Thermal and electromagnetic behavior in NbTi/CuNi superconducting wires under fast changing transport current

In superconducting wires with a CuNi matrix for A.C. use, normal transition is easily induced by various disturbances because CuNi matrix has a high electrical resistivity and a very low thermal conductivity. In A.C. use of superconductivity, we also need to know the thermal and the electromagnetic behavior during abrupt increase of transport current. We have investigated the influence of current diffusion during increase of transport current on quench current degradation in a few kinds of wires. To investigate the current diffusion during increase of transport current which has an effect upon quench current degradation in more detail, we prepared four types of sample wires with different cross-sectional geometry and different material of matrix. We measured the quench current of these wires as a function of current sweep rate with initial transport current and different cooling conditions as parameters. Experimental data are compared with analytical results by the finite element method taking the magnetic and the thermal diffusion in radial direction of wire cross-section into account. From these comparisons, the influence of conductor geometry, epoxy layer on the surface of the sample and initial transport current on current diffusion in radial direction of wire cross-section and on quench current degradation is discussed.<
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