AC losses in superconducting composite strips in a magnetic field in the form of a standing wave

TL;DR

This paper derives analytical formulas to evaluate AC losses in superconducting composite strips subjected to standing wave magnetic fields, considering different contact conditions and the influence of induced currents.

Contribution

It introduces a two-dimensional model for AC losses in superconducting-metal composites under standing wave magnetic fields, accounting for transverse currents and contact conditions.

Findings

Losses are mainly due to longitudinal currents in most cases.

Electric contact increases maximum loss density at high magnetic fields.

Transverse currents significantly affect AC losses when strips are in contact.

Abstract

Analytical expressions for the evaluation of AC losses in a superconductor-metal composite strip in a nonuniform AC magnetic field having the form of a standing wave are derived. The considered configuration models superconducting tapes, thin films and coated superconductors. A distinctive feature of the problem is the appearance of a transverse component of the induced current that converts the problem to a two-dimensional one. Bean's critical state model for a superconductor and a low frequency approximation for a metal are used. In the framework of this approximation the influence of eddy currents in the metal on the magnetic field is neglected, and the current distribution in the superconductor is determined by an external field. Two cases were considered: (1) superconducting and metal strips electrically separated; (2) they are in an electric contact. It is shown that for most practical cases enough to take into account only the losses generated by induced longitudinal currents in a composite strip. When an electric contact between strips exists, the maximum loss density in high fields (above 2 T) can be determined by the transverse component of the current.