Development of high Sn content bronze processed Nb3Sn superconducting wire for high field magnets

Bronze processed Nb₃Sn superconducting wire with Cu-16wt%Sn-0.3wt%Ti (16%Sn bronze) matrix has been developed. For the development, two-step approach was taken. At the first step, two kinds of small size round wires, having a bronze to niobium ratio (bronze ratio) of 2.5 and 1.9, were prepared. Heat treatment was made on these wires at 650°C or 700°C and the effects of bronze ratio and heat treatment temperature on critical current density (J_c) in magnetic field region from 18 to 25 T were examined. A sample with a bronze ratio of 2.5 and heated at 700°C was found to show the highest J_c of all. In the second step, we manufactured commercial scale rectangular cross-sectioned wire using 16%Sn bronze. J_c n-value in high magnetic field region are estimated for this wire. As a result, the wire showed J_c and n-value of 115 A/mm₂ and 37, respectively, at 22 T, 2.1 K, demonstrating the possibility as a candidate superconducting wire for high field magnets such as over-920 MHz NMR magnet.