Superconducting strip in an oblique magnetic field

TL;DR

This paper provides an analytical study of the critical state in a superconducting strip under an oblique magnetic field, revealing how the magnetic field application method influences current and magnetic field distributions.

Contribution

It presents the first analytical solutions for the critical state in a finite-thickness superconducting strip in an oblique magnetic field, considering different field application scenarios.

Findings

Critical state depends on how the magnetic field is applied.

Shapes of flux-free core and current regions are characterized.

Magnetic moment component parallel to the strip is nonmonotonic.

Abstract

As an example for a seemingly simple but actually intricate problem, the Bean critical state is studied in a superconducting strip of finite thickness d and width 2w >> d placed in an oblique magnetic field. The analytical solution is obtained to leading order in the small parameter d/w. The critical state depends on how the applied magnetic field is switched on, e.g., at constant tilt angle, or first the perpendicular and then the parallel field component. For these two basic scenarios the distributions of current density and magnetic field are obtained in the critical states. In particular, we find the shapes of the flux-free core and of the lines separating regions with opposite direction of the critical currents, the detailed magnetic field lines (along the vortex lines), and both components of the magnetic moment. The component of the magnetic moment parallel to the strip plane is a nonmonotonic function of the applied magnetic field.