Study On Characteristics Of He/N₂ Mixture At Atmospheric Pressure Glow Discharge Between Coaxial Electrodes

A glow discharge at atmospheric pressure controlled by dielectric barriers possesses a broad prospect for application and has always been a spot hot of the researches ever since the first report of the discharge in 1988. Dielectric barrier discharge is one of major devices used for generating non-equilibrium plasmas. This dissertation uses the jet glow device—coaxial cylinder electrode structure, and conducts the research on the characteristics of the discharge at atmospheric pressure controlled by dielectric barrier through numerical simulation after an insulated dielectric board is inserted between electrodes and plasma fluid dynamics model is used. The research mainly consists of two parts: first, one-dimensional model of self-consistent fluid is employed to study the characteristics of a glow discharge at atmospheric pressure controlled by dielectric barriers in the mixture of helium and nitrogen, and the influences of a small number of nitrogen impurities on the glow discharge at an even atmospheric pressure of helium are discussed. Then, in the two-dimensional fluid model, the axial evolution of a glow discharge at an even atmospheric pressure is studied. When numerical simulation is computed, finite difference method proposed by Scharferter and Gummel is employed to solve the continuity equation of particles, and Poisson equation is replaced with current conservation equation to solve electric field, which saves a large amount of computing time.The results of the simulation show that the incorporation of nitrogen impurities in small quantity has a great impact on the discharge. Since the Pennington ionization process between molecular nitrogen and metastable atom helium provides more electrons for the discharge, the breakdown discharge can thus occur more easily. Therefore, the voltage of gas breakdown reduces with the increased concentration of impurities, which brings down the current rate of the discharge. The reduction of ionization gives rise to the decrease of the charged particles density.In the two-dimensional numerical simulation of a glow discharge at atmospheric pressure, the axial evolution of the discharge is comprehended through the analysis on discharge current, electron density and the axial distribution of ion density, and the evolution can be explained by the spatial distribution of space electric field and accumulated charge on the dielectric surface. The research shows that the glow discharge at atmospheric pressure occurs along axial direction not in entire uniformity, but in some certain axial structures.The discharge occurs first in the central area of the electrode; at this moment the electronic field in central area is higher than that in the marginal area, and the density of charged particles and charge density accumulated on the surface of dielectric board are higher than those in the marginal area. As the discharge expands to the marginal area, the electric field, charged particle density and charge density accumulated on the surface of dielectric board in the area are higher than those in the central area of electrode.