Local measurement of current density by magneto-optical current reconstruction in normally and overpressure processed Bi-2223 tapes

Magneto-optical current reconstruction has been used for detailed analysis of the local critical current density (J/sub c/) variation in monocore Bi-2223 tapes. We find, even in high quality tapes with bulk transport j/sub c//spl sim/40 kA/cm/sup 2/ (77 K, 0 T), that there exist local regions which possess current densities of more than 200 kA/cm/sup 2/. Overpressure processing at 148 bar significantly improved J/sub c/ to 48 kA/cm/sup 2/ by improving the connectivity. For the overpressure-processed sample we find that the current distribution is more uniform and that the maximum local current density at 77 K is increased almost to 300 kA/cm/sup 2/.