Improvement of 4K GM Cooling Performance with a New Regenerator Material

Abstract

Sumitomo’s 4K GM cryocooler was commercialized in 1997, and has been successfully applied to a number of cryogenic applications, such as helium recondensing of MRI magnets and direct cooling of superconducting magnets. The rare earth material, HoCu2 and Sumitomo’s patented unique seal technology are used in the 2nd stage displacer of the Sumitomo 4K GM cryocooler (SRDK-408D). These two technologies contribute to the large cooling capacity and high temperature stability for long-term and orientation-free installation. Recently, a new regenerator material, Gd2O2S (GOS), which has extremely high volumetric specific heat around the 4K region, has been developed. This regenerator material has promising possibilities for the improvement of the 2nd stage cooling capacity of the 4K GM cryocooler. In this study, GOS is applied to a two-stage 4K GM cryocooler and evaluated for its cooling capacity improvement. By replacing 50% of HoCu2 with GOS, the cooling capacity ofthe 2nd stage at 4.2 K was improved approximately 10%. The most important thing for the industrial use of this new material is its reliability for long term operation. Reliability test data are also reported in this paper.