High-Field Current-Carrying Capacities of ‘Titanium Bronze’ Processed Multifilamentary Nb₃Sn Conductors with Pure and Alloy Cores

Abstract

It is required for multifilamentary Nb₃Sn conductors to have more improved current-carrying capacities in high magnetic fields to meet the demands for the 1st phase target of making a 190 mm-diam bore coil operating at 14 T in the high-field superconducting magnet project at NRIM and also to meet the near future demands for the applications such as fusion reactor magnets and high energy particle accelerators. We have shown that the composite-processed multifilamentary Nb₃Sn conductors with small amount of titanium addition to the core are feasible for these requirements. It is revealed that the multifilamentary Nb-3at%Ti/Cu-7.5at%Sn conductors heat treated at 700°C for 200 hr and 750°C for 100 hr show overall critical current densities J_c(overall)’s over 2.5 × 10⁴ A/cm² at 16 T and 1.0 × 10⁴ A/cm² at 20 T, respectively.¹ The uniaxial strain sensitivity of critical current Ic for the multifilamentary Nb-3Ti/Cu-7.5Sn composite wire is shown to be much reduced as compared to that for pure multifilamentary Nb₃Sn wires.² Recently, it has been reported that the small amount of titanium addition to the bronze matrix also significantly increases the growth rate and the critical current density Jc in high magnetic fields of the Nb₃Sn layer for the composite-processed single-core Nb₃Sn wires in the same way as that to the niobium core does.³