Tunable magnetic flux avalanches triggered by a focalized laser spot

Abstract

Magnetic flux avalanches caused by thermomagnetic instabilities are a common phenomenon occurring in type II superconducting films. The unpredictability of these catastrophic events threaten the application of superconducting thin film equipment, such as high-temperature superconducting magnets. In the present work, through the fast Fourier transform method, we numerically investigate artificially triggered flux avalanches in superconducting films by a focalized laser, unveiling new features beyond those associated to naturally occurring avalanches. The numerical modeling is validated by reproducing previous experimental results. We investigate the effects of laser irradiation on the nucleation and evolution of flux avalanches for different cases, namely varying the laser irradiation position, laser power, laser-spot size, ramping rate of applied magnetic field and working temperature. We find that the laser irradiation can control and guide the position of flux avalanches at applied magnetic fields with small ramping rate, while similar guidance effect cannot be observed at high ramping rates. We demonstrate that such phenomenon can be tuned by the environmental temperature, and the underlying physical mechanism can be ascribed to current crowding and local heating around the laser spot. Furthermore, by considering a pair of laser spots, we observe two possible scenarios depending on the laser power, (i) single flux avalanche triggered at one of the laser spots and (ii) double flux avalanches triggered at both laser spots.