Temperature dependence of filament-coupling in Bi-2223 tapes: magnets-optical study

Coupling through random superconducting bridges between filaments in a mult ifilamentary Ag-sheathed Bi2Sr2Ca2Cu3O10+delta tape has been investigated b y magneto-optical imaging at temperatures from 20 K up to T-c. Magnetic flu x distributions have been measured on the surface of an intact tape in the remanent state on applying a strong perpendicular magnetic field. The flux distributions observed at low temperatures reflect the arrangement of indiv idual filaments. At high temperatures, the distribution becomes more simila r to that for a uniform monocore tape, indicating that superconducting conn ections appear between the filaments. To discuss the relative contributions of the intra- and inter-filament currents, a simple model based on the Bea n critical state was proposed and applied to analyse the temperature depend ent behaviour. The inter-filament coupling, increasing with temperature, re aches at 77 K a point where the currents flowing in large inter-filament lo ops are roughly equal to the intra-filament currents.