The Influence of Impurities and Gas‐Puff on MARFE Evolution in TEXTOR Tokamak

Abstract

The 2D multifluid code TECXY is used to study the evolution of so-called Marfes, 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.

Modelling with the 2D multifluid code TECXY of TEXTOR discharges in the presence of DED

“…The DED replaces the former bumper limiter which was liable to trigger the evolution of Marfes. Since the parallel and radial transport of particles and heat is of crucial importance for the onset and strength of Marfes, the stochastic magnetic field, as produced by the magnetic perturbations from DED coils, strongly affects the Marfe evolution [10,11]. In the present paper we will restrict on experimental conditions and parameter regimes where the onset of Marfes can be avoided.…”

“…In particular, the code was successfully used to explain the biasing and polarization experiments on TEX-TOR tokamak [2,14]. It was possible with the code results to explain the MARFE appearance and evolution in TEXTOR tokamak plasmas [5,10,11] as well as the observed poloidal asymmetries of plasma parameters at the edge [15].…”