Instability of NbTi/CuNi superconducting wires

The quench current degradation in multifilamentary NbTi superconducting wires with a CuNi matrix have been measured and analyzed by the finite-element method. The authors measured the degradation of the quench current as a function of the current sweep rate in the range of 10 A/s to 100 kA/s, and the initial current, which was a transport current just before current changing. Experimental data are compared with analytical results taking the magnetic and the thermal diffusion in the radial direction of wire cross-section into account. From these comparisons, the relation between the rate of current changing and the degradation of the quench current in superconducting wires is discussed.<>