Development and Experimental Testing of a Differential Thermal Expansion Type Gas-Gap Heat Switch for Dilution Refrigerators

Abstract

The gas-gap heat switch, with its stability and reliability, high switching ratio, and a design that is simple, flexible, and easily scalable, has become the preferred option for efficient pre-cooling in various low-temperature devices such as dilution refrigerators. We have successfully developed a differential thermal expansion type of gas-gap heat switch. This paper details its basic principles, fabrication process, performance testing, and preliminary application in dilution refrigerator system. The typical thermal conductivity of the gas-gap heat switch in the temperature range of 4–30 K has been experimentally measured in both ON and OFF states, and the results are generally consistent with the calculated data. Tests in a dilution refrigerator with a cooling power of approximately 400 μW at 100 mK showed that the developed gas-gap heat switch assembly could perform its functions of thermal connection and disconnection properly and reduce the temperature of the still cold plate to about 7 K within roughly 24 h, significantly improving the original cooling time. Additionally, its heat leakage in the millikelvin temperature range does not affect the attainment of temperatures around 10 mK. Finally, combining the calculated results, we quantitatively analyzed the impact and feasible solutions for the performance improvement of this type of gas-gap heat switch. The research work presented in this paper is of reference value for efficient pre-cooling in dilution refrigerators and other low-temperature equipment.