Study of AC loss mechanisms by systematically etching the Ag matrix in PbBi2223 tapes with twisted filaments

The main obstacle to an effective loss reduction in standard PbBi2223 tapes is the low resistivity of the pure Ag sheath, which leads to a low critical coupling field and a high coupling current loss. To formulate an effective loss reduction strategy, it is important to assess the contribution of different loss mechanisms. The aim of the present work is to quantify the distribution of the coupling current by systematic removal of Ag using chemical etching. Our result showed that the majority of the coupling current flows transversely through the superconductor-Ag matrix, instead of the outer sheath enclosing the filaments. It was also found that the coupling field B-C between the filaments and the inverse of the time constant of coupling current tau(-1) increase linearly with the percentage of etching, while the matrix resistivity for the un-etched area is expected to change very little. By completely uncoupling about a half of all the filaments, the reduction of the total loss was about 40-50% in the coupling-current dominated regime with filament uncoupled. The loss reduction for partially coupled regime is more than 80%. (C) 2002 Elsevier Science B.V. All rights reserved.