Analytical model for coupling loss in filamentized high-temperature superconducting tapes

Composite wires containing superconducting filaments embedded in a metallic matrix are used in various applications. In the presence of time-varying magnetic fields, electrical currents are induced in the loops where superconductor and normal metal regions are connected in series, causing energy dissipation known as coupling loss. Commonly accepted analytical formulas provide a basic understanding of this phenomenon. Recently, tape-shaped conductors containing a single layer of high-temperature superconductor striated in several parallel filaments have gained attention for use in nuclear fusion reactors, particle accelerators, and motors. It was found that, in spite of a dissimilar geometry, the analytical formulas deduced for round composites provide a fair qualitative interpretation of the experimental data obtained for this new kind of conductor. However, because of the used postulation of uniform local magnetic field, these models cannot correctly predict the dissipation near the peak in frequency dependence. We derived an analytical model starting from the assumption of an exponential decrease of magnetic field from the tape ends towards its center. This model is free of fitting parameters, with the peak dissipation controlled by the tape width only. Compared to previous models, it predicts ∼ 40% lower peak loss. We demonstrate its decent agreement with experiments.