THE INFLUENCE OF GEOMETRY ON SELF-FIELD AC LOSSES OF AG SHEATHED PBBI2223 TAPES

We measured axial fields along an Ag sheathed PbBi2223 superconducting tape a mm wide and 0.03 mm thick carrying 47 Hz alternating currents. The critical current of the tape at 77 K was 15 A corresponding to a critical current density of 16 000 A/cm(2). The axial electric field w as measured by pairs of voltage leads brought out in a plane perpendic ular to the tape axis, turned axially to meet and so led out to a volt meter. The spatial variation and the current dependence of the electri c field, obtained from several pairs of taps closed at different radia l positions, were consistent with the prediction for a uniform superco nducting thin rectangle with a critical current I-c rather than a supe rconductor of elliptical cross-section. Our results also showed that t he hysteretic losses at currents below I-c can be measured with an acc uracy of about 5% using a pair of taps closed at a radial distance abo ut three times the tape half-width.