Overall Thermal Conductance and Thermal Contact Resistance in No-Insulation REBCO Magnet

In no-insulation (NI) REBCO coils, thermal contact resistance (TCR) between winding turns has important influence on thermal stability of REBCO magnets under varying magnetic field or even in case of quench. Reduction of TCR between winding turns is one of the crucial factors to develop thermally stable magnets cooled by conduction. To avoid a delamination problem, epoxy is not usually used between winding turns and the significant TCR exists in NI magnets. Then, thin epoxy layers between coil surfaces and metallic conduction plates are used to enhance thermal conduction in conduction cooled magnets. To design thermally stable NI REBCO magnets cooled by conduction, TCR, induced by dry contacts of winding turns, should be properly evaluated. This paper describes measurements of overall thermal conductance using a model coil without conduction plates and epoxy layers from 10 to 40 K in a conduction test apparatus. TCR is evaluated using the measured overall thermal conductance and previously reported transverse thermal conductivity of a REBCO wire. In another model coil with conduction plates and epoxy layers, enhanced overall thermal conductance is measured and compared with finite element analysis results that include the measured TCR.