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We fabricated 55-filament Bi-2223/Ag tape and evaluated the dependence of critical current (Ic) and index n in an external magnetic field up to 30 T at 4.2 K, in order to explore the possible application for a magnet in persistent current mode. Ic and index n were characterized as a function of temperature and the magnitude and orientation of the magnetic field by increasing and decreasing field. It was observed that Ic was dependent on the magnitude and orientation of the magnetic field. The Ic decreased exponentially as the field increased; in a parallel and increasing field, Ic was 128 A at 30 T, which is approximately 40% of the Ic in self-field. On the other hand, index n was not significantly dependent on the field up to 30 T, nor did it vary significantly on increasing or decreasing field; the n value in the range of 0.1∼1 μV/cm was 23.0±5.2 and 27.8±8.0 on increasing and decreasing field, respectively, in the range of 0∼30 T. In addition, we observed that local Ic and index n of a long length of tape (4.2 m) were dispersed over a wide range and that the variation of each of these two values with the position of the tape was similar, suggesting that these properties depend on the microstructural uniformity.