  New results of the investigations critical current problems in the high
temperature oxide superconductors are presented, basing on an analysis of the
flux pinning on nano-sized centers. New model of the interaction pancake
vortices with the nano-sized centers is proposed, while comparison of obtained
results with others pinning forces approaches 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, while variation of
the screening currents for such configuration has been considered and initial
calculations of the influence this effect on the current-voltage
characteristics performed. The dependence of the critical current on the
pinning centers parameters has been obtained while comparison with experimental
data is given. Pinning force has been calculated and its temperature
dependence, which is in qualitative agreement with an experiment. Critical
current determines the magnetic induction profiles and therefore flux trapping,
very important parameter from the point of view of an application HTc
superconductors as permanent magnets. The influence of the critical current on
the flux trapping in ceramic granular superconductors is calculated as well as
influence of various other material parameters - grain radius, surface barrier,
fulfillment of the ceramic with superconducting grains. Influence of the
critical current on a.c. losses in second generation HTc tapes with magnetic
substrate is discussed briefly too.
