Current transfer lengths in multifilamentary superconductors with composite sheath materials

We describe current transfer processes between a metallic matrix and superc onducting filaments through high-resistance layers, using a simple model to analyze current-voltage data of composite superconductors in terms of basi c material parameters. Until recently, multifilamentary high Tc conductors nearly always consisted of ceramic filaments embedded in a uniform metallic matrix. This has changed with the introduction of highly resistive barrier layers, aimed at reducing filament coupling under alternating-field condit ions. While such layers indeed have significant effects on the AC loss prop erties of the conductor, they also tend to complicate issues such as curren t injection at terminals and current << healing >> around local filament de fects. In order to gain a better understanding of these processes, we use a simple and quantitative model which relates the barrier and matrix resisti vity directly to a characteristic current transfer length. This relation ca n be used to gain direct experimental access to the electrical barrier prop erties. We illustrate its usefulness with typical data obtained on composit e-sheathed Bi(2223) tapes.