The magnetic field, temperature, strain and angular dependence of the critical current density for Nb-Ti

Abstract

Abstract A scaling law for J c in commercial Nb-Ti wire is proposed that describes its magnetic field, temperature and strain dependence. The scaling law is used to fit extensive measurements of the total strand critical current density, J c,TS(B, T, ε), with the applied field orthogonal to the axis of the wire. We present critical current density, heat capacity and resistivity measurements to obtain B c 2 * ( θ ) , which shows clear angular anisotropy. At 4.2 K, the resistivity data show B c 2 * ( B ∥ J ) − B c 2 * ( B ⊥ J ) ≈ 1 T . We also discuss whether the fusion community should consider re-optimising standard commercial Nb-Ti wires that were developed for MRI applications at ~ 5 T, to produce higher J c at say 10T, and higher upper critical fields, perhaps using quaternary Nb-Ti alloys with artificial pinning centres.