An experimental and theoretical study on the formation of electric field induced flow shear in the tokamak edge

The plasma edge plays an important role in the physics of improved confinement. In this region, shear in the E→×B→ flow can be responsible for the suppression of turbulence. An electric field and sheared flows are set up by plasma edge polarisation and are measured by probe and atomic beam diagnostics. The measurements are then compared with the predictions of a one dimensional fluid model. In this model, parallel viscosity, neutral friction and compressibility were already identified as important components to explain the strong and localised electric fields and rotation velocities. In the present paper we focus on anomalous convection and shear viscosity and their subsequent reduction by the quenching of the turbulence. We show that without this effect, it is impossible to explain the magnitude and the shape of the measured electric field.