Optimization of Bronze Processed ${\hbox {Nb}}_{3}{\hbox {Sn}}$ Strand for ITER at WST

Abstract

Operated under high magnetic field (>;11 T), the toroidal field (TF) system consists of complex conductors using Nb3Sn as superconducting material. According to the strand requirements for the ITER TF conductor, bronze processed Nb3Sn strands with high superconducting performance have been manufactured using high tin content bronze at WST. The studies on filament diameter, diffusion barrier, sample heat treatment and annealing temperature have been carried out to enhance Nb3Sn strand properties. The results of these investigations have been presented. The result indicates that the different filament diameter has a weak influence on the critical current (Ic) value for the different reaction degree. In the manufacturing process the annealing temperature should be kept below 500°C to realize a high n value. The continuous Nb3Sn layer formation on the internal surface of the barrier causes a considerable increase of hysteresis loss when single Nb barrier is used. There is almost no difference of Ic, hysteresis loss and grain morphology for two heat treatments: ITER heat treatment cycle B and WST heat treatment cycle.