Scaling law for the strain dependence of the critical current in an advanced ITER Nb3Sn strand

Measurements have been made of the critical current on an Nb 3 Sn superconducting strand destined for the ITER (International Thermonuclear Experimental Reactor) prototype cable-in-conduit conductors. Characterization of the strand was performed on a recently developed spring device, named Pacman, allowing measurements of the voltage–current characteristic of an Nb 3 Sn strand over a wide range of applied axial strain, magnetic field, temperature and currents up to at least 700 A. The strand was measured in a magnetic field between 4 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 the deformation-related parameters for the scaling of measured results, based on the so-called ‘improved’ deviatoric strain model. We also demonstrate that the same values can be derived from a partial critical-current data set without spoiling the overall scaling accuracy. This indicates that the proposed scaling relation can be used not only as a fitting tool, but is promising for reliable extrapolation as well, providing substantial savings in cost and time for the experimental routine.