Magnetic field dependence of loss-frequency characteristics of multi-filamentary superconductors

AC losses of multi-filamentary superconductors for an ac magnetic field with a large amplitude, where a strong nonlinearity between the applied field and the penetrated flux into a superconducting filament become a problem, have been studied theoretically. The present theory, based on an effective complex permeability expressing the hysteresis property of superconducting filaments, is shown to explain quantitatively observed magnetic field dependences of loss-frequency characteristics in Nb-Ti multi-filamentary superconductors. It is pointed out that due to the nonlinearity the shape of the frequency characteristics of an eddy current loss is markedly shifted and deformed from the Lorentz type shown by Carr.