Characteristics of critical current and index n of Bi-2223/Ag tape up to 30 T at 4.2 K

We fabricated 55-filament Bi-2223/Ag tape and evaluated the dependence of critical current (I_c) 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. I_c 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 I_c was dependent on the magnitude and orientation of the magnetic field. The I_c decreased exponentially as the field increased; in a parallel and increasing field, I_c was 128 A at 30 T, which is approximately 40% of the I_c 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 I_c 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.