Simulation and Optimization of the Number of Thermal Buses in ADR Salt Pills

As an important part of the adiabatic demagnetization refrigeration, the design and structure of salt pills directly affect the performance of the ADR. The primary goal of designing salt pills is to provide the largest cooling capacity within the operating temperature range. For the low-temperature ADR stage, the use of hydrated salt is necessary. Because of the poor thermal conductivity of the hydrated salt, the thermal bus structure is the commonly used method to improve its performance. The determination of the number of thermal buses is a compromise of the effective thermal conductivity and the volume (mass) of the CPA crystal. Increasing the number of thermal buses will effectively increase the effective thermal conductivity of salt pills, but the reduction of paramagnetic salt mass may lead to the reduction of the effective cooling capacity of salt pills. To better guide the design and construction of salt pills, this paper uses COMSOL Multiphysics to simulate the adiabatic and isothermal demagnetization processes of salt pills under different numbers of thermal buses to observe the temperature distribution inside the salt pill, and then determine the optimal number of thermal buses to ensure salt pills can provide effective cooling capacity as much as possible within the working temperature range.