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

The authors have investigated experimentally and theoretically normal phase propagating velocities along superconducting wires immersed in a cooling normal helium bath. 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 assumes a transient heat transfer mechanism between the wire wall and the normal helium bath. The transient heat transfer term added to the steady heat transfer term is of the form α θ/sup 2/ /partial deriv/θ//partial deriv/t, where θ is the temperature relative to the normal helium bath temperature. The transient heat transfer coefficient, α, between the wire wall and the cooling bath is then defined and a good agreement between the theoretical and experimental data is obtained. The transient heat transfer coefficient α depend on the bath temperature and, non randomly, on the maximum power per unit surface released to the normal helium bath, which in its turn depends on the wire radius, critical current and resistivity