Stirling-type pulse tube refrigerators have at-tracted academic and commercial interest in recent years due to their more compact configuration and higher effi-ciency than those of G-M type pulse tube refrigerators. In order to achieve a no-load cooling temperature below 20 K, a thermally coupled two-stage Stirling-type pulse tube refrig-erator has been built. The thermally coupled arrangement was expected to minimize the interference between the two stages and to simplify the adjustment and optimization of the phase shifters. A no-load cooling temperature of 14.97 K has been realized with the two-stage cooler driven by one linear compressor of 200 W electric input. When the two stages are driven by two compressors respectively, with total electric input of 400 W, the prototype has attained a no-load cooling temperature of 12.96 K, which is the lowest temperature ever reported with two-stage Stirling-type pulse tube refrigera-tors.
