SELF-FIELD EFFECT AND CURRENT DISTRIBUTION IN BI(2223) TAPES AT 77-K

The transport critical current distribution of a rolled Bi(2223) tape with j(c)(77 K, O T) = 28 kA/cm(2) has been found to vary from 20 kA/cm(2) at the tape centre to 53 kA/cm(2) at the tape sides. The self-field generated by the high currents flowing in this tape has been studied at the liquid-nitrogen temperature. Numerical calculations of the self-field distribution have been performed, taking into account both the filament shape and the critical current distribution in lateral direction. The self-field component oriented along the tape normal reaches a maximum at the tape sides, and its average value is about 20 G, for a current flowing in the tape equal to I-c. This self-field can be drastically reduced by means of a simple experimental setup which is described in the present work. It has been thus possible to determine a more appropriate value of critical current in the absence of magnetic fields, which results in an at least 7% higher value than in the presence of self-field.