The cryogenics community lost one of its most influential figures with the passing of Ray Radebaugh in February 2026. Over a career spanning more than five decades, Radebaugh helped shape modern cryogenic engineering through pioneering research, devoted mentorship and an unwavering willingness to share knowledge. His work on cryocoolers, dilution refrigeration and low temperature thermodynamics helped define the field, while his generosity toward colleagues and students left a lasting personal impact on generations of scientists and engineers.
After studying physics at the University of Michigan, where he operated helium liquefiers and assisted with heat capacity measurements, Radebaugh joined the National Bureau of Standards (later NIST) in Boulder in 1966. There he became a central figure in the Cryogenic Engineering Laboratory during a period of rapid growth in low temperature science and technology.
His early research focused on the thermodynamic properties of 3He–4He mixtures used in dilution refrigeration. His work provided essential data for systems operating below one kelvin and laid the groundwork for future advances in millikelvin cooling. In later years he became equally well known for his contributions to cryocooler technology, including work on Stirling and pulse-tube refrigeration systems capable of reaching temperatures near 4 K.
Throughout his career, Radebaugh combined deep theoretical understanding with practical engineering skill. John Pfotenhauer of the University of Wisconsin–Madison recalled that Ray’s abilities in the laboratory were just as remarkable as his theoretical insights. “Although Ray’s thorough knowledge of the theoretical foundations of cryocooler research was impressive,” he wrote, “it was his hands-on skill in the lab that elevated him to hero status in my mind.”
Radebaugh also became widely known for his commitment to education. His short courses on cryocooler fundamentals, taught at conferences around the world, helped introduce generations of engineers and scientists to the field. Weisend noted that these courses were among the most consistently well attended at major conferences. Through them, he wrote, “Ray introduced a lot of people to the technology of cryocoolers, providing valuable theoretical and practical information.”
Students and younger researchers often experienced his generosity firsthand. Ryan Snodgrass of NIST recalled meeting Radebaugh while visiting the institute as a prospective postdoctoral researcher. “Ray carved out a significant chunk of his time to meet with me, even though he was already retired for a decade,” Snodgrass wrote. “Whenever I had challenging cryocooler questions I could reach out to Ray. He would respond quickly, usually with enlightening thoughts and never expected anything in return.”
For those who worked with him more closely, his patience as a mentor left a lasting impression. Yunda Wang of the Hong Kong University of Science and Technology (Guangzhou), who collaborated with Radebaugh during his doctoral studies, remembers long discussions in Ray’s office at NIST. “He patiently explained the governing equations and modeling details to me step by step,” Wang wrote. “His rigorous attitude toward scientific work is something I will always respect and learn from.”
Beyond his scientific contributions, colleagues frequently remarked on his humility and warmth. Professor S. Vanapalli of the University of Twente wrote that despite his worldwide reputation, Radebaugh remained “modest and warm-hearted,” always willing to engage with others at conferences and discussions. Even later in life, he remained deeply engaged with the field, attending meetings, studying posters and exchanging ideas with younger researchers.
Radebaugh contributed extensively to the cryogenic community through professional service. He played a key role in developing the International Cryocooler Conference and served the Cryogenic Engineering Conference in multiple roles, including board member and awards chair. In 2001, he received the Cryogenic Society of America’s Vance Award. His involvement with CSA included workshops, lectures, and editorial contributions to Cold Facts. Laurie Huget, former executive director of CSA, recalled the importance of those efforts: “Ray was extremely important to the success of our Society. The courses and workshops he led all over the world were among the major drivers of our success as the world leader in low temperature physics, engineering and technology.”
For many who knew him, however, Radebaugh’s greatest legacy lies not only in his technical achievements but also in the spirit with which he approached science and collaboration. As Pfotenhauer observed, everyone who interacted with him encountered “a warm-hearted gentle person who nevertheless exuded an excitement about anything related to cryocoolers.”
His colleagues, students and friends will continue to feel his influence for many years to come.
We asked members of the Cold Facts community to share memories and pictures of their time with Ray Radebaugh.
During my PhD at the University of Colorado Boulder (2009–2012), I had the privilege of working at NIST as a visiting student, where I worked closely with Ray on research related to micro cryogenic systems. He provided important guidance throughout that period and was also a member of my dissertation committee. Ray’s accomplishments in cryogenics are well known. What impressed me most, however, was his calm and friendly personality. I still clearly remember sitting in his office — surrounded by awards and stacks of technical papers — discussing fluid modeling issues in micro heat exchangers. He patiently explained the governing equations and modeling details to me step by step. Discussions with Ray helped me a great deal and influenced the way I approach research problems.
