Dynamic stability of superconductors cooled by pool boiling

Abstract

The transient one-dimensional heat conduction equation in a NbTi composite superconductor with an initial localized heated zone and cooled by pool boiling of liquid helium ( 4He) has been analysed numerically. The initial excess thermal energy associated with the localized heated zone was about the level of that associated with the minimum propagating zone (MPZ) equilibrium. The heat transfer characteristics of boiling helium, the variation with temperature of the heat capacity and thermal conductivity of the conductor and the temperature dependence of the Joule heat dissipation of the electric power were all stored in a computer to be referred to by a program. The stability of the conductor—coolant system was thus investigated. The conductor experienced quenching in many cases with the initial excess thermal energy less than the excess thermal energy stored at the MPZ equilibrium, and the recovery quenching was surprisingly dependent on the space-wise distribution of the initial excess thermal energy along the conductor. Thus, the MPZ criterion does not always guarantee safe operation of superconductors, though it might be an important quantity characteristic of a conductor—coolant system.