The dynamics of current density distribution in Ag-sheathed TBCCO tape in changing gradient field

The dynamics of current density distribution across the TBCCO tape width was studied under steady and also varying ambient gradient field applied to tape with transport current. Self-field map values were extracted from local magnetic field mapping in vicinity of the tape and used in procedure of inverse problem calculation to get linear current density distribution within edges of a selected tape cross-section. It was suggested that inhomogeneity and asymmetry of current density distribution across the tape width can be determined in gradient field even without field mapping by comparing I/sub c/(B, grad B, x) and I/sub c/(B, -grad B, -x) critical current-position curves measured during step-wise shift of the tape in direction x of local gradient (x/spl perp/j and x/spl perp/B) in the plane of tape. The symmetry of curves achieved by entering the ´left-side´ gradient (i.e. x<0) and afterwards ´right-side´ gradient (i.e. x>0) of the same ambient field, after rotating the tape 180/spl deg/ in its plane, proves the symmetry in current density distribution across the tape width and vice versa. The role of history can be suppressed and virgin conditions preserved by self-heating of the tape after transition to normal state prior to further measurement step.