Enhancement of Trapped Magnetic Field Using a Large-Size REBCO Bulk in a Desktop Type Superconducting Bulk Magnet

We have developed a desktop type superconducting bulk magnet using a Stirling cryocooler with the aim of miniaturizing the magnet system. In our previous study, the lowest achieved temperature of 51.3 K and the maximum trapped field of approximately 2.8 T were achieved by cooling and magnetizing tests using a GdBCO bulk material 45 mm in diameter. For this paper, we remodeled the bulk magnet system in order to attach a large bulk 60 mm in diameter for the purpose of enhancing the total magnetic flux. This was based on the idea that the total magnetic flux was increased if the volume of the bulk was expanded, while we were concerned about the reduction of the trapped field due to the low cooling capacity of the refrigerator and the high ultimate temperature. When cooling and magnetizing tests were carried out using φ60-mm GdBCO bulk, the sample was cooled from room temperature to an ultimate temperature of 55.6 K for approximately 6.5 h, and the total magnetic flux was 2.0 mWb, which was approximately twice that of φ45-mm bulk, indicating that the aim of this study was achieved. The maximum trapped field was 3.0 T, which was the maximum value in pulsed-field magnetization using a large bulk at temperatures beyond 50 K.