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

We present critical current density ( J C ) data as a function of magnetic field, temperature (4.2 K≤ T ≤14 K) and intrinsic strain (ε I ) for a high performance powder-in-tube (PIT) Nb 3 Sn strand. Although the critical current density is very high, it is demonstrated that there is no stronger strain sensitivity than for Nb 3 Sn strands of other types and that the reversible strain window encompasses at least −0.60%<ε I <0.25%. The n -value of the PIT Nb 3 Sn 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+ rI C s , where r and s are approximately 3 and 0.5 respectively. We conclude that the increase in J C and the n -value for PIT strands is achieved while maintaining good tolerance to strain.