Berlin 2005 – scientific programme
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P: Plasmaphysik
P 21: Poster: Plasma-Wand Wechselwirkung 2, Theorie 2, Dichte Plasmen 1, Schwerionen- und lasererzeugte Plasmen 2
P 21.4: Poster
Monday, March 7, 2005, 16:30–18:30, Poster HU
Ion wall velocity distribution in a weakly collisional capacitive RF discharge — •Daniel Israel1, Karl-Ulrich Riemann1, and Lev Tsendin2 — 1Theoretische Physik I, Ruhr-Universität Bochum — 2St. Petersburg State Technical University
A simple model describing the ion velocity distribution at the wall in a weakly collisional capacitive RF discharge is presented. It starts from the Lieberman model [1] of the collisionless sheath in the frequency range ωpi ≪ ω ≪ ωpe. Generalizing the ion dynamics for finite ion inertia, the ion velocity at the wall is modulated slightly by the RF bias, which results in the well known double peak structure in the distribution function at the wall. In order to extend the model to finite collisionality, charge exchange collisions between primary ions and cold neutral particles in the sheath are taken into account. By the restriction to the weakly collisional case only very few secondary ions are generated by collisions, and the potential of the collisionless case is hardly changed. Thus the secondary ions can be considered as test particles in the collisionless field. The corresponding distribution function of secondary ions at the wall shows the well known multi peak structure found in experimental data. By a detailed analysis, the formation of the distribution function, including the position and the relative height of the peaks, can be described. Alternatively, the collision cross section may be re-calculated from the ion velocity distribution at the wall. This method offers a suitable means to determine cross section data from measured distribution functions.
[1] M.A. Lieberman, IEEE Trans. Plasma Sci. 16, 638 (1988)