Investigations on the throttling process of 3He in a dilution refrigerator used for cooling superconducting quantum chips

With the rapid progress of the superconducting quantum computing technology, the cryogenic technology capable of providing appropriate cooling in the millikelvin temperature region is desirable. The cryogen-free dilution refrigerator featuring high reliability, long lifetime, and continuous cooling has become one of the most promising cryocooler candidates for this purpose. As one of the key components of the dilution refrigerator, the impedance component is used to control the flow and to liquefy ³He, which is crucial to achieving the millikelvin temperature. In this paper, a throttling model is proposed to analyze the dilution cycle and to eventually improve the refrigeration performance, which focuses on the influences of the complex physical properties of ³He and the dilution cycle from the subcooled state to saturation state. The effects of the inlet pressure and inlet temperature on the flow rate are studied, and the energy conversion on the throttling process is discussed. It indicates that the throttling model can reasonably predict the flow rate under different inlet pressure and inlet temperature and is helpful to the design and optimization of the millikelvin cryogen-free dilution refrigerator.