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Atmospheric pressure Radio Frequency discharges, diagnostic and numerical modeling

Abstract : The aim of this thesis is to investigate the properties of a Radio Frequency capacitive discharge at atmospheric pressure in argon. In these conditions where the pressure•distance product is around 150 Torr.cm, the discharge usually consists of several locally hot filaments. By pulsing the RF generator with an appropriate width and period, it was found possible to control the filament to glow transition in order to obtain a diffused and stable plasma.
The 2 mm gap between the electrodes is open to the ambient air and fed with argon via one hundred submillimetric holes regularly spread on the surface of the top electrode. This configuration allows “on-line” surface treatment of polymer films without having to turn the discharge off between successive samples. An important and lasting improvement of the polymer wettability is quickly obtained without risk of damage.
The plasma diagnostic methods are emission spectroscopy and electric measurements. The Stark broadening of the Balmer β transition line of atomic hydrogen is measured to determine a plasma density of 10^15/cm3 in the filamentary mode. The glow mode density estimation was based on power balance yielding a density of 5×10^11/cm3. Emission line ratios between neutrals and Ar+ ions are used in the Saha equation to calculate the electron temperature. It results in an approximation of 1.3 eV for the glow mode and 1.7 eV for the filaments.
A unidimensional self-consistent fluid model is developed to gain insight into the homogeneous discharge behaviour. Poisson's equation for the electric field is coupled to the first moments of the Boltzmann equation (continuity equation, drift-diffusion equation and energy equation). Transport and reaction coefficients are obtained from the mean energy of the electrons.
The model is applied to a reduced argon kinetic with the main ionization and excitation processes. Simulation results are in agreement with experimental measurements. The atmospheric pressure RF discharge is similar to a lower pressure RF discharge for which the ionization occurs mainly inside the oscillating sheaths where electrons are the most energetic.
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Contributor : Nicolas Balcon <>
Submitted on : Monday, January 21, 2008 - 11:42:31 AM
Last modification on : Friday, January 10, 2020 - 9:10:05 PM
Long-term archiving on: : Thursday, April 15, 2010 - 1:49:01 AM

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  • HAL Id : tel-00211176, version 1

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Nicolas Balcon. Atmospheric pressure Radio Frequency discharges, diagnostic and numerical modeling. Atomic Physics [physics.atom-ph]. Université Paul Sabatier - Toulouse III; Australian National University, 2007. English. ⟨tel-00211176⟩

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