Effect of current sweep rate on critical current of superconducting Ag-Bi-2223 tapes

The effect of sweep rate of applied current (dl/dt) on critical current (I-c) of Ag-sheathed Bi2PbxSr2-xCa2Cu3Oy (Ag-Bi-2223) tapes was studied by the four-probe measurement method of V-l curves. It was found that the V-l curves were affected apparently by dl/dt, resulting I-c, decreases with increasing dl/dt for all critical current criterions used here. This result implies that the I-c determined at very large dl/dt supplied, for example, by the pure current system will be significantly smaller than the I-c measured at small dl/dt usually used in the d.c. method. The possible influences of the present results on published V-l data and I-c measurement technique are discussed. We have shown that the ohmic heat at the current contact leads of our Ag-sheathed Bi-2223 samples immersed in liquid nitrogen is negligible. (C) 1998 Elsevier Science Ltd. All rights reserved.