Magnetization study of ITER-type internal-Sn Nb3Sn superconducting wire

Through magnetization measurement with a SQUID magnetometer the heat treatment optimization of an international thermonuclear experimental reactor (ITER)-type internal-Sn Nb$_{3}$Sn superconducting wire has been investigated. The irreversibility temperature $T^*(H)$, which is mainly dependent on A15 phase composition, was obtained by a warming and cooling cycle at a fixed field. The hysteresis width $\Delta M(H)$ which reflects the flux pinning situation of the A15 phase is determined by the sweeping of magnetic field at a constant temperature. The results obtained from differently heat-treated samples show that the combination of $T^*(H)$ with $\Delta M(H)$ measurement is very effective for optimizing the heat reaction process. The heat treatment condition of the ITER-type wire is optimized at 675$\,^\circ$C/128~h, which results in a composition closer to stoichiometric Nb$_{3}$Sn and a state with best flux pinning.