Transient Electrical Characteristics of No-Insulation REBCO Coil Impregnated With GaInSn Liquid Metal

Due to higher critical current density and better self-protection, no-insulation (NI) high-temperature superconducting (HTS) coils wound by REBCO coated conductors have been widely studied and used in various superconducting magnets. When HTS coils are applied in rotating machines and high filed magnets, epoxy resin impregnation is indispensable to improve their mechanical stability. However, the use of epoxy resin may cause delamination problems and increase the turn-to-turn characteristic resistance when the epoxy penetrates through the winding turns. Although the solder impregnation method has been demonstrated to enhance the mechanical robust of NI coils, the solder needs to be heated and melted into a liquid before it can be used, which makes the impregnation process extremely inconvenient. The gallium-indium-tin (GaInSn) alloy is liquid at room temperature with a melting temperature of 10.5 degrees C. Therefore, GaInSn liquid metal alloy can be applied as impregnation material, which makes the impregnation process more convenient. In this article, NI HTS coils with and without GaInSn impregnation are fabricated and tested for comparison. The transient electrical characteristics including charging and sudden-discharging tests are conducted at 77 K. The critical current experiment shows that the conductor of the impregnated coil can he reused. These results can provide useful data for the potential application of GaInSn impregnated NI HTS coils.