His rigorous attitude toward scientific work is something I will always respect and learn from. At the same time, his gentle and approachable character left a lasting impression on me. I will always remember him as an outstanding scientist, a mentor and a genuinely kind person. He will be greatly missed by all of us. My thoughts are with his family and friends.
– Yunda Wang, Ph.D.
The Hong Kong University of Science and Technology (Guangzhou)
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I heard with great shock that the legendary figure Ray Radebaugh had passed away in February. I had originally planned to visit Ray during the conference this year, but the gathering in Hawaii 2023, where we took the photo together, turned out to be our last one.
I first met Ray over 20 years ago. The photos show us sightseeing in the Forbidden City in Beijing. His profound contributions to numerous cryogenic technologies are, of course, globally recognized. But beyond that, he was also modest and warm-hearted. My connection with him began in the early days when we worked on pulse tube and thermoacoustic refrigerators. I remember once sending him a newly finished paper about thermodynamics on pulse tube coolers, joking that it might help him to fall asleep on his flight back to the US.
Later, as I led my team in dilution refrigeration research, I discovered that some very classic papers in the field were also authored by him. It has been my great privilege that our work over the last two decades received his generous recognition. I also deeply appreciate his support in my personal career.
I have always been inspired by his dedication. Even at an advanced age, he persisted in research, performing calculations and analyses and attending academic conferences. In Hawaii, I often saw him browsing posters and exhibition booths, engaging in discussions with others. At that time, he had gotten an injury on his face, which gave him a rugged look.
There is no better way to conclude than by quoting the CSA memorial tribute: “Many of us were fortunate to learn directly from Ray, not only about cryocoolers but about curiosity, rigor, and the joy of solving hard problems.”
He may be gone, but his spirit and influence will forever inspire generations to come. May he rest in peace.
– Dr. Wei Dai
Technical Institute of Physics and Chemistry, Chinese Academy of Sciences
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Ray was an extremely talented and selfless scientist. When I first visited NIST as a prospective postdoc in 2019, Ray carved out a significant chunk of his time to meet with me, even though he was already retired (for a full decade by then!) and my postdoc was not to be with him, but a different group at NIST. Whenever I had challenging cryocooler questions I could always reach out to Ray. He would respond quickly, usually with enlightening thoughts, and never expected anything in return. Every time I interacted with Ray he had a smile on his face. His dedication to science – and even more so his willingness to help others – is exemplary.
– Dr. Ryan J. Snodgrass
NIST Boulder
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It is with great sadness that we learn of the passing of Ray Radebaugh. At the CNRS-CRTBT (now Néel Institute) in Grenoble, France, many of us worked for many years on advanced cryogenics, particularly dilution refrigeration, inspired and guided by Ray Radebaugh’s pioneering work.
We would like to offer our warmest and most sincere condolences to his family, friends, and colleagues.
– Henri Godfrin
Institut Néel, Grenoble, France
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I first met Ray very early in my career, at the International Cryogenics and Refrigeration Conference in Hangzhou, China in 1989. I was still a graduate student at Wisconsin at the time and Ray and I were some of the few Americans at the conference.
I recall Ray being very friendly and supportive during that first meeting and later came to realize that Ray was naturally friendly, humble and always very supportive of students and new colleagues in the field.
Since Ray’s specialty was cryocoolers and dilution refrigerators, I didn’t have much direct professional contact with him until I started to help organize Short Courses for the CSA. Ray’s course on Cryocooler Fundamentals was one of our first courses and from then on was almost always held at the Cryogenic Engineering Conference, the International Cryocooler Conference and even at the Applied Superconductivity Conference on occasion. Ray was always happy to teach these courses. These courses were generally the best attended of our short courses and the students were always pleased with Ray’s instruction. In this way, Ray introduced a lot of people to the technology of cryocoolers, providing valuable theoretical and practical information.
Ray assisted me with a number of other activities over the years, including paper reviews, suggestions for short course instructors and background information on the early days of NBS Boulder. Ray was always cheerfully helpful.
When Anne DiPaola and I started to interview people for our Pioneers of Cryogenics column in Cold Facts, Ray was the first person we approached. His interview (Cold Facts, Volume 40, Number 4 – Sept 2024) is well worth reading. One fact that sticks out for me was that for his high school science fair project, Ray hand built a functioning air liquefier. This illustrates his early skill and curiosity.
I found Ray highly competent, generous with his time and always willing to help. His passing is a loss to all of us.
