Influence of High-Thermal-Conductivity Plastic With Negative Thermal Expansion Coefficient on Cooling Performance in Conduction-Cooled HTS Coils

We evaluated an insulative-high-conduction plastic (IHCP) sheet, which had high thermal conductivity perpendicular to its plane, as an electrical insulation sheet in a high-temperature superconducting (HTS) coil. Thermal conductivity of the IHCP was measured at cryogenic temperatures and was found to be 20-40 times higher than that of a glass-fiber-reinforced plastic (GFRP). Next, the thermal strain of the IHCP was measured, and a negative thermal expansion coefficient was found along the fiber direction. The IHCP expanded to produce a strain of approximately 0.4% during cooling from room temperature to liquid nitrogen temperature. Finally, a short HTS tape was sandwiched by the IHCPs and was quenched with a local heater placed on the tape. The time required for quenching with the IHCP was several times longer than that with the GFRP. From numerical simulations of the quench tests, the IHCP's thermal contact resistance with the HTS tape was estimated to be approximately 35-40% lower than that for the GFRP. We think the IHCP is effective for increasing the thermal stability of an HTS coil.