Scaling law for the strain dependence of the critical current in an advanced ITERNb3Sn strand

Abstract

Measurements have been made of the critical current on anNb3Sn superconducting strand destined for the ITER (International ThermonuclearExperimental Reactor) prototype cable-in-conduit conductors. Characterizationof the strand was performed on a recently developed spring device, namedPacman, allowing measurements of the voltage–current characteristic of anNb3Sn strand over a wide range of applied axial strain, magnetic field, temperature andcurrents up to at least 700 A. The strand was measured in a magnetic field between4 and 11 T, temperatures of 4.2–10 K and applied axial strain ranged from−0.9% (compressive)to +0.3% (tensile). The critical currents were then used to derive the superconducting and thedeformation-related parameters for the scaling of measured results, based on theso-called ‘improved’ deviatoric strain model. We also demonstrate that the samevalues can be derived from a partial critical-current data set without spoiling theoverall scaling accuracy. This indicates that the proposed scaling relation canbe used not only as a fitting tool, but is promising for reliable extrapolation aswell, providing substantial savings in cost and time for the experimental routine.