Refrigeration for cryogenic sensors and electronic systems

Abstract

There are, of course, some applications where lower temperatures are required in any case.In short, the purpose of the first conference was to define the problem.The present conference was organized quite differently.It was open to all interested participants, and most papers were contributed.Invited papers are those by Roubeau and by Nisenoff, the former being a rather free-ranging discussion of some unconventional approaches to cryogenic technology, and the latter a comprehensive review of recent developments in high-T superconducting devices and materials.The contributed papers are on refrigeration concepts, systems and components suited to the support of cryogenic sensors and electronic systems below 20 K. Techniques and components developed for higher temperatures that are applicable to low-temperature refrigeration are included.In reviewing the progress that has been made during the last three years, it is apparent that the desired goals have not been achieved.Nevertheless, there have been some notable developments.Several funding agenices, in particular the Office of Naval Research and Wright-Patterson Air Force Base, are now supporting conceptual studies and developments of low-power cryocoolers for superconducting instruments, and a number of such projects are underway. As described in this report, a helium 1 iquefier-cryocooler for a superconducting computer has been built and is being tested. Also in this report are papers demonstrating increasing interest and emphasis on gas refrigerators using resonant mechanical systems driven by linear reciprocating electric motors and supported by gas bearings or magnetic suspensions. These systems offer the potential of ultimate simplicity, freedom from contamination, long life, and (eventually) low cost. Although the operation of such systems may at ftrst glance appear somewhat subtle, we might point out the obvious, namely that the mathematical description of a resonant reciprocating cryocooler is identical (except for non-linearities) in all essentials to that of coupled electrical resonant circuits with a sinusoidal driving force, a system as familiar as sunrise to most electronic engineers (Probably even the non-linearities are analogous to a considerable extent).Finally, a book by Prof. Q. Walker, Stirling Machines, has just been published by Plenum Press, and a companion book, Cryocoolers, is in press. These books are a very comprehensive source of information and references on the whole technology.• 1 Approximatley one-half (57) of the participants at this meeting returned a questionnaire, distributed during the meeting, with answers to three questions. To the question "Has the conference been worthwhile?", 56 said yes and 1 said somewhat.To "Should it be held again?", the answer was yes, unanimously.To "At what interval?" 11 said 1 year, 33 said 2 years, 12 said 3 years, and 1 said 4 years.There were several useful comments and criticisms. One was to allow more lead time and to provide for distribution of reprints at the meeting.Some comments concern...