Tandem GM type-pulse tube refrigerator with novel rotary valve and bypass valve mechanism

A single-stage tandem pulse tube refrigerator has been fabricated, which is driven by two pulsating pressures of opposite phase. The refrigerator is designed as the first stage machine of a 4 K pulse tube refrigerator using a recuperator as the second stage regenerator. In this tandem configuration, two pressure pulsations are generated by a single GM-cryocooler compressor. Two identical pulse tube refrigerators are operated with a novel rotary valve that can supply high and low pressures simultaneously. The pressure measurement at the regenerator inlets of the pulse tube refrigerators confirmed the proper pressure wave of two pulsating pressures in opposite phase. Detrimental DC-flow characteristic of double-inlet GM-type pulse tube refrigerator has been suppressed by the newly designed bypass valve mechanism. This new bypass valve set has one more extra degree of freedom than usual ones to eliminate DC-flow easily. This paper describes a novel feature of the bypass valve set and its performance in the experiment. The two twin pulse tube refrigerators in a tandem mode respectively reached 35 K at no load.