Manufacturing of titanium-bronze processed multifilamentary Nb3Sn conductors

It has been revealed that small amount of titanium addition to the bronze matrix is most effective for improving the high-field current-carrying capacities of bronze-processed multifilamentary Nb3Sn conductor. Multifilamentary Nb/Cu-7.5 at %Sn-0.4 at %Ti round wires with 4-5 μm-diam 31×331-cores fabricated through drawing process only showed the overall critical current density Jc(overall) over 3.5 × 10⁴A/cm²at 15 T after the heat treatment at 690°c for 200 hr. It was also shown that the critical current anisotropy became larger with increasing aspect ratio of the rectangular shaped multifilamentary Nb/Cu-7. 5Sn-0.4Ti conductors. Rectangular shaped 5 μm-diam 31 × 361-core Nb/Cu-7.5Sn- 0.45Ti conductors prepared through double extrusions showed about the same tendencies in the aspect ratio dependence of Ic( as those prepared through drawing process only, after the heat treatment at 690°C for 200 hr. 9.5 mm wide and 1.8 mm thick Nb/Cu-7.5Sn-0.4Ti conductors with 5 μm-diam 349 × 361-cores have been successfully fabricated in full production scale through three steps hydrostatic extrusion process. These rectangular shaped practical multifilamentary Ti bronze Nb3Sn conductors make feasible to generate a central magnetic field over 16 T in the 190 mm winding inner diameter intermediate coil of the 18 T superconducting magnet at NRIM.