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

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 opti mised for a practical application. In the ring bundle barrier (RBB) conduct or design we have bundles of filaments which are twisted around a central r esistive core. The RBB structure was prepared via the powder in tube assemb le and react (PITAR) route. In these tapes six bundles of seven filaments a re twisted around a resistive layer of a mixture of 50% SrCO3 and 50% SrZrO 3 in the centre of the tape. A series of tapes with twist lengths down to 3 .3 mm was prepared. We present the measured AC losses of these tapes in ext ernal perpendicular magnetic fields. By using existing models, a descriptio n of the losses in the low (B) over dot range was possible, leading to a se paration into hysteresis, eddy current and coupling current losses. The fre quency dependent loss contribution is dominated by the coupling current los ses, from which the coupling current decay time constant, the effective per meability, the matrix resistivity and the critical B, for filament coupling were extracted. In tapes with a twist length below 5 mm the typical loss b ehaviour for decoupled filaments is observed at frequencies up to 500 Hz. C ompared to the untwisted tapes, a loss reduction of up to 70% for low field amplitudes (below 10 mT) was achieved. (C) 2001 Elsevier Science B.V. All rights reserved.