PROJECT TITLE :

An Investigation Into the Heat Treatment Tolerance of WST Nb3Sn Strands Produced for Massive Fusion Coils

ABSTRACT:

Multistep heat treatments are needed to provide the superconducting Nb3Sn in the International Thermonuclear Experimental Reactor toroidal field coils; but, deviations within the temperature and dwell time throughout heat treatment of the massive conductors are unavoidable, and these could have an effect on the performance of the Nb3Sn strands. To investigate the influence of heat treatment tolerances, both internal-Sn- and bronze-process-sort Nb3Sn strands were heat treated with completely different cycles. For the internal-Sn process strands, the crucial current density increases because the temperature will increase from 630 °C to 650 °C and remains unchanged at 670 °C for one hundred h. The Sn content in the filament increases with increasing temperature, and also the grain sizes significantly increase from a mean of 130–202 nm from 630 °C to 670 °C. For both the inner-Sn process strands and bronze route strands, seldom changes when the duration at 650 °C is increased from one hundred to two hundred h. Despite these changes, this study shows that Nb3Sn strands don't seem to be terribly sensitive to small heat treatment variations at 650 °C, and a variance of ±five °C is acceptable for both varieties of Nb3Sn strands.