-fin PCHEs through systematic characterization of test samples with varying geometric parameters. Results reveal that the etching process significantly deteriorates PCHE performance through both channel-level and pin-fin-level dimensional deviations. At the channel level, etched geometries exhibit 4.5% reduced average etching depth and 8.5% increased wall thickness, resulting in 0.34% effectiveness loss and 41%-45% pressure drop increase with 95% confidence. Pin-fin-level deviations prove more severe, comprising height reduction, diameter oversizing, and sidewall tapering that collectively reduce effectiveness by 0.5% (corresponding to 57% system cooling capacity loss) and increase pressure drop by up to 193%. Geometric sensitivity analysis reveals size-dependent responses to etching effects: small-diameter pin-fin configurations suffer greater thermal degradation, while large-diameter designs experience more severe hydraulic penalties and reduced compactness. Additionally, cryogenic experimental investigations are conducted on high-effectiveness PCHEs, achieving 96.8% testing effectiveness. The impact of operating conditions is also experimentally evaluated. These findings provide essential design guidelines for high-effectiveness PCHEs that must account for etching-induced deviations, with applications extending to other etched pin-fin systems in thermal management applications. These findings provide essential design guidelines for high-effectiveness PCHEs that must account for etching-induced deviations, while offering crucial cryogenic experimental study for high-effectiveness cryogenic PCHEs.

To enable accurate design and performance optimization of low-temperature plate-fin heat exchangers (PFHEs) in cryogenics systems, this study establishes a multiscale integrated research framework in which numerical simulation serves as the leading approach, experimental validation provides the core support, and engineering design constitutes the final objective. Through stepwise information transfer and cross-validation across the fin scale, experimental scale, and heat-exchanger system scale, this framework enables the reliable mapping of the true surface performance of fins under cryogenic conditions to the overall heat-exchanger design. First, three-dimensional numerical simulations are performed for serrated fin channels based on realistic thermophysical property models and variable-property treatment under low-temperature conditions, allowing for a systematic analysis of flow and heat-transfer characteristics within the fin channels. The results indicate that, compared with ambient-temperature conditions, the heat-transfer performance of serrated fins deteriorates significantly under cryogenic conditions. Subsequently, cryogenics experiments conducted in liquid nitrogen (LN2) and liquid helium (LHe) temperature ranges are used to validate the numerical predictions and to obtain the true performance data of serrated fins under cryogenic operating conditions. The experimental results quantitatively assess the applicability limits of empirical correlations reported in the literature when extrapolated to LN2 and LHe temperature ranges, demonstrating that the direct use of ambient-temperature correlations for cryogenic heat-transfer evaluation is subject to substantial limitations. On this basis, fin-level characteristics in terms of j(Re, T) and f(Re, T), validated by both numerical simulations and experiments, are explicitly incorporated into the Aspen Exchanger Design and Rating (Aspen EDR) platform for system-level modeling and engineering design of plate-fin heat exchangers. The resulting heat-exchanger model is capable of accurately capturing the heat-transfer and flow behavior of serrated fins under cryogenic conditions, enabling the integrated optimization of heat-transfer area, core dimensions, and pressure-drop distribution for helium refrigeration applications.In summary, the proposed integrated research framework establishes a systematic linkage between the microscopic mechanism analysis of cryogenic fin structures and the macroscopic engineering design of PFHEs.

Impedance, a Joule-Thompson (J-T) expansion device, isenthalpically expands the gas/liquid below its inversion temperature to lower its temperature. Impedances are used in wet dilution refrigerators (DRs) to maintain a ∼1 K pot, or in dry DRs to liquefy 3 He. The characterization of impedance is generally performed at room temperature under isothermal conditions using gaseous N 2 , He, or air. Experimentally, impedance is determined by measuring pressure drop (ΔP) and volumetric flow rate (V̇) through it and using the proportionality of ΔP ∝ V̇, impedance Z is calculated. While Z is purely a geometric property, it remains to be experimentally and theoretically validated whether Z is indeed independent of isenthalpic expansion for both gas and liquid and independent of temperature. For example, the assumptions underlying the above proportionality relation hold at room temperature for an ideal gas but do not extend to cryogenic temperatures, where liquid is isenthalpically expanded to a lower temperature, yielding a liquid-vapor mixture whose composition, density, and viscosity are strongly temperature- and pressure-dependent. Our study presents the experimental design, methodology, and numerical methods to determine Z at cryogenic conditions and compare it with room-temperature values. We first characterize the impedances of micron-sized annular capillary tubes at room temperature by varying input pressure and keeping the exit pressure constant at atmospheric conditions. As expected, Z remains within the error bar of experiments for varying input pressures. We then measure the same impedances at LN 2 temperatures by expanding LN 2 from 1 atm to lower pressures and measuring V̇ and temperature. The theoretical expressions for isenthalpic expansion are re-derived for cryogenic temperatures to relate the ΔP and V̇ and calculate Z. These newly derived expressions are also applicable for impedance used in the 1 K pot. The calculated Z values obtained using the above experimental design and re-derived expressions show minimal change relative to room-temperature values. However, with the same measured data, if room-temperature proportionality relations were used, the Z values would differ significantly. We further report the transient temperature drop, ΔP, and V̇ data of the impedance before the equilibrium flow is established at LN 2 temperatures. At present, experiments are ongoing to characterize the impedances at LHe temperatures.

Eta Space is funded by NASA to test cryogenic fluid management technologies in low Earth orbit. The LOXSAT payload has completed the design, analysis, and assembly phase and has completed all environmental testing in preparation for launch. This presentation will give a summary of the LOXSAT mission objectives, high level design concepts, and results of all assembly, integration and testing (AI&T). In addition, preliminary designs of a follow on "Cryo-Dock" mission will be given.

Micro-gravity gas-liquid separation technologies have become indispensable for numerous current and future space missions, especially long-duration missions that demand in-orbit engine restart and propellant replenishment. The screen channel liquid acquisition device (SCLAD), which has been successfully applied in storable propellant systems, is widely recognized as one of the most promising solutions for the orbital gas-liquid management of cryogenic fluids. To gain deeper insights into the working performance of SCLAD under cryogenic conditions, a typical four-channel semi-communicating SCLAD prototype was designed. Using liquid nitrogen (LN 2) and gaseous nitrogen (GN 2 ) as the working mediums, bubble point pressure and anti-gravity outflow tests were conducted on SCLAD samples integrated with three distinct Dutch-Twill Weave (DTW) screens. The experimental setup mainly comprises an experimental Dewar, a vacuum pumping module, a working medium supply module, an image acquisition module and a data acquisition module. To address the limitations of the traditional window-based visualization measurement method, a transparent glass experimental Dewar with a double-layer vacuum nested structure was developed. The outer Dewar, filled with LN 2 , functions as a cold shield for the inner Dewar, thereby enabling the fully transparent inner vessel to achieve an optimal balance between superior thermal insulation performance and excellent optical observability. During the experiments, key processes of the SCLAD samples, including gas bubble breakthrough, single-phase liquid acquisition, and liquid acquisition failure, were clearly visualized and recorded. The bubble point pressure was determined by measuring the pressure difference across the screen channel at the moment when the first bubble was observed on the screen surface. The bubble point pressures for the DTW 200×1400, DTW 325×2300, and DTW 450×2750 screens were measured as 1738 Pa, 2694 Pa, 3903 Pa, respectively. With increasing woven density of the screen, the bubble point pressure increases due to a reduction in its pore size. The results show only minor deviations from literature values, indicating that the structural configuration of SCLAD does not significantly influence the screen’s bubble point pressure, namely, the device’s gas barrier capability. After pressurizing the inner Dewar, LN 2 inside the Dewar flowed through the screen into the channels and was discharged through the top pipe. During the outflow process, as the liquid level decreases, anti-gravity acquisition of single-phase LN 2 was successfully achieved even most of the screen surface was exposed to the ullage. This result verifies the effectiveness of SCLAD in phase separation and liquid acquisition of cryogenic fluids under variable gas-liquid phase distributions. The occurrence of gas entry in the glass tube indicates the failure of all-liquid outflow through the SCLAD. With an increase in the pressurization pressure (i.e., an increase in the liquid outflow rate), the device experienced earlier failure. Under the same pressurization conditions, SCLAD samples equipped with denser screens exhibited later failure, which corresponded to a higher evacuation rate. This study provides valuable insights into the operational mechanisms of device-level SCLAD under cryogenic conditions, thereby laying a solid foundation for promoting the engineering application of SCLAD in cryogenic propellant systems.

Due to nonzero heat leakage through the tank wall, buoyancy-driven flow develops within liquid propellant tanks. Consequently, a vertical temperature gradient is established, commonly referred to as thermal stratification. Because stratification strongly influences temperature uniformity and thermal stability within the tank, a comprehensive understanding of stratified-layer growth is essential for the optimal utilization of cryogenic fluids and efficient cryogen management. The present study conducts a numerical investigation of thermal stratification in liquid propellant tanks. Simulations are performed using a numerical model of a cylindrical tank subjected to a uniform sidewall heat flux, in which a two-dimensional representation of the liquid region is coupled with a one-dimensional model of the ullage region. The development of thermal stratification is examined with respect to tank geometry, wall heat flux, and the degree of liquid subcooling. The numerical results show that the growth rate of the stratified-layer thickness, normalized by the liquid height, is higher in tanks with a smaller radius and a lower liquid height. In terms of operating conditions, the results indicate that the normalized stratified-layer growth rate is suppressed under reduced heat ingress and increased liquid subcooling. The underlying mechanisms of these trends are further investigated through detailed visualizations of unsteady flow and thermal fields, enabling an in-depth analysis of stratification dynamics that are difficult to access experimentally. Further analysis of the numerical results based on an existing theoretical model indicates that accurate quantification of stratification growth requires a well-defined criterion to distinguish the warm stratified layer from the colder bulk liquid. Accordingly, a new stratification criterion is proposed in conjunction with a simplified theoretical model, which may facilitate the design and operation of cryogenic liquid propellant tanks. This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korean government(MSIT) (No. RS-2023-00279896).

Pulsating Heat Pipes are two-phase heat transfer devices that utilize self-sustained thermally driven oscillating flow of liquid slugs and vapour plugs to transfer heat between a source and a sink without any external power input. Distinguished by their wickless capillary tube structure with meandering turns, PHPs offer higher heat transfer efficiency and structural simplicity. The extension of this technology into the cryogenic domain, for example, by using the PHP as a thermal link between the cryocooler and the system to be cooled, allows one to easily address the thermal management challenges associated with the conventional alternative of using solid copper straps in similar situations. Some critical applications where cryogenic PHPs can be a viable alternative include cooling superconducting magnets, infrared detectors, and optical arrays in space telescopes. Despite these applications, the thermo-hydrodynamics of cryogenic PHPs remains poorly understood in space environments and thus warrants further investigation. To address this, a numerical study has been conducted to examine the start-up and thermal performance of a cryogenic PHP operating under terrestrial (1g) and microgravity (0.01g) conditions. The CFD model has been developed using ANSYS Fluent software. Neon is chosen as the working fluid. The Volume of Fluid (VOF) multiphase model has been used to model multiphase flow, with the Lee model solving the mass transfer due to evaporation and condensation. The PHP has been constructed with a capillary tube having an inner diameter of 1.5 mm, which exceeds the theoretical critical diameter (1.27 mm) defined by the classical Bond number criterion. Stainless steel is selected as the tube material to account for the conjugate heat transfer within the CFD model. The PHP orientation is bottom heat mode. The evaporator section is supplied with a constant heat flux boundary condition, while the condenser section is set to a constant temperature of 27 K. The results reveal that the PHP successfully operates in gravity and microgravity conditions, despite exceeding the theoretical critical diameter. The flow visualizations indicate a more discrete flow pattern at ground conditions, whereas in microgravity conditions, a sharp slug flow pattern forms, indicating the dominance of surface tension. This investigation also suggests that the ground-based design criteria are conservative for microgravity operations of the PHP, suggesting the potential of larger-diameter PHPs for space applications.

In deep-space exploration missions, cryogenic propellants within spacecraft tanks are subjected to complex variable-gravity environments. During this process, the gas-liquid interface undergoes drastic changes, triggering intense phase-change and significant alterations in thermodynamic behavior. This study establishes a liquid oxygen (LOX) reorientation experimental system based on drop-tower platform. During the initial drop phase, the liquid propellant undergoes a step change from normal gravity (g=1g 0 ) to microgravity (g=10 -3 g 0 ). After LOX climbing along the inner wall, the LOX interface undergoes underdamped oscillations. Within 2.5 s, the temperature in the gaseous region increased by 0.48 K, and the pressure rose by 4.4 kPa. When the drop tower system re-entered the recovery net, the gravity level of LOX transitioned from microgravity (g=10 -3 g 0 ) to a high-overload condition (g=10 g 0 ), causing the contact line to descend and the interface center to deform. Subsequently, the transition of gravity level caused LOX to roll up along the inner wall, forming a liquid film, which triggered a rapid pressure rise. The pressure rose by about 27.25 kPa in the 1 s and then rapidly fell back to 225 kPa. Meanwhile, the temperature dropped rapidly by 15 K within 0.5 seconds and then stabilized. The present study could provide guidance for the design of on-orbit management for cryogenic propellants.

Pulse tube refrigerators (PTRs) are widely utilized in aerospace and infrared detection due to their long service life, attributed to the absence of moving parts at the cold end. In space applications, enhancing the efficiency of PTRs is critical, which means that the low-temperature environment can be achieved with lower electrical power consumption. To optimize efficiency and phase-shifting characteristics, this study employs a warm displacer as a phase shifter. Initially, numerical simulations were conducted to analyze the influence of piston stiffness, moving mass, and the rod-to-piston diameter ratio on the phase-shift behavior of the warm displacer. Based on these findings, a PTR prototype was designed and fabricated. Subsequent experimental validations were performed to verify the conclusions drawn from the numerical analysis. Finally, the performance of the warm-displacer PTR was evaluated. Experimental results demonstrate that at an input power of 400 W, the refrigerator achieves a cooling capacity of 26.4 W, corresponding to a relative Carnot efficiency of 18%.

GKN Aerospace was one of the partners in HyFIVE, a UK research programme to develop liquid hydrogen fuel systems for electric propulsion in civil aircraft. As part of the work, a test facility called Hy4 was designed and built for testing sub-scale hydrogen tanks and other components. The vacuum vessel of this facility incorporates a large removable aperture, allowing the equipment under test to be removed and exchanged easily. In this paper the design of the facility and the first test campaign are described and analysed. Two loss of vacuum scenarios (slow and rapid) were carried out with a 250 litre stainless steel tank filled with liquid hydrogen to three different levels. The performance and responses of the system are presented, and compared with the ISO 21013‑3 standard for the design of pressure relief systems for cryogenic vessels.

In the regeneration cooling and pipeline pre-cooling processes of aerospace cryogenic propulsion systems, the flow boiling of cryogenic fluids generates complex interfacial interactions and unsteady processes, which directly affect the system's stable operation. This paper focuses on the heat transfer and flow characteristics of liquid nitrogen nucleate boiling in horizontal rectangular channels, combining visual experiments with numerical simulations. For the experimental investigation, a visual experimental system for liquid nitrogen flow boiling was constructed, and experiments were conducted within the ranges of 5.5 bar and 7 bar system pressures, mass flow rates of 40–60 kg/h, and heat fluxes of 25–175 kW/m 2 . For the numerical simulations, a two-dimensional model based on the Volume of Fluid (VOF) method and conjugate heat transfer was established to simulate the boiling processes under different operating conditions. Experimental results reveal that elevated heat flux predominantly drives bubble nucleation and growth, markedly increasing nucleation site density and encouraging coalescence. Higher mass flow delays boiling onset through enhanced flow shear, which accelerates bubble detachment and migration. Increased pressure raises saturation temperature, thereby augmenting subcooling and suppressing bubble activity. Bubbles display a multi‑scale size distribution; individual bubble motion is governed by mainstream drag and buoyancy, yet becomes increasingly influenced by bubble‑bubble interactions as density rises. Simulation outcomes further demonstrate that heat flux intensifies phase change and flow instability, exacerbating spatial non‑uniformity. In contrast, mass flow exerts a stabilizing influence via convective and shear effects—higher rates improve convective heat transfer while suppressing large‑scale vortices. Increased pressure weakens the thermodynamic driving force for nucleation, leading to smaller bubble sizes and attenuated overall fluctuations. The flow boiling behavior is thus governed by the coupled effects of heat flux, mass flow, and pressure. By integrating experimental visualization with numerical modeling, this work elucidates the underlying mechanisms governing bubble dynamics and heat transfer during liquid nitrogen nucleate boiling. The results offer theoretical insights and empirical support for the thermal design and stability optimization of cryogenic flow systems.

The studies of the cosmic microwave background (CMB) face significant technical constraints. To obtain accurate maps, the instrument must be capable of measuring fluctuations on the order of microkelvin over long observation periods (larger than two years). The Planck mission was a success, but with performance of 0.1 µW at 100 mK, its lifetime was limited by the maximum amount of helium that could be loaded onboard the satellite. Indeed, the refrigerator operated as an open-cycle dilution refrigerator (OCDR) venting both helium isotopes into space. Future space missions require more cooling power, lower temperatures, and extended lifetimes. Consequently, it is necessary to close the dilution cycle using a phase separator. Know-how transfer has been arranged between CEA-CNRS, to develop the Closed Cycle Dilution Refrigerator (CCDR) from a proof-of-concept model (TRL4) at Institut Néel to an experimental model (TRL 5-6) at the Département des Systèmes Basse Température (DSBT). The learning process can therefore be summarized in three phases: (i) Confining the ³He /⁴He mixture with capillary forces using a porous material at a temperature of about 1 K, (ii) separating the two isotopes through the fountain effect coupled with superfluidity and then (iii) recirculating each of the isotopes to the mixing chamber with a capillary. Currently, only the ⁴He’s circulation aspect (iii) has been addressed. Multiples test campaign has allowed us to observe the behaviour of superfluid helium in our device. Further tests with porous materials will help us to understand the mixture’s confinement (i) requirements.

The aerospace sector is a significant and growing contributor to global greenhouse gas emissions, accounting for approximately 2.5% of global CO 2 emissions in 2023, and with a 5.3% increase in demand between 2024 and 2025. It is predicted that air traffic could double over the next 20 years, so it is clear that the decarbonisation of aviation, and therefore the electrification of aircraft, should be a key focus of the industry in order to meet international net-zero targets. Hydrogen-electric propulsion systems are one such method of doing so, as they generate their power from fuel cells, and eliminate the emissions typically associated with traditional combustion engines. There are a number of key technology enablers which are required for hydrogen-electric propulsion systems to be adopted in aviation, one of which are cryogenic power distribution networks. These can lightweight and enhance the performance of such propulsion systems when compared to traditional or high-voltage power distribution. By using the liquid hydrogen fuel as a heat sink with a secondary supercritical helium cooling loop, the electrical conductors and machines can be cooled to sufficiently low temperatures so that they operate with substantially reduced resistive losses. This translates into smaller and lighter systems that are more suited for use on aircraft. The increased efficiency also has cascading benefits for the size and weight of the fuel and power generation systems. However, aircraft must operate within multiple flight phases, and whilst offering lightweighting opportunities for the power generation system, the inclusion of energy storage systems can decouple the relationship between fuel flow and propulsive power. System modelling of the cryogenic cooling loop is therefore required to understand the dynamic interactions between power levels, mass flows, temperatures and pressures. Here, the functional details of a one-dimensional system model for a cryogenic cooling loop on a hydrogen-electric aircraft are described, and preliminary results on the stability and operation of the cooling loop are presented. The model was created using MATLAB Simscape, with custom code to account for the variation of material and fluid properties at cryogenic temperatures, accurately model the behaviours of cryogenic components, and estimate boiling heat transfer coefficients for hydrogen. Results show that in some circumstances, low-power flight phases such as descent, landing, and taxiing may become limiting design points for the cryogenic cooling loop, and that operating temperature limits may be exceeded during transitions between flight phases. This work will form the basis of further studies into how cryogenic cooling loops can be safely and stably operated on an aircraft, and into the viability of using superconducting technologies on aircraft.

Liquid hydrogen (LH 2 ) exhibits unparalleled performance advantages of high specific impulse, non-toxicity and pollution-free nature, which make it as the preferred propellant selection for the upper stage of launch vehicle. With the growing demand of deep-space exploration, there is an increasing requirement for cryogenic upper stages to be equipped with the capability of long-duration coasting under microgravity condition. During the coasting phase, heat flux from space solar radiation and planetary albedo could bring about temperature rise of the cryogenic propellant as well as the tank pressurization. However, a successful in-space restart of the upper stage engine requires that the LH2 temperature should be maintained below a specified value and the tank pressure should be controlled within a defined operational range. To meet these requirements, on-orbit venting and liquid flash inside the cryogenic propellant tank is regarded as an effective approach for regulating tank pressure and propellant temperature. Given that the coasting period may last from several hours to several days, the self-pressurization and venting-flashing processes alternately occur, and the thermodynamic performance of liquid hydrogen should be known in advance for the propellant management designs. In this study, a thermal multi-zone model (TMZM) was established to systematically investigate the thermodynamic behaviors and mass transfer characteristics for the cyclic process of self-pressurization and venting-flashing in microgravity condition. This model established continuity and energy governing equations across six region nodes, including ullage, liquid, interface, flash bubble, ullage-contacted wall and liquid-contacted wall. To predict the flashing rate, a thermal non-equilibrium model (TNEM) incorporating the wall nucleation hypothesis along with bubble growth and transport analysis was implemented. Moreover, a dimensionless thermodynamic analysis method was further developed to quantify the contributions of heat and mass transfer terms on the variation rates of pressure and the temperature. The results show that the maximum error between the experimental data and the simulation results of the developed model were 2% for the self-pressurization process and 6.2% for the venting-flashing process, respectively. During the venting-flash process, liquid cooling is predominantly driven by the latent heat required for the flashing phase transition, accounting for up to 98.9% of the liquid temperature reduction in the baseline case. In the ullage region, both of the generation of flashing vapor and the ullage-wall heat transfer act to suppress the depressurization rate, whereas the temperature decrease in the ullage, caused primarily by flashing vapor and gas venting, is the dominant factor contributing to pressure reduction. Furthermore, it indicates that the venting tube diameter exerts a significant impact on the depressurization rate and the propellant consumption, while gravitational condition exhibits a relatively weak effect. Time-dependent accumulation and gravity-dependent parameters, such as ullage-wall heat transfer and interfacial evaporation, are identified as the main contributors for the thermodynamic variations. In terms of the overall self-pressurization and venting-flashing cycle, the results show that daily propellant consumption under temperature control band is 3% higher than that under pressure control band. When the pressure control band is expanded from 25 kPa to 50 kPa, the daily propellant consumption decreases by 6%. As the filling ratio increases from 17.2% to 47.5%, daily propellant consumption rises by 27.6% due to increased flashing losses. This work provides valuable insights for optimizing on-orbit pressure and propellant temperature control strategy of the cryogenic upper stage.

Cryogenic liquids are essential working fluids in a wide range of engineering applications, including space propulsion, superconducting systems, and energy technologies. When cryogenic liquids come into contact with room-temperature systems, a chilldown (or quenching) process occurs. In liquid propulsion systems, efforts to reduce propellant consumption and overall system mass make the selection of structural materials and geometric dimensions a crucial design consideration. Experimental studies have demonstrated that chilldown characteristics-particularly the minimum heat flux (MHF) and the corresponding surface temperature-exhibit strong dependence on both plate geometry and material. Accordingly, a systematic investigation of material and geometric effects on quenching is required to improve prediction capability and provide deeper physical insight into cryogenic chilldown phenomena. In this study, quenching experiments are performed on horizontal plates submerged in a liquid nitrogen pool. Stainless-steel plates with varying diameters are first examined to determine the minimum diameter required to neglect edge effects. Then, plates made of stainless steel, aluminum, and copper with varying thicknesses are tested. The experimental results show that specimens with lower thermal mass exhibit shorter regime transition times defined as the time required to reach the MHF point. For a fixed diameter, boiling curves obtained for different materials and thicknesses indicate that the MHF decreases with decreasing thickness for all tested metals. For relatively thick plates (L >1.0 mm), the MHF ranks in the order of stainless steel > aluminum > copper. The MHF temperature is also strongly influenced by plate thickness and exhibits asymptotic behavior for thicknesses above 2 mm. Among the three metals, copper shows the lowest MHF temperature, whereas stainless steel shows the highest, indicating that the MHF temperature decreases with increasing thermal effusivity. Based on the experimental data, an empirical correlation is developed relating the MHF temperature to thermal capacity per unit area. This expression effectively reproduces the observed variations in MHF temperature with material properties and plate thickness. These observations indicate that both thermal properties and thermal mass play key roles in determining quenching characteristics. Thus, these findings can be used as practical guidelines for designing cryogenic systems, particularly for material selection and dimensional sizing under quenching conditions. This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korean government(MSIT) (No. RS-2023-00279896).

With the advancement of space exploration missions, the demand for efficient and lightweight cryogenic technology in the liquid hydrogen temperature range (20–30 K) is increasingly urgent. Pulse tube cryocoolers (PTCs), with their no-moving-part cold end, simple structure, and high reliability, have become the ideal choice for refrigeration in this temperature range. This paper presents a simulation and experimental study of a highly compact, two-stage gas-coupled coaxial pulse tube cryocooler, designed for liquid hydrogen temperature range applications, with a frequency of up to 90 Hz. The cryocooler utilizes an inertance tube and gas reservoir for phase adjustment, with the introduction of a double-inlet to further optimize the phase distribution. The phase distribution characteristics of the two-stage cold fingers and the heat loss in the regenerator of the liquid hydrogen temperature range under high-frequency conditions are analyzed. The experimental results show that, using only the inertance tube and gas reservoir for phase adjustment, the cryocooler achieved a minimum temperature of 18.4 K under no-load conditions with a compressor input power of 300 W, charging pressure of 4 MPa, and a frequency of 90 Hz. The system provided cooling capacities of 146 mW and 1120 mW at 20 K and 30 K, respectively. After adding double-inlet phase adjustment, the no-load minimum temperature decreased to 17.0 K at a frequency of 88 Hz, with cooling capacities of 217 mW and 1050 mW at 20 K and 30 K, respectively. This study demonstrates the feasibility of the lightweight design of a pulse tube cryocooler in the liquid hydrogen temperature range under high-frequency operation conditions and provides valuable insights for future space cryogenic applications.

The chilldown process is crucial for the high flow rate and stable transfer of cryogenic fluid. As a highly transient process, the cryogenic chilldown process is complex. The two-phase flow pattern change could bring about significant flow instability, and the pipe structure and gravity condition also exert influence on the two-phase flow variation. At present, most chilldown experiments usually adopt small-sized horizontal test pipes where the two-phase stratified flow induced by gravity is not clearly manifested. To give a clear exhibition of the pipe size influence on the chilldown performance, liquid nitrogen is selected as the test fluid, and two chilldown experiments with pipe inner diameters of 15 mm and 25 mm are conducted in the present study. In these tests, the variations of the two-phase flow during the chilldown process are captured through a high-speed camera, and the wall temperature, flow rate, pressure difference, and inlet pressure are also monitored. The results reveal that both cases undergo stratified film boiling, stratified nucleate boiling, wavy flow, and full-liquid flow. In the DN25 chilldown event, the stratified flow is more stable, with few liquid contacts the top region of the wall. Combined with the results of flow rate, the pressure difference, and wall temperatures along the tube, it is found that heat transfer at the top primarily relies on vapor convection for the DN25 chilldown event, and the temperature here decreases slowly. The sidewall is dominated by intermittent liquid contact, causing violent fluctuations in heat flux. In contrast, the tube with a smaller diameter mostly maintains a higher liquid level, and the sidewall region could contact the liquid phase during the chilldown process, which yields a smoother variation of the heat flux curve. Moreover, the large-diameter tubes have greater temperature differences between the top wall and the bottom wall during the chilldown process. The maximum temperature difference occurs when the bottom finishes the film boiling, with a value of 98.7 K. In the small-diameter tube case, the maximum temperature difference is about 65.5 K. An energy analysis reveals that although the heat capacity of the large-diameter pipe is approximately 1.74 times that of the DN15 pipe, the DN25 pipe chilldown requires 2.25 times longer to complete chilldown than the DN15 pipe, and the liquid nitrogen consumption of the DN25 chilldown case is about 7 times of the small tube case. To enable the liquid to reach the upper region of the pipe and increase the cooling rate, the large-diameter pipe is more suitable for adopting a high-Re chilldown. In addition, the flow instability in the chilldown process is mainly caused by boiling heat transfer and plug flow near pure liquid flow. In the DN15 tube case, pure liquid flow is basically approached as soon as the wall is sufficiently chilled so that the combined effect of the above two factors induces pressure fluctuation. Comparatively, the large-diameter pipe firstly meets the chilldown purpose and then reaches the pure liquid flow state. Therefore, two distinct oscillations would be experienced. It is also indicated that the pressure shock caused by plug flow is more severe. That is, during the chilldown process, even if the pipe wall is sufficiently cooled, great attention should be paid to the pressure fluctuations near the pure liquid flow. Furthermore, it is demonstrated that the results from the small-diameter tube chilldown tests are not suitable for representing the chilldown performance in a large-sized pipe, and thus, more chilldown tests using a large-sized tube should be performed.

In cryogenic upper stages of launch vehicles, liquid hydrogen (LH 2 ) tanks experience self-pressurization during extended coast phases between engine cut-off and restart. Intermittent settled venting effectively controls tank pressure and conditions propellant temperature prior to reignition, but the low boiling point of LH 2 and strict pre-restart temperature requirements limit allowable coast durations. This experimental study investigates thermodynamic behavior and venting strategies for LH 2 during coast phases. A ground-based facility with a 0.245 m 3 tank was constructed directly using LH 2 as the working fluid rather than a simulant like liquid nitrogen. Transient temperature and pressure responses were measured under intermittent venting within a pressure control band of 130–170 kPa. Results show that LH 2 temperature decreases from 21.5 K to 21.1 K during each venting cycle, yielding a cumulative hydrogen loss rate of only 2.6% over a 7-hour coast phase. Reducing the vent orifice diameter from 1/2 inch to 1/8 inch decreases the number of venting cycles from 24 to 12 while causing only minor changes in total vented mass. These findings provide valuable experimental support for optimizing intermittent venting strategies and extending coast durations in LH 2 -fueled upper stages.

Cryogenic fluids undergo rapid phase changes when introduced into systems at ambient temperatures far above their saturation temperatures. Consequently, prior to normal operation, a chilldown (quenching) process is required to cool the system to the cryogenic temperature levels. Accurate control of the chilldown process is therefore critical in cryogenic applications for meeting safety requirements and reducing cryogen consumption. The chilldown process is dominated by the film boiling regime; thus, the minimum heat flux (MHF) point, where the film boiling regime is terminated, plays a key role in determining the overall chilldown time. Experimental studies have shown that the MHF point is significantly affected by the thermal mass and material properties of the system. Therefore, a reliable prediction of the MHF temperature and its impact on the chilldown time is essential for the thermal design of the cryogenic systems. Although numerous theoretical studies have proposed correlations to predict the MHF temperature, no existing model accurately quantifies the effects of system geometry and solid thermal properties on the MHF point. This study develops a theoretical model to predict the MHF temperature and regime transition time—the time required to reach the MHF point—for a flat metal plate immersed in a liquid nitrogen pool. Using the proposed model, the effects of geometric dimensions and material properties on the chilldown process are systematically analyzed, and the following conclusions are obtained: (1) The regime transition time is linearly proportional to the thermal capacity of the specimen. (2) The MHF temperature depends on the system thermal mass, with smaller thermal mass leading to higher MHF temperature and shorter regime transition time. (3) When local liquid-solid contact occurs at the fluid-solid interface, metals with low thermal effusivity and diffusivity experience greater local temperature drop, resulting in shorter regime transition time. It is worth noting that the chilldown process involves coupled transient conduction and boiling at the fluid-solid interface, which complicates the interpretation of quenching data. Accordingly, a universal approach to understanding quenching is proposed, in which the contribution of transient conduction is first interpreted independently. To validate the proposed approach, a universal quenching curve is introduced, onto which individual quenching curves collapse, independent of material properties and geometric dimensions. The effects of various parameters, including material properties and geometric dimensions, are then analyzed separately to clarify their roles in the boiling process. These findings provide a unified method for interpreting quenching data under various material and geometric conditions. This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korean government(MSIT) (No. RS-2023-00279896).

Helium-isotope separation by cryogenic distillation often requires a long time to reach a stable separation regime, which can markedly limit experimental throughput and increase operating costs. Because ³He is scarce and experiments are expensive, optimizing start-up is particularly important. In this study, we develop a dynamic simulation model for a ³He/⁴He distillation column and compare alternative start-up schemes in terms of the time needed to reach steady state. Based on these results, we propose operational recommendations to shorten start-up time, providing guidance for subsequent experiments and engineering operation.

An experimental platform is designed to investigate the flow field of superfluid helium (He II) using laser interferometry. The platform consists of a cryostat with optical windows and a Mach–Zehnder interferometer. A heater installed inside the cryostat induces variations in the He II flow field and several heat transfer phenomena, including thermal boundary layers and second sound. Heating-induced perturbations lead to changes in the density and refractive index of He II, with the corresponding flow field information encoded in the interference images. Interference images are acquired in real time by a high-speed camera, and variations in the He II flow field can be analyzed by comparing a series of such images. This platform provides a non-contact, visualized measurement method for the He II flow field, which is of great significance for investigating its unique heat transfer phenomena and mechanisms. Currently, the platform has been fully constructed, and preliminary experimental results have been obtained.

A system for the automatic low-temperature calibration of thermometers using the comparison method has been designed and fabricated. The system can simultaneously calibrate four capsule-type thermometers and four long-stem thermometers. Utilizing liquid nitrogen, the cryostat achieves precise temperature control in the range from −180 °C to 30 °C. The calibration uncertainty for platinum resistance thermometers using this system is approximately 5 mK, with a 95% confidence interval. Due to the lack of commercial calibration baths for temperatures below −100 °C, this system extends the temperature range for the calibration of thermometers via the comparison method. The key component of the system is a low-temperature cryostat, designed for high thermal stability and uniformity. The cryostat features two copper blocks that ensure accurate temperature control at the calibration points. The system is equipped with a precise temperature control mechanism that integrates heaters and thermocouples to regulate the temperature. Cooling is achieved through liquid nitrogen, and the system is designed to automatically adjust the thermometer temperatures to the target values without manual intervention. A notable innovation in the system is the automatic refilling mechanism for liquid nitrogen, which ensures that the cryostat maintains sufficient cooling power for stable temperature control at the calibration block, eliminating the need for manual refills. The system operates through a dedicated algorithm that manages the temperature rise from −180 °C to ambient temperature, enabling calibration at multiple temperature points without interruption. This automation significantly reduces calibration time and effort, ensuring high efficiency and accuracy. During validation, four standard platinum resistance thermometers were calibrated. The results showed that the system could calibrate these thermometers with an uncertainty of approximately 5 mK, which is acceptable for calibration by comparison method. Additionally, the system is capable of automating the calibration of other types of resistance thermometers, thermistors, and thermocouples, making it versatile for various industrial and scientific applications. The development of this automatic calibration system represents a significant advancement in the efficiency and accuracy of low-temperature calibration, with potential applications in industries requiring precise temperature measurements, including cryogenics, aerospace, and biotechnology.

A sudden loss of vacuum (SLV) in a liquid-helium (LHe)-cooled superconducting RF (SRF) beamline is a high-consequence failure mode: rapid ingress of warm gas triggers intense cryocondensation that can contaminate the beamline and impose a large transient heat load, driving helium boil-off and a rapid pressure rise within the cryomodule. While prior studies in simple straight tubes immersed in LHe qualitatively showed that cryopumping can slow down the gas flow, the field has lacked a predictive framework capable of quantifying gas-front propagation in the full, realistic geometry of SRF cavities—information essential for specifying credible response requirements for vacuum-break protection and pressure-relief systems. Here we develop a comprehensive, time-dependent numerical model that simulates transient gas propagation, cryocondensation, and frost-layer growth during SLV events in LHe-cooled accelerator beamlines with full-scale cavity geometry. The model resolves compressible gas dynamics in real space while coupling wall cryocondensation and mass deposition to heat transfer into the LHe bath, enabling direct prediction of gas-front evolution, spatially resolved frost accumulation, and the resulting thermal loading. Validation against our prior measurements demonstrates that the simulations accurately reproduce the observed slowing of gas propagation due to cryopumping. We then apply the validated framework to realistic multi-cell SRF cavities and obtain quantitative cavity transit times over a range of inlet mass flow rates. These results yield a compact correlation between cavity traversal time and inlet mass flow rate, providing a physics-based basis for setting protection-system response requirements in SRF beamline applications. Beyond these engineering metrics, the simulations reveal a striking compressible-flow feature: the formation of Mach disks inside the cavity driven by the extreme pressure ratio and the converging cavity geometry. The Mach-disk location evolves in time and exhibits a clear dependence on inlet mass flow rate, suggesting a potential diagnostic signature for estimating leak severity during practical vacuum-break events.

Shenzhen Superconducting Soft-X-ray Free Electron Laser (S 3 FEL) is a linear accelerator based on superconducting radio frequency (SRF) technology in continuous wave (CW) aiming to produce high-quality electron beam with repetition rate up to 1 MHz and energy up to 2.5GeV. The electrons will be accelerated by 1.3 GHz superconducting cavities with cooling capacities cooled down to the temperature of 2 K from S 3 FEL cryogenic system. The S 3 FEL cryogenic system comprises three independent helium cryogenic plants with different cooling capacities, which each is the Test Facility Cryoplant (TFCP), Prototype Accelerator Cryoplant (PACP), and Accelerator Cryoplant (ACCP). Similarly, the S 3 FEL cryogenic system also has three independent cryogenic control systems which each is corresponding to the three cryogenic systems. The paper will focus on the control system overview for the S 3 FEL project. And furthermore this paper reports on the development progress of the S 3 FEL cryogenic control system.

At the Institute for Plasma Research (IPR), the Steady State Superconducting Tokamak (SST-1) utilizes advanced cryogenic systems comprises two main temperature sections 4.2 K and 77 K which are primarily used for cooling superconducting magnet coils and minimizing heat loads. Operating at such extreme temperatures and high pressures involves significant safety challenges. The behaviour of materials under these conditions differs drastically from that at room temperature, often leading to unexpected outcomes in strength and performance. Typical hazards include material embrittlement, pressure build-up from rapid vaporization, accidental leaks, and oxygen-deficient environments, any of which can result in catastrophic failures if not properly managed. The cryogenic helium plant consists of several critical subsystems that demand continuous attention and regular inspection to ensure personnel safety and prevent equipment damage. Key systems include: high pressure at 150 bar (g) in helium gas pressure vessels, safety mountings as safety valve, rupture disc and Non-Return Valve, LHe and LN2 fluid cryogenic transfer lines, Thermal and vacuum insulation, 80 K vent line, high pressure helium gas cylinders for filling and testing, low temperature lab experiments at 4.2 K and 77 K, materials testing at cryogenic temp and high pressure. A centralized alarm monitoring system developed on the Wonderware Supervisory Control and Data Acquisition System (SCADA) platform is vital for ensuring operational safety. It continuously tracks critical process parameters across various subsystems and delivers real-time notifications through both audible alarms and visual indicators whenever abnormal conditions occur. All key data are displayed in real time on a control room monitor, enabling operators to quickly identify and resolve issues without needing constant on-site supervision. This system has significantly reduced human error, helium and cryogen losses, and potential equipment failures. Recent operational challenges, such as cryogen leakage due to bellows failure, ruptured safety discs in high-pressure vessels, thermal insulation degradation, and helium leak mitigation, have been efficiently identified and rectified through systematic monitoring and timely intervention. Furthermore, comprehensive risk assessments, personnel training programs, and emergency response planning have greatly strengthened operational safety. With the increasing complexity of the SST-1 cryogenic infrastructure, the integration of advanced monitoring technologies and automated safety systems has become essential. To ensure a safe working environment and effective emergency handling capability, the Cryogenics Division has established and consistently follows robust safety practices, norms, and culture. These measures collectively minimize accident risks, ensure reliable operation of cryogenic and high-pressure systems, and foster a safety culture aimed at achieving zero accidents at IPR. This presentation highlights the mandatory aspects of cryogenic safety, including safe handling, hazard identification, protective and preventive measures, emergency actions, and safety guidelines for cryogenic and high-pressure systems. It also shares practical experiences, case studies, and lessons learned from real operational incidents, demonstrating the continuous improvement of safety procedures, norms, and equipment within the SST-1 cryogenic and high-pressure facilities. Keywords: Cryogenic plant, Cryogenics and high pressure systems, 4.2 K & 77 K, Helium leak tightness, Safety implementation

Cryogenic cooling technology is essential for modern applications, such as magnetic resonance imaging and quantum computing; however, it currently relies heavily on critical resources such as helium and heavy rare-earth elements. As demand for cryogenic cooling increases, developing alternative technologies that reduce reliance on these scarce resources is crucial. This study introduces regenerator materials from abundant elements—copper, iron, and aluminum—that function as Gifford–McMahon (GM) cryocoolers. These materials achieve cryogenic cooling through the spin frustration effect, where competing magnetic interactions enhance magnetic heat capacity. CuFe 1-x Al x O 2 demonstrates effective cooling capacity at the helium condensation temperature comparable with that of conventional heavy rare-earth-based materials and surpasses the performance specifications of commercial GM cryocoolers.[1] These findings demonstrate the potential of non-rare-earth magnetic materials for sustainable cryogenic technology, reducing dependence on critical resources. [1]Noriki Terada, Hiroaki Mamiya, Akiko T. Saito, Shinji Masuyama, Scientific Reports. 15 44240 (2025).

Pulse tube cryocoolers working at liquid-helium temperatures have been widely used in high-tech fields such as quantum computing, cryogenic superconductivity and cutting-edge medical applications, benefitting for its low vibration and long life. Double-Inlet valves, as a core mechanism for regulating the phase of the alternating mass flow, play an important role to enhance the performance of the cryocooler. However, how to get the optimized performance in different situations, such as requirements of cooling down time, 1 st stage or 2 nd stage cooling power with specified valve opening sequence, is becoming an interesting question with practical significance and demand. This study proposes to regulate the double-inlet circuits of the 1 st -stage and 2 nd -stage pulse tubes with time-dependent valves. An entire-system Sage model and an experimental platform of a two-stage 4 K pulse tube are constructed. The effects of the double-inlet valves parameters (time-dependent opening characteristics and flow area) on the gas flow ratio, energy flow, and refrigeration performance of each stage are systematically analyzed to optimize the cryocooler design. Both numerical and experimental results show that the proposed time-dependent valve regulation strategy effectively enhance the refrigeration performance, with the cooling capacities of the 2 nd stage reaching 1.8 W@4.21 K.

Cryogenic refrigeration, as a crucial supporting technology for modern applications such as gas liquefaction and energy storage, is experiencing continuously growing demand. Thermoacoustic driven cryocoolers are garnering significant attention due to their ability to directly utilize thermal energy as a driving source, operate independently of electrical power, and possess a simple structure. However, the current technical bottleneck of thermoacoustic driven cryocoolers lies in the inherent limitations collectively determined by the hot source, cold end, and ambient temperatures. To achieve a lower cold end temperature, a correspondingly higher optimal hot source temperature is often required, which may exceed the permissible range of existing heat exchanger materials, thereby constraining their practical application. To address the aforementioned challenges, this paper proposes an innovative acoustic power bypass structure. This structure is designed to effectively enhance the acoustic power output of a thermoacoustic engine at lower hot source temperatures, thereby improving its capability to drive a cryocooler and ultimately achieving efficient cryogenic refrigeration. This innovative design is detailed in this study, and geometric parameters of its key components were optimized using SAGE software. Based on this optimization, relevant experimental investigations were conducted, and preliminary experimental results fundamentally validate the effectiveness of the new structure in reducing the optimal hot source temperature. This technology broadens the range of hot source options, offering new insights for the future design and optimization of thermoacoustic driven cryocoolers. It is also expected to promote their practical application in areas such as waste heat-driven air liquefaction for energy storage, carbon dioxide capture, and natural gas liquefaction and storage.

This paper presents an overview of recent development of the high-capacity cryogen-free dilution refrigerator (DR) systems in authors’ laboratories to meet the demanding cooling requirement of the developing superconducting quantum computer (SQC) with over 1,000 bits. A DR system is complicated, employing the mixture of 3 He and 4 He as the working fluid, and can be generally divided into four parts. The first part, called as Precooling unit, consists of two pulse tube cryocoolers with a gross cooling power of 6.0 W at 4.2 K, which is used to cool the working fluid from the initial atmosphere temperature to 4.2 K. The second part, named as Joule-Thompson unit, further lowers the working fluid to around 0.86 K. The third part is named as dilution Unit, in which the mixture of 3 He and 4 He achieves the target operating temperature range of 5 mK to 100 mK. And the fourth part, called as pumping unit, consists of several special pumps and tubes and ensures the working fluid circulates in the overall system. A no-load temperature of 6.5 mK is achieved by the developed DR systems. The typical cooling capacity of a single DR system is 1,350 μW at 100 mK and 35 μW at 20 mK, while a composite system formed by three identical DR subsystems can achieve 4,000 μW at 100 mK and 100 μW at 20 mK, respectively. This paper introduces the application background, design philosophy and optimization approaches of the DR systems, and then presents their performance characteristics in detail. The integration technology of the DR systems with the developing SQC is also discussed.

A never-ending quest in instrumentation is to develop more sensitive and accurate sensors. For digital detectors, one can increase the sensitivity greatly by reducing the operating temperature and thus the thermal noise levels. As an example, the gravitational wave (GW) detector KAGRA, Japan, has used this principle and so will the next-generation GW detector, the Einstein Telescope (ET). ET aims to achieve an amplitude-spectral-density strain sensitivity in the order of 10^-24 m/sqrt(Hz), and such sensitivities can only be obtained when the thermal noise, mainly stemming from the mirror coating, is significantly reduced. The use of conventional coolers however introduces high levels of mechanical noise, as the compressors utilize pressure oscillations in the order of 10^6 Pa. In KAGRA, the mechanical decoupling from such sources implies also a thermal decoupling, resulting in a competition between thermal management and noise suppression. Thermal decoupling however increases cold-down time of the payload (i.e. the mirrors of the interferometer) and puts a cap on the acceptable heat load during measurements. A promising alternative to mechanical coolers is the sorption cooler. Here, the mechanical compression step is fulfilled by adsorbing low pressure gas at low temperatures by activated carbon and releasing it by heating the carbon. The use of check-valves will direct the in- and outflow, and thus providing a pulsating compressor. Buffers will regulate the flow rates further downstream to provide a constant cooling power at the Joule-Thomson restriction. The expected pressure-fluctuations in the downstream section is expected to be several decades lower than for mechanical coolers In our contribution, we will present the latest developments of our a three-stage sorption cooler. Our sorption cooler has a cooler chain of three stages: a 35 K neon stage, a 18 K hydrogen stage and a 8 K helium stage. Each stage provides a heat leak intercept and pre-cools the successive cooler to generate 3 watt, half a watt and 50 mW respectively. We will explain the concept of the sorption cooler. Using numerical modelling, we show the performance and predicted cooldown behaviour of the payload. Then, we focus on several detailed-design principles to avoid flow-induced vibrations, such as the transition to turbulence, governed by the Reynolds number. Suppression of secondary instabilities arising from bended pipes, scaling with the Reynolds number and the non-dimensionalized curvature, is avoided by strict design limitation, whereas we avoid the boiling crisis in our LN2 precooler by optimizing the heat sinks. We are currently realizing three of these coolers, including two which are to be integrated into the Dutch ETPathfinder lab. The aim of this research lab is to be a platform for the development and integration of key next-generation gravitation-wave-detector technology, such as the cryogenic infrastructure. Although being a scaled down-version of the envisioned Einstein Telescope mirror towers, our cooler has a modular cryochain design, which can easily be scaled up to meet the requirements of the ET payloads. Our efforts will thus provide a competitive low-vibration cooler to enable the realization of the next-generation gravitation-wave-detector and with that, a powerful instrument to study the physics of the universe.

A high-capacity closed-cycle 1 K cryostat based on a capillary Joule–Thomson (J–T) expansion stage is developed and experimentally characterized for low-temperature physical property measurements of superconducting detectors. The cryostat achieves a base temperature of 1.37 K and provides a cooling power of approximately 30 mW at 1.54 K. By employing a lower-impedance capillary, the cooling power can be increased up to 110 mW, at the expense of a moderate increase in the base temperature. The steady-state cooling performance is analyzed using an enthalpy-based thermodynamic model that accounts for both latent and sensible heat contributions of helium in different operating regimes. The cryostat also exhibits excellent temperature stability, with root-mean-square temperature fluctuations below 3.3 mK under typical thermal loads, satisfying the requirements for precision low-temperature material characterization. The demonstrated high cooling capacity, stable operation, and clear performance scaling provide practical design guidelines for capillary-based J–T cryostats targeting superconducting detector development and related cryogenic measurement applications.

During the transportation of liquid hydrogen, sloshing induces fluid disturbance, disrupts the initial thermodynamic equilibrium within the tank, promotes mixing between the subcooled liquid and superheated vapor, and thereby significantly influences the thermodynamic performance of the tank. The role of anti‑slosh baffles in mitigating sloshing is well established. However, the lower boiling point and latent heat of vaporization of liquid hydrogen also imply that baffles may potentially act as “thermal bridges”, exacerbating hydrogen evaporation. Therefore, to enhance the overall performance of liquid hydrogen transport tankers, it is necessary to investigate the coupled thermo‑fluid‑structural behavior under sloshing excitation after installing baffles, capture changes in temperature stratification within the tank, and examine the effects of different baffle configurations on liquid hydrogen sloshing and flash‑evaporation behavior. In this study, the impacts of various structural parameters—including opening geometry, location, baffles curvature, thickness, number, and arrangement—on the thermohydrodynamic responses inside the tank are systematically compared. Using evaporation rate, von Mises stress, and displacement of the baffles as key parameters, and aiming for the dual optimization of evaporation control and sloshing suppression, novel baffle structures and layouts for liquid hydrogen tankers have been developed.

To overcome the critical technical bottleneck of insulation layer failure induced by cryogenic shrinkage in large-scale liquid hydrogen storage tanks during pre-cooling,an innovative design scheme for a 10,000m 3 spherical liquid hydrogen storage tank equipped with an external supplementary silo is proposed. A three-dimensional thermo-mechanical coupled model was established using the ANSYS finite element suite to systematically analyze the comprehensive performance of the tank under steady-state heat transfer, stress linearization, and multi-directional seismic response conditions, thereby elucidating the influence mechanisms of key parameters on structural stability and insulation performance. It is demonstrated that the external silo accurately compensates for the cryogenic shrinkage of the inner tank; furthermore, a daily boil-off rate as low as 0.038% is achieved by the composite insulation system utilizing 205 mm elastic felt, representing a significant improvement over traditional configurations. Horizontal seismic components dominate the tank’s thermo-mechanical response, and the structure maintains complete tightness even under extreme seismic loads. Fluctuations in internal pressure and liquid level have negligible impact on the mechanical properties of external components. This research provides technical support for the optimal design of ultra-large liquid hydrogen storage facilities and promotes the large-scale application in the field of hydrogen energy storage and transportation.

Large-scale Liquid Hydrogen (LH₂) storage remains one of the most critical challenges in the hydrogen energy transition. Although hydrogen liquefaction technologies have reached maturity, LH₂ storage has not yet been realised at the scale required by emerging LH₂ supply chains. This shortfall is driven by the lack of insulation systems that suppress heat ingress while accommodating structural supports that penetrate the insulation envelope. Therefore, large LH₂ storage deployment demands containment architectures that intrinsically couple high-performance, pressure-optimised insulation systems with structural support elements. In response, this study delivers experimentally derived characterisation on cryogenic insulation configurations. Using the CS500 boil-off calorimeter, new hybrid insulation systems were systematically characterised across vacuum pressures spanning 0.001–100,000 Pa, incorporating materials including aerogels, perlite, glass microspheres, and Multi-Layer Insulation (MLI). The combined effects of material selection, layer sequencing, and hybridisation were resolved experimentally, with boil-off rates translated into effective thermal resistance values. This establishes pressure-dependent insulation behaviour and material combination interactions that have not previously been quantified for large cryogenic storage applications. In parallel, the study quantifies the coupled thermal contribution of insulation systems and structural supports, accounting for support-induced heat ingress within integrated insulation configurations. Purpose-designed insulation specimens incorporating embedded support materials (stainless steel and fibre-reinforced polymer composites) were tested under varying vacuum conditions using the CS500 apparatus, enabling resolution of conductive heat transfer along load-bearing paths under representative cryogenic conditions. The resulting measurements directly inform insulation–support interaction effects governing heat ingress across the principal containment regions of large cryogenic liquid storage tanks. To further characterise support performance within the coupled insulation system, cryogenic mechanical testing was conducted at 20 K using a newly commissioned testing apparatus capable of tensile and compressive loading up to 50 kN. The testing assessed the structural integrity and axial load-bearing performance of support materials and joint configurations under LH₂-relevant conditions. By testing support elements that also act as conductive thermal paths, the mechanical response of insulation–support interfaces was linked to the thermal behaviour quantified in the insulation assessment, confirming structural viability. Subsequently, the experimentally derived insulation performance was validated using a physics-based numerical boil-off modelling framework capable of resolving time-dependent LH₂ evaporation behaviour. The model incorporates experimentally informed thermal resistances and heat-flux inputs, explicitly resolving vapour–liquid heat transfer, transient vapour temperature evolution, and liquid mass depletion under representative conditions. This numerical assessment confirmed strong consistency between experimentally observed insulation behaviour and predicted evaporation performance across the evaluated vacuum pressure ranges. Building on the experimentally validated and numerically interpreted insulation behaviour, a coupled thermal–structural Finite Element Modelling (FEM) framework was developed to assess large-scale LH₂ storage performance. An LNG FCT philosophy was adopted as a representative reference configuration, reflecting containment geometries, insulation zoning, and structural separation at capacities reaching 200,000 m³. Within this framework, an LNG FCT system (200,000 m 3 ) was treated as a thermal baseline, enabling systematic evaluation of new insulation configurations under LH₂ storage conditions. Thermal performance was quantified through comparative analysis of Daily Volumetric Boil-off Percentages (DVBP), with vacuum pressure, validated hybrid insulation configurations, and associated thicknesses as governing parameters. Overall, the results show that introducing a pressure-optimised hybrid insulation layer beyond the LNG FCT primary containment boundary substantially reduces heat ingress across all principal surfaces. With an additional insulation thickness of 0.2–0.4 m, DVBP values were reduced to below 0.04%, approaching LNG benchmark performance, while stabilising containment interface temperatures within 140–150 K across the tank shell, base, and roof. The most pronounced performance gains were achieved under soft-vacuum conditions (

Safe storage and transportation of liquid hydrogen is crucial to the hydrogen value chain. Among the types of cryogenic vessels with the same volume, the spherical tank is one of the promising selections for the large-scale storage and delivery of liquid hydrogen due to its lowest static daily boil-off ratio. In this paper, a new correlation for predicting the dynamic process of self-pressurization for spherical liquid hydrogen tanks is proposed from the experimental data and the grey forecast method. The proposed correlation obtains an average deviation of 14%, which is lower than other correlations and can prove its reliability. In addition, the effects of initial liquid fill ratios, initial pressure, total heat leak, and tank volume on the average pressurization rate within 5 days in liquid hydrogen spherical tanks are analyzed by utilizing this correlation. The present work can benefit the design and optimization of liquid hydrogen spherical tanks.

