CHARACTERIZATION OF VARIOUS DIVERTOR BIASING SCHEMES ON TDEV

The fact that the inner and outer divertor plates of the Tokamak de Varennes can be biased independently in a double-null or a single-null configuration makes it possible to characterize various biasing schemes. Current injection, in which the potential difference is applied on the same flux surface, and plasma biasing, in which the potential difference appears between the separatrix and the wall, are generic modes of particular interest. Current-voltage characteristic curves and induced electric fields are discussed for each mode. Finally, this study indicates that biasing only one electrode with respect to bath the vessel and the other strike points of the separatrix yields a hybrid behaviour resembling current injection when the electrode is negative and resembling plasma biasing when the electrode is positive.