The generation of poloidal pressure gradients in the SOL of TdeV by plate biasing

Abstract

In the TdeV tokamak, the convection of the plasma towards the divertors can be studied by changing the radial electric field in the scrape-off-layer (SOL) through biasing the divertor plates relative to the vacuum vessel wall. Electrostatic probes were used to determine the plasma parameters on both the outboard midplane and the bottom of the discharge. From these measurements, poloidal differences in the electron kinetic pressure were seen to arise due to the application of the biasing voltage on the neutralizer plates and that these pressure differences were correlated to the changing radial electric field. By using a linear relation between the poloidal kinetic pressure drop and the radial electric field averaged between the two observation points, an experimental value of 8.8 × 10 −3 (Ω m) −1 is obtained for the perpendicular conductivity. A comparison with current models would tend to favor inertia and viscosity over friction with neutrals to counterbalance the j × B force during biasing although the scaling of the conductivity with the toroidal magnetic field, plasma density and plasma current should be verified to confirm this conclusion.