Electromagnetic Analysis Evaluation of Split NbTi Superconducting Magnet for Scaled-Up Active Magnetic Regenerative Refrigeration System

Active magnetic regenerative (AMR) refrigeration is expected to be used for hydrogen liquefaction owing to its wide operating temperature range. In a previous study, a reciprocating type of AMR refrigerator (Prototype 1) was used to demonstrate hydrogen liquefaction. In this study, a scaled-up version (Prototype 2) was developed to increase the amount of liquefied hydrogen. For Prototype 2, the main coils were split into two parts to extend the range of the 5 T magnetic field applied to the larger AMR beds filled with magnetic particles. As in Prototype 1, the arrangement of the AMR beds in series helped reduce the axial magnetic forces that hinder the reciprocating motion of the AMR beds and induced voltages in the superconducting magnet. To reduce AC losses, the filament radius of the NbTi superconducting wire used (in Prototype 2) was 10 µm, in contrast to the 30 µm wire used in Prototype 1. By improving the electrical design, the scaled-up magnetic refrigeration system can operate without any electromagnetic problems, such as magnetic forces, induced voltages, and AC losses.