Showing papers by "Detlev Reiter published in 1995"

Kinetic Description of Elastic Processes in Hydrogen-Helium Plasmas

Abstract: Recent experiments with high density divertor plasma operation in tokamaks and future tokamak design projects have revived interest in the much earlier work on elastic collision processes between neutral and charged components in hot plasmas. In revisiting these papers, we employ classical methods to calculate deflection functions, cross sections and collision rates for the most important of such elastic collision processes. A physically motivated cut-off procedure for the model interaction potential function is introduced. An algorithm for implementation of such processes into kinetic Monte Carlo neutral gas transport models is described, which accurately accounts also for possible singularities in the deflection function. Data fits for the relevant quantities are provided for hydrogenic and helium species. The relevance of elastic neutral-ion collisions is illustrated by a numerical simulation of an ITER relevant divertor model. (orig.) 28 refs.

The influence of impurities on limiter tokamak plasmas and relevant mechanisms

Abstract: The paper gives a survey on recent experimental and theoretical investigations on the tokamak TEXTOR concerning the influence of impurities on the plasma behaviour. A broad spectrum of diagnostics allows the measurements of the spatial distributions of densities, temperatures and radiation of impurity and background particles. The plasma density critical for development of the radiative instability observed in the core of ohmically heated plasmas in discharges with high-Z limiters is estimated on the basis of a simple analytical model. The results of modelling by the code RITM of plasmas polluted by low-Z impurities are presented. An interpretation of different stability of OH and additionally heated plasmas to detachment, of improvement of energy confinement with neon seeding is proposed. The importance of impurities in the plasma dynamics in the vicinity of strong sources of impurities through their influence on the electric field is discussed.