Current-Penetration Patterns in Twisted Superconductors in Self-Field

Abstract

In a straight and untwisted superconducting wire, the current penetrates from the edges and flows along the wire's axis. The generated self-field is in the wire's cross-section plane and always perpendicular to the current. Bean's critical state model (CSM) describes the mesoscopic current and magnetic field penetration in such a configuration. Also, by using power-law resistivity, an eddy current problem can be formulated to simulate such a case. However, when a conductor is twisted, the self-field is no longer perpendicular to the helicoidal trajectories of the filaments. When this non-perpendicularity of the magnetic field occurs, the current does not flow along the helicoidal lines of the filaments. If that was the case, the central regions of the filaments would not be shielded from the magnetic field. In this paper we investigate current penetration in a twisted configuration by means of numerical simulations. We used the finite element method to solve eddy current formulations where the resistivity in the superconducting regions was described with an isotropic power-law model.