Improvement of the Trapped Field Performance of a Holed Superconducting Bulk Magnet

Our goal is to generate a strong magnetic field using a REBCO bulk superconductor activated by pulsed field magnetization (PFM) for industrial application using the bulk magnet. As the diameter of the material increases and its critical current density rises, magnetic field trapping by PFM is difficult due to the strong magnetic shield. We have proposed a holed superconducting bulk magnet to improve the trapped field performance in large-size and high- J_c bulk material. Magnetic flux can be supplied efficiently by reducing superconductivity in the portion with holes artificially. To confirm the validity of the proposed method, an experiment, in which a single pulsed field was applied with changing amplitude of the magnetic field and temperature, was carried out using a GdBCO bulk superconductor with four small holes. Although the magnetic flux penetrated at a lower applied field, there was a problem in that the maximum trapped field and the total magnetic flux decreased. In this paper, the size and number of holes were optimized to manage both the increase in the trapped field and easy flux penetration. A hole 1mm in diameter was drilled to half of depth of the thickness at the rim of a sample after investigating the magnetization characteristic of a GdBCO bulk 60 mm in diameter and 20 mm thick. A trapped field performance was evaluated in the sample, and afterwards, the hole was bored completely to the full depth. Then, the same experiment was carried out. The trapped field for a single hole was improved compared to the four holes, and it was confirmed that the 1-mm-diameter hole did not degrade the magnetization performance.