Electric field-induced plasma convection in tokamak divertors

Measurements of the electric fields, E in the DIII-D tokamak divertor region @J. C. Luxon and L. G. Davis, Fusion Technology 8, Part 2A, 441 ~1985!# are quantitatively consistent with recent computational modeling establishing that E3BT circulation is the main cause of changes in divertor plasmas with the direction of the toroidal magnetic field, BT . Extensive two-dimensional measurements of plasma potential in the DIII-D tokamak divertor region are reported for the first time. The resulting E3BT /B 2 drift particle flux is calculated for standard ~ion 1BT drift toward divertor X-point! and reversed BT direction and for low ~L! and high ~H! confinement modes. Perpendicular field strengths of up to E;5 kV/m are observed at the separatrix between the divertor private region and the scrape-off layer ~SOL!. The E3BT drift, which reverses with reversal of BT , creates a poloidal circulation pattern in the divertor that convects 25%–40% of the total ion flow to the divertor target. The circulation strongly couples the various regions of the divertor and SOL and fuels the X-point region. An outward shift of the profiles is seen in reversed BT . © 2000 American Institute of Physics. @S1070-664X~00!01104-6#