Fluxon-induced losses in niobium thin-film cavities

New data obtained with niobium film cavities allow a refinement of the physical explanation of RF losses by trapped magnetic flux at small RF field amplitudes. A stationary model explains these data. As the diameter of the fluxons decreases, the RF bypasses them, and the RF losses are due to the voltage, to which the normal conducting electrons, located in the fluxon core, are subject to. This loss mechanism is similar in origin to that of the so-called BCS losses. (13 refs).