NORMAL-ZONE PROPAGATION VELOCITY IN SUPERCONDUCTING WIRES HAVING A CUNI MATRIX

Superconducting wires for persistent current switches and AC applications have a matrix of CuNi or mixture of CuNi and Cu. CuNi has high electrical resistivity and low thermal conductivity comparing with the properties of copper. Therefore, the thermal and the electromagnetic behaviour of such wires during quench is apparently different from that of conventional copper-stabilized composites. To investigate these properties, we consider the effects of temperature gradient in radial direction of wire cross-section and the redistribution of currents at normal front in this paper. We measured longitudinal normal-zone propagation velocities of NbTi/CuNi composite wires (strands) which have different cooling condition and compared them with analytical results by the three-dimensional finite element method (the 3-D FEM) taking into account the redistribution of currents; the influence of the transverse electrical conductance on the current sharing in a composite. The analytical results agree well with experiments. From these comparisons, the mechanism of normal-zone propagation in superconducting wires with a CuNi matrix is discussed.