Peculiarities of transport current penetration in a composite superconductor taking into account different models of flux creep

Abstract

The flux-creep diffusion of transport current in superconducting composite slab and cylinder based on a hard superconductor is investigated theoretically. Power and exponential current–voltage characteristics were used to define the electric field in the flux-creep regime. Using scaling solutions, the Maxwell equations describing transport current penetration in a one-dimensional superconducting composite are solved analytically. A proposed analysis indicates the existence of special macroscopic distribution of electromagnetic field in superconductor during the flux creep. It is shown that the flux-creep electromagnetic field cannot promptly propagate into the composite and penetrates at the finite rate like in the flux-flow regime. Therefore, a moving current boundary exists in the superconducting composite. It separates the region where the current flows from free current region. Moreover, in the flux creep specific conditions are fulfilled at moving boundary in contrast to the flux-flow regime. According to these conditions the electric and magnetic field induced by current charging smoothly approach to its undisturbed values. They are independent of any parameters of current–voltage characteristics and appear due to zero value of the differential resistivity of the composite at moving boundary. To confirm these results, the numerical calculation based on more general model is executed. The equations describing the violation of stable distribution of fully penetrated current are defined.