Alternating-current transport losses of Ag-sheathed (Bi, Pb)2Sr2Ca2Cu3Ox monocore round wires and tapes

Ag-sheathed (Bi, Pb)2Sr2Ca2Cu3Ox monocore round wires and tapes with different core geometry have been fabricated by a powder-in-tube method. The alternating-current transport losses of these wires and tapes were measured at 77 K as a parameter of frequency between 50 and 1000 Hz in a self-field. The round wires have lower transport losses than the tapes in the investigated frequency range, even in the cases of nearly the same critical currents. The hysteresis loss for the wires is derived from the experimental data and found to be well below the prediction for a thin-strip superconductor. This is attributed to the inhomogeneous Jc distribution in a radial direction in the core, which is expressed as a sharp rise of Jc in going from the core centre to the interface with the Ag sheath. An increase in frequency enhances the loss generation in the round wires because of significant eddy-current loss. In the tape samples, an increase in the aspect ratio accompanied by significant core deformation raises the loss value, so that it approaches the value predicted for an elliptic superconductor tape. (author)