Numerical modelling of pump limiter biasing on TEXTOR-94 and Tore Supra

Abstract

The two-dimensional multifluid code TECXY has been used to model the biasing (with respect to the first wall) of the toroidal belt limiter ALT-II on the tokamak TEXTOR-94 and of the new toroidal pump limiter being installed on Tore Supra tokamak in the framework of the CIEL project. It is well known that the edge flow pattern can be influenced by the poloidal electric drifts from imposing radial electric fields. The modelling with TECXY introduces imprinted bias currents in the scrape-off layer (SOL) for the case of negative (limiter) biasing, and imprinted bias potentials for the case of positive biasing. This allowed us to simulate sufficiently well the experimental I -V characteristics for either biasing of ALT-II and also reproduced the essential features and trends of the observed plasma profiles in the SOL of TEXTOR-94. For negative biasing a moderate improvement of the pumping exhaust efficiency can be achieved in the case of TEXTOR. For Tore Supra, however, only a negligible improvement of the limiter performance with biasing can be predicted, which is explained by the relatively weak drift flows in Tore Supra.

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

“…An analytical description of two groups of neutrals allows to take into account plasma recycling as well as sputtering and self-sputtering of impurity atoms at the ALT-II limiter surface. The present version of the code ( [2], [13]) incorporates drift motions and currents in a fully self-consistent way with plasma and impurity dynamics. In order to consider plasma drifts and currents, additional equations are added to standard equations, which are obtained from the diamagnetic and radial components of Ohm's law and the equations of motion.…”

“…The details of the model are described in [2], [4]- [8], [13] and the references cited therein. In this paper we concentrate on the role of neutrals recycled from the DED surface and on the role of stochastic transport from the DED perturbation field for plasma and carbon transport, radiation and carbon screening.…”

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

“…The source term from the momentum transfer by cx with neutrals has been written as: [11,12,15]. It has been shown [10,15] that eq.…”

Numerical analysis of the influence of different kinds of transport on the edge plasma profiles in TEXTOR tokamak

“…Therefore, in the present paper we apply a simplified model and use analytical formulae from mixing length approximation to analyze self-consistently the influence of different turbulence modes on plasma profiles in the boundary layer of TEXTOR-DED tokamak. The new model for the radial transport has been introduced to the 2D multifluid code TECXY to be capable of describing plasma profiles in the edge region of TEXTOR tokamak [1]- [4]. In the present study we restrict ourselves only to the comparison of the new model for the anomalous transport with our usual Alcator-like scaling for the anomalous transport, and we neglect the effect of the new dynamic ergodic divertor (DED) [5] configuration on the edge plasma profiles (no currents in the DED coils).…”

“…The physical model in the TECXY code is based on Braginskij-like equations for the background plasma and rate equations for the impurity ions [1]- [4]. It describes the electrons and various ion species in their different charge states as separate fluids.…”