Development of JT precooled Dilution Refrigerators and Refrigerant-free Dilution Refrigerators

摘要

A review is given of development and applications of the JT precooled Dilution Refrigerators (JTDR's) which use no pumped ~4He bath to condense the circulating ~3He. Further developments and current achievement of Refrigerant-free Dilution Refrigerators (RFDR's) are presented. RFDR's are realized by combination of JT precooled DR's and He closed cycle refrigerators, especially, hybrid refrigerator of the pulse tube and Gifford McMahon(GM) refrigerators. Although continuous operation of such a machine to below 50 mK has been achieved there remains problems of vibration isolation and thermal contact to reach much lower temperatures. Experiences with such a refrigerator are described and discussed along the line of authors' experiences.