Fluid modeling of a microwave micro-plasma at atmospheric pressure

This paper presents the modeling of an argon micro-plasma produced by microwaves (2.45 GHz) at atmospheric pressure. The study uses a one-dimensional stationary fluid-type code that solves the transport equations for electrons, positive ions Ar+ and Ar+2, and the electron mean energy, together with Poisson's equation for the space-charge electrostatic field, Maxwell's equations for the electromagnetic excitation field and the gas thermal energy equation. The model uses a simple kinetic scheme for Ar that includes the ground state, an excited state representing the lumped 4s levels, and two ionization states associated to the atomic and the molecular ions. The ions are assumed to be in thermal equilibrium with the neutral gas, having the same temperature profile

Large microwave plasma reactor based on surface waves

A microwave plasma reactor without magnetic fields has been designed for large surface treatment or deposition. Using the surfaguide principle, a 2.45GHz wave is coupled to the plasma created in a 12cm tube diameter surrounded by a metallic cylinder of 18.8cm diameter. The aim of this paper is to characterize this plasma, particularly the spatial homogeneity over the cross section. Argon and oxygen gases have been used. Pressure and microwave power were in the range 1 to 1000 Pascal and 200 to 2000Watt. Wave propagation study has shown that mainly a plasma mode (surface wave) of azimuthal hexapolar symmetry (π/3 periodicity) propagates. In argon gas, electron density (1011 to 1012 cm-3) and mean energy (1 to 3 eV) are locally measured by probes. Emission spectroscopy provides information on excited states distributions. They depend on the electric field distribution : azimuthally π/3 periodic and radially maximum near the wall due to the surface wave profile. Weakly modulated at high pressure, they are quite homogeneous at lower pressure due to the diffusion phenomenon. Actinometry has shown that the atomic oxygen density is rather homogeneous over the cross section whatever the pressure, which is promising for future surface treatment applications.Un réacteur plasma micro-onde sans champ magnétique pour le traitement de grandes surfaces ou le dépôt de couches minces, est présenté. Une onde à 2.45 GHz est couplée à un plasma créé dans un tube de 12 cm de diamètre entouré d'un cylindre métallique de 18.8 cm de diamètre. Ce papier présente une caractérisation du plasma, plus particulièrement pour l'étude de l'homogénéité spatiale du milieu sur sa section. Argon et oxygène ont été utilisés. Pression de gaz et puissance micro-onde ont été respectivement de 1 à 1000 Pascal, et de 200 à 2000 Watt. Une étude de propagation d'onde montre que le plasma est entretenu principalement par le mode plasma (onde de surface) à symétrie hexapolaire (de périodicité π/3). Dans l'argon on obtient des valeurs de densité et d'énergie des électrons de l'ordre de 1011 à 1012 cm-3 et de 1 à 3 eV. La distribution des états excités du plasma dépend du champ électrique : azimutalement π/3 modulée et radiallement maximum près du tube (onde de surface). Aux plus basses pressions, le phénomène de diffusion rend plus homogène la distribution de ces espèces. L'oxygène atomique est quant à lui assez homogène quelque soit la pression

Fluid modeling of a microwave micro-plasma at atmospheric pressure

This paper presents the modeling of an argon micro-plasma produced by microwaves (2.45 GHz) at atmospheric pressure. The study uses a one-dimensional stationary fluid-type code that solves the transport equations for electrons, positive ions Ar+ and Ar+2, and the electron mean energy, together with Poisson's equation for the space-charge electrostatic field, Maxwell's equations for the electromagnetic excitation field and the gas thermal energy equation. The model uses a simple kinetic scheme for Ar that includes the ground state, an excited state representing the lumped 4s levels, and two ionization states associated to the atomic and the molecular ions. The ions are assumed to be in thermal equilibrium with the neutral gas, having the same temperature profile

Microwave microplasma sources based on microstrip-like transmission lines

In this paper, we study two microwave sources based on a planar transmission line configuration, corresponding to linear resonators. In both sources, micro-plasmas are produced within the 50–200 $\mu$m gap created between two metal electrodes placed at the open end of a microstrip-like transmission line. The study of the sources follows a complementary approach that uses simulation and experiment. Simulations analyze the electromagnetic behavior of the sources, using the commercial tool CST Microwave Studio®, and characterize the plasmas produced, using a fluid-type code to describe the dynamics of charged particles. Experimentally, the return loss of the sources (hence their quality factors) is measured without and with plasma. Plasma diagnostics (in air and in argon), based on optical emission spectroscopy measurements, enable to obtain the typical plasma temperatures and the electron density (using Stark broadening measurements of the H$_{\beta}$ line-emission profile). Results reveal that the sources have similar quality factors (~15–20), yielding high-density (~1014 cm$^{-3})$, low-power (~10–50 W), non-equilibrium micro-plasmas (with rotational temperatures of ~950–1400 K in air and ~550–630 K in argon, vibrational temperatures of ~5200–5800 K in air and excitation temperatures of ~5800 K in argon), over volumes of ~10-4–10-3 cm3

Hydrodynamic study of a microwave plasma torch

A hydrodynamic model was developed to simulate the flow and the heat transfer with the gas/plasma system produced by a microwave-driven (500–900 W at 2.45 GHz) axial injection torch, running in atmospheric pressure helium at 3–9 L min−1 input gas flows. The model solves the Navier-Stokes’ equations, including the effect of the plasma upon the momentum and the energy balance, in order to obtain the spatial distributions of the gas velocity and temperature. The model predicts average gas temperatures of 2500–3500 K, in the same range of those obtained by optical measurements. Simulations show that the plasma influences the gas flow path and temperature, promoting an efficient power transfer

Study of a fast high power pulsed magnetron discharge: role of plasma deconfinement on the charged particle transport

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