AC Operation of Gd–Ba–Cu–O High ${\rm T}_{\rm C}$ Superconducting Magnet for Magnetic Refrigeration

Magnetic refrigeration requires a strong magnetic field and its alternation for the magnetization and demagnetization processes. In this paper, a conduction-cooled HTS magnet system was fabricated and tested for a magnetic refrigerator. It consists of a HTS magnet, a pair of metallic and HTS current leads, and a cryocooler. The Gd-Ba-Cu-O coated conductor with polyimide tape insulation was used for the HTS magnet and wound by standard layer-wound method. Stainless steel bore was assembled with OFHC copper supporting plates of the HTS magnet. The OFHC copper strips were inserted between interlayers of the conductors to enhance axial thermal conduction. Apiezon N grease with hexane solution was applied on every layer of the HTS magnet to minimize thermal contact resistance between the conductor and the OFHC copper strips. The HTS magnet was cooled to 17 K. The charging and discharging of the HTS magnet were achieved by the unipolar power supply and an external dump resistor. Stable magnetic field of 3.25 T was achieved with 150 A. Alternating magnetic field was stably generated with the peak of 2.16 T (0.11 T/s). In this paper, the fabrication method of AC magnet and the operational issues of the conduction-cooled HTS magnet are discussed.