The influence of the poloidal variation of the density on the locally measured velocities induced by biasing experiments

The plasma edge plays an important role in the physics of improved confinem ent, III this region, the shear of the radial electric field and the relate d rotation are thought to be responsible for the suppression of turbulence. We have developed a consistent set of experiments and theory to analyse th ese important phenomena, An electric field is set up with a biasing electro de, The resulting rotation velocities are measured with an inclined Mach pr obe. The measurements are then compared with the predictions of a theoretic al fluid model, In this model, parallel viscosity and neutral friction were already identified as important components to explain the very important a nd localised electric fields. In this paper we focus on compressibility eff ects and show that it is necessary to take the poloidal variation of the de nsity into account to explain the measured rotation velocities. (C) 2001 El sevier Science B.V, All rights reserved.