Development of Nb3Sn superconductors for a 1GHz NMR magnet -: Dependence of high-field characteristics on tin content in bronze matrix

To realize a 1GHz NMR magnet, superconducting properties such as critical current density (J(c)) and n-value are fundamental for conductors. J(c) improvements of 15% to 27% have been observed in the conductor with Cu-15wt%Sn0.3wt%Ti matrix compared with J(c) in a conductor with Cu-13wt%Sn-0.3wt%Ti matrix. In contrast to J(c), differences in n-values between conductors have not appeared. In this study, systematic analysis for dependence of J(c) and n-value in the high field region on Sn content over 13 wt% in bronze was examined based on the microstructures, i. e. the amount of reacted layer, grain size of Nb3Sn, and upper critical field (H-c2) supported with stoichiometric analyses.