An experimental and theoretical study of the effect of local heating on composite superconductors

Experiments have been performed where a short section of long, stabilized, NbTi conductor was driven normal and the voltage was recorded as a function of position and time. Conductors tested included samples with internal cooling channels or electrically insulating coatings. Heater power or pulse energy, conductor current, and background magnetic field were varied. The data show a number of interesting effects not previously noted in experiments where the entire conductor length was heated. These effects are discussed, as are the detailed comparisons of the steady-state results with the predictions of numerical computations. In general, the computation accurately predicts the power required to form a normal zone as a function of field and current. Both experiment and theory show that the temperature interval bracketing the nucleate-to-film-boiling discontinuity in the heat transfer coefficient can be traversed smoothly without any corresponding discontinuity in the curve of maximum wire temperature vs heater power. The normal zone is hotter and longer than predicted, however, necessitating modifications to the previously published results for apparent heat transfer in the film boiling regime.