Calculation of normal zone propagating velocities and transient thermal effects dependence on the superconducting wire parameters

Normal phase propagation velocities along superconducting wires immersed in a cooling normal helium bath were investigated experimentally and theoretically. The measurements have been done for bare tin wires with different radii and resistivities. The theoretical calculations of the normal zone propagation velocity versus the circulating current assume a transient mechanism for heat transfer between the wire wall and the normal helium bath. The transient-heat-transfer term is of the form alpha theta /sup 2/ delta theta / delta t, where theta is the temperature relative to the normal helium bath temperature. The transient-heat-transfer coefficient, alpha , is then defined, and good agreement between the theoretical and experimental data is obtained. The coefficient depends on the bath temperature and, nonrandomly, on the maximum power per unit surface released to the normal helium bath, which in turn depends on the wire radius, critical current, and resistivity.< >