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 650degreesC or 700degreesC 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 7001 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) and n-value in high magnetic field region are estimated for this wire. As a result, the wire showed Jc and n-value of 115 A/mm(2) 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.