VARIOUS DIVERTOR BIASING CONFIGURATIONS AND IMPROVED DIVERTOR PERFORMANCE WITH BIASING ON TOKAMAK-DEVARENNES (TDEV)

Electrically insulated divertor plates are used on TdeV (Tokamak de Varennes) [18th EPS Conference on Controlled Fusion and Plasma Physics Berlin (European Physical Society, Petit-Lancy, 1991), Vol. 15C, Part I, pp. 1-141] to produce various biasing configurations, which can be decomposed into two basic modes. Plasma biasing, with a radial electric field E(r) in the scrape-off layer (SOL), is most promising for divertor applications. The E(r) field is produced with a particular divertor plate geometry, causing a nonambipolar radial current and a particle flow in the E(r) X B(T) direction, toward one of the divertors (the active divertor). The pressure and impurity retention in the active divertor are shown, in the Ohmic regime, to be strongly increased by biasing. He exhaust through this divertor is increased by a factor of almost 3 with modest biasing voltages and currents scalable to larger devices. Biasing also modifies the power repartition between the divertors, with the active divertor also receiving a larger fraction