Simulation research on the effect of magnetic field uniformity on a single-stage adiabatic demagnetization refrigerator

Adiabatic demagnetization refrigerators (ADR) are being widely used in space exploration projects and frontier scientific research fields. During the design process of ADR, the assumption of a uniform magnetic field is often used to determine the amount of magnetocaloric material and to predict the cooling capacity. However, the actual magnetic field produced by a superconducting magnet is usually non-uniform, and the non-uniformity inside the salt pill results in reduced cooling capacity. To investigate the impact of magnetic field non-uniformity on the performance of an ADR system by changing the length of the salt pill, a simulation model that incorporates both the superconducting magnet and salt pill is established. The model is verified by experiment with cooling power of 0.76 mW@1 K. Performance of the ADR with different cooling powers, different working temperatures and different pre-cooling temperatures are compared and analyzed. When the maximum magnetic flux density is 4 T, the cooling power is 0.7 mW, the initial temperature is 2.68 K and the working temperature is 1 K, the largest net cooling capacity of 5.39 J can be achieved corresponding to the length ratio of 1.1.