Sloshing refers to the undesired motion of the liquid-vapour interface in a partially filled tank subjected to external excitation. In cryogenic storage tanks, in addition to the complex interface dynamics caused by tank motion, significant heat transfer occurs due to heat inleak and condensation-evaporation at the liquid-ullage interface. It is imperative to suppress sloshing using a reliable baffle insert to ensure the safety of the cryo-container. Conventional solid baffles are often heavy and unsuitable for weight-sensitive applications, such as in the aerospace sector. On the other hand, porous baffles are lightweight, occupy less volume, and can mitigate sloshing under various external loads. Moreover, cooldown time and cryogen loss are much less for a porous baffle than for a conventional baffle. The present work investigates open-cell metal foam as a potential slosh-suppression device for cryogenic applications. The favourable thermo-hydraulic characteristics of metal foam, such as high thermal conductivity, high porosity, and tunable pore densities, make it a promising candidate for cryogenic applications. CFD modelling is carried out to capture both the hydrodynamic and thermal aspects of a sloshing hydrogen tank. The standard k-epsilon (k-ε) turbulence model is employed to represent the intricate thermo-physical behavior in the vapor regime. The Peng-Robinson equation of state, in conjunction with temperature-dependent thermophysical properties, has been applied to the vapor phase, whereas constant properties have been utilized for the liquid phase. The Lee model is used to evaluate the condensation-evaporation rates at the liquid-ullage interface, while the VOF method is used to track the interface motion precisely. The model has been successfully validated with the experimental data reported (by the NASA scientists) on pressure collapse in a hydrogen sloshing tank. The ullage pressure collapse and free-surface elevation are obtained using the developed CFD framework for various sloshing frequencies and amplitudes. A metal foam baffle with high porosity and low pore diameter provides slosh suppression comparable to that of a solid baffle, resulting in significant weight savings. The free surface elevation has also been found to diminish significantly in the baffled tank, thereby shifting the tank's natural frequency and ensuring its safety. Finally, the thermo-hydraulic performance of the baffled tank is systematically compared with that of the clean (unbaffled) tank.

Hydrogen is a key energy carrier in the transition to a sustainable system in various sectors, such as transport. Hydrogen stored in liquefied form (LH 2 ) has several attractive properties that make it suitable for the energy infrastructure of these sectors. It has a relatively high energy density, high purity, zero emissions at point-of-use and is non-toxic. In its distribution chain, it has the energy-intensive step, liquefaction, where electricity is cheap. It’s critical challenge to economic feasibility, however, is managing the high boil-off rate (BOR) during long-term storage. Tanks with 20-100 m 3 storage capacity, have a daily BOR of 0.6-1.0 vol%. Efficient and distributed cooling systems have the potential to recondense the boil-off hydrogen and achieve a state of zero boil-off (ZBO). The techno-economic potential of these systems is analyzed. A non-thermal equilibrium model able to capture the thermodynamic behavior of LH 2 storage via a lumped-element approach, was developed. This model was coupled with literature data on LH 2 insulation materials, ambient conditions and economic aspects. Consequently, a parametric study was conducted for a distributed ZBO cooling architecture to estimate the OPEX and CAPEX and compare it against a benchmark. Results show that a system with an overall second law efficiency of η C = 10%, can still reduce the economic impact of boil-off losses by 80%. This is for a worst-case scenario, which is based on maximum electricity cost and minimal liquid hydrogen cost. For such a system, the return of investment (ROI) time is expected to be 1 year. This demonstrates the feasibility in further development of a modular hydrogen boil-off recondenser for medium-scale LH 2 storage. This work is part of the HyTROS program under the Dutch GroenvermogenNL initiative to advance hydrogen storage and transport technologies.

Cryogenic liquid hydrogen has distinct advantages as a transportation fuel. These include a specific energy of combustion 2.8 times greater than gasoline or jet fuel and zero carbon emissions. It can be utilized by fuel cells, turbine engines and internal combustion engines. The high specific energy of combustion of liquid hydrogen is particularly important in aviation where fuel mass can dramatically impact range and usable payload. Heat leak into tanks containing liquid hydrogen needs be minimized to reduce loss of hydrogen due to boiloff especially in long endurance applications. An effective and common practice is to insulate the tank with a hermetic shell and a vacuum of less than 10 -2 Pa pressure, creating a dewar. The tank is usually wrapped with multilayer insulation (MLI) in the vacuum space to further enhance the insulation. If the insulating vacuum is lost by the accidental leakage of air or hydrogen, the heat transfer into the tank is greatly increased, creating a high boiloff flow of hydrogen gas. For safety, the tank relief and vent system needs to be properly sized to handle these flows. To date, there has been very limited published data on the heat flux into the tank under loss of vacuum conditions on which to base these flow calculations. We report on tests that were done with a 600 liter liquid hydrogen dewar which was insulated with vacuum and MLI. The insulation space was pumped to a high vacuum and the dewar tank was filled with 35 kg liquid hydrogen at a pressure of 300 kilopascal. The insulation space was filled in two tests with air, in another test with gaseous hydrogen and in another test with liquid hydrogen. Tank pressure, insulation space pressure, vent flow rate and temperature data were taken frequently from the time of vacuum loss until the liquid hydrogen contents were depleted. Test data and calculated heat fluxes are presented and are compared to heat fluxes assumed in the current safety standards for such dewars.

Accurate prediction of self-pressurization in liquid hydrogen tanks is a key technology for safe storage and transportation, but the self-pressurization mechanism remains unclear currently and experimental data is scarce. Therefore, this paper designed and manufactured an experimental setup of self-pressurization and thermal stratification for a liquid hydrogen tank. The liquid hydrogen tank composed of an inner tank and an outer tank. The inner tank was suspended from the outer head by three support rods. The outer head and outer tank were connected by flanges. The inner and outer tanks were insulated with insulation materials of multiple layers and high vacuum. The inner tank had a volume of 450 L, an outer diameter of 612 mm, and a height of 1605mm. The outer tank had an outer diameter of 1300 mm and a height of 3089 mm. The self-pressurization range was from 0 to 1.6 MPa. One flow meter was installed to measure the daily evaporation rate under different operating conditions. Four pressure sensors and 25 temperature sensors were arranged. One capacitive level gauge and one differential pressure level gauge had been installed to measure liquid level of liquid hydrogen. Two methods were used to regulate different heat leakage conditions: heating plates and controlling the vacuum degree of the interlayer. The self-pressurization change of liquid hydrogen under different heat leakages and liquid levels has been studied. The results shown that the liquid hydrogen self-pressurization test system is reliable. The self-pressurization and thermal stratification patterns of liquid hydrogen under different liquid levels and heat leakage conditions were accurately captured. These experimental data provide experimental support for the precise prediction of ventless storage of liquid hydrogen tanks.

The thermal management of liquid hydrogen (LH 2 ) during liquefaction, storage, and transfer is key to the efficiency of the overall supply chain. Optimized thermal management is therefore essential for the large-scale deployment of liquid hydrogen infrastructure, supporting clean energy transition and decarbonization goals. In this context, ITP Interpipe is developing an innovative pipe-in-pipe system for liquid hydrogen transfer, building on its existing cryogenic pipeline technology for LNG with dimensions from 3’’ to 36’’ using 36% Nickel alloy. This highly insulated pipe-in-pipe uses Izoflex® as the thermal insulation material combined with a soft vacuum, instead of a high vacuum. Izoflex® is a microporous non-ageing material featuring a combination of thermal and mechanical properties, making it a good candidate for thermal insulation in a pipe-in-pipe system installed subsea, buried in a trench or above ground without requiring maintenance throughout the pipeline design life: It offers low thermal conductivity with soft vacuum and sufficient load bearing properties to eliminate the need for structural supports. This paper presents the experimental qualification of this pipe-in-pipe insulation system using the Cryostat CS900 system and connected LS20 refrigerated LH 2 supply system both developed by GenH2. The test apparatus, methodology, and thermal performance calculations follow the guidance of standard ASTM C1774. The CS900, a cylindrical boiloff calorimeter with a 203-mm diameter by 1,168-mm tall cold mass inside a 610-mm diameter vacuum chamber, is a simulation test platform that replicates real-world environments and provides an absolute measurement of heat transmission under controlled conditions of vacuum pressure, different environments, and temperatures from 4 K to 400 K. Insulation system prototypes are manufactured by wrapping Izoflex® material on the cryostat cold mass following a procedure intended to mimic the manufacturing process defined for the real production item: four layers of insulation are applied on the cold mass, drying and pressure reduction are performed in the annulus before cooling and stabilizing to 20 K with liquid hydrogen. Several test runs are performed with different vacuum pressures to study the sensitivity of the thermal conductivity. The measured heat flow rate is used to calculate the effective thermal conductivity (k e ) of the total insulation system between 20 K cold boundary temperature and 293 K warm boundary temperature. The lambda thermal conductivity of each insulation layer is also calculated using temperature sensors placed between each layer. This approach provides additional characterization of the thermal performance with temperature dependence from 20 K to 293 K. Through this testing campaign, the thermal performance of the soft vacuum pipe-in-pipe insulation system is documented with absolute measurements obtained on a unique test platform, currently unmatched worldwide. The sensitivity tests on vacuum pressure demonstrate high thermal performance over a wide range of soft-vacuum conditions to further validate the robustness of the insulation system.

Hydrogen is commonly transported and stored for use as a liquid. As use of fuel cells and hydrogen as a fuel increases, the amount of liquid hydrogen to be stored and dispensed increases. Boil-off of liquid hydrogen during storage has a significant economic and environmental cost over the long term. Current methods of managing the boil-off gas from a distribution storage tank include use of the boil off gas directly to produce energy, compression and storage of the gas in cylinders, or if all other options are not available it is vented to atmosphere. Compression is viable when there is a regular use of the compressed gas, for example filling vehicle fuel tanks, but has limited capacity due to the low volumetric density of compressed gas. An alternative is to reliquefy the gas and return it to the storage tank, effectively producing zero boiloff and enabling long term storage. Fabrum and Plug Power have developed a hydrogen reliquefier using Fabrum's existing and proven diaphragm-based pulse tube cryocooler coupled to a Joule Thompson expansion for phase change. The system offers three stage precooling plus a liquefaction stage, thereby improving inherent efficiency at a small scale. This paper describes the development of a 100 kg/day hydrogen reliquefier that can fit inside a shipping container. The configuration, thermodynamic modelling and optimisation, to building and factory testing the first prototype will be discussed.

Cryo-compressed hydrogen composite vessels are critical load-bearing components in hydrogen energy systems and cryogenic engineering applications. In such systems, low temperature and high internal pressure coexist. Under these extreme service conditions, the mechanical response of composite cylindrical shells is strongly affected by thermo-mechanical coupling. Consequently, conventional design approaches based on room-temperature assumptions are no longer sufficient. In this study, an analytical thermo-mechanical framework is developed to investigate the mechanical response and failure behavior of type III cryo-compressed hydrogen composite vessels. The vessels are subjected to a combined condition of 20 K temperature and 35 MPa internal pressure. A hoop–helical–hoop winding configuration is adopted due to its high manufacturing efficiency and favorable load-sharing characteristics in engineering practice. The winding layer numbers are preliminarily determined using netting theory. Failure assessment is then performed based on composite material failure criteria. The composite overwrap is made of T700 carbon fiber reinforced polymer. The analysis focuses on the coupled effects of the helical winding angle and winding layer number on stress distribution and failure characteristics. A baseline winding configuration of [/±/] is selected. Failure boundaries are identified by systematically varying the helical winding angle. The numbers of helical and hoop layers are also varied. The results show that increasing the helical winding angle accelerates the approach to the failure boundary of the composite layer. In addition, insufficient winding layer numbers can lead to structural failure even when the helical winding angle is relatively small. These results demonstrate that structural safety is jointly governed by winding angle and winding layer number. No single parameter plays a dominant role. Under cryogenic conditions, thermo-mechanical coupling significantly amplifies the sensitivity of failure behavior to variations in winding parameters. As a result, the allowable design window becomes drastically narrower than that under room-temperature conditions. Quantitative evaluation indicates that, for the investigated vessel configuration and material system, the allowable upper bound of the helical winding angle decreases from approximately 18° at room temperature to about 13°–16° under cryogenic conditions. The specific limit depends on the adopted failure criterion and the winding layer combination. Further comparison based on the Tsai–Hill and Tsai–Wu failure criteria shows that discrepancies between different criteria become more pronounced under cryogenic high-pressure conditions. This behavior is attributed to enhanced multi-axial stress interactions within the composite layers. These findings highlight the necessity of adopting conservative failure assessment strategies in cryo-compressed hydrogen vessel design. The proposed analytical approach combines netting theory with thermo-mechanical analysis. It provides an efficient tool for identifying safe winding parameter ranges in cryo-compressed hydrogen composite vessels. The approach also offers practical guidance for preliminary design, prototype development, and subsequent experimental validation.

Hydrogen liquefaction remains a highly energy-intensive and costly process, with more than 30% of the hydrogen's energy content expended during cryogenic liquefaction. This underscores the pressing need for more efficient and cost-effective liquefaction technologies. In this work, we present the design, modeling, and proof-of-concept experimental results for a dual-stage modular cryogenic cooler capable of achieving liquid hydrogen temperatures (20 K) at operating pressures up to 1.0 MPa. The proposed system is based on a direct current (DC) flow architecture utilizing a Modified Collins Cycle. Key innovations include lightweight floating piston-type expanders without mechanical linkages, enabling high-efficiency and high-pressure ratios, alongside smart electromagnetic valves and recuperative heat exchangers. The first stage can provide 100 W of cooling at 90 K, which enables the second stage to achieve 25 W at 20 K. This modular liquefier achieves efficiencies comparable to large-scale cryogenic systems (continuous DC flows), while preserving the compactness and reliability of cryocoolers (oscillating AC flows). The system is governed by a fully automated, real-time FPGA-based control platform that enables a projected efficiency of 25% of Carnot. This control architecture coordinates the sequential actuation of low-temperature, computer-controlled valves with shaped actuation pulses to minimize dissipation, along with four high-temperature throttle valves connected to sealed gas reservoirs. These reservoirs are maintained at intermediate pressures between the high- and low-pressure streams of the compressor. Precise valve sequencing facilitates gas expansion and pre-cooling before heat is transferred to the system’s thermal load. The floating piston operates quasi-statically at low velocity, governed by the throttled gas flow in and out of the warm-end cylinder. To maintain efficient expansion under these quasi-static conditions, the operating frequency of the piston expanders must remain below the natural resonance frequency of the piston–gas-spring system. Current prototypes operate at frequencies in the range of 1–3 Hz, indicating the need for further optimization. To validate the control architecture and system model, a single-stage room-temperature floating piston machine using air as the working fluid is experimentally demonstrated. This work introduces a paradigm shift from conventional scale-up approaches to a modular “number-up” strategy, in which highly efficient cryocooling units are replicated to achieve scalable, small-to-medium hydrogen liquefaction capacities (on the order of kg/day or small TPD); a critically underserved segment of the current hydrogen supply chain. This modular architecture not only enables cost-effective manufacturing and simplified maintenance but also enhances thermodynamic efficiency at smaller scales. Moreover, it supports distributed deployment and operational flexibility, significantly lowering both capital and operating expenditure.

As the global transition toward decarbonization matures, liquid hydrogen (LH2) is establishing its role through distinct advantages in high-duty applications. This presentation reviews critical hardware and infrastructure advancements across the road, marine, and aviation sectors, while detailing a novel delivery logistics standard essential for supporting this distributed network. In the road sector, current development focuses on sLH2 (subcooled liquid hydrogen) storage and "Liquid-to-Gas" refueling architectures to optimize density and minimize refueling time for long-haul trucking. Maritime applications are advancing through the industrialization of high-flow bunkering loading arm interfaces and safety protocols for large-scale onboard storage. Simultaneously, aviation is validating LH2 viability through megawatt-scale propulsion demonstrators and first man flight testing. Logistical constraints, primarily driven by boil-off losses during transit, have previously hindered the liquid hydrogen value chain. Recent breakthroughs in delivery infrastructure have addressed this, reducing evaporation by approximately 80% while enhancing the commodity's thermodynamic state. The resulting ability to deliver colder, higher-quality liquid not only improves economic feasibility but also streamlines pumping operations at station interfaces. Ultimately, the integration of optimized storage architectures with high-efficiency, zero-loss delivery mechanisms resolves critical economic and operational bottlenecks. This holistic approach accelerates the commercial viability of liquid hydrogen, strengthening its role as a viable energy vector for decarbonizing the global heavy-transport sector.

Liquid hydrogen (LH 2 ) has high hydrogen storage density, greatly improving the range of fuel cell heavy-duty truck. In order to offer stable hydrogen supply pressure, two kinds of self-pressurizing system for on-board LH 2 cylinder under supercritical pressure is developed, one is gravity fed return-flow pressurization (GFRP), the other is internal heating pressurization (IHP). On-board LH 2 system experimental prototypes with GFRP and IHP are developed separately, and the pressurization pipelines in the LH 2 cylinder are both positioned on the liquid level 95%. Pressurizing experiments are conducted with LH 2 , and the results show that: (1) At 75% filling level in LH 2 cylinder, the pressurization rate of GFRP is 0.012 MPa/min, while the pressurization rate of IHP is 0.051 MPa/min when hydrogen supply flow rate is 1 g/s and pressurization rate of 0.065 MPa/min when hydrogen supply flow rate is 2 g/s. (2) When the filling level in the LH 2 cylinder decrease to 50%, the pressurization rate of GFRP is 0.014 MPa/min, while the pressurization rate of IHP is 0.025 MPa/min when hydrogen supply flow rate is 1 g/s and pressurization rate of 0.031 MPa/min when hydrogen supply flow rate is 2 g/s. (3) When the filling level in the LH 2 cylinder decreases to 25%, the pressurization rate of GFRP is 0.00083 MPa/min which is significantly lower than the results in higher filling level, while the pressurization rate of IHP is 0.011 MPa/min when hydrogen supply flow rate is 1 g/s and pressurization rate of 0.013 MPa/min when hydrogen supply flow rate is 2 g/s. (4) The results of these two kinds of self-pressurizing system indicate that pressurizing rate of IHP is higher than GFRP, which means supercritical hydrogen is more sensitive with temperature variation. The driving force of GFRP is the differential pressure between the top pressure of LH 2 in the cylinder and the bottom, and thus decreases with decreasing liquid level significantly. A three-region thermal analysis model under supercritical pressure is proposed to calculate the state parameter of LH2 during pressurization. The results deviation of thermal analysis model compared with experimental results is approximately 10% under low liquid level condition, but increase to 22% under high liquid level condition. The cause of deviation is analyzed by comprehensively comparing computational and experimental results of the temperature in LH 2 cylinder during pressurizing experiments. The experimental results of the temperature in LH 2 cylinder shows that: (1) At 75% filling level in LH 2 cylinder, the experimental temperature of supercritical hydrogen in the ullage space of the cylinder increases significantly faster than the computational results. (2) At 50% filling level in LH 2 cylinder, the LH 2 temperature from experiment remains 24.2 K about 3 minutes, then it increases slightly to 24.3 K and is kept until the end of the experiment; at 25% filling level, the LH 2 temperature from experiment stays at the initial value 23.7 K throughout the experiment, which is 0.5 K lower than the temperature of LH 2 at 50% filling level. However, the computational LH 2 temperature maintains a linear increasing trend. (3) The experimental LH 2 temperature trend indicates that heat flow from the ullage space does not immediately cause the increase of LH 2 temperature, and thus the process of heat transfer is not instantaneous. However, instantaneous heat transfer from the ullage space to LH 2 region during pressurization in the cylinder is assumed in the computational model. It leads to overestimate the heat transfer from the pressurization tube via the supercritical hydrogen in the ullage space to LH 2 . On the other hand, comparing LH 2 temperatures of experimental results at 50% and 25% liquid level show that certain temperature difference exhibits between at different heights in LH 2 region, while the computational model assumes a uniform temperature distribution in LH 2 region, which also contributes to calculation deviation.

The refueling of liquid hydrogen (LH 2 ) presents a critical challenge in its application as an alternative to conventional fuels. Common concerns within the industry are the safety and cost implications of vented gaseous hydrogen (GH 2 ) during the refueling process. To ensure both environmental benefits and operational cost efficiencies, it is essential to minimize or eliminate vented emissions. Using subcooled LH 2 for refueling leads to the condensation of gas in the tank, resulting in a reduced pressure increase and, consequently, lower or possibly no vented GH 2 . Refueling with subcooled liquid can be achieved by employing LH 2 pumps or pressurized LH 2 tanks. To improve existing technology and develop new refueling systems, such as those for airplanes or ships, the physical processes that occur need to be described with sufficient accuracy. This study addresses the challenge of refueling with subcooled LH 2 , including the corresponding pressure change and GH 2 emissions, and develops a thermodynamic model to simulate these processes. Preliminary results demonstrate the model's effectiveness in simulating LH 2 refueling with subcooled liquid. The developed model divides the tank wall and the fluid in the tank into control volumes and solves their mass and energy balances. With this, it is possible to dynamically simulate the tank behavior during refueling. The model incorporates effects such as the heat transfer between the tank wall and the fluid, as well as the condensation of gas in the tank due to the entering subcooled liquid. To simulate the thermal cooldown of the refueling system upstream of the tank, a simplified model is employed that includes the thermal mass of pipes and couplings, as well as their heat exchange with the flowing LH 2 . The model is applied to the refueling of LH 2 trucks using the subcooled liquid hydrogen (sLH 2 ) technology developed in cooperation by Linde and Daimler Truck. This technology feeds subcooled liquid into the tank using a pump while no gas is vented from the tank. The model is validated using novel measurement data for tank pressure and stored hydrogen mass from an sLH 2 truck refueling station in Woerth, Germany [1]. The model shows good agreement with the measured data for several refueling scenarios that differ in initial refueling system temperature, initial tank filling level, and initial tank pressure. It is thus able to reproduce the real-world tank behavior and the physical phenomena that occur during refueling with sufficient accuracy. The presented work provides a validated model for the refueling of LH 2 tanks, which can be applied to various use cases, including the refueling of trucks, airplanes, and ships. Therefore, it advances the modeling of LH 2 systems, particularly in the context of LH 2 refueling. Due to its low computational effort in comparison to CFD simulation, the model can be used for parameter studies and system optimization. Looking ahead, we plan to expand the validation process to include experimental scenarios for airplane tanks and LH 2 tank trailers conducted within the ALRIGH2T project. These future experiments aim to provide insights into the scalability and adaptability of the model across different applications. References [1] Daimler Truck AG: Internal data provided for scientific analysis, unpublished

Liquid hydrogen (LH₂) is a promising carbon-free fuel for future transport systems, but its use introduces significant technical challenges for fueling systems operating at cryogenic temperatures near 20 K. For developing these fueling components, a laboratory scale setup will be designed and constructed. To this end, a dimensional analysis is performed based on representative hydrogen-powered systems: (1) a 1 MWe fuel cell stack consuming 70 g/s of hydrogen, and (2) a turbine aircraft operating at approximately 30 g/s during cruise and up to 250 g/s at full throttle. The objective is to replicate the relevant multiphase flow behavior of these systems within a laboratory-scale setup. Using these reference systems, scaling is applied to define the dimensions of a laboratory setup. To quantify the achievable operating envelope of the laboratory setup relative to the turbine aircraft, fuel-cell system, and other existing facilities, an algorithm was developed to compute ranges of relevant dimensionless numbers based on varying pressure, temperature, and mass flow rate. Additional scaling challenges were identified. Reducing the pipe diameter would shift the laboratory operating regime for some dimensionless numbers closer to that of the fuel-cell system but would likely introduce capillary-dominated flow. Alternatively, increasing mass flow rates and pipe diameters would improve similarity but would significantly increase both capital and operational costs due to the high cost of LH₂ and limited availability of large-scale storage infrastructure. Consequently, direct scaling to full system conditions is economically prohibitive. Based on these considerations, the laboratory facility, named Multiphase Investigations in a Cryogenic Environment (MICE), was designed to operate with mass flows of up to 4.2 g/s with pipe diameters of 1/4″ and 1/2″, and temperatures between 20 K and 300 K. A modular design was adopted to enable future modifications, such as conversion to closed-loop operation or the use of alternative cryogenic fluids, and multiple system configurations were investigated. The setup also allows for variations in pipe inclination and incorporates provisions for visualizing multiphase flow. This project is supported by the Cryogenically Optimized and Operable LH₂ Pipe (COOL Pipe) project, part of the Dutch Luchtvaart in Transitie (LiT) program.

The accurate prediction of boil-off gas (BOG) generation and self-pressurization inside liquefied natural gas (LNG) cargo tanks is crucial for ensuring safe and energy-efficient LNG carrier operation. During a voyage, heat ingress from the surroundings vaporizes LNG and causes a progressive pressure rise inside the tank, behavior strongly influenced by liquid level, vapor stratification, and discharge flow rate. To quantitatively assess these effects, this study developed and validated two complementary thermodynamic models—the Thermal Equilibrium Model (TEM) and the Thermal Multi-Zone Model (TMZM)—using operational data from a 3,750 m³ membrane-type LNG storage tank. The TEM assumes vapor–liquid equilibrium and provides a fast and simple way to analyze pressure evolution under nearly uniform temperature conditions. In contrast, the TMZM divides the vapor and liquid regions to capture stratification effects and non-equilibrium heat transfer across the vapor–liquid interface. Both models were implemented using Python-based frameworks, with thermophysical properties retrieved from the NIST REFPROP database. Validation utilized measured voyage data, including tank pressure, temperature profiles, and discharge flow rates during laden and ballast operations. Interfacial heat transfer parameters were optimized using the Nelder–Mead and Brent algorithms to minimize RMSE between simulated and measured pressure trends. Simulation results revealed distinct thermodynamic characteristics between laden and ballast conditions. During laden voyages (filling ratio ≈ 96%), the tank remained close to equilibrium with minimal stratification and small pressure variations, and the TEM predicted pressure within 2.5% accuracy. Conversely, during ballast voyages (filling ratio ≈ 21%), the vapor zone expanded and stratification developed, producing nonlinear time-dependent pressure and temperature variations. The TMZM captured this behavior with average self-pressurization errors below 3%, and optimized interfacial heat transfer coefficients varied by more than a factor of three depending on discharge conditions. During static storage or when the vessel is moored, the tank maintains a near-equilibrium state and interfacial heat transfer optimization is unnecessary. Under voyage conditions, however, ship motion, sloshing, and discharge variations disturb equilibrium, making optimization essential for accurate prediction. The TMZM effectively incorporates such dynamic variations, enabling real-time simulation of convection, evaporation, and pressure rise. Boil-Off Rate (BOR) analysis also revealed clear differences between operating modes. During laden voyages, BOR values ranged from 0.083% to 0.215% per day, driven by increased evaporation associated with higher discharge flow rates. In contrast, ballast BOR ranged from 0.007% to 0.171%, with broader variation due to vapor-layer stratification and discharge magnitude. Under closed conditions, most heat ingress contributed to sensible heating rather than evaporation. As stratification intensified, the pressure-rise mechanism transitioned from thermal-expansion-dominant to vaporization-dominant, while active discharge produced venting-dominant behavior. These findings highlight three thermodynamic regimes—thermal expansion, vaporization, and venting—governed by the interplay of heat ingress, interfacial heat transfer, and discharge rate. Compared with equilibrium-based approaches, the multi-zone non-equilibrium model provides more realistic prediction of heat transfer and pressure evolution under voyage conditions. In summary, this research presents a validated and extendable thermodynamic modeling framework for simulating LNG cargo tank behavior under realistic voyage conditions. The approach captures complex interactions between heat ingress, vapor stratification, and pressure evolution, bridging the gap between equilibrium-based prediction and real operational phenomena. The results clearly demonstrate that interfacial heat transfer optimization is unnecessary under quiescent storage conditions but becomes indispensable during voyage when dynamic heat ingress and sloshing occur. By coupling physical modeling accuracy with operational applicability, the proposed TMZM framework provides a robust foundation for improving the design, control, and safety of LNG containment systems in support of efficient and sustainable marine energy transport.

Venting is a critical mechanism for safety and control in cryogenic storage tanks, directly influencing pressure evolution, material loss, and thermal behavior during both steady-state and transient operation. In tanks containing a two-phase fluid, venting is strongly coupled to the thermodynamic state of the liquid and vapor phases through phase change and non-equilibrium mass and energy transfer. However, venting is often represented by empirical valve or choked‑flow correlations rather than derived consistently from the tank’s thermodynamic state [1–4]. Such simplifications treat venting independently of the evolving thermodynamic state, which may lead to physically inconsistent transient behavior. This work presents a unified, thermodynamically consistent formulation of venting models for cryogenic two‑phase tanks, applicable to both equilibrium and non‑equilibrium regimes. Building on the single‑phase venting derivation in [5], the model is formulated from mass and energy conservation for the liquid and vapor control volumes, leading to a framework in which venting emerges as a consequence of the imposed control objective rather than an externally prescribed boundary condition. Non-equilibrium effects are represented through corrected thermodynamic states referenced to equilibrium conditions, ensuring physical consistency while allowing for deviations during transients. The influence of these assumptions on the resulting system of equations and their consistency with equilibrium models is examined. Two control strategies are derived within this framework. In pressure-controlled venting, an algebraic constraint on the system pressure is coupled with differential equations for mass and energy conservation in both phases, forming a unified differential-algebraic equation (DAE) system. In liquid‑level‑controlled venting, the imposed constraint maintains a prescribed liquid fill height, while pressure evolves as an additional dynamic variable. Non-equilibrium between the liquid and vapor phases is retained in both cases, providing a physically consistent description of transient behavior under different control objectives. Equilibrium models are obtained as limiting cases when interfacial transfer processes are assumed infinitely fast, and phase states are constrained to saturation. These limiting cases illustrate how the unified formulation reduces to equilibrium behavior and identify operating regimes in which non‑equilibrium effects must be retained to ensure physical consistency. The proposed framework provides a rigorous theoretical basis for developing and analyzing venting models in cryogenic tank simulations, enabling transparent formulation of pressure- and liquid-level-control strategies. It is applicable to a broad range of cryogenic fluids and storage configurations, including liquid hydrogen systems, test facilities, and spaceflight tanks. The framework is demonstrated using liquid nitrogen as a representative cryogenic fluid, but is readily extendable to other cryogens such as hydrogen or helium. By linking venting control, thermodynamic assumptions, and governing equations within a consistent framework, this work advances physically grounded modeling and control of cryogenic two‑phase storage systems. References [1] Damme L. ten, van Put M., Gangoli Rao A. Simulation of the refuelling process for an LH 2 -powered commercial aircraft part 1 - Modelling and validation. International Journal of Hydrogen Energy 2025;195:152168. https://doi.org/10.1016/j.ijhydene.2025.152168. [2] Weber C. Dynamic modelling of incidents for the protection of helium cryostats against excessive pressure [Dissertation]. Karlsruhe: Karlsruher Institut für Technologie; 2021. [3] Petitpas G. Simulation of boil-off losses during transfer at a LH 2 based hydrogen refueling station. International Journal of Hydrogen Energy 2018;43(46):21451–63. https://doi.org/10.1016/j.ijhydene.2018.09.132. [4] Daigle M. J., Smelyanskiy V. N., Boschee J., Foygel M. Temperature Stratification in a Cryogenic Fuel Tank. Journal of Thermophysics and Heat Transfer 2013;27(1):116–26. https://doi.org/10.2514/1.T3933. [5] Hamacher J., Stary A., Stops L., Siebe D., Kapp M., Rehfeldt S., Klein H. Modeling the thermodynamic behavior of cryo-compressed hydrogen tanks for trucks. Cryogenics 2023;135:103743. https://doi.org/10.1016/j.cryogenics.2023.103743.

Cryogenic propellants are extensively utilized in modern aerospace missions; however, the management of these fluids in microgravity environments presents significant challenges. In microgravity, the unpredictable behavior of liquid-vapor interfaces often compromises acquisition reliability, thereby driving the development and application of Liquid Acquisition Devices (LADs). While previous research on LADs has predominantly relied on macroscopic experimental measurements and simplified numerical models, these approaches often overlook the complex capillary flow mechanisms occurring at the pore scale. Consequently, there remains a critical knowledge gap regarding how the specific geometry of screen micro-channels governs fluid dynamics in cryogenic and microgravity environments. The lattice Boltzmann (LB) Method is introduced as a robust tool for this study, as it is inherently well-suited for simulating pore-scale dynamics and resolving intricate boundary conditions in screen-based structures. Specifically, a pseudopotential LB model is developed to investigate the capillary dynamics of liquid hydrogen LH 2 within screen micro-channels. The simulation successfully captures the intricate capillary flow characteristics of cryogenic fluids at the pore scale. The results reveal the influence of pore geometry and surface wettability on wicking performance, providing essential theoretical insights for the structural optimization of LAD screens in space-based applications.

Liquefied natural gas (LNG) cold energy provides considerable potential for power generation, yet its effective utilization in organic Rankine cycle (ORC) systems strongly depends on system configuration and natural gas (NG) distribution pressure. In this study, four ORC configurations are investigated, including a basic ORC (BORC), a recuperative ORC (RORC) equipped with an internal heat exchanger (IHE), as well as their corresponding systems integrated with direct expansion (DE), namely DE-BORC and DE-RORC. A unified thermo-economic multi-objective optimization and decision-making framework is developed to identify optimal system configurations and operating conditions under different NG distribution pressures, while the applicability of DE and IHE is systematically evaluated. Among the investigated systems, the DE-BORC configuration is consistently identified as the optimal option across all NG distribution pressures, with R170/R134a selected as the corresponding optimal working fluid. At a distribution pressure of 2.5 MPa, the DE-BORC system achieves a specific net power output (SNPO) of 118.19 kJ/kg, an exergy efficiency of 22.25%, and an electricity production cost (EPC) of 0.102 $·kWh⁻¹. NG distribution pressure exerts a pronounced influence on system performance, particularly for DE-integrated systems; when the pressure decreases from 7 MPa to 0.6 MPa, the SNPO and exergy efficiency of the DE-BORC system increase by 233.88% and 86.48%, respectively, accompanied by a 65.20% reduction in EPC. At low heat source temperatures, the introduction of an IHE may deteriorate the thermo-economic performance, whereas its benefits become evident only when the temperature exceeds 80 °C. At 170 °C and 0.6 MPa, the RORC system increases the SNPO by 5.86% and reduces the EPC by 12.95% compared with the BORC system. These results provide a quantitative basis for selecting system configurations and appropriate working fluids in practical LNG cold energy power generation applications.

Multilayer insulation (MLI) is widely adopted in the liquefied natural gas (LNG) tanks due to its outstanding insulation performance when operated in a high-vacuum pressure. Due to the material outgassing taking place in the annular space of the LNG tank, the vacuum pressure can slowly build up and degrade the thermal performance of MLI, leading to an increase in the heat leakage during the long-term storage and transportation process of LNG. To reveal the effect of the outgassing on the MLI performance, a sub-model describing the changes in the vacuum pressure due to the material outgassing characteristics testing is developed. Based on the sub-model, a modified layer-by-layer model considering the transient behaviors of the vacuum pressure is also established to analyze the impact of the material outgassing on the thermal performance of MLI for LNG tanks. The results indicate that the outgassing of the materials in the annular space of the tank causes a two times higher heat leakage into the LNG tank for years. Therefore, some pretreatments of accelerating the outgassing of the material are vital to adopt before the MLI is installed on the LNG tank. This study provides theoretical guidance for the design and optimization of high-performance LNG tanks.

In accordance with the global decarbonization-based policies, hydrogen is attracting a lot of attention as a next-generation energy carrier due to its contributions to carbon neutrality and distinct energy characteristics (e.g., high energy density, resource abundance, etc.). To successfully transition to a hydrogen-based energy economy, reliable transportation technologies are essential. In particular, from the major hydrogen-exporting regions, intercontinental maritime transportation could contribute to a stable and cost-effective supply chain, accelerating the hydrogen-based energy transition. Among the hydrogen transportation strategies, such as high-pressure gas, liquified hydrogen (LH 2 ), and chemical carrier, LH 2 offers high safety and enables the large-scale transportation of high-purity hydrogen without an additional reconversion process. However, LH 2 has an extremely low boiling temperature and heat of vaporization, which leads to boil-off gas generation, thereby degrading the stability and cost-efficiency of the LH 2 transportation. To reduce the boil-off loss of cryogenic LH 2 , a vacuum insulation system has been recognized as an LH 2 carrier. In a vacuum insulation system, LH 2 is stored in the inner tank, which is surrounded by an outer jacket, forming a vacuum-insulated annular space (i.e., vacuum space). This insulation system effectively suppresses heat transfer due to the low-thermal conductivity of the vacuum space. In general, because conductive and radiative heat transfers dominantly induce the boil-off rate, various vacuum insulation types were suggested, including multi-layer insulation (MLI) and particulate insulation. An MLI effectively reduces conductive and radiative heat transfers via numerous reflective layers and spacers; however, its insulation performance is highly sensitive to the vacuum level. Eventually, an MLI should be installed under highly controlled conditions, including humidity and dust contamination, to achieve a high vacuum level ( 2 transportation Compared to MLI, a particulate insulation-filled vacuum insulation system is less sensitive to vacuum level; however, its vacuum level is still one of the most dominant design factors to ensure insulation performance. However, the filled-insulation significantly varies the gas evacuation characteristics, because the microscale powders reduce the gas permeability and increase the outgassing rate. As a result, a more efficient vacuum system design and an appropriate treatment method for insulation are required. More specifically, the volatiles, which are adsorbed on a large effective surface area, have high desorption energy. Furthermore, low permeability through the granular space increases the flow resistance. Eventually, the gas evacuation characteristics, such as pump-down time and outgassing rate, are strongly degraded. These factors deteriorate economic feasibility; therefore, to ensure efficient operation of particulate insulate-filled vacuum insulation systems, the gas evacuation characteristics should be investigated as a priority. In this study, the gas evacuation characteristics associated with the condition of the particulate insulation were mainly evaluated. The used particulate insulation, called glass bubble, has been reported to have higher insulation performance comparable with MLI under a moderate vacuum level (~50 mTorr). In addition, its high crush strength and excellent flowability enable uniform filling with reduced insulation voids, making it attractive for large-scale cryogenic insulation applications. To do this, a lab-scale vacuum insulation system was designed, and various vacuum characteristics (e.g., dew points, outgassing rate, pump-down time, etc.) were systematically measured depending on the well-established N 2 purging process. Consequently, this study will provide guidelines for insulation pre-treatment aimed at efficient vacuum conditions, while serving as fundamental data for the economical design of a vacuum system in a particulate insulation-filled vacuum insulation system.

As demand for large-scale liquid hydrogen storage increases, controlling the exothermic ortho-to-para hydrogen conversion (OPC) is essential to reduce boil-off losses that can reach 75%. This work evaluates 5 wt% platinum group metals (PGMs) supported on Al₂O₃ as alternatives to conventional IONEX catalysts, which are commonly limited by low activity and slow conversion kinetics. Catalytic OPC performance was measured at 77 K and 0.1 MPa using an advanced in-line Raman probe over flow rates of 0.3–3 SLPM. The rhodium- and ruthenium-based catalysts exhibited significantly higher first-order rate constants, measured at 484 min -1 and 401 min -1 , respectively, in contrast to the lower value of 214 min -1 obtained for IONEX. The enhanced performance is correlated with changes in catalyst magnetic behavior where materials that are diamagnetic prior to activation transition to ferro- and/or paramagnetic behavior after activation, as verified by vibrating sample magnetometry. The influence of activation on OPC kinetics is therefore discussed in detail. In addition, the effect of an external magnetic field (1.0 T) on the activity of all tested catalysts is presented. These results provide practical insights for catalyst selection and system design in hydrogen liquefaction and storage and demonstrate a robust in-line methodology for quantifying OPC kinetics under cryogenic conditions.

Lightweight engineering is a key discipline to enable decarbonization in aviation. With liquid hydrogen (LH 2 ) as a potential fuel in future sustainable aircraft technology, the significance of lightweight engineering becomes even more pronounced. LH 2 onboard systems usually consist of heavy, stainless steel components (tank, pipings, etc.) unsuitable for aircraft applications. Therefore, recent research and development is concerned with replacing those stainless steel components with lightweight, fiber reinforced polymer components. The research project HYTANK, funded by the German Federal Ministry for Economic Affairs and Climate Action, considers modularly designed LH 2 fuel tanks made from such carbon fiber reinforced polymers and their assembly process. In particular, the mechanical properties of adhesive materials and adhesive bonds are investigated under conditions similar to the later use case. Hence, a cryostat insert that allows for tensile testing of various adhesive materials under cryogenic conditions was developed within the project. The setup enables tensile testing under 77 K liquid nitrogen (LN 2 ), 4 K liquid helium (LHe) and 20 K LH 2 conditions. Moreover, testing at intermediate temperature levels can be realized by cooling with helium cold gas (GHe). This paper focuses on two aspects: Firstly, on the design of the test setup; secondly, on first measurement results of tensile testing of adhesives and adhesive bonds at room temperature (300 K) and under cryogenic conditions in LN 2 , LHe, LH 2 and in GHe at 20 K. From these results, it is apparent that the mechanical behavior of the adhesives under consideration is mostly influenced by the temperature level and not by the specific medium itself.

Abstract. In the preceding study, a single-stage pulse tube cryocooler (PTC) with a total weight of 2.6 kg and an operating temperature range of 80-20 K was reported. This cryocooler was capable of directly replacing the second-stage cryocooler, and its operating frequency was increased to 56 Hz. In this study, the regenerator filling combination was optimised and the size of the phase shifters was improved, with Er 3 Ni and stainless steel screen being selected as the regenerator materials. Concurrently, the volume of the gas reservoir underwent a reduction, the operating frequency was increased to above 80 Hz. The total weight of the enhanced PTC system (with the precooling device excluded) has been reduced to 2.2 kg. In the experiment, the compressor, the hot-end heat exchanger and the phase shifters were precooled to 80 K by using liquid nitrogen precooling technology. The operating frequency was set at 65 Hz and the input power was 10 W. The no-load temperature of the PTC was measured to be 16.0 K. It was demonstrated that the system can achieve an effective cooling capacity of 0.5 W in the 25.3 K temperature range. By reducing the volume of the gas reservoir to a greater extent, the optimal operating frequency was increased to 84 Hz. At this juncture, a no-load temperature of 17.8 K was attained under constant power input, while a cooling capacity of 0.5 W was sustained at the 28.2 K temperature level. The experimental findings demonstrate that the PTC exhibits the highest operating frequency and the smallest weight-volume characteristics reported in the current literature within the 20 K temperature range.

Linear compressors, characterized by high efficiency, mechanical reliability, oil-free operation, and precise controllability of flow rate and pressure, have demonstrated significant application potential in deep cryogenic refrigeration systems, including Gifford–McMahon (GM), pulse tube, Stirling, and Joule–Thomson (JT) cryocoolers. However, the unique thermophysical properties of helium—specifically low density and high viscosity—combined with dynamic delay in valve response under high compression ratios and leakage through piston-clearance gaps have posed major challenges to the investigation of transient characteristics in valve-equipped linear compressors. To address these issues, a multi-physics computational fluid dynamics (CFD) model was established by coupling clearance leakage behavior with the opening and closing dynamics of intake and exhaust valves. The model was validated using experimental data obtained with helium as the working fluid. Simulations were performed under compression ratios ranging from 2.0 to 6.0 with a fixed piston stroke of 14 mm, yielding detailed insight into the evolution of transient flow structures within the compression chamber, the spatiotemporal distribution of temperature and pressure, mass transfer behavior at valve ports, and leakage phenomena between the working and back chambers. Comparison with experimental results indicates that indirect estimation of working chamber pressure using back-chamber measurements fails to capture pressure oscillations caused by valve flutter and reverse flow during closure, resulting in significant discrepancies between experimental data and classical thermodynamic model predictions during compression and expansion phases. Moreover, eccentric motion of the free piston introduces asymmetric leakage, which further amplifies the deviation between measured and simulated pressure profiles. The developed model provides a physically consistent and computationally validated foundation for analyzing unsteady flow and mass transfer processes in valve-equipped linear compressors, offering important theoretical support for future structural optimization and control strategy development.

Cryogenic cooling is increasingly required for emerging technologies, including superconducting electronics, infrared devices, and quantum platforms, where stable low-temperature operation is essential for performance, sensitivity, and noise suppression. Joule–Thomson (J–T) cryocoolers are attractive for such applications due to their compact architecture, mechanical simplicity, and inherently low vibration. However, a key challenge is the lack of single-component refrigerants with boiling points between nitrogen (77.4 K) and neon (27.1 K), thereby necessitating the use of mixed refrigerants at this temperature range. In this study, a Ne–O₂–N₂ mixture is formulated and tailored for 50 K Joule–Thomson cryocooler operation. The thermophysical properties of the mixture are predicted using the Helmholtz energy equation of state (HE EOS), enabling consistent evaluation of mixture enthalpy behaviour under cryogenic conditions. Cooling potential is quantified using the isothermal enthalpy difference between the high- and low-pressure states. To evaluate the contribution of each component and enable further optimisation, partial molar enthalpy analysis is employed. Results show that the Ne–O₂–N₂ mixture achieves an isothermal enthalpy difference of 604.2 J/mol at 50 K, indicating a promising cooling potential in the targeted temperature range. It provides a practical route to address the cooling gap at 50 K, supporting the development of Joule-Thomson cryocoolers.

Low-temperature superconducting detector magnets in high-energy physics, typically based on Nb-Ti superconductors, are conventionally cooled with liquid helium. Such systems rely on large cryogenic infrastructure, including helium liquefiers, pumps, valve boxes, and multi-channel transfer lines. Although capable of providing high cooling power, these installations require substantial capital investment and consume relatively large amounts of helium during operation. Compact, commercially available cryocoolers represent a potential alternative for superconducting magnet systems. These systems offer reduced investment and operational complexity and allow for decreased helium consumption. However, cryocoolers provide modest cooling power, typically on the order of a few watts at liquid-helium temperatures. Their use therefore imposes rigorous constraints on the total heat load of the magnet system, necessitating substantial reductions in the parasitic heat leaks. This includes, in particular, efficient thermalisation of magnet current leads at the intermediate temperature level and the elimination of active helium circulation. This study presents the design and experimental evaluation of a remote-cooling demonstrator comprising two independent cooling loops: a 56 K helium gas loop cooled by a single-stage Gifford–McMahon cryocooler and a liquid helium-based system driven by a two-stage pulse-tube cryocooler with passive circulation at 1-1.5 bar (absolute). The system cools an Nb-Ti shunt connecting two custom-designed BSCCO-2223 current leads operating at 3 kA. Intermediate heat interception in the current leads is provided by the helium gas loop and is shown to extract approximately 350 W of heat load. The Nb-Ti shunt is cooled by liquid helium circulated via the thermosyphon effect, with a total design heat load below 2 W. The demonstrator incorporates custom thermal interfaces, including a copper cold-plate heat exchanger in the gas loop, integrated heat sinks in the current leads, and a condenser with a custom liquid-helium level gauge. All thermal interfaces are experimentally characterised prior to integration. In this work, the thermal performance of the complete remote-cooling system, together with the electrical and thermal behaviour of the current leads, is presented and compared with theoretical predictions.

An expander is the core component of any cryogenic system. It works in different operational conditions during initial cooldown, in case of change of cryogenic load etc. All these regimes are characterized by different set of working parameters such as inlet and outlet pressure, inlet temperature and gas volume flow. Same machine can use different gases, e.g. for tests, commissioning and experiments. For every set of operational parameters turboexpander has a certain (optimal) speed of rotation at which it demonstrates maximum efficiency. This speed can be found either with an experiment or computer simulation. The ability to control rotational speed of turboexpander based on aforementioned parameters allows to maintain maximum efficiency of cryogenic refrigerator all the time. At the same time such approach transforms relatively complex way of refrigerator control to “simple” control of compressor part only. There is PID control of compressor performance with feedback parameter such as expander outlet temperature, cryogenic load temperature etc. As a result, cryogenic refrigerator can easily run at different temperature levels, for example, for cryogenic temperature sensors calibration. Neon cryogenic refrigerator of 1,5 kW @ 65 K performance was built for HTS application. Cold neon used for cooling liquid nitrogen circulating through HTS power line. Refrigerator consists of three highspeed turbocompressor connected in series (with intermediate and end cooling), highspeed turboexpander, heatexchangers, instruments and controls. Both compressors and expander have the same motor/generator part with gas foil bearings and maximum shaft power of 15 kW @ 82000 rpm. They’re 2-pole permanent magnet machines which operate with VFD. During expander’s operation the power from generator is transferred to one compressor motor through DC connection between two corresponding VFDs. Preliminary tests were carried out using nitrogen as refrigerant. Cryogenic load was simulated by the heater. The tests’ results were presented as a chart of expander’s parameters: inlet pressure and temperature, outlet pressure and optimal speed. Optimal speed was defined as one at which the lowest outlet temperature was reached with fixed other parameters. As the outlet pressure for expander is more or less constant, the optimal speed was described as a function of pressure ratio and inlet temperature. Approximating function of two variables for optimal speed was created and used for expander control. VFD makes this control very simple. A series of experiments were conducted with different cryogenic load and temperatures. Refrigerator’s control system used expander’s outlet temperature as feedback parameter. PID control manages compressors speed to maintain temperature setpoint. The tests carried out confirm simplicity and reliability of proposed approach to control refrigerator’s performance.

A standalone cooling system comprising of a 4 K cryocooler and two pulsating heat pipes for cooling of High Temperature Superconducting (HTS) magnets – particularly with magnetic fields above 20 T – is presented in this paper. As a starting point, such a cooling system has been tested for a 10 T class HTS magnet with a ‘Metal-as-Insulation’ (MI) winding. The magnet configuration, derived from the R&D of the Laboratory for Superconducting Magnet Research (LEAS) of the Accelerator, Cryogenics and Magnetism Division (DACM) of CEA Paris-Saclay, are traditionally cooled by helium baths. However, apart from being economically expensive, recent studies have shown a degradation in the convective boiling heat transfer between the bath and the magnet due to generation and distribution of magneto-gravitational forces at very high magnetic fields. The technical interest of pulsating (or oscillating) heat pipe (PHP), stemming from the R&D of the Cryogenic Laboratory and Test Stations (LCSE) of the same division is linked to its functionality in reduced gravity environment, passive operation, lightness and simplicity of construction. As an indication, these PHPs offer several orders of magnitude higher equivalent thermal conductivity and are much lighter than a thermal strap made of copper at cryogenic temperatures. The unprecedented combination of these two technologies on a demonstrator generating a few teslas is an important advancement for the development in cryocooling techniques of high magnetic field HTS magnets. Details of the design and assembly of the PHP-magnet integrated system with a two-stage Gifford-Mcmahon cryocooler as the cold source are presented. The magnet chosen is a REBCO solenoid whose classic design has been modified with thermal fins to optimize cooling. These are thermally connected to two 0.4 m long PHPs attached to the cryocooler second stage. The PHPs operate with neon that maintain the magnet temperature at about 30 K. Test results conducted at various DC and AC magnet currents are reported. The cryogenic PHPs are observed to be dynamic and react rapidly to the magnet’s heat load thereby establishing their capability as efficient cooling system for superconducting magnets.

In space missions, cryosorption JT coolers are commonly used to cool the vibration-sensitive detectors to cryogenic temperatures. Cooling loads vary with the lowest cold-end temperature of 20 K or 4.2 K, depending on the application. However, the cryosorption JT cooler differs from the conventional JT cooler in its pressure generation technique. In the spaceborne device, the mechanical compressor is replaced with a vibration-free sorption compressor, improving reliability, an essential requirement for long-duration space missions. The required pressure swing is created by the reversible adsorption-desorption of the working fluid in a cyclic order. Desorption occurs by heating the compressor with an internal heater, whereas adsorption requires the inflow of working fluid at low temperature. Because it is intermittent, the cooler requires multiple cells to maintain a continuous flow. The low temperature is sourced from outer space at 3 K (acting as a heat sink), and the compressor is connected via a passive radiative cooler with a gas-gap heat switch. A series of heat transfer devices, such as an aftercooler, a counter-current heat exchanger, a precooler, a JT exchanger, and an evaporator, follow the compressor, of which both the aftercooler and the precooler reject heat to the low-temperature environment (by radiation). The aftercooler, subjected to a variable heat load due to variations in the discharge fluid temperature (of the heated adsorbent bed), continually cools the flow to 80 K. Conversely, the precooler operates at fixed temperatures of 70 K and 60 K. The present study aims to provide an in-depth numerical analysis of the sorption compressor and to evaluate the performance of the passive radiative cooler, which serves as the heat sink, aftercooler, and precooler in the cryosorption JT cooling system. Instead of solid metal, the passive radiator fins are made of open-porous aluminium metal foam, which offers low weight and high surface area density. Aluminium has been chosen for the radiator due to its high thermal conductivity and low-temperature compatibility. The complete cycle of the cryosorption compressor involves four steps: (a) compression by heating the adsorbent cell electrically, (b) discharge of high-pressure gas, (c) cooling down the adsorbent cell after complete depletion by connecting it to the heat sink, and (d) decompression by adsorbing the gas at low temperature. Since each step is inherently transient, the mass, momentum, and energy conservation equations are solved separately for each stage using the commercial software, COMSOL Multiphysics. The sorption compressor simulation is followed by a detailed analysis of the complete cooling cycle and the refrigeration produced. In this study, a 2D axisymmetric model of the cylindrical adsorbent cell with an internal height of 225 mm and a diameter of 25.6 mm has been considered, with activated carbon-hydrogen as the adsorbent-adsorbate pair. A detailed analysis of the complete sorption compressor cycle has been carried out, starting from an initial condition of stored hydrogen in activated carbon at 5 bar and 80 K. The sorption compressor is capable of delivering hydrogen at a flow rate of 2-2.5 mg/s at 50 bar(a) pressure. Since the cooling capacity strongly depends on the effectiveness of the JT exchanger and the hydrogen mass flow rate, the sorption cooler generates 500–600 mW of refrigeration at 20K, depending on flow rate.

