Cryogenic mechanical properties of low thermal expansion ZrW2O8 /epoxy composites and their application in impregnated REBCO superconducting coils

Rare-earth barium copper oxide (REBCO) coated conductor (CC) tapes are promising for high-energy and high-field applications. In epoxy-impregnated REBCO superconducting windings, during the cooling process, the delamination induced by thermal mismatch stress significantly threatens stable operation due to the weak c-axis strength of REBCO CC tapes. Therefore, reducing the coefficient of thermal expansion (CTE) of the impregnation material will serve as an effective measure to enhance the structural safety of impregnated REBCO superconducting coils. In this research, a series of ZrW2O8/epoxy composites were fabricated by doping different proportions of negative thermal expansion powders into epoxy. The CTE within the temperature range of 4.2–285 K, along with the tensile and shear properties at room temperature and 77 K, were examined. Moreover, high temperature superconducting coils (HTS) were impregnated with optimized improved epoxy composite material, and the Voltage-Ampere characteristics at 77 K in self-field were explored. The results indicate that ZrW2O8/epoxy resin as an impregnation material effectively mitigates the thermal mismatch stress of superconducting coils and enhances their structural stability at extremely low temperatures. Finite element simulation provides supporting evidence of the experimental results. This study will offer an important foundation for optimizing the impregnation materials of high-field superconducting magnets and is highly significant for enhancing the performance and reliability of superconducting magnets.