This paper describes the design and performance of 4.5°K closed-cycle refrigerator.
Using a Gifford-McMahon cycle refrigerator (manufactured by Cryomech Inc.) for cooling helium gas down to 16°K, the addition of a Joule-Thomson expansion circuit provides 1 watt (using Cryomech GB 02 refrigerator, without LN₂), and 1.6 watts (using Cryomech GB 12 refrigerator, with LN₂) of refrigeration power at 4.5°K.
Performance is shown in Table 1.
The refrigerators feature (1) to be automatic, maintenancefree and compact size, which can run continuously for about 3, 000 hours without operator, (2) to have a high efficient small heat exchangers, (3) to have a simple thermal switch to make short the cool-down time by automatically precooling the low temperature parts, (4) to have a fixed J-T valve and an automatic by-pass valve.