Prof. Dr. Jihyun Hwang holds a PhD in offshore cryogenic liquefaction process optimization from graduate school of Seoul National University, South Korea. He is an experienced Hydrogen, LNG, Oil & Gas process professional who brings 24 years of relevant experience to specific projects and technology development. He is a Professor, Head of Hydrogen Energy at KENTECH (https://www.kentech.ac.kr), a managing director for FIP (Fraunhofer InnovationPlatform) H2Energy@KENTECH (FIP-H2ENERGY@KENTECH) as well as Head of the HYLOT R&D lab (https://hylot.kentech.ac.kr), specialized in Hydrogen & LNG processes and project engineering. Before joining KENTECH, Prof. Dr. Jihyun Hwang worked as an expert in different international companies in South Korea, the United States, the Netherlands, and Germany. He is an esteemed technology development leader for (floating and onshore) hydrogen production & storage projects with in-depth knowledge and technical expertise in process engineering for cryogenic processes (Hydrogen, LNG) and liquefaction engineering, natural hydrogen, blue hydrogen, green and blue ammonia, methanol production, and CCUS (Carbon Capture Utilization and Storage).

This lecture introduces the principles and applications of hydrogen liquefaction, with a focus on cryogenic process design and future large-scale development. First, fundamental concepts of cryogenic thermodynamics and typical process configurations for ultra-low temperature systems are reviewed. Second, current precooling practices in commercial hydrogen liquefaction plants, which commonly rely on liquid nitrogen (LN₂), are discussed, and alternative precooling concepts utilizing LNG cold energy or LNG-based refrigeration cycles are presented as promising options for future large-capacity plants. Finally, liquefier process configurations based on the Claude cycle using hydrogen as the refrigerant are examined, with emphasis on technical challenges and strategies for large-scale capacity application, energy efficiency improvement, and integration with emerging hydrogen infrastructure.

Prof. Milind Atrey is currently the Deputy Director-ART(Academics, Research and Translation) at IIT Bombay and the INOX Chair Professor of Cryogenics in the Department of Mechanical Engineering. He has held significant leadership roles at the institute, including serving as the Dean (R&D) for over four years and the Professor-in-Charge of SINE (Society for Innovation & Entrepreneurship) for six years, where he oversaw the institute's business incubator. Prof. Atrey earned his PhD from IIT Bombay in 1991, specialising in Stirling cryocoolers, which laid the foundation for his extensive career in low-temperature technology.
His professional journey includes two years in industry followed by a three-year post-doctoral fellowship at the University of Giessen, Germany. He spent four years in the cryogenics section of the Department of Atomic Energy, Government of India, before moving to the UK as a Principal Engineer for Oxford Instruments Superconductivity. During his five years in the UK, he conducted critical research on MRI/NMR cooling systems, cold probes for electronic cooling and worked extensively on Pulse Tube Cryocooler technology. Prof. Atrey returned to IIT Bombay as an Associate Professor in 2005, becoming a full Professor in 2009 and then Chair Professor in 2017.
Prof. Atrey is a Fellow of the Institution of Mechanical Engineers (FIMechE), the Indian Cryogenics Council (FICC), and the International Academy of Refrigeration. He serves on the International Cryogenic Engineering Committee (ICEC) and the International Editorial Advisory Board of the journal Cryogenics. He is the former President of the Indian Cryogenics Council (ICC). He has edited a book called Cryocoolers: Theory and Applications (International Cryogenics Monograph Series). He has also been the sole instructor of a widely utilised NPTEL course on Cryogenics, the benefit of which has reached to millions of students and researchers in the world. His current research interests focus on miniature cryocoolers, quantum cooling, sloshing, and the development of innovative, high-efficiency cooling solutions.

This short course lecture is meant for new students of cryogenics or researchers in this field. Cryocoolers are machines that produce low temperatures in a closed cycle manner and are a popular choice today. They replace cryogens such as liquid helium for many laboratory applications or for smaller devices. Liquid Helium is increasingly unsustainable due to rising costs and limited reserves.
Cryocoolers are broadly classified based on the kind of heat exchangers used in the machines, eg. recuperative and regenerative types. Recuperative designs, including Joule–Thomson (J–T), Brayton, and Claude cycles, rely on steady-flow heat exchangers. Regenerative cryocoolers, such as Stirling, Gifford–McMahon (GM), and Pulse Tube systems, employ cyclic heat exchange and regenerative matrices. Each type presents trade-offs in efficiency, vibration, size, and operating frequency. Mixed refrigerant J–T coolers have reduced compression pressures from ~200 bar to 15–20 bar, enabling compact, efficient cooling through tailored mixtures and specialised heat exchanger designs.
This lecture will provide the basic working of these cryocoolers, along with some simple design concepts for J-T coolers and regenerative coolers. It will also highlight applications of cryocoolers, including infrared sensor cooling, gas liquefaction, and magnet cooling. By bridging thermodynamic principles with engineering innovation, cryocoolers offer sustainable alternatives to cryogen-based systems.

John Weisend is a Senior Accelerator Engineer at the European Spallation Source specializing in large scale cryogenics and He II. He is the Chair of the Cryogenic Society of America and the International Cryogenic Engineering Conference Board. He is Editor-in-Chief of the journal Interactions. His books include: Superfluid, He is for Helium, The Handbook of Cryogenic Engineering (ed), Cryostat Design (ed), and Cryogenic Safety (with T. Peterson).

Cryogenics is an enabling technology in accelerators, high energy physics and fusion energy. In many cases, work in these fields is only possible at cryogenic temperatures. Cryogenics is used to cool superconducting magnets, superconducting RF cavities, provide dense pure liquids for moderators, targets and particle calorimeters and at sub-Kelvin temperatures to provide environments for the detection of rare events and dark matter. Over the years, innovations in these fields and in large scale cryogenics have fed into each other; resulting in new technologies and scientific discoveries.
This class will survey the use of cryogenics in accelerators, high energy physics and fusion energy. It will describe motivations, the innovations developed and give examples of many systems. The features of large scale cryogenic plants will also be described.