THE EFFECT OF POTENTIAL CONTACT POSITION ON AC LOSS MEASUREMENTS IN SUPERCONDUCTING BSCCO TAPE

AC losses in (Bi, Pb)(2)Sr2Ca2Cu3Ox silver-sheathed tape were measured as a function of frequency and amplitude of a sinusoidally varying transport current. Experimental results show that energy losses are purely hysteretic in nature in the range of applied frequencies for transport currents below the critical value I-c. The lossy component of the measured voltage is very dependent on the position of the potential taps placed onto the surface of the tape. This can be explained using the theory of Norris [J. Phys. D3 (1970) 489] for ellipsoidal conductors. It means that neither voltage gives an accurate measurement of the loss. The error is least for the side contacts but still varies from 40% at I-c to a factor of four at 0.1 I-c.