Frequency dependence of coupling losses in twisted superconducting structures

The coupling loss density per cycle in twisted structures (filaments in strands, strands in cables) is re-examined as a function of the frequency of the applied magnetic field. It is shown to be inversely proportional to the square root of the frequency in the high frequency limit, like the eddy current losses in normal metals. After attaining the maximum, this skin-effect type behaviour causes the decrease not to be as steep as for the calculations based on the simple model of the dipole mechanism for multifilamentary superconductors. The results are modified in a proper way to ensure easy comparison with the experiments, related to the maximum coupling losses per cycle and the characteristic frequency at which this maximum occurs.