Helium liquefaction by a Gifford-McMahon cycle cryocooler

This paper describes the principal design features and performance test results of a three-stage Gifford-McMahon cycle cryocooler by which the authors have achieved no-load temperature of 3.3 K and succeeded in helium liquefaction. The key point of the success is the selection of GdχEr1-χRh compounds as a regenerator material. The refrigeration capacity was 20 mW at 4.2 K and the helium liquefaction rate was 10 cm3/h. This is the first success that a Gifford-McMahon cycle cryocooler has liquefied helium without precooling.