EXPERIMENTAL AND ANALYTICAL INVESTIGATION OF DISSIPATION AND HEATING IN A YBCO FILAMENT

We measured the onset of heating in a YBCO filament between 64 and 92 K with a current pulsing system. The experimental data show that the c urrent at the onset of heating is greater by a factor of at least two than the measured critical current defined by the 1 mu V/cm criteria. We show analytically that the voltage drop in the flux-flow regime dep ends not only on the current but also on d rho(ff)/dT and dJ(c)/dT, wh ere rho(ff) is the flux-flow resistivity and J(c) is the critical curr ent density of the superconductor. A model of current density distribu tion is incorporated in the numerical solution of the heat conduction equation to predict the onset of heating in the flux-flow regime. The numerical model is capable of predicting the trend of the experimental data from 64 to 85 K. Above 85 K, the experimental data indicate that the superconductor is in a transition state between the flux-flow sta te and the normal state. The relevance of the issue of onset of heatin g in practical applications is discussed. Published by Elsevier Scienc e Ltd.