This paper reports an experimental study of the effect of the evaporator size on the thermal performance of a small dimension cryogenic pulsating heat pipe (PHP). The tests consist of injecting a power, Q, in the evaporator part and measuring the temperature difference, ΔT, between the evaporator and the condenser parts to construct the thermal resistance, R = ΔT/Q, of the PHP. They have been carried out for different heat inputs and filling ratios in vertical orientation only and at neon temperature at saturation conditions around the atmospheric pressure. The PHP made of 1 mm inner diameter stainless-steel tube arranged in 5 turns is cooled by a Sumitomo CH-208L 10K two-stage cryocooler. The overall dimensions of the PHP are approximately 190 mm long and 110 mm wide. Initially, the evaporator and condenser parts are made of CUC1 copper and are both 50 mm long and 110 mm wide. A second evaporator has been constructed and installed to study the effect of the heat transfer surface area on the thermal performance. Its dimensions are 25 mm x 110 mm; half the heat transfer surface. The condenser temperature was always maintained at around 27.1 K while different filling ratio from 10% to 80% were tested as a function of Q ranging from 1 to 11 W. The results obtained with the smaller evaporator show approximatively 15% lower thermal performance for all filling ratio tested.

As a key sub-Kelvin technology, adiabatic demagnetization refrigerator (ADR) is increasingly adopted in space missions and frontier cryogenic research. As the core component of an ADR, the salt pill largely determines the cooling capacity that can be effectively delivered to the load. For the sub-Kelvin stage, hydrated salts such as CPA are typically employed, and metallic thermal buses are introduced to enhance internal heat transport. However, finite thermal conductivity, thermal contact resistance, and the resulting internal temperature gradients reduce the realizable cooling capacity. To better support the design of CPA salt pills, this study evaluates the cooling utilization under different operating and geometric conditions. A transient COMSOL model is developed to simulate the demagnetization process of a CPA salt pill with thermal-bus structures and realistic thermal resistances under varying temperature regimes, load conditions, and geometries. By comparing the actual cooling output with the ideal cooling capacity, the utilization of the salt-pill cooling capacity is quantified for each temperature case. Based on these results, the effects of load conditions and geometric scale on the cooling utilization are analyzed, with the aim of providing design guidance for ADR salt pills under different operating conditions.

The cool-down time of a cryogenic system determines the cadence of low-temperature experiments. Accurate prediction of the transient cool-down characteristics of a cryocooler under external load conditions is an important technical support for improving the operational efficiency of large cryogenic systems. Although some studies have investigated the cool-down process of cryocoolers, their transient behavior under complex load conditions remains difficult to predict. This study focuses on the transient cool-down process of cryocoolers operating under load conditions and proposes a transient cool-down prediction method based on the equivalent simulation of external loads using heating resistors. This method dynamically adjusts the resistive heating power according to the real-time temperature variation of each cold head, thereby achieving an equivalent simulation of the thermal load imposed by external loads. A two-stage G-M type pulse tube cryocooler is employed as the cold source, and cooldown experiments are carried out under different load conditions. The influence of load conditions on the transient cool-down characteristics of the cryocooler is analyzed in detail, and the errors between the equivalent cool-down predictions and the actual cool-down results are compared. The results show that the equivalent prediction agrees well with the actual cool-down time, demonstrating the accuracy of the proposed method in predicting the transient cooldown characteristics of cryocoolers under load conditions. The findings of this study provide theoretical guidance for estimating the startup time of large cryogenic systems and for optimizing the design of precooling-stage cryocoolers in applications such as quantum computing and superconducting magnet cooling.

Cryogenic refrigeration is an enabling technology of superconducting magnet for its low-operating temperature. A cryocooler is usually used for cooling HTS devices, but it constantly demands electric power and its noise-generating characteristics is sometimes undesirable in certain applications. Cryogenic thermal battery with its high thermal storage capacity is attractive to temporarily operate HTS devices in a very quiet and independent mode without being connected to external power source. While a thermal battery is intrinsically needed to absorb the direct heat inleak to the HTS system and maintain its cryogenically operating temperature, it is beneficial to install another one at the intermediate temperature level between the first thermal battery temperature and room temperature. This second thermal battery plays an effective role to thermally anchor the parasitic heat inleak from room temperature and reduce the ultimate cooling load of the HTS system. This presentation examines the benefit of such a cascade thermal battery concept that may utilize various thermal battery materials. The extended operation time of the superconducting device is calculated for each case when radiation or conduction heat load is dominant. The overall system efficiency can be increased by adopting a proper cascade configuration of distributing thermal battery masses.

In recent years, large-scale production of MgB 2 wires has enabled the manufacturing of high-field magnets and high-current cables. In scientific applications, for instance at CERN, they help power LHC Hi-Lumi magnets, carrying up to 120 kA continuous current across sub-cables at low voltage. In medicine, MgB 2 wires have been successfully implemented in the commercial MRO-open MRI system. Multiple projects validate MgB 2 cables as economically and technically viable for energy transmission in power grids, heavy industry, and renewable integration. The EU-funded Best Paths project (2014-2018) developed a 320 kV/10 kA (3.2 GW) HVDC MgB 2 cable, with design, testing, and economic analysis showing 25% cost savings over resistive HVDC lines.​ Recent efforts include several projects: IRIS (Italian NRRP/NextGenEU, led by INFN), where ASG supplies a 130 m single-pole cable rated at 40 kA/25 kV MVDC (1 GW scale), the world's highest-power medium-voltage superconducting cable for a new test facility; SCARLET (EU-funded under Grant Agreement No.101075602 ) demonstrates a 20 kA/25 kV MVDC MgB 2 cable cooled by liquid hydrogen, doubling as an H 2 pipeline, with type and long-term tests planned through 2027; SURE (SUperconducting Reliability and Efficiency) proposes a groundbreaking advancement in the field of superconducting power transmission by designing, manufacturing, and demonstrating the first low‑voltage DC superconducting cable integrated into a real operational grid to supply a data center. Another project, V-ACCESS (EU funded under Grant Agreement 101096831), advanced a marine SMES MgB 2 prototype to TRL5, tested with dedicated power electronics in simulated naval architecture. This paper overviews ASG projects on cables and SMES, highlighting design and manufacturing milestones, installation and testing challenges, as well as technical and regulatory insights for industrialized energy solutions.

Ion trap quantum computing imposes stringent requirements on the cryogenic environment, necessitating both low temperatures and minimal mechanical vibrations to ensure qubit coherence and operational fidelity. Although Gifford–McMahon (GM) cryocoolers provide high cooling capacity and long-term reliability, their intrinsic low-frequency mechanical oscillations severely limit direct integration into vibration-sensitive quantum systems. To address this challenge, this work investigates two distinct thermal coupling strategies for vibration mitigation while maintaining efficient heat transfer. The first approach employs a helium gas heat exchange chamber as a non-rigid thermal coupler, fully decoupling mechanical vibrations between the cold head and the experimental stage. This configuration reduces the cold-head displacement from 50,000 nm to 200 nm at the cryogenic platform, while achieving a base temperature of 3.4 K with temperature fluctuations limited to 0.02 K. As a compact and fully solid-state alternative, flexible thermal links based on oxygen-free high-conductivity copper are optimized through controlled vacuum and nitrogen annealing. Metallographic and vibration measurements show that grain growth and mechanical compliance strongly depend on annealing temperature, enabling substantial stiffness reduction without compromising thermal performance. Building on these results, future development will integrate a GM pulse-tube cryocooler with cryogenic quasi-zero-stiffness isolation structures to further suppress residual vibrations to the nanometer level, aiming to meet the stringent stability requirements of next-generation quantum and precision measurement platforms.

As Quantinuum continues progress along its development roadmap, the need for increased cooling capacity is required to meet the cryogenic requirements for quantum computers with larger qubit counts. Expansion of the current helium liquefaction plant is necessary to meet the increasing cooling demands required for system development while simultaneously supplying the demand for the operation of commercial quantum computers. To address this, Quantinuum partnered with Air Liquide Advanced Technologies (ALAT) to design a new helium liquefaction plant incorporating a cryogenic liquefier supplied by ALAT. The main components of this new helium liquefaction plant include two Kaeser compressors, one helium purification system, one oil‑removal system (ORS), one cryogenic liquefier (Cold Box), and one 3000‑L dewar. With liquid nitrogen pre‑cooling, the new plant is capable of producing up to 320 L/h of liquid helium. In the new system, compressed raw gas (recovered helium) from high‑pressure storage vessels first flows into the purification system, where impurities are removed using a liquid‑nitrogen‑cooled cryogenic adsorption bed operating at 77 K. The purified gas stream then enters an 80 m 3 helium buffer tank before being recompressed by two water‑cooled helium cycle compressors to a pressure of 14.7 bara. The helium gas then undergoes a second conditioning stage in the ORS, which includes a lube‑oil filter and a charcoal adsorber. From here the high‑pressure gas enters the Cold Box Liquefier, flowing through a heat exchanger cooled by the low‑pressure return stream from the dewar. The high‑pressure flow then passes through a series of heat exchangers and turbine expanders until it reaches a condensing temperature becoming into liquid helium before entering the 3000‑L dewar for subsequent distribution to the quantum systems.

Gas gap heat switches are widely used in cryogenic systems to provide controllable thermal coupling between temperature stages, particularly with ultra-low temperature systems. Their operation relies on the thermal conductance across a narrow gap by controlling the presence or absence of an exchange gas. In the “on” state, gas conduction enables efficient heat transfer between stages, while in the “off” state, evacuation of the gas suppresses conduction, leaving only parasitic contributions from radiation and structural supports. This simple yet robust mechanism makes gas gap heat switches attractive for staged cooldown and thermal isolation in cryogenic environments. In dilution refrigerator systems, gas gap heat switches are commonly employed to precool lower-temperature components such as the still, the cold plate or the mixing chamber. Once the target temperature is reached, the switch is turned off to thermally isolate the lower temperature stages, thereby minimising unwanted heat loads. Over the years, gas gap heat switches have largely been characterized in isolation, with emphasis on steady-state thermal conductance in both on and off states. The present work investigates the cooldown dynamics of different stages of a dilution refrigerator using gas gap. Three primary parameters are identified which effectively controls the cooldown performance of such systems and they are (i) radial clearance between the concentric copper bodies, (ii) material quality of copper—represented by its residual resistivity ratio (RRR), which dictates bulk thermal conductivity—and (iii) heat lift capacity of the cryocooler’s second stage. Radial clearances in practical designs typically range from 0.1 mm to 0.2 mm, and conventional theory suggests that increasing this gap reduces gas conduction, thus degrading the performance. To quantify this effect, a systematic study is conducted by varying the clearance and evaluating its impact on transient thermal conductance and overall cooldown time. In parallel, the influence of copper purity is examined. During the course of the study, we investigated the effect of copper quality on the thermal performance of the switch in conjunction with the other identified parameters. Our simulations indicate that even use of the highly conductive copper has a large temperature gradient along the length of the switch. A study setup was erected to quantify the effect of these parameters working in consonance for both steady state as well as transient state. Result from the analysis and experiments reveal that the dominant bottleneck in system performance is frequently not the radial clearance or the intrinsic thermal conductivity of copper, but rather the available heat load capacity of the cryocooler’s second stage. When the cryocooler operates near its heat lift limit, improvements in gap spacing or material purity yield diminishing returns. Comparative simulations and supporting experimental measurements are presented to evaluate cooldown time constants across different clearance values and RRR grades, providing a more system-level perspective on gas gap heat switch optimization. The results provide design guidelines for optimizing gas gap heat switches in dilution refrigerator systems, balancing rapid precooling capability with minimal parasitic heat leak in steady-state operation. The study contributes to improved cooldown efficiency and enhanced operational reliability of cryogenic platforms targeting millikelvin temperature regimes.

Vitrification-based cryopreservation is a promising approach for preserving small-volume bio samples. Previous studies have shown that the risk of damage to biological cells or tissues during the rewarming and thawing stage is significantly higher than that during the freezing stage. Extremely high rewarming rates are expected to suppress devitrification and minimize thermal damage. As a result, laser-based rewarming has emerged as an attractive ultra-rapid rewarming technique. Despite its potential, the underlying ultrafast heating dynamics of vitrified droplets remain poorly understood, as temperature evolution has been predominantly inferred from numerical simulations, with limited direct experimental evidence. In this study, we developed an integrated experimental platform that combines in situ vitrification by liquid nitrogen and laser rewarming, enabling real-time measurement and visualization of the ultrafast temperature evolution of vitrified samples under laser irradiation. Experimental results show that a 1 μL vitrified droplet can achieve rewarming rates as high as 1.8 × 10 6 K/min during laser rewarming. In addition, the apparent morphological evolution of the vitrified sample was captured during the ultra-rapid laser rewarming process, revealing transient superheating phenomena induced by instantaneous energy deposition. This work represents the first systematic experimental investigation of the thermal response of vitrified droplets during laser rewarming. The proposed platform provides a physics-based monitoring approach for evaluating and ensuring the safety of this ultra-rapid rewarming strategy.

This study addresses a key clinical need in laser treatment of vascular and pigmentary skin disorders, such as port-wine stains and Nevus of Ota: precise and efficient cooling of healthy tissue. The currently prevalent spray cooling agent R134a is limited by drawbacks including heat transfer inhibition due to liquid film formation, high global warming potential, and restricted refrigeration effectiveness, which hinder further advances in treatment safety and efficacy. In recent years, environmentally friendlier alternatives such as the mixed refrigerants R1234yf, R454B and R513A, along with liquid CO₂, have emerged as promising candidates. However, systematic investigation and comparative assessment of their spray cooling performance in the context of laser medicine—particularly against conventional refrigerant R134a—remain insufficient. To address this gap, this study systematically conducted comparative transient spray cooling experiments on five refrigerants (R454B, R513A, R134a, R1234yf, and liquid CO 2 ) to identify optimal cooling solutions for clinical applications. Experiments employed a straight-tube nozzle with an inner diameter of 0.8 mm and length of 40 mm. Under conditions slightly exceeding the saturated vapor pressure at room temperature for each refrigerant, various operating parameters were investigated, including spray height (20 mm and 50 mm) and spray duration (20 ms, 50 ms, and 100 ms). A comprehensive evaluation of each refrigerant’s cooling performance and heat transfer behavior was conducted through monitoring transient surface temperature, heat flux density, and heat transfer coefficient on an epoxy resin phantom, complemented by observations of spray morphology and liquid film distribution. Results indicate that due to differences in physicochemical properties and phase transition mechanisms, the cooling behavior and applicable scenarios of different refrigerants vary significantly. Moreover, alternative solutions outperforming the conventional refrigerant R134a in key performance metrics exist across all operating conditions. At short spray distances (H=20 mm), liquid CO 2 demonstrated optimal cooling capacity at a spray duration of t=100 ms. Its heat transfer mechanism, characterized by the absence of a liquid film and dominated by dry ice particle impact and sublimation, achieved a maximum heat transfer coefficient (h max ) of 23.06 kW·(m 2 ·K) -1 , representing approximately a 5-fold improvement over R134a. At long spray distances (H=50 mm), the low-boiling-point mixed refrigerant R454B formed a thin yet extensive liquid film, enhancing single-phase heat transfer. It achieved a maximum heat flux density of 212.86 kW·m -2 at a spray duration of t=100 ms, representing an approximately 0.5-fold improvement over R134a. Notably, the blended refrigerant R513A consistently outperformed R134a and R1234yf—both with similar boiling points—under all test conditions: at H=20 mm and t=20 ms, its h max increased by 229.5% and 50.4% compared to R134a and R1234yf, respectively; and at H=50 mm and t=50 ms, its h max increased by 65.9% and 170.5% over the two refrigerants, respectively. In contrast, despite a boiling point close to R134a, R1234yf forms a thick, concentrated liquid film, with cooling performance even inferior to R134a at long spray distances. Mechanistic analysis further reveals that spray morphology and liquid film characteristics are key factors causing performance differences: Liquid CO 2 lacks liquid film obstruction but exhibits particle accumulation lag; R454B and R513A, form thin and uniform liquid films, fundamentally overcoming the heat transfer obstruction caused by R134a's liquid film; while R1234yf exhibits more pronounced liquid film issues than R134a, limiting its potential as a replacement refrigerant. In summary, liquid CO 2 shows significant potential under specific operating conditions, but its high impact force may pose operational risks. The novel mixed refrigerants R454B and R513A demonstrate stable and superior cooling performance across a broader range of operating conditions, coupled with lower saturation pressures, enhancing operational safety in clinical applications. This study confirms the potential of both as viable alternatives to R134a, providing experimental evidence and selection guidance for optimizing auxiliary cooling solutions in laser skin surgery.

Facilities that manage temperature-sensitive materials rely on specialized cold-storage systems, whose reliability is crucial for continuous operation. In many biotechnology settings, this function is provided by large freezer farms that contain medical-grade cryogenic freezers, which preserve high-value research samples and products. Damage to these units can lead to significant financial losses and major disruptions to facility operations. While anchorage and restraint systems are commonly employed to limit external movement and uplift under seismic loading, the resulting internal stresses and deformations within the freezer structure itself have received relatively little attention. In this case study, Finite Element Analysis (FEA) is used to investigate the structural performance of a representative cryogenic freezer. The model incorporates both gravity and seismic loading to identify critical stress concentrations and assess potential structural weaknesses, aiming to enhance the understanding of the seismic sensitivity of cryogenic storage equipment in biotechnology facilities. The analysis highlights localized overstress in the inner spool and in the upper portion of the outer shell near the lid opening. These results indicate that, although overall stability is maintained, internal components of cryogenic freezers may be prone to localized damage during strong shaking. Accordingly, future freezer designs intended for high-seismic regions should explicitly incorporate seismic performance into their design criteria to improve system-level resilience.

A liquid nitrogen (LN₂) multiphase reactor was developed to explore the potential of LN₂ as a direct-contact coolant for freeze concentration. Fundamental studies were carried out to clarify the heat and mass transfer phenomena that govern the process. The evaporation and heat transfer behavior of LN₂ droplets injected into immiscible liquids were investigated using theoretical modeling and experiments, revealing conduction-dominated cooling in the initial stage and the progressive influence of buoyancy-driven convection. To capture the solidification dynamics, a one-dimensional model of ice front growth and solute redistribution was established, in which a sigmoidal law accurately described the variation of the intrinsic partition coefficient with freezing front velocity. This model was validated using sucrose–water solutions, offering a transferable framework for other solute systems. On the system level, a proof-of-concept LN₂ direct-contact freezer was constructed and tested. The experiments demonstrated efficient ice particle formation and concentration of sugar solutions, with measured partition coefficients around 0.6. A subsequent material and energy balance model confirmed the feasibility of scaling up the process, with sample calculations indicating production capacities on the order of hundreds of kilotons per year. These results highlight the promise of LN₂-based direct-contact freeze concentration as an efficient cryogenic separation technology.

“…the United Nations General Assembly (UNGA) declared 2025 as the International Year of Quantum Science and Technology…” [1] to celebrate 100 years of quantum mechanics and recognize its impact on science and technology worldwide. The formulation of quantum mechanics in 1925 laid a lasting foundation for our physical understanding of nature. Today, we can see the impact of quantum mechanics on all areas of our culture, science, technology and art as well as various technological developments such as LEDs, transistors, lasers and medical imaging techniques such as magnetic resonance imaging (MRI). Quantum technology can be divided into the fields of Quantum Communication, Quantum Sensing and Quantum Computing. In the presentation we focus on the cooling of quantum computing. Today quantum computers have a small number of qubits. There is enormous progress in the development of quantum computers, and in near future the interconnection of millions of qubits will enable the construction of commercial useful quantum computers. Above this threshold Quantum computing is expected to drive significant advancements in climate modeling, drug discovery, clean energy, advanced material design and encryption. There exist several technology platforms for quantum computing. Most of these require deep cryogenic temperatures, these extreme cooling demands require sophisticated solutions. In the field of photonic based quantum computers, Linde Kryotechnik AG signed an agreement with PsiQuantum to build and deliver the largest cryogenic plant ever planned for quantum computing, furthermore it is also one of the most powerful cryogenic refrigeration systems ever built. This cryogenic cooling plant for the world’s first utility-scale quantum computer in Brisbane, Queensland, Australia has a total cooling capacity of 36 kW at a temperature of 4.5 K. It will cool tens of thousands of PsiQuantum’s new Omega photonic chips housed in cryostats that will be networked together with standard optical fiber. On the other hand, in the field of matter-based qubits most quantum computers require millikelvin temperatures. Linde Kryotechnik AG, Switzerland and Bluefors, Finland combine their efforts to create integrated cooling solutions for utility-scale quantum computing at any cryogenic temperatures down to millikelvin temperature level. The result is an efficient cryogenic plant delivering cold for the next generation of this quantum computing technology. [1] https://www.unesco.org/en/years/quantum-science-technology?hub=167999

Bi-2212 is a viable conductor for high-field magnets. It is a fabricated as a round wire using the powder-in-tube method and can have a variety of architectures. The round wire can be be aspected to form rectangular wire, twisted, and cabled. This presentation will discuss recent advances in the processing of Bi-2212 wire and its application in test coils at the Applied Superconductivity Center at the National High Magnetic Field Laboratory. Supported by US DOE OHEP under Award DE-SC0010421, STTR Phase II under Award DE-SC0018683, US ARDAP through LBNL DE-AC02-05CH11231/AWD00007176, NSF DMR-2128556, NIH-RO1 grant 1RO1GM154600, and the State of Florida. This work is carried out within the broader context of the US DOE-MDP.

ASG Superconductors' production process enables fully reacted MgB 2 wires and tapes up to 5-6 km in length, with customizable layouts tailored to specific applications. These conductors exhibit excellent mechanical properties, making them ideal for react-and-wind techniques in magnet manufacturing and react-and-cable processes for power cables. Both tapes and round wires are commercialized in various sizes for magnet integration. Ad-hoc doped powders optimize performance up to 4-5 T fields. Round wires support power cable applications, with production flexibility allowing customization of wire diameter, filament size, twist pitch, and coatings (e.g. copper) to match cable designs. About 1000km of wires have been manufactured and fully qualified by CERN for the superconducting link of the HI-LUMI projects, and many projects are now using MgB 2 , demonstrating that the technology is reliable and suitable across diverse applications: from power grids for energy transmission to protection and storage systems. This work presents the characteristics of our commercialized wires, the manufacturing process, the key applications, and ongoing R&D activities to enhance performance, unlocking new frontiers.

MgB 2 is an attractive material owing to its superconducting transition temperature (T c ) of approximately 40 K, which enables low-field superconducting applications below 30 K, including liquid-hydrogen temperatures. This material feature offers a pathway toward the practical realization of hydrogen-related hybrid energy systems, particularly superconducting power devices combined with hydrogen storage or transport technologies for advanced energy management. In response to these emerging opportunities, significant efforts have been devoted to the development of polycrystalline MgB 2 wires. Commercial MgB 2 wires developed to date are typically fabricated using ex situ or in situ processes. When the latter process is employed, wire cores are formed by randomly oriented MgB 2 grains. These grains exhibit anisotropic in-plane and out-of-plane dimensions due to preferential in-plane growth associated with the layered hexagonal structure. Such anisotropic growth is caused by strong covalent B–B bonding within the boron layers of the MgB 2 crystal structure. The directional nature of this bonding is also responsible for the T c of 40 K, which arises from strong coupling between in-plane boron lattice vibrations (phonons) and charge carriers in the quasi-two-dimensional (quasi-2D) σ bands. This coupling mechanism gives rise to anisotropic superconductivity along the in-plane direction. The MgB 2 electronic structure also contains nearly three-dimensional (3D) π bands. However, charge carriers in the π bands responsible for nearly isotropic superconductivity are weakly coupled to phonons. The weak behavior of phonon coupling causes nearly isotropic superconductivity to be more easily suppressed under high magnetic fields than anisotropic superconductivity along the in-plane direction. This easily suppressed superconductivity can significantly affect the critical current performance of polycrystalline MgB 2 wires under magnetic fields. The underlying reason is that when electrical current is transported through wire cores consisting of randomly oriented MgB 2 grains, supercurrent flows across out-of-plane as well as in-plane interfaces between grains. A thorough understanding of in-plane and out-of-plane crystallinity of MgB 2 grains would allow accurate control of crystallographic properties in both directions and contribute to further improvement in the transport properties of MgB 2 wires. However, the crystallographic characteristics in each direction are still not comprehensively understood. This is because the crystallinity (e.g., grain/crystallite size and lattice strain) of MgB 2 wire cores has mostly been analyzed using isotropic models. In this presentation, we therefore report the crystallographic characteristics of in situ processed and undoped MgB 2 wires from the viewpoint of the in-plane and out-of-plane crystallinities. Based on these findings, we also discuss how controlled crystallinity in each direction has the potential to further enhance the transport performance of MgB 2 wires.

HTS tapes assembled in a compact stack are one of the most common methods for increasing the critical current of a single superconducting current-carrying element. Stacks also serve as sub-elements for larger superconductors. However, a stack of HTS tapes consists of parallel-connected conductors with zero resistance. The current distribution among the tapes in a stack and its voltage-current characteristic may deviate from the typical power law, depending on factors such as the number of tapes, the rate of current increase, and the bending of the stack. This deviation can lead to additional heat generation in the superconductor, particularly due to the emergence of resistive conductivity in the voltage-current characteristic, which can subsequently decrease the critical current of the stack or the larger superconductor. This paper presents the results of an experimental study on the current-voltage characteristics of tape stacks soldered with indium-tin solder, examining various stack sizes, rates of current increase, and bending radii. The measurement results are discussed, and a numerical model is presented. The calculated results are compared with experimental findings.

Iron-based superconducting (IBS) wires have emerged as promising candidates for high-field applications, where achieving both high critical current density (J c ) and low production cost is essential for practical large-scale deployment. Here, we report a scalable, stress-engineered nano-defect strategy that introduces unprecedented dislocation pinning centers by directly twisting the rigid crystal lattice of Ba 1-x K x Fe 2 As 2 (BaK122) at the angstrom scale. This process activates interlayer slip and twisting along a close-packed crystalline plane, generating uniformly distributed, high-density dislocations (ρ~10 9 mm -2 ) with diameters of 3-4 nm and lengths of hundreds of nanometers. These tilted line defects act as quasi-correlated vortex pinning centers and evolve via thermal activation, as revealed by in situ high-temperature TEM. As a result, the IBS wires achieve an extraordinarily large irreversibility field of 120 T and an ultrahigh J c of 4.5×10 5 A/cm 2 at 4.2 K and 10 T, which maintains 2×10 5 A/cm 2 even at a high field of 33 T. This performance exceeds the best-reported IBS wires by a factor of five and even outperforms pristine BaK122 single crystals, highlighting the remarkable effectiveness of our dislocation-engineering strategy. Our study offers a breakthrough in controllable defect engineering for high-performance, low-cost superconductors.

We began the short-circuit experiment on the HTS tape several years ago, aiming to simulate a short-circuit accident in a superconducting DC power cable (SCDC). Since the superconducting cable is a coaxial structure and many DC/AC converters have a capacitor at the DC output, the equivalent circuit capacitance is high. Therefore, we construct a capacitor bank power supply to perform short-circuit testing of the HTS tapes. As the HTS tape is composed of a superconductor (SC) and a normal metal conductor (NC), the equivalent circuit is a parallel circuit of these two conductors. We measured the resistance of the HTS tape from the room temperature to ~60 K and estimated the NC resistance from 77 K to the transition temperature (R n ). We also estimated the SC resistance (R s ) from a standard critical-current measurement using the power law as follows: R s = Al /I s (I s /I c ) n where A is the fitting parameter, l is the distance of the voltage taps, Is is the superconductor current, Ic is the critical current, and n is the n-value. Finally, we constructed the physical circuit model for numerical calculations using LTspice. At the same time, we introduced several fitting parameters in the physical model. The calculation method is to solve the circuit equations, with the measured voltage waveform as the input parameter. These equations, considering the mutual inductance (), are given by V input = L s dI s /dt + M d n /dt + R s I s V input = L n dI n /dt + M d s /dt + R n I n where V input is the measured voltage, I n is the current of the NC part of the HTS tape. Then, we obtained the calculated NC and SC currents. After we calculated the NC and SC currents, we added them and compared the total calculated current with the experimental current. After the LSspice calculation, we evaluated two current waveforms using the coefficient of determination (CoD) as a standard technique in the least-squares fitting. Since the CoD of some analytical results is higher than 0.99, the fitting analysis is sufficient to reconstruct by the physical model, and the separation of the NC and SC currents should be successful. These analytical results will be useful for evaluating the basic behavior of the short-circuit test for the HTS tape and the SCDC cable.

SuperMag Technology Ltd., a nascent enterprise spun off from Shanghai Jiao Tong University, has demonstrated remarkable progress in both R&D and manufacturing capabilities despite its recent inception in late 2022. In just one year, the company has successfully set up a production line based on an IBAD+PLD process route. This paper reports the latest progress in high-performance 2G-HTS tape production at SuperMag. We developed an ultra-fast pulsed laser deposition (PLD) technique with a peak growth rate of 200 nm/s. By combining REBCO formula optimization and deposition process improvements, REBCO films achieve excellent pinning performance, i.e., I values of over 245 A/4 mm-w @ 50 K, 5 T, and 340 A/4 mm-w @20 K, 20 T. The new-generation products synergistically deliver strong low-temperature/high-field performance and excellent electromechanical properties. This product offers both improved cost-effectiveness and increased manufacturing throughput, providing an optimized solution for high-field magnets, particularly in fusion applications. Parallelly, SuperMag has established in-depth collaborations with clients and is actively advancing research in areas such as filamentization and joining technologies.

Faraday Factory Japan (FFJ) is the world leader in manufacturing second-generation high-temperature superconducting (2G HTS) tapes, operating one of the largest production facilities globally dedicated to REBCO coated conductors. Since 2011, FFJ has been developing ion beam assisted deposition (IBAD) and pulsed laser deposition (PLD) technologies for industrial-scale 2G HTS wire production. All FFJ products are based on electropolished Hastelloy substrate, IBAD-MgO buffer layer technology, and PLD-REBCO superconducting layer, with standard widths of 4 mm and 12 mm. Custom Hastelloy thickness, widths, and other specifications are available upon request to meet specific application requirements. Customization options include thicker Cu stabilization layers, solder plating, insulation, face-to-face soldered stacks with improved mechanical properties and current sharing capability. In 2024, FFJ started the new factory in Zama city and achieved a significant milestone with cumulative delivery exceeding 1 Giga-Ampere-meter (over 8,000 km of 4 mm wide tape) to customers across four continents pursuing various applications including compact fusion, power cables, magnets, and rotating machinery. FFJ offers a range of 2G HTS products optimized for specific operating conditions. The Hermes tape, our established fusion-grade product, features YBCO superconductor modified with Y 2 O 3 nanoparticles and oxygen overdoping, achieving average engineering current density (Je) approaching 1,000 A/mm² at 20 K and 20 T. Our current annual production capacity has reached 3,000 km/year of standard Hermes tape (4 mm width), with potential for further expansion up to 1.0 GAm/year. In 2025, FFJ introduced the newly developed Mirai tape, which represents a significant performance advancement, with Je exceeding 1,200 A/mm² (20 K, 20 T) and lift factor (Ic(20 K, 20 T)/Ic(77 K, s.f.)) up to 1.5 — a performance level targeting next-generation high-field magnet applications up to 40 T and beyond. In 2026, FFJ released a new product for power cable applications — Electra tapes achieving critical current (Ic) of approximately 1,200 A/12 mm (or >300 A/4 mm) at 77 K in self-field. Additionally, we started to manufacture filamentized wires produced by laser scribing with 10–15 filaments per 4 mm width, designed for reduced AC losses in cable and rotating machinery applications. This presentation provides an overview of FFJ's manufacturing capabilities, product specifications, and quality control systems, demonstrating our readiness to support the growing global demand for high-performance 2G HTS conductors across diverse applications. Keywords: 2G HTS, REBCO, coated conductors, superconducting tape, fusion, manufacturing

High magnetic fields of up to 20 T in tokamak-type fusion devices require High-Temperature Superconductors (HTS) and a promising candidate is REBCO tape. The large Lorentz forces occurring under these operating conditions may locally generate high values of mechanical stress, which can affect or irreversibly degrade the critical current of the superconductor. For the optimal design of full-size cabled conductors, detailed structural finite element analysis (FEA) based on accurate material electromagnetic and mechanical properties under relevant electromagnetic load levels is needed for reliable and optimal operation. Knowledge of the critical current and irreversibility limits under various loading conditions of REBCO tapes is therefore essential. For this purpose, experiments applying axial tensile stress–strain, local transverse stress and helical winding on different core diameters have been performed on REBCO tapes from several manufacturers in upgraded and new facilities. The evolution of the transport properties was measured at 77 K in self-field for cyclic and stepwise increasing loading on striated and non-striated tapes. Full-scale 3D FE models of the tapes have been developed and validated using the measured electrical and mechanical material properties of the used superconducting tapes. The combined results are the basis to predict quantitively the impact of Lorentz load on composite REBCO-based Cable In Conduit Conductor design optimisation.

The 33T cryogen-free superconducting magnet (33T-CSM) is under construction at the High Field Laboratory for Superconducting Materials (HFLSM), IMR, Tohoku University, Japan [1]. It consists of a 19T-REBCO insert and a 14T-LTS (Nb 3 Sn and NbTi) outsert magnets. The 19T-REBCO insert is a 64-stacked pancake coil with a “robust coil structure” [2], comprising two REBCO tapes, one Hastelloy tape and one polyimide tape, which are co-wound with edge-impregnation. The 40 µm Cu-plated REBCO tapes (FESC-SCH04) produced by Fujikura Ltd. were adopted for the 19T-REBCO insert coil. The total length of the REBCO tapes shipped is approximately 18.6 km. The I c values at 77.3 K and self-field are between 150 A and 235 A. In this study, we present the J c performances of the REBCO tapes for the 33T-CSM in low temperature and high field region. For the J c measurements, DC currents up to 20 A were used for the bridge samples and the pulsed currents up to 2 kA for 4 mm width samples were used [3, 4]. The REBCO tapes (FESC) are EuBCO tapes with BaHfO 3 (BHO) nanorods on 50 µm thick Hastelloy. However, no explicit peaks for B//c were observed in the angular dependence of J c at 20 T and 20 K, although the BHO nanorods works as pinning centers. It is due to the segmented BHO nanorods and fluctuation of the rod’s axes due to the high growth rate [5]. For the 19T-CSM, the minimum J c is determined at an angle of 65˚-80˚ and a field 15 T-24 T at the central field of 33 T, although it depends on the temperature. The operation temperature would change from 5 K to 15 K during magnet operation due to the ac losses. The temperature dependence of the J c peaks around B//ab is important for the 33T-CSM. The angular dependence of J c will be discussed in terms of the flux pinning and of the magnet design. [1] S. Awaji et al., IEEE TAS 35 (2025) 4300406. [2] S. Awaji et al., IEEE TAS 31 (2021) 4300105. [3] Y. Tsuchiya et al. SuST 30 (2017) 104004. [4] Y. Tsuchiya et al., IEEE TAS 35 (2025) 9500805. [5] S. Fujita et al., IEEE TAS 29 (2019) 80015055. Acknowledgment This work was supported by the Moonshot R&D Program “MILLENNIA” (Grant No. JPMJMS24A2) of the Japan Science and Technology Agency (JST), JSPS KAKENHI (Grant No. 22H00142) and by the New Energy and Industrial Technology Development Organization (NEDO, Project No. JPNP20004).

Uniform thickness is a critical factor determining the performance of High-Temperature Superconducting Coated Conductors (HTS CCs) used in HTS magnet technologies. Addressing the limitations of existing inspection methods, we present a novel Reel-to-Reel (R2R) measurement solution capable of real-time, non-contact thickness profiling. By integrating high-precision chromatic confocal displacement sensors, our system achieves a measurement accuracy of +/- 1 um and visualizes surface topology through 3D mapping. While the current system operates stably at 300 m/h, the design incorporates vibration suppression mechanisms to support industrial-scale production rates of up to 600 m/h, meeting the demands of mass production. This technology provides a robust solution for in-line quality control and offers critical data for optimizing downstream processes. Specifically, the generated thickness profiles enable precise analysis for corrective measures, such as rolling and supplemental deposition, significantly contributing to the consistent production of high-performance HTS magnets with uniform coil geometry. Keywords: HTS CCs, Thickness measurement system, Reel-to-reel, Confocal laser sensor Acknowledgement: This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korea government (Ministry of Science and ICT)(RS-2022-NR068578).

Coated conductors (CCs) with a thin (around 1.6-2 μm) REBCO (RE=Y, Gd, Eu, Nd, Sm, Dy, etc.) superconducting layer textured along the c-axes are considered to be the most promising high-temperature superconducting (SC) materials for various applications such as motors, generators, long-length transmission cables, superconducting magnetic energy storage (SMES), magnetic levitation (MAGLEV) trains, and high-field magnets for scientific and medical equipment such as NMR and MRI, etc. The level of superconducting characteristics of CC, and the critical current density, J c , in particular, to high extent depends on the oxygenation process, which affects the amount of the charge carrier density, n H , in the REBCO layer and pinning centers. The effect of oxygenation under pressure 1-16 MPa and temperature 250 -800 °C on critical current density, J c , of GdBCO and EuBCO coated conductors and of REBCO (RE=Y, Gd, Er) films deposited on SrTiO 3 (STO) substrate has been studied. The observed effect of critical current density increase is associated with an increase in the charge carrier density, n H (estimated from the Hall effect measurements using the Van der Pauw technique at 100 K by Quantum Design PPMS). After reoxygenation through the Ag layer at 16 MPa O 2 and 800 o C for 3 h, the J C (77K,0T) of GdBCO_CC has been increased for 21.5 % as compared to the commercial GdBCO_CC tape, i.e. from 2.12 to 2.70 MA/cm 2 ; n H increased from 6.55 to 7.3×10 21 cm -3 and the c-parameter decreased from 1.1735 to 1.1727 nm). Critical current density, J c , as a result of oxygenation of tetragonal YBCO film (250+-7% nm thick) under 10 MPa O 2 pressure at 600 o C for 8 h was increased by 61 % (at 77 K) and 74% (at 5 K) compared to the values after standard oxygen saturation at 1 bar, 450 o C, 3.5 h: J c (77 K, 0 T)=3.74 MA/cm 2 , J c (5 K, 0 T)=33.34 MA/cm 2 versus J c (77 K, 0 T)=2.28 MA/cm 2 , J c (5 K, 0 T)=24.83 MA/cm 2 . The charge carrier density, n H (100 K) increased from 3.2 ×10 21 cm -3 to 10.78×10 21 cm -3 , c-parameter reduced from 1.1695 to 1.1678 nm. We acknowledge funds from MUGSUP, UCRAN20088 project from CSIC programme from the scientific cooperation with Ukraine, the Spanish Ministry of Science and Innovation and the European Regional Development Fund, MCIU/AEI/FEDER for SUPERENERTECH (PID2021-127297OB-C21), Matrans42 “Severo Ochoa” Program for Centers of Excellence in R&D (CEX2023-001263-S), and HTS-JOINTS (PDC2022-133208-I00), the Catalan Government for 2021 SGR 00440, NAS of Ukraine Project III-7-24 (0788). AK acknowledge financial support from Spanish Ministry of Science, Innovation, Universities through the FPI grant PRE2020-091817, and SPS 8391 Project.. Authors also thanks Fujikura for supplying the samples.

Iron-based high-temperature superconductors are promising candidates for high field applications owing to their high critical temperatures, high upper critical fields, and intrinsically advantageous grain-boundary properties [1]. An overview of our recent progress in high-pressure-assisted synthesis of iron-based polycrystalline superconductors, focusing on the complementary 122 and 1111 material systems will be introduced. The 122 system is characterized by low electromagnetic anisotropy, whereas the 1111 system offers the highest critical temperature potential among iron-based superconductors. High-pressure processing plays a key role in addressing the distinct synthesis challenges associated with each system. For the 122 system, we demonstrate a data-driven process design based on pressure-assisted spark plasma sintering, which enables efficient synthesis of dense (Ba,K)Fe 2 As 2 bulk materials exhibiting a record-high, uniformly trapped magnetic field [2-4]. For the 1111 system, we focus on a topotactic reaction route for hydrogen doping in SmFeAsO [5] using laboratory-made, improved-purity parent phase [6]. The effects of subsequent post-annealing with hydrogen sources, as well as hot-isostatic-pressing will be reported. Acknowledgements This work was supported by JSPS KAKENHI (JP 24K21734, JP21H01615), JST CREST (JPMJCR18J4), the NIFS Collaboration Research program (NIFS25KIEA070), and the Collaborative Research Projects of Materials and Structures Laboratory, Institute of Integrated Research, Institute of Science Tokyo. References [1] T. Hatano et al., NPG Asia Mater. 16, 41 (2024). [2] A. Yamamoto et al., NPG Asia Mater. 16, 29 (2024). [3] M. D. Ainslie et al., Supercond. Sci. Technol. 38, 105025 (2025). [4] S. Ishiwata et al., Supercond. Sci. Technol. 38, 065014 (2025). [5] J. Matsumoto et al., Phys. Rev. Mater. 3, 103401 (2019). [6] F. Shimoyama et al., IEEE Trans. Appl. Supercond. in-press (2026).

High magnetic fields of up to 20 T in tokamak-type fusion devices require High-Temperature Superconductors (HTS) and 50 kA/20 T class, full-size REBCO Cable In Conduit Conductors (CICC). Conductors based on a helical winding of tapes on a round core, such as Conductor on Round Core (CORC®) cable and the Highly Flexible REBCO Cable (HFRC), are among others, proposed for the Central Solenoids of the European “DEMOnstration Power Plant” (DEMO) and the Chinese “Burning Plasma Experimental Superconducting Tokamak” (BEST) fusion reactors. The large Lorentz forces occurring under these operating conditions locally generate high mechanical stress, which can irreversibly degrade the critical current of the superconductor and impact the contact resistance between tape layers. For this reason, CORC® and HFRC cable samples, manufactured by Advanced Conductor Technologies and ASIPP (Hefei, China), have been tested under incremental and cyclic loading in the Twente Cable Press. The samples have been loaded with geometric configurations resembling as close as possible the loading conditions of their respective CICC designs. The critical currents, n-values, irreversibility limits and contact resistances of tapes selected from different layers have been measured at 77 K and in self-field. In addition, the compression versus applied load was measured representing the cable stiffness, elastic and plastic deformation of the conductor elements. In addition, a detailed structural finite element analysis (FEA) method of the conductors has been completed, which is able to handle the full CORC®-CICC geometry including all REBCO tapes. The model inputs are based on the actual REBCO tape electromagnetic and mechanical properties and their tensile and compressive irreversibility limits, also measured at the University of Twente for axial, transverse and winding stress. The model predictions agree well with experimental results. The model is then being used to perform parametric studies and predict quantitively which configurations can best withstand Lorentz load and what the impact is of proposed geometric and material design optimisations. An overview is given of tape and CICC experimental and modelling results.

The research on superconducting joint technology for REBa2Cu3O7-x (REBCO) coated conductors (CC) contributes to the extension of REBCO tape and the development of high-temperature superconducting magnets. Melt diffusion heat treatment is the core step in fabricating REBCO tape superconducting joints, enabling direct joining of two superconducting layers without any intermediate medium. This process requires rapidly heating the superconducting layer to 800–850°C under low oxygen partial pressure to achieve surface melting and brief isothermal holding, while preserving its superconducting properties and microstructure to the greatest extent possible. However, REBCO is relatively sensitive to temperature, which poses challenges for melt diffusion heat treatment. Current research on the temperature sensitivity of REBCO typically focuses on 200°C, a common temperature in the welding process, while the effects of higher temperatures remain understudied. We systematically investigated the effects of parameters such as oxygen partial pressure, heating rate, peak temperature, soak time, and cooling rate on the properties and microstructure of REBCO-coated conductors, thereby determining the optimal parameters for the melt-diffusion heat treatment. SEM, XRD, Raman, and XPS analyses indicate that the crystal structure of the superconducting phase is less adversely affected during the optimized rapid melt-diffusion heat treatment.

In high-temperature superconducting (HTS) systems, including superconducting magnetic energy storage (SMES) devices, a promising direction is the use of HTS tapes with artificially formed pinning centers, which provide an increase in critical current density and stability in high external magnetic fields [1]. One effective way to create such pinning centers is heavy ion irradiation, which leads to the formation of prolonged defects in the superconducting layer. It is well known that the maximum efficiency of pinning centers is achieved when the characteristic defect size is comparable to the coherence length of the superconductor, which determines the need for controlled formation of nanoscale defects. In this respect, this study considers numerical modeling of defect formation in the layered architecture of HTS tape based on REBa2Cu3O7-x compounds (REBCO, where RE is a rare earth element) under ion irradiation, aimed at obtaining nanoscale defects with specified geometric and energy characteristics. A wide range of computational approaches are used to study radiation-induced defects, including molecular dynamics, stochastic particle transport methods, and continuous energy release models. The latter, as a rule, considers homogeneous media and ignores both the layering and the anisotropy of thermophysical properties characteristic of HTS composites. This study proposes an alternative continuous approach to describing radiation damage in composite HTS tapes, based on the numerical solution of a system of equations using the finite element method. The energy release associated with ion traverse is modeled as a linear heat source distributed along the length, whose parameters are determined by the particle energy and the time of its interaction with individual layers of the multilayer structure. The model includes the heat transfer equation in combination with a phase-field description of the transition between the solid and liquid phases, which allows reproducing the sequence of processes of local melting of the material and its subsequent ultra-fast solidification. This formulation makes it possible to directly evaluate the geometry of a radiation-induced defect in a multilayer HTS tape and establish a quantitative correspondence between the parameters of the heat source in a continuous setting and the energy of the incident ion. Based on the developed model, the temporal evolution of the temperature field near the ion track at different levels of specific energy release is analyzed, and the conditions for the formation of a residual defect are investigated. It is shown that the contrast in the thermophysical properties of individual layers leads to local changes in the track radius near the interlayer boundaries, while the decrease in ion energy release as it travels deeper into the material causes a gradual narrowing of the defect within each layer. Calculated estimates of the characteristic sizes of the damaged area in the YBCO superconducting layer, ranging from 1 to 7 nm, are in agreement with experimental data obtained for tracks formed by heavy ions of comparable energies. This work was supported by the Ministry of Science and Higher Education of the Russian Federation within the State Assignment (project FSWU-2025-0014) References 1. X. Li, M. M. Ainslie, D. Song, Superconductor Science and Technology, vol. 38, no. 3, p. 033001, 2025/02/17 2025.

The program for testing Nb 3 Sn Rutherford cables in the Bonding Experiment (BOX) has revealed how the choice of impregnation and insulation can affect the training behavior of Nb 3 Sn cables. However, the underlying mechanisms for the differences in training behavior have not yet been identified in detail. New results are presented from testing Nb 3 Sn Rutherford cable in the Bonding Experiment now equipped with specially designed quench antennas. The cable in question is a 10 mm wide cable with 108/127 RRP type Nb 3 Sn strands for use in accelerator magnets, featuring a critical current of some 17 kA at 10 T. The sensors are strategically positioned in close proximity to the cable in the BOX sample, meticulously measuring the electromagnetic footprint of the seven cable sections during a quench. The RUtherford NEtwork model (RuNe) software is the tool used to directly simulate the antenna signals caused by the current redistribution in the cable after a local (training) quench. By fitting the measured and simulated signals we can identify the precise location of the quench initiation with a spatial resolution of five strands in the cross section and 10 mm along the length of the Rutherford cable. The analysis of a Nb 3 Sn BOX sample with CTD-101K impregnation revealed that the initial training quenches exhibit similarities. It appears they occur in multiple strands concurrently distributed along the wide edge of the cable and at locations where a relatively large amount of epoxy is present due to cable bending when preparing the sample. Furthermore, if a quench re-occurs in the same location, fewer strands are activated simultaneously. New BOX samples with antenna instrumentation are planned to provide further evidence for these observations. These BOX sample tests, a collaborative effort of the University Twente, CERN and PSI, will showcase a variety of insulation and impregnation methods which were not previously explored in the BOX program

Multi-Layer Insulation (MLI) is essential for the efficient long-term storage of liquid hydrogen. Although MLI demonstrates superior insulation performance under ideal conditions, it inherently exhibits anisotropic characteristics, where thermal performance varies depending on the incident radiation direction. In practical applications, the layer edges are often exposed to thermal radiation due to structural interfaces; however, the thermal degradation induced by such edge exposure has not been quantified. The impact of edge radiation was experimentally investigated using a vertical cylindrical boil-off calorimeter complying with ASTM C1774 and C740 standards. Two experimental configurations were tested sequentially using a single 10-layer MLI specimen composed of aluminum foil and glass fiber spacers. To isolate the effect of edge radiation, Experiment 1 was conducted with the bottom layer edges fully exposed to the warm boundary (300 K), after which Experiment 2 was conducted with these edges completely sealed. All other parameters, including layer density and vacuum pressure (10 -4 torr), were strictly controlled. The results indicated that the total heat leakage for the exposed-edge configuration increased by 110% compared to the sealed-edge configuration. Furthermore, the layer temperature distributions exhibited qualitatively distinct behaviors between the two configurations, notably exhibiting a temperature crossover near the warm boundary. This suggests that localized edge radiation induces a change in the internal thermal equilibrium of the MLI system. To explain this degradation, a physical mechanism is proposed wherein the exposed layer edges behave as a near-blackbody surface due to a cavity effect, significantly absorbing incident radiation. The absorbed heat is hypothesized to propagate laterally through in-plane solid conduction and oblique interlayer radiation. To quantify the magnitude of this additional heat load without multidimensional simulations, a modified analytical model based on the McIntosh layer-by-layer method was developed. Crucially, the energy balance equation was reformulated by introducing an explicit edge radiation term as an independent heat source. The model predictions for total heat flux showed good agreement with the experimental data, with a deviation of less than 5%. This result demonstrates that incorporating the edge radiation term is sufficient to predict the macroscopic thermal degradation. However, due to the limitation of the lumped-parameter approach, the model could not reproduce the localized temperature crossover observed in the experiments. Consequently, this study underscores that edge radiation is not a negligible boundary condition but a potential governing factor for thermal performance. It suggests that relying solely on conventional insulation analysis without accounting for edge effects may lead to a substantial underestimation of boil-off rates in liquid hydrogen storage systems.

Variable-density multilayer insulation (VD-MLI) materials significantly enhance thermal insulation performance under liquid hydrogen storage conditions by optimizing layer density distribution. However, traditional theoretical prediction models, such as the Lockheed model and the Layer-by-Layer model, exhibit limited prediction accuracy and generalizability in variable-density scenarios due to simplifications of complex physical processes and sensitivity to key parameters such as emissivity and thermal conductivity. To improve prediction accuracy, this study developed an experimental dataset of variable-density MLI materials incorporating various layer densities and spacer materials. A data-driven random forest model was introduced, and its predictive performance was compared with the two aforementioned classical physical models. The results show that the random forest model achieved an outstanding coefficient of determination (R²) of 0.9864 on the test set (traditional models had R² ≤ 0.92), with mean absolute error (MAE) and root mean square error (RMSE) as low as 0.1107 W/m² and 0.1295 W/m², respectively (traditional models had MAE ≥ 0.24 W/m² and RMSE ≥ 0.34 W/m²). This study demonstrates that machine learning methods can effectively capture the nonlinear heat transfer characteristics of variable-density MLI materials, offering a new technological approach for the rapid and precise design and optimization of high-performance insulation materials.

Liquid hydrogen (LH2) storage is essential for maximizing the range and efficiency of heavy-duty hydrogen mobility. A primary challenge for commercialization lies in minimizing Boil-Off Gas (BOG) through effective thermal insulation. While Multi-Layer Insulation (MLI) is the standard solution for these cryogenic applications, optimizing its design remains difficult due to the complex heat transfer mechanisms involved. Conventional thermal analysis methods, such as the Lockheed equation or the standard McIntosh Layer-by-Layer (LBL) model, are widely utilized but exhibit distinct limitations. A major drawback is the inability to accurately predict performance under high layer densities. Specifically, standard models often fail to account for the non-linear increase in solid thermal conductivity caused by spacer compression. Consequently, a continuous improvement in insulation performance is erroneously predicted as layers are added, contradicting physical reality and precluding the determination of an "optimal layer density." To address this issue, the solid conduction term within the existing LBL model was improved in this study. By integrating a power-law correlation that reflects the physical changes in spacer conductivity under compression, the realistic trade-off between radiation shielding and solid conduction is captured by the enhanced model. The proposed approach was validated against experimental data from literature (Fesmire, 2018; Li, 2006). It was demonstrated that the enhanced model successfully reproduces the characteristic "U-shaped" curve of effective thermal conductivity, accurately identifying the optimal density range that conventional models fail to predict. Finally, the validated model was applied to evaluate MLI systems currently under development for LH2 storage tanks. Model predictions were compared with in-house test data to identify potential areas for design improvement. Analysis indicates that the layer density of current candidates has not yet reached the theoretical optimum. It is suggested that adjusting the layer density could yield improved insulation performance compared to the baseline design. This study provides a more realistic design tool than the simplified semi-empirical models often used in the industry. A practical foundation for optimizing MLI specifications is established, contributing to the advancement of liquid hydrogen storage technology.

