Thermal and electrodynamic aspects of the superconductive transition process

Abstract

The dynamic processes occurring in the transitions back and forth between the normal and superconducting states dominate the practical aspects and engineering considerations of virtually all superconductive computational devices, yet represent an area of greatest deficiency in theoretical understanding. However, in the case of the superconducting-to-normal transition induced in a thin wire or strip of film by the flow of a sufficient electric current, one of the chief dynamic aspects of the process can be discussed simply on the basis of a proper accounting of all heat generation and heat flow, particularly of the joulean heat generated in an already normal region. The derivations are outlined of the formulas describing the velocity of propagation of the transition and of the relations between current, bath temperature and the quenching characteristics of the material. The approximations necessary are indicated. In many other cases, such as expulsion of or quenching by an external magnetic field, or in certain extreme conditions of current quenching and recovery, the chief aspects of the process are electrodynamic. While the Londons' equations and boundary conditions give a complete characterization of the electrodynamic properties of the superconductor, they do not apply to the transition process itself. Some considerations are given for an appropriate generalization of these equations, and those of more recent theories, to the transition, and a few simple, heuristic models are used to suggest specific equations.