Numerical analysis of plasma instabilities in the TEXTOR tokamak edge plasma

In the present paper we study the evolution of Kelvin-Helmholtz and short-wavelength interchange instabilities in the TEXTOR tokamak boundary layer. The unstable modes are related to the drift flows and develop in regions of steep radial gradients close to the separatrix and in regions of unfavorable curvature, especially in the vicinity of the limiter. We investigate the behavior of these instabilities as a function of the numerical grid spacing and for different plasma parameters in the SOL. We have found that the most dangerous one is the Kelvin-Helmholtz instability, which arises at the ion side of the limiter. If a special kind of radial damping of the fluctuations is introduced, then it is possible to kill the KH instability and consequently the interchange instability can show up. We observed also short-wave oscillations which are localized in the transition layer. (C) 1999 Elsevier Science B.V. All rights reserved.