Large single-grain bulk RE-Ba-Cu-O (RE: rare earth elements) superconductors can trap large fields exceeding several teslas and thus can function as very strong quasi-permanent magnets. However, for large grain materials, either the thermal stress or the electromagnetic stress sometimes causes cracking. We have recently found that epoxy resin can penetrate into the bulk superconductors when they are immersed in liquefied resin under low pressures. Dispersing quartz filler can control the thermal expansion coefficient of the resin. With this process, the cracks that are prone to be generated on the large-diameter bulk superconductors can be effectively prevented. In order to reinforce the resin, we also employed the process to cover the bulk surface with the glass fiber fabric followed by resin impregnation. It has been confirmed that both the stability and field-trapping capability are greatly improved with such resin impregnation.
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