Coupling Losses in Superconductors With Twisted Filaments, Stripes, or Striations

All contributions to coupling losses in superconducting flat structures with twisted filaments, stripes or striations with different normal conducting central parts are summarized. It is shown that in some structures the contribution, caused by the induced currents between filaments, stripes or striations on the same side of a flat tape or cable, can be decisive for the total coupling losses. This contribution was usually omitted in considering the coupling losses in twisted or cabled superconductors. Assuming an ideal insulating central layer in the central part between two superconducting regions on both sides of a flat structure, like in the present YBCO coated conductors with stabilizing layer, the contribution mentioned above is decisive for the coupling losses. Knowing the resistivity of the stabilizing layer above the filaments or striations and the parameters of the coated conductor, one can give the restrictions for obtaining reliable coupling losses of the whole structure. Thus, the maximum value of the twist length for these structures can be estimated. The most favorable position and shape of the stabilizer (from the viewpoint of coupling losses) are also recommended.