The influence of impurities and gas-puff on Marfe evolution in TEXTOR tokamak

The 2D multifluid code TECXY is used to study the evolution of so-called Mattes, thermal instabilities which arise locally in the front of the bumper limiter of the TEXTOR tokamak. The physical model is based on Braginskij-like equations and incorporates drift motions and currents in a fully self-consistent way. The radial electric field in the transition layer inside the separatrix is derived from the global ambipolarity condition. We model the bumper region by assuming high additional recombination losses inside this region and a suitably chosen profile for the recycled neutrals penetrating from the bumper surface into the adjacent plasma. A parameter study has been carried out to investigate the influence of impurities and of localized gas-puffing on the Marfe evolution. Results of numerical simulations are compared with experimental measurements. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim