抄録
We constructed a scanning Hall-sensor microscope with an active area of 50μm×50μm, which can be served as a simple tool for non-destructive evaluation for 1m lengths of Ag-sheathed Bi2223 tapes usable at 77 K. Using this equipment, we measured two-dimensional magnetic field profiles due to trapped currents in a remanent state on surfaces of the tapes with the mono-, 19-, 37- and 61-filaments of Bi2223 superconductor, and compared with the results for the distribution of critical currents (Ic) along a length direction. Except for the case of 19 filaments, all tapes were prepared by the conventional powder-in-tube method. In the case of 19 filaments, however, another kind of the tape was prepared by covering the filaments with insulating barriers from a practical point of view for AC use, and the result was compared with that for the conventional tape without barriers. The monofilamentary tape shows the inhomogeneity in magnetic field profile due to weak links, which seems to be consistent with the Ic distribution along a length direction. An increase in filament number homogenizes both the magnetic field profile and the Ic distribution, but the tape with insulating barriers still remains the inhomogeneity in both the magnetic field profile and the Ic distribution. The respective tapes show a correlation between the magnetic field profile and the Ic distribution along a length direction, independent of the number of filaments and also of whether or not insulating barriers were introduced.
