High efficient two-stage GM refrigerator with magnetic material in the liquid helium temperature region

This paper describes experimental results obtained from a two-stage Gifford-McMahon (GM) refrigerator which uses a rare earth compound as a 2nd regenerator matrix instead of a Pb matrix. The refrigeration capacity below 10 K for a conventional two-stage GM refrigerator is so small that the lowest temperature achieved is limited to the 8 K level. The purpose of this study is to improve the refrigeration performance in the temperature region below 10 K. The technical point is to use Er3Ni as a 2nd stage regenerator matrix, because it has much larger volumetric specific heat than Pb below 15 K and has almost the same specific heat as Pb at higher temperature. The reciprocating speed was optimized to improve the refrigeration performance. Refrigeration capacity of 1 W at 6.59 K and no load temperature of 4.50 K were obtained from the Er3Ni regenerator. The refrigeration loss mechanism below 10 K is also discussed. 11 refs