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Helium sorption cooler, one of the important refrigeration technologies to obtain Sub-Kelvin temperature, usually requires the use of liquid helium or GM type cryocooler to provide pre-cooling temperatures below 4 K, which is insufficient in terms of life, weight, and power consumption, thus limiting its application in some ground low-temperature experiments, but also more importantly, in space exploration. The use of lightweight mechanical refrigerators to replace the above-mentioned pre-cooling methods is an important development direction of the sorption cooler. The composite cooling system of "multi-stage Stirling/pulse tube cryocooler + JT refrigerator" and the Stirling-type pulse tube cryocooler (SPTC) are important lightweight refrigeration methods that can obtain temperatures below 4 K, but their cooling capacities are very small (especially for SPTC, its 4 K cooling capacity is only a few milliwatts), which is a severe challenge for the development of lightweight sub-Kelvin sorption cooler. This paper proposes a novel pre-cooling process that can effectively reduce the requirement for 4 K cooling capacity by cascade utilization of the SPTC cooling power, that is, cooling the radiation shield, sorption pump, and pump tube of the sorption cooler by outputting the cooling capacity at higher temperature positions of the SPTC, and only the evaporator/condenser remains on the 4 K cold head. A calculation model of the sorption cooler is established, and some verification experiments are carried out. The results show that the novel process can reduce the required cooling capacity from 13.4 mW at 4 K to 3.0 mW at 4 K in the condensation stage, and from 91.8 mW at 4 K to 29.7 mW at 10 K in the stable evaporation stage, which can save hundreds to thousands of watts of electrical power according to the current SPTC cooling efficiency. [ABSTRACT FROM AUTHOR]

Liquid-helium temperature is a widely used working temperature in low-temperature physics. At present, liquid-helium or low-frequency cryocoolers, including Gifford Mahon (GM) cryocoolers or GM pulse tube cryocoolers, are usually employed to obtain a cooling temperature of about 4 K. The use of closed-cycle mechanical cryocoolers to replace liquid helium and the development of mechanical cryocoolers toward lightweight are advantageous development directions for refrigeration technology, and certain progress has been made in recent years. This paper summarizes the development status of lightweight cryocoolers, including Joule–Thomson cryocoolers, high-frequency pulse tube cryocoolers, and Vuilleumier cryocoolers, which have the advantages of small size and low power consumption compared with GM-type cryocoolers. The evolutionary ideas of miniaturization, the research advances, the characteristics of different types of cryocoolers, and the future development directions are also systematically introduced. [ABSTRACT FROM AUTHOR]