Flux Flow and Thermal Stability of Stabilized Superconductors

Abstract

Test equipment has been designed in such a way that complete test cycles with bare or insulated compound conductor samples in unrestricted liquid-helium flow can be easily obtained. Sample currents up to 2000 A and fields to 80 kG can be used. An evaluation of the recovery points yields magnetoresistance data for the stabilizer material. Using these stabilizer resistance values, it is possible to split the total current into the superconductor and the stabilizer components. The tests show that, in general, the take-off points cannot be explained by the transition from nucleate to film boiling of the liquid helium. The V vs I curves in the flux-flow zone seem to indicate a heat-transfer law in the form Q=h*τn with n≃2 5 in the nucleate boiling regime. Tests with poorly stabilized samples (either bare or insulated) can be explained by assuming that parts of the sample are in the superconducting state, while other parts are in the normal state or in the flux-flow state.