Two-Stage Double-Inlet Pulse Tube Refrigerator down to 10 K

Abstract

A two-stage pulse tube refrigerator, driven by a 6 kW compressor equipped with magnetic valves, has been developed with the objective of evaluating how well pulse tube technology can compete with comparable Gifford-McMahon refrigerators.

The first stage, when operated separately as a double-inlet system, achieved more than 30 W at 80 K; the no-load temperature was 26 K. The second stage is of similar construction and is fed by a portion of the gas flow from the cold end of the first-stage regenerator. The second stage is provided with a cold phase shifter, whereby the orifice, bypass, and buffer volume are integrated into a single copper block that is in direct thermal contact with the first-stage cold end. The cold valves are actuated by a cardanic rod system with vacuum-sealed feedthrough. This enables adjusting the optimum phase shift of the second stage without interruption of operation.

First measurements of the two-stage double-inlet system showed a minimum no-load temperature of 15 K and a cooling power of 1 W at 19 K. Stepwise modification of both stages has improved the performance to a typical value of 11 K minimum temperature, and 20 K for 10 W and 2 W heat loads at first and second stage, respectively. Additional future improvement is expected.