In the thermal management of cryogenic superconducting magnets, high-purity copper is commonly used as a heat sink. However, its effective thermal conductance at 4 K is relatively limited, leading to significant temperature differences, thereby constraining further improvements in heat dissipation performance. Pulsating heat pipes (PHPs), owing to their self-excited oscillatory driving mechanism and high heat-transfer capability, show strong potential to replace or enhance copper-based heat sinking. As helium has a low surface tension at cryogenic temperatures, the two-phase flow and heat transfer mechanisms in helium-based PHPs remain poorly understood. In this study, two-dimensional CFD numerical simulations of a helium-based PHP are performed using a volume-of-fluid (VOF) two-phase model. The simulations capture the oscillatory behaviour of gas-liquid plug flow. The results indicate that increasing the heating power from 0.04 W to 0.131 W reduces the thermal resistance from 8.9 to 6.4 K·W⁻¹, a 28.1% reduction, and increases the effective thermal conductivity from 630.8 to 830.1 W·m⁻¹·K⁻¹, a 31.6% increase. At a heating power of 0.131 W, the two-phase contours are more continuous and exhibit a more uniform alternation of gas and liquid plugs than at 0.04 W. Frequency of oscillations is also reported. Keywords: Pulsating heat pipe; Helium; Numerical simulation; Two-phase plug flow; Effective thermal conductivity

The interest of using liquid hydrogen (LH 2 ) as fuel vector in mobility is increasing because (i) it has 3 times more energy per unit of mass than fossil fuel on average, and (ii) frigories can be used to cool down the power unit. Unfortunately, near atmospheric pressures, LH 2 must be stored at temperatures lower than -253°C, while permanently evaporating due to heat inputs. The rate of its evaporation is proportional to the amount of energy absorbed by the liquid phase, hence on the thermal distribution. To avoid losing hydrogen and to reduce the evaporation, the vent line of the tank is closed, and the pressure naturally rises due to accumulation of mass and energy in the ullage. This natural increment of pressure, called self-pressurisation, produces thermal stratification, which is the accumulation of warm LH 2 near the interface. This phenomenon, however, increases the net evaporation rate and the self-pressurisation. To avoid excessive mechanical stresses on the wall of LH 2 tank, these walls must be thicker than the ones of fossil fuel tank, thus heavier, disadvantaging the use of LH 2 as fuel vector for mobility. To properly predict the pressure rise, and optimising the mass of LH 2 tank, a physical model of the cryogenic tank, coupled with an approach for computing the thermal distribution, is required. Several models have been proposed to calculate the self-pressurisation and the thermal stratification. Even if models with discretized vapour and liquid qualitatively and quantitatively predict these phenomena, the numerical instability of solving conservation laws in the side wall boundary layer makes them unsuitable for fast and preliminary calculation. For this purpose, equilibrium models are the best approaches, but they are strongly imprecise because they underestimate the pressure rise. Moreover, these models rely on simplified thermodynamic models which cannot properly describe the LH 2 saturation conditions. These models lack of understanding the role of vapour-to-interface and dry wall-to-wet wall heat transfers in the thermal distribution because they consider it independent from the temperature gradient in the vapour bulk. The proposed equilibrium model is based on the hypothesis of thermodynamic equilibrium between the vapor and the liquid. Hence, the temperature is uniform and equal to the saturation temperature. During self-pressurisation, only the mass exchanged between vapour and liquid is considered. The heat inputs that are calculated during the simulations are functions of the internal temperature with an effective thermal coefficient, which is deduced from the initial heat inputs. The model predicts lower pressure rises than the experimental ones, but when it is parametrized with experimental data, the average mean error remains below 1 %. Under the hypothesis of homogeneous liquid and vapour, the thermal distribution is calculated considering the dry wall-to-wet wall, the liquid-to-interface, and the vapor-to-interface heat transfers. The vapor-to-interface heat flow reduces with increasing temperature gradient in the ullage, which decreases by increasing the filling ratio. The dry wall-to-wet wall heat flow increases as the filling ratio increases, transferring more heat to the liquid. At steady state, the liquid absorbs 85.8, 70.7, and 60.5 % of overall heat input, respectively at 75, 50, and 35 % of the filling. The evaporation rate increases with the filling ratio. As self-pressurisation starts, the fraction of the energy absorbed by the liquid increases of 1, 19.1, and 38.4 % respectively, due to the increment of vapour-to-interface heat transfer, cooling the ullage, but not sufficiently to slow down the pressure rise. The use of LH 2 as fuel vector for the mobility requires a physical model to calculate the self-pressurisation and the thermal distribution. In this study, an Experimentally parametrized equilibrium model has been proposed, and the thermal distribution is calculated with a homogeneous approach. This equilibrium model is sufficient to predict self-pressurisation in preliminary calculation. As a result of the thermal distribution analysis, vapour-to-interface heat flow must be increased during self-pressurisation to lower the pressure rise. The dry wall-to-wet wall heat flow must be reduced at steady state to limit evaporation.

Superfluid helium (He II) exhibits unique transport behavior below the λ transition, forming a thin film that can spontaneously spread and climb along solid surfaces. The suppression of superfluid helium film creep is a critical challenge in the thermal management of cryogenic systems, particularly for space-borne Dewars and sub-Kelvin experiments, where the film induces significant heat leaks and mass loss. The main approaches for suppressing superfluid film transport include the use of small orifice, local heating, and knife-edge structures. Among these, the knife-edge approach impedes film flow by modifying the local van der Waals potential through a sharp geometric curvature, without introducing parasitic heat loads or imposing substantial flow resistance. A numerical investigation is conducted using a superfluid helium film thickness model formulated in the weak form of Partial Differential Equations (PDEs). The simulation resolves the chemical potential equilibrium, balancing the van der Waals disjoining pressure against gravitational potential and the surface tension induced by knife-edge. The investigation first characterizes the suppression mechanism of a single knife-edge structure, quantifying the sensitivity of film thickness to the knife-edge curvature radius to identify the geometric thresholds for effective thinning. Building upon the assumption of film continuity, the model is extended to multi-knife-edge configurations. Experimental observations of knife-edge suppression are used as auxiliary validation to support the reliability of the numerical model. This approach provides a numerical basis and quantitative design guidelines for understanding and designing knife-edge-based superfluid helium film suppression structures in dilution refrigerator stills and related cryogenic systems.

SHiP (Search for Hidden Particles) is a new general purpose experiment under preparation in the North Area at CERN, designed to look for any type of feebly interacting long-lived particles. Its spectrometer magnet is a large aperture (4 x 6 m 2 ) iron-dominated dipole with 0.6 - 0.7 T.m bending strength and nominal field on axis of around 0.15 T. The significant electrical power consumption of the initial resistive design (~1.2 MW) motivated the current superconducting design using MgB 2 cable that has the potential to be 10 times more energy efficient. Due to the experiment’s location and estimated heat loads, the chosen cooling scheme uses cryocoolers to cool a closed loop forced flow helium circuit that transports and extracts the heat deposited on and generated by the cold mass. The cooling circuit is thermally coupled to the magnet’s supporting structure (aluminium alloy former), in which the superconducting cable is wound. This dry, indirect cooling strategy of medium- and large-scale magnets necessitates an in-depth characterisation of the thermal interfaces between the superconductor and its cooling source, as they become the major contributors to temperature gradients in the cold mass. A comprehensive study of thermal contact resistance between the superconducting cable and its former is presented. With the goal to optimize thermal gradients in the composite structure, as well as to improve thermal stability of the conductor itself, parameters such as groove dimensions, surface finish, cable insulation scheme, and filler materials are investigated. This includes the use both traditional contact enhancers, such as varnish or epoxy or grease, and of newly developed putty mixes, tailored to have suitable thermal properties while remaining practical from an application standpoint. Results of effective thermal contact resistance are presented for the various configurations and discussed with a focus on the applicability of such techniques and materials for large-scale magnet structures concerning reliability of thermal performance, manufacturability, and reproducibility.

Background: Joule–Thomson (JT) cryocoolers are widely employed in compact and spaceborne cryogenic systems due to their structural simplicity, high reliability, and the absence of moving parts in the cold region. In such systems, the throttle valve is a key component that produces a large pressure drop and induces partial liquefaction of helium, leading to inherently multiphase flow during expansion. A detailed understanding of the associated flow structure and thermodynamic irreversibilities is crucial for enhancing cooling performance and improving overall system efficiency. Methods: In this work, a comprehensive numerical investigation of multiphase helium flow through a micro–JT throttle valve is conducted. A compressible multiphase mixture model coupled with real-gas thermophysical properties is employed to simulate the expansion and phase change process under cryogenic conditions. Moreover, a conventional flow-field analysis and a second law-based entropy generation framework are implemented to quantify irreversible losses due to both viscous dissipation and thermal conduction. Further, the effects of orifice length on the flow structure, phase distribution, and entropy production are systematically examined. Findings: The results reveal that rapid expansion through the micro-orifice leads to strong flow acceleration and the formation of a distinct liquid–vapor mixture region immediately downstream of the throttling section. The size and strength of the two-phase region are observed to vary significantly with the orifice length. Longer orifices promote stronger viscous dissipation and enhanced entropy generation within the restriction, whereas shorter orifices shift the dominant irreversibility to the downstream expansion region. However, the quantitative comparisons show that an optimal orifice length exists at which the total entropy generation is minimized while maintaining the desired pressure drop and cooling effect. Therefore, the present study provides detailed physical insight into the complex multiphase throttling process of helium, offering useful guidelines for the optimal design of miniature JT valves for high-performance cryogenic cooling applications.

Cryogenic desublimation is recognized as a highly promising carbon capture technology owing to its superior product purity, compact system configuration and environmental benignity. However, the continuous accumulation of solid frost layer increases the thermal resistance on heat transfer surfaces, thus necessitating periodic system switching to fulfill the demand for continuous carbon capture. In contrast to mechanical defrosting that may incur potential damage to equipment, thermal defrosting enables the recovery of approximately 578.0 to 596.3 kJ/kg of latent heat of sublimation, thereby significantly reducing capture energy consumption. The thermophysical properties of cryogenic frost layers differ remarkably from those in other scenarios (e.g., cryogenic water vapor frosting), and relevant experimental and simulation studies remain scarce to date. In this work, a visualized experimental system for cryogenic sublimation was developed, utilizing a Gifford-McMahan (GM) cryocooler integrated with a precision heater for rigorous temperature control. Desublimation experiments were conducted on flue gas with a concentration of 15% under cooling-flow conditions, which simulates the typical post-combustion capture scenario, and the primary data of desublimation capture within 0–60 minutes were acquired. Subsequently, the sublimation characteristics of the frost layer on metal surfaces were investigated under different degrees of superheat and two temperature control strategies, including the morphology, frost layer thickness, surface roughness, and the Cryo-bubble phenomenon first discovered by our team. The results demonstrate that the sublimation rate varies significantly with heating strategies, and the peak value of the non-crushing defrosting rate reaches approximately 99.04 μm/min. Finally, a mathematical model was proposed to interpret the heat transfer characteristics and profile evolution law during the heating and sublimation process of CO 2 frost layers, and the effects of initial geometric dimensions and nucleation number on the sublimation process were explored. This study reveals the fundamental mechanisms and characteristic differences of thermal elimination for CO 2 frost crystals under cryogenic conditions, and the obtained experimental data and theoretical model can provide quantitative references for the system design and heat transfer analysis in practical cryogenic carbon capture applications.

The FCC-hh foresees a 90 km-class proton–proton collider operating at centre-of-mass energies around 85 TeV, enabled by high-field Nb3Sn dipole magnets reaching approximately 14 T [9, 2]. The baseline cooling solution for FCC-hh remains operation at 1.9 K in pressurised He II, as adopted in the Conceptual Design Report [1]. In parallel, alternative cooling concepts based on forced-flow helium near 4.5 K are being investigated to reduce cryogenic complexity, helium inventory, and electrical power consumption [3]. In all cases, the impregnated nature of Nb3Sn windings and the presence of multiple insulation layers limit direct access of helium to the conductor. This constrains heat transfer even at 1.9 K, where the superfluid properties of He II may partially mitigate internal temperature gradients but cannot fully eliminate the thermal bottlenecks imposed by impregnation and interfaces. At 4.5 K, this situation could be further exacerbated by the loss of superfluidity of He above the lambda point [8], which could limit access of the coolant to the heat sources, despite the higher thermal conductivity of the solids. A numerical method investigates the resulting temperature profiles and maximum temperatures in impregnated Nb3Sn FCC-hh dipoles using a two-dimensional thermal conduction model of the BOND cross section [6], under steady-state and transient heat loads representative of FCC-hh operation [3]. The analysis focuses on the role of interfa-cial contacts—such as copper–epoxy/fiberglass, Kapton–stainless steel, and iron–stainless steel—in shaping radial temperature gradients and peak coil temperatures. The results indicate that these interfaces contribute significantly to the overall radial thermal resistance and strongly influence the resulting temperature profiles, regardless of whether cooling is provided by a helium bath or by conduction toward cooling channels. Owing to the scarcity of experimental data on interfacial contact resistance at cryogenic temperatures, particularly for mixed metal–polymer interfaces [5, 4], the modelling is complemented by a planned experimental campaign at CERN [7]. The study highlights that bulk coil impregnation and interfacial heat transfer remain key challenges for both baseline and alternative FCC-hh cooling schemes and must be quantified to reliably assess thermal margins in high-field Nb3Sn magnets. References [1] A. Abada et al. “FCC-hh: The Hadron Collider: Future Circular Collider Conceptual Design Report Volume 3”. In: European Physical Journal: Special Topics 228.4 (2019). issn: 19516401. doi: 10. 1140/epjst/e2019-900087-0. [2] M. Benedikt et al. “Future Circular Collider Feasibility Study Report: Volume 2, Accelerators, Technical Infrastructure and Safety”. In: (Apr. 2025). doi: 10.17181/CERN.EBAY.7W4X. url: http: //arxiv.org/abs/2505.00274%20http://dx.doi.org/10.17181/CERN.EBAY.7W4X. [3] Patricia Borges de Sousa et al. “Toward a Reduced Helium Content Cryogenic Cooling Scheme at 4.5 K for CERN’s FCC-hh Accelerator”. In: IEEE Transactions on Applied Superconductivity 36.3 (2026). issn: 15582515. doi: 10.1109/TASC.2025.3604763. [4] R. C. Dhuley. Pressed copper and gold-plated copper contacts at low temperatures – A review of thermal contact resistance. 2019. doi: 10.1016/j.cryogenics.2019.06.008. [5] E. Gmelin et al. “Thermal boundary resistance of mechanical contacts between solids at sub-ambient temperatures”. In: Journal of Physics D: Applied Physics 32.6 (Mar. 1999), R19. issn: 0022-3727. doi: 10.1088/0022-3727/32/6/004. url: https://iopscience.iop.org/article/10.1088/ 0022-3727/32/6/004%20https://iopscience.iop.org/article/10.1088/0022-3727/32/6/ 004/meta. [6] Juan Carlos Perez et al. “Conceptual Design of BOND: A 14 T Dipole for FCC-Hh”. In: IEEE Transactions on Applied Superconductivity 35.5 (2025). issn: 15582515. doi: 10.1109/TASC.2025. 3536445. [7] Jared Valois, Gregory Nellis, and John Pfotenhauer. “Measurement of thermal contact resistance and the design of thermal contacts at cryogenic temperatures”. In: Cryogenics 142 (2024). issn: 00112275. doi: 10.1016/j.cryogenics.2024.103922. [8] Steven W. Van Sciver. Helium cryogenics: Second edition. Springer New York, Jan. 2012, pp. 1–470. isbn: 9781441999795. doi: 10.1007/978-1-4419-9979-5/COVER. [9] Frank Zimmermann. “Scenarios for the FCC-hh” Open report (2024). https://indico.cern.ch/event/1439072/contributions/6106995/attachments/2917946/5120981/FCC_hh_scenarios.pdf .

The European Spallation Source (ESS) is a neutron-scattering facility being built with extensive international collaboration in Lund, Sweden. An essential part of the project is the linear 2.0 GeV proton accelerator (linac). Its superconducting part consists of cryomodules of two different types. The elliptical cryomodules (both medium- and high-beta) are filled with 220 liters liquid helium each and the spoke cryomodules with 170 liters liquid helium each. When fully installed, the linac will have 13 spoke and 30 elliptical cryomodules, resulting in a total liquid inventory of 9 m 3 at an operating temperature of 2 K. The current worst case helium release scenario is based on the assumption that, during a malfunction, a maximum of four elliptical cryomodules release their helium into the tunnel rapidly, i.e. the gas equivalent of nearly 900 liters of liquid helium (around 700 m 3 ) is released into the tunnel via the cryomodules' rupture disks within a short time frame of a couple of seconds. A rapid helium release raises the ambient pressure in the tunnel. The volume of the building into which the helium can expand is 14'000 m 3 . An estimation of the potential global pressure increase in the tunnel was carried out with the main assumption of a completely sealed tunnel (no ventilation). In a different approach, computational fluid dynamics (CFD) was used to identify the location, time and amplitude of the maximum pressure increase, including effects of the tunnel ventilation. ANSYS Fluent software was used for the CFD simulation. A steady-state simulation of the ventilated tunnel was performed first. Then, a transient simulation was initiated with the results of the steady-state simulation as the initial field, in which helium was released through the four cryomodules’ rupture disks. After a predetermined length of time the leakage was stopped, and the simulation continued for some time until it was observed that the pressure wave had subsided. The governing equations included in the CFD simulation were mass conservation, momentum conservation (Navier-Stokes), energy transport, and species transport. k-ω SST was used for turbulence modeling. The results of both approaches were compared and the potential impact on the building and its infrastructure was evaluated.

The absolute scale of neutrino mass has recently been updated by the KATRIN experiment, giving an upper limit on the mass of the electron anti-neutrino of 0.45 eV. In order to go beyond this limit, future neutrino mass experiments require new detector technologies. Quantum sensors like magnetic microcalorimeters are promising candidates for such ground breaking new technologies in neutrino mass experiments. One of the most obvious challenges is to cool the quantum sensors down to a few tens of milli-Kelvin, while providing a windowless coupling to a beta-electron source operated typically at 80 K or room temperature. Our approach is to build a magnet chicane structure to avoid a direct line of sight to the sensors, while guiding the electrons magnetically from the source to the quantum sensors. This paper reports on the first result of the thermal simulation of a 1.5-meter-long cryogenic demonstrator chicane.

The LHC (Large Hadron Collider) Run 3 campaign began in April 2022 and concluded in June 2026, encompassing approximately 1,000 days of nominal cryogenic operation over five years. Over this period, the LHC achieved numerous performance milestones, including record integrated luminosities in both the ATLAS and CMS experiments, each exceeding 500 fb-1, surpassing the initial target. These exceptional results were enabled not only by beam parameters that outperformed expectations but also by the high operational availability of the accelerator, to which cryogenic systems contributed significantly. This paper reviews the cryogenic operation of the LHC, ATLAS and CMS during Run 3, highlighting key achievements as well as operational challenges and the various encountered issues. It presents relevant statistics and describes the actions and system consolidations implemented to reach these performance levels.

The High Luminosity upgrade of the Large Hadron Collider (HL-LHC), currently under construction at CERN, will require the replacement of the final-focusing superconducting magnets, the implementation of new superconducting links to power them and the installation of new Superconducting Radio-Frequency crab cavities on both sides of the ATLAS (P1) and the CMS (P5) experiments. To cool these new and reconfigured cryogenic devices, a new Cryogenic Distribution System will replace part of the existing LHC cryogenic distribution line on each side of the experiments. Two multi-header cryo-distribution lines (QXL) at each point will connect the HL-LHC machine components to a new helium refrigerator located in a cavern next to the LHC tunnel, as well as to the existing LHC cryogenic lines. The QXL, with a length of approximately 750 m per point, will be installed in two phases: first in the underground service galleries and then in the LHC tunnel. This article describes the four sections of the QXL that will be installed in the LHC tunnel, which include all active control components and interfaces to the HL-LHC cryogenic devices. The global architecture of the system is presented along with its functional requirements and operating conditions. The article details the cryogenic and mechanical design of the modules which will be joined in the LHC tunnel to build the system, comprising straight modules, step modules, tee modules, return modules, junction modules and service modules integrating cryogenic process equipment.

After a brief introduction about the design of the Grenoble 43 T Hybrid Magnet based on a large bore Nb-Ti superconducting outer coil of 1100 mm internal diameter and 2 sets of copper alloys resistive inserts, we will focus on the first 3 years of operation of its cryogenic system. The cryoplant is constituted of a stand-alone liquid helium liquefier with an adjustable production capacity from 70 to 150 litres/hour, an helium pumping system of 5000 m3/h, a recovery system with balloon, compressors and high pressure tanks, a cryogenic satellite to produce the superfluid pressurised liquid helium static bath at 1,8 K with a cooling power greater than 60 W, to allow the superconducting coil to be operated at this temperature. The cryostat containing the vessel with the superconducting coil and 1400 litres of liquid helium is equipped with two sets of thermal screens actively cooled to 40 K and 90 K by a circulation of gaseous helium. The entire process is controlled via a PLC and a human-machine interface with home-made programs specifically designed and developed for this application. The Hybrid magnet is operated twice a year during several weeks : once during spring and once during autumn. Between these periods, the 24 tons cold mass including the superconducting coil is partially warmed-up and maintained at 95 K with the help of a liquid nitrogen circulation prior being re-cooled down to 1.8 K and maintained at this temperature during all the operational phases. The whole cryogenic process and the main problems/issues encountered during these 3 years of operation will be described in detail with an emphasis on lessons learned to benefit to similar further projects.

Ultra-high-field superconducting magnets have significant application value in frontier research fields such as condensed matter physics and life sciences. However, the construction of such magnets faces numerous challenges. After more than a decade of dedicated R&D, the Institute of Electrical Engineering, Chinese Academy of Sciences (IEE, CAS) has mastered a complete set of independent key technologies for the design, construction, commissioning, and operation of 30T ultra-high-field all-superconducting magnets. It has successfully developed 30T/φ35mm and 26T/φ50mm all-superconducting user magnets for the "Comprehensive Extreme Condition Experimental Facility." Currently, both user magnet systems have been stably operating for over two years, supporting multiple major scientific discoveries. Developing all-superconducting magnets of ≥35T in the future still faces huge theoretical and technical challenges, such as accurate analysis models under extremely complex operating conditions, stress control methods, and theories for generating high-homogeneity magnetic fields. This report will discuss these challenges.

Renaissance Fusion is advancing the development of a stellarator-based commercial nuclear fusion reactor by combining several key enabling technologies. Firstly, our magnet development program employs a three-step approach combining wide high-temperature superconductor (HTS) manufacturing, laser engraving of the superconductor to generate twisted stellarator field profiles, and the construction of high field HTS magnets generating up to 10 tesla on axis. Secondly, in addition to the stellarator plasma confinement, the magnets are used to guide hot liquid metal flowing over the internal reactor walls to ensure effective neutron shielding and efficient thermal management. The presentation will provide an overview of these developments, with principal focus on high field magnets integrated with a high temperature liquid metal loop. As a proof of concept, we have constructed a 1.2 metre diameter HTS pseudo-Helmholtz coil pair capable of producing a 1 tesla hot bore, demonstrating liquid metal deflection around the perimeter of a 1 metre diameter chamber. The magnets employ non-insulated, dry-wound HTS coils, conduction cooled by a custom cryogenic system delivering up to 120 W at 20 kelvin. A major challenge was the thermal isolation of the superconducting magnet, positioned less than 40 mm from the 700 °C liquid metal chamber, which was addressed by an innovative combination of insulators and heat extraction. We present an in-house built HTS coil winding system, initial magnet testing, integration with the hot liquid metal loop, commissioning, quench event, subsequent investigation and thermal upgrading.

Superconducting joining is one most critical technologies of the modern whole-body MRI magnets operating in persistent current mode, where extremely low electrical resistance (∼10 -12 –10 -15 Ω) is essential to maintain outstanding temporal magnetic field stability (≤0.1 ppm h -1 ) required for high-quality imaging. Present-day whole-body MRI magnets are predominantly constructed using multifilamentary NbTi conductors with a critical temperature of 9.2 K and are therefore operated at 4.2 K. The temporal stability of the magnetic field in a superconducting MRI magnet is strongly influenced by the quality of the superconducting joints, extending beyond their electrical characteristics to include microstructural integrity and compatibility when joining multifilamentary NbTi conductors with different metallic matrices. The superconducting joints are fabricated using the solder matrix replacement method, focusing on multifilamentary NbTi conductors with filament diameters in the range of 20–50 μm. The influence of joint fabrication parameters on its performance is investigated through detailed microstructural and compositional analysis. SEM and EDX show the key microstructural features such as filament distribution, formation of voids in the superconducting solder region, the elemental composition and spatial distribution of elements within the superconducting joint, specially to analyse the presence of any resistive or impurity element in the superconducting joints. The electrical performances of the superconducting joints in presence of any background magnetic field are measured using an indigenously developed helium bath- cooled 4K test rig using current decay method. A large amount current (400-600A) can be induced into the test loop using superconducting micro-transformer. A 1.5T superconducting solenoid magnets generate the necessary background field for the joints. However, the increasing scarcity of liquid helium and its erratic variation in cost have accelerated the development of conduction-cooled MRI magnets as a more sustainable alternative. This transition necessitates a detailed understanding of the performance and reliability of NbTi superconducting joints under cryogen-free conditions. A dedicated test rig based on a 4.2 K GM cryocooler is designed and developed to evaluate joint performance at operating currents up to 600 A. The resistance of the superconducting joints is determined using the flux conservation principle by monitoring the current decay in a superconducting coil, enabling resistance measurements down to 10 -14 Ω. The cryogen-free test rig comprises of a superconducting primary coil, a secondary coil i.e. the test coil, and a 1.5 T NbTi solenoid magnet. Two pairs of high-temperature superconducting (HTS) current leads are used to energize both the primary coil and the background solenoid magnet, minimizing thermal heat load while ensuring stable operation. Multiple joints can be tested simultaneously in this 4K test rig. This paper presents a comprehensive characterization of superconducting joints formed between multifilamentary NbTi conductors with different resistive matrices. Detailed analyses of elemental distribution, filament orientation, and residual traces of resistive matrix materials within the joint region are systematically investigated. This paper also discusses the detailed description of the helium bath-cooled test rig along with the test results of the superconducting joint. The design and thermal simulation of the 4K cryogen -free test rig along with the details of the solenoid magnet, primary coil has also been discussed in this paper.

A 4.2 T superconducting wiggler was installed into the storage ring in 2021 and has been in normal operation since September 2022. A new 6.5 T superconducting wiggler is required for the concept of next generation storage ring and is under development. The superconducting magnet has 2.5+2 periods, and consists of NbTi/Cu winding and DT4C core and yoke. The period length is 130 mm. The pole gap is 25 mm. The vertical and horizontal beam aperture is 19 mm and 50 mm, respectively. The superconducting magnet is placed in a Helium vessel and cooled in Helium bath. Instead of cryogenic plant, Gifford-Mcmahon cryocoolers provide cooling capacity for the system and realize zero Helium vaporization during normal operation. This paper reports the design of the 6.5 T superconducting magnet and the cryostat. Test results of the superconducting coils will be presented and discussed.

As part of the High Luminosity LHC (HL-LHC) upgrade, the existing Inner Triplet (IT) magnets will be replaced with a 60 m-long assembly of new superconducting magnets, including Nb 3 Sn magnets operating at 1.9 K in pressurised He II. Power to the magnets will be supplied through a cold powering system based on MgB 2 and high-temperature superconductors (HTS). To validate the collective behaviour and gain operational experience with the new Nb 3 Sn magnets, the MgB 2 superconducting link, and associated systems, a dedicated test facility – the HL-LHC IT String – has been constructed. This paper presents the cryogenic commissioning of the IT String. The cooldown is performed under conditions as close as possible to those planned for the HL-LHC operation. The commissioning programme includes optimisation of operating parameters, simulation of magnet powering and other operating modes ahead of the powering phase of the IT String experimental programme. Moreover, a thermal characterisation of the system is performed including the measurements of static and dynamic heat loads of the magnets, the superconducting link and the cryogenic system, thermal impedance measurements and He II conduction studies, characterisation of subcooling heat exchangers, and measurements of the heat extraction capacity of the bayonet heat exchanger inside the magnets. The commissioning results are discussed and the measured parameters are compared with the expected design values.

ITER is a fusion experimental reactor equipped with a superconducting magnet system. The ITER toroidal field (TF) coils, a particular type of ITER superconducting magnet having D-shape with a height about 16.5 m and a weight of about 320 tons. TF coils are required to withstand huge electromagnetic forces at cryogenic temperature (4.2 K). Consequently, the minimum 0.2% proof stress required for structural materials is over 1,000 MPa. In certain regions of TF coil, extra-thick (535 mm) plates are required. Approximately 5,000 tons of cryogenic structural materials have been manufactured for the ITER TF coils. Since the 1980s, QST (formerly JAERI until 2006, and JAEA until 2016) has been developing the cryogenic structural materials for fusion reactors. Based on these results, it was determined that JJ1 stainless steel (12Cr-12Ni-10Mn-5Mo-0.2N) and nitrogen-enhanced 316LN stainless steel (17Cr-11Ni-2Mo-0.2N) would be the optimal structural materials for the ITER TF coils. This report summarises the qualifications, manufacturing results, and quality control for the actual ITER TF coil materials. Almost all mechanical tests at 4.2 K required for these activities were conducted by QST. QST have reported more than 1,000 data on these cryogenic structural materials. The test methods and its part of results are reviewed in this report. Moreover, the correlation between 0.2% proof stress at room temperature and carbon + nitrogen content, and the 0.2% proof stress at 4.2 K have been applied for the design and quality control of ITER TF coil materials. This report presents an example in which high-strength (0.2% proof stress >1,200 MPa) materials were developed by applying this correlation as a prediction formula. Based on experience of manufacturing structural materials for ITER TF coil, this study discusses the application of prediction formulas for the future material development and quality control, in addition to material specifications. The views and opinions expressed herein do not necessarily reflect those of the ITER organization.

Liquid hydrogen is recognized as a potential energy carrier for various applications in the field of transportation and energy. With this the demand for material and component qualification in cryogenic and hydrogen environment is growing. Therefore, test methods related to the specific application are put forward to ensure a comprehensive characterization. This supports the development and design in the hydrogen context of various projects at Karlsruhe Institute of Technology (KIT). Hydrogen projects at KIT are highlighted and the cryogenic test methods in hydrogen environment at the cryogenic material test laboratory CryoMaK are introduced. The test possibilities range from ex-situ hydrogen charged material characterization to in-situ test configurations at low temperature, all of them having different challenges. Examples of cryogenic material test results complement the overview.

As the use of liquid hydrogen has recently attracted significant attention as a means to maximize the efficiency of hydrogen storage and transport in a future hydrogen economy, interest in the material properties under deep-cryogenic environments below 20 K has continued to grow. To investigate changes in the mechanical properties of metallic materials at cryogenic temperatures, our research team operates a mechanical property evaluation system capable of cooling specimens down to 4 K, the temperature of liquid helium, for mechanical testing. In addition, recognizing the importance of cryogenic thermal conductivity in minimizing external heat ingress via thermal conduction in cryogenic environments, we have developed and are currently operating an apparatus capable of measuring thermal conductivity at approximately 10 K. In this presentation, we examine the cryogenic mechanical property variations of a range of metallic materials that are expected to be applicable in liquid-hydrogen environments. We also share our analysis of plastic deformation behavior under cryogenic conditions. Furthermore, we investigate changes in thermal conductivity, along with mechanical property variations, as a function of microstructural evolution in metallic materials. Based on these results, we present our findings from the perspective of microstructure and property optimization for materials intended for liquid-hydrogen storage systems.

Hydrogen is predicted to be one of the principal clean energy sources of the future, particularly liquid hydrogen, which offers high energy density, high purity, and the potential for low-pressure storage. However, hydrogen significantly deteriorates the characteristics of metals, presenting significant challenges for structural materials utilized in the production, transportation, and storage of hydrogen. The austenitic 304 steel also experiences the effects of hydrogen when use in service as a container or pipe. In this regard, knowledge of the impact of hydrogen exposure on 304 steel at various temperatures is necessary for the successful integration of hydrogen in real-world systems. This study assesses the hydrogen-induced modifications by comparing the results of mechanical testing on hydrogen-pre-charged specimens, hollow specimens charged in-situ by hydrogen during testing as well as those of non-charged ones. Tensile and fracture measurements were conducted at various temperatures, from room temperature to 4 K, to evaluate the impact of the hydrogen content on the mechanical properties. The description of potential deformation processes was further supported by the microstructural observation. In addition, the impact of hydrogen presence and its interaction with the microstructure at specific strain levels have been demonstrated by interrupted tensile tests. The results indicate that the modification of material properties, especially ductility and fracture toughness, is strongly impacted by hydrogen. Furthermore, the hydrogen embrittlement (HE) is evident between ambient temperature and 200 K, however at 77 K, hydrogen mobility caused the HE trend to shift. Moreover, fractographic analysis of different samples presented hydrogen-assisted fracture characteristics.

Aluminum-copper alloys, particularly the 2219-T81 grade, have been used extensively for liquid hydrogen (LH2) tanks in the space industry for decades due to their good weldability and high strength-to-weight ratio. To develop hydrogen powered aircraft, it is required to deepen our understanding of the mechanical behavior, deformation mechanisms and durability of these materials under extreme environmental conditions. This study uses ex-situ high-resolution digital image correlation (HR-DIC) to investigate the microscale evolution of strain localization in a 2219-T81 aluminum alloy at cryogenic temperatures. By bridging the gap between macroscopic mechanical testing and microscopic characterization, this research provides insights into how the alloy accommodates plastic deformation at the grain level when subjected to extreme temperatures. Furthermore, to examine the underlying physics of these localization events, TEM lamellae were extracted from targeted regions of high strain. These foils were analyzed via transmission electron microscopy (TEM) to characterize dislocation density, nanotwinning, and the atomic-scale structure of the alloy’s precipitate-hardened matrix. The experimental results demonstrate a significant simultaneous increase in both strength and ductility with decreasing temperature from 293 K to 20 K a phenomenon often observed in certain FCC alloys but rarely characterized at this level of microstructural detail. The HR-DIC maps allowed to identify the same deformation mechanisms at all temperature, with grain boundary sliding combined with intragranular slip. However, a distinct transition in dislocation morphology was identified. At ambient temperatures, the deformation appears relatively diffuse and homogeneous. In contrast, at 20 K, the dislocations organize into concentrated, high-density slip bands. The increase of ductility at cryogenic temperature is attributed to a delocalization of the facilitating a more uniform distribution of plastic flow across the grain structure at low temperatures, delaying the onset of strain-induced damage and accommodating significantly higher total plastic strain before the final transgranular fracture occurs.

The construction of large-scale liquefied hydrogen (LH2) storage tanks is a prerequisite for achieving a carbon-neutral society, positioning austenitic stainless steel SUS316L as a critical structural material due to its excellent cryogenic ductility. However, ensuring the structural integrity of weld metals remains a challenge because they inevitably contain retained δ-ferrite to prevent hot cracking, which degrades fracture toughness at the boiling point of hydrogen (20 K). While the embrittlement of BCC-structured ferrite at low temperatures is well-known, the specific mechanical interaction between the FCC γ-matrix and BCC δ-ferrite at 20 K has not been fully elucidated. This study aims to clarify the governing micro-mechanisms of fracture toughness in 316L weld metals and to validate the safety margins of conventional evaluation methods. A multi-scale approach was employed, combining fracture toughness tests on actual welded joints (TIG, SMAW, SAW), numerical simulations of strain-induced martensitic transformation (α'), and tensile tests on specially fabricated single-phase bulk materials of γ and δ phases to isolate their individual mechanical behaviors. The most significant finding is the "anomalous strength reversal" phenomenon observed at 20 K. Experimental results demonstrated that while the yield stress of the BCC δ-phase shows weak temperature dependence below 77 K, the FCC γ-phase exhibits a substantial increase in yield stress with decreasing temperature. Consequently, the yield stress of the γ-matrix exceeds that of the δ-ferrite at 20 K, drastically altering the local deformation behavior. This strength reversal promotes severe strain localization within the relatively softer δ-ferrite and at the δ/γ interface, leading to interface decohesion and the observed reduction in fracture toughness. Furthermore, large-scale wide-plate tensile tests conducted using a 80-MN testing machine exhibited higher J-R curves compared to Compact Tension (CT) specimens due to constraint loss effects, confirming that standard laboratory testing provides a conservative safety assessment. These findings provide a fundamental understanding of phase interactions at 20 K, offering essential guidelines for the material design and structural integrity assessment of future hydrogen infrastructure.

Hydrogen is widely regarded as a key energy carrier for a future CO₂-neutral society, with liquid hydrogen (LH₂) offering particular advantages due to its high energy density, low storage pressure, and relevance for transportation and mobility applications. The safe and reliable operation of LH₂ systems critically depends on the mechanical performance and long-term integrity of structural materials under combined cryogenic temperatures and hydrogen exposure. Within the framework of the national hydrogen lead projects funded by the BMFTR, Karlsruhe Institute of Technology (KIT), together with partners of the technology platform TransHyDE, was addressing the transport and application of liquid hydrogen in the lead project AppLHy!. A central focus is the experimental characterization of materials under gaseous hydrogen and LH₂ conditions in order to understand hydrogen–material interactions and potential degradation mechanisms at cryogenic temperatures down to 20 K. By combining long-term exposure, of 30 years in cryogenic gaseous H 2 and liquid H 2 environment as well as controlled thermal H pre-charging with mechanical testing at cryogenic temperatures, this work contributes to a deeper understanding of material behavior and reliability in LH₂ environments. Moreover, microstructural and fractographic analysis complement the investigation, as well as the evaluation of the ratio in reduction area with decreasing in temperature. The results will be discussed and compared to non charged material.

The Fe-36%Ni alloy exhibits an exceptionally low coefficient of thermal expansion at low temperatures, making it a suitable material for precision measuring instruments, electric power transmission, and liquefied natural gas (LNG) transportation and storage. Recently, hydrogen has attracted considerable attention as a clean energy source. The materials utilized in liquid hydrogen will undergo more severe thermal impact, since the boiling point of liquid hydrogen (20 K) is lower than that of LNG (111 K). Additionally, the materials exhibit a decrease in phase stability at low temperatures, resulting in changes of their mechanical properties and coefficient of thermal expansion. It is imperative to prevent or minimize degradation of mechanical properties and an increase in the coefficient of thermal expansion. Therefore, the Fe-36%Ni alloy is particularly well-suited for applications in liquid hydrogen and hydrogen gas environments. In the present study, the tensile properties of the Fe-36%Ni alloy were evaluated at temperatures ranging from 20 K to room temperature (RT), and its phase stability was analyzed using X-ray diffraction (XRD) and electron backscatter diffraction (EBSD). As the test temperature decreased, the 0.2% proof stress, tensile strength, and elongation exhibited an increase, respectively. The absence of martensitic transformation upon cooling to 20 K was detected. The strain-induced α’-martensite was not observed during tensile testing at RT. However, strain-induced α’ martensitic transformation and deformation twinning were detected in the tested specimens at temperatures of 77 K and 20 K, respectively. A smaller amount of α’ martensite was formed in the specimen tested at 77 K compared with that at 20 K. Approximately 10% α’ martensite was detected in the specimen subjected to a strain of 0.3 at 77 K. The contribution of the α’ martensitic phase transformation and deformation twinning to the mechanical property was discussed in terms of the mechanisms of transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP). The coefficients of thermal expansion ranging from 83 K to 308 K were measured for samples pre-strained at 77 K and higher temperatures. The average coefficient of thermal expansion for the sample pre-strained by rolling with 50% reduction at 77 K, containing approximately 7% α’ martensite in volume, increased to 2.4×10 -6 K -1 when compared with the coefficient of the annealed state, which was 1.1×10 -6 K -1 . The change in the coefficient of thermal expansion can be attributed to the martensitic phase and lattice defects introduced during deformation at cryogenic temperatures.

Austenitic stainless steels such as 304L and 316L are commonly used in various applications, including liquid hydrogen (LH 2 ), due to their excellent cryogenic mechanical properties. However, a significant concern is the formation of strain-induced martensite. During plastic deformation at low or cryogenic temperatures, austenite may convert into martensite, creating pathways for hydrogen diffusion that can lead to hydrogen embrittlement (HE). Therefore, evaluating the reliability and hydrogen compatibility of these materials under such conditions in high-pressure hydrogen environments is essential. This study explores the temperature-dependent HE behavior of austenitic stainless steels STS304L and STS316LH using small-punch testing (SPT) and hollow-specimen slow-strain-rate tensile testing (SSRT). Tests were performed under 10 MPa nitrogen (N 2 ) and hydrogen (H 2 ) environments from room temperature (RT) down to 77 K. Results showed that both samples experienced a continuous increase in ferrite content with decreasing temperature after SPT and hollow-specimen SSRT, indicating strain-induced martensite transformation (SIMT). STS304L exhibited higher ferrite content than STS316LH from RT to 77 K, correlating with higher strength at low temperatures. In STS304L, ferrite content significantly increased at RT, leading to notable HE effects, while STS316LH showed a similar rise at −60 ℃, where severe HE was also observed. Below −100 ℃, both steels displayed improved HE resistance due to slower hydrogen diffusion. At −120 ℃ and −150 ℃, SPT results indicated that STS304L had higher HE resistance, especially at increased deformation rates, compared to STS316LH. At 77 K, STS316LH’s strength dropped relative to higher temperatures, possibly due to grain boundary weakening under biaxial stress, resulting in rough fracture surfaces with stretched cup-and-cone dimples. In contrast, above −150 ℃ under N 2 , fracture surfaces appeared flat, showing micro-void coalescence or dimple-honeycomb patterns, suggesting higher strength. Both testing methods revealed similar HE behaviors, with negligible HE in both samples, suggesting that the hydrogen concentration did not reach critical levels at stress-concentration sites, even during martensitic transformation at cryogenic temperatures. Acknowledgment: This work was supported by the KETEP grants funded by the Korean Government (MOTIE) (Grant No.: RS-2024-00449309 and RS-2022-KP002825). The authors thank POSCO Co. for supplying samples.

The hydrogen energy industry is rapidly growing, and in the near future, hydrogen energy is expected to be used in its liquid form due to its high energy density. Therefore, it is crucial to study the cryogenic mechanical properties and hydrogen embrittlement for ensuring the safety and long-term reliability of structures and facilities utilizing liquefied hydrogen. To understand the impact of liquefied hydrogen on the mechanical properties of materials, testing in a liquefied hydrogen environment is the most straightforward method. However, conducting such tests in liquefied hydrogen environments is not easily accessible. First, the cost of liquefied hydrogen is high, as the technology for hydrogen liquefaction has not yet been commercialized. Second, large amounts of hydrogen gas are generated during testing, which requires specialized facilities and systems to manage the gas. Third, for safety reasons, a separate laboratory building is necessary. In this study, an alternative approach is employed to evaluate hydrogen embrittlement at cryogenic temperatures. Specifically, specimens were thermally hydrogen-charged and tested at cryogenic temperatures using a cryo-cooler. The test procedure is as follows: first, specimens were thermally charged for a sufficient period to ensure hydrogen saturation within the steel. The charging conditions included a hydrogen pressure of 50 MPa and a temperature of 300°C. For testing at 20K, a cryo-cooler was used to cool the cryostat, and the specimen was further cooled through heat exchange with helium gas in the specimen chamber. The specimen temperature was controlled using a resistance heater. In this study, the tensile properties and hydrogen embrittlement of various steels were evaluated across a temperature range from room temperature to the temperature of liquefied hydrogen. Additionally, fracture toughness tests were performed, and differences in the J-R curve and Load-COD results were observed due to thermal hydrogen charging. Fracture surface analysis was conducted to investigate the deformation and fracture mechanisms of the specimens.

In this study, an in-situ mechanical testing methodology using pressurized hollow cylindrical specimens was applied to test two structural materials proposed for a coaxial hybrid pipeline design. Austenitic stainless steel 316Ti was suggested for the inner pipe in contact with liquid hydrogen, while ferritic 9% Ni steel, commonly used for liquefied natural gas storage and transport, was assessed as a potential outer pipe material. Specimens were pressurized with hydrogen or helium from the inner hollow tube side with up to 200 bar and subjected to tensile loading under cryogenic conditions. For 316Ti, tests were conducted from ambient temperature down to 20 K, whereas 9% Ni steel was tested down to 77 K. Our results indicate that hydrogen effects in both materials become significant primarily after substantial plastic deformation, while the overall strength is largely unaffected, at ambient temperature. Intermediate cryogenic temperatures cause pronounced changes in the mechanical properties and in the fracture behavior. These findings emphasize the importance of accounting for temperature-dependent hydrogen effects in material selection and structural design. The study provides essential insights for developing safe and efficient hybrid liquid hydrogen pipeline systems.

9 mass%Ni martensitic steel exhibits a combination of moderate strength and excellent toughness at temperatures below 77 K, making it a suitable material for cryogenic applications, such as liquefied natural gas (LNG, 111 K) storage tanks. The balanced strength and toughness of the steel result from the synergistic mixed-microstructure of hard martensite (BCC-Fe; α') matrix and soft retained-austenite (FCC-Fe; γ) phase, formed through the conventional quenching and tempering (QT) process. The retained γ transforms into α' during plastic deformation, thereby enhancing the ductility via transformation-induced plasticity (TRIP), which constitutes one of the primary toughening mechanisms. The cryogenic toughness of the steel can be further enhanced by incorporating lamellarization treatment into the QT-process, referred to as the QLT-process. The lamellarization treatment is a process that involves the intercritical annealing of ferrite (α) + γ, followed by rapid cooling. This process promotes the formation of finely dispersed retained γ in the subsequent tempered microstructure. The microstructure provides the TRIP to a greater extent and leads to increases in cryogenic toughness by 96 J at 77 K and 164 J at 4 K compared with the conventional QT condition, as measured by impact absorbed energy (Y. Kim, et al., Mater. Sci. Eng. A, 914 (2024) 17167). However, the phase fraction of retained γ does not necessarily correlate with the cryogenic toughness. The microstructural factors, including sites, morphology and size of retained γ, segregation of elements, and hardness and size of matrix, may competitively contribute to toughening. Therefore, elucidating not only the amount of retained γ but also its state and the interactions with the α' matrix is imperative. Moreover, it has been reported that the excessive formation of reversed γ during high-temperature tempering can lead to a deterioration in cryogenic toughness, even in QLT-treated steels. This deterioration is attributed to the retransformation of formed reversed γ into fresh α' upon cooling, which promotes crack propagation during impact deformation. Accordingly, the cryogenic toughness of 9%Ni steel is governed by a variety of microstructural factors, highlighting the necessity for a systematic investigation in which individual heat-treatment parameters are independently varied to clarify the underlying toughening mechanisms.

Structural steels for liquefied natural gas (LNG) containment are required to maintain high fracture resistance at extremely low temperatures. Although 7% Ni steels have attracted increasing attention as a cost-effective alternative to conventional 9% Ni steels, their cryogenic fracture behavior strongly depends on alloy design and heat treatment. In this study, the effect of manganese content on cryogenic toughness and fracture behavior was systematically investigated in 7% Ni steels subjected to intermediate heat treatment. Charpy impact tests at −196 °C revealed that the absorbed energy increases with decreasing manganese content, despite a reduction in the volume fraction of retained austenite. Detailed investigations were conducted on steels containing 0.2% and 0.8% manganese to clarify the roles of retained austenite stability and morphology. Instrumented Charpy impact testing demonstrated that the low-manganese steel exhibited consistently high absorbed energy over a wide range of intermediate heat treatment temperatures, whereas the higher-manganese steel showed a strong sensitivity to heat treatment, including unstable fracture and cleavage initiation at specific conditions. Fractographic observations revealed cleavage-type brittle fracture in the 0.8% Mn steel subjected to the intermediate heat treatment temperature of 630°C, while such fracture was not observed in the 0.2% Mn steel. The retained austenite was quantitatively characterized using X-ray diffraction and SEM/EDS analyses focusing on local nickel enrichment. The results showed that unstable fracture in the higher-manganese steel was associated with the formation of coarse retained austenite grains with lower nickel concentration, indicating reduced phase stability. Tensile tests at −196 °C further revealed an accelerated strain hardening behavior in this steel, consistent with deformation-induced martensitic transformation of unstable retained austenite. These findings indicate that cryogenic fracture resistance is not governed solely by the volume fraction of retained austenite, but critically by its stability and grain size distribution.

In metallic materials, the microstructure, strength, toughness, and other properties are significantly affected by the additive elements, which are attributed to the interatomic interactions. The essence of this interaction can be understood through the chemical bonding between atoms with orbital electrons (s, p, d, f, ..). In this standpoint, the origin of material strength is the strength at absolute zero, and as the temperature rises, the bonds loosen and the strength decreases. For stable interatomic bonds, an increase in temperature is extra thermal energy, and the bonds loosen because they are forced to be passed the energy around like hot stones. Here, 1 eV is roughly equivalent to 7,740 K and melting points of most metals are less than 3,000 K (less than 0.4 eV). We have to realize that the room temperature 300 K (0.04 eV) is high enough temperature for most atoms to re-bond or deform with extra energy, such as force. (The energy that a 3 Å cube receives at a force of 1 GPa is calculated to be approximately 0.17 eV.) In other words, atoms aggregate and bond by sharing the energy field of orbital electrons with similar energy levels, lowering their energy state and transferring energy (passing it around = lattice vibration phenomenon) to disperse and maintain stability. They absorb, propagate, and mitigate temperature and strain energy to maintain their bonds; this is the law of conservation of energy. Absorbing energy to maintain stability is energy metabolism. In bcc alloy steels, the direction of recombination (slip) of the d orbitals of the main bonds with the orbitals of adjacent atoms is different from the direction of slip of the p bonds that promote strengthening. Even if a strained p orbital bond attempts to relieve energy by slip, it is difficult for the orbitals to recombine, and when the d orbital slip reaches an excessive energy state, the bonds break and lead to brittle fracture, like the cracking of a diamond 1) . Most phenomena can be explained by the behavior of chemical bonds among atoms, and more discussion on strength from the perspective of chemical bonds is expected 2) . References: 1) Ogata, T. Development of Mechanical Testing Methods, Standardization and Strengths and Orbital Electron. Bull. Iron Steel Inst. Jpn. 2018, 23, 404–413. (In Japanese), https://portal.isij.or.jp/ferrum/PDF/PDFOpen_New.php?PNAME=OPN/VOL02308/2018_Vol.023_No.08_0404.pdf 2) Ogata, T., Hydrogen Does Not Embrittle Materials Themselves but Inhibits the Work Hardening of Materials, Processes 2025, 13, 3236, https://doi.org/10.3390/pr13103236

Cryogenic structural steels with high yield strength well above 1200 MPa are necessary for next-generation magnetic confinement fusion. China has embarked on the design of the China Fusion Engineering Demo Reactor (CFEDR), which is envisioned to provide 1.5-3 GW fusion power. In 2015, Prof. Laifeng Li from the TIPC sponsored a program on R&D of cryogenic structural steels with high yield strength as well as appropriate fracture toughness at liquid helium temperature. The purpose of this project is to establish cryogenic structural steels through screening tests or development of novel ones. Soon after, the Nitronic 50 has been considered as a candidate material and optimizations of the chemical composition as well as steelmaking process have been suggested. In 2018, a project supported by the Ministry of Science and Technology of the PRC was launched. In 2021, an alliance including more than 10 institutes, universities, and steel companies was established and then the modified Nitronic 50 steel was established as the CICC jacket material of the TF coils and CS coils as well as the case material of the TF coils of the Burning plasma Experimental Superconducting Tokamak (BEST) in year 2022. The very low-carbon grade Nitronic 50 obtained through vacuum induction melting furnace will be used as conductor jacket materials, whereas the heavy-section plate obtained through medium-frequency induction melting furnace will be used as the TF case material. Both undergo an electro-slag re-melting (ESR) process to refine the steel. This article presents a brief progress of the development of modified Nitronic 50 steel and its application in the BEST device in China.

The need to expand carbon-free energy production has accelerated the development of high-power technologies, among which nuclear fusion is a promising option. The leading magnetic-confinement concepts are the tokamak and the stellarator. ITER, currently under construction, acts as a cornerstone for next-step tokamak devices such as the European DEMO and compact tokamak concepts including SPARC and ARC. These systems rely on superconducting magnets generating magnetic fields up to ~13 T in ITER and potentially ~23 T in ARC. The recent development of high-temperature superconductors has also accelerated progress in stellarator concepts. In all these devices, the magnets are supported by large structural components that must withstand very high Lorentz forces and therefore require high strength, high damage tolerance and predictable fracture behaviour at cryogenic temperatures. Austenitic stainless steels such as 304LN and 316LN have long been the reference materials for cryogenic structural applications because of their excellent toughness, stable crack propagation and low magnetic permeability. However, the mechanical requirements of next-generation magnetic systems are steadily increasing and are now approaching the strength limits of these alloys. In this context, the JAERI box targets at 4 K (σ₀.₂ > 1200 MPa and KIC > 200 MPa√m), once considered ideal design goals, are increasingly regarded as necessary performance levels. These growing requirements have renewed interest in high-strength Ni-based alloys such as UNS N07718 for cryogenic structural applications. UNS N07718 according to the ASTM standard (718ASTM) has been widely used in cryogenic environments owing to its high yield strength while maintaining significant ductility, with a specified minimum yield strength of about 1030 MPa at room temperature (ASTM B637). Examples include its use in the Cryolegs of W7-X, which connect and support the central support structure, as well as in ITER for heavy-gauge fasteners of the gravity supports of the toroidal field coils and for the Pre-Compression Counter Flange system in the form of threaded rods (M80–M110). For the latter application, very stringent requirements (Rp0.2 > 1350 MPa at 4 K) are specified, demonstrating the high performance required. Nevertheless, fracture-toughness values of ~60 MPa√m and unstable crack propagation at 4 K may limit its use when fracture toughness becomes the governing design parameter, highlighting the need for improved toughness retention. An alternative variant, UNS N07718 according to the API 6A CRA standard (718API), was specifically designed for enhanced corrosion resistance and long-term mechanical performance at high temperature in aggressive environments. Consequently, its industrial use has remained almost exclusively within the oil and gas sector. Although 718ASTM and 718API share similar chemical compositions, their different heat treatments produce distinct microstructures and mechanical responses. The lower room-temperature yield strength specified for 718API (827–1000 MPa) reflects these microstructural differences. Because yield strength increases as temperature decreases, and given the well-known relationship between yield strength and fracture toughness, this lower strength at room temperature may be beneficial for fracture-toughness retention at cryogenic temperatures. However, its mechanical behaviour at 4 K has not yet been systematically investigated, and both yield-strength and fracture-toughness data are lacking in the literature. In this work, the mechanical behaviour of 718API was investigated at 4 K using tensile and fracture-toughness testing. The relationship between microstructure and crack propagation was analysed by scanning electron microscopy and electron backscatter diffraction, and directly compared with 718ASTM. The results show that 718API provides a promising balance between strength and fracture toughness. This behaviour is associated with reduced δ-phase precipitation and the absence of a continuous grain-boundary δ-phase network, which promotes more stable crack propagation at cryogenic temperatures. These findings identify 718API as a strong candidate for heavy-gauge cryogenic structural components and highlight its potential for structural applications in next-generation high-field fusion magnets and future fusion devices.

