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

Abstract

Ag-sheathed (Bi, Pb)2Sr2Ca2Cu3Ox monocore round wires and tapeswith different core geometry have been fabricated by a powder-in-tube method.The alternating-current transport losses of these wires and tapes weremeasured at 77 K as a parameter of frequency between 50 and 1000 Hz in aself-field. The round wires have lower transport losses than the tapes in theinvestigated frequency range, even in the cases of nearly the same criticalcurrents. The hysteresis loss for the wires is derived from the experimentaldata and found to be well below the prediction for a thin-stripsuperconductor. This is attributed to the inhomogeneous Jc distribution in aradial direction in the core, which is expressed as a sharp rise of Jc in goingfrom the core centre to the interface with the Ag sheath. An increase in frequencyenhances the loss generation in the round wires because of significanteddy-current loss. In the tape samples, an increase in the aspect ratioaccompanied by significant core deformation raises the loss value, so that itapproaches the value predicted for an elliptic superconductor tape.