A three-stage Stirling pulse tube cryocooler reached 4.26 K with He-4 working fluid

• A three-stage Stirling pulse tube cryocooler was optimized experimentally.
• The mutual influence relations among different operating parameters were revealed.
• A no-load temperature of 4.26 K was obtained with He-4 working fluid.

Multi-stage Stirling pulse tube cryocoolers (SPTCs) working at liquid helium temperatures are attractive because of their promising potential in tactical and space applications. However, it is still a challenge for a SPTC to operate below 5 K with He-4 as working fluid instead of the rare He-3. In this study, the operating characteristics of an in-house made three-stage SPTC were experimentally investigated. The mutual influence of precooling temperature, operating frequency, input power, and charge pressure on the cooling performance of the third stage was studied. A no-load temperature of 4.26 K was achieved by the three-stage SPTC, which is the lowest temperature ever obtained by a multi-stage SPTC operating with He-4 as working fluid.