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

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 ${B}_{{\rm{c}}2}^{* }(\theta )$, which shows clear angular anisotropy. At 4.2 K, the resistivity data show ${B}_{{\rm{c}}2}^{* }(B\parallel J)-{B}_{{\rm{c}}2}^{* }(B\perp J)\approx 1\,{\rm{T}}$. 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.