EXPERIMENTAL-STUDY OF STAGING METHOD FOR 2-STAGE PULSE TUBE REFRIGERATORS FOR LIQUID-HE-4 TEMPERATURES

The first two-stage pulse tube refrigerator, providing a lowest temper ature of 2.23 K and a cooling power of 370 mW at 4.2 K, employed a par allel arrangement of the two pulse tubes with phase shifters located a t room temperature(1). With the aim of increasing the COP at liquid He -4 temperatures, three modified staging methods were tested in this pa per. All refrigerator versions operate with the same two regenerators as already used in the first two-stage setup(1) and also the same 6 kW He-compressor combined with a redesigned G-M rotary valve. The best p erformance is achieved with a parallel arrangement two-stage refrigera tor by introducing proper negative DC flow and impedance tubes. So far the highest cooling power achieved on the second stage at 4.2 K was 0 .5 W. With a heat load of 20 W at 67 K on the first stage, the second stage can provide a cooling power of 0.42 W at 4.2 K. Details of the d esign of the different refrigerators and a comparison of their perform ance are presented. (C) 1998 Elsevier Science Ltd. All rights reserved .