[Abstract]
This paper presents the design and performance improvement of a three-stage Stirling-type pulse tube cryocooler (SPTC) aimed to achieve effective cooling at 4.2 K for the low-Tc  superconducting quantum interference device (SQUID). The system integration of the three-stage SPTC and the low-Tc SQUID is described, and the cryocooler is arranged with the thermally coupled configuration. A developed electrical circuit analogy model is proposed to analyze the internal operating mechanisms of the three-stage SPTC. In addition, a three-stage thermally coupled SPTCis simulated and fabricated. The performance of each stage is tested individually. The first-stage SPTC can achieve 15.67 W at 80 K. A no-load cooling temperature of 17.4 K can be obtained by the two-stage SPTC with a total input acoustic power of 424.0 W. Under the precooling of the first two stages of SPTC, the simulated results indicate that the third-stage SPTC can acquire 6.35 mW at 4.2 K when the input acoustic power is 49.5 W, and the displacement of the cold end turns out to be 1.45 μm from peak to peak.