Critical currents in high-T c ceramics by force-induced fluxon movement

The effects of external magnetic fields on the critical currents jc in YBaCuO ceramic due to Lorentz force-induced fluxon movement are discussed. Two cases for applied magnetic fields are investigated: (i) The external field and the self-field are circular in the superconductor; (ii) the external field is homogeneous and perpendicular to the current in the superconductor. The first case is a one-dimensional problem that allows a simple analytical calculation. It is assumed that the critical state in the cross section of the sample is governed by the condition jc B=const with B as local magnetic induction. The critical currents calculated under these conditions agree qualitatively with measurements.