Investigations on a 1 K hybrid cryocooler composed of a four-stage Stirling-type pulse tube cryocooler and a Joule-Thomson cooler. Part B: Experimental verifications

• Experimental verifications are conducted on the hybrid cryocooler described in Part A. • A no-load temperature of 1.36 K is achieved with He-3 in JTC while He-4 in SPTC. • The cooling capacity of 13.6 mW at 1.8 K for the hybrid cryocooler is measured. • A bypass-accelerated-cooling approach is adopted to speed up the cool-down process. • Satisfactory agreements are observed between theoretical and experimental studies. In this part, a hybrid cryocooler composed of a four-stage Stirling-type pulse tube cryocooler (SPTC) and a Joule-Thomson cryocooler (JTC) is worked out to verify the theoretical analyses carried out in Part A. The heat loss on each precooling stage is calculated to evaluate the feasibility of thermal coupling between the SPTC and the JTC. The JT compressors are tested and then the compression capacity is studied. A bypass-accelerated-cooling approach is adopted to speed up the cool-down process. The experimental results show that with He-4 in the SPTC and He-3 in the JTC, a no-load temperature of 1.36 K is reached when the three precooling temperatures are kept at 71.2 K, 40.5 K and 8.12 K, respectively. The cooling capacity of 13.9 mW at 1.8 K is measured with the JT loop high pressure and the last stage precooling temperature being at 0.5 MPa and 8.1 K, respectively. Satisfactory agreements are observed between theoretical and experimental studies.