Nonlinear mechanisms of the thermal instability propagation in composite superconductors during magnetic flux creep

Abstract

The features of the irreversible propagation of thermal instabilities in composite superconductors are investigated under different cooling conditions (intensive and non-intensive) during magnetic flux creep. The analysis was performed with two models of the voltage-current characteristic of a superconductor: an ideal model having a jump-like transition from a superconducting state to a normal, and an actual model described by a power equation. The non-stationary and quasi-stationary (autowave) propagation velocities of the thermal instabilities along the composite are calculated taking into account the nonlinear properties of the composite and the refrigerant. The calculations of the propagation velocities of thermal instability are performed for both subcritical and supercritical currents. It is shown that the autowave velocities of the irreversible propagation of the thermal instability in the intensively cooled composite may only be positive since the conditions of the equal-area theorem may not be fulfilled. It is proved that the propagation of thermal instabilities in the composite superconductors is similar to the diffusion phenomena occurring in chain reactions of the exploding type.