Screening of Eddy Current Loss in Metal Layers of Coated HTS Conductors

The influence of weakly-magnetic substrate materials on the AC loss of HTS coated conductors has been explored in a number of studies. In the case of magnetic AC loss in perpendicular orientation, at low field amplitude the superconductor effectively diverts magnetic flux into the parallel orientation in the substrate, concentrating the flux and increasing the substrate loss compared to that expected in perpendicular field. At intermediate field amplitudes, flux deflection in the substrate retards flux penetration of the superconductor and so reduces the loss. At higher field, with the tape fully penetrated, the flux is nearly perpendicular to the tape, substrate loss is negligible, and the loss in the superconductor is unaffected by the substrate. We present here experimental results and modeling which demonstrate that a similar effect occurs with the eddy current losses in the metallic layers of coated conductor tapes. At low field amplitude the superconducting layer of a coated conductor deflects the flux away from the perpendicular orientation so the eddy current loss in metallic layers is reduced, by almost an order of magnitude in the present case. At high field amplitude the eddy current loss is unaffected. In addition we present measurements showing the small changes in AC loss associated with the ends of sample tapes.