Cryocoolers 9

The last two years have witnessed an explosion in interest in pulse tube cryocoolers follow­ ing the achievement by TRW of high efficiency long-life pulse tube cryocoolers based on the flexure-bearing Stirling-cooler compressors from Oxford University, and have seen the initiation of development of long-life, low-cost cryocoolers for the emerging high temperature supercon­ ductor electronics market. Hydrogen sorptioncryocoolers achieved their first operation in Space this year, and closed-cycle helium Joule-Thomson cryocoolers continue to make progress in promising long-life space applications in the 4 K temperature range. On the commercial front, Gifford-McMahoncryocoolers with rare earth regenerators are making greatprogress inopening up the 4 K market, and new closed-cycle J-T or throttle-cycle refrigerators are taking advantage of mixed refrigerant gases to achieve low-cost cryocooler systems in the 65 - 80K temperature range. Tactical Stirling cryocoolers, now commonplace in thedefense industry, continue to find application in a number ofcost-constrained commercial applications and space missions, but are shrinking in numbers as the defense industry goes through a period ofconsolidation. Building on the expanding stable of available cryocoolers, numerous new applications are being enabled; many ofthese involve infrared imaging systems, and high-temperature supercon­ ductors in the medical and communications fields. Application experiments, designed to ex­ plore, troubleshootand resolve product integration issues, continue tooccur onan ever widening front, particularly in the fields of infrared imaging and spectroscopy, gamma-ray spectroscopy, and high-temperature superconductor applications.