MEASURED PLASMA PARAMETERS IN TDEVS CLOSED POLOIDAL DIVERTORS

Measurements in TdeV in the double null configuration show strong asymmetries between the upper and lower diverters. The divertor to which the ion del B drift is directed has a higher density, which varies little with the central line-average density. The electron temperature also exhibits a poloidal variation which depends on the direction of the toroidal magnetic field. The divertor plasma shows a double peak structure which evolves as a function of the central density, with the outer peak varying more rapidly. We have measured flow reversal near the separatrix in the bottom divertor when the ion del B drift is directed away from the X-point. Divertor plate biasing allows us to control the flux of plasma in the SOL; under negative biasing there is a strong increase of the electron density in the active divertor, the one favoured by the E X B flow. Calculations of the energy deposition derived by flush-mounted probes agree well with measurements of the heat load derived from the temperature increase of the divertor tiles.