Large Predicted Self-Field Critical Current Enhancements In Superconducting Strips Using Magnetic Screens

Abstract

A transport current distribution over a wide superconducting sheet is shown to strongly change in the presence of bulk magnetic screens of a soft magnet with a high permeability. Depending on the geometry, the effect may drastically suppress or protect the Meissner state of the sheet through the enhancement or suppression of the edge barrier critical current. The total transport current in the magnetically screened Meissner state is expected to compete with the critical current of the flux-filled sheet only for samples whose critical current is initially essentially controlled by the edge barrier effect.

Overcritical states of a superconductor strip in a magnetic environment

“…2 Two sorts of specimens are considered: those possessing the large edge barrier against magnetic vortex entry which dominates over the pinning, and those possessing strong pinning masking completely the edge barrier.…”

Strong reduction of ac losses in a superconductor strip located between superconducting ground plates

“…As was recently predicted special curved magnetic and superconducting surroundings may even significantly enhance the current-carrying capability of strips and weak links in the fluxfree Meissner state [5][6][7] as well as in the flux-filled critical state [8,9]. Experimentally, critical current enhancements [10,11] and ac losses reduction [12][13][14] were observed recently in magnetically shielded strips and filaments.…”

Superconductor strip in a closed magnetic environment: Exact analytic representation of the critical state

“…1. This exhibits a flattening of the current profiles together with an increase in the magnitude of the total current up to saturation, when the radius of the magnetic cavity is reduced, precisely as in the case of topologically open magnetic cavities [1,2].…”

“…AC losses in superconductor strips caused by the latter type of fields are anticipated to greatly decrease when the strips are exposed to suitably designed magnetic environments [2,3]. Exact analytic representations of sheet current distributions in superconductor strips located between two highpermeability magnets occupying infinite half-spaces were derived before [1,2]; these configurations allowed to find the respective current distributions for various other topologically open shielding geometries by application of the method of conformal mapping. Utilization of the latter tool for analyzing sheet current distributions and AC losses in the presence of topologically closed magnetic environments of practical interest requires corresponding reference results.…”

“…Recently, a suggestion for improving the current-carrying capability of superconductor strips [1,2,3] and for reducing AC losses in superconductor cables [4] based on the idea of magnetic shielding of applied fields as well as current self-induced fields was put forth. AC losses in superconductor strips caused by the latter type of fields are anticipated to greatly decrease when the strips are exposed to suitably designed magnetic environments [2,3].…”