Performance investigation on a three-stage Stirling pulse tube cryocooler operating below 5 K

A separate three-stage Stirling pulse tube cryocooler (SPTC) was designed and studied for satisfying the urgent demands of compact, long-life and reliable cryocoolers in the space and military fields. The design of the regenerator, pulse tube and phase shifter of the third stage is discussed in detail. The relationship between the length and the temperature distribution of the regenerator working below liquid helium temperature is emphatically analyzed. Finally, a bottom temperature of 4.97 K was achieved by the SPTC with helium-4 as its working gas, the cooling power was 25 mW at 6.0 K. The third stage was working at 0.91 MPa, 29.9 Hz and an input power of 100 W. It is the first time that a temperature below the critical point of helium-4 is achieved by a three-stage SPTC.