– John G. Weisend II
European Spallation Source ERIC
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Ray Radebaugh has been a rich resource for the cryogenics world through many decades. Even before I ever met him, I repeatedly came across his written contributions in journal articles and book chapters, such as the multiple topics he contributed to Graham Walker’s “Cryocooler” volumes. Those caught my attention because of the broad scope of his interests – everything from dilution refrigeration to a rubber-band refrigerator. Learning from him in those chapters that any physical mechanism that is accompanied with a change of entropy is a mechanism that has the potential to produce refrigeration was an eye-opening inspiration.
In the summer of 1992, I enrolled in Ray’s week-long cryocooler course. I was aware that he had been teaching the course for many years by that time and I was excited to finally enjoy the opportunity of consuming the full course. It was a very rewarding experience; one which launched my own research into pulse tube and JT coolers. As with all of Ray’s presentations, the material was well organized, clearly communicated, and filled with lots of practical content.
Roughly a decade later my family and I lived in Louisville, Colorado while I worked with Ray and his group at NIST Boulder. During that time, I was able to learn directly from Ray about the design principles of pulse tube refrigerators, inertance tubes, and regenerators, while also observing his participation in laboratory activities. Although Ray’s thorough knowledge of the theoretical foundations of cryocooler research was impressive, it was his hands-on skill in the lab that elevated him to hero status in my mind.
Both professionally and personally, Ray Radebaugh was a generous and kind person. It was my pleasure and honor to work with him. He will be missed by us all.
– John Pfotenhauer
University of Wisconsin–Madison
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In my tenure as Executive Director of the Cryogenic Society of America, we were blessed with so many persons who contributed to the success of our organization. Ray Radebaugh was one of the most outstanding. He was greatly revered and will be greatly missed.
When CSA took over the Space Cryogenics Workshop (SCW), I had a fast learning curve. The event, held in Milwaukee, was our first venture into sponsoring this collaboration. Facilitating SCW came to be a real favorite part of my job, as the camaraderie, intellectual curiosity and cutting edge science, engineering and technology were inspiring.
I had the honor of presenting the Robert Vance Award to Ray at that workshop. It felt so right to be honoring him for his many contributions up to that point, but it became even more appropriate as his years of involvement and service to CSA progressed.
Ray was extremely important to the success of our Society. The courses and workshops he led all over the world for us were among the major drivers of our success as the world leader in low temperature physics, engineering and technology. At these courses and presentations Ray made himself available to the participants in a very collaborative way. It was clear that he enjoyed sharing his deep and wide knowledge.
Personally, I want to add that Ray, on top of his erudition, was a generous, truly nice person. In his quiet way, he contributed immeasurably to our cryogenics community. And, as I found out at the Space Cryogenics Workshop in New Orleans, he was a terrific dancer.
– Laurie Huget
Cryogenic Society of America (retired)
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I was fortunate to have Ray Radebaugh supervise part of my doctoral research, during which I worked at NIST Boulder on high frequency pulse tube cryocoolers. Ray always made time for open and thoughtful discussions, often continuing late into the night. Beyond his exceptional scientific insight, he was a genuinely kind and generous person, deeply invested in the growth of young researchers. I remain grateful for his guidance, his patience, and the lasting influence he had on my work and career.
– Prof. Dr. ir. S. Vanapalli
University of Twente
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As a junior engineer I used to accompany Dr. Thomas M. Flynn when he occasionally visited his friend Ray Radebaugh in his NIST lab.
Ray typically was working on cryocoolers and he proudly showed us his test equipment setups which were a far cry from the mature technology that we see in commercial hardware today.
Ray was always pushing the boundaries. I have always had great respect for him due to both his hard work in the lab as well as for his teaching cryocooler courses. The willingness to share that knowledge with those that continue the research and the use of those technologies has been an inspiration to me as a cryogenic instructor.
I learned a lot from Ray Radebaugh and he and his talents will be missed in the cryogenic realm.
– David J. Roth
CRYOCO LLC
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Ray gave a series of lectures on cryogenics in ZJU between 2004 and 2016, invited by Prof. Zhihua Gan. I had the privilege of attending almost all of them since 2008.
His talks broadened our horizons immensely. He provided a comprehensive overview of cryogenics from its inception and touched upon nearly every related technology and application worldwide. When I started, my knowledge was limited to pulse tube cryocoolers, but Ray taught us about all other regenerative cryocoolers, including Stirling cryocoolers. He even shared the story of a unique cryocooler developed for the Hubble Space Telescope, whose installation required a dedicated spacewalk mission! May Ray continue his speeches, surrounded by attentive audiences, in paradise.
To read the full tribute, visit https://2csa.org/cao.
– Qiang CAO
Tongji University, Shanghai, China
