Modifications to the edge current profile with auxiliary edge current drive and improved confinement in a reversed-field pinch

Auxiliary edge current drive is routinely applied in the Madison Symmetric Torus [R. N. Dexter, D. W. Kerst, T. W. Lovell , Fusion Technol. 19, 131 (1 991)] with the goal of modifying the parallel current profile to reduce cur rent-driven magnetic fluctuations and the associated particle and energy tr ansport. Provided by an inductive electric field, the current drive success fully reduces fluctuations and transport. First-time measurements of the mo dified edge current profile reveal that, relative to discharges without aux iliary current drive, the edge current density decreases. This decrease is explicable in terms of newly measured reductions in the dynamo (fluctuation -based) electric field and the electrical conductivity. Induced by the curr ent drive, these two changes to the edge plasma play as much of a role in d etermining the resultant edge current profile as does the current drive its elf. (C) 2000 American Institute of Physics. [S1070-664X(00)04109-4].