Over-Current Test of REBCO Pancake Coils Impregnated With Electrically Conductive Epoxy Resin Under Conduction-Cooled Conditions

Abstract

Since REBa 2 Cu 3 O 7-δ (REBCO) coils have high thermal stability, the possibility of quenching is considerably lower than low-temperature-superconducting coils. However, if thermal runaway is observed in a conduction-cooled system, a REBCO coil will almost certainly be burned out. A recently reported technique of producing a REBCO coil without turn-to-turn insulation, called a no-insulation coil, is a promising method of quench protection. In order to apply the NI winding technique to a conduction-cooled REBCO coil, a coil using electrically conductive epoxy resin was developed. If thermal runaway is observed, the excessive current can be automatically bypassed through the conductive epoxy resin. We fabricated a single pancake coil wound with REBCO-coated conductor using conductive epoxy resin and tested it at 40 K. Although the coil voltage increased rapidly at 415 A, the current was automatically bypassed through the conductive epoxy resin. Before and after an over-current test under conduction-cooled conditions, the coil was tested in liquid nitrogen. The voltage-current curve of the coil was the same as the one obtained before the over-current test, which indicates that damage due to thermal runaway can be avoided by using conductive epoxy resin.