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The magnetic effects of granularity in YBCO tapes are investigated using model granular systems. Numerical simulations of the field profile, current distribution and ac susceptibility in simple granular configurations have been carried out under a critical-state, magnetic energy minimization approach. Experimentally, an artificially patterned ‘multigranular’ YBCO epitaxial thin film has been fabricated and used to investigate the geometry-related magnetic effects of granularity. High-resolution Hall probe microscopy measurements have allowed us imaging the evolution of the magnetization distribution with the applied field, and deduce the circulation of inter- and intragranular critical-currents. Ac-susceptibility measurements up to high driving-fields evidenced that ac losses arise mainly from dissipation at the artificial ‘grain boundary’ network. [ABSTRACT FROM AUTHOR]

The force generated when a zero-field-cooled superconductor is displaced laterally from an initially cylindrically symmetric situation is numerically calculated. An unstabilizing lateral force, according to previous measurements, is obtained. Approximate analytical expressions for both lateral and vertical force are also presented for small lateral displacements. In this case, it is concluded that the lateral stiffness is independent of the lateral disturbance, whereas the cross-stiffness is zero. [ABSTRACT FROM AUTHOR]

We study theoretically the AC susceptibility of hard type-II superconducting multifilamentary tape when placed in a perpendicular AC magnetic field. We focus on three different arrangements of identical filaments of rectangular cross-section: three filaments stacked in the applied field direction (vertical array), three filaments aligned in the field perpendicular direction (horizontal array), and the case of a 3 × 3 filament matrix. Real and imaginary AC susceptibility are calculated within the critical state framework. For the geometries of horizontal array and matrix are studied the cases whether the critical current returns inside each filament or it returns to the other filament placed symmetrically in the horizontal direction. [ABSTRACT FROM AUTHOR]