A method for determining critical currents from current-voltage curves of silver-sheathed bismuth tapes

We are at present measuring current-voltage characteristics of Ag-sheathed Bi(2223) tape samples, in DC, AC and transient phenomena conditions. One of our aims is the precise determination of our samples' critical currents. In this paper, we present a critical-current determination method, based on the search for an optimal fit of our curves, approximated by an exponential law, in DC and AC current conditions. This method made it possible to avoid the arbitrary choice of a voltage threshold that did not allow a significant comparison between the AC and DC curves. Furthermore, we were able to determine the parameters of the exponential law, which appears to agree well with our experimental results. (author)