Current distribution and critical state in superconducting silver-sheathed (Bi,Pb)-2223 tapes

A novel method for the unambiguous determination of the self-field critical current of superconducting silver-sheated (Bi,Pb)(2)Sr2Ca2Cu3Ox ((Bi,Pb)-2223/Ag) tape conductors is presented which is based on the measurement of the distribution of the perpendicular magnetic field component above current-carrying tapes by scanning Hall probe magnetometry. From the evolution of the sheet current density distribution across the tape width with increasing transport current, a characteristic current I* can be identified, above which additional current is distributed homogeneously over the entire (Bi,Pb)-2223 and Ag volumes, respectively, and which represents a realistic estimate of the intrinsic critical current associated with the critical state scenario: It corresponds to full penetration of the transport current into the volume of the superconductor and does not depend, as is the case for the determination of the transport critical current from current-voltage characteristics, on experimental parameters such as the choice of an electric field criterion. (C) 1998 Elsevier Science B.V. All rights reserved.