Development of current leads using RE-Ba-Cu-O bulk superconductors

High-temperature superconducting (HTS) current leads are used to reduce the heat load on a cryogenic system. We have developed new HTS current leads using Dy-Ba-Cu-O bulk superconductors, which have the distinctive feature of a high critical current density at 77 K in strong magnetic fields and a lower thermal conductivity. In our current leads, the bulk superconductor is rigidly reinforced by the glass fiber-reinforced plastics (GFRP) double-fastened by epoxy resin bond and stainless steel bolts. Thermal cycle and mechanical tests were conducted. The rapid cooling from room temperature to the liquid nitrogen temperature of 77 K was repeated 100 times in the thermal cycle test, and the copper electrode of the HTS current lead was plastically deformed in the bending test. Nevertheless, very little change was observed in the transport properties in liquid nitrogen between, before, and after the thermal cycle and mechanical tests, indicating that the GFRP rigid reinforcement profoundly improves the mechanical properties of the HTS bulk current lead, with the total heat load kept low. It is concluded that a compact, robust, and reliable HTS bulk current lead can be achieved by combining Dy-Ba-Cu-O bulk superconductors with the GFRP rigid reinforcement.