Critical current density of superconductors as a function of strain in high magnetic fields

Abstract

A probe has been designed and built to measure the critical current density ( J C) of short superconducting wires and tapes as a function of strain ( ϵ) in small bore high field magnets. The probe can measure currents of up to 100 Amps and strains of ±1.0% on both low and high temperature superconductors. Measurements can be made in our 40 mm bore 17 T high magnetic field system in pumped cryogens. Strain is measured using commercial strain gauges pasted directly onto the samples. A Ag-sheathed Bi 2Sr 2Ca 2Cu 3O X tape has been measured at 4.2 K in magnetic fields up to 12 T. J C is hysteretic in high magnetic fields and is weakly dependent on magnetic field and tensile strain up to ∼0.29%. Beyond ∼0.29% strain, the filaments break and J C drops precipitously. Results are also presented for the effect of tensile and compressive strain for a 0.37 mm diameter Nb 3Sn wire at 4.2 K and 2.9 K from 10 T up to 14 T. The data confirm that a simple scaling law that includes the upper critical field ( B C2( T, ϵ)) and the reduced field ( B/ B C2( T, ϵ)) alone cannot accurately describe the field, temperature and strain dependence of J C.