The effective resistance between twisted superconducting filaments in tapes

We consider two mechanisms, which influence the effective resistance betwee n crossing strands on flat cables or filaments in twisted tapes. The one-la yer classical Rutherford-type cable and the tapes with twisted BSCCO filame nts in silver matrix are taken as analogous cases. The amount of the matrix between strands or filaments increases the effective conductance compared with the direct current paths (determined by the touching area of the filam ents). The increase factor is about two and can easily be suppressed by oth er effects, like the contact resistance between the superconductor and the matrix. The second mechanism is due to the existence of induced voltage bet ween any points of crossing filaments. This leads to an additional effectiv e conductance, proportional to the square of the total number of filaments. Both effects are not very important for isotropic superconductors, but due to the strong anisotropy of critical parameters they can dominate for high temperature superconductors. The first one may partially compensate the in fluence of the usually weaker critical current density perpendicular to the tape. The contribution due to the second effect can explain the higher res istivity of the matrix in BSCCO tapes compared with pure silver. It seems t hat to obtain low AC coupling losses in BSCCO tapes, structures with small filament number are required. (C) 2001 Elsevier Science B.V. All rights res erved.