Numerical study of normal-zone evolution and stability of composite superconductors

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Abstract
A numerical procedure has been implemented to dynamically simulate the evolution of a normal zone in a superconducting composite. The model considers the nucleate/film boiling heat transfer of helium, the effect of current sharing, the longitudinal and turn-to-turn conductions, and the temperature variation of the thermal conductivity and specific heat. For a given set of conductor parameters and initial conditions, the evolution of a zone can be followed and its behavior established as either growing or shrinking (recovering). In between these two types of behaviors, a small region exists in which stagnant zones can be observed. Limiting recovery current density JL and heat flux QL tend to converge toward constant values for large LN. Turn-to-turn conduction allows higher JL and QL values as compared to isolated conductor cases. The minimum quench energy is calculated and compared with experimentally measured results, and reasonable agreement is obtained if an optimistic helium heat-transfer characteristic is assumed. The experiment was carried out by Wilson and Iwasa at MIT National Magnet Laboratory.