High strength and toughness at low temperatures make nitrogen-strengthened austenitic stainless steels promising materials for cryogenic structural components. This study evaluates the high-cycle fatigue (HCF) properties of an extra-thick plate (ETP) of XM-19 (22Cr–13Ni–(Mn, Mo, Nb, V)–N) at 77 K, focusing on through-thickness section dependence and subsurface crack initiation. The plates were solution treated at 1373 K and 1473 K for 21.6 ks followed by water quenching. The average grain size was 35 μm (quarter-section) and 42 μm (midsection) for the 1373 K condition, and 76 μm (quarter-section) and 101 μm (midsection) for the 1473 K condition. Load-controlled fatigue tests were performed at 77 K using unnotched hourglass specimens under a stress ratio of R = 0.01 and a frequency of 10 Hz. Specimens for the 1473 K plate were taken from the quarter and midsections parallel to the transverse direction (TD). In addition, rolling direction (RD) specimens were taken from the quarter-section for both the 1373 K and 1473 K plates. The run-out criterion was 10 7 cycles. For the plate tested in TD, the midsection exhibited higher fatigue strength than the quarter-section, at 10 7 cycles, the ratio of fatigue strength to tensile strength (s max /UTS) was 0.575. the TD quarter-section showed a pronounced decrease in fatigue strength between 10⁵ and 10⁶ cycles. In RD, the 1473 K quarter-section exhibited the higher fatigue strength, at 10 7 cycles with s max /UTS was 0.65, whereas the 1373 K RD quarter-section showed a sharp drop in s max /UTS from 0.7 to 0.55 between 10⁶ to 10 7 cycles. Fracture surfaces were examined by SEM. At higher cyclic stress, cracks initiated at the specimen surface, whereas at lower cyclic stress the dominant initiation mode transitioned to subsurface initiation beyond 10 6 cycles. The subsurface crack initiation site size was quantified using the √area parameter. The subsurface crack initiation site size increased as stress decreased, showing an inverse dependence between facet size and applied stress. The √area-based stress intensity estimation indicated that the Stage I–Stage II transition is associated with an approximately constant with ΔK Imax in the range of 5–11 MPa√m. The microstructure and deformation structure are examined using SEM-EBSD and TEM to discuss on the fatigue crack generation.

The reliability and stability of superconducting magnetic energy storage devices (SMES) are largely determined by the nature of transient processes during quench—a sudden local thermal transition of a superconductor to a normal state as wells as minimum quench energy (MQE). In this regard, the development of numerical mathematical models that describe the processes of quench occurrence and the dynamics of subsequent propagation of the normal zone (NZP), taking into account the properties of materials, conductor geometry, and cooling conditions, is one of the key tasks in analyzing the stability of SMES operation. This study presents a combined numerical and experimental analysis of NZP processes in HTS conductors under various current loads and cooling conditions. The numerical model is based on the finite element method, and uses a non-stationary heat transfer equation as its governing equation. Temperature-dependent electromagnetic and thermophysical properties of superconducting materials, such as the thermal conductivity, resistivity, specific heat and density, are used in numerical simulation. Moreover, the geometry and architecture of current-carrying elements was taken into account. Normal zone propagation processes were analyzed in singular superconducting element—high-temperature superconducting (HTS) tape based on REBa2Cu3O7-x compounds, where RE is a rare earth element (hereinafter REBCO). A comparative analysis of the normal zone in multi-tape HTS cables of various architectures was performed: CORC, Röbel-type cables, and twisted stack of the HTS tapes (TSTC). The influence of the geometry and cable architecture (for example winding direction of HTS tapes in CORC cable) was studied. The numerical data was verified with experimental NZP velocity and MQE values. In the experiment we used distributed voltage and temperature sensors integrated with a multi-channel measurement system. Two distinct cooling conditions were considered: with pumped liquid nitrogen bath in the temperature of 65–77 K, and with a cryocooler in the temperature range of 20-65 K. In this study, we established temperature and current load dependencies of NZP velocity and MQE in self-field and the magnetic fields typical for SMES. Numerical and experimental data appeared to be in a good agreement. The results obtained are in the same order of magnitude as analytical estimates and literature data. It has been established that the cable architecture significantly affects the dynamics of the normal zone development. Röbel-type cables demonstrate the highest NZP velocities and energy losses, while CORC cables, on the contrary, are characterized by low NZP velocities and increased thermal stability. The TSTC configuration lies in between. For the CORC cable the counter-winding of HTS tapes in CORC cable (i.e. when the tapes in the cable are wound cross-directionally) leads to a reduction in the longitudinal normal zone propagation velocity by 30–100% or more compared to cables with parallel winding, which is associated with the peculiarities of temperature distribution and thermal stabilization of the cable. The results show that the dependence of the NZP velocity on the transport current is distinctly nonlinear and partially correlates with the magnitude of alternating current losses (AC losses). At the same time, the fundamental difference in the physical nature of these processes is emphasized: energy losses are generated in a quasi-stationary mode, while the development of the normal zone is a non-stationary cascade-like thermal process The results obtained can be used when selecting the optimal architecture of superconducting cables used in SMES and the parameters of SMES quench protection systems, while taking into account the thermal stability and quench detection and protection efficiency for different cable configurations. This work was supported by the Ministry of Science and Higher Education of the Russian Federation within the State Assignment (project FSWU-2025-0008)

Superconducting Magnetic Energy Storage (SMES) systems are promising high-efficiency energy storage devices. SMES units have various applications, including smart microgrids, renewable energy systems, hybrid electric vehicles, and other power engineering devices. For stable and efficient operation of inductive energy storage systems and superconducting cables, a well-designed cooling system is required, enabling higher critical currents and reduced AC losses. In this study, the characteristics and operating regimes of inductive energy storage elements and two types of superconducting cables were compared: CORC cable and twisted stacked-tape cable (TSTC), manufactured using second-generation (2G) composite high-temperature superconducting (HTS) tapes. The outer diameter of the CORC cable former was 8 mm, and the helical winding angle was 22°. The number of tapes in both cable types varied from 5 to 20. Industrial second-generation HTS tapes produced by S-Innovations, based on ReBa₂Cu₃O₇−x with a critical temperature of 92 K, were used in the study. The critical current of 4 mm wide tapes is 140 A at liquid nitrogen temperature in self-field conditions. A model was developed to analyze transient current processes in superconducting elements based on the solution of non-isothermal Maxwell equations using H and T–A formulations within the finite element method. The model incorporates the electrical and thermophysical properties of composite HTS tapes. The temperature dependence of the critical current, thermal conductivity, and heat capacity is taken into account. The current–voltage characteristic (E–J power law) is used to describe the superconducting state, while normal resistance and normal zone propagation are considered during the transition to the normal state. For liquid nitrogen cooling, a boiling hysteresis curve describing nucleate and convective heat transfer regimes is implemented. For cryocooler-based cooling, heat transfer through solid conduction or convective heat exchange using gaseous helium is considered. As a result of the study, operating points in terms of transport current and temperature were determined for cable elements and storage windings under different cooling conditions: liquid nitrogen, solid nitrogen, and cryocooler-based cooling, including the use of heat-exchange gas. Based on the obtained data, stable operating regimes of the elements under various cooling conditions were analyzed. For liquid nitrogen and cryocooler cooling cases, load curves of superconducting cable elements and SMES inductive storage elements were measured under DC and AC currents (50–200 Hz). The experimental results were used to validate the numerical models. Losses under different cooling regimes and current injection conditions were evaluated. Based on the obtained results, recommendations for cable type selection and cooling regime optimization were formulated. This work was supported by the Ministry of Science and Higher Education of the Russian Federation within the State Assignment (project FSWU-2025-0008)

The whole-body superconducting MRI magnet stores a large amount of energy, which needs to be safely dissipated in the magnet while quenching. The MRI magnet must operate for many years in the hospital, and thereby, it must be completely self-protecting by means of self-activating quench propagation heaters to spread the normal zone in a larger volume of the magnet during a quench i.e. the passive protection system. We have designed a passive quench protection system of the whole-body 1.5T superconducting magnet made of wire-in-channel NbTi conductor. The stored energy is 3.7 MJ. The coils are subdivided into equal halves. The actively-shielded MRI magnet has six primary coils and two shield coils. There are two quench propagation circuits in the quench protection system, which gets self-activated whenever there is an imbalance in the voltage. There are many voltage taps connected across various coils and the various sections of the quench protection circuit. All the voltage taps from the magnet are fed to the fast data acquisition system through a high-voltage isolation system. Recently, we have tested the quenching of the whole-body MRI magnet developed indigenously at the Inter-University Accelerator Centre. The voltage at different parts of the quench protection circuit has been measured to validate the simulated protection circuit. The current through the different sections of the propagation circuit has been calculated from the measured voltage. The rise in pressure of the helium bath during such quench has been analysed along with the performance of the cryogenic safety. This paper briefly discusses the quench protection circuit and the voltage profile across various parts of the multi-coil MRI magnet system during the quench. The paper also discusses the analysis of the quench of the whole-body superconducting magnet system and compares it with the simulated results.

REBCO tape has been widely used as the insert magnet of an extremely high magnetic field (over 25T). Under extremely high fields, the REBCO tape carrying hundreds of ampere currents will suffer tremendous stress, making the mechanical properties of REBCO tape one of the critical parameters. The Ic vs. tensile stress is typically measured by in-situ tensile Ic measurement equipment. In this paper, we want to show a new process of Ic vs. tensile measurement to eliminate the negative effect of voltage tap during the tensile process. REBCO commercial tapes from multiple manufacturers have been measured. It is confirmed that the Ic will not degrade until the elastic limit of REBCO tape, which conflicts with most of the previous literature results. It is shown that the mechanical strength was underestimated in most of the previous research. The fatigue results also show the same rules. We hope this result can help the research groups to better understand the REBCO mechanical properties.

The dielectric strength of insulating materials has been studied under shear stress to evaluate the insulation performance of a rectangular conductor toroidal filed coil in a fusion reactor. Particular attention was paid to the problem of insulation properties under stress. In the parallel direction to the reinforcements in the composite, the dielectric strength began to decrease at lower stress where macroscopic mechanical defects (visually detectable defects by optical microscope) were introduced. This phenomenon was observed at both room and liquid nitrogen temperatures. Examination of the discharge path showed that the discharge was along the yarn. It was suggested that the discharge path was formed by connecting micro-cracks at the interface between the glass filament and the resin, which accompanied the deformation of the yarn. A similar test was performed in the direction perpendicular to the reinforcements. The breakdown voltage decreased due to the introduction of cracks into the matrix or the subsequent crack opening due to stress. These phenomena mean that the dielectric strength of the insulating material is lowered by external stresses. Irradiation effects of gamma-ray was also considered.

The 40 µm Cu-plated REBCO tapes (FESC-SCH04) produced by Fujikura Ltd. were adopted for the 19T-REBCO insert coil of a 33T cryogen-free superconducting magnet (33T-CSM) at the High Field Laboratory for Superconducting Materials (HFLSM), IMR, Tohoku University, Japan [1]. The maximum hoop strain in the 19T-REBCO insert for 33T-CSM is approximately 0.3 % under the central magnetic field of 33 T. The 40 µm Cu-plated REBCO tapes (FESC-SCH04) produced by Fujikura Ltd. were adopted for the 19T-REBCO insert coil. We evaluated the mechanical and electromechanical properties of the REBCO tapes for 19T-REBCO tapes in a wide temperature range from 77 K to 20 K using a pulsed critical current measurement system [2, 3]. As the temperature decreases, Young's modulus increased from room temperature and tends to saturate in the low temperature region. Thanks to the pulsed critical current measurement system, the electromechanical properties for the 4 mm wide REBCO tapes could be evaluated without microbridge fabrication. The critical current I c values were about 200 A at 77K and about 1500 A at 30 K in the absence of an external magnetic field. The strain dependence of I c under stresses/strains below the irreversible limits was very small. Irreversible strains determined by 98% of the initial I c before applying the stress/strain were approximately 0.4%, independent of the temperature, and were below the yield strain. The electromechanical properties of the 40 µm Cu-plated REBCO tapes will be discussed from the viewpoint of their application to the 33T-CSM. [1] S. Awaji et al., IEEE TAS 35 (2025) 4300406. [2] Y. Tsuchiya et al., IEEE TAS 35 (2025) 9500805. [3] S. Kume et al., IEEE TAS (2026) in press. Acknowledgment This work was supported by the Moonshot R&D Program “MILLENNIA” (Grant No. JPMJMS24A2) of the Japan Science and Technology Agency (JST), JSPS KAKENHI (Grant No. 22H00142) and by the New Energy and Industrial Technology Development Organization (NEDO, Project No. JPNP20004).

In recent years, socioeconomic trends have increasingly driven research aimed at establishing hydrogen as a clean energy carrier, with the decarbonization of transportation emerging as a key challenge. The utilization of hydrogen in weight-sensitive applications such as aircraft imposes unique constraints on the system architecture, particularly with respect to limited space and proposed mass gains, due to the integration of designated tanks, distribution systems, and propulsion components. In addition, the cryogenic nature of liquid hydrogen requires the use of specialized materials and tailored design approaches. Within this context, the use of additive manufacturing and high-performance thermoplastics offers considerable potential. These technologies have a proven track record of reducing part count and weight while exhibiting promising low-temperature mechanical behavior and inherent resistance to hydrogen embrittlement. In general, thermoplastics display a pronounced temperature-dependent material response. Whereas elevated temperatures are typically associated with increased ductility and a reduction in strength, cryogenic conditions tend to reverse these trends. Quantifying the magnitude of these effects is essential for the safe deployment of thermoplastic components in cryogenic engineering applications. Furthermore, additively manufactured thermoplastics differ fundamentally from conventionally processed ones due to their intrinsic anisotropy and layer-wise microstructure. By exploiting these characteristics, the printing process enables targeted tailoring of mechanical properties through deliberate selection of process parameters and print strategy. This paper investigates the cryogenic mechanical performance of four high-performance thermoplastics suitable for material extrusion additive manufacturing. Uniaxial tensile tests are performed at room temperature, as well as in liquid nitrogen, and liquid hydrogen environments. Anisotropy is especially accounted for by evaluating specimens printed in both XY and Z orientations. To address the typically inferior interlayer strength in the Z direction, a response-surface based design of experiments is employed to systematically optimize relevant printing parameters with the objective of maximizing interlayer bonding and the resulting cryogenic tensile performance. The measured mechanical properties are correlated with polymer microstructure and detailed fractographic analyses to evaluate dominant failure mechanisms and temperature-dependent deformation behavior. Based on the experimental results, material-specific processing recommendations for additively manufactured PAEK-based polymers in cryogenic environments are derived. These findings provide critical engineering data and demonstrate the suitability of additively manufactured high-performance thermoplastics for weight-sensitive liquid hydrogen infrastructure components, particularly in aerospace applications.

Metastable austenitic stainless steel 316L can exhibit a Lüders like yield plateau in the stress strain behaviour at cryogenic temperatures. This results in local plastic strains that propagate as a macroscopic deformation front coupled to deformation-induced martensitic transformation (DIMT) [1,2]. This discontinuous flow behavior strongly affects strain redistribution and structural stability of cryogenic components. In this study, we investigate the mechanisms leading to the suppression of Lüders-like strain-front propagation in fused filament fabricated (FFF) 316L, produced by material extrusion followed by debinding and sintering, compared to conventionally processed 316L. Dog-bone specimens of both materials were tested under quasi-static uniaxial tension at room temperature and 77 K (liquid nitrogen). Full-field digital image correlation (DIC) was employed to quantify the evolution of local strain fields and front propagation, complemented by an RMS-based measure for strain-field heterogeneity. Magnetic phase measurements (Feritscope) were used to track the formation of ferromagnetic α′-martensite, with calibration for δ-ferrite fractions present in the FFF material. SEM, EBSD, and EDS were applied to correlate local strain accumulation with microstructural heterogeneity such as pores and Fe-δ islands. At 77 K, conventional 316L displays a distinct Lüders-like yield plateau accompanied by a propagating strain front. In contrast, FFF 316L exhibits a smooth transition into plastic flow without a macroscopic yield plateau. While the overall amount of strain-induced martensite formed at 77 K is comparable between both materials, its spatial distribution is markedly different. In FFF 316L, DIMT nucleates preferentially at elongated pores and interlayer boundaries, leading to multiple localized transformation zones that suppress a coherent front. These findings suggest that porosity and microstructural heterogeneity disrupt the mechanical coordination required for Lüders-band propagation [3]. To further elucidate the role of porosity, pore-resolved finite-element (FE) simulations were performed on single-pore and pore-field representative volume elements. The simulations reproduce the experimentally observed “diffuse yielding” by showing that distributed pores act as local stress concentrators initiating multiple overlapping plastic/transformational wavefronts. The resulting interference prevents the formation of a single macroscopic Lüders band, providing mechanistic insight into how microstructural topology alters cryogenic flow localization. The close qualitative agreement between DIC and FE data underscores that strain front suppression is not solely a statistical artifact but a physical outcome of the pore-induced interaction of strain and transformation fields. Beyond the mechanistic relevance, these results also have implications for cryogenic component design. Controlled porosity and microstructural tailoring in additively manufactured 316L can be used to mitigate discontinuous yielding, promoting more stable deformation under cryogenic loads. [1] Tabin, J. (2021). Kinematic and thermal characteristic of discontinuous plastic flow in metastable austenitic stainless steels. Mechanics of Materials, 163, 104090. [2] Li, S., Withers, P. J., Deng, Y., Yan, K. (2024). Deformation microstructures and martensitic transformation pathways in cryogenically deformed 316L stainless steel. Journal of Materials Science, 59(5), 2134–2154. [3] Tabin, J., Kawałko, J., Schob, D., et al. Ziegenhorn, M. (2026) Deformation-induced martensitic transformation in fused filament fabricated austenitic stainless steels during tension at wide range of temperatures (77 K, RT). Materials Science and Engineering: A, 950, 149552.

Additive manufacturing has enabled the fabrication of structural composite materials with complex geometries; however, the strong dependency of mechanical performance on processing induced features such as layer orientation and porosity remains a major challenge for engineering design. Most existing studies rely heavily on experimental investigations, while design oriented analytical frameworks that link processing parameters to structural properties are still limited. This study presents a literature based parametric mechanical modeling approach to analyze the processing structure property relationships of 3D printed structural composites without conducting direct experimental work. Mechanical properties reported in peer reviewed literature for fiber reinforced polymer composites fabricated via fused filament fabrication are used as input data for analytical models. A modified rule of mixtures incorporating orientation efficiency and porosity correction factors is employed to evaluate the effective elastic modulus and strength of the printed composites. Parametric analyses are performed to investigate the influence of fiber volume fraction, printing orientation, and porosity level on the resulting structural performance. The results demonstrate that layer orientation and porosity exert a more pronounced influence on stiffness and strength degradation than fiber content alone. Increasing fiber volume fraction improves mechanical performance only when favorable orientation and low porosity are maintained. Based on the analytical results, design envelopes and sensitivity maps are proposed to support material selection and process optimization for load bearing additive manufactured components. The proposed framework provides a simple yet physically meaningful tool for preliminary structural design of 3D printed composites and offers practical insights for engineers and researchers seeking performance oriented additive manufacturing strategies

Superconducting motors and generators are a promising technology for mobile applications such as aircraft and high speed ships requiring MW scale machines with low weight and volume. In these applications, the AC coils present the biggest challenge for cooling. In this paper we assess the cable format developed by the Korea Electrotechnology Research Institute (KERI), where REBCO tapes of 1mm width, or less, are stacked and then diffusion bonded to create a cable. In theory, the narrow tape will improve AC loss performance, but consolidation will promote excellent coupling between the tapes, which degrades performance. The stacked tapes do have very advantageous mechanical and thermal properties, however, which makes them immediately attractive for any practical motor design. To develop a clear understanding of the tradeoffs, we assess this cable as we have done with other candidate conductors, using the Robinson Research Institute 3MW fully superconducting motor design. This is a 3-phase synchronous air-cored architecture using saddle coils for both rotor and stator, with a 4500rpm rated speed. The cooling budget for the cryogenic system is set by assuming that electrical power is supplied by fuels cells using liquid hydrogen, which also provides a proportional cooling capacity, via an intermediate helium circuit. We developed a five degree of freedom model based on finite element simulations of cable AC loss which allows us to evaluate trade-offs for a range of cable and machine design parameters including stack geometry, operating frequency and cable operating point relative to critical current. By optimising the operating point, we find that the cable is very close to viability, relative to the cooling budget, and a high priority for more detailed experimental evaluation and optimisation.

A five-year project to underpin the MW-level fully superconducting motors for aviation applications has been started at Robinson Research Institute, Victoria University of Wellington funded by MBIE (Ministry of Business, Innovation, and Employment) of New Zealand. The project will leverage our understandings and address reliability of various cryogenic components in aircraft conditions identified by international industry partners such as AIRBUS. We will develop capability to solve challenges associated with MW-level fully-superconducting motors designed for aviation industry requirements using the on-going AETP SSIF (Advanced Energy Technology Strategic Science Investment Fund) program as the foundation for the expanded research project under this new SSIF Platform. At this stage, it is not known what types of superconductors need to be used in the HTS stator windings nor how to cool the stator windings. Furthermore, there is no agreed-upon concept for the HTS field winding geometry, how to energise the field windings, nor how to cool the rotor. While using the materials and manufacturing science experiences based on the additive technologies achieved from the ongoing work, we will explore new combinations of materials including specific high entropy alloys and their consolidation mechanisms to find more efficient solutions for the heat exchangers and rotor and stator structures. We will demonstrate a fully superconducting motor through separate demonstrations of an HTS stator operating at 77 K (liquid nitrogen temperatures) and an HTS rotor energized using flux pumps operating at 50 K. Then we will achieve an operating temperature range of 20 K to 40 K for the HTS stator windings in order to increase the power density of the motor. A fully superconducting motor rated at 100 kW will be demonstrated under realistic operating conditions for aviation applications. By obtaining investment from industry partners, we will try to build a fully superconducting MW-level motor for aviation within the lifetime of the new SSIF. This presentation will show our detailed project plan and will cover significant developments that have been achieved in AETF SSIF program. These include 1. Iron-free fully superconducting machine concept 2. Cryogenic cooled rotor prototype 3. REBCO saddle coils 4. Additive manufactured cryogenic helium heat exchangers 5. Superconducting power supply for field windings 6. Stator conductor selection and AC loss management 7. Stator cooling circuit design for liquid hydrogen cooling

We present a study of sub‑micron‑scale Nb‑Al‑Nb planar Josephson junctions, in which the intrinsic superconductivity of the aluminium weak link plays a decisive role in enhancing device performance. The fabricated structures, featuring an interelectrode distance of approximately 100 nm and an active area of about 5 × 10⁴ nm², demonstrate a critical current of around 50 μA and a characteristic voltage of approximately 1 mV at a temperature of 4 K. Notably, these junctions maintain hysteresis‑free current‑voltage characteristics, which is essential for applications in superconducting electronics. Our theoretical analysis, based on self‑consistent solutions of the Usadel equations, reveals that the observed enhancement in critical current stems from the coexistence of induced superconductivity and intrinsic electron pairing in the aluminium layer. This effect is particularly pronounced at optimal boundary resistance, where the interplay between the superconducting properties of aluminium and the proximity effect from the niobium electrodes leads to improved transport characteristics. Structural investigations confirm the presence of epitaxial Nb/Al interfaces with minimal intermixing, which ensures reproducible fabrication and reliable device operation. The combination of compact dimensions, intrinsic non‑hysteretic behaviour at temperatures above 4 K which eliminates the need for external shunting, and competitive electrical positions Nb‑Al‑Nb junctions as promising candidates for high‑density superconducting circuits. These findings underscore the potential of aluminium‑based weak links to address key challenges in the miniaturization and scalability of superconducting electronics, offering a viable pathway toward more efficient and densely integrated cryogenic devices.

Hydrogen is expected to be an essential secondary energy source for achieving carbon neutrality. To implement hydrogen in society, Japan launched the Green Innovation Fund Projects managed by the New Energy and Industrial Technology Development Organization (NEDO). One of them is the Large-scale Hydrogen Supply Chain Establishment project. To make the cost of supplying hydrogen competitive with fossil fuels, a group of companies is advancing a commercialization project for a large-scale hydrogen supply chain using liquefied hydrogen. On the other hand, structural materials used in components that make up liquefied hydrogen infrastructure are exposed to liquefied hydrogen or high-pressure hydrogen gas. These structural materials must not be susceptible to low-temperature embrittlement or hydrogen embrittlement. To support the establishment of a cost-effective liquefied hydrogen supply chain, NIMS has developed a state-of-the-art materials properties evaluation facility to advance equipment R&D for the Large-Scale Hydrogen Supply Chain Establishment project. This facility enables the evaluation of mechanical properties of structural materials under low-temperature hydrogen environments, including liquefied hydrogen. A specialized experimental laboratory has been constructed to house advanced testing systems capable of performing tensile, fatigue and fracture toughness tests under liquefied hydrogen, hydrogen, or helium gas environments. To advance research and development of structural materials for liquefied hydrogen-related equipment, we are accumulating experience and knowledge regarding the safe and stable operation of the materials evaluation facility through various tests conducted under diverse test conditions. This presentation is based on results obtained from a project commissioned by NEDO.

Using hydrogen as an energy source is one of the most important solutions for achieving carbon neutrality. Currently, the replacement of fossil fuels with hydrogen is being considered in the fields of transportation, power generation and manufacturing. In order to facilitate this transition, a stable and affordable supply of hydrogen is mandatory, which could be supported by liquefied hydrogen (LH₂) as an energy carrier. One of the biggest problems is ensuring the compatibility of materials with LH 2 . Since the boiling temperature of LH 2 is 20 K, materials must have sufficient mechanical properties in a low-temperature gaseous hydrogen environment. We have developed unique testing equipment using 'hollow specimens', which enables hydrogen compatibility testing in a high-pressure, cryogenic, gaseous hydrogen environment. In this study, the effects of hydrogen on the strength and ductility of austenitic stainless steel were investigated at various temperatures, including cryogenic temperatures. Austenitic stainless steel (SUS316L, JIS G4304), composed of 0.017 C–0.52 Si–0.84 Mn–0.029 P–0.002 S–12.08 Ni–17.44 Cr–2.23 Mo balanced with Fe, was tested. The material was supplied in the form of 30 mm thick plates after solution heat treatment at 1120 °C for 4 minutes, followed by water cooling. Hollow specimens having gauge section with outer diameter, inner diameter and length of 6.25, 1 and 37.5 mm, respectively, were machined. Slow strain-rate tensile (SSRT) tests were conducted at temperatures ranging from 40 K to room temperature while the hole was filled with 105 MPa of hydrogen. Hydrogen compatibility was evaluated in terms of elongation (EL) and reduction in area (RA). EL and RA were mostly degraded by hydrogen at 200 K, but as the temperature increased or decreased, degradation was mitigated, with few hydrogen effects observed at 100 K. The temperature effect was also confirmed via fracture surface observation: hydrogen changed the morphology from micro-void coalescence (MVC) to quasi-cleavage around 200 K, whereas below this temperature, hydrogen did not alter the morphology. Such a complicated temperature effect was mainly related to martensitic transformation and hydrogen diffusion. In the presentation, we will reveal the cause of this temperature dependence in relation to the above-described phenomena.

Laser Powder Bed Fusion (PBF-LB/M) of austenitic 316L stainless steel enables complex geometries for cryogenic and hydrogen infrastructure but produces steep thermal gradients that leave parts with high residual stresses and microstructural heterogeneities. Surface stresses are typically tensile, while the bulk is compressive and triaxial, with magnitudes strongly controlled by scanning strategy, interlayer time and heat accumulation [1]. In parallel, studies on conventionally processed 316L and hydrogen-resistant steels show that deep cryogenic treatment can substantially modify internal residual stresses, often by 50–60%, through grain refinement and dislocation rearrangement without necessarily inducing a phase transformation. First explorations on additively manufactured 316L further suggest that cryogenic exposure can alter hardness, residual stress state and porosity [2]. However, a systematic link between repeated deep-cryogenic cycling, residual stresses, microstructure and pore population in PBF-LB/M 316L, under load-free conditions, is still missing. This work addresses that gap by quantifying how repeated deep-cryogenic cycles between room temperature and cryogenic temperatures (77K and 4K) affect the residual-stress state, microstructure and porosity of PBF-LB/M 316L. A single PBF-LB/M parameter set is used to fabricate the 316L specimens. The Specimens are subjected to a series of cryogenic cycles without external load. The evolution of surface residual stresses is mapped by X-ray diffraction (before and after cryogenic cycling), complemented by electrochemical polishing to minimize roughness artefacts and better capture subsurface stress extrema. Internal residual stresses are obtained via the contour method, using precision wire Electrical Discharge Machining, high-resolution surface profilometry and finite-element back-calculation of the normal stress field on the cut plane [3]. Microstructural changes are characterized by optical microscopy, Electron Backscatter Diffraction and Transmission Electron Microscopy, focusing on grain size and morphology, texture, grain-boundary character and dislocation structures. Serial X-ray micro-computed tomography with micrometre-scale voxels is used before and after cryogenic cycling to quantify the three-dimensional pore population and its possible evolution. The combined data set enables direct correlation between local residual stress, microstructure (including dislocation-related lattice curvature) and pores, and allows to test whether residual-stress relaxation proceeds primarily via dislocation rearrangement and microplasticity rather than via phase transformation, as reported for hydrogen-resistant steels. By isolating deep-cryogenic cycling from mechanical loading and conventional heat treatment, this study provides a surface and bulk benchmark for the residual-stress response of PBF-LB/M 316L under cryogenic conditions. [1] M. Sprengel et. al., „Triaxial Residual Stress in Laser Powder Bed Fused 316L: Effects of Interlayer Time and Scanning Velocity“, Adv. Eng. Mater., Bd. 24, Nr. 6, S. 2101330, Juni 2022, doi: 10.1002/adem.202101330. [2] M. Sugavaneswaran und A. Kulkarni, „Effect of Cryogenic Treatment on the Wear Behavior of Additive Manufactured 316L Stainless Steel“, Tribol. Ind., Bd. 41, Nr. 1, S. 33–42, März 2019, doi: 10.24874/ti.2019.41.01.04. [3] Q. Yang, Z. Dong, R. Kang, und Z. Wei, „Effect of ultrasonic vibration and deep cryogenic treatment on the residual stress, mechanical properties and microstructures of HR-2 austenitic stainless steel“, Mater. Sci. Eng. A, Bd. 900, S. 146502, Mai 2024, doi: 10.1016/j.msea.2024.146502.

Mechanical testing of materials at cryogenic temperatures is essential for realising safe and reliable liquid hydrogen infrastructure, where structural materials are exposed to cryogenic temperatures approaching 20K. Structural materials used in liquid hydrogen storage infrastructure including metals, polymers, and advanced composites exhibit fundamentally different mechanical behaviour at cryogenic temperatures compared to ambient conditions. Despite this, reliable experimental data in this temperature regime are scarce due to the lack of specialised mechanical testing capabilities. This abstract presents the design, fabrication, commissioning and operation of a mechanical testing cryostat that can test structural materials up to 20K. Conventional mechanical testing cryostats rely on liquid cryogens to maintain specimens at fixed temperatures, most commonly using liquid nitrogen at 77 K and liquid helium at 4 K. However, liquid hydrogen infrastructure requires material characterisation at approximately 20 K which is not directly addressed by these traditional systems. Moreover, the use of liquid helium is costly and operationally demanding, making it impractical for routine mechanical testing. To address these challenges, the cryostat was developed using a Gifford–McMahon cryocooler, where cooling is provided by recirculated helium gas acting as the heat transfer medium. The design of the cryostat required consideration of multiple factors, including material compatibility at cryogenic temperatures, target operating temperatures and allowable heat loads, the capacity and dimensions of the specimen chamber, vacuum insulation, cryogenic piping and expansion joints, instrumentation and feedthroughs, load transfer mechanisms, integration with testing machines, cryogenically compatible grippers and supporting structures. The sample well is filled with low-pressure helium exchange gas and cooled using the second stage of the Gifford–McMahon cryocooler. Multi-stage radiation shielding is employed around and within the sample chamber to reduce radiative heat transfer. Within the well, the sample is secured in a specially designed gripper system optimized for cryogenic conditions. These grippers are currently capable of performing tensile tests on sub-sized metals, polymers, and composite materials in accordance with ASTM standards. The sample well and the cold stages of the cryocooler are enclosed in an insulating vacuum shroud. The sample well temperature is controlled by a resistance heater and a silicon diode temperature sensor to monitor the temperature. The top sample gripper is attached to a solid stainless-steel rod, which transmits the load from the testing machine to the sample. The bottom gripper is connected to a jig system that channels the forces into the mounting frame and subsequently to the self-reacting frame of the testing machine. The sample is first mounted on the grippers, and the jig system is inserted into the cryostat. The cryostat is then secured onto the supporting frame and fixed to the testing machine. A turbomolecular vacuum pump evacuates the vacuum shroud to a stable pressure below 0.01 Pa. A compressor provides the required helium gas flow at high and low pressures for the cryocooler to achieve the desired refrigeration capacity, with a chiller connected to dissipate the generated heat. Once the vacuum stabilizes, the cryocooler is activated to cool the sample chamber. The system reliably reaches temperatures as low as 11 K within approximately six hours. Using the integrated heater, the temperature is controlled to the desired setpoint. Load is applied through the testing machine until material failure occurs. A Kapton viewing window is installed on the sample chamber, allowing external observation and enabling Digital Image Correlation (DIC) measurements. This mechanical testing cryostat represents a cost-effective solution for cryogenic materials characterisation, capable of testing a wide range of structural materials. Its versatile design allows precise control of temperature and mechanical loading, enabling reliable tensile testing down to 11 K. The system is currently being upgraded to expand its capabilities to measure additional material properties, such as fracture toughness, further enhancing its utility for research and development in cryogenic infrastructure. By providing robust, reproducible, and multi-material testing at cryogenic temperatures, this cryostat significantly advances Australia’s sovereign capabilities in cryogenic materials science.

The development of linerless Type V composite tanks is crucial for the efficient and lightweight storage of liquid hydrogen (LH₂), a key clean energy carrier. While carbon fiber-reinforced polymer (CFRP) composites offer high specific strength, the inherent brittleness and poor crack resistance of the epoxy matrix at cryogenic temperatures remain a major bottleneck. Traditional toughening approaches often compromise tensile strength, creating a challenging trade-off. This study addresses this limitation by incorporating thermoplastic polyethylene glycol (PEG) into an epoxy matrix, aiming to achieve a synergistic enhancement of both cryogenic strength and toughness. The underlying mechanisms are elucidated through a combined approach of molecular dynamics (MD) simulations and comprehensive experimental characterization. A diglycidyl ether of bisphenol A (DGEBA) epoxy resin (E51) was cured with polyetheramine (D230) and modified with PEG at varying contents (1~9 wt%). The composites were fabricated using a sequential mixing procedure to ensure homogeneous PEG dispersion prior to network formation. Cryogenic mechanical properties were evaluated at 77 K via tensile tests and instrumented impact tests. Thermal properties, crosslinking density, and fracture morphology were analyzed using TGA, DSC, TMA, and SEM. Complementary MD simulations were performed to model the cured network architecture and probe the molecular-scale interactions at both 298 K and 77 K. The experimental results demonstrate a remarkable synergistic effect at cryogenic temperatures. The optimal composition with 7 wt% PEG achieved a cryogenic tensile strength of 90.2 MPa, representing a 12.9% increase over the pure epoxy (79.9 MPa). Simultaneously, its cryogenic impact toughness reached 35.75 kJ/m², a 110.54% improvement from the baseline of 16.98 kJ/m². In contrast, at room temperature, PEG addition primarily increased toughness but reduced tensile strength, highlighting a distinct, temperature-dependent reinforcing mechanism. MD simulations provided critical insights into this dichotomy. At cryogenic temperatures, PEG incorporation led to a higher density of shorter hydrogen bonds (average count: 216 vs. 200 for pure epoxy), strengthening the dynamic crosslinked network. The flexible ether-oxygen segments in PEG acted as hydrogen bond acceptors with matrix hydroxyl groups, enhancing intermolecular cohesion. Concurrently, cryogenic contraction induced a molecular-level densification effect, facilitated by a more uniform distribution of free volume in the PEG-modified system, enabling efficient stress transfer. Furthermore, PEG increased the overall free volume and reduced the crosslinking density of the network, as evidenced by a systematic decrease in glass transition temperature. This structural alteration, while reducing stiffness, is crucial for cryogenic toughening. It provides the necessary nano-scale free volume for localized segmental motion of PEG's flexible chains, allowing energy dissipation via micro-yielding and crack deflection even when bulk molecular motion is frozen. SEM fractography corroborated this, showing a transition from smooth, featureless brittle fracture in pure epoxy to rougher surfaces with dimples and tear ridges in PEG-modified systems, indicative of enhanced crack path tortuosity and plastic deformation. In conclusion, this work successfully demonstrates that PEG modification can effectively break the conventional strength-toughness trade-off in epoxy resins under cryogenic conditions. The synergistic enhancement is governed by a dual mechanism: PEG strengthens the epoxy network through cryogenic-induced hydrogen bond densification and chain packing, while it simultaneously toughens the material by regulating free volume and introducing localized flexible domains for energy dissipation. The optimal 7 wt% PEG formulation presents a promising matrix candidate for developing high-performance CFRP composites suited for next-generation lightweight LH₂ storage tanks.

Lightweight carbon fiber reinforced polymer (CFRP) composites are increasingly recognized as demanding materials for next-generation cryogenic infrastructure, particularly for liquid hydrogen storage and transport systems where mass efficiency, mechanical integrity, and thermal reliability are critical. While thermoset epoxy matrices have historically dominated cryogenic composite applications, their inherent brittleness, limited fracture toughness, and susceptibility to micro-cracking under severe thermal contraction constrain performance at cryogenic temperatures. Recent advances in manufacturing technologies, such as automated fiber placement and automated tape laying , have renewed interest in high-performance thermoplastic matrices. However, despite their potential, the deployment of thermoplastic CFRPs is hindered by two primary bottlenecks: a fundamental lack of understanding regarding structure–property relationships at the molecular level and the complexity of experimental testing of mechanical properties at cryogenic temperatures (20 K). This study addresses these gaps through a dual-track approach involving reactive molecular dynamics simulations and the development of a novel cryogenic tensile testing facility. To address the first bottleneck, this study provides a comprehensive assessment of the molecular performance of CFRPs under cryogenic conditions through the application of multiple reactive force-fields. The primary objective is to evaluate the technical strengths, inherent limitations, and necessary refinements in computational modelling in extremely low-temperature environments. Two specific high-performance matrices, polyetheretherketone (PEEK) and low-melt polyaryl ether ketone (LM-PAEK) are investigated to determine the convergence of atomistic data and the feasibility of integrating molecular dynamics into the cryogenic material design pipeline. Tensile properties and fracture properties of thermoplastics are assessed, specially focusing on the ductile-to-brittle transition. Furthermore, the polymers are assessed through free volume analysis, coefficient of thermal expansion (CTE), and nano-void growth. This framework sets a future direction for adopting molecular modelling to design new thermoplastics, ultimately minimizing the high financial burden associated with iterative experimental testing. To bridge the critical gap between atomistic simulation and practical engineering, this study details the experimental validation of thermoplastic composites using a novel cryogenic tensile testing facility. Engineered to achieve 20 K, this platform replicates the extreme environments required for liquid hydrogen storage. The design philosophy of the testing cryostat system centers on structural integrity testing of the jig system and robust thermal architecture minimizing parasitic heat loads. The system is desinged to operate with a single two-stage Gifford-McMahon (GM) cryocooler to reach the target temperature of 20 K within a six-hour window. The study addresses the significant technical hurdles inherent in testing CFRPs at these extreme temperatures adhering to the existing engineering standards. Special attention is directed towards unidirectional (UD) composites, which are particularly susceptible to premature failure and gripping complications due to required higher tensile testing loads. Experimental results are presented alongside a critical analysis of these challenges. By integrating the molecular insights from simulations with the testing platform's mechanical outputs, this research provides a more definitive pathway for the design and development of next-generation cryogenic thermoplastic composite materials.

The expanding interest in liquid hydrogen as an aviation fuel is driving a parallel need for structural and fluid‑handling components capable of operating reliably at cryogenic temperatures. As hydrogen systems impose steep thermal gradients, extreme contraction strains and unique durability demands, understanding the mechanical behaviour of candidate polymer‑based composites becomes essential for ensuring safe and lightweight storage and transport solutions. Developing robust test methods to characterise these materials across the full cryogenic spectrum is therefore a key enabler for the aviation industry’s broader adoption of thermoplastic composites in future liquid‑hydrogen architectures. To investigate the mechanical response of materials at extreme low temperatures, bespoke equipment, specifically cryostat-based test frames, is required. In this study, a wet-type LHe cryostat was utilized for all temperature setpoints, to minimize variability. Cool-down to 77 K relied on direct liquid‑nitrogen immersion, while achieving 20 K required a liquid helium boil‑off control system. At this temperature, the steep thermal gradients, limited convective heat transfer and high contraction rates of polymeric laminates demand careful management of grip alignment, load‑train contraction, strain measurement and thermal equilibrium. These challenges are widely documented in cryogenic composite testing efforts, where thermal‑stress development, embrittlement of the polymer matrix, and temperature dependent stiffness changes complicate the transfer of standard mechanical procedures to the cryogenic regime. Within this study, two classes of thermoplastic composite were evaluated: a self‑reinforced thermoplastic system and a carbon fibre‑reinforced thermoplastic system, both under consideration within aviation development activities for liquid hydrogen storage and transfer components. Their appeal lies in the inherently low density, high specific properties and the favourable coefficient‑of‑thermal‑expansion (CTE) characteristics of thermoplastic matrix composites in cryogenic environments. However, literature indicates that neither stiffness nor strength evolution with temperature should be deemed linear, particularly as polymers transition far below their glass transition temperature, where molecular mobility of the matrix decreases sharply, residual stresses accumulate, and microcracking, delamination or interfacial debonding can develop due to fibre–matrix CTE mismatch. These effects necessitate characterisation across the full cryogenic spectrum rather than reliance on 77 K data alone, since studies have shown that composite behaviour at 20 K can differ markedly from that at 77 K, with changes in modulus, strength and failure mechanisms not always following smooth or predictable trends. Across the tensile and in-plane shear (via ±45° tension) datasets, the thermoplastic composites exhibited low‑temperature responses that departed from the simple strengthening trends often assumed for polymers under these conditions. While intermediate cryogenic temperatures produced the expected increases in stiffness and load‑bearing capacity, behaviour at deeper cryogenic conditions revealed a more complex balance between matrix embrittlement, thermal‑stress accumulation and temperature‑dependent failure processes. In particular, stiffness continued to rise, yet strength did not increase proportionally and, in some cases, decreased relative to higher temperature results. These observations underscore the importance of experimentally resolving cryogenic behaviour rather than extrapolating from data at limited temperature points.

The Einstein Telescope (ET) is a third generation gravitational wave detector planned in Europe, combining a low-frequency (LF) and a high-frequency (HF) laser interferometer. Cryogenic operation of ET-LF in the temperature range of 10 K to 20 K is essential to suppress a limiting fundamental noise source at low frequency: the suspension thermal noise. This requires suspension materials with high thermal conductivity and low mechanical dissipation at cryogenic temperatures. The baseline payload design for ET-LF foresees two possible cooling concepts, both of which include the implementation of monolithic suspensions made of silicon and sapphire, respectively. Hence, the quality and the compatibility of such recently developed suspensions must be investigated experimentally. The mechanical Q-factor provides physical insight into the dissipative mechanisms of material samples and their applicability as payload suspensions in gravitational wave detectors. Q is measured by the ring-down method, exciting the suspensions to resonant vibrations and analyzing the decay time. First cryogenic Q-factor measurements of monolithic silicon suspensions for ET-LF are carried out at a cryogenic test facility at KEK. We present the results of these measurements, including the design and limitations of the current experimental setup. Required enhancements to be implemented in the GRAVITHELIUM test facility are explained, which is being commissioned at KIT.

Liquid hydrogen (LH2) is increasingly regarded as a key energy carrier in pathways toward net-zero emissions, creating strong demand for structural materials capable of reliable operation under extreme cryogenic conditions. Structural components in LH2 storage systems, including inner tanks and load bearing supports, must maintain adequate mechanical performance at temperatures down to 20K while minimising parasitic heat leaks. Conventional cryogenic materials such as stainless steels, aluminium alloys, and titanium alloys offer well established performance but are often constrained by high density and thermal conductivity. As a result, fibre reinforced polymer (FRP) composites have attracted increasing interest for cryogenic structural applications. Carbon fibre reinforced polymers (CFRP) and glass fibre reinforced polymers (GFRP) are particularly attractive due to their high specific strength, low density, and the ability to tailor their properties. While CFRPs offer superior strengths, their relatively high thermal conductivity is a disadvantage specially in cryogenic support structures where thermal efficiency is critical. GFRPs, in contrast, exhibit significantly lower thermal conductivity but comparatively lower mechanical strength. Enhancing the mechanical performance of GFRPs while preserving their favourable low thermal conductivity therefore represents an optimal materials solution for LH2 applications. Nano-scale reinforcement has been widely reported as an effective approach to enhance the cryogenic performance of FRPs. Building on this, the primary objective of this research is to improve the mechanical strength of GFRP composites at cryogenic temperatures while preserving their low thermal conductivity. Accordingly, the cryogenic mechanical behaviour of nano-modified GFRP composites intended for LH2 structural support applications was experimentally investigated. Experimentally validated mechanical property data for FRPs at LH2 temperatures remain scarce, primarily due to the challenges of testing at 20K, with most studies limited to liquid nitrogen conditions. This highlights the need for systematic investigations that directly evaluate both baseline properties and performance enhancements of GFRP composites at LH2 temperatures. In this study, cryogenic mechanical testing was conducted using a custom-designed cryogen-free facility operating at 20K. The system, based on a closed cycle cryocooler, reliably achieved 20K within approximately six hours, enabling controlled and repeatable evaluation of material behaviour. Graphene oxide (GO) was selected as the nano reinforcement due to its demonstrated ability to enhance mechanical strength at low addition levels without significantly impacting the thermal conductivity. Prior to composite fabrication, GO was comprehensively characterised using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and Raman spectroscopy to confirm its chemical structure, functional groups, and degree of functionalisation. The cryogenic mechanical performance of the epoxy matrix was first evaluated with varying GO contents from 0.1% to 1%. GO was dispersed in acetone, sonicated for uniform exfoliation, and mixed into the epoxy resin. The modified resins were cast and cured under specified conditions. Tensile testing was conducted at 20K, while complementary flexural and fracture toughness tests at 77K according to ASTM standards. Results showed that tensile strength increased with GO addition up to an optimum concentration, beyond which further addition offered negligible improvement or slight reduction in strength. This behaviour indicates that moderate GO loading effectively reinforces the epoxy matrix, while excessive content may lead to agglomeration or suboptimal dispersion. The improvements were attributed to the functional groups of GO enhancing matrix stiffness and load transfer at cryogenic temperatures. Following matrix-level evaluation, GFRP laminates with different GO concentrations were fabricated using vacuum-assisted resin transfer moulding (VARTM). Similar to matrix level, tensile testing of the GFRP specimens was performed at 20K, with complementary mechanical testing at 77K according to ASTM standards. The results showed that tensile strength improved with GO addition up to an optimal concentration, demonstrating that matrix modification translated effectively to the composite level. Overall, the results demonstrate that graphene oxide can significantly improve the tensile performance of both epoxy and GFRP laminates at LH2 temperatures, with an optimal concentration providing maximum benefit. By achieving higher strengths without increasing thermal conductivity, this work provides practical guidance for designing mechanically robust, thermally efficient GFRP structural components for LH2 applications.

The ITER project represents a global effort to advance nuclear fusion technology, with critical reliance on large-scale cryogenic systems to maintain superconducting magnets and other temperature-sensitive components at operational cryogenic temperatures. This paper presents the design, manufacturing, and testing of the auxiliary cold boxes and their associated subsystems. Key aspects include system architecture, material selection, thermal performance optimisation, safety considerations, instrumentation integration, and quality control, will be discussed. The present paper will detail the design specifications chosen to meet the requirements of the clients, e.g. superconducting magnets, cryopumps, etc., while ensuring the reliability, efficiency, and safety of cryogenic operations. The paper will also give special attention to challenges encountered during the design, fabrication, testing, as well as the protective packing and controlled delivery of components. The lessons learnt and the methodologies described here may contribute to achieving the broader goals of the ITER program.

Renewable energy sources such as solar and wind are inherently intermittent, making effective energy storage essential . Liquid Air Energy Storage (LAES) is considered a suitable option for long-duration energy storage; however, its charging process based on air liquefaction is highly energy-intensive. To reduce this demand, cold recovery systems that store cold during discharge and reuse it during charging have been widely investigated. Despite their benefits, large-scale implementation of cold recovery systems is constrained by high costs, increased system complexity, and the requirement for large cold storage volumes. Previous studies indicate that LAES systems with cold recovery require between 800 and 1600 kJ /kg of specific work, whereas systems without cold recovery typically require 2500 to 9000 kJ /kg. This work examines the application of a cascade liquefaction process during the charging stage of LAES and proposes a process layout specifically designed for this purpose. The proposed cascade configuration achieves a specific work of 1317 kJ /kg without the use of cold recovery, offering a simpler and potentially more economical alternative.

This study proposes a novel liquefied air energy storage (LAES) system that integrates the cold energy of liquefied natural gas (LNG). During off-peak electricity periods, The high-quality LNG cold energy and the gaseous air separated by the gas-liquid separation tank work together to cool the air, causing it to liquefy and be stored in the tank. Meanwhile, low-quality LNG cold energy is utilized to reduce the air temperature at the compressor inlet, markedly reducing the power consumption of the compressors. During peak electricity periods, the stored liquid air is released to generate power. The continuously released LNG cold energy and the liquid air cold energy are harnessed by an organic Rankine cycle (ORC) system for additional electricity generation. By integrating the continuously available cold energy from LNG regasification as an auxiliary energy source with the LAES system, this design reduces the volume of reflux air, thereby enhancing the liquefaction rate. Furthermore, the system employs a cascade utilization strategy for LNG cold energy (sequentially applied for air liquefaction and compressor inlet air cooling), which improves overall energy efficiency and minimizes energy losses. Additionally, during the energy release phase, utilizing both the cold energy from liquid air and LNG for ORC power generation eliminates the need for the separate cold storage system typically required in conventional air energy storage setups, reducing both footprint and capital investment. This work establishes a thermodynamic model and an economic evaluation model for the coupled system, utilizing Aspen HYSYS software for process simulation and conversion efficiency analysis. Taking a single, commonly adopted 200 t/h LNG regasification line at receiving terminals as a case study and considering electricity prices in the Guangdong region, an economic evaluation of the system was performed. The results indicate that the electricity-to-electricity conversion efficiency of the system exceeds 78%, which is approximately 30% improvement in exergy efficiency compared to conventional LAES systems. The proposed energy storage project demonstrates economic feasibility, with peak electricity prices having the most significant impact on its economic benefits. This research provides an important reference and basis for the application of LNG cold energy in long-term energy storage and peak shaving projects for power plants.

To deploy liquid air energy storage (LAES) in the urban areas, efficient and compact cold storage is essential. Conventional fixed packed beds, while cost-effective, suffer from efficiency losses due to dynamic thermocline degradation during cycling. To overcome this, this study introduces a multi-segment packed bed utilizing "discretized counterflow heat exchange." The proposed system discretizes a packed bed into series-connected segments equipped with valve-controlled manifolds. Sequential valve actuation dynamically shifts the fluid inlet and outlet, simulating the counterflow effects of moving beds without physical particle movement. This approach maintains a stable temperature gradient and consistent heat transfer driving force while avoiding the mechanical reliability risks of moving components. This study examines the system's operating principles and numerical models. The design offers three key advantages: (1) Thermocline Control: It confines the temperature gradient to specific active segments, suppressing diffusion and ensuring controllable storage processes. (2) Design Flexibility: Adjusting the active segment count allows for the optimization of heat transfer efficiency versus surface area requirements. (3) Compactness: The segmented flow strategy reduces pressure drop, permitting high-aspect-ratio beds with greater storage density. In conclusion, this technology provides a robust, engineering-friendly solution for managing temperature gradients in fixed-bed storage.

