Staircase penetration of magnetic flux into a superconducting flat ring

Abstract

We analyzed the distribution of the Meissner shielding currents in a flat superconducting ring and quantitatively described the penetration of magnetic avalanches (dendrites) inside it. Using a recurrent procedure, the external field $H_{ext}$, in which a perforating (rim crossing) avalanche appears, is calculated. A staircase dependence of the mean field trapped inside a ring, $\left\langle H\right\rangle$, vs. $H_{ext}$, is comprehensively described. A staircase slope appears to be a universal function of a ring shape (rim width to ring diameter ratio). The heat released by a penetrating dendrite grows linearly with each next perforation. Flux pinning, if present, modifies a staircase dependence and makes steps smaller. Our theoretical results are in a good accordance with the experimental data.