Magnetic AC loss in twisted-filament Bi-2223 tapes

In AC power-engineering applications, the energy dissipation in the superconductor is dominated by the magnetization due to alternating fields. To reduce this type of loss, conductors are being developed with twisted filaments and an increased matrix resistivity. The magnetic AC loss has been well described for low-T/sub c/ (wire) conductors. In Bi-2223 tapes the picture is different due to strong anisotropy, granularity, flux creep and large aspect ratio of the tape. The magnetic AC loss is investigated at power frequencies in various Bi-2223 tapes (twisted and nontwisted) and with different materials for the matrix (Ag, Ag alloys and ceramic barriers). When the field is parallel to the tape plane, the filaments in twisted tapes can be decoupled and the AC loss is decreased even when the matrix is silver. In tapes with ceramic barriers between the filaments, first indications of filament decoupling are observed also in perpendicular field. Compared to a round wire, there are essential differences between the AC loss mechanisms occurring in a long twisted tape and those in a short piece of nontwisted tape.