THERMAL EQUILIBRIA AND STABILITY OF A SUPERCONDUCTOR

The criterion of ''equal area'' is known as a necessary and sufficient condition in order that a one-dimensional superconductor of infinite length, submitted to fixed current density and magnetic fields, could not evolve towards the resistive state after an accidental local overheating. It concerns only the source term of heating (competition between the heat power generate by the Joule effect and the one which is absorbed by the cryogenic bath) and is only sufficient in the case of infinite length, which is the case of an uncooled region situated between two others, well cooled by the cryogenic bath. We give here a new criterion, which is now necessary and sufficient and allows other physical characteristics of the conductor to be brought into play in order to extend the field of stability of its superconducting properties (Bonzi, 1990).