Flux Penetration in Superconducting Strip with Edge-Indentation

TL;DR

This study numerically investigates how an edge indentation affects flux penetration in a superconducting strip, revealing significant excess penetration and the smoothing effect of flux creep, with results matching experimental observations.

Contribution

It provides a detailed numerical analysis of flux penetration near edge indentations in superconducting strips, highlighting the impact of nonlinear E(j) laws and flux creep.

Findings

Excess flux penetration can be about 50% larger than the indentation radius.

Flux creep reduces flux front distortion and excess penetration.

Results agree well with magneto-optical experimental data.

Abstract

The flux penetration near a semicircular indentation at the edge of a thin superconducting strip placed in a transverse magnetic field is investigated. The flux front distortion due to the indentation is calculated numerically by solving the Maxwell equations with a highly nonlinear $E(j)$ law. We find that the excess penetration, $\Delta$, can be significantly ($\sim$ 50%) larger than the indentation radius $r_0$, in contrast to a bulk supercondutor in the critical state where $\Delta=r_0$. It is also shown that the flux creep tends to smoothen the flux front, i.e. reduce $\Delta$. The results are in very good agreement with magneto-optical studies of flux penetration into an YBa$_2$Cu$_3$O$_x$ film having an edge defect.