Optimization of critical currents in composite-processed multifilamentary Nb3Sn conductors with Nb-Ti alloy cores

Multifilamentary Nb
3
Sn conductors with Nb-(1,2,3, 5at%) Ti alloy cores were successfully fabricated, and the relationships among the amounts of titanium addition to the core, core sizes, heat treatment conditions ,Nb
3
Sn grain structure and the superconducting properties have been studied. The multifilamentary Nb-3Ti/ Cu-7.5Sn conductor shows the highest overall critical current density J
c
(overall) at 16 T for all the core sizes of 17 μm-diam, 10 μm-diam and 7.5 μm-diam, after the optimum heat treatment. The optimum heat treatment condition for the multifilamentary Nb-3Ti/Cu-7.5Sn conductor varies slightly with core diameter. The J
c
( overall) of multifilamentary Nb-3Ti/Cu-7.5Sn conductor with 10 μm-diam 6,289-cores heat treated at 700°C for 200 hr exceeds 2.5×10
⁴
A/cm
²
at 16 T. The amount of residual tin in the Cu-Sn matrix of the multifilamentary Nb-Ti/Cu-7.5Sn conductor after heat treatment decreases with increasing titanium content in the core and decreasing core diameter. The multifilamentary Nb-3Ti/Cu-7.5Sn conductor showed appreciably improved uniaxial strain dependence of critical current I
c
at 14.5 T, as compared to that for a typical multifilamentary Nb
3
Sn conductor. The multifilamentary Nb-3Ti/Cu- 7.5Sn conductor developed in this study makes feasible to generate a magnetic field of 16 T.