Field angle dependence of ac losses in stacked Bi-2223 Ag-sheathed tapes

In case of applying oxide superconducting tapes to power devices, they are usually stacked face-to-face to form a parallel conductor for the enlargement of current capacity. The accurate estimation of ac losses in the stacked tapes is very important for the basic design of the superconducting devices. In this study, we discuss the angular dependence of the ac losses in the stacked Bi-2223 Ag-sheathed tapes exposed to an external ac magnetic field. First we measure the ac losses in the nontwisted Bi-2223 tapes using a saddle-shaped pickup coil. The experimental results show that the ac losses observed in the transverse magnetic field, whose direction has any angle with respect to the wide face of the tapes, can be well reproduced by a simple summation of the parallel- and perpendicular-field losses. Next we compare the measured ac losses with theoretical ones, which were predicted from the critical current characteristics of a short sample observed in dc magnetic fields.