Flux diffusion losses in stabilized conductors

The "ac" losses in normal metal sheaths around superconductor composites are calculated. Three cases are considered: (1) the composite region is assumed to have a finite constant resistance, (2) flux lines are assumed to move from the normal metal into the superconductor at constant velocity, and (3) complete equations of motion and continuity of flux are used in both the normal and superconductor region. Case (1) is incorrect since it predicts a decrease In losses for an increase in rate of change of applied magnetic field, in contradiction to case (3). Case (3) is, of course, complete and accurate but complex enough to require numerical solutions. Case (2) however is only in error by a few percent for charging rates in the order of one tesla/h. Case (3) can be applied for any charging rate as long as the superconductor filaments are transposed, not just twisted.