Numerical analysis of plasma instabilities in the TEXTOR tokamak edge plasma

In the present paper we study the evolution of Kelvin-Helmholtz and short-w avelength interchange instabilities in the TEXTOR tokamak boundary layer. T he unstable modes are related to the drift flows and develop in regions of steep radial gradients close to the separatrix and in regions of unfavorabl e 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 mos t dangerous one is the Kelvin-Helmholtz instability, which arises at the io n side of the limiter. If a special kind of radial damping of the fluctuati ons is introduced, then it is possible to kill the KH instability and conse quently the interchange instability can show up. We observed also short-wav e oscillations which are localized in the transition layer. (C) 1999 Elsevi er Science B.V. All rights reserved.