Liquid Air Energy Storage (LAES) is a promising grid-scale technology characterized by high energy storage density, geographical flexibility, and environmental friendliness. The system operates by compressing and liquefying air during the charging phase and subsequently regasifying the liquid air to generate electricity during the discharging phase. Crucially, the efficiency of cold energy storage significantly influences the liquefaction process and determines the round-trip efficiency of the entire system. While packed bed cold storage offers advantages in terms of deployment flexibility and cost-effectiveness compared to conventional liquid-based systems, traditional gas-based packed beds suffer from lower efficiency and limited energy storage density. To address these limitations, this study proposes an innovative cold storage configuration that incorporates a liquid heat transfer fluid (HTF) within a packed bed. A numerical simulation based on the continuous solid phase model was developed to evaluate the performance of packed beds using different HTFs, specifically air, dichloromethane, and methanol. A systematic analysis was conducted to investigate the impact of key parameters, including cut-off temperature, particle diameter, and aspect ratio. The results demonstrate that the liquid-based packed bed exhibits a lower pressure drop, higher cold storage efficiency, and superior energy storage density. These findings validate the technical feasibility and performance advantages of liquid-based packed bed cold storage in LAES systems, offering a compact, efficient, and scalable solution for future grid-integrated energy storage applications.

Liquid air energy storage (LAES) achieves high energy density through the compression, deep cooling, and liquefaction of air, with the charging and discharging stages corresponding to the efficient release and storage of cryogenic energy. Conventional cold‑storage technologies are generally categorized into liquid‑phase organic working‑fluid systems and solid‑particle packed‑bed systems. Liquid‑phase systems employ organic liquids as both the heat‑transfer medium and the cold‑energy carrier, offering relatively high storage efficiency but incurring substantial material cost and introducing potential flammability and explosion hazards. Solid‑particle systems rely on gas heat transfer and solid particles as the storage medium, providing low material cost and intrinsic safety. However, the dynamic evolution of gas–solid heat transfer within packed beds leads to gradual degradation of storage efficiency, thereby constraining overall system performance. To reconcile these trade‑offs, this study integrates the gas heat‑transfer and particle‑based cold storage of packed‑bed systems with the counter‑current heat‑exchange configuration typical of liquid‑phase systems. A counter‑current cold‑storage scheme combining gas‑phase heat transfer with moving particles is proposed. The effects of heat‑transfer gas type, gas pressure, and gas–solid velocity on counter‑current gas–solid heat‑exchange behavior are systematically investigated, providing theoretical guidance and engineering references for the development of efficient and cost‑effective cold‑storage units in LAES systems.

Liquid Air Energy Storage (LAES) technology has become a crucial pillar for renewable energy grid integration due to its advantages of high energy storage density and freedom from geographical constraints. Traditional LAES systems typically employ two cold storage methods: solid-phase cold storage using pebbles or glass beads as carriers, and liquid-phase cold storage using propane or methanol-water solutions as media. However, solid-phase storage suffers from low efficiency due to the thermocline effect, while liquid-phase storage using organic fluids like propane introduces potential risks of combustion and explosion to the system. To address these issues, this paper innovatively proposes using a nitrogen-based compression refrigeration cycle to upgrade the quality of LNG cold energy during regasification. This upgraded cold energy is used for air liquefaction, replacing traditional cold storage units, while the remaining low-grade cold energy is utilized for the low-temperature compression of air. During the energy release phase, solar energy is introduced for supplementary heating to enhance the work capacity of the air. This paper performs a process optimization design for the established LAES-LNG (CRC) coupled system and develops a thermodynamic model. It investigates the effects of different compression and expansion stages on system performance while optimizing key parameters. Thermodynamic analysis demonstrates that the round-trip efficiency of the system can reach 144.54%, with an exergy efficiency of 73.6%, where the heat exchanger is the largest source of exergy destruction.

Conventional liquid air energy storage (LAES) systems predominantly employ solid or liquid-phase cold storage methods, which impose certain limitations on system efficiency and safety. Integrating the substantial amount of cold energy released during the regasification of liquefied natural gas (LNG) into LAES systems represents a crucial pathway to promoting its broader application. This study proposes an innovative system that enhances the grade of LNG cold energy via a compression refrigeration cycle, applying it to the air liquefaction process in LAES to replace traditional cold storage units; the remaining low-grade LNG cold energy is used for low-temperature air compression. During the energy discharge phase, solar energy is introduced for supplementary heating to improve the system's power generation capacity. This paper establishes an economic model for the proposed coupled LAES system and investigates the impact of various factors on system economics, including initial equipment investment costs, electricity price fluctuations, and regional differences. Economic analysis reveals a net present value of USD 30.42 million and a dynamic payback period of only 2.17 years. The optimized system process achieves efficient cascading utilization of energy, providing a feasible pathway for the large-scale application of liquid air energy storage technology.

The China Spallation Neutron Source II (CSNS-II) commenced in March 2024, requiring the construction of a new 1000W@2K helium cryogenic system to supply superfluid helium for 18 sets of superconducting cavity modules. The helium cryogenic system employs a combination of cold compressors and room-temperature pumps. Additionally, to enable long-distance transfer, a method of locally throttling supercritical helium to generate superfluid helium is adopted.According to the requirements of the superconducting cavities, the operational workflow of the cryogenic system mainly consists of six stages: gas evacuation and purging, cooling from 300K to 120K, cooling from 120K to 50K, cooling from 50K to 4.5K, cooling from 4.5K to 2K and warm-up. To enhance system reliability, an online replacement device for the cold compressors has been designed. Furthermore, a 2K liquid helium vessel is utilized to simulate the thermal load.The design of the helium cryogenic system has been completed, and the manufacturing of the major equipment has now entered the production phase.

Against the global backdrop of addressing climate change and energy transition, the penetration rate of renewable energy continues to rise. The International Energy Agency (IEA) predicts that the share of installed renewable energy capacity will exceed 25% by 2030. However, the inherent volatility and intermittency of wind and solar power generation pose significant challenges to the safe and stable operation of power systems, creating an urgent need for large-scale long-duration energy storage technologies. Liquid Air Energy Storage (LAES) has become a focal point in the energy storage field due to its significant advantages, such as high energy storage density, freedom from geographical constraints, and environmental friendliness. Although extensive research exists on the thermodynamic analysis and steady-state process optimization of LAES systems, studies on the dynamic response characteristics of the system under variable operating conditions and transient processes remain insufficient. Focusing on the energy release subsystem of the LAES system, this paper establishes dynamic mathematical models for its core components—the multi-stage expander and inter-stage reheaters—based on the laws of conservation of mass and energy. Building on this, the study performs a dynamic simulation of the expander's cold start-up process under off-design conditions, deeply investigating the time-varying laws and coupling characteristics of key thermodynamic parameters, including air mass flow rate, as well as the inlet and outlet pressures and temperatures of the expander during the start-up period. The results of this study provide a theoretical basis for the safe operation of LAES systems.

A process simulation model is utilized as a diagnostic tool for the CTF refrigerator (LINDE LR280: 650 W at 4K) to analyze system behavior and support control strategy development. The model was initially benchmarked against the manufacturer’s technical specifications and demonstrated good agreement, followed by validation using process data from actual operation. During the validation process, a major revision was required to account for a substantial pressure drop at the Turbine 2 inlet, which degraded overall refrigeration capacity. This paper presents the development of the process simulation model and the validation methodology used to quantify deviations in refrigeration capacity between the modeled and actual system performance.

As the global energy mix accelerates toward a clean and low-carbon transition, energy-intensive industries such as liquefied natural gas (LNG) production face multifaceted challenges in improving energy utilization efficiency, enhancing supply reliability, and accommodating fluctuating renewable energy sources. To address these issues, this study proposes an integrated energy system that deeply integrates liquid air energy storage (LAES) with the LNG liquefaction process (LAES-LNG), aiming to build a flexible energy supply system capable of meeting diverse demands for cooling, heating, and power simultaneously. The scheme uses liquid air as both the energy carrier and core cold source, achieving synergistic natural gas liquefaction and power output through multi-stage heat exchange and expansion generation, thereby improving overall energy grade utilization efficiency. The system is designed to operate in coordination with renewable energy sources, such as wind and solar power, enabling scaled-up liquid air production during periods of abundant renewable energy generation to facilitate the accommodation of green power, while releasing stored energy when grid support is insufficient to ensure continuous and stable operation. This significantly reduces dependence on the external grid, enhancing energy supply autonomy and resilience. This integrated system offers an economical, reliable, and environmentally friendly multi-energy supply pathway for LNG plants and similar energy-intensive industries in off-grid or weak-grid areas, contributing positively to promoting green and low-carbon transformation in the industrial sector.

The current helium cryogenic system at the Taiwan Photon Source (TPS) is a single-plant configuration designed to support up to four superconducting RF cavities. While reliable in routine operation, the single-system architecture poses a critical vulnerability: any warm-up maintenance, scheduled overhaul, or unexpected repair requires a complete shutdown of the cryoplant, interrupting helium supply and affecting SRF availability. To eliminate this single-point risk, TPS proposes a dual-system approach for upgrading its helium cryogenic infrastructure. By adding a second, fully independent refrigeration system, continuous helium supply can be maintained under all conditions—including planned servicing, component replacement, or unforeseen failures. With either cryoplant capable of sustaining essential SRF cooling on its own, the dual-system configuration ensures uninterrupted operation and greatly enhances overall facility resilience. This upgrade is essential for supporting long-term SRF stability and future accelerator development at TPS.

The cold storage unit is a core component of the liquid air energy storage system, responsible for recovering and storing the cold energy of liquid air and reutilizing it during the air liquefaction process, exerting a significant influence on system efficiency. Gas–solid packed-bed cold storage, which employs a gaseous heat transfer medium, is a widely adopted technical approach. However, its performance improvement is constrained by inherently weak gas–solid heat transfer, large pressure losses, and spreading of the thermocline. Replacing the gaseous heat transfer medium with a liquid-phase fluid suitable for cryogenic energy storage represents a promising strategy to enhancing cold storage efficiency. In this study, the flow and heat transfer characteristics of gas–solid and liquid–solid packed-bed cold storage technologies are numerically investigated and comparatively analyzed. The pressure drop and temperature distribution in both packed beds are investigated under varying operating conditions, including flow velocity, temperature range, and idle duration. The results demonstrate the effectiveness of liquid–solid packed-bed cold storage in improving cold storage efficiency, providing technical support for the high-efficiency operation of the liquid air energy storage system.

Moving solid-phase cold energy storage represents a novel approach for cryogenic energy recovery and storage, in which solid cold storage media are transported by mechanical conveying systems. During the transportation process, thermal energy exchange between the solid media and the heat transfer fluid is achieved, enabling cold energy charging and discharging. Owing to its operational flexibility and scalability, moving solid-phase cold energy storage exhibits considerable application potential in large-scale cryogenic engineering systems, such as liquid air energy storage. In this application, the solid media undergo intermittent, multi-cycle thermal energy exchange and mechanical motion across a wide temperature range of 80 K to 300 K. To further investigate the mechanical integrity of solid cold storage media under repeated thermal cycling, this study characterizes the mechanical properties of three representative media, including glass beads, alumina, and brown corundum, at different temperatures. In addition, the mechanical strength of these media before and after 500 ambient-to-cryogenic thermal cycles is systematically evaluated, accompanied by microstructural morphology observations. The results provide essential experimental data to support the engineering implementation of the moving solid-phase cold energy storage technique.

UKRI-STFC Daresbury Laboratory has a large vertical cryostat capable of testing 3 large jacketed HB704 SRF cavities for ESS or a single 650 MHz jacketed cavity for PIP-II. As a part of the development of SRF Thin Films Cavities a smaller 300 litres mini-cryostat has been developed and added to the vertical test facility (VTF) enabling testing of a range of bare cavities at operating temperatures between 2K and 4.2K. The 400 mm ID bath cryostat has a modular cavity support insert fully equipped with all the necessary cryogenic and RF instrumentation. The top plate of the cryostat is designed in such a way that the Cryogenic, Vacuum, RF and other control interfaces are compatible with the existing VTF infrastructure for easy switch over between the different cavity tests runs. In this paper we discuss the design and associated process details for the new mini-cryostat with some initial results.

The LCLS-II X-ray light source operates with a 700-meter superconducting LINAC cooled by a 4 kW, 2.0 K helium refrigeration system (HRS). To facilitate the LCLS-II-HE upgrade involving installation of 23 additional cryomodules, a controlled warm-up of the LCLS-II LINAC and HRS from 2.0 K to 290 K was executed over 3 weeks. An automated control system was implemented to maintain a target warming rate of 2.0 K/hr to prevent excessive temperature gradients and thermal stress. Early in the procedure, significant off-gassing in the insulating vacuum threatened both the vacuum pumping system and SC LINAC integrity. This required holding the SC LINAC at reduced temperatures to control off-gassing rates while maintaining acceptable insulation vacuum levels. Combined with the need to limit temperature gradients across the LINAC, these constraints reduced the achievable warm-up rate to 1.0 K/hr, extending the warm-up from 7 days as initially scheduled to 12 days. This paper describes the warm-up procedure, the operational challenges encountered, and the mitigation strategies implemented to ensure system integrity during the thermal transition.

Against the backdrop of energy structure transformation, large-scale energy storage technology is crucial for accommodating renewable energy and ensuring power grid stability. Liquid Air Energy Storage (LAES) has emerged as a highly promising long-duration large-scale energy storage technology due to its advantages of high energy storage density, strong geographical adaptability, and excellent safety. However, its application is constrained by relatively low electrical roundtrip efficiency and long payback periods. Coupling with air separation units (ASUs) is a core pathway for LAES to reduce costs and improve efficiency. Nevertheless, in existing ASU-LAES integration schemes, excessive consumption of liquid air by the ASU leads to cold energy surplus, making the nitrogen outlet temperature of the main heat exchanger in the ASU dropping below -170℃. Although this theoretically reduces the energy consumption of nitrogen compressor of the ASU, it imposes stringent requirements on its equipment and technologies, significantly degrades the quality of cold energy utilization, thereby limiting the application of this coupling technology. To address this issue, this study proposes a cold storage method to store the surplus cold energy in the coupled system. The key lies in using waste nitrogen gas produced by the ASU itself as the cold storage medium, enabling efficient and high-quality transfer and utilization of cold energy between the two systems. Results show that this optimized scheme can significantly increase the system’s electrical roundtrip efficiency from 69% to 80%, with a growth rate of 15.9%. Taking a 40,000 Nm³/h ASU as an example, the system can achieve an energy storage power of 2.8 MW and an energy storage capacity of 45 MWh. This study not only significantly improves system efficiency but also provides a feasible technical pathway and theoretical support for the large-scale and high-efficiency application of LAES technology.

The Lawrence Berkeley National Laboratory (LBL) is developing a new helium liquefaction system to support performance testing of novel superconducting magnets. The existing liquefier with piston-type expanders, which has been in operation for over 45 years, can no longer meet current testing requirements due to degraded performance, helium leakage, and frequent failures. The new helium liquefaction system consists of a helium liquefier, a 2000 L liquid helium dewar, cryogen (LHe and liquid nitrogen) transfer systems, gas helium storage and buffer tanks, warm piping systems, instrumentation and control system, and utility supplies. The helium liquefier includes a warm compressor system equipped with a variable frequency driver, an oil removal system, and a cold box. It is capable of supplying a mixed liquefaction rate of 80 L/hr and refrigeration capacity of 35 W at 4.5 K without LN 2 precooling, or a mixed liquefaction rate of 140 L/hr and refrigeration capacity of 35 W at 4.5 K with LN 2 precooling. This paper presents updates to the heat load estimates, the piping and instrumentation diagram (P&ID), and layout plan of the whole system, and describes the design of interfaces to the existing test cryostat, and the LN 2 supply system. This new helium liquefaction system will significantly enhance LBL’s capabilities in advanced superconducting magnet technologies.

The Dalian Advanced Light Source (DALS) will deliver extreme ultraviolet (EUV) free electron laser (FEL) with a repetition rate up to 1MHz, featuring a 1 GeV superconducting radio frequency linear accelerator in continuous wave mode. For comprehensive performance evaluation of the cavities, cryomodules, and electron beam, the DALS test facility has been established in Dalian, China, including a vertical cryostat (VTC), a horizontal test bench (HTB), and an injector test bench (ITB). A cryoplant is devoted to servicing these test benches with a cooling capacity of 370 W@2 K, which comprises the warm compressor system, the 4.5 K coldbox, the process vacuum pump system (PVPS), the helium storage system and the purification system. Following one-year installation and integration, commissioning of the DALS test facility cryogenic system was initiated in June 2024 and the acceptance test was subsequently conducted in November 2024 before moving into operation. Cumulative 2 K operational time currently stands at 1000 hours for VTC and 2000 hours for HTB. A 100MHz, 100pC and 100MeV electron beam was successfully generated by the ITB in July 2025 and the stationary operation was maintained through February 2026. This paper presents the acceptance test results and initial operation along with the subsequent optimization of the DALS test facility cryogenic system.

The China Spallation Neutron Source Phase II (CSNS-II) project will construct a cryogenic system for ultracold neutron (UCN) capture, designed to achieve a temperature of 0.5 K under a heat load of 100 mW. The system primarily consists of three refrigeration cycles: a 0.5 K ³He cycle, a 1.4 K ⁴He cycle, and a 0.65 K ultra-pure ⁴He cycle. The 1.4 K ⁴He cycle, together with three GM refrigerators (each providing 1.5 W of cooling power at 4 K), supplies precooling at three temperature stages—50 K, 4 K, and 1.4 K—to both the 0.5 K ³He cycle and the 0.65 K ultra-pure ⁴He cycle. After this three-stage precooling, the ³He at 1.4 K is further cooled to 0.5 K through a combination of throttling and depressurization. Meanwhile, the ⁴He in the 1.4 K ultra-pure cycle undergoes purification via an ultrafiltration unit and a thermo-mechanical process, reducing the ³He concentration below 10⁻¹⁰. The purified ultra-pure ⁴He is then cooled to 0.65 K by the 0.5 K ³He cycle through a hydrogen-helium heat exchanger. Finally, the 0.65 K ultra-pure ⁴He fills a neutron converter cavity with dimensions of 7 cm × 7 cm × 100 cm, providing the necessary cryogenic environment at 0.65 K for the conversion of cold neutrons into ultracold neutrons.

Heat switches are widely used in sub-Kelvin refrigerators to accelerate its precooling process. Passive convective heat switches (PCHS) utilize the physical properties of the working fluid to achieve control of “on” and “off”. When the cold end’s temperature is higher than the working fluid’s solidification point, the hot end will be cooled by the cold flow from the cold end. On the contrary, when the cold end’s temperature is lower than the solidification point, the working fluid will solidify at the cold end, resulting in extremely low pressure inside the PCHS, which greatly reduces thermal convection between the fluid and the PCHS’s wall, as well as the fluid flow between the cold and hot ends. In this paper, a two-tube PCHS using argon as working fluid is designed, manufactured and tested. The PCHS is installed between 40 K and 1 K stages of dilution refrigerators, which can reduce the time required for the precooling process.

This study presents an experimental investigation of a printed circuit heat exchanger (PCHE) intended for application in air-refrigerant reverse Brayton cryogenic refrigeration systems. A laboratory-scale similarity-based test facility was designed and constructed to experimentally evaluate the thermal and hydraulic performance of the air to coolant PCHE under steady-state operating conditions. The similarity experiments were conducted at an elevated temperature while preserving the relevant thermo-hydraulic similarity conditions. The test rig consists of an air blower, air to coolant PCHE, coolant circulation loop, electric heater, and calibrated instrumentation for temperature, pressure, and mass flow measurements. The experiments were conducted under operating conditions scaled to represent full-scale system behavior. The measured results indicate that the PCHE achieves an overall heat transfer coefficient in the range of 140–150 W/m²·K, with a maximum heat exchanger effectiveness of 0.89. The corresponding air-side pressure drop was maintained at approximately 2 kPa, demonstrating favorable thermo-hydraulic characteristics for air based reverse Brayton cryogenic cycles. The experimental results confirm that the proposed PCHE provides high thermal effectiveness with low pressure loss and is a viable component for –100°C class air-refrigerant cryogenic chiller systems.

The cryogenic centrifugal pump is a critical power component in cryogenic engineering applications, with its performance directly influencing the efficiency and reliability of cryogenic fluid transportation. This study addresses the need for miniaturization and submersion capabilities in cryopumps by proposing a new structure for a high-speed centrifugal submersible liquid nitrogen pump based on hydrodynamic bearings. To investigate the flow characteristics and hydraulic performance of cryogenic centrifugal pumps at high rotational speeds, this study conducted a numerical analysis on the hydraulic behavior of the pump. The analysis focused on cavitation under high-flow-rate conditions and the vortex structure and its dynamic evolution under low-flow-rate conditions. Additionally, experimental tests were carried out on a cryogenic pump performance test rig to evaluate the pump performance using liquid nitrogen. The experimental results validated the accuracy of the numerical model. Theoretical investigations revealed that under low net positive suction head available (NPSHa) conditions, cavitation bubbles initially form on the suction side of the impeller blades and progressively develop downstream. As the flow rate decreases, the vortex structures within the impeller become increasingly prominent and propagate in the direction opposite to the impeller rotation, with a relative propagation speed of 250.75 rpm. This work provides valuable insights for the optimization and performance enhancement of cryogenic centrifugal pumps in China. This research was funded by the National Natural Science Foundation of China (Project No. 52276017).

Magnetic confinement fusion experimental devices require reliable superconducting magnet systems and cryogenic systems. In order to enhance system reliability and reduce the manpower needed for system operation, we have applied machine‑learning techniques to the superconducting magnet and cryogenic systems. Thus far, monitoring systems for the superconducting coils and helium turboexpanders in the Large Helical Device have been developed using machine‑learning techniques and put into operation. In this study, a condition‑monitoring system for the cold compressors in the LHD cryogenic system was developed using principal component analysis (PCA), an unsupervised machine‑learning technique. The cold compressors form a two‑stage series of centrifugal compressors equipped with gas‑foil bearings. They generate subcooled helium, which is supplied to the LHD superconducting helical coils to improve the thermal stability and operating current of the coils. During compressor operation, multiple operating parameters were monitored, resulting in high‑dimensional data. The developed condition‑monitoring system applies PCA to reduce the dimensionality of these parameters, thereby lowering the operator workload associated with the LHD cryogenic system. This paper presents the PCA results of cold‑compressor operation data accumulated during the LHD plasma experiments. It also describes the condition‑monitoring system for the cold compressors and presents the results of its commissioning.

The Knudsen pump based on the thermal transpiration effect is an effective microfluidic transport pump without moving parts, and has significant application prospects in vacuum generation, fluid delivery, and gas separation. In this paper, a novel low-temperature-driven multistage and multichannel Knudsen pump (LT-MM KP) is designed and fabricated. The alumina porous ceramics with a pore size of 0.1 μm are selected as the enabling elements. The effects of key factors, including the number of stages, flow area, and gas rarefaction degree, on the pressurization performance and flow performance of the LT-MM KP are systematically investigated. The findings of this study provide a foundation for the application of Knudsen pumps without moving parts in cryogenic fields such as space exploration and hydrogen energy transportation.

Large-scale superfluid helium cryogenic systems are key installations for the development of superconducting accelerators and their corresponding large-scale scientific projects. The use of cold compressors to boost low-temperature, sub-atmospheric helium pressure within the system represents the optimal choice after comprehensive consideration of factors such as system efficiency, reliability, and compactness. Current research on cold compressors predominantly focuses on the performance of individual components and has not yet established connections with the actual operating conditions of superconducting cavities or the flow characteristics within helium vessels. There remains a lack of quantitative modeling for the 2K depressurization-cooling transition process and the helium pressure fluctuation dynamics in cryogenic superconducting systems, as well as a scientifically sound and comprehensive control strategy for cold compressors. To address these gaps, this project proposes to develop an unsteady polytropic centrifugal flow model for the complex internal passages of cold compressors. By integrating this with a ternary two-phase flow model of the superconducting cavity helium vessel and matching their internal and external characteristic curves, the transient thermodynamic behavior of the cold compressor will be predicted. Ultimately, this study aims to establish a mapping relationship between the helium pressure fluctuation characteristics in the superconducting cavity and the transient response of the cold compressor. Using the stability of superconducting cavity helium pressure as the key performance indicator, the control strategy for the cold compressor within the cryogenic superconducting system will be optimized. The implementation of this project will enrich the theoretical framework for solving both forward (performance prediction) and inverse (optimization control) problems related to cold compressor operation. It holds significant theoretical and practical value for enhancing the efficiency and operational stability of domestically produced cold compressors and promoting their application in the field of cryogenic superconductivity.

Performance maps and similarity laws for turbo-compressors are traditionally formulated using ideal-gas assumptions, in which reduced speed and mass flow are expressed as simple functions of inlet temperature and pressure. While this approach is adequate for air and for helium at ambient conditions, it becomes increasingly inaccurate for cryogenic cold compressors for helium liquefaction, where real-gas effects, strong thermophysical property variations, and proximity to the critical point invalidate ideal-gas scaling. In this work, a real-gas similarity framework for cryogenic helium compressors is developed by reformulating the corrected variables in terms of inlet density and speed of sound. The proposed real-gas corrected speed and mass flow preserve Mach-number and flow similarity rigorously and reduce to the classical expressions in the ideal-gas limit. The methodology is implemented using accurate helium thermophysical properties and is applied to representative operating conditions spanning room temperature to deep cryogenic regimes. A quantitative comparison between ideal-gas and real-gas corrections demonstrates that significant deviations arise at low temperatures and elevated pressures, leading to substantial errors in performance mapping when classical scaling laws are used. The results highlight the necessity of real-gas similarity corrections for the reliable analysis, scaling, and comparison of cryogenic helium compressor performance in large cryogenic systems.

Air separation is a crucial industrial process for producing high-purity oxygen, nitrogen, argon, and other industrial gases. As a key equipment in cryogenic air separation units, the optimal design of turbo expander parameters holds significant importance for energy conservation and consumption reduction of the entire unit. Aspen.Plus is utilized in this paper to simulate the cryogenic air separation process and conducts an operational analysis on the application of fan-brake expanders, ambient temperature booster expanders, and low temperature booster expanders in the air separation process. The analysis results indicate that the use of ambient temperature booster expander process reduces the energy consumption of the air separation unit by approximately 2% compared to the fan-brake expander process, with an air-to-nitrogen ratio of approximately 2.2 for both processes. The use of low temperature booster turbo expanders to boost low temperature gases at -150 to -190℃ significantly increases the pressure ratio, resulting in a reduction of energy consumption by approximately 21% and an increase in extraction rate by approximately 20% compared to the ambient temperature booster expander process. Additionally, the low temperature booster expander process features simpler equipment, reduced demand for rotating equipment, lower failure rates, lower equipment manufacturing costs, and a smaller footprint. The work presented in this paper provides valuable guidance for optimizing the cryogenic air separation process.

Traditional refrigerants like CFCs and HCFCs are being phased out quickly due to the greenhouse effect and ozone layer preservation legislation. CO₂ has become the preferred refrigerant in low-temperature refrigeration and liquefaction applications due to its zero ODP, extremely low GWP, and non-toxic, non-flammable properties. However, in transcritical carbon dioxide cycles, the throttling process results in significant exergy loss, limiting system efficiency. This paper proposes a novel transcritical CO₂ refrigeration cycle for low-temperature applications, substituting throttle valves with turbine expander. First, models of two transcritical CO₂ refrigeration systems—one using throttle valves and the other employing turbine expander—are constructed. Their specific energy consumption, exergy efficiency and economic viability are compared. Second, a parameter sensitivity analysis is conducted on the transcritical carbon dioxide refrigeration system employing the turbine expander. The analysis focuses on investigating the effects of evaporation temperature and condensation temperature on the system's coefficient of performance (COP) and exergy efficiency to determine optimal operating conditions. Third, to cope with the rapid changes in the properties of the working fluid during the expansion process in transcritical carbon dioxide cycles, one-dimensional meanline design model for radial turbines and complete three-dimensional aerodynamic model are developed. Based on entropy production theory, the flow loss mechanism within the turbine is analyzed. By optimizing the nozzle exit angle as the variable, the geometry with minimal loss is identified to enhance turbine efficiency. Finally, by coupling dynamic load parameters, the off design performance of the carbon dioxide turbine is analyzed to verify its aerodynamic stability and efficiency maintenance capability under all operating conditions. This study is expected to quantify the thermodynamic and economic benefits of turbine expander technology in CO₂ refrigeration cycles.

This paper describes the design methodology and simulation analysis of a hydrogen radial-inflow turbine for the Claude cycle of a 10-ton-per-day hydrogen liquefier. Based on the inlet/outlet boundary conditions verified for the 10-TPD hydrogen liquefaction process, an iterative cycle of 1-D design and 3-D CFD is performed, and the empirical coefficients are continually revised so that the final design satisfies all requirements. The influence of key geometric parameters—such as nozzle inlet/outlet angle and rotor inlet/outlet blade angles—on expander efficiency is systematically investigated. Finally, based on the optimized 3-D model, the expander’s performance map is computed to allow rapid operating-point selection in actual production.

In the context of global energy transition and carbon peaking and carbon neutrality goals, hydrogen energy, as a clean secondary energy, has become a focus in the energy field. Liquid hydrogen, with its high energy density, high safety, and other advantages, holds broad application prospects in fields such as aerospace propulsion and clean energy. Acting as the "heart" of liquid hydrogen transfer injection system, liquid hydrogen pumps must operate at ultra-high speeds under extreme physical properties, including ultra-low temperatures and viscosity, while strictly avoiding cavitation and performance instability, presenting a significant technical challenge in their design. Targeting liquid hydrogen transfer injection conditions, this study independently designed an ultra-high-speed (20,000 rpm), low-specific-speed, two-stage centrifugal pump. Utilizing the real physical properties of liquid hydrogen and employing high-precision Computational Fluid Dynamics (CFD) numerical simulations, the complex internal flow characteristics were revealed. Simulation results indicate that at the design point (20,000 rpm, 7.5 m³/h, inlet total pressure of 2 bar), the designed pump achieves a head of 3126.8 m and an efficiency of 51.5%. Analysis of characteristic maps under varying flow rates, rotational speeds, and inlet pressures demonstrates that the pump can operate stably and efficiently across a relatively wide range. Internal flow field analysis confirms that the inducer effectively enhances anti-cavitation performance, while the inter-stage spatial guide vanes achieve excellent recovery of kinetic energy and flow rectification, creating ideal inlet conditions for the secondary impeller. This study provides an aerodynamic design scheme for a high-performance pump in liquid hydrogen transfer systems. The complete operational characteristic maps offer crucial guidance for system control and safe operation, holding significant theoretical reference and engineering guidance value for the future development of advanced equipment such as liquid hydrogen turbopumps.

During the long-term operation of 2K superfluid helium refrigerator, the return helium gas from 2K load is often non-uniform when it reaches to the inlet of the cold compressors, resulting in a deviation between the aerodynamic performance and the theoretical design. With numerical simulation analysis method, this article focused on the changes in aerodynamic performance under non-uniform conditions such as inlet temperature and so on. The results show that in the design of the cold compressor, not only the steady-state operating conditions should be considered, but also the impact of the changes in actual operating conditions on its performance.

Large-scale hydrogen liquefaction is a key enabling technology for efficient hydrogen energy storage and transportation, in which screw compressors for small molecular-weight gases play a core role. As one of the critical components in large-scale cryogenic systems, the reliability of screw compressors directly determines the reliability of the entire system. This paper presents the reliability testing methods and vibration signal analysis for oil-injected screw compressors. Firstly, accelerated life tests were conducted based on a generalized lifetime model, with temperature and rotational speed used as accelerating stresses. The tests achieved an equivalent of over 10,000 hours of wear degradation, and the results verified that the compressor's mean time to failure (MTTF) exceeds 8,000 hours. High-sensitivity multi-directional accelerometers were installed at key parts of the compressor to capture dynamic vibration signals under different operational conditions. Time-domain and frequency-domain analyses were performed to extract key parameters reflecting the operational status of the equipment. The results showed that specific frequency components and their harmonic features effectively characterize the evolution of the rotor-bearing system, enabling accurate early fault detection. Based on long-term operational test data, vibration thresholds suitable for small molecular-weight gas screw compressors were determined, and a correlation between vibration features and typical fault modes was established. The real-time performance and accuracy of the fault diagnosis system were optimized, providing a more solid technical foundation for the intelligent operation and maintenance of screw compressors and ensuring the high-reliability operation of liquid hydrogen systems.

A stable cryogenic environment is essential for superconducting applications. This paper presents the process optimization of a neon reverse Brayton refrigerator system and the design of its core component, a compressor‑expander with magnetic bearings. The system is designed to provide a cooling capacity of 18 kW at 70 K with a coefficient of performance (COP) exceeding 0.1. System‑level optimization of the pure‑neon working‑fluid cycle was carried out by coupling process simulation software with the genetic algorithm. The use of pure neon effectively eliminates the inherent composition‑drift problem associated with multi‑component mixed refrigerants. Based on the optimized cycle, the expander impeller was further refined, including its geometry, back‑sealing structure, and volute. As a result, the expander achieves an isentropic efficiency of over 85 % under various operating conditions. The refrigerator system is currently under integration, and the optimized design will be validated experimentally. This work is expected to provide key cryogenic‑technical support for the large‑scale deployment of superconducting technology in China.

Helium screw compressors serve as one of the core components in large scale cryogenic systems and are characterized by stable operation, high efficiency, and pulsation free performance under normal operating conditions. Their operational reliability directly affects the continuity and stability of the entire cryogenic system. Therefore, developing intelligent fault diagnosis for helium screw compressors is of great significance for the safe, stable, and reliable operation of cryogenic systems. This study selects the MYCOM compressor for fault diagnosis research, which is a high efficiency compound screw compressor designed specifically for large flow helium circulation systems. The core advantage of this unit lies in the superior displacement capacity provided by its dual long rotor configuration, which meets the ultra large volume flow demands of large-scale scientific facilities. This paper proposes a research scheme for intelligent fault diagnosis based on the Industrial Internet of Things and edge computing technologies. The scheme adopts a three-layer architecture comprising a data acquisition layer, a local monitoring layer, and an intelligent operations and maintenance cloud platform. By deploying wireless sensors that integrate vibration and temperature monitoring, real time data capture is achieved for key components such as the compressor motor drive end and the screw input and output sides. In terms of diagnostic methods, this study combines equipment mechanisms with monitoring schemes to systematically analyze the fault types and phenomena of helium screw compressors, covering power frequency faults and rolling bearing faults. On this basis, a multi-dimensional fault feature extraction system including kurtosis, skewness, impulse index, and frequency domain energy is constructed. This study introduces edge intelligent computing technology to move data preprocessing, false signal filtering, and feature calculation to the acquisition end, which effectively reduces transmission latency and improves alarm timeliness. By combining precision signal processing algorithms such as time domain statistical indicators, spectrum analysis, and envelope demodulation, the system achieves early identification and precise localization of typical faults like rotor unbalance, spalling on the inner and outer races of bearings, and cage fracture. This significantly enhances the operational reliability and the level of intelligent operations and maintenance of helium screw compressors. Keywords: Helium screw compressor, Fault diagnosis, Edge computing, Industrial Internet of Things, Condition monitoring

In this paper, we focus on a trace neon purification system from the feed gas of helium extracted from natural gas. And the neon adsorption system consisted of the switching purification unit and the regenerative unit was designed to meet the continuous and automatic operation of the helium liquefier. During the design of the neon adsorber, molecular simulation method with the Monte Carlo as the algorithm is adopted to calculate the isothermal adsorption curves of the adsorbent. Finally the developed neon adsorption system can achieve purification, regeneration, and dust filtration with the help of the control logic reported in this study. And the designed structure parameters of the adsorber is presented under the design input conditions of this paper. The technique presented in this paper should be useful in the process design of helium liquefier employed by the helium recovery from natural gas.

The free piston Stirling generator (FPSG) is a promising energy conversion system for deep space exploration. Although various articles have studied the impacts of a wide range of parameters on the generator performance, few have focused on the phase adjustment effects of the bounce space. This paper innovatively proposes a novel FPSG configuration with an inertial tube and a gas reservoir connected to the bounce space. In this study, the commercial software Sage is used to establish a thermodynamic model of the FPSG, whose reliability is verified by experimental results. Based on this model, the influences of key parameters such as the length, inner diameter of the inertial tube, and the volume of the gas reservoir on phase adjustment, piston motion characteristics, and output power are systematically investigated. This research provides theoretical and design references for the structural optimization of FPSG, thereby laying a foundation for improving its energy conversion efficiency and achieving applications in deep space exploration.

Gas bearings and clearance sealing technology are critical to achieving efficient and reliable operation of reciprocating pistons in generators or compressors. During piston reciprocation, gas ejected from the bearing's throttle orifices propagates within the clearance and interacts with the alternating leakage flow in the sealing gap, thereby generating a complex flow field within the air film. Aiming to elucidate the dynamic response of air bearings in complex flows, a numerical simulation is employed to analyze the operational variations in load capacity and gas consumption of the bearings. Concurrently, the leakage characteristics of the sealing clearance are examined to identify factors governing piston offset, ultimately yielding quantitative reference data for mitigating offset in generators.

Isotope separation technology has demonstrated immense value in multiple fields such as national defense and security, medical diagnosis and scientific research. So far, there are various techniques such as cryogenic distillation and thermal diffusion that can achieve isotope separation. Among these techniques, cryogenic distillation is more commonly used in the process of separating a large number of isotopes. The design principles and boundary conditions of cryogenic distillation have been comprehensively introduced. And a literature review is conducted on the application of cryogenic distillation in the separation of hydrogen isotopes, neon isotopes and helium isotopes. Additionally, the common key technologies of cryogenic distillation in these isotope separation processes are presented. Taking helium isotope separation as an example, the design process of cryogenic distillation is discussed. The calculation results indicated that a purity of about 99.9% for product helium-3 can be obtained using cryogenic distillation.

In magnetic confinement fusion devices, the helium cryogenic system is often subjected to thermal load fluctuations from users, leading to frequent off-design operation of turbine expander, which subsequently affects the stability and performance of the cryogenic system. Therefore, investigating the effects of operating parameter variations on the performance of turbine expander is of great significance for ensuring the stable operation of the cryogenic system. A numerical simulation approach is adopted to systematically examine the influence of inlet temperature, rotational speed, and mass flow rate on both the refrigeration efficiency and power of the turbine expander. In addition, sensitivity analysis is conducted to quantify the degree to which efficiency and power are sensitive to deviations in these operating parameters. The results indicate that efficiency is most sensitive to variations in inlet temperature, exhibiting a sensitivity coefficient of -48% under a 10% positive deviation in inlet temperature. The effect of rotational speed on efficiency shows a marked contrast: the sensitivity coefficient is relatively low under positive deviations but significantly higher under negative deviations. Power output is highly sensitive to changes in mass flow rate, with an average sensitivity coefficient of approximately 137.9% that remains relatively stable across variations in the deviation of mass flow rate. Additionally, with increasing rotational speed deviation, the corresponding sensitivity coefficient of power is observed to diminish.

Heat switch is essential for cyclic cooling systems such as adiabatic demagnetization refrigerators as it provides controllable thermal pathways that can connect or isolate an object being cooled from a cryocooler. Among various types of heat switch, gas gap heat switch utilizing adsorption mechanism offers advantages over mechanical alternatives as no moving parts are required. The proposed cylindrical heat switch uses helium as the exchange gas and activated charcoal as the adsorbent, with a 0.2 mm gas gap between concentric copper fins. In the ON state, the sorption pod is heated to release helium into the gap, enabling heat transfer between the hot and cold fins. In the OFF state, the sorption pod is cooled so that helium is adsorbed, thermally isolating the two fins. The proposed heat switch is specifically designed for the Single-shot Dilution Refrigerator (SDR) system, where the hot fin operates at 30 K and the cold fin is anchored to the 2nd stage of Gifford-McMahon cryocooler at 4 K. Both steady-state and dynamic analyses were conducted. Steady-state results show an ON conductance of 0.5 W/K achieved when the sorption pod reaches 19.5 K, and an OFF conductance of 1.82 × 10 - ⁴ W/K when the pod cools to 7.7 K. These threshold temperatures can be adjusted by controlling the adsorbent mass to meet specific system requirements. Dynamic analysis was performed with heater power to be 0.05 W, considering heat load to the GM cryocooler. Turn-on time was 15 seconds, independent of tube material selection. However, turn-off time depended critically on tube material since the connecting tube is the only cooling path for the sorption pod. With a brass tube, turn-off requires 200.5 seconds, whereas a stainless-steel tube requires 1257.1 seconds. Copper tubing was not considered, as its high thermal conductivity would prevent heating of the sorption pod without imposing excessive heat load on the cryocooler. Experimental validation for ON and OFF conductance of the suggested geometry was conducted.

Helium is a costly consumable resource in cryogenic facilities, with extensive applications in space exploration, medical, and energy research. During the circulation of liquid helium in large-scale cryogenic systems, trace impurities such as nitrogen, oxygen, moisture, and oil can be introduced. These impurities may crystallize at low temperatures, potentially damaging the turbo‑expanders in the cold box and thereby degrading system efficiency. Therefore, a helium purification system is designed as a critical component of the cryogenic system. Its purpose is to separate contaminants from impure helium, delivering helium with a purity of 99.9995% to the liquefier, thereby enabling helium recovery and reuse. The purification process is primarily based on two principles: cryogenic adsorption using activated charcoal and molecular sieves, and cryogenic condensation via tubular heat exchangers. This paper focuses on the experimental study and analysis of fractional condensation and purification in the primary finned coiled‑tube heat exchanger of the internal purifier within a helium liquefier. It specifically investigates the factors influencing the purity of helium after purification of helium‑based gas mixtures, as well as the effects of mixture composition and pressure variations on the UA value of the finned coiled‑tube heat exchanger.

Phase change materials (PCMs) are a promising option for recovering waste cryogenic cold from sources such as liquefied natural gas (LNG) and liquid air regasification facilities. The recovered cold can compensate for the refrigeration demands in various applications, thereby enhancing overall energy sustainability. The PCMs are housed in a packed bed through which a cold/warm gas flows through dedicated inlet and outlet ports. The packed bed operates in a cyclic manner, alternating between charging and discharging modes. During charging, cold gas from the source flows through the bed, transferring cold to the PCM. During discharging, a warmer gas stream is passed through the bed, during which the stored cold is released to the gas. These operating modes are triggered by the availability of cold at the source and demand at the application, respectively. As a result, the packed bed system is subjected to varying inlet temperatures and mass flow rates across different cycles. Under these fluctuating operating conditions, reliable estimation of the bed state of charge (SoC) is essential for effective operation and energy management. The SoC of a packed bed is derived from the temperature distribution inside the packed bed. This necessitates measuring temperatures at multiple locations within the bed volume. However, practical considerations such as reduction in effective storage volume, heat inleak through the sensor wires, etc., often reduce the accuracy of the measured temperatures. Therefore, a theoretical model based on the transport phenomena is usually adopted. The need for accurate predictions of the bed temperature profile leads to the complexity of both the model equations and the solution strategy. This renders the theoretical approach unpopular for real-time monitoring and forecasting of the system performance. The adaptation of machine learning tools has enabled meeting this need in various applications. Such tools demand not as much information about the internal system (temperature field) as conventional models require, but can provide highly accurate predictions using significantly fewer measurements of operating and process parameters. While machine-learning methods have been applied to batteries and steady-state packed-bed performance predictions, their use for real-time SoC estimation of cryogenic packed beds has not been explored. In this study, different machine learning (ML) models were compared for real-time SoC prediction of a packed bed cryogenic energy recovery system operating under different charge–discharge cycles. Four ML models—multilayer perceptron (MLP), Extreme gradient boosting (XGBoost), simple recurrent neural network (RNN), and long short-term memory (LSTM) RNN network—were evaluated. The models were trained using only measurable inputs and outputs: inlet mass flow rate, inlet temperature, outlet temperature, and the current SoC. Due to the scarcity of long-duration experimental data for continuously operated cryogenic packed beds, the training and validation datasets were generated using a validated heat-transfer-based numerical model. The results show that the Simple and LSTM RNN models yielded comparable prediction accuracies, with R-squared values of 0.993 and 0.982, respectively. In comparison, the MLP and XGBoost models exhibited slightly lower prediction accuracies, with R 2 values of 0.91 and 0.93, respectively. In each subsequent cycle, if the charging or discharging were not complete, the prediction accuracy of MLP and XGBoost came down because, unlike the RNNs, these methods do not keep a track of the “history” of the events (charging/discharging). The improvement in prediction accuracy of RNNs came at the cost of higher computation time. Thus, it is concluded that RNN-based models are better suited for SoC prediction than MLP and XGBoost; however, due to their higher execution time, a trade-off has to be made on a case-by-case basis to select the appropriate model for SoC prediction.

Hydrogen is a promising future energy carrier, and its liquefaction enables efficient large-scale storage and transport; however, accidental releases of liquid hydrogen can lead to rapid vaporization and the formation of extensive flammable or explosive hydrogen–air clouds, posing significant safety challenges. Consequently, a comprehensive understanding of the LH₂ accidental release process and the development of effective mitigation strategies are critical for ensuring the safe utilization of liquid hydrogen. In recent years, our team has systematically investigated LH₂ release phenomena and mitigation strategies through the development of OpenFOAM-based CFD models, large-scale outdoor LH₂ release experiments under various environmental conditions, and numerical studies of protective measures such as bund walls and active flow-control systems. Among these approaches, the “air wall,” formed by controlled air jets to confine, redirect, and dilute flammable hydrogen clouds, has been proposed and its effectiveness in modifying hydrogen dispersion has been demonstrated in previous numerical studies. To enhance the understanding and practical applicability of air wall systems, this study investigates the effect of jet width on air wall performance during accidental LH₂ releases using numerical simulations of a realistic LH₂ storage yard under representative environmental conditions, with a focus on hydrogen cloud evolution, dispersion behavior, and hazard characteristics. The simulation results indicate that increasing the jet width significantly enhances the overall strength of the air wall. Wider jets generate stronger upward momentum and entrainment, making the hydrogen cloud more susceptible to vertical lifting by the induced airflow. As a result, the horizontal downwind spread of the hydrogen cloud is effectively suppressed, while mixing with ambient air is accelerated, leading to faster dilution. For small jet widths, the hydrogen cloud dispersion closely resembles an unimpeded free-dispersion mode, with limited influence from the air wall. In contrast, for larger jet widths, the dispersion regime changes markedly, exhibiting a pronounced lifting effect and a substantial reduction in hydrogen concentration near the ground. Quantitatively, when the jet width is increased from 0.1 m to 2.0 m, the downwind dispersion distance decreases from 92 m to 43 m, corresponding to a reduction of 53.26%. Meanwhile, the maximum flammable volume is reduced from 1,830 m³ to 690 m³, representing a decrease of 53.29%. These results demonstrate that jet width is a key design parameter governing air-wall effectiveness and provide valuable guidance for the optimization and engineering implementation of air-wall systems for LH₂ safety protection.

The reduction of cryogenic liquids and, consequently, the development of a safe design for the storage and transportation of liquid cryogens is a critical challenge. Reliable prediction of boil-off dynamics is therefore crucial for designing insulation systems, monitoring pressure, and installing relief devices. Most numerical approaches for estimating evaporation rates rely on classical phase-change formulations, including the Hertz–Knudsen–Schrage model, Statistical Rate Theory, and Transition State Theory, which are developed under the assumptions of quasi-equilibrium at the liquid–vapor interface, negligible vapor-side thermal resistance, and weak sensitivity to variations in thermo-physical properties. While these assumptions are generally valid for ambient liquids such as water, their applicability becomes limited under cryogenic conditions. Evaporation of cryogenic and non-cryogenic fluids shares some common principles. In both cases, it is dictated by the interfacial thermal gradient. However, cryogenic liquids exhibit much lower latent heat of vaporization, larger liquid-to-vapor density ratios, and steeper saturation pressure–temperature relationships than non-cryogenic liquids; because of this, cryogenic liquids experience much higher liquid boil-off and vapor expansion. These do not allow the establishment of equilibrium at the vapor-liquid interface during the heat ingress from the ambient. Numerous studies have shown that kinetic theory of gases (KTG)–based phase-change models fail to reliably predict cryogenic boil-off due to their dependence on the accommodation coefficient. Although several modified closures based on KTG, Statistical Rate Theory, and Transition State Theory have been proposed, no universal formulation has emerged. In this context, the present study investigates the applicability of conventional and modified KTG-based models by isolating the governing interfacial transport mechanisms, rather than relying on empirical tuning of accommodation coefficients. A two-fluid modelling approach was adopted to simulate cryogenic boil-off under unsteady heat ingress. The liquid and vapor phases were treated as interpenetrating continua. The liquid–vapor interface is captured using a Volume of Fluid (VOF) method, which enables the explicit tracking of interfacial motion. The Navier–Stokes equations, coupled with energy conservation in both phases, along with interfacial phase change, were modeled using a non-equilibrium Stefan energy balance, which allowed for a finite temperature jump at the interface. Thermodynamic consistency at the interface is implemented through the Clausius–Clapeyron relation. Initially, the liquid phase is assumed to be at saturation temperature, while the vapor phase is thermally stratified from the interface to the ullage space. Our result showed that the present model is able to predict the trend reported in the experimental study correctly. However, quantitatively, the model under-predicted the experimental study by 3%. This deviation may be attributed to various factors, including initial temperature discontinuity at the interface and conduction-based interfacial energy balance. All these factors should be studied, and the relative effect on boil-off characteristics due to each of these factors must be investigated in the future.

To address the reliance of hydrogen liquefaction plants on liquid nitrogen (LN₂) supply across diverse application scenarios, this study systematically examines the effects of three LN₂ precooling configurations—open-loop, closed-loop, and integrated nitrogen recovery/on-site generation systems—on the performance and economic viability of hydrogen liquefaction plants at different scales. Numerical simulations and economic analyses were performed on two representative plant capacities: 1 t/d and 30 t/d. The 1 t/d plant adopted an "LN₂ precooling + helium reverse Brayton refrigeration" process, while the 30 t/d plant employed an "LN₂ precooling + dual-pressure hydrogen Claude refrigeration" process. Exergy analysis was conducted to quantify the energy loss distribution under each precooling configuration, thereby identifying the critical pathways for optimizing energy consumption in the precooling stage. Economic evaluation results indicate that although the closed-loop LN₂ cycle and on-site nitrogen generation scheme entail a significant increase in initial capital investment, they effectively eliminate dependence on external LN₂ supply, resolving the on-site LN₂ provision challenge in remote areas or regions with underdeveloped industrial infrastructure. Based on these findings, an economic evaluation model incorporating initial investment and ten-year operating costs was established. This work provides a theoretical foundation and engineering guidance for the selection and design of precooling processes in industrial-scale hydrogen liquefaction plants.

Unmanned aerial vehicles (UAVs) have shown significant application potential across a wide range of fields, leading to increasing demands for improved endurance and payload capacity. Conventional battery-powered UAVs face limitations due to insufficient flight duration and load capability, while fossil fuel-powered UAVs raise environmental concerns. Liquid hydrogen, with its high specific energy density and zero-carbon emissions, presents a promising solution that aligns well with the requirements for long-endurance and heavy-lift UAV operations. In this study, a dynamic model was developed that integrates a liquid hydrogen storage tank, vaporizer, fuel cell, lithium battery, and control valves, enabling analysis of the system’s dynamic response during key flight phases—takeoff, climb, cruise, and landing. Simulation results show that after one hour of continuous flight, the relative liquid level in the tank decreases by 6.58%. The lithium battery primarily supports rapid power delivery during the initial three minutes of takeoff. Furthermore, apart from noticeable pressure fluctuations in the liquid hydrogen tank caused by abrupt power demands during takeoff and landing, the deviation between actual and setpoint tank pressure remains within 5.5% throughout all other operational phases.

A compact hydrogen liquefaction system utilizing a two-stage Gifford–McMahon (GM) refrigerator as the sole cryogenic source was developed and experimentally validated in a dedicated hydrogen laboratory. In contrast to conventional hydrogen liquefaction systems that rely on Joule–Thomson expansion, helium refrigeration cycles, or large-scale precooling infrastructure, the proposed system adopts a simplified liquefaction architecture aimed at laboratory-scale applications, where experimental access to liquid hydrogen is often limited by high capital and operating costs, system complexity, and safety constraints. In the developed system, ambient-temperature hydrogen at micro-positive pressure is directly cooled and liquefied through a two-stage cooling process provided by the GM refrigerator. The first stage is responsible for sensible heat removal and precooling, while the second stage enables condensation and liquefaction without the use of expansion valves or auxiliary cryogenic loops. The GM refrigerator is mechanically integrated with a 100 L vacuum-insulated Dewar, allowing liquid hydrogen formed at the cold end to be delivered directly into the storage vessel with minimal thermal loss and simplified transfer pathways. Experimental results demonstrate stable and repeatable liquefaction performance under steady operating conditions. A maximum liquefaction rate of 17.28 L/day was achieved, with the liquefaction pressure maintained within the range of 120–190 kPa. To enhance thermal conditioning and hydrogen quality control, a liquid-nitrogen bath heat exchanger equipped with an ortho–para hydrogen conversion catalyst was incorporated upstream of the cold end. Although the precooling contribution was limited due to the low hydrogen mass flow rate, the heat exchanger exhibited stable operation and provided controlled ortho–para conversion during continuous liquefaction. The storage performance of the integrated Dewar was also evaluated. Zero-boil-off operation was successfully achieved by automatically adjusting the cooling capacity of the GM refrigerator in response to internal pressure variations, demonstrating effective coupling between liquefaction, storage, and pressure control. This confirms the feasibility of long-term liquid hydrogen storage in small-scale experimental systems without venting losses. Notably, this work demonstrates, for the first time at the laboratory scale, that a single two-stage GM refrigerator can simultaneously achieve hydrogen liquefaction and zero-boil-off storage within a 100 L Dewar through direct mechanical integration and pressure-based cooling control. The operational results and engineering experience gained from this study provide a practical and scalable reference for the design, safe operation, and experimental utilization of small-scale hydrogen liquefaction systems, thereby supporting broader cryogenic research and technology development involving liquid hydrogen.

