Evaluation of Self-Field Distributions for Bi2223 Tapes With Oxide Barriers Carrying DC Transport Current

For AC loss reduction in Bi2223 tapes subjected to an AC external magnetic field, twisting the superconducting filaments and/or introducing oxide layers as highly resistive barriers around each filament are required. However, the structure of barrier tape becomes very complex and longitudinal uniformity of both transport property and tape structure could be easily deteriorated. To improve the current transport capability and its longitudinal uniformity for barrier tape for AC use, simple and non-destructive techniques to characterize them should be indispensable. In this paper, we examined the self-field distributions for Bi2223 tapes with oxide barriers carrying DC transport current by a scanning Hall-probe microscopy (SHM). Non-twisted and twisted 19-filamentary tapes with SrZrO₃+Bi2212 barriers were prepared by powder-in-tube process. The distributions of self-field in perpendicular to the broader face of a tape carrying DC current below critical current I_c was measured at 77 K by SHM with an active area of 50 μm × 50 μm, at 0.5 mm away from the tape surface. Based on the measured self-field distributions, longitudinal non-uniformity of transport properties and the presence of local defects to obstruct the current transport in barrier tapes were investigated.