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

S B L Chislett-Mcdonald,D P Hampshire,E Surrey,M Kovari,Y Tsui

doi:10.1088/1742-6596/1559/1/012063

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 , which shows clear angular anisotropy. At 4.2 K, the resistivity data show . 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.

Highlights

Nb-Ti is the current ‘workhorse’ of the superconductivity industry
The exponential model of Bordini is preferred for computational work because it is reasonably accurate at high fields and most importantly ensures that at high strains Jc falls to zero
The Jc and Cp measurements provide bulk properties and confirm that the angular increases in Bc∗2 observed in the as-supplied wire when the field is applied along the wire is an increase in a bulk property

Summary

Introduction

Nb-Ti is the current ‘workhorse’ of the superconductivity industry. Its ductility, relative ease of manufacture, and low cost make it the natural choice for MRI applications operating up to about 5 T. We characterise the Jc data using a simple scaling law that includes Bordini et al.’s recent work [7] on the strain dependence of Bc∗2.

Results

Conclusion