Development of bronze-processed Nb3Sn superconducting wires for high field magnets

High performance bronze-processed Nb₃Sn superconducting wires are desired to realize a compact, easy to operate high field magnet system. To meet the requirements, we carried out an investigation to increase Sn concentration in the bronze to improve the critical current density, and performed a trial manufacture of a newly designed wire to raise the tensile strength. Our findings indicated that a high critical current density of 135 A/mm² at 20 T, 4.2 K could be obtained by increasing the Sn concentration in the bronze to 16 wt%. In addition, a high strength bronze-processed Nb₃Sn wire reinforced with composite filaments incorporating Th exhibiting a high 0.2% proof stress of near 300 MPa and adequate overall J_cs at 4.2 K, was developed.