ANISOTROPIC PINNING IN MACROSCOPIC ELECTRODYNAMICS OF SUPERCONDUCTORS

Anisotropy of critical currents and electric fields in superconductors with strong pinning has been ascribed in the macroscopic model to fea tures of the material equation system relating the electric field to t he current density in a superconductor. The anisotropy of the pinning proper is described by an operator relating the pinning force density to the vectors of magnetic induction and Lorentz force. In the approxi mation of an extended critical state model, a feasible expression of t his operator is given in the form of an algorithm based on the concept of a collective anisotropic potential well containing fluxoids. The c urrent-carrying capacity of a strongly anisotropic niobium-titanium fo il as a function of the orientation of the current density and applied field with respect to the principal axes of the material has been inv estigated in detail. Given measurements of the transverse electric fie lds in the foil under magnetic fields normal to the foil plane, we can plot cross sections of surfaces describing the pinning force density in the space of magnetic induction and Lorentz force. (C) 1997 America n Institute of Physics. [S1063-7761(97)01909-4].