Development of Nb/sub 3/Sn superconductors for a 1 GHz NMR magnet. Dependence of high-field characteristics on tin content in bronze matrix

To realize a 1 GHz NMR magnet, superconducting properties such as critical current density (J/sub c/) and n-value are fundamental for conductors. J/sub c/ improvements of 15% to 27% have been observed in the conductor with Cu-15wt.%Sn-0.3wt.%Ti matrix compared with J/sub c/ in a conductor with Cu-13.wt%Sn-0.3wt.%Ti matrix. In contrast to J/sub c/, differences in n-values between conductors have not appeared. In this study, systematic analysis for dependence of J/sub c/ and n-value in the high field region on Sn content over 13wt.% in bronze was examined based on the microstructures, i.e. the amount of reacted layer, grain size of Nb/sub 3/Sn, and upper critical field (H/sub c2/) supported with stoichiometric analyses.