Liquid hydrogen moderator, renowned for its ability to prevent radiation damage, is intended for the next generation MW-class high-brightness and high-intensity neutron source, including European Spallation Source (ESS) and Oak Ridge National Laboratory Second Target Station Project (SNS). At the ESS, high-energy spallation neutrons are generated by impinging a proton beam onto a rotating tungsten target. These neutrons are subsequently moderated through a combination of two hydrogen moderator and a light water premoderator, resulting in the production of a cold neutron beam. A butterfly-type moderator was designed to achieve the world’s highest luminosity in the neutron beam by optimizing the parahydrogen fraction to more than 99.5%. In the energy region essential for cold neutron production below 14.5 meV, the total neutron cross section of parahydrogen is approximately 2.5 orders of magnitude lower than that of orthohydrogen. Consequently, even a small percentage of orthohydrogen significantly impacts neutron scattering characteristics. At ESS, the cryogenic moderator system (CMS), which supplies subcooled liquid hydrogen (LH2) at a temperature of 17.5 K and a pressure of 1.0 MPa to each moderator, incorporates an ortho-to-parahydrogen catalyst, primarily composed of hydrous ferric oxide, commercially known as IONEX® Type OP to ensure a parahydrogen fraction above 99.5%. Catalyst activation of the hydrous ferric oxide is an essential process before its use. Authors clarified that the catalyst’s conversion performance was improved with increasing the activation temperature up to 160℃, due to the removal of water. However, at the activation temperature of 230℃, which was higher than 160℃, the catalyst performance deteriorated to a level comparable to that observed at 130℃. The results indicated that an activation temperature of 160℃ was optimal for achieving the maximum conversion performance. However, the activated catalyst may be inadvertently exposed to air with moisture entering the CMS as a result of mishandling during maintenance activities, for example, during equipment replacement or vacuum pumping when an unexpected leak is present, which potentially leads to degradation of its performance. In this study, the catalyst activated at 160℃ was intentionally exposed to air with moisture. The ortho-to-parahydrogen ratios were measured by flowing normal hydrogen through the air-exposed catalyst immersed in liquid nitrogen, using Raman spectroscopy. Based on these measurements, the effect of air exposure on the degradation of catalyst’s conversion efficiency was evaluated.

The European Spallation Source ERIC (ESS) will provide long-pulsed cold and thermal neutron fluxes with very high brightness to the research community. Spallation neutrons are produced by a linear proton accelerator with an ultimate average beam power of 5 MW and are subsequently moderated to cold and thermal energies by the moderators. In the initial configuration, ESS will install two hydrogen moderators above the target wheel, with the nuclear heating estimated to be 6.7 kW. The ESS cryogenic moderator system (CMS) circulates subcooled liquid hydrogen at a temperature of 17 K and a pressure of 1 MPa, with a total flow rate of 0.5 kg/s, to remove the nuclear heating at the moderators. The heat load is efficiently removed through a plate-fine type He-H2 heat exchanger located in the CMS cold box by a large-scale 20 K helium refrigeration system, the Target Moderator Cryoplant (TMCP), with the cooling capacity of 30.3 kW at 15 K. High-pressure helium streams at a temperature of 16 K are transported from the TMCP cold box to the CMS cold box via a 300 m-vacuum insulated cryogenic helium transfer line (CTL). A valve box installed into the TMCP and positioned adjacent to the CMS cold box regulates the helium feed flow rate to adjust the cooling capacity required to compensate for dynamic heat load variation, when the proton beams are injected or tripped. In addition, the helium return temperature to the TMCP cold box is controlled at 21 K by mixing ambient-temperature helium, thereby preventing thermal disturbance to two parallel turbines and avoiding adverse effects on the helium supply temperature. In this study, a simulation model of the active cooling-power adjustment performed in the TMCP valve box and the heat exchanger in the CMS cold box was developed to optimize operating parameters of the thermal-compensation approach. The validity of the model was demonstrated through comparison with experimental results obtained during the CMS commissioning with helium under identical operating conditions.

Liquid hydrogen is often stored in spherical tanks to reduce thermal loss and improve structural integrity. However, they are susceptible to complex sloshing phenomena even under low-amplitude external excitations. In this study, the sloshing dynamics of liquid hydrogen in a partially filled spherical tank has been investigated, with particular emphasis on the emergence of weakly nonlinear and rotational sloshing flow behaviour. We used numerical simulations based on a multiphase computational fluid dynamics framework to capture the coupled liquid-vapour motion under transient lateral excitation. The excitation conditions remained below the threshold of violent wave breaking, allowing controlled examination of the intrinsic nonlinear system response. The bulk liquid motion was characterised using global flow measures, enabling identification of transitions from predominantly planar oscillations to rotary sloshing modes. The results from the simulations demonstrate that rotational motion can emerge naturally through nonlinear coupling between orthogonal fluid responses, even when the imposed excitation remains small. This behaviour results in sustained internal motion and coupled hydrodynamic force components that persist beyond the period of external forcing. These findings indicate that sloshing behaviour in spherical liquid hydrogen tanks cannot be adequately described using purely linear or planar assumptions. Consideration of weakly nonlinear and rotary sloshing dynamics is therefore essential for accurate prediction of internal fluid motion and hydrodynamic loading. The outcomes of this work provide guidance for the improved analysis and design of cryogenic liquid hydrogen storage systems operating under dynamic conditions relevant to maritime, aerospace, and terrestrial transport applications.

A wide-range operating condition ortho-para hydrogen catalyst conversion performance testing platform has been developed in this study. A G-M cryocooler is used to provide cooling capacity, and the conversion temperature and hydrogen flow rate are coupled and regulated through temperature controller and flow controller. The testing platform can experimentally analyze the conversion performance of ortho-para hydrogen catalysts under different flow conditions in the temperature range from liquid hydrogen to liquid nitrogen. In addition, a sapphire of appropriate geometric dimensions is installed between the cold head of the cryocooler and the reactor. By taking advantage of its thermal conductivity, high-temperature activation and low-temperature reaction requirements of the catalyst can be achieved without disassembly, which increases the convenience of experimental operation.

In recent years, the utilization of hydrogen as a clean energy carrier has been actively promoted, and liquid hydrogen is advantageous for its transportation and storage due to its density being approximately 800 times higher than that of gaseous hydrogen. Accurate control of the liquid level is essential for the transportation and storage of liquid hydrogen; however, liquid-level sensors for liquid hydrogen are limited in availability on the market. We have therefore been developing a superconducting liquid hydrogen level sensor using MgB₂ wires that achieves high accuracy and fast response. Superconducting liquid-level sensors require heating by a heater to realize high measurement accuracy, but this heating leads to boil-off of liquid hydrogen, making the reduction of heater input power a key challenge. In this study, MgB₂ wires with various diameters were fabricated and their characteristics were evaluated with the aim of reducing the required heater input power by wire diameter reduction. The effects of wire diameter reduction on the superconducting critical temperature (T c ) and critical current density (J c ) were investigated.

Large-scale liquid hydrogen (LH₂) cargo containment requires thin metallic barriers that can accommodate restrained in-plane deformation while maintaining integrity under cyclic loading and cryogenic temperature excursions. This study reports a room-temperature experimental validation of standardized corrugated 316L stainless-steel membrane panels, focusing on the deformation-accommodation function of corrugation. Under quasi-static tensile loading, full-field digital image correlation (DIC) was employed to quantify global strain evolution and spatial strain partitioning. The measured strain fields show that the imposed deformation is preferentially accommodated by the corrugation features, while nominally planar areas remain at comparatively lower strain, consistent with a geometry-driven compliance mechanism that reduces local strain demand under displacement-controlled conditions. Complementary fatigue tests were performed to examine cyclic durability, with in situ acoustic emission (AE) monitoring to track damage-related activity during cycling. Within the investigated loading protocol, the specimens sustained cyclic deformation without macroscopic damage, and AE responses were consistent with stable damage evolution. In addition, a small-scale demonstrator was subjected to several liquid-nitrogen (LN₂) filling cycles as a preliminary integrity check against cryogenic thermal excursions; post-test inspection revealed no visible damage to the membrane structure. Although mechanical testing at LH₂ temperature is beyond the scope of the present work, these combined observations provide experimental evidence supporting the corrugated membrane concept and establish a basis for subsequent cryogenic qualification.

Sloshing of cryogenic fluids during transportation affects both hydrodynamic and thermal stability because of their low viscosity and low normal boiling point ( Previous studies have examined the increase in boil-off gas (BOG) rate under open-vent conditions during sloshing. They also reported a pressure drop caused by condensation at the vapour–liquid interface. This occurs because sloshing mixes the stratified liquid near the interface with the colder, subcooled liquid at the bottom of the tank. As a result, the interface temperature decreases. This effect has been observed in closed containers where thermal stratification exists in both the liquid and vapour columns before sloshing begins. In the present study, we experimentally compare non-homogeneous self-pressurization under stationary conditions, caused by external heat ingress, with the pressure evolution during sloshing. The sloshing experiments are conducted for a thermally homogeneous liquid column, with the ullage space initially at atmospheric pressure, at excitation frequencies of 0.5 Hz, 1.0 Hz, and 1.5 Hz. Liquid nitrogen is used as the working fluid in a 50-liter upright cylindrical cryogenic tank at a 50% fill level. Ten temperature sensors are mounted along the tank axis to measure thermal stratification and its evolution during sloshing. Additional experiments are performed with water in a transparent tank of the same diameter and fill level to visualize the free-surface motion. It is observed that sloshing in a homogeneous liquid column leads to pressurization. The pressurization rate increases with an increase in the external excitation frequency. Near the first asymmetric natural free-surface frequency at 1.5 Hz, a relatively high pressurization rate is observed. This occurs due to the transition of free-surface motion from a planar wave to a swirl wave. At the onset of sloshing, the vapour space begins to cool, which tends to reduce the pressure. However, viscous dissipation of the liquid kinetic energy at the fluctuating interface generates heat. This heat is available for evaporation and results in net pressurization. Near the first asymmetric natural frequency at 1.5 Hz, a larger mass of liquid moves relative to the tank and forms a swirl motion. This leads to greater dissipation of kinetic energy into heat. As a result, a higher pressurisation rate is observed at 1.5 Hz compared to the stationary case (0.0 Hz) and the 0.5 Hz and 1.0 Hz excitation frequencies. These results provide mechanistic insight relevant to the design of cryogenic tanks for sea and road transportation of cryogens.

Hydrogen is one of the most discussed alternative fuels for decarbonizing the maritime sector. It´s conversion to energy produces no carbon dioxide, offering the potential of zero-emission ship operation. The full potential of such decarbonization is reached when hydrogen is produced via electrolyses with renewable electricity, known as e- or green hydrogen. Among the available storage technologies, storing hydrogen in liquid form at cryogenic conditions with temperatures of -253 °C in dedicated cryogenic tanks is particularly attractive. This method offers an increased volumetric storage density, enabling more energy to be stored on board and extending the operational range. Hydrogen fuel cells are designed for clean energy production on board ships, offering high electrical efficiency, quiet operation and reduced maintenance. In maritime applications, a Proton Exchange Membrane (PEMFC) fuelled by hydrogen requires a gaseous hydrogen flow at a conditioned pressure and temperature at the inlet. Therefore, an evaporation and conditioning unit is required to bring hydrogen from a liquid to a gaseous state using adequate heat exchangers and thermal energy sources from seawater or onboard heat recovery systems. The resulting gaseous hydrogen is brought to the suitable temperature and pressure to meet the inlet requirement using an electric heater and pressure regulators. This paper presents a simulation model of a liquid hydrogen storage and evaporation system designed for maritime applications. The system is designed to be used on the DLR research platform, which is dedicated to test alternative fuels in real conditions. This work demonstrates the handling and operation of a liquid hydrogen system onboard a ship to power a fuel-cell system by studying the evolution of the hydrogen mass flow rate in a storage tank over time during tank filling as well as during the ship’s operation. This work also covers the optimization of aspects including safety, efficiency and boil-off. The Simulation work is carried out using EcosimPro, a simulation tool capable of modelling l simple and complex physical processes that can be represented in terms of differential algebraic equations or ordinary differential equations and discrete event simulation.

At the European Spallation Source (ESS) ERIC, spallation neutrons are moderated using a combination of a hydrogen moderator and a light-water premoderator, producing a cold neutron beam. The nuclear heating in this two-moderator configuration is estimated to be 6.7 kW at a proton beam power of 5 MW. The cryogenic moderator system (CMS) is designed to supply subcooled liquid hydrogen with a temperature of 17.5 K and a parahydrogen fraction of greater than 99.5% to the moderators. When 5 MW proton beams are injected, a stepwise heat load is instantaneously applied to the hydrogen moderators, resulting in a 1.76 K increase in hydrogen temperature. This temperature fluctuation propagates downstream at the flow velocity. The resulting temperature rise and its propagation can lead to a corresponding pressure increase, because the CMS forms a closed loop. To mitigate these pressure fluctuations, a pressure control buffer tank (PCB) with a diameter of 0.3 m and a volume of 0.072 m3 is equipped with four band heater units mounted on the tank wall from the bottom to the mid-height. Copper wool was introduced to enhance thermal contact between the band heaters and the PCB wall, particularly under vacuum conditions, where uneven or insufficient contact may occur. The heaters have a function to increase a pressure by evaporating liquid hydrogen. In addition, a control valve installed on the top of the PCB tank reduces the pressure by recondensing released hydrogen gas and returning it to the suction side of the circulation pumps through a small secondary heat exchanger. The liquid level in the PCB tank is monitored using a differential pressure transmitter and six silicon diode temperature sensors located at volumes of 2.75, 8.33, 15.3, 20.8, 26.3, and 31.1 liters. In this study, performance tests of the heaters were conducted to optimize operating conditions. The heater temperatures increased proportionally with the applied heat load, but deviated from linearity above a threshold due to increased thermal resistance from band heater expansion. The tests confirmed that the required heat load for each heater remained below the degradation threshold. Furthermore, liquid levels measured using a differential pressure transmitter closely matched the hydrostatic pressure head estimated from temperature variations under static conditions. Under liquid hydrogen circulation conditions, however, the influence of localized pressure rise near the branch pipe connected to the differential transmitter was observed. Under nominal operating conditions, the combined operation of the band heaters and the release control valve successfully regulated the system pressure at the desired setpoint.

The environmental impact of aviation and mobility needs to be reduced. To obtain this, liquid hydrogen has been identified as promising energy carrier. By using it directly in a fuel cell in combination with an electric motor, potentially zero-emission can be reached. In the Netherlands, Cryoworld plays a significant role as liquid hydrogen knowledge partner for initiatives that investigate the use of liquid hydrogen for aviation and mobility. As such, Cryoworld is involved in the development of fuel tanks, components for ground-based liquid hydrogen infrastructures and other products for storage and safe handling. This paper will present the aluminium fuel tanks developed for a drone, a hydrogen range extender and a 1-seater aircraft and a stainless steel fuel tank for heavy duty transport. The design and manufacturing challenges of the fuel tanks will be discussed as well as their performances. Further, an overview will be given on the development of ground-based infrastructure that is supplied to research centres, consisting of refuelling stations, vent stacks and storage dewars. Cryoworld further has started the development of a lab-scale hydrogen liquefier platform to fulfil the growing demand for small quantities of liquid hydrogen available at any time for testing of hydrogen equipment and technologies. The platform aims to provide hydrogen liquefiers with a capacity in the range of 2 to 15 kg/day. A demonstrator system is designed and manufactured in which the liquefaction is achieved by two cryocoolers and liquid nitrogen precooling. The demonstrator aims for a liquefaction capacity of 9 kg/day. This paper ends with discussing the design and manufacturing of the demonstrator system and presenting the first test results.

The development of fuel cell vehicles requires corresponding infrastructure. There are two different types of refueling stations, i.e., liquid hydrogen storage and gaseous hydrogen storage. Liquid hydrogen refueling stations offer the advantage of low refueling energy consumption, which is only 10–20% of that of gaseous hydrogen refueling stations. Due to the cold energy waste during regasification of LH 2 and high specific energy consumption during liquefaction, the development of conventional liquid hydrogen refueling stations is limited. This study proposes a liquid hydrogen supply system integrated with cold energy recovery from liquid hydrogen regasification. A nitrogen circulation is integrated into the LH 2 regasification system to recover cold energy. The cold energy is utilized to precool hydrogen to 84.45 K. In the proposed system, the hydrogen is further cooled to 20.5 K with a helium refrigeration cycle. This proposed system also incorporates an ejector to achieve hydrogen liquefaction and boil-off gas treatment. The specific energy consumption for liquefaction of this system is 8.487 kWh/kgLH₂, among which 10.1% is attributed to liquid hydrogen pressurization. The proposed system enables low-cost liquid hydrogen pressurization, utilization of cold energy during liquid hydrogen gasification, as well as self-supply of liquid hydrogen for liquid hydrogen refueling stations. It is worth noting that the cold energy recovered from the regasification of one kilogram LH₂ enables the precooling of approximately 1.23 kg of hydrogen. Therefore, besides high-pressure gaseous hydrogen refueling, the system can also undertake a portion of liquid hydrogen refueling function to meet the requirements of large-scale hydrogen fuel cell electric vehicles with different hydrogen storage schemes.

This paper presents the design, fabrication, and experimental validation of a novel 50 L/day (LPD) small-scale hydrogen liquefier developed. This system adopts an innovative low-pressure open-cycle architecture integrated with full-temperature-range continuous ortho–para hydrogen conversion. Experimental results demonstrate a liquid hydrogen production rate exceeding 60 L/day, para-hydrogen concentration ≥99%. The system exhibits high stability, modularity, and rapid deployability—making it ideally suited for on-site applications such as university laboratories, UAV refueling stations, and remote scientific expeditions. This work advances compact, energy-efficient hydrogen liquefaction technology and supports the scalable development of low-carbon hydrogen infrastructure.

Liquid sloshing in cryogenic liquid storage tanks under external excitation may induce severe structural safety problems. In this study, the dynamic stress responses of spherical tanks with a diameter of 500 mm were systematically investigated under the combined conditions of peak accelerations (0.1g, 0.2g, and 0.3g) and liquid filling rates ranging from 10% to 90%. Meanwhile, the stress types, stress extremums, stress concentration areas, and dynamic stability were monitored and analyzed. The results show that the stress concentration areas migrate significantly with the variation of liquid filling rate: for low filling rates, stress concentrates in the middle-lower or middle-upper parts of the tank; for medium filling rates, stress concentrates in the narrow areas of the middle or middle-upper parts; for high filling rates, stress concentrates in the high liquid level area. When the peak acceleration is 0.3g and the liquid filling rate is 30%, the maximum compressive stress reaches 29.46 MPa at the 90% liquid level of the tank, with the direction along the circumferential direction of the tank. Under the same acceleration level, when the liquid filling rate is 10%, the maximum tensile stress reaches 6.06 MPa at the 90% liquid level of the tank, with the direction along the circumferential direction of the tank. Alternating tension and compression phenomena occur under low filling rate conditions, and dynamic stress fluctuations are observed under certain high acceleration conditions, which increase the risk of fatigue failure. Notably, no significant stress changes are detected in the specific filling rate range of 30%, 50%, and 60% under the acceleration of 0.1g, indicating a relatively safe state.

At the Japan Proton Accelerator Research Complex (J-PARC), high-energy neutrons in the MeV range, produced by a spallation reaction between 3-GeV protons and a mercury target, are moderated to cold neutrons suitable for neutron scattering experiments, by passing through three types of hydrogen moderators: a coupled moderator (CM) for high intensity, a poisoned moderator (PM) for sharp pulse shape, and a decoupled moderator (DM) that provides a balance between intensity and pulse sharpness. The cryogenic hydrogen system (CMS) was designed to supply cryogenic hydrogen with a para-hydrogen concentration greater than 99 % at a pressure of 1.5 MPa, which is supercritical pressure, and temperature of 18 K to the three hydrogne moderators where the nuclear heating is estimated to be 3.8 kW for 1-MW proton beam operation. Based on the moderator requirement, the circulation flow rate was determined to be 0.162 kg/s, which is providedby two hydrogen pumps in parallel, to maintain average temperature rise across each moderator. The CMS is cooled by a 20 K-helium refrigerator with a refrigerator power of 6.45 kW at 15.6 K, which is equipped with an expansion turbine and a liquid-nitrogen precooling system. The feed helium temperature is regulated by an electrical heater located at the final stage of heat exchangers. The CMS forms a closed loop filled with imcompressible fluid. A slight temperature rise caused by the nuclear heating results in a significat pressure increase. A heater with a capacity of 5 kW compenstates for dynamic heat loads to avoid thermal disturbance propageted to the helium refrigerator, while an accumulator with bellows filled with compressible helium passively adsorbs pressure fluctuations. For hydrogen safety, the low-temperature hydrogen region is enclosed not only by a vacuum envelope but also with an additional enclosure filled with helium. The region containing hydrogen at ambient temperature is covered with nitrongen-filled housing, since freezing is not a concern in this region. Furthremore, the vacuum envelope is monitored by a helium leak detector and mass spectrometer are installed in the vacuum envelop to identify leaks of hydrogen from the process line or helium from the barrior enclosure. All hydrogen in the CMS is discharged to the outside via a dedicated vent line when the CMS is warmed up. All the CMS operation modes from cooldown to warm-up are performed automatically. When an off-normal event is detected, the CMS is automatically shut down. The CMS was installed from August 2006 to March 2007. Commissioning has been completed in March 2008, and the J-PARC achieved first beam on Target in May 2008. Proton beam powers was gradually increased and reached the goal of 1 MW in 2018. The J-PARC CMS has demonstarated stable operation for over 10 years, despite experiencing several issues during the initial stages. This paper presents the current operational status of the J-PARC CMS and the operational experiences gained in achieving stable operation.

Large-scale energy storage technologies play a critical role in facilitating the integration of renewable energy sources and ensuring the stable operation of power grids. As a promising large-scale and long-term energy storage technology, Carnot batteries store and release energy through an electricity-heat-electricity conversion process. Free from geographical constraints and capable of coupling with various energy forms, Carnot batteries exhibit broad application potential. However, the relatively low round-trip efficiency (RTE) remains a major barrier to large-scale deployment. In the liquefied natural gas (LNG) industry, a substantial amount of cold energy is released during the regasification process at LNG receiving terminals, which is often inadequately utilized, leading to significant energy losses. The synergistic integration of these two systems offers the potential to simultaneously enhance energy storage performance and improve the energy utilization efficiency of LNG infrastructure. Consequently, a Carnot battery system integrated with LNG regasification is proposed in this study. The system utilizes the LNG regasification process as a low-temperature heat sink, thereby expanding the operating temperature range during the discharging process. A thermodynamic model of the integrated system is established, and thermodynamic analysis is conducted to investigate the effects of key parameters on system performance. The results demonstrate that the utilization of LNG cold energy can significantly improve the performance of Carnot batteries and expand their potential application scenarios. The findings provide valuable insights into the application of thermophysical energy storage in low-temperature domains.

The low density of hydrogen at ambient temperature and the high technical difficulty associated with hydrogen liquefaction have constrained the large-scale deployment and application of hydrogen energy. Cryo-compressed hydrogen (CcH 2 ), characterized by high volumetric storage density and low intrinsic energy consumption, has been regarded as a promising and emerging hydrogen storage approach. The cooling load involved in the CcH 2 cooling-filling process is composed of both the sensible heat of hydrogen and the compression heat generated during the hydrogen filling process. The hydrogen sensible-heat load presents a distributed-load characteristic, whereas the compression heat generated during filling is a time-dependent dynamic load; if the latter is not removed in a timely manner, a significant temperature rise (approximately 36 K) may occur, resulting in a reduction in hydrogen storage density. Existing studies mainly consider the hydrogen sensible heat, which is insufficient to capture the realistic and complex thermal-load characteristics of the CcH 2 cooling-filling process. In this study, the CcH 2 cooling-filling process is simulated and analyzed under typical operating conditions of 85 K and 50 MPa. A Claude cycle using helium as the working fluid is employed to generate low-temperature helium, which is utilized for both cooling high-pressure hydrogen and removing the compression heat generated during the hydrogen filling process. The proposed process features relatively low manufacturing requirements for heat exchangers, while achieving a high hydrogen volumetric storage density of 69.7 kg/m 3 and a low intrinsic energy consumption of approximately 6.2 kWh/kg. The results provide theoretical support for the engineering implementation of CcH 2 production and are of significance for promoting the large-scale application of hydrogen energy.

The shipping industry is vital to global trade, transporting 80% of goods while remaining the most energy-efficient mode of transport. However, it contributes around 2.6 % of global greenhouse gas (GHG) emissions. As international trade expands and vessels grow in size, emissions are expected to rise, with maritime CO₂ projected to increase by 90–130 % by 2050 under business-as-usual scenarios (IMO, 2021; EMSA, 2025). The maritime sector must lower greenhouse gas emissions to comply with both current and upcoming regulations. Transitioning to zero- and low- emission fuels is therefore a key focus. The adoption of alternative fuels—including LNG, LPG, methanol, ammonia, and hydrogen—is steadily increasing in maritime transport (DNV, 2025; SEALNG, 2024). Currently, 1,369 LNG dual-fuel vessels are in operation or on order, representing approximately one-third of the new-build orderbook, indicating significant investment and growing fleet share (DNV, 2025; SEALNG, 2024). As of December 2025, 144 ammonia-fueled vessels and 302 ammonia-ready vessels have been ordered or announced, with 84 ammonia-ready vessels already operational (Ammonia Energy Association, 2025). The transition to liquid fuels presents significant technical challenges. Both LNG and ammonia require specialized fuel handling systems capable of managing cryogenic/low-temperature fluids. Fuel pumps, heat exchangers, and associated piping must reliably operate at extreme temperatures—approximately –162 °C for LNG and –33 °C for refrigerated ammonia—while minimizing energy losses and maintaining high operational reliability. A central challenge in liquid fuel systems is twophase flow—the coexistence of liquid and vapor phases within a pump or feed line. Twophase flow can lead to performance degradation, flow instability, vibration, cavitation, and reduced controllability, all of which are highly undesirable for safetycritical marine systems. As such, contemporary pump and fuel system designs aim to avoid twophase flow wherever possible, particularly in booster and main fuel pumps feeding dualfuel engines, by ensuring superheated liquid conditions, adequate subcooling, and robust thermal management throughout the system. Thanks to years of development and operational experience, LNG fuel pump systems have reached a proven level of reliability in commercial service. Successful deployments have demonstrated that cryogenic liquid pumps can operate continuously under realistic vessel load profiles and environmental conditions, meeting classification society rules and industry safety standards. These achieved outcomes provide a valuable foundation for extending liquid fuel handling technologies to nextgeneration fuels. Ammonia presents distinct technical and safety challenges compared to LNG. Its toxicity and corrosive properties require careful attention to material selection, seal design, lubrication strategy, and fuel system safety architecture. Furthermore, the industry must address ammonia’s higher vapor pressure and its interaction with refrigerated liquid conditions, which can complicate pump and piping design. These factors underscore the need for targeted research and innovation to qualify maritime pump systems capable of handling ammonia safely and efficiently. This contribution presents ongoing research and development efforts aimed at addressing these challenges. We discuss key design strategies for cryogenic liquid pumps that minimize twophase flow risk, material and sealing solutions compatible with ammonia environments, and systemlevel considerations for integrating these pumps into marine fuel supply chains. By building on the established experience of LNG fuel systems and extending it to future fuel scenarios, the maritime industry can accelerate progress toward compliance with IMO regulations and the broader goal of sustainable, lowcarbon global shipping. IMO, 2021 Fourth IMO GHG Study 2020: Highlights. https://www.imo.org/en/MediaCentre/Pages/WhatsNew-1596.aspx DNV, 2025 Energy Transition Outlook 2025 – Maritime Forecast to 2050. DNV. EMSA, 2025 European Maritime Transport Environmental Report 2025: Energy transition in the EU maritime transport sector. Publications Office of the European Union. SEA‑LNG, 2024 Accelerating LNG adoption in shipping: Market update and projections. https://sea-lng.org/ Ammonia Energy Association, 2025 LEAD: Ammoniafueled vessels. Ammonia Energy Association. https://ammoniaenergy.org/lead/vessels/

Holding time is a key parameter that determines the thermal performance and operational feasibility of a cryogenic storage tank. It is defined by the duration that is required for the internal pressure of a tank to increase from an initial equilibrium state to the set pressure of a pressure relief device (PRD). This pressure rise occurs because of unavoidable heat ingress from the surroundings. In practical applications, engineers often estimate holding time via a simplified approach based on an energy balance assumption, as adopted in ISO 21014. Although this approach is computationally efficient and widely accepted, it hardly accounts for spatially resolved thermal and fluid dynamic phenomena inside the tank. In this study, we evaluate the holding time of a cryogenic tank for liquid hydrogen using two different modeling approaches under an identical heat ingress condition. The first approach is a simplified energy balance model. The second approach is a three-dimensional (3-D) computational fluid dynamics (CFD) model. The CFD model incorporates the Volume of Fluid (VOF) method and a phase change model to simulate evaporation and condensation processes. This study examines the applicability and limitations of the simplified energy balance model through a comparison with a spatially resolved 3-D CFD model. First, we conduct a 3-D heat transfer analysis of the cryogenic tank to evaluate the heat ingress into the tank. It considers heat conduction through the inner vessel, outer vessel, support structures, and insulation layers. Radiative heat transfer across the vacuum region between the inner and outer vessels is also considered. The integrated heat ingress over the tank’ outer walls is used as a consistent input for both models. As mentioned earlier, holding time is generally defined as the time required for the tank pressure to reach the set pressure of the PRD. However, the holding time may also be governed by the time at which the filling ratio reaches the prescribed storage limit. According to ISO/DIS 13985, the holding time measurement should commence at an initial filling ratio of at least 80%. Furthermore, ISO 21014 defines the reference quantity as 98% of the tank volume below the inlet of the PRD. The simplified energy balance model estimates holding time from the increase in the internal energy of the stored cryogenic fluid under the evaluated heat ingress. It assumes mass conservation and thermodynamic saturation between the liquid and vapor phases throughout the pressurization process. Therefore, we use saturated-state thermophysical properties of the cryogenic fluid, which are represented by fitted functions of pressure. If the heat ingress remains constant over time, the holding time can be evaluated as the ratio of the change in internal energy to the heat ingress. The 3-D CFD model resolves the internal thermal-fluid behavior of the cryogenic fluid within the tank. Through this approach, we can observe internal flow structures, thermal stratification and localized phase change effects. The CFD model does not fully consider the tank structure, such as the insulation system to reduce the computational cost. Instead, we impose the heat ingress obtained from the 3-D heat transfer analysis as a heat flux boundary condition on the tank’s inner walls. This approach ensures that the CFD analysis is performed under the same heat ingress condition as the simplified energy balance model. The transient analysis captures the pressure rise and saturation-temperature increase induced by evaporation, along with liquid expansion, which can be used to estimate the holding time of the cryogenic tank. The comparison focuses on pressurization behavior and the physical mechanisms that are responsible for discrepancies between the simplified energy balance prediction and spatially resolved 3-D simulation. In addition, it clarifies the applicability and limitations of simplified energy balance models in the initial design and assessment of cryogenic storage systems. * This work was supported by the Korea Institute of Energy Technology Evaluation and Planning(KETEP) and the Ministry of Climate, Energy & Environment(MCEE) of the Republic of Korea (No. RS-2025-16063865).

Natural gas power generation, characterized by flexible startup and rapid response, is often co-developed with renewable energy to ensure stable power output. However, even within this renewable-natural gas hybrid mode, scenarios persist where renewable generation exceeds electricity demand. To address this imbalance, this paper proposes a Liquefied Natural Gas Energy Storage (LNGES) system integrated directly into the natural gas power plant. The system utilizes the on-site natural gas infrastructure as the storage medium, liquefying natural gas during off-peak periods and expanding it for power generation during peak demand. Current research on cryogenic energy storage predominantly focuses on Liquid Air Energy Storage (LAES), which typically relies on gas expansion refrigeration cycles. However, these cycles are thermodynamically less efficient compared to the mature phase-change refrigeration technologies established in the LNG industry. To bridge this gap, this study proposes a novel LNGES configuration based on single mixed refrigerant (SMR) liquefaction process and conducts a comparative thermodynamic analysis against a baseline LAES system. Both systems are modeled and simulated in Aspen HYSYS. To ensure a unified evaluation criterion, the optimization objective for both the SMR-LNGES process and the baseline LAES process is defined as the maximization of Round-Trip Efficiency (RTE). Specifically, for the SMR-LNGES system, a Genetic Algorithm is employed to optimize the molar composition of the mixed refrigerant (nitrogen, methane, ethane, propane, and i-butane) and operating pressures to achieve this peak efficiency. To elucidate the underlying thermodynamic mechanisms, the study performs a comparative Heat Transfer Analysis using Composite Curves, contrasting the superior temperature glide matching of the SMR cycle against the sensible heat transfer profile of the LAES baseline. This is complemented by a detailed comparative Exergy Analysis, which quantifies the irreversibility distribution in both systems. Simulation results reveal the fundamental thermodynamic superiority of the SMR approach over the LAES baseline. Under the optimized conditions for maximum RTE, the SMR-LNGES system achieves a specific liquefaction work of 0.365 kWh/Nm³, representing a 25.6% reduction compared to the LAES baseline (0.491 kWh/Nm³). The comparative T-Q analysis demonstrates that the mixed refrigerant successfully minimizes the weighted mean temperature difference, whereas the LAES baseline suffers from large temperature gaps inherent to gas expansion cycles. Consequently, the SMR-LNGES configuration achieves a projected RTE of 46.82%, outperforming the LAES baseline (41.46%). In conclusion, this study validates that for hybrid renewable and natural gas power plants, the proposed SMR-LNGES concept offers a highly synergistic solution. It not only solves the renewable curtailment problem but also significantly enhances the energy efficiency of the storage process by leveraging industrial liquefaction processes. Keywords: Liquefied natural gas energy storage (LNGES), Liquefied air energy storage (LAES), Single mixed refrigerant process, Round-trip efficiency, Exergy Analysis

Antarctic environmental simulation facilities require stable, reliable, and energy-efficient cooling systems capable of long-term operation under extremely low-temperature conditions. Such facilities are widely used for the performance testing of cryogenic equipment, advanced materials, and energy systems exposed to harsh polar environments. However, conventional refrigeration technologies often suffer from high energy consumption, complex multistage compression, and limited flexibility in providing multiple temperature levels simultaneously. Liquefied natural gas (LNG), which releases a large amount of high-grade cryogenic cold energy during regasification, offers a promising alternative cooling source when its cold energy is systematically recovered and cascaded. In this study, a cascade LNG cold energy utilization system is proposed and thermodynamically analyzed to supply cooling at three characteristic temperature levels, namely -80 ℃, -50 ℃, and -10 ℃. The -80 ℃ deep-cryogenic stage is designed for Antarctic environmental simulation chambers, the -50 ℃ stage is intended for intermediate low-temperature applications such as freezer rooms (ultra-low-temperature cold storage) and data center cooling, and the -10 ℃ stage is used for air-conditioning and conventional cold-storage. The cascade configuration allows progressive utilization of LNG cold energy with decreasing temperature grade, improving overall thermodynamic efficiency and system flexibility. Different heat-transfer fluids (HTFs) are selected for each temperature zone according to operating temperature, safety requirements, and thermophysical properties. In the near-ambient temperature zone (-10 ℃), a 30 wt% ethylene glycol–water solution is adopted as the HTF due to its good thermal stability, low freezing point, and widespread industrial application. In the intermediate low-temperature zone (-50 ℃), multiple HTF candidates are considered, including a 70 wt% ethylene glycol–water solution, R410A, and HFO-1243zf. Considering safety and operational risks, flammable and toxic working fluids such as ammonia and methanol are deliberately excluded from the proposed scheme. The focus of this work is placed on the -80 ℃ deep-cryogenic loop, where HTF selection plays a critical role in determining system performance. Several HTFs are evaluated for this temperature level, including R22, R134a, R23, R245fa, low-temperature silicone oil Syltherm XLT, and the fluorinated fluid 3M HFE-7000. Mixed refrigerant formulations are also investigated as flexible HTF candidates for the -80 ℃ loop. Several combinations composed of conventional refrigerants (e.g., R22/R134a, R14/R23, and similar systems) are systematically screened and designed based on key thermophysical constraints, including freezing point, viscosity, specific heat capacity, and heat-transfer characteristics. This strategy aims to enhance temperature matching with the LNG cold source while maintaining acceptable hydraulic performance and operational robustness under deep-cryogenic conditions. Steady-state process simulations are conducted to quantify the influence of HTF selection on key thermodynamic indicators. The overall heat-transfer coefficient–area product (UA), circulation mass flow rate, pump power consumption, and exergy destruction in the -80 ℃ heat exchanger are selected as dependent variables, while the HTF type is treated as the independent variable. This approach enables a systematic evaluation of heat-transfer performance, hydraulic characteristics, and thermodynamic irreversibility associated with different HTFs. Results show refrigerant-based HTFs generally outperform single-phase organic fluids at deep-cryogenic temperatures. R22, R134a, R245fa and well-tuned refrigerant mixtures require moderate UA and balanced circulation flow, yielding relatively low pump power and exergy destruction. R23 demands higher mass flow due to lower specific heat but still attains acceptable pump power and exergy loss. In contrast, Syltherm XLT and HFE-7000 require substantially higher UA and pump power because of elevated viscosity and lower heat-transfer coefficients at -80 ℃. In particular, the introduction of mixed-refrigerant HTFs provides an effective design degree of freedom, enabling tailored thermophysical properties through component selection and composition adjustment, which is especially advantageous for deep-cryogenic LNG cold energy recovery. Overall, the proposed cascade LNG cold energy utilization system effectively satisfies the cooling demands of Antarctic environmental simulation, intermediate low-temperature applications such as freezer rooms (ultra-low-temperature cold storage) and data center cooling, as well as air-conditioning applications across three temperature levels. The comparative thermodynamic analysis provides clear guidance for HTF selection in deep-cryogenic LNG cold energy recovery systems and establishes a solid foundation for further optimization, system integration, and experimental validation.

TOP LOAD CRYOGENIC LARGE SIZE BALL VALVES WITH FOCUS ON LIQUIFIED HYDROGEN Ander Gabirond , Leire Colomo1) 1) AMPO Poyam Valves, ES- 20213 Idiazabal, Gipuzkoa, Spain Angle globe valves have been traditionally used in all cryogenic systems. The energy sector is transitioning towards environmentally sustainable technological facilities. Hydrogen represents a key value chain within this sector's focus. Nevertheless, the expansion of these plants presents certain inherent techno-economic challenges. Ball valves can offer significant advantages to this emerging field by providing superior flow capacity performance, resulting in improved Kv flow coefficient values. These enhancements are particularly valuable to process engineers aiming to boost efficiency and, consequently, optimize the hydrogen liquefaction value chain. Competitiveness and process efficiency are paramount objectives for innovative solutions in large-scale systems. The main motivations of this new thinking are: - Large-sized valves require flow Kv coefficient values that render ball valve suitable. - Majority of the big Energy Players are considering the actual LNG value chain and business model for the projected LH2 supply chain with cargo vessels are the drives to design the large-scale value chain. - Low-pressure distribution for storage and transportation cargo processes conditions are at ambient temperature. - High-pressure processes demand a higher differential Temperature in the inlet at Cryogenic plant. Throught this poster paper, AMPO POYAM VALVES will present a large top load-valve with the following focus: -Vacuum jacketed top-load cryogenic ball for G/LNG and G/LH2 as well as also for L/GHe -Low heat load attributed to the innovative design and jacket design configuration. -Double-jacket concept aimed at reducing operating cost by maintaining the vacuum within pipeline. - Comparison with angle globe cryogenic designs of equivalent Kv values. A novel approach grounded in an innovative solution concept that addresses the challenges of cryogenic service conditions across the full temperature and pressure spectrum. This modern valve concept, incorporating the latest manufacturing technologies, enhances the efficiency of cryogenic processes and delivers added value to the market. Keywords: Top Load Ball Valves, Big size, Liquid Helium, Liquid Hydrogen, Low Heat Load, Low Maintenance.

Leire Colomo , Ander Gabirondo 1) 1) AMPO Poyam Valves, ES- 20213 Idiazabal, Gipuzkoa, Spain Cryogenics with gases like helium, hydrogen and sometimes also with neon, nitrogen, or air gain today more attraction as enablers for new green technologies in the energy sector as well as further industrial areas as in chemistry, semiconductor, steel and glass production etc. Cryogenic helium in all stages is used to cool superconducting devices allows efficient high energy research and fusion research. Liquefied hydrogen is a high dense energy vector and could be at the same cooling superconducting cables and power devices. Neon seems a potential candidate to enable highly efficient cryogenic processes. Subcooled liquefied nitrogen is used to cool high temperature superconductor cables and devices in the power system. The cryogenic process of liquefying and warming up air is used to store fluctuating production renewable power. The specific focus on hydrogen as an energy carrier paves the energy transition away for the current fossil-based system. The new energy system will be electric and based on renewables with hydrogen as energy carrier. However, many areas are still depending on importing green energy: a new global green hydrogen market and trade will emerge. Thus, production, storage and transport of green hydrogen will become key elements of the decarbonizing of the global energy system towards a new energy economy. The storage and transport of hydrogen can take place in various forms. Liquid hydrogen is, due to its high energy density, ambient storage pressure, high purity and not at least also due to the mature cryogenic technology available well suitable for these, over long distances or even in airplanes tanks as fuel. Following this, hydrogen liquefaction, storage and transport using cryogenics gaining increased attention in the industry worldwide. More players are getting active in the market and proposing new concepts and products. Exemplary as well we will show these developments and their consequences for an SME industrial firm, so far mainly active in the LNG field. This motivates innovations in cryogenics technology which are also expected to have positive effects for cryogenic with helium or nitrogen for cooling of superconducting devices and even for potential hybrid applications for power and liquid hydrogen transfer in one. Consequently, valve industry faces techno-economic complex challenges to answer the demands of these expanding sectors that will play an essential role in the upcoming decades. This paper describes identified techno and economic challenges for a modern cryogenic angle valve. Focus is on applications in liquified hydrogen but also considerations regarding the special requests for helium are highlighted. Some key design topics are - Thermal efficiency. - Flexibility to absorb thermal contractions in the piping connection. - Interior and exterior tightness - Valve flow capacity. - Precise flow control - Flexible actuating system with low energy consumption - Suitable for industrial serial manufacturing processes At the core of this innovation is AMPO’s electric actuation system, based on stepper motor technology with an integrated electronic fail-safe mechanism. This solution offers: · Precise, repeatable positioning for accurate flow regulation. · Low energy consumption, contributing to overall system efficiency. · Plug-and-play integration, eliminating the need for complex pneumatic infrastructure. · Enhanced safety, with electronic fail-safe functionality ensuring secure operation in case of power loss or system failure. According to the EnEffAH study, traditional pneumatic systems operate at only 6–15% efficiency, with significant energy losses in compression and distribution. AMPO’s electric solution not only overcomes these inefficiencies but also reduces CAPEX and OPEX, while improving system compactness and maintainability. This poster presents AMPO’s comprehensive approach to cryogenic valve design for liquid helium applications, addressing the full range of thermal, mechanical, and operational challenges. The result is a high-performance, electrically actuated valve that supports the future of sustainable, high-efficiency cryogenic systems. Keywords: Valves, Liquid Helium, Liquid Hydrogen, Low Heat Load, Fine Flow Control, Innovative Flex Inset, fail safe electric actuation

Principles learned from the liquefaction of natural gas, -an integrated precooling with single mixed refrigerants-, enables a meaningful use of large scale turbocompressors for hydrogen liquefaction. As a side effect of the added components for increasing the molecular weight of the hydrogen for turbo-compression, these components will also act as additional refrigerants. In the reverse Carnot cycle, their additional heat removal at higher temperatue level increases the efficiency and the economics of the hydrogen liquefaction process. Specific energy of liquefaction can be reduced to less than 7.5 kWh/kg with today's technical tools. Considering logistic costs of distribution of liquid hydrogen, costs of the molecule at the fueling station are shown to be cost competitive to conventional fuels.

Efficient purging of liquid hydrogen (LH 2 ) storage tanks is critical for mitigating the risk of flammable or explosive mixtures, and to avoid the clogging of the tank pipework with condensed air. Purging is the process of displacing oxygen (or air) from a tank before the introduction of hydrogen. This process is usually done by using an inert gas like nitrogen or helium to act as the displacer medium, or by removing the air by applying vacuum to the tank. Purging with inert gas can be done in two ways: (i) continuous sweep purge and (ii) cyclic hold purge. Sweep purge is performed by continuously flowing the inert medium through the tank until the oxygen concentration drops below the level at which explosive mixtures can form. In the hold purge, an inert gas at a pressure higher than the tank pressure is fed into the tank and held to mix with the tank's original contents. Upon mixing, the concentration of oxygen in the mixture drops. Once sufficient mixing has occurred, the mixture is vented from the tank. Because of the higher internal pressure, the contents are expelled, reducing the oxygen concentration inside the tank. This process of holding and venting is repeated several times to reduce the oxygen concentration below the desired level. Although the process of both sweep and hold purges are well known ( for example the PD CEN/TR 15281:2022), to the best of our knowledge, there are no standard guidelines on: 1. At what flow rate and for what time should the inert gas be swept through the tank to reduce the concentration of oxygen below the desired level? 2. What should be the duration of the hold step, and how many cycles are required to reduce the concentration of oxygen below the desired level? Determining the answers to these questions is challenging, as the geometry of the tank significantly influences the final concentration of oxygen in the tank. Oxygen or air can get trapped in pockets inside the tank. These pockets may be the entry to pipelines from the tank or may be safety devices like pressure relief valves fitted on the tank. At present, purge operations rely on prior experience and are executed with a conservative safety approach. In the case of a hydrogen aircraft awaiting fuelling, if a purge operation is required, the conventional approach will lead to a loss of time, which will affect the turnaround time of the aircraft. Furthermore, the conventional approach will lead to the loss of inert gas, which is a pronounced economic challenge when the inert gas used is helium. In this study, a theoretical model to predict the history of oxygen concentration in a hydrogen tank during the purge operations is presented. The model resolves the transient oxygen concentration at the tank outlet under the two purge strategies. The governing equations are based on species conservation within a well-mixed control volume. Parametric studies are performed by varying the purge times and flow rates of the inert medium to gain insights into their relationship and the efficiency of purging. The contribution of the work is its focus on defining optimal purge strategies for different tank geometries.

To examine the effect of heat treatments on the superconducting properties of MgB 2 , a series of heat-treated MgB 2 powders were prepared by the increase of the annealing temperature T an . Characterizations are studies of the magnetization M for both pure and a series of heat-treated MgB 2 powders. Both the isothermal mass magnetizations M(H) of a series of samples at different fixed temperatures and M(T) in fixed field, employing a SQUID-VSM(Vibrating Sample Magnetometer; Quantum Design), were measured. That is, the superconducting properties of heat-treated MgB 2 powders were investigated. The critical current density (J c ) was determined by applying the modified Bean model to the irreversible magnetization (DM irr (H)) data, which was derived from the magnetization M(H) loop. The evolution of superconducting properties in heat-treated MgB₂ powders was examined as a function of increasing annealing temperature. A decrease in the superconductivity of MgB₂ due to heat treatment was observed, with a specially annealed temperature at which the superconductivity suddenly began to decrease being observed. Appreciable change which accompanies degradation of superconducting properties was observed when MgB₂ was annealed above a special temperature. Additionally, the correlation between the shape of the magnetization M(H) loops and surface barrier effects under varying annealing conditions was explored. These and other results will be discussed.

Sam Dong Co., Ltd., a Korean company established in 1977, is a manufacturer of continuously transposed conductors and various insulated wires based on oxygen-free copper. Building on its extensive experience in wire production, the company has extended its activities into the fabrication and research of MgB 2 superconducting wires. Over the past decade, an integrated manufacturing process has been developed, covering superconducting precursor powder processing, wire fabrication, and cabling. Based on the developed manufacturing process, an 18-filament MgB 2 superconducting wire with a diameter of 0.83 mm has been continuously fabricated in lengths of up to 3 km, exhibiting a critical current of approximately 190 A at 20 K and 2 T. In addition, key design parameters of the MgB 2 wires, including starting materials, wire fabrication, and wire architecture, have been systematically optimized for application in a broad range of superconducting systems, such as Magnetic Resonance Imaging (MRI) and Superconducting Magnetic Energy Storage (SMES). This presentation reports the superconducting properties and performance characteristics of MgB 2 wires developed at Sam Dong.

While Ic degradation in epoxy-impregnated REBCO conductors is often attributed to thermal-expansion mismatch, additional loading sources may become decisive under magnet-relevant conditions. We investigate the coupled role of curing-induced residual stress and electromagnetic-force-assisted damage using a process-resolved laminate model validated by in situ FBG strain monitoring during encapsulation. Electrical measurements and microstructural observations support a mechanism in which curing and cool-down jointly elevate the tensile strain in the superconducting layer, facilitating crack formation; applied magnetic fields can further exacerbate performance loss through additional electromagnetic forces superposed on the pre-existing residual stress state. The results highlight the necessity of considering “cure-to-cryo” history when interpreting field-dependent degradation and when selecting impregnation materials and cure schedules for REBCO magnets.

For the first time, we reported the clear effect of tensile stress on the anisotropy of the Ic angle dependence in both the out-of-plane and in-plane directions of a commercial REBCO tape. The results showed that severe tensile stress not only causes simple Ic degradation but also alters the shape of the Ic angle dependence curve. It demonstrated the strong coupling between stress and Ic angle dependence, which proves that the Ic value of the RECBO tapes was a function of the temperature (T), applied field (B), out-of-plane angle (θ), in-plane angle (j), and stress (σ). Such a discovery is critical to both the manufacturer and magnet designer of REBCO tapes. For the manufacturer, it can help them better understand the superconducting properties of the product, which may open new investigation directions into the cross-scaling between macroscopic stress and microscopic structure. For the magnet designer, this paper can support convincing data of the coupling between stress and Ic angle dependence, which may help them to better simulate the quench process of the extremely high field magnet.

REBCO-coated conductor (CC) tapes are promising candidates for high-field applications such as fusion power plants. However, the thermal mismatch between the layers in their composite architecture, combined with the enormous temperature difference between the deposition process and the cryogenic service environment, can induce significant residual stresses. These stresses are known to significantly influence the critical current of CC tapes.In this study, a finite element model which includes all the major layers of a CC tape is established to analyze the residual stress evolution during its production and cooling process. The model incorporates the actual deposition and plating temperatures, as well as their sequences. The results show that after the cooling process, the residual stress in the Ag layer approaches its yield strength, while considerable compressive stress is generated in the REBCO layer. This stress state could strongly affect the electromechanical properties of the CC tapes.

High-temperature superconducting composite conductors consisting of REBa 2 Cu 3 O y (REBCO) tapes and low-resistivity materials such as Cu or Al have been developed for high-current devices including superconducting rotating machines and high-field magnets. However, localized heat generation near the joint between the current leads and the conductor is one of the issues. Although this heating is localized, the high thermal stability of REBCO-based composite conductors leads to slow heat propagation, which can allow hot-spot persistence and potentially result in local burnout. Therefore, understanding the current distribution near the joint is essential for mitigating heat generation. In this study, finite element analysis and current-electric field (I-E) measurements were carried out on composite conductors consisting of one or two REBCO tapes and a copper plate. Three-dimensional finite element models (FEM) were created for each conductor geometry, and their validity was verified by comparing the analysis of the simplest configuration, one REBCO tape soldered to a copper plate, with both experimental results and the analytical solution from an electrical equivalent circuit model. Subsequently, we created two conductor models consisting of two REBCO tapes and analyzed them: (1) a simple stacked conductor, in which the superconducting layers of both tapes face the copper plate, and (2) a Face-to-Face Double Stacked (FFDS) conductor, in which the superconducting layers of the two tapes face each other. Additionally, conductors identical to the conductor model were fabricated and the I-E characteristics were measured at a point on the copper plate 15 mm from the current lead end. In the simple stacked conductor, the voltage increased once the transport current exceeded the I c of a single tape, then converged toward I-E characteristics expected for two-tape conduction, showing kink features in the range of 10 -3 to 10 -2 V/m. These kink features are attributed to the joint resistance between the first and second REBCO tapes. In contrast, the FFDS conductor showed no kink behavior and exhibited linear resistive characteristics in the low electric field region. Thereafter, the non-linear voltage increase occurred near the combined I c of two REBCO tapes, and the I-E characteristics at the high electric field region matched those of the simple stacked conductor. The linear resistance observed in low fields suggests that the current flowing from the leads takes a long distance to reach the superconducting layer of the first tape, while the absence of kink features is consistent with the tape-to-tape interface without insulating layers. Detailed results, including current distribution analysis, will be discussed. This work was supported in part by the New Energy and Industrial Technology Development Organization (NEDO) and by JSPS Grants-in-Aid for Scientific Research 23K23289 and 25H00739.

Increasing the critical current of coated conductors has been widely pursued to enable broader commercialization of HTS superconducting applications. However, reducing the cost of coated conductors is also essential. SuNAM has traditionally supplied coated conductors based on the reactive co-evaporation deposition and reaction (RCE-DR) process, particularly for grid applications such as power cables and fault current limiters. To further improve performance under high magnetic fields, SuNAM has also established pulsed laser deposition (PLD) capabilities. Recently, SuNAM has been optimizing its PLD process using liquid-assisted processing (LAP) to improve both growth rate and superconducting performance. Coated conductors fabricated under various LAP-PLD conditions were characterized in terms of transport critical current and structural properties. This presentation discusses the current status of SuNAM’s PLD development to enhance both productivity and performance of coated conductors. Acknowledgments: This work was supported by the National Research Foundation of Korea grant funded by the Korean government (2022M3I9A1076681). It was also supported by the Ministry of Trade, Industry and Energy and Korea Institute for Advancement of Technology through the “International Cooperative R&D program”(P0028337).

