Effect of combining a DC bias current with an AC transport current on AC losses in a High Temperature Superconductor

摘要

Creating complex flux configurations by superposing a dc current or magneticfield onto the ac current in a type II superconducting tape should lead to avariety of peculiar behaviors. An example is the appearance of the Clem valley,a minimum in the ac losses as a function of the dc bias amplitude, which hasbeen theoretically studied by LeBlanc et al., in the continuation of Clem'scalculations. These situations have been investigated by applying a dc currentto a silver-gold sheathed Bi-2223 tape at 77 K (critical current 29 A), inaddition to the usual ac transport current. The ac losses were measured by thenull calorimetric method to ensure that the total losses were being accountedfor. These were recorded for different values of the ac and dc currents,leading to the observation of two different behaviors depending on the accurrent. Our revelation of the Clem valley is, to our knowledge, the firstexperimental validation of this phenomenon in high temperature superconductors,and may provide a simple way of reducing the ac loss in industrial applicationsof these materials.