A hybrid 3He Joule-Thomson cryocooler designed for precooling the space dilution refrigerator

Space sub-Kelvin refrigeration technology is an indispensable part of many deep space exploration missions. The dilution refrigerator (DR) is one of the sub-Kelvin refrigerators used in space missions. The space DR requires a closed-cycle design for a longer service life. The 3He Joule-Thomson (JT) cryocooler is an excellent choice among the space mechanical cryocoolers for precooling the space closed-cycle DR (CCDR) because it can provide a stable, vibration-free precooling environment. In this paper, the required cooling capacity of the CCDR's final precooling stage is calculated. The design goal of the 3He JT cryocooler is to obtain 3.6 mW of cooling power at or below 1.7 K. A third-stage counter-flow heat exchanger (CFHX3) is designed for the 3He JT cryocooler with an actual heat exchange efficiency higher than 99 %. A four-stage JT compression system consisting of two oil-free linear compressors is developed based on space compressors verified by many space missions of China. The JT expansion impedance consists of two orifices with diameters of 27 mu m and 26 mu m in series. Then, experiments are conducted on the coordination of the CFHX3, the JT expansion impedance, and the JT compression system. Hence, a hybrid 3He JT cryocooler is successfully designed, fabricated, and tested for the CCDR and obtains a noload temperature of 1.40 K with a power consumption of 277 W. Furthermore, with a power consumption of 320 W, the 3He JT cryocooler attains a cooling power of 3.75 mW at 1.54 K with temperature fluctuation lower than +/- 0.02 K.

Automated summary

Space sub-Kelvin refrigeration technology is essential for deep space exploration missions, and the dilution refrigerator (DR) is commonly used in space missions. The 3He Joule-Thomson (JT) cryocooler is chosen for precooling the space DR due to its stability and vibration-free environment. A hybrid 3He JT cryocooler is successfully designed, fabricated, and tested for the CCDR, achieving a noload temperature of 1.40 K and a cooling power of 3.75 mW at 1.54 K with low temperature fluctuation.