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 Nb
3
Sn 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 J
c
(overall) over 3.5 × 10
⁴
A/cm
²
at 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 I
c
(
H_{\parallel})
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 Nb
3
Sn 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.