Reversible critical current degradation of high-temperature superconducting coils under compressive stress

Analytical and experimental studies were conducted to elucidate the reversible degradation of the transport current characteristics in high-temperature superconducting (HTS) coils, as observed in a previous study. Detailed structural simulations revealed no stresses or strains associated with the deterioration, indicating a nonmechanical phenomenon. Compression tests on the HTS coil initially revealed reversible degradation; however, this phenomenon was eliminated by installing fiber-reinforced polymer (FRP) plates with gas vent holes above and below the coil. With this revised test configuration, the transport current characteristics did not degrade, even under 50 MPa compression. This demonstrated the feasibility of achieving the high strength required for large HTS generators.