Influence of heat treatment excursion on critical current and residual resistivity ratio of ITER Nb3Sn strands. (12th June 2017)

• Record Type: Journal Article
• Authors: Lu, J; McGuire, D R; Hill, S; Niu, R; Chan, K; Martovetsky, N N
• Is Part Of: Superconductor science & technology. Volume 30:Number 7(2017:Jul.)
• Publication Date: 2017-06-12
• Subjects: Nb3Sn -- heat treatment -- critical current -- RRR -- Cr diffusion; Superconductivity -- Periodicals; Superconductors -- Periodicals; 537.623
• DOI: 10.1088/1361-6668/aa67ab
• Languages: English
• ISSNs: 0953-2048

Abstract

Abstract: Heat treatment is critically important to the performance of Nb3 Sn superconducting strands. For very large Nb3 Sn magnet coils, such as the International Thermonuclear Experimental Reactor (ITER) central solenoid (CS) coils, heat treatment carries the risk of temperature and time excursion, which may result in performance degradation. Therefore, it is prudent to study the effect of possible excursion on Nb3 Sn performance. In this study, Nb3 Sn strands used for ITER CS coils are heat treated at different temperatures for different times. Their critical current, residual resistance ratio and hysteresis losses are measured. It is found that in the range we studied, critical current and hysteresis losses do not change significantly. Residual resistance ratio, however, decreases with increasing heat treatment temperature and time. This is attributed to the diffusion of metallic elements from the plated Cr layer to the copper stabilizer. Based on a model of metallic elements diffusion, a numerical code is developed to predict residual resistance ratio as a function of heat treatment temperature and time.