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FZJ-2018-02480

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png The influence of cross field diffusion and convection on the impurity ion transport in the limiter shadow region of a tokamak 1: Analytical formulae

Claaßen, H. A.FZJ* ; Gerhauser, H.FZJ*

1985
Kernforschungsanlage Jülich, Verlag Jülich

Please use a persistent id in citations: http://hdl.handle.net/2128/18162

Report No.: Juel-1971

Abstract: In reference [1] the transport and redeposition of trace amounts of metal impurities sputtered from a limter or divertor target by hydrogen ion bombardment were studied without considering diffusion and convection perpendicular to the mapletic field (m.f.). This study had therefore two basic implications a) All sputtered impurity atoms, which are ionized in the plasma scrape-off layer (s .c .l.), are redeposited an the target. The ionization probability depends an the plasma parameters and the angular and energy distribution of the sputtered impurity atoms. b) The charge state population and the penetration depth of the impurities are solely determined by electron impact ionization and deceleration (acceleration) along the m.g.. The driving forces are the presheath electric field and the friction force exerted by the hydrogen ions of the counterstreaming plasma. In the present report an attempt is morde to extend the impurity transport analysis by inalusien of diffusion and convection processes perpendicular to the m.f.. In this more realistic case both the neutral and the ionized impurities may escape the s.o.l. across the magneticfield lines. Rather than accounting for neoclassical drifts, which as mail effects may be treated iteratively within the drift kinetic farmalism of [1], we consider diffusion and perpendicular convection processes induced by plasma edge turbulence. Because of the lack of a proper theory of plasma turbulence in the s.c.l. we link the time- and gyro-averaged parts of the electric drift and the distribution function of the impurity ions in such a way as to satisfy Bohm's diffusion law and to produce a simple convection term. But even then the resulting drift-kinetic equation for the impurity ions is too complicated to be solved analytically for arbitrary plasma parameters. In the following we there-fore assume that the plasma parameters are constant parallel to the target (perpendicular to the m.f. ) ignoring an essential feature of thes.c.l. and the most likely mechsnism for driving plasma turbulence. In this case there is, however, a rigorous analytical solution to the problem, which may serve as a, benchmark for more complicated numerical calculations.

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Contributing Institute(s):

1. Publikationen vor 2000 (PRE-2000)

Research Program(s):

1. 899 - ohne Topic (POF3-899) (POF3-899)

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