The onset of full coupling in multi-filament superconducting tapes exposedto an alternating external magnetic field

At high amplitudes and frequencies of the external magnetic field, the supe rconducting filaments in a composite conductor are fully coupled. This caus es a high magnetisation loss. Methods to decouple the filaments are well kn own for the low-T-c superconductors and have recently been applied also to high-T-c composites. In this paper, expressions are derived for the magneti c-field amplitude and frequency where full coupling sets in, as well as for the twist length required for decoupling the filaments in a general rectan gular composite. A comparison is made with other expressions found in the l iterature. The filaments in a typical Bi-2223/Ag tape in parallel magnetic fields are decoupled just by twisting. In perpendicular fields a high trans verse resistivity is required to decouple the filaments and decrease the ma gnetisation loss. (C) 2000 Elsevier Science B.V. All rights reserved.