Speaker
Description
Paramagnetic salt CrK(SO4)2·12H2O (CPA) is one of the main refrigerants in the temperature range below 0.5K for adiabatic demagnetization refrigerator (ADR). In practical applications, to improve the thermal performance of salt pill containing CPA, thermal bus structure is generally used. A CPA salt pill typically includes CPA crystal, a high-purity copper thermal bus, and thermal interface. The cooling efficiency and capacity of the CPA salt pill are contingent upon several factors including grain size uniformity, thermal bus quality, and the Kapitza resistance. So far, there are few published detailed studies dedicated to the evaluation of CPA salt pill. In this paper, a comprehensive experimental and numerical investigation is undertaken to assess the performance of a 212 g CPA salt pill with the crystal growing on copper fingers made through electric discharge machining. In the experiments, a two-stage ADR system is built, which includes a 4 K pulse tube cooler, a first-stage using a GGG salt pill, a second-stage using the CPA, and two thermal switches. Isothermal demagnetization of the second stage is conducted at different temperatures below 0.5K through PID control. The cooling performance as well as the heat leakage are thus evaluated using different methods. Meanwhile, a COMSOL model for the CPA salt pill is established to help understanding its performance. Specially, influence of the copper RRR value and the temperature-dependent Kapitza thermal resistance are evaluated.
