The effect of self-field on current capacity in Bi-2223 composite strands

We have investigated the effect of aspect ratio and current on the self-field critical current of Ag-sheathed Bi-2223 composite tapes. We have fabricated assemblies of monofilament tapes with different aspect ratio and current capacity. In such a manner, we could study the effect of the composite geometry on the self-field suppression of the critical current while maintaining the quality of the superconducting filaments constant. We find that a large aspect ratio is favorable for achieving higher self-field critical currents which is consistent with a reduction of the self-field. We have also used a modified configuration of several tapes with opposing currents to reduce the perpendicular component of the self field. As a consequence, we have observed large enhancements of the critical current at zero applied magnetic field, and have also been able to reveal the magnetic field dependence of the critical current at low magnitudes of the external field where the self-field usually dominates the externally applied field. We have studied these effects in several tapes with different levels of current capacity.