In the fabrication of REBa 2 Cu 3 O y (RE = rare earth, REBCO) coated conductors by the trifluoroacetate metal-organic deposition (TFA-MOD) method, it is common to reduce the Ba content from the stoichiometric ratio of RE:Ba:Cu = 1:2:3 and employ a Ba-poor composition with a Ba/RE ratio of 1.5. This approach has been adopted because the Ba-poor composition enables higher growth rates while suppressing the formation of residual unreacted Ba-containing compounds, which would otherwise degrade intergranular connectivity. Meanwhile, the introduction of artificial pinning centers (APCs) has been extensively pursued to further enhance the in-field performance. In this study, we measured and compared the in-field critical current (I c ) characteristics of APC-doped REBCO coated conductors fabricated with different starting compositions. The samples were 8-mm-wide TFA-MOD coated conductors containing 10 mol% BaZrO 3 (BZO) as APCs. Two starting compositions with Ba/RE ratios of 1.5 and 1.8 were employed. For I c measurements, microbridges were fabricated by photolithography and wet etching, and the in-field I c characteristics were measured at 65 K, 70 K, and 77 K. The angular dependence of I c showed peaks at magnetic field orientations other than parallel to the tape surface. This behavior is attributed to the BZO particles within the REBCO films, which act as random point pinning centers. From the magnetic field dependence of I c in the perpendicular field, it was confirmed that the coated conductors fabricated using the Ba/RE = 1.8 starting composition exhibited higher I c values over a wider magnetic field range compared with those fabricated using the conventional Ba/RE = 1.5 composition. This work was supported in part by “the New Energy and Industrial Technology Development Organization (NEDO)” and “JSPS Grants-in-Aid for Scientific Research 23K23289 and 25H00739”, and conducted as collaborative research at the Institute for Materials Research, Tohoku University under Project 202412-HMKPC-0038 and 202412-HMKGE-0030.

A series of high temperature superconducting GdBCO coated conductors (V-series) were prepared by vacuum heat treatment (200 o C to 600 o C). The superconducting properties of V-series HTS GdBCO CCs were investigated using a Quantum Design PPMS-14. Magnetic moment m(H) measurements were performed on V-series HTS GdBCO CCs at temperatures ranging from 10 K to 100 K in magnetic fields up to 12 T. The critical current density J c was estimated using the Bean model. In addition, the lower critical field H c1 , penetration field H*, and irreversibility magnetic field H irr are obtained from their m(H) curves. The hole concentrations in V-series HTS GdBCO CCs are estimated from the generic parabolic dependence of T c upon doped hole concentration p. The evolution of superconducting properties in V-series HTS GdBCO CCs are examined as a function of increasing vacuum annealing temperature T an . The correlation study between T c values and other superconducting properties (J c , H c1 , H*, and H irr ) as a function of T an , that is, the variation of superconducting properties with the vacuum annealing condition, was performed. These and other results will be discussed.

With the rapid advancement of machine learning algorithms, the integration of active learning, namely Bayesian optimization (BO), has emerged as a powerful tool for materials synthesis [1] . In superconductor research, we have recently demonstrated this effectiveness by synthesizing the strong K-doped BaFe 2 As 2 (Ba122) magnet [2] through data- and researcher-driven approaches. The BO algorithm is well-suited for material synthesis because of its ability to guide synthesis parameter selection with limited training data. In this study, we applied BO to optimize the critical current density (J c ) of polycrystalline Y-doped Ba 0.6 K 0.4 Fe 2 As 2 superconductors [3] with sintering temperature and dwelling time during spark plasma sintering as the input parameters. To mitigate the high experimental cost associated with J c measurements, we employed surrogate measurement proxies (relative density and phase purity) as pre-screening filters within the BO loop. Various strategies, including random search, single objective BO (SOBO), filtered SOBO with floor padding [4] , and filtered SOBO without padding, were systematically benchmarked. We performed simulations with synthetic functions and validated the promising strategy through hands-on experiments. The filtered SOBO approach achieved J c values comparable to those obtained using standard SOBO, while substantially reducing the number of J c measurements required. [1] A. Yamamoto, et al., Sci. Technol. Adv. Mater. 26, 2436347 (2025). [2] A. Yamamoto, et al., NPG Asia Mater. 16, 29 (2024). [3] N. R. Ayukaryana, et al., September 1-6, 2024, Applied Superconductivity Conference, Salt Lake City, USA. [4] Y. K. Wakabayashi, et al., npj Comput. Mater. 8, 180 (2022).

It is known that the tape shaped REBCO-coated conductor has a large AC-loss under vertical magnetic field to the tape surface. In order to reduce the loss, making a multi-core with thin filaments is an effetive method. However, that usually involves a lot of degrease of critical current of wire. In this study, we proposed a multi-branched structure in REBCO layer without perfect separation between the filaments. The multi-branched structure can be fabricated by intermittent cracks using rolling cutters. Many samples were prepared and critical current and AC-loss were measured at 77 K. The results show that critical currents in some samples almost keep the original value, and the AC-loss is also improved.

A low-temperature diffusion joint technique based on a novel chemical surface activation technique was applied to fabricate stacked REBCO conductors by directly connecting the Cu stabilizing layers of REBCO tapes. The joint process enables solder-free Cu-Cu bonding at temperatures sufficiently low to avoid degradation of the superconducting layer. The effects of joining parameters, including heating time, applied pressure, and joint length, on the interfacial resistivity were systematically investigated to establish optimized conditions for uniform and low-resistance joints. I-V measurements revealed that the critical current (I c ) and n-value of the jointed tapes were well preserved compared with non-jointed tapes. Furthermore, a two-tape stacked REBCO conductor with length about 10 cm was fabricated using the optimized joint conditions. The stacked conductor exhibited an I c enhancement of approximately 1.7 times relative to a single tape, demonstrating efficient current transfer through the joint region and stable electrical connection between stacked layers. These results suggest that the proposed citric-acid-assisted diffusion joint technique is well suited for production of stacked REBCO conductors and provides a practical and reliable approach for high-current superconducting applications. Acknowledgment The authors thank Mr. S. Kato and Mr. K. Moriyasu for their assistance with the experiments, and Dr. Sergey Lee for providing the REBCO tapes. Part of this work was performed with the support of, and under the auspices of, the NIFS Collaboration Research Program (NIFS24KIEA052).

The reliable operation of REBCO coated conductors in high field superconducting magnets requires a detailed understanding of their mechanical and electro-mechanical performance and property uniformity over long lengths. In this work, a commercial REBCO tape with a total length of 120 m was systematically evaluated along its length to assess variability in mechanical properties and critical current (Ic) versus strain at 77 K. Specimens were extracted every 10 m along the length of the conductor and subjected to uniaxial tensile testing at 77 K to determine elastic modulus and yield strength. Ic–strain measurements were performed at 77 K under controlled axial loading to quantify irreversible strain limits and to elucidate the coupling between mechanical deformation and superconducting performance. In addition, profile of copper thickness across the tape 4 mm width was also measured at these locations examine whether variation in copper thickness correlates with the electro-mechanical property. The results show small lengthwise variations in mechanical and Ic-strain properties. The overall electro-mechanical response was consistent along the conductor, with no major differences observed in mechanical strength, Ic–strain behavior. The conductor demonstrated stable and reproducible performance under applied strain at cryogenic temperature, indicating good uniformity over long lengths. This study highlights the consistency of long-length mechanical and electro-mechanical properties for REBCO conductors intended for high-field applications and contributes to design margin assessment for high field superconducting magnet systems.

Second-generation high-temperature superconducting tapes (2G HTS tapes) composed of rare earth yttrium barium copper oxide (REBCO) are increasingly in demand in high-field systems such as fusion magnets, superconducting magnetic energy storage, magnetic resonance imaging, and nuclear magnetic resonance. All of these applications, especially large-scale systems such as tokamak-type systems and magnetic energy storage devices, require 2G HTS tape with lengths greater than several kilometers. However, the maximum length of a single HTS tape is currently several hundred meters due to technical limitations of the HTS tape production process. Therefore, to produce longer sections of HTS tape, technologies for creating low-resistance joints between individual sections of tape are required. This study proposes a method for creating low-resistance contacts between 2G HTS tapes using low-temperature plasma coating with copper. This research is part of a larger effort to develop a superconducting magnetic energy storage system based conductor on a round-core cable (CORC) and explores the feasibility of using low-resistance HTS tape joints in such a system. Samples with different deposition parameters were fabricated. The joints resistances were measured using direct transport method. 4 mm wide copper-coated HTS tapes were used for the study. The electromechanical properties of low-resistance connections subjected to external mechanical loads were also examined. The mechanical loads were longitudinal stretching of the joined HTS tapes, as well as helical winding on a round core at various winding angles and tensions. This winding simulates the stresses occurring in a CORC cable. All measurements were duplicated on HTS tape joints made using the classic soldering method. The measurement results show high potential for using the low-temperature plasma coating method to create low-resistance joints of HTS tapes. This work was supported by the Ministry of Science and Higher Education of the Russian Federation within the State Assignment (project FSWU-2025-0008)

The electromechanical durability of REBCO coated conductor (CC) tapes under cyclic loading is a critical factor for their reliable application in high-field magnets and rotating machinery. While high-cycle fatigue (HCF) data at low stress exists, this study presents an accelerated low-cycle fatigue (LCF) assessment to efficiently characterize performance limits and degradation trends at higher stress amplitudes. Low-cycle fatigue tests were performed on commercially available IBAD/ PLD processed CC tapes at 77 K using a triangular waveform with a stress ratio of R = 0.3 and a frequency of 0.1 Hz. The maximum stress (σmax) for cyclic test was defined as a percentage (100% to 130%) of the irreversible stress limit, identified as the point of 5% critical current (I c ) degradation. The I c was monitored in real time at intervals up to 1,000 repeated cycles. Results demonstrate excellent fatigue resilience at stress levels at or below σ irr , with I c degradation of less than 3% after 1000 cycles. However, a pronounced and accelerated degradation was observed at 130% σ irr , where I c degraded to ~73% of its initial value. This LCF methodology successfully identifies a stress threshold for rapid performance decline, complementing conventional HCF data. It provides an efficient framework for evaluating the long-term electromechanical integrity of CC tapes and for establishing design safety margins for practical applications. Acknowledgements: This work was supported by a grant from the KEIT, funded by MOTIE (Grant No. RS-2024-00435492). Partially funded by the NRF grant from MSIT (No. RS-2022-NR068578). The authors would like to thank SuNAM for providing samples.

The introduction of a transient liquid phase into industrial pulsed laser deposition (PLD) systems has enabled the ultrahigh-rate growth of superconducting films (≥ 100 nm s −1 ), allowing opportunities for cost-effective, large-scale fabrication of second-generation high-temperature superconducting tapes. However, the growth mechanism of superconducting films under ultrahigh-rate industrial PLD conditions remains unclear. Here, a statistical investigation of industrial samples is conducted and a plate-like orthorhombic BaCu 3 O 4 phase is identified for the first time on the EuBa 2 Cu 3 O 7− δ (EuBCO) surface, which shows strong correlation with its superconducting performance. Comprehensive characterization reveals that BaCu 3 O 4 is an epitaxially stabilized intermediate phase. Notably, BaCu 3 O 4 plays a key role in the high-rate epitaxial growth of EuBCO by reacting with the Y/Eu species that migrate to the growth front, forming superconducting phases — a mechanism further supported by the formation of oriented YBa 2 Cu 3 O 7− δ . Based on these results, a growth model is proposed whereby the epitaxial BaCu 3 O 4 intermediate phase serves as a crucial reactant, driving the formation of c-axis-oriented EuBCO in transient liquid-assisted growth. This work provides novel insights into the underlying mechanisms of transient liquid-assisted growth in PLD-grown REBa 2 Cu 3 O 7− δ films and establishes a framework for further optimization of industrial PLD processes.

In cryogenic engineering fields such as aerospace, nuclear fusion, and liquid hydrogen systems, the thermal conductivity of materials is recognized as a key thermophysical parameter governing system reliability and operational efficiency. The steady state method is widely recognized as a reliable and cost-effective technique for measuring thermal conductivity over a wide temperature range. Nevertheless, its practical application is frequently constrained by long testing durations and low measurement efficiency. In this study, a multi-channel parallel thermal conductivity measurement platform for cryogenic temperatures is developed, enabling the simultaneous testing of up to six specimens over a temperature range from 10 K to 300 K. The platform is primarily intended for bulk engineering materials. A Gifford-McMahon (G-M) cryocooler is used as the cooling source. A rapid specimen exchange design allows sample replacement without system shutdown, reducing the testing time by more than 10 hours per measurement cycle. Calibration experiments conducted using copper and stainless steel 304 (UNS S30400) show that the measurement deviation remains within 10 percent at test temperatures of 10 K, 20 K, 40 K, 80 K, and 160 K. Therefore, the developed platform ensures the accuracy of results, significantly improves the efficiency of cryogenic thermal conductivity measurements while reducing operational cost, and is suitable for application in small and medium scale research institutions and industrial laboratories.

Austenitic stainless steels (ASSs) have been expected to be applied for structural components in next-generation magnetic confinement fusion and aerospace industries due to their excellent mechanical performance at cryogenic temperatures. Cryogenic strain strengthening technology, a forming process conducted at liquid‑nitrogen temperature (77 K), has been verified to generate higher yield and tensile strengths compared with those achieved by conventional forming processes at ambient temperature. However, the hardening mechanisms of the ASSs after cryogenic processing were closely related to their phase stability at cryogenic temperatures, and a systematic comparison between grades that are susceptible or resistant to cryogenic martensitic transformation remained lacking. Therefore, the present study investigates two contrasting materials: a widely-used 316LN ASS undergoing deformation-induced martensitic transformation at cryogenic temperatures, and a novel CHN01 ASS designed to remain fully austenitic under similar conditions. The effects of cryogenic tensile pre-strain (applied at 77 K at levels of 0%, 15%, 25%, and 35%) on their subsequent mechanical properties and hardening behaviors were systematically compared. This study highlights the important role of cryogenic martensitic transformation capability in determining the hardening mechanisms of cryogenic tensile pre-strained ASSs, thereby providing a critical theoretical basis for material selection and safety assessment in advanced cryogenic engineering applications.

Cryogenic insulation materials are finding increasingly widespread application in fields such as superconducting cables, superconducting nuclear fusion, and quantum computing. In cryogenic environments, system reliability largely depends on the performance of the insulation materials. Accurately acquiring the cryogenic dielectric property data of insulation materials is of paramount importance for the optimized design of cryogenic insulation systems, novel material development, and fault diagnosis. Currently, there is an urgent need for a system capable of efficiently and accurately measuring the cryogenic dielectric properties of insulation materials. Therefore, this paper designs and constructs a dielectric impedance test system for insulation materials, utilizing a G-M cryocooler as the cooling source, suitable for a temperature range from room temperature down to 10 K. This system can accommodate three samples simultaneously, enabling concurrent cooling cycles for multiple specimens. The test fixture is housed within a helium gas atmosphere, and both sample cooling and uniform sample temperature are achieved through symmetric thermal conduction by upper and lower cooling components. Furthermore, the apparatus allows for material measurements in various atmospheric environments, thereby accurately reflecting the material's performance under specific operating conditions.

In synchrotron radiation light source applications, high-precision X-ray spectroscopy experiments require extremely high sensitivity to distinguish characteristic spectral lines at the sub-electronvolt level, thereby determining the composition of samples. Microwave Kinetic Inductance Detectors (MKIDs) exhibit excellent sensitivity and can be arrayed through semiconductor fabrication processes, enabling large-scale, multi-channel two-dimensional measurements. Unlike conventional detectors, MKIDs operate in an ultra-low temperature environment of several kelvins down to 100 millikelvins. Multiplexing technology must be employed to reduce the number of readout cables to maintain the stability of the low-temperature environment. Therefore, the multiplexed readout method is also a key factor determining the array element scale of the detector. The core of an MKID is a superconducting microwave resonator, and microwave multiplexed readout is a critical approach to achieving high-multiplexing-ratio readout for MKID arrays. To implement microwave signal multiplexed readout, we have developed a room-temperature readout electronics prototype based on the ZCU111 evaluation kit. This prototype can be applied to high-precision X-ray spectrometers based on MKID arrays. In this prototype, we have implemented the Polyphase Filter Bank (PFB) algorithm, which is capable of synthesizing and resolving microwave signals across 256 channels within a bandwidth of 4–6 GHz. This prototype system has the potential to read out hundreds of channels simultaneously; currently, we have achieved simultaneous readout of 4 channels, and a single-photon energy resolution of 0.48 eV has been realized in joint tests with the detector. In the future, we will carry out further functional optimization and integration, expand the number of channels it can read simultaneously, and conduct the design of new dedicated readout electronics based on this prototype.

The sensitivity of the Einstein-Telescope’s low frequency laser interferometer (ET-LF), a third-generation gravitational wave detector planned in Europe, is limited by the mirror suspension thermal noise between 3 Hz to 30 Hz. Requiring cryogenic operation of the main Fabry-Pérot optical cavity. The ERC project GRAVITHELIUM will investigate the dissipative behaviour of full-scale suspensions of the cryogenic core optics in ET-LF. Two possible suspension concepts are currently considered, using either monocrystalline suspension fibres made of silicon and sapphire, respectively or titanium suspension tubes filled with static He-II. The dissipative behaviour of these suspensions is characterized by the mechanical Q-factor measured by the ring-down method, where suspensions are excited to resonance frequencies followed by the analysis of the decay time. The dissipation of a test set up measuring the Q-factor is a systems characteristic. Hence measuring the suspensions intrinsic Q-factor feasibly can be challenging. This can be achieved by reducing the extrinsic dissipations as much as possible, especially the dissipation caused by the clamping geometry via an adequate suspension support system. Using finite element analysis, the suspension support system is designed to have a lower extrinsic dissipation than the intrinsic dissipation of the respective suspension being measured. The anticipated Q-factors range between 10 6 to 10 8 . Theoretical modal analyses shows that the first to the third modes of the suspensions are measurable, occurring between 3 Hz to 160 Hz . This work will present the design approach for the low dissipative suspension support system for the Q-measurements.

Abstract In fusion reactors, insulation materials must exhibit exceptional resistance to neutron irradiation, as prolonged exposure can degrade both material and component properties, ultimately affecting reactor performance. Experimental studies show that, under high neutron fluence (ranging from 10¹⁴ to 10²² n/m²), mechanical properties such as tensile and interlinear shear strength can deteriorate by up to 30%. This study focuses on the development and evaluation of insulation materials suited for high-neutron environments, specifically for future domestic superconducting (SC) fusion magnets. The insulation material developed is a Glass Fiber Reinforced Plastic (GFRP) composite, made from boron-free S-glass fibers and liquid-modified bisphenol epoxy resin. Earlier investigations involved irradiating the insulation material samples up to a neutron fluence of 1.0×10²¹ n/m² and a gamma dose of 0.5 MGy at 32 MWt reactor power in the fast breeder test fission reactor at IGCAR, Kalpakkam. The mechanical and electrical testing of both unirradiated and irradiated samples was conducted at a government-approved laboratory. The results showed minimal degradation (less than 2%) in tensile strength, shear strength, and electrical breakdown strength. In-house developed epoxy-based dissimilar material (DM) joints, consisting of GFRP composite and stainless steel, were irradiated near the reactor core enclosure plate assembly to validate their performance in a neutron-rich environment. The estimated gamma dose rate at DM joint was 1.1x10 7 R/h at 1 MW irradiation with neutron flux of 3.5 x 10 15 n/m 2 /s of fast neutron energy of >0.1 MeV. The cadmium sheet was wrapped on sample to absorbed thermal neutrons and reduces neutron irradiation induced dose. These tests were conducted at the APSARA (U) reactor, BARC, Mumbai, under irradiation conditions that included a neutron fluence of 1.0×10²¹ n/m² and a gamma dose of 9.0 MGy at 800 kW of fast neutron energy (>0.1 MeV). The radiation tolerance thresholds for the GFRP material were established as a neutron fluence of 1.0 × 10²² n/m² and a gamma dose of 10 MGy. The helium leak-tightness of the irradiated DM joint was found to be within an acceptable value of 1.7×10 -8 mbar-l/sec. The mechanical testing under tensile pull load condition revealed no significant degradation was found. The in-house developed epoxy resin system has been found to exhibit exceptional radiation stability under high neutron flux, potentially advancing the development of future fusion magnet technologies. This paper outlines the in-house development of a neutron-resistant composite insulation material, covering irradiation experiments, post-irradiation observations, and performance test at 300 K and 77 K for unirradiated and irradiated cryogenic components. Keywords: Irradiation with fast breeder radiation environment, superconducting magnet, insulation material, S-glass composite, mechanical and electrical performance

Acoustic Emission (AE) monitoring is a critical non-destructive testing (NDT) technique for ensuring the structural integrity of superconducting magnets and cryogenic fuel storage systems. However, cryogenic environments pose significant challenges to sensor reliability. This paper presents a comprehensive comparative study between Fiber Optic sensors and conventional Lead Zirconate Titanate (PZT) ceramic sensors in cryogenic environments ranging from 298 K (room temperature) to 77 K (liquid nitrogen temperature).The experimental setup utilized a distinct cryostat chamber to simulate the operational environment. Standardized Hsu-Nielsen pencil-lead break tests were conducted to generate broadband acoustic signals. The performance evaluation focused on three key metrics: spectral response sensitivity, thermal stability, and signal-to-noise ratio (SNR).The results indicate a fundamental divergence in the physical response mechanisms of the two sensor types under cryogenic conditions. The PZT sensors exhibited a notable degradation in sensitivity, attributed to the reduction of the piezoelectric coefficient and the embrittlement of the couplant layer at 77 K. Furthermore, the PZT sensors showed increased susceptibility to electromagnetic interference, resulting in a lower SNR in the electrically noisy cryogenic pump environment. Conversely, the fiber optic sensors demonstrated superior stability. While a thermo-optic wavelength shift was observed, the dynamic strain sensitivity of the fiber optic sensors remained virtually constant across the temperature gradient. The fiber optic system achieved an SNR improvement of approximately 15 dB over the piezoelectric counterpart due to its inherent immunity to electromagnetic interference.This study concludes that while PZT sensors remain cost-effective for room-temperature applications, fiber optic AE sensors offer a more robust and reliable solution for Structural Health Monitoring (SHM) in harsh cryogenic environments. The findings provide essential guidelines for selecting sensor modalities in next-generation superconducting and aerospace applications.

The development of advanced materials often requires the ability to probe their properties under various external impact in real-time. In this study, we present the development of a multi-field coupled variable-temperature Raman testing system, used to investigate the intrinsic properties of materials such as high-temperature superconducting (HTS) tapes under controlled experimental conditions. The system integrates strain, electrical, and temperature fields, enabling comprehensive multi-condition in-situ Raman spectroscopy studies. The multi-field coupled testing system is designed to operate from cryogenic temperatures (10K) to room temperature using a GM cryocooler to achieve a low-temperature environment. Helium is employed as an auxiliary cooling medium under low-temperature experimental conditions to compensate for the insufficient thermal equilibrium of high-temperature superconducting tapes under certain conditions and in order to reduce experimental costs. The electrical testing device using standard four-probe method allows the system to monitor the resistance changes, which is the critical parameter for HTS tapes, in-situ during the experiment. In addition, the system is equipped with a strain loading device that integrates a servo motor and a displacement platform, allowing the simulation of the working environment of test specimens under strain conditions. In order to coordinate multiple coupled test environments, insulation design was implemented in the specimen clamping device to ensure the stability of testing. To accommodate the requirements of optical tests and visualization studies, the system is designed with a dual-layer optical window that allows direct observation of the sample, with the outer optical window to the sample stage surface complies with the requirements of the working distance requirements of a 50× objective lens. Furthermore, to address the impact of GM refrigerator vibrations on optical tests, the system utilizes a high-thermal-conductivity flexible connection. This work provide a innovative experimental tool for understanding the complex interactions between electronic, phononic, and mechanical properties in HTS materials under operational conditions.

The cryocooler which can cool down to 4.2 K is widely utilized such as MRI and semiconductor manufacturing. The cooling efficiency of the cryocooler is depend on the values of the specific heat for materials in regenerator. To enhance the cooling performance, there is a strong demand for the development of magnetic regenerator materials that exhibit a specific heat peak associated with a magnetic phase transition below 10 K. We focus on the rare-earth compounds RCoC (R=Gd and Ho) which crystallizes in the YCoC-type structure. GdCoC shows ferromagnetic order at 16 K and HoCoC shows antiferromagnetic order at 7.5 K. In the present work, we expected that the magnetic transition temperature (T M ) can be tuned by substituting Gd for Ho in HoCoC. The polycrystalline samples of Ho 1-x Gd x CoC (x≤0.7) were prepared by the arc-melting method and then annealed at 1000 deg for 72 h. The crystal structure was checked by the power X-ray diffraction (XRD) technique. Specific heat was measured at temperatures ranging from 2 K to 30 K by the relaxation method. The main peaks in the XRD patterns of Ho 1-x Gd x CoC were indexed to the tetragonal YCoC-type structure. The lattice constants increased with increasing x, suggesting successful Gd substitution. The peaks of the impurity phase RCoC 2 were detected, whose mass fraction was estimated to be less than 5 wt%. Therefore, the influence of RCoC 2 on the specific heat is considered to be small. The temperature dependence of the volumetric specific heat for x = 0 showed a peak at 7.5 K due to the antiferromagnetic transition, consistent with previous studies. For 0.1 ≤ x ≤ 0.6, the peak temperature remained almost constant at 7.5 K, while the peak value decreased with increasing Gd content. This reduction is attributed to atomic randomness introduced by the substitution. For x = 0.7, the behavior changed significantly, showing a broader peak at 9 K and a small peak at 5 K. The magnetic entropy at T M increased with Gd content, reflecting the large degeneracy of the Gd 3+ 4f electron state (J = 7/2), which supports successful Gd substitution. This entropy increase suggests a larger area under the specific heat curve, potentially improving the cooling capacity of cryocoolers. T M remained almost unchanged up to x = 0.6 and increased at x = 0.7. This non-linear behavior is similar to that observed in isostructural Er 1-x Gd x CoC system. For x ≤ 0.6, the increase in T M was likely suppressed by the competition between the antiferromagnetic Ho-Ho and ferromagnetic Gd-Gd interactions. At x = 0.7, the ferromagnetic interaction became dominant, leading to the observed increase in T M . In conclusion, Ho 1-x Gd x CoC system exhibits a non-linear T M dependence on Gd content, characteristic of alloys with competing magnetic interactions. These findings demonstrate that alloying antiferromagnetic and ferromagnetic materials is an effective strategy for developing new regenerator materials with enhanced specific heat.

Increasing magnetic field intensity in limited space is an important strategy to obtain high parameter plasma and improve the fusion power. The next generation of fusion magnets will have a peak magnetic field greater than 17 T, such as China Fusion Engineering Demonstration Reactor (CFEDR). The development of cryogenic structural materials with high strength and toughness is critical for advancing the application of high-field cable-in-conductors (CICC). For future CICC jackets, the 0.2% yield strength (YS) must exceed 1500 MPa, and the fracture toughness (K IC ) must be better than 130 MPa·m 1/2 at 4.2 K. Currently, jacket materials such as 316L, 316LN, and JK2LB struggle to achieve the YS above 1100 MPa at 4.2 K, even after cold working. Based on Nitronic 50 (N50) super-austenitic stainless steel, China has developed a modified version, CHSN01 (Chinese High-nitrogen steel No.1). This study systematically investigates the mechanical properties of CHSN01 jackets under different degrees of cold working (0 % ~ 20 %) and two distinct heat treatment regimes: Nb 3 Sn (maximum temperature 665 ℃) and Bi-2212 (maximum temperature 890 ℃). Additionally, the potential microstructure mechanisms affecting the mechanical properties of CHSN01 jackets at 4.2K were investigated, providing a reference for the subsequent practical application of CHSN01 for future fusion applications.

Maritime deployment of liquid hydrogen (LH₂) as a zero-carbon fuel requires onboard tank systems that remain demonstrably safe under combined cryogenic temperature (20 K), ship-motion-induced sloshing loads, and frequent pressure/thermal cycling throughout service life [1]. Austenitic stainless steels such as 304L are widely considered for inner tank structures onboard ships where sensitivity to weight is non-critical. While their well-documented cryogenic toughness, excellent weldability, mature supply chains for large-scale fabrication, and lower cost relative to grade 316L make them an attractive proposition [1], questions remain regarding this grades susceptibility to hydrogen induced cracking at welded interfaces, despite its approved use down to liquid helium temperatures in pressure equipment. Furthermore, the performance of welded austenitic stainless steels under LH₂-relevant maritime duty cycles is not yet underpinned by any comprehensive, maritime-specific mechanical property database, and more specifically for weldments and their heat-affected zones, where local microstructure, residual stress, and defects can govern crack initiation and arrest [1-3]. One crucial limitation within existing cryogenic tensile data, particularly in the 77–4 K regime, is the presence of pronounced serrations “data spikes” in stress–strain responses of unwelded austenitic stainless-steel specimens, especially in the onset regime of plastic deformation [2-7]. BS ISO 6892-4 [8] describe specimen designs with specific profiles or features for enhanced gripping but also acknowledge serrations in the curves and attribute them to unstable plastic flows and arrests arising from the inability to maintain adiabatic conditions along the gauge length of specimens, particularly when cooled directly in liquid helium. However, “microslip” between the specimen and grips indicated by repeated spikes in load signal are equally difficult to avoid during cryogenic mechanical tests, making it challenging to distinguish these effects from genuine material behaviour. Overall, such artefacts can cause misinterpretation of strain hardening, extraction of yield and ultimate strength properties, and the transferability of results into design allowables. This study aims to validate improved cryogenic tensile fixtures and test protocols that suppress specimen microslip to determine if serrations in the dataset observed at 20 K do arise from discontinuous yielding, while simultaneously assessing the accuracy of stress-strain measurement techniques at ultra-low temperatures. The initial work then provides the foundational work to confidently characterise the cryogenic tensile behaviour and of welded austenitic stainless steels specimens, that accurately represent the fabrication thicknesses expected to be used in maritime LH₂ tanks. Mechanical testing will be complemented by weld-zone microstructural and fractographic analysis to identify controlling deformation and fracture mechanisms, and to establish correlations between weld features and cryogenic-temperature performance. While other specimens will begin a campaign to understand the comparative effects between electro-chemical and gas charging. Acknowledgements Facilities from the Institute of Cryogenics of University of Southampton are acknowledged. References [1] Wang Z, A review of metallic tanks for H2 storage with a view to application in future green shipping. International Journal of Hydrogen Energy. 2021;46(9):6151-79. [2] Afshan S, High‐performance metallic materials for applications in infrastructure and energy sectors. Steel Construction. 2023; 16(3):144-150. [3] Li W, Cryogenic hydrogen embrittlement of 316plus (EN 1.4420) stainless steel at 77 K and 20 K. International Journal of Hydrogen Energy. 2026; (Under review). [4] Ishtiaq M, Serration-induced plasticity in phase transformative stainless steel 316L upon ultracold deformation at 4.2 K. Materials Science and Engineering: A. 2025; 921:147591. [5] Zheng C, Low temperature mechanical behaviour of fine- and ultrafine-grained 304 austenitic stainless steel fabricated by cryogenic-rolling and annealing. Materials Characterization. 2022; 191:112084. [6] Kim M, Tensile and fracture characteristics of 304L stainless steel at cryogenic temperatures for liquid hydrogen service. Metals. 2023; 13(10):1774. [7] Fernandez-Pison P, Flow and fracture of austenitic stainless steels at cryogenic temperatures. Engineering Fracture Mechanics. 2021; 258:108042. [8] BS ISO 6892-4:2015, Metallic materials: Tensile testing. Part 4 – Method of test in liquid helium.

The Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Sciences in Krakow has developed a Test Stand (IFJTS) for the Testing of Superconducting Wires at 4.2K. The IFJTS facility comprises of a 16 Tesla solenoid, liquid helium cryostat, cryogenic system, power supply, control and data acquisition system. The IFJTS was integrated with cryogenic infrastructure at IFJ PAN which includes both the helium delivery and the helium recovery systems. The IFJ PAN infrastructure is additionally equipped with facilities for the supply of liquid nitrogen and liquid helium and vacuum system for pumping out helium gas to lower the temperature of liquid helium bath down to 1.8 K. The integration of this system with IFJTS is under way. The Test Stand has now been commissioned at 4.2K and its performance validation will be carried out by benchmarking it with respect to the facility at CERN. The paper will present the current status and future plans for IFJTS.

Carbon Fiber Reinforced Polymer (CFRP) composites are the preferred material for both Type IV and Type V liquid hydrogen fuel tanks in aerospace applications, owing to their lightweight, high strength and corrosion resistance. In practice, these tanks are subjected to withstand harsh cryogenic environments, long-term mechanical loads, and cyclic temperature fluctuation, which can easily induce microcracks and subsequent hydrogen leakage. In this study, we develop a cryogenic hydrogen permeability measurement system based on a GM refrigerator, capable of operating from 20 K to 300 K. The system allows for precise characterization of hydrogen permeation through CFRP laminates under liquid hydrogen temperature conditions. To distinguish between different permeation mechanisms, we propose two specific testing devices：one for measuring the intrinsic permeability of CFRP laminates and the other for evaluating microcrack-induced permeability under uniaxial tensile loading. This work is crucial for understanding the behavior of CFRP composites under extreme cryogenic temperatures. It provides valuable data on hydrogen permeation that will aid in assessing the long-term service reliability and safety of CFRP-wrapped hydrogen tanks in aerospace and other cryogenic applications.

With global warming intensifying, hydrogen energy has emerged as a pivotal clean energy source and a critical enabler of the global transition to a sustainable energy system. Liquid hydrogen, characterized by its high volumetric energy density, is especially suitable for large-scale storage. The mechanical properties of materials in hydrogen service across a wide temperature range from 20 K to 300 K are fundamental to the safety and reliability of energy equipment throughout the hydrogen value chain, including production, storage, transportation, and utilization. In this study, a cryogenic tensile testing machine was established, utilizing two GM cryocoolers to provide the necessary cooling capacity. This setup enables the measurement of the mechanical properties of structural materials under two distinct environments: 20 K liquid hydrogen immersion and 20 K–300 K gaseous hydrogen. The detailed design process—encompassing the P&ID, structural, thermal, safety, and control system aspects—is thoroughly elaborated. This experimental platform is expected to supplement and refine the existing database on the mechanical properties of hydrogen-compatible materials, thereby significantly contributing to the commercial advancement of the hydrogen energy industry.

The development of high-field superconducting magnets for compact fusion devices, such as SPARC at Commonwealth Fusion Systems (CFS), often requires high strength fiberglass composites selected as materials for magnet insulators. In particular, bucked tokamak designs often rely on their central solenoid (CS) coils taking massive compressive and interlaminar shear stress (ILSS) while still maintaining high voltage isolation from the rest of the magnet systems. Standard methods for characterizing the ILSS of composites at cryogenic temperatures (77 K and 4 K) including double V- notch, short beam shear or lap shear only test materials in an unconstrained state. This often leads to severely underestimating the maximum allowable mixed mode shear stress under compressive load which components and structures made from fiberglass composites undergo in real application. To address this gap in materials testing, this work presents fixtures and methods for studying the shear strength in fiberglass composite bulk material and bonded joints when also subjected to compressive stress perpendicular to their layers at cryogenic temperatures (77 K and 4 K). The first apparatus, focused on studying bulk material properties, is based on the Iosipescu specimen standard and test. However, it has been modified to allow for compression through the width of the Iosipescu specimen. The second apparatus, intended to study adhesive bonds between fiberglass composites and steel, is based on a double-lap shear specimen and fixture. Similar to the other apparatus, it has been modified to allow for compressive load across the bonded area of the double-lap shear specimen. Both fixtures have been designed for use and have been utilized at cryogenic temperatures (77K and 4K) to conduct such studies.This work contains the design, analysis, validation, and commissioning data to showcase fixture performance. This work does not include final data generated to make engineering decisions within SPARC. The fixtures and methodology described in this work are most applicable to those designing magnet systems and composite pressure vessels, two fields of study which rely heavily on composite shear properties at cryogenic temperatures. This work establishes fixtures which are compatible with standard composite specimen architecture as well as widely available universal test frames. Unlike past studies, these fixtures are designed to decouple clamping loads and shear loads applied to the specimen, and utilize instrumented compliant mechanisms for maintaining and measuring bi-axial load at cryogenic temperatures down to 4 Kelvin.

Tri-axial compressive properties of polymer-matrix composites at cryogenic temperatures are essential for the design of superconducting magnet support structures and other cryogenic engineering components; however, systematic datasets obtained under well-controlled multi-axial boundary conditions are still scarce. This work investigates the tri-axial displacement-controlled compression response and rate-dependent failure behavior of a unidirectional (0°) M40J carbon fiber/epoxy composite at room temperature, 77 K, and 4.2 K. A cubic fixture was designed and fabricated to apply the same compressive displacement rate along three orthogonal axes, enabling a reproducible tri-axial compressive strain state. Three-directional strains were monitored using multi-channel strain gauges, and post-mortem failure morphologies were recorded and analyzed. At room temperature, the composite exhibits progressive damage accumulation under tri-axial compression, and the peak load shows pronounced sensitivity to displacement rate. At 77 K, the response becomes more brittle, with earlier stiffness drop and more evident delamination/splaying features in the fractured specimens. At 4.2 K, the strain evolution in the three directions is highly synchronous and nearly linear up to catastrophic failure, indicating strongly suppressed inelastic relaxation and rapid crack propagation at liquid-helium temperature. Overall, decreasing temperature drives a transition from progressive failure at room temperature to discontinuous brittle fracture at 77 K, and further to near-elastic energy storage followed by catastrophic fragmentation at 4.2 K. The observed rate sensitivity and failure-mode transitions are primarily governed by matrix/interface embrittlement at cryogenic temperatures in combination with the imposed multi-axial constraint.

The purpose of this study is to analyze the hydrogen embrittlement behavior of X65 seamless steel pipes used for high-pressure hydrogen transportation under hydrogen environments. Specimens were extracted along the rolling direction of the pipe, and the microstructure was analyzed using optical microscopy and electron backscatter diffraction (EBSD). To evaluate hydrogen embrittlement behavior, slow strain rate tests (SSRT) were conducted under nitrogen and hydrogen atmospheres, and the relative notch tensile strength (RNTS) values of H₂/N₂ were determined. The pressures of nitrogen and hydrogen were set at 130 bar and 200 bar, respectively. After the SSRT, fracture surface analyses of each specimen were performed using scanning electron microscopy (SEM). The microstructure of the X65 steel pipe, which was quenched and then tempered at 650 °C, consisted of polygonal ferrite (PF), acicular ferrite (AF), and carbides. As a result of the SSRT conducted under different environments, the RNTS value at 130 bar was 0.91, indicating suitability for hydrogen service, whereas at 200 bar, the RNTS decreased to 0.61, showing clear hydrogen embrittlement behavior. Fracture analysis revealed that under nitrogen atmosphere, ductile fracture characterized by dimples was observed in all regions regardless of pressure. In contrast, under hydrogen atmosphere, brittle fracture was observed near the surface, while ductile fracture behavior was found in the interior region. At the higher pressure of 200 bar, the ductile fracture region in the interior decreased compared to that at 130 bar. Fracture initiated at the surface and final fracture occurred in the interior, which is attributed to hydrogen initially penetrating from the surface and being trapped at grain boundaries, dislocations, and vacancies, followed by diffusion into the interior during SSRT, ultimately leading to fracture. Acknowledgment This research was supported by the Korea Institute for Advancement of Technology (KIAT), funded by the Ministry of Trade, Industry and Resources by (MOTIR) of the Republic of Korea (Project No. RS-2024-00449107).

Space free piston Stirling generator technology is an important thermoelectric conversion technology in space reactor energy system. However, vibration in free piston Stirling generators is one of the key issues limiting their application. To reduce its vibration, the free piston Stirling generator with a common expansion space is proposed in this paper. Meanwhile, its cooperative operation mechanism is investigated. Due to gas exchange between the two generators, pressure fluctuations within their working spaces can theoretically be synchronized. This facilitates the pistons' opposing motion to counteract casing vibrations. However, gas exchange complicates energy exchange, piston movement, and casing vibration throughout the generator system. Therefore, a theoretical model of the common expansion sapce is established to investigate the transfer and conversion processes of internal power, and the motion of pistons. Subsequently, a generator test system with a common expansion sapce was constructed to investigate the dynamic response process of the generator system from startup to steady state, as well as its output characteristics under various operating conditions. Finally, the theoretical model was refined by comparing experimental results with simulation results.

In high-precision cryogenic applications, the micro-vibration of mechanical cryocoolers critically impacts the performance of sensitive instruments, particularly optical detectors. Although conventional dual-opposed linear compressors effectively suppress fundamental frequency vibrations to approximately 0.2 N, residual high-order harmonics and lateral forces remain a significant issue, often causing resonance with the supporting structures of the payload. This paper investigates the generation mechanism of these high-order vibrations and proposes a comprehensive suppression strategy to reduce vibration forces in all three orthogonal axes (x, y, z) to below 0.1 N. A multi-physics coupling model, integrating electromagnetic, thermal, and structural dynamics, is established to analyze the non-linear coupling parameters and the influence of manufacturing asymmetries in flexure springs and motor components on vibration transmission. Additionally, a fluid-solid-thermal coupling simulation of the piston-cylinder system is employed to capture internal fluid dynamic behaviors. Guided by these theoretical analyses, structural mode optimization and magnetic circuit refinements are implemented to avoid high-frequency resonance and balance internal forces. The results demonstrate that these optimization techniques successfully minimize the intrinsic vibration output, providing a theoretical basis and practical solution for the design of ultra-quiet cryocoolers for next-generation vibration-sensitive systems.

With the upgrade of CSNS-II, the proton beam power will be increased from 100 kW to 500 kW. Accordingly, the target station cryogenic system is being upgraded to accommodate the increased dynamic heat load, which will rise from 560 W to 2800 W. All upgrade and commissioning activities are scheduled to be completed by April 2028. This paper presents the major technical challenges encountered during the upgrade, including excessive flow resistance, temperature and pressure fluctuations across the transcritical region, and catalyst pulverization, as well as the corresponding mitigation strategies. These measures involve process flow optimization and the development of key cryogenic equipment.

The development of large-scale cold storage technologies is critical to future net-zero energy systems, particularly in enabling cryogenic applications such as liquid air energy storage (LAES), Carnot battery and cryogenic energy recovery from liquefied natural gas (LNG). Conventional liquid-based cold storage approaches are associated with safety concerns and environmental risks arising from the use of flammable or potentially polluting working media, which motivates the exploration of solid-based alternatives. Among these, packed-bed cold storage has received increasing attention. However, its performance is often limited by the thermocline, which compromises the exergy grade of the cold energy and reduces storage efficiency. To address these challenges, this study proposes a cold storage concept based on moving-bed technology. Quartz sand is employed as the thermal storage medium, while direct gas-solid contact heat transfer is utilized to enhance interfacial heat exchange. A coupled gas-solid heat transfer model is established to characterize the thermal behavior of the moving bed, and the effects of key structural and operating parameters on heat transfer performance are systematically investigated. The results demonstrate that the proposed moving-bed cold storage system exhibits excellent exergy performance, achieving a cold storage exergy efficiency exceeding 90%, thereby highlighting its strong potential as a safe, efficient, and environmentally friendly solution for large-scale cold storage applications.

Liquid air energy storage (LAES), as a long-duration energy storage technology independent of geographical conditions, is a promising solution for renewable energy utilization and power system dispatching processes. With the increasing demand for compact and high-efficiency heat exchange equipment in LAES systems, the performance prediction and structural optimization of multi-stream plate-fin heat exchangers under 110 K and 10 MPa have become key issues in current engineering design. This study carries out design and sensitivity analysis for the aforementioned operating conditions to extract engineerable design criteria. Based on Aspen EDR, a four-stream heat exchanger model was developed, with the mean temperature difference (MTD≥3 K) and the pressure drop limit for each stream (ΔP≤1 bar) as the evaluation criteria. The effects of the number of parallel units, fin geometric parameters, core dimensions and layer allocation of the control stream on the heat exchange performance were investigated. The results show that the baseline scheme is close to the MTD boundary, and the cold-side high-flow stream has the minimum pressure drop margin, which is the key factor determining the feasible region. The pressure drop is most sensitive to the cold-side fin density and layer allocation, while the total heat transfer capacity (UA) and temperature difference matching are more significantly affected by fin height and core width. When the cold-side fin density is increased to 1.2 times that of the baseline, the UA is significantly improved (~10%), but the pressure drop of the control stream rises remarkably (~60%) and the MTD decreases further, resulting in overall infeasibility under the dual constraints of 1 bar and 3 K. Increasing the number of parallel units can effectively reduce the pressure drop and expand the feasible region, yet it will induce coupled changes in heat exchange and temperature difference indicators, which requires coordinated adjustment with fin density and layer number. Inlet temperature disturbances make the MTD more prone to approaching the threshold, and a reasonable configuration of the number of parallel units and layers is conducive to enhancing the system robustness. The sensitivity analysis process and key laws obtained in this study can provide a reference for the engineering selection and optimization of cryogenic high-pressure compact heat exchangers.

This study adopts the mode of dual mixed refrigerant refrigeration combined with hydrogen expansion and throttling refrigeration to design the hydrogen liquefaction cycle. By reducing the irreversible loss in the heat transfer process, it improves the exergy efficiency and reduces the energy consumption during the liquefaction process. The research on the liquefaction cycle is divided into three main parts: Primary mixed refrigerant precooling with a refrigeration temperature of around -160℃. Secondary mixed refrigerant precooling with a refrigeration temperature of -196℃ or even lower. Expander plus throttling refrigeration. By investigating the composition and proportioning of refrigerants for refrigerators at different stages, the energy consumption of the hydrogen liquefaction process is reduced.

The CERN Neutrino Platform contributes to a globally coordinated programme of neutrino research. This effort includes supporting state-of-the-art cryogenic systems associated with large-scale liquid argon Time Projection Chamber detectors (TPC). The Deep Underground Neutrino Experiment (DUNE) foreseen to be installed at the Sanford Underground Research Facility (SURF) in Lead, SD, USA, involves TPCs housed in four liquid argon cryostats with a total liquid argon volume of about 50,000 m 3 , installed in underground caverns at about 1.5 km below the surface. As part of the extensive DUNE prototyping programme, CERN has installed two 550 m 3 liquid argon cryostats (NP-02 and NP-04) in a charged particle beam in the North Area. The ProtoDUNE cryogenic system, equipped with copper-based liquid and gaseous argon purification systems, was developed based on the principles defined for the DUNE experiment. It has been successfully operated for several years and demonstrated that the achieved liquid argon bath purity ( Building on the experience gained, the CERN Neutrino Platform is responsible for the supply of the DUNE Cryogenic Condensers System (DCCS) for two DUNE cryostats, scaling up the prototype systems in both size and complexity. The main functions of the DCCS are to recover the cryogenic heat loads in steady state (100 kW @ 88 K), to maintain a stable cryostat pressure of 1.050 bara ± 5 mbar, to circulate the condensed liquid to purification before returning it to the cryostat, and to fill the cryostats with a flow rate consistent with the available cooling power (300 kW). Due to the access shaft imposing the assembly underground and limiting the size of equipment, the DCCS involves several units working in parallel. This paper first briefly reminds the DUNE principles, and the ProtoDUNE developments and results for cryostat and cryogenics, before describing the ProtoDUNE parallel pump test. It then focuses on the development of the DCCS and outlines the design challenges and integration strategy.

The Shenzhen Superconducting Soft X-ray Free Electron Laser (S 3 FEL), currently under development at the Institute of Advanced light Source Facility (IASF), is an X-ray free-electron laser (XFEL) facility based on a superconducting continuous-wave linear accelerator. Its primary objective is to generate a high-repetition-rate (1 MHz), high-quality electron beam for producing high-brightness soft X-ray radiation in the 1~30 nm range. The project incorporates three independent cryogenic plants. As one of the critical pre-research facilities for S 3 FEL, the LINAC Test Facility (LTF) will be established to validate the accelerator design and support the main construction. The cryogenic system of LTF provide a superfluid helium environment for five 1.3 GHz and two 3.9 GHz TESLA-type superconducting cryomodules, along with a single 9-cell cavity cryomodule. It simultaneously delivers cooling capacity at three temperature levels: 2 K, 5 K~8 K, and 40 K~80 K, to meet both static and dynamic operational requirements. The key design specifications for this LINAC Test Cryoplant (LTCP) are as follows: 1.5 kW @ 2 K, 600 W @ 4.5~8 K, and 6 kW @ 40~80 K. This paper presents the design progress of the cryogenic system, covering the distribution system design, overall configuration, and the specifications of major components.

The High Luminosity LHC (HL-LHC) project is aiming to upgrade of the Large Hadron Collider (LHC) at CERN will increase peak luminosity by a factor of five with respect to its nominal value. This upgrade will include the replacement of the final focusing superconducting magnets and additional superconducting radiofrequency crab cavities in the long straight sections of the interaction points 1 and 5 of LHC. The increased luminosity will significantly increase the cryogenic heat loads in points 1 and 5 of the LHC accelerator. Therefore, two new refrigerators will be required in points 1 and 5, with each an equivalent capacity of 14 kW@4.5 K, including 3.25 kW@1.9 K. A cryogenic transfer line is being developed to connect the surface-installed cold box to the underground cold compressor cold box at CERN. The system includes a vertical transfer line section that must accommodate significant thermal contraction, mechanical loads, and alignment constraints while ensuring reliable cryogenic operation. This paper presents the functional requirements and the conceptual design of the compensation mechanism implemented in the vertical core of the transfer line. Particular attention is given to the management of differential thermal contraction and mechanical stability over the full operating temperature range. In addition, the thermal design of the associated cryogenic spool is described, including heat-load mitigation strategies and insulation concepts. The proposed solutions aim to ensure safe operation, maintainability, and long-term performance of the cryogenic distribution system.

Hydrogen liquefaction is a main high-density hydrogen storage large-scale application. Current hydrogen liquefiers are precooled liquid nitrogen. Although liquid nitrogen is a cheap commodity which is a by-product in air separation plants, it is still not convenient for those green hydrogen plants based on wind and solar power generation in remote areas or offshore. The maritime transportation and long-distance land transportation cost of liquid nitrogen is high, while the vaporization of long-time liquid nitrogen storage is also nonnegligible. Besides, the large-temperature-difference heat transfer process between liquid nitrogen and hydrogen could lead to a big exergy loss. As a comparison, a closed mixed-refrigerant (MR) precooling system could be a satisfying choice for those remote green hydrogen plants. These MR precooling systems which could run only with power and cooling water supply, free of a long-term stable supply of liquid nitrogen. A MR precooling system is developed for a 300 kg/d small hydrogen liquefier. As the construction of this liquefier is already completed, its precooling heat exchanger could not be changed, which is designed for normal liquid nitrogen precooling. Thus, the MR precooling system is based on a dual mixed-refrigerant process, which consists of a main MR refrigeration cycle and a secondary MR cycle to deliver cooling power from the main MR cycle to hydrogen liquefaction cycle. The main MR cycle could generate most of the cooling power, which is driven by a single-stage oil-lubricated semi-hermetic reciprocating compressor, using a neon-nitrogen-hydrocarbon mixture as refrigerant. The secondary MR cycle is driven by an oil-free open compressor, using a mixture of helium-nitrogen-propane mixture as refrigerant. The cold secondary MR is sent into the precooling heat exchanger of the hydrogen liquefier instead liquid nitrogen. The whole main MR cycle and the compressor unit of the secondary MR cycle are integrated into two skids respectively, which are independent of the hydrogen liquefier. The configuration of the precooling heat exchanger and cold box is unchanged in this 300 kg/d hydrogen liquefier, which could be a favorable technical improvement of current in-service hydrogen liquefiers. As the 300 kg/d hydrogen liquefier could not be stated due to the delay in construction, the performance test of this MR precooling system is conducted with a simulated load by an adjustable electric heater instead of an alignment joint-test with the hydrogen liquefier. For the 300 kg/d hydrogen liquefier, liquid nitrogen of 160 L/h and

The SLAC National Accelerator Laboratory houses LCLS-II, a superconducting linear accelerator (LINAC) that began operations in October 2023. Central to this advanced accelerator technology are two 4 kW @ 2.0 K Cryoplants. Supporting their operation is a dedicated Cooling Water System (CWS) with a total capacity of 2,000 m³/h. Most of the water is directed to the Warm Helium Compressor (WHC) stations, which deliver a combined mechanical power of approximately 9.0 MW. Additionally, the CWS supplies a secondary water loop with finer filtration to serve smaller components such as recovery compressors, expansion turbines, cold compressors, and vacuum pumps. This paper describes the SLAC CWS and reviews the challenges encountered with cooling water chemistry during the first year of operation. Two remediation approaches were evaluated for restoring the Cryoplant Cooling Water System: (1) a vendor-supplied turnkey cleaning package and (2) an in-house program executed by cryogenic operations personnel. The in-house approach was selected based on cost effectiveness and reduced intrusiveness, particularly for critical equipment including the Warm Compressor Station helium and oil heat exchangers. This paper gives details of the cleaning methodology, challenges encountered during execution, and the mitigation measures implemented to achieve a successful cleaning of the system.

ITER cryogenic system commissioning is well advanced on site in Cadarache. An integral part of the overall ITER cryogenic system is EU-supplied LN2 Plant and Auxiliary Systems, comprising two nitrogen liquefiers/refrigerators (1300 kW @ 80K), two GHe circulation loops dedicated to Tokamak thermal shield cooling (840 kW @ 80K), as well as a comprehensive He recovery, analysis and purification system, He and N2 warm and cold storages and a small air separation unit dedicated to compensation of N2 operational losses. Most of the above equipment is now at different stages of commissioning and performance testing. The status of different subsystems, preliminary results of performance testing, stability and flexibility of plant operation in different modes, as well as the main challenges and lessons learnt will be described below. Looking ahead, the final validation of systems integration and the verification of fully automatic operation are planned to ensure long-term reliable performance of all the equipment of ITER cryogenic system. This will facilitate seamless transition of the LN2 Plant and Auxiliary Systems into service, supporting ITER’s rigorous requirements for future equipment testing and operation.

The cryogenic system of the European Spallation Source (ESS) requires a large helium inventory to support the operation of three helium refrigerators, 33 superconducting cryomodules in the LINAC, one cryomodule in the elliptical cryomodule test stand, and numerous scientific experiments at the neutron instrument stations. To ensure reliable operation of the entire cryogenic infrastructure, accurate and real-time monitoring of the helium inventory is important. Dedicated tools and methods have been progressively developed to track helium usage throughout major operational phases, enabling comprehensive management of the helium inventory’s distribution, consumption, and recovery status. Meanwhile, helium leakage has posed a significant challenge during both commissioning and the start of steady-state operation. Such leaks must be identified promptly to minimize helium loss. The experience and methods presented in this paper contribute to more efficient helium management for current and future cryogenic operations. Key words: Helium management; Cryogenic system; Leak detection