Inter-filament resistance, effective transverse resistivity and coupling loss in superconducting multifilamentary NbTi and Nb3Sn strands

The effective transverse resistivity of a range of multi-filamentary Nb3Sn and NbTi strands is measured with a direct four-probe method and the data are compared to the transverse resistivity values obtained from AC coupling loss experiments. Correspondence between both is satisfactory provided that all contributions to the current path are properly taken into account. Quantitative knowledge of the inter-filament resistance and of the effective transverse strand resistivity leads to a better insight into the physical mechanisms that govern not only AC coupling losses, but also a variety of current distribution and redistribution processes, e.g. the current entry length in short-sample measurements or critical current degradation with bending strain. The wires are state-of-the-art commercial superconductors that are presently applied in ITER, JT-60SA and LHC magnets. The influence of filament-to-matrix contact resistance, of the (possibly inhomogeneous) matrix resistivity and of the cross-sectional strand layout on the AC coupling losses in these wires is discussed