Critical persistent current for a loop formed by a Bi-2223Ag-sheathed superconducting tape

A persistent current loop formed by a Bi-2223 Ag-sheathed superconducting t ape has been fabricated by tape joint technique. The current decay measurem ent was used to determine the persistent current of the loop at 77K. A de c urrent exceeding the critical current I-c of the loop defined by 1 muV/cm c riterion was transmitted into the loop. The persistent current is found to about 25% of its I-c value of the tape. Based on detailed measurements of t he voltage-current curves, the low level resistances down to very low volta ge (< 1 nanovolt) at the jointed and unjointed parts were tested, respectiv ely. The jointed section has a larger I-c value of 1 muV/cm criterion than the unjointed one. However, it is found that the persistent current of this test loop is limited by the jointed section, because the residual resistan ce of the jointed section is larger. These results illustrate that in the j ointed section the flux motion is more serious and the weaker grain boundar ies or jointing interfaces limits the persistent transport currents.