Relationship between the<i>n</i>-value and critical current in Nb₃Sn superconducting wires exhibiting intrinsic and extrinsic behaviour

Abstract

The relationship between the n-value and critical current (IC) is investigated for six different ITER-candidate Nb3Sn wires characterized as a function of magnetic field (B≤28 T), temperature (4.2 K ≤T≤12 K) and intrinsic axial strain (−1%≤εI≤+0.4%). For the five wires exhibiting intrinsic behaviour, n(IC) can be parameterized by a modified power law of the form n = 1+rICs, where s is a constant with a value of 0.41 ± 0.03. The parameter r decreases as the magnitude of the intrinsic strain increases and is a relatively weak function of temperature. For one of the wires, the n-value saturates at high critical currents (low magnetic fields), characteristic of extrinsic filament nonuniformities.