Direct Measurement of Inter-Filament Resistance in Superconducting Multifilamentary NbTi and ${\rm Nb}_{3}{\rm Sn}$ Strands

A quantitative knowledge of inter-filament transverse resistance will allow us to describe current redistribution processes inside strands more accurately. This is particularly important for the analysis of the influence of strain and crack distribution patterns in Nb₃Sn filaments on the shape of the voltage-current curves. Several indirect methods are commonly used to assess inter-filament resistance. Here we use a direct method to measure transverse inter-filament resistance and filament-to-matrix contact resistance. Two four-probe voltage-current methods are developed for measurements below 10 K at various background magnetic fields. In addition to FEM (Finite Element Method) simulation, also a new 3D strand model is developed to simulate the current- and voltage distributions. The experimental methods, first results as well as the simulations using the FEM method and new 3D strand model are described.