AC losses in perpendicular external magnetic fields in ring bundle barrier multifilamentary BSCCO(2223) tapes with a central resistive barrier

Abstract

For the most common AC frequencies, the main components of the AC losses in multifilamentary Bi(2223) tapes are caused by both hysteresis and coupling losses. These losses can be reduced by increasing the matrix resistivity, applying a twist to the filaments and by the use of a conductor design optimised for a practical application. In the ring bundle barrier (RBB) conductor design we have bundles of filaments which are twisted around a central resistive core. The RBB structure was prepared via the powder in tube assemble and react (PITAR) route . In these tapes six bundles of seven filaments are twisted around a resistive layer of a mixture of 50% SrCO 3 and 50% SrZrO 3 in the centre of the tape. A series of tapes with twist lengths down to 3.4 mm was prepared. We present the measured AC losses of these tapes in external perpendicular magnetic fields. By using existing models, a description of the losses in the low B ̇ range was possible, leading to a separation into hysteresis, eddy current and coupling current losses. The frequency dependent loss contribution is dominated by the coupling current losses, from which the coupling current decay time constant, the effective permeability, the matrix resistivity and the critical B ̇ c for filament coupling were extracted. In tapes with a twist length below 5 mm the typical loss behaviour for decoupled filaments is observed at frequencies up to 500 Hz. Compared to the untwisted tapes, a loss reduction of up to 70% for low field amplitudes (below 10 mT) was achieved.