Development of multi-stage Stirling type pulse tube cryocooler below 20 K in SITP, CAS

Long-life mechanical refrigeration technology is an important technology which provides support for space scientific researches and exploration. The cryocooler can reduce the background noise and improve the signal-to-noise ratio, sensitivity, and resolution of the optical detector. The cryocoolers play an important role in infrared detection that provide an essential low temperature working environment for infrared detectors and equipment. Nowadays, the sensitivity requirements of infrared detectors have increased, and it is gradually necessary to provide a cooling temperature region below 20 K. It is also necessary to provide cooling in the liquid helium temperature region for the very long waves and microwaves infrared detection. Stirling type pulse tube cryocooler (SPTC) has become one of the most popular mechanical refrigerators due to its advantages of no moving parts at the cold end, low vibration, high stability, and simple structure. In the form of multi-stage coupling, the SPTC can realize the space application in the temperature range of 4-20 K, and a series of multi-stage cryocoolers have been developed in Shanghai Institution of Technical Physics of Chinese Academy of Sciences (SITP, CAS). A two-stage SPTC operating in 20 K (PT2C-20) has been developed for cooling infrared detectors and per-cooling helium JT cryocooler. For easy adjustment and high efficiency, the driven compressor of the SPTC is designed as two independent linear compressors. The second stage cold finger uses an active warm displacer as phase shifter to maximize the cooling performance. By optimizing the operating parameters of the active warm displacer piston and the pre-cooling temperature, the cryocooler can obtain a maximum cooling capacity of 1.31 W at 20 K with the total input electrical power of 470 W and the pre-cooling temperature of 80 K. For the multi-stage pulse tube cryocoolers working at 20 K, the design of the regenerator in the low temperature section is the key to improving the cooling capacity and efficiency of the refrigerator. In order to further lower the no-load temperature and improve the efficiency of the cryocooler at 15 K, we studied the influence of the regenerator in the low temperature section of the second stage pulse tube refrigerator by simulation and experiments. The structural parameters of the regenerator and other key components were optimized and improved, and a new two-stage SPTC (PT2C-15) was designed for the 15 K temperature region. The cryocooler can obtain a cooling capacity of 0.91 W at 15 K with a total input electrical power of 386 W whose cooling capacity and efficiency are greatly improved. In order to realize the applications of liquid helium temperature region, we have developed the three-stage pulse tube cryocooler technology, especially for the large cooling capacities. A third-stage SPTC is thermally coupled with the developed two-stage SPTC (PT2C-20) and successfully obtained a three-stage SPTC (PT3C-7) which can work at 4-10 K. Within the total input electrical power of 500W, the PT3C-7 with He-4 as working fluid can obtain a minimum temperature of 3.96 K, and a typical cooling capacity of 145mW at 7 K. The development in the multi-stage SPTC working in the temperature range of 7-20K of SITP, CAS will provide very low-temperature technical support for detection in the field of infrared astronomy.