Thermalization of atomic particles in gases
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TICAL, NONLINEAR, AND SOFT MATTER PHYSICS
Thermalization of Atomic Particles in Gases V. A. Volpyas* and A. B. Kozyrev St. Petersburg State Electrotechnical Institute (LETI), St. Petersburg, 197376 Russia *email: [email protected], [email protected] Received July 15, 2010
Abstract—A model of the atomic particle thermalization process due to scattering in various gases with appli cation of the Born–Mayer potential is presented. The thermalization process of atomic particles using the statistical modeling method is considered. Our thermalization model is adapted to a wide class of atomic col lision partners, takes into account the real energy and angular distributions of atomic particle sources, and makes it possible to calculate the parameters of the spatial zone of their thermalization and transfer into the diffusion motion mode. The energy range of applicability for the atomic particle thermalization model is interesting for many applied problems in plasma physics, gas discharge, and ion plating processes. DOI: 10.1134/S1063776111060227
1. INTRODUCTION Atomic particle thermalization is the process by which atomic particles lose energy during collisions with particles of the scattering medium up to a state of thermodynamic equilibrium with it. Quantitative esti mates of the extent of the atomic particle thermaliza tion zone make it possible to determine the boundary between their ordered motion and the transition to the diffusion propagation mode in a gas medium. This in turn makes it possible, in describing atomic particle transfer processes, to use the precise mathematical apparatus corresponding to the character of their motion—ordered or diffusion. Existing models of the atomic particle transfer pro cess in a gas medium, if we are considering questions of transfer from the viewpoint of particle thermaliza tion [1–3] and thermalized particle flow diffusion [4– 6], do not permit a correct description of atomic par ticle density, flow, and velocity distributions. For instance, procedures for averaging the free path length [1] or the scattering angle of atomic particles [2] do not take into account the real scattering of transferred energy during atomic collisions. An approximation of continuous energy losses in the transfer of atomic par ticles in a gas medium [4] is justified in the case of pre dominant atomic energy losses, but not pulse losses. This corresponds to scattering of heavy atomic parti cles on the light atoms of the gas medium. A change in the size of the cross section of elastic scattering and scattering angles as a function of the relative motion velocity of atomic particles [7] complicates descrip tion of the transfer process from the position of classi cal scattering theory. It is possible to estimate the extent and the bound aries of a onedimensional atomic particle thermaliza tion zone using the nonlinear diffusion model [8], which considers the atom transfer process as diffusion
with “superthermal” velocity. This nonlinear diffusion mechanism, which allows for the departure of sc
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