Overcritical state in superconducting round wires sheathed by iron

TL;DR

This study demonstrates that iron sheathing enhances the critical current density in MgB2 superconducting wires under certain magnetic conditions, due to magnetic interactions affecting supercurrent distribution.

Contribution

It introduces a phenomenological model explaining how magnetic interaction between iron sheath and superconductor influences critical current density in superconducting wires.

Findings

Iron sheathing increases J_c in MgB2 wires over a wide magnetic field range.

Magnetic history and orientation significantly affect the magnetic behavior of sheathed wires.

A magnetic interaction model explains the redistribution of supercurrents in the superconductor.

Abstract

Magnetic measurements carried out on MgB_2 superconducting round wires have shown that the critical current density J_c(B_a) in wires sheathed by iron can be significantly higher than that in the same bare (unsheathed) wires over a wide applied magnetic field B_a range. The magnetic behavior is, however, strongly dependent on the magnetic history of the sheathed wires, as well as on the wire orientation with respect to the direction of the applied field. The behavior observed can be explained by magnetic interaction between the soft magnetic sheath and superconducting core, which can result in a redistribution of supercurrents in the flux filled superconductor. A phenomenological model explaining the observed behavior is proposed.