The field, temperature and strain dependence of the critical current density of a powder-in-tube Nb₃Sn superconducting strand

Abstract

We present critical current density (JC) data as a function of magnetic field, temperature (4.2 K≤T≤14 K) and intrinsic strain (εI) for a high performance powder-in-tube (PIT) Nb3Sn strand. Although the critical current density is very high, it is demonstrated that there is no stronger strain sensitivity than for Nb3Sn strands of other types and that the reversible strain window encompasses at least −0.60%<εI<0.25%. The n-value of the PIT Nb3Sn strand, derived from the electric field–current density (E–J) characteristics, is two or three times larger than those of strands made using other production processes. However, the normalized n-index as a function of intrinsic strain still shows a similar behaviour to those for other strands. The relation between the n-index and the critical current is described by the empirical power law of the form n = 1+rICs, where r and s are approximately 3 and 0.5 respectively. We conclude that the increase in JC and the n-value for PIT strands is achieved while maintaining good tolerance to strain.