Nucleation and propagation of thermomagnetic avalanches in thin-film superconductors

TL;DR

This paper reviews recent theoretical and experimental insights into thermomagnetic avalanches in thin-film superconductors, highlighting their development, propagation dynamics, and the importance of stability analysis for applications.

Contribution

It introduces a combined linear stability and numerical analysis framework to understand ultra-fast flux avalanches in superconductor films, including dendritic growth and anisotropic flux patterns.

Findings

Flux front velocities up to 100 km/s during dendritic avalanches

Propagation regimes similar to ray optics observed in coated films

Enhanced flux pattern anisotropy due to specific dynamics

Abstract

Stability of the vortex matter -- magnetic flux lines penetrating into the material -- in type-II superconductor films is crucially important for their application. If some vortices get detached from pinning centres, the energy dissipated by their motion will facilitate further depinning, and may trigger an electromagnetic breakdown. In this paper, we review recent theoretical and experimental results on development of the above mentioned thermomagnetic instability. Starting from linear stability analysis for the initial critical-state flux distribution we then discuss a numerical procedure allowing to analyze developed flux avalanches. As an example of this approach we consider ultra-fast dendritic flux avalanches in thin superconducting disks. At the initial stage the flux front corresponding to the dendrite's trunk moves with velocity up to 100~km/s. At later stage the almost constant velocity leads to a specific propagation regime similar to ray optics. We discuss this regime observed in superconducting films coated by normal strips. Finally, we discuss dramatic enhancement of the anisotropy of the flux patterns due to specific dynamics. In this way we demonstrate that the combination of the linear stability analysis with the numerical approach provides an efficient framework for understanding the ultra-fast coupled non-local dynamics of electromagnetic fields and dissipation in superconductor films.