Normal-zone propagation velocity in superconducting wires having a CuNi matrix

The thermal behavior and the electromagnetic behavior of superconducting wires during quench are apparently different from those of conventional copper-stabilized composites. To investigate these properties, the authors consider the effects of the temperature gradient in a radial direction of the wire cross-section and the redistribution of currents in the normal-zone wavefront. They measured longitudinal normal-zone propagation velocities in NbTi/CuNi composite wires (strands) with different cooling characteristics and compared the measurement results with analytical results obtained by means of the three-dimensional finite-element method (3-D FEM), taking into account the redistribution of currents and the influence of the transverse electrical conductance on the current sharing in a composite. The analytical and experimental results agree well. On the basis of these comparisons, the mechanism of normal-zone propagation in superconducting wires with a CuNi matrix is discussed.