Avalanches Injecting Flux into the Central Hole of a Superconducting MgB2 Ring

TL;DR

This study uses magneto-optical imaging to observe flux avalanches in a superconducting MgB2 ring, revealing how avalanches create heated channels that inject flux into the central hole, affecting the current and temperature.

Contribution

It provides direct visualization and quantification of dendritic flux avalanches and their impact on flux injection and current reduction in MgB2 rings.

Findings

Avalanches connect outer and inner edges of the ring.

Injected flux reduces current by about 15%.

Maximum temperature in the channel reaches 100 K.

Abstract

Magneto-optical imaging was used to observe dendritic flux avalanches connecting the outer and inner edges of a ring-shaped superconducting MgB2 film. Such avalanches create heated channels across the entire width of the ring, and inject large amounts of flux into the central hole. By measuring the injected flux and the corresponding reduction of current, which is typically 15%, we estimate the maximum temperature in the channel to be 100 K, and the duration of the process to be on the order of a microsecond. Flux creep simulations reproduce all the observed features in the current density before and after injection events.