Development of a 4 K separate two-stage pulse tube refrigerator with high efficiency

Compared to the traditional 4 K cryocoolers, the separate 4 K pulse tube refrigerator (PTR) consists of two independent PTRs, which are thermally connected between the cold end of the first stage and some middle position of the second stage regenerator. It is possible to use different frequency, valve timing, phase shifter and even compressor for each stage for better cooling performance. A 4 K separate two-stage PTR was designed and manufactured. The first stage was separately optimized. A minimum temperature of 12.6 K and cooling capacity of 59.0 W at 40 K was achieved for the first stage by adding some Er3Ni at the cold part of the regenerator. An experimental investigation of valve timing effects on the cooling performance of the 4 K separate two-stage PTR is reported. The experiments show that the optimization of valve timing can considerably improve the cooling performance of the PTR. Cooling capacity of 0.59 W at 4.2 K and 15.4 W at 37.0 K were achieved with an actual input power of 6.6 kW. Effect of frequency on the performance of the separate two-stage PTR is also presented.