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

Abstract

The effect of sweep rate of applied current (d I/d t) on critical current ( I c) of Ag-sheathed Bi 2Pb xSr 2-xCa 2Cu 3O y (Ag-Bi-2223) tapes was studied by the four-probe measurement method of V– I curves. It was found that the V– I curves were affected apparently by d I/d t, resulting I c, decreases with increasing d I/d t for all critical current criterions used here. This result implies that the I c determined at very large d I/d t supplied, for example, by the pule current system will be significantly smaller than the I c measured at small d I/d t usually used in the d.c. method. The possible influences of the present results on published V– I 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.