Performance of Stirling-type non-magnetic and non-metallic co-axial pulse tube cryocoolers for high-Tc SQUIDs operation

A set of Stirling-type non-magnetic and non-metallic co-axial pulse tube cryocoolers, intended to achieve portable cryogen-free systems with very low interference for high-T_c SQUIDs operation, have been designed and tested in TIPC/CAS. The key feature is that all cooler components in the vicinity of SQUIDs pick-up loops are made of non-magnetic and non-metallic materials, in order to eliminate complicated interference and realize direct couple with SQUIDs. The cooling options, cooler interference and corresponding solutions are reviewed briefly, and then we focus our attention on the cryogenic design and selection of the materials. Over 30 cooler samples have been fabricated and tested systematically. A typical cooling power of over 100 mW at 80 K with 70 W input electrical power has been achieved. Detailed cooling performance and elementary interference characteristics of the coolers are also analyzed and evaluated.