Influence of the Flux Pinning on Critical Current in HTc Superconductors with Nano-Sized Defects

Performed analysis of the flux pinning on nano-sized centers, allowed to receive new results on the critical current problems in the high temperature oxide superconductors. A new model of the interaction pancake vortices with the nano-sized centers is proposed and comparison of obtained results with others pinning forces approaches is presented. The energy balance approach is applied, which leads to the appearance of the potential barrier determining the pancake vortices movement in the flux creep process. Various initial positions of the captured vortex have been analyzed and variation of the screening currents for these configurations has been considered. Initial calculations of the influence of this effect on the current-voltage characteristics have been performed. The dependence of the critical current on the pinning centers parameters has been determined, as well as comparison with the experimental data presented. Pinning force has been calculated and its temperature dependence, which is in qualitative agreement with experiments. The critical current determines the magnetic induction profiles and therefore also flux trapping, very important parameter from the point of view of application HTc superconductors as permanent magnets. The influence of the critical current and granular structure parameters on the flux trapping in ceramic superconductors is regarded. The influence of the critical current on a.c. losses in second generation HTc tapes with magnetic substrate is briefly discussed too.