A Study on the Electrical Contact Resistance and Thermal Conductivity of Soldered-Metal Insulation Coil With Conduction Cooling

The no-insulation (NI) winding method has been widely used in the fabrication of superconducting coils owing to its excellent thermal stability and mechanical stiffness. In the NI coil, there is a charging delay and heat loss due to leakage current. Therefore, the metal insulated (MI) winding method was proposed to reduce the charging delay and the heat loss due to the leakage current and the increased contact resistance by the metal tape. However, it is difficult to quantify the contact resistance between the turns of the coil during the design stage. To resolve this problem, a new winding method, called soldered metal insulation (SMI), was proposed by the authors, and the electrical properties were evaluated in a bath of liquid nitrogen. As a follow-up to the previous research, experimental investigations were conducted in a conduction cooling test apparatus to investigate the electrical and thermal characteristics of the SMI coil below 77 K. The electric contact resistances were evaluated through sudden discharge experiments. Then, the thermal contact resistances were measured using a heater installed on the outer turn of the coil. It is believed that the SMI winding technique can be applied to fabricate rare-earth barium copper oxide (REBCO) coils with predictable electrical and thermal contact resistances.