Dendritic Flux Avalanches of the Nonhomogeneous/Granular Superconducting Thin Films: Numerical Simulations

Abstract

Superconductors can get unstable in the applications due to its thermomagnetic instability characteristics. Superconducting thin films, fabricated by either the pulsed laser deposition or chemical evaporation, usually show nonhomogeneous or granular microstructures. Thus, nonhomogeneous distribution of the superconducting properties is intrinsically introduced into the thin films. In this paper, we study the flux avalanche behaviors of the nonhomogeneous/granular MgB 2 thin films under applied magnetic field by numerically solving the coupled nonlocal and nonlinear thermomagnetic equations. The influences of the grain sizes and thickness of the channels between islands on the propagation paths of the dendritic flux avalanches are considered in the simulation. It is found that the flux avalanches preferentially propagate along the channels, and the smaller the critical current density inside the channel the more avalanches propagate along it. The numerical simulation results are consistent with the experimental results. In addition, we have investigated the effect of environment temperature and magnetic field ramp rate on the flux avalanche behaviors of nonhomogeneous MgB 2 thin films. Our results may be beneficial to the design and real application of the thin film superconducting devices.