Current distribution and enhancement of the engineering critical current density in multifilament Bi-2223 tapes

The spatial distribution of the critical current density (Jc) and engineering critical current density (Je) along the tape width direction was studied by a cutting technique on Bi-2223 multifilamentary tapes. In general, an increase of Jc towards the centre of the tape was measured. We attribute this tendency to the stress-strain experienced in the tape during the rolling process.

Jc of 50 kA/cm2 and Jeof 18 kA/cm2 was measured at the centre part (185 μm wide and 200 μm thick) of a tape cut from a 500 meters long tape (average Je of 8 kA/cm2). The low Jc of the edge part is a result of the porous microstructure with a great amount of secondary phases. Local variation of Jc was measured within the centre segment of the tape.

This indicates the influence of other factors on Jc, such as filament shape, connectivity of the filaments, and sausaging. Enhancement of Je has been pursued in which average Je of 12.7 kA/cm2 (Ic of 67 A) was obtained at 77 K and self-field in a 55 filament tape. Jeof more than 20 kA/cm2 with Jc of more than 70 kA/cm2 was measured in the centre part of this tape.