CHARACTERIZATION OF VARIOUS DIVERTOR BIASING SCHEMES ON TDEV

The fact that the inner and outer divertor plates of the Tokamak de Va rennes can be biased independently in a double-null or a single-null c onfiguration makes it possible to characterize various biasing schemes . Current injection, in which the potential difference is applied on t he same flux surface, and plasma biasing, in which the potential diffe rence appears between the separatrix and the wall, are generic modes o f particular interest. Current-voltage characteristic curves and induc ed electric fields are discussed for each mode. Finally, this study in dicates that biasing only one electrode with respect to bath the vesse l and the other strike points of the separatrix yields a hybrid behavi our resembling current injection when the electrode is negative and re sembling plasma biasing when the electrode is positive.