Flux-line cutting in rotating type-II superconductors in parallel geometry

Abstract

Experimental results of a type-II superconductor, undergoing slow oscillations in a static magnetic field, have been theoretically investigated. The theoretical description considers the occurrence of flux-line cutting since the critical currents have a parallel component to the magnetic induction B. For this purpose, the elliptic flux-line-cutting critical-state model has been employed to calculate the magnitude B and orientation alpha(x) of the magnetic induction. Hysteresis loops, at different initial magnetic states and, at relatively small and large amplitudes of oscillation, are calculated numerically and compared with experimental data of a Nb disk. The complex behavior of the hysteresis loops is associated with the magnetic induction consumption. Our results are compared with those obtained employing the generalized double critical-state model. Our elliptic model is not restricted by the isotropic condition, that establishes that the electric field E is parallel to the current density J, but considers an induced anisotropy by flux line cutting. The limits of applicability of the elliptic model are discussed. (c) 2008 American Institute of Physics.