Losses due to moving fluxoids in superconductors

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Abstract
A macroscopic description of the intermediate state in hysteretic superconductors, previously applied to the case of near-static fluxoid distributions, has now been extended to the case of fluxoids constrained to move at definable average velocities. The model allows the prediction, analytically and semi-quantitatively, of the results of flux-flow experiments and it establishes an analytic correlation between those results and measurements of the frequency dependence of the apparent critical current density determined by a.c. magnetization. Since a number of physical parameters of the superconductors is incorporated into the model, a variety of checks on the validity of the model description is available. Samples having a single composition and metallurgical history were tested extensively both in the flux-flow geometry and in a.c. magnetization under a variety of test conditions. Analysis of these experimental results in terms of the model constitutes both a test of the model and a quantitative correlation between metallurgical structure and superconducting properties for this system.