The course begins with a discussion of cryocooler applications, followed by a study of thermodynamic and heat transfer fundamentals, which are then used to explain how various types of gas-cycle cryocoolers achieve temperatures from about 2 K to 150 K. The operating principles and advantages/disadvantages of the three major recuperative cycles and the three major regenerative cycles are explained. Ralph Longsworth provides a special emphasis on the Gifford-McMahon cryocooler including its early development history, operating principles, and applications. The course covers modeling, design approaches, fabrication techniques, and measurement methods. Millikelvin cooling technologies that can be combined with cryocoolers for cryogen-free operation at sub-kelvin temperatures are also briefly described.
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Dr. Longsworth started in the Advanced Products Department (APD) of Air Products & Chemicals, Inc. in 1968. The business, which is now called SHI Cryogenics of America, was acquired by Intermagnetics General Corporation (IGC) in March 1987, and subsequently acquired by Sumitomo Heavy Industries (SHI) in January 2002. He retired in April 2003 from his position as Chief Scientist and has been working part time since then as a Cryogenic Consultant.
His work has included the development of new closed-cycle refrigerators for commercial applications of high and low temperature superconductivity and Joule-Thomson refrigerators for military and space sensor cooling applications. He has been responsible for the development of the Displex refrigeration equipment, the liquid helium transfer Cryo-Tip units, which won IR-100 Awards, new improved miniature J-T cryostats, cryopumps, a Split-Stirling Cycle refrigerator, a long hold-time helium dewar, a refrigerator vibration isolator, a vacuum swing adsorption nitrogen generator, several new 4 K GM/ J-T refrigerators, fast cooldown J-T cryostats operating at temperatures from 10 K to 90 K. The 10 K JT BETSCE cooler flew on the Shuttle in 1996. He built the first pulse tube refrigerator as a graduate student and recently has contributed to the development of two-stage 4 K GM type pulse tubes. In the late 1990’s he led the commercialization of closed throttle cycle refrigerators which use mixed gases to produce refrigeration above 70 K with single stage oil lubricated compressors. Other helium temperature equipment includes a laboratory helium liquefier, helium screw compressors, a helium purifier, and a prototype refrigerator for a Josephson technology computer. He also contributed to the design of a small, efficient, thermal compressor for use as a power supply for an implantable artificial heart. In addition to hardware development, he has performed studies including refrigeration requirements for helium-cooled super conducting (SC) and LN2 cooled cryoresistive power transmission lines, cooling of SC magnets for Maglev trains, solid H2 rocket propellants, cooling of VLPC detectors at 6.5 K, HTS interconnects for MCMs, and refrigeration of HTS transformers and energy storage magnets. Theoretical studies and experimental work includes investigations into shuttle heat transfer thermal losses, regenerator thermal losses, pulse-tube refrigeration, and analysis of Solvay Cycle, Vuilleumier Cycle, and Split-Stirling Cycle Units.
Dr. Longsworth is a member of Tau Beta Pi and the American society of Mechanical Engineers. He is a past member of the American Vacuum Society, the Board of The Cryogenic Engineering Conference, and the Board of the International CryoCooler Conference. He has served on several cryogenic review committees at the Fermi National Accelerator Laboratory and the Electric Power Research Institute. In the area of community activities, he served for over 30 years as President of a non-profit housing corporation which has rehabilitated houses in center-city Allentown and has recently resigned his seat on the Board.
Dr. Longsworth has authored and co-authored over 60 published papers and over 70 patents.
Dr. Ray Radebaugh is a NIST Fellow Emeritus with the Applied Chemicals and Materials Division. He joined NIST in 1966 as a post doc for the first two year and stayed on in a permanent position since then. He was the leader of the Cryogenic Technologies Group from 1995 until his retirement in 2009. His research focused on cryogenic refrigeration and material properties. He has taught short courses on cryocoolers since 1981.