Indirect measurement of current distributions in Bi-2223/Ag tapes by pickup coil method

We develop a quantitative measurement method to evaluate current distributions in high T_c superconducting tapes. In our measurement the current distributions are indirectly found from the results of the self-field distributions measured by a group of coils, which is composed of nine small pickup coils, located around the tape. It is confirmed that the accuracy and the sensitivity of this measurement method, using a group of pickup coils, are good enough to measure the current distributions for the high T_c superconducting tapes by adopting it to a dummy conductor composed of insulated copper wires. Using this method, we have measured the current distributions in multifilamentary Ag-sheathed Bi-2223 tape at 77 K. Measured and numerical self-field distributions are compared. The comparison between the experimental and numerical results shows that the current distribution in the tape is not uniform and that distribution changes as the amplitude of the transport current increases. In addition, no frequency dependence of the current distributions is observed. Further, we investigate the influence of the external magnetic field on the current distributions. On the basis of the obtained results the characteristics of the current distributions in the high T_c superconducting tape are discussed