Investigation of ITER use internal-sn Nb₃Sn superconducting wire through irreversibility temperature measurement

By means of a SQUID magnetometer, the irreversibility temperatures and magnetization transitions of an ITER-type internal-Sn Nb₃Sn superconducting wire were measured during warming and cooling cycles at a fixed magnetic field. The results obtained show that the irreversibility temperature T* (H) is strongly dependent on A15 phase composition and can be used to optimize the heat treatment process for the internal-Sn Nb₃Sn wire. The A15 phase composition in internal-Sn Nb₃Sn wire is temperature independent for full-time reaction. From T*(H) and magnetization transition analysis, the heat treatment condition of our ITER use wire is optimized as 675 °C/128 h, which results in the best A15 phase composition suitable for high-field application.