Response of Bi-2223 tapes to over-critical current excursions

A digital lock-in amplifier has been used to perform V-I time series acquisition, when transport currents with amplitude above I-c are driven through Bi-2223 tapes. The current waveform is triangular, sinusoidal or with arbitrary shape, and is applied for several consecutive cycles. The generator frequencies are selected to be 0.05, 0.1, 0.5, 1, 10 and 59 Hz. The amplitude of the applied current is varied from 2 to 20 times the value of I-c. The invariance of the V-I curves during several consecutive cycles and the resistive behaviour of the tapes in the over-I-c regime show that Bi-2223 tapes have very good stability to such type of transport current perturbations. (C) 2000 Elsevier Science B.V. All rights reserved.