ac losses in Bi,Pb(2223) barrier tapes

For many applications of Bi,Pb(2223) tapes involving alternative currents a nd/or fields, their ac losses are still too high. Several methods have been tried for reducing these losses and at present the most successful one is the introduction of a resistive barrier between filaments combined with fil ament twisting. At the University of Geneva, we tested an extensive series of different materials for their suitability as barrier materials. In this paper, we start by treating the different criteria these materials should m eet fur their use as barrier: no reactivity with Bi,Pb(2223) precursor, goo d deformability and low cost. We show why we used first BaZrO3 and later Sr ZrO3 as barriers and explain the differences between these two materials. W e next discuss which modifications of deformation process are needed in ord er to have tapes with smooth and continuous barrier layers and to avoid too high a degradation of the critical current density. Finally, we show the e ffect of barriers on the ac losses and the effective matrix resistivity. (C ) 2001 Elsevier Science Ltd. All rights reserved.