Basic Research on a Magnetic Refrigeration System for Cooling to Liquid Hydrogen Temperature

Magnetic refrigeration technology is expected to be a highly efficient process at a temperature of around 20 K, which is the hydrogen liquefaction temperature. In magnetic refrigeration, a magnetic field change is applied to a magnetocaloric material (MCM) to obtain a magnetocaloric effect. In addition, since the greater the magnetic field change, the better the cooling characteristics, the magnetic field strength of permanent magnets is insufficient, and the use of superconducting coils that can generate strong magnetic fields with low power consumption is essential. We are researching and developing a static magnetic refrigeration system (SMRS) that does not have moving parts to obtain magnetic field changes, and generates them by altering the energizing current to the coil. The key to devising this system is an AC loss of the superconducting coil. In this study, we measured the AC loss under energization conditions of multiple palm-sized REBCO coils at liquid nitrogen temperature, and calculated the efficiency of the SMRS by improving the accuracy of the analysis method for evaluating the AC loss, based on the results. We report the results and discuss the technical feasibility of SMRS.