Alternating Field Losses in Superconducting Strip Conductors

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Abstract
A wattmeter technique is described which advances the measurement of alternating field losses in superconducting materials. In particular, it allows realistic experiments on strip conductors, the geometric form most promising for application to electrical power engineering. Uniform current distribution is achieved, contact problems are eliminated, and sample preparation is minimal. It is shown how the alternating field measurements can be interpreted to yield values for several properties of the material studied. Critical fields, the surface shielding currents, and the bulk critical currents can all be determined. When these quantities are inserted into expressions derived from a modified critical state model, a good match to the experimental results is obtained. Comparison of the measured alternating field dissipation with the area enclosed by magnetization curves, derived in slowly varying fields, confirms the validity of the technique and the applicability of critical state models to results obtained at audiofrequencies.