Current transfer lengths in multifilamentary superconductors with composite sheath materials

We describe current transfer processes between a metallic matrix and superconducting filaments through high-resistance layers, using a simple model to analyze current-voltage data of composite superconductors in terms of basic material parameters. 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 conditions. While such layers indeed have significant effects on the AC loss properties of the conductor, they also tend to complicate issues such as current injection at terminals and current ´healing´ around local filament defects. In order to gain a better understanding of these processes, we use a simple and quantitative model which relates the barrier and matrix resistivity directly to a characteristic current transfer length. This relation can be used to gain direct experimental access to the electrical barrier properties. We illustrate its usefulness with typical data obtained on composite-sheathed Bi(2223) tapes.