Interplay of dendritic avalanches and gradual flux penetration in superconducting MgB2 films

TL;DR

This study investigates how dendritic flux avalanches and gradual flux penetration coexist in MgB2 superconducting films, revealing complex behaviors and underlying thermo-magnetic mechanisms through experimental imaging and simulations.

Contribution

It provides new insights into the interplay between dendritic avalanches and gradual flux penetration in MgB2 films, supported by combined experimental and simulation analysis.

Findings

High flux density gradient across dendrites

Decreasing peak flux density with increasing field

Evidence of thermo-magnetic instability mechanisms

Abstract

Magneto-optical imaging was used to study a zero-field-cooled MgB2 film at 9.6K where in a slowly increasing field the flux penetrates by abrupt formation of large dendritic structures. Simultaneously, a gradual flux penetration takes place, eventually covering the dendrites, and a detailed analysis of this process is reported. We find an anomalously high gradient of the flux density across a dendrite branch, and a peak value that decreases as the applied field goes up. This unexpected behaviour is reproduced by flux creep simulations based on the non-local field-current relation in the perpendicular geometry. The simulations also provide indirect evidence that flux dendrites are formed at an elevated local temperature, consistent with a thermo-magnetic mechanism of the instability