AC loss in Bi-2223 superconducting tapes in alternating magnetic field

We have investigated the AC loss caused by an alternating external magnetic field in various Bi-2223 superconducting tapes. This magnetic AC loss plays an important role in applications like power transformers. It can be significantly decreased only when the filaments in the tapes are electrically decoupled by introducing filament twist and increasing the matrix resistivity. We measured the magnetic AC loss at power frequencies with a pickup method at 77 K. In moderate fields parallel to the tape plane, the filaments can be decoupled and the AC loss is decreased by twisting, even if the matrix is pure silver. In perpendicular field it is much more difficult to decouple the filaments, due to the very flat tape geometry. However, in tapes with high-resistance ceramic barriers between the filaments, first indications of filament decoupling are observed also in perpendicular field. When the tape carries a DC or AC transport current close to its critical current, the transport loss becomes important as well. We have measured the dependence of this transport loss on the external AC magnetic field. The results are compared to theoretical models describing the magnetic and transport loss.