Calculations using the helical filamentary structure for current distributions of a six around one superconducting strand cable and a multifilamentary composite

Abstract

The current and magnetic-field distributions within a twisted six around one (6-1) superconducting strand cable and a twisted simple superconducting multifilamentary composite have been studied with the assumption that the current distribution within each strand or each filament is uniform. For this purpose, the vector potential and the magnetic field due to a helical conductor with a circular cross section is calculated from the numerical integration of the analytical expression for a helical thin conductor. The current distributions among each strand or each filament are obtained by minimizing the magnetic energy for the case of the insulated strands or filaments, and by requiring zero magnetic flux enclosed between any pair of strands or filaments for the case of the noninsulated strands or filaments. For the case of the untwisted insulated strands or filaments, it is confirmed that the calculated results coincide with those due to the inductance. The screening circulation currents among strands within a multistrand cable or filaments within a composite are obtained as the difference between the current distributions for the case with the noninsulated strand or filament and for the case with the imaginarily insulated strand or filament. As a result, it is revealed that the negative current in the inner strands or filaments is a universal feature of the current distributions for superconducting multistrand cables and multifilamentary composites during the current sweep. Finally, the magnetic field distributions of a twisted 6-1 superconducting strand cable and a twisted simple superconducting multifilamentary composite have been obtained.