Reducing ac losses of Bi(2223) multifilamentary tapes by oxide barriers

A new type of sheath material, consisting of a thin layer BaZrO3 around each filament, has been used to fabricate Bi(2223) multifilamentary tapes. The transverse resistivity is enhanced by a factor of 10, thus leading to a significant reduction of ac coupling losses in Bi(2223) multifilamentary tapes. The electric decoupling effect of these barriers is clearly demonstrated by "magnetic length scale" and Hall sensor magnetisation experiments. Moreover, it is possible to twist these tapes with a pitch length of 2 cm, thus yielding an even higher decoupling effect without deterioration of the transport properties. The uniformity of filament size and barrier layer thickness have been improved by a modified PIT method using four-roll deformation. The critical current density of these Bi(2223) tapes with BaZrO3 oxide barriers so far reaches 15kA/cm(2) (77 K, 0 T). (C) 1998 Elsevier Science B.V.