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

The relationship between the n-value and critical current (I-C) 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% <= epsilon I <= +0.4%). For the five wires exhibiting intrinsic behaviour, n(I-C) can be parameterized by a modified power law of the form n = 1 + rI(C)(s), 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.