Modeling of Atmospheric-Pressure Dielectric Barrier Discharges in Argon with Small Admixtures of Tetramethylsilane

Plasma Chemistry and Plasma Processing - A time-dependent, spatially one-dimensional fluid-Poisson model is applied to analyze the impact of small amounts of tetramethylsilane (TMS) as precursor on...     

The homogeneity of a stabilized discharge-pumped XeCl* laser

* laser arrangement. The special pumping technique of this laser discharge is based on the additional use of a stabilizing low-current preliminary discharge. The model takes into account the time-dependent electron Boltzmann equation including electron–electron interaction for the determination of the electron kinetics, an extensive reaction kinetics involving various heavy particles and photons, and the relevant electrical circuit equations. The study has shown that density perturbations of preionization electrons lead to the inhomogeneity of the discharge plasma and the laser output. Furthermore, the impact of the spatial distribution of preionization electrons, of the HCl portion of the gas mixture, and of a low-current preliminary discharge for the discharge operation is discussed. Received: 10 September 1996/Revised version: 21 July 1997     

Spatial Transition of the Electron Gas from the Active to the Remote Plasma State

Starting from the active region of a weakly ionized plasma the spatial transition of the electron gas through an adjacent field decay region into the field-free remote plasma is studied in neon on a rigorous basis by using two independent kinetic approaches. The main objective of the analysis concerns the complex features of the electron gas in its transition process from a field-driven active plasma to a purely diffusion-driven remote plasma. In addition to the energy resolved characterization of the velocity distribution, in particular, the spatial decay behavior of important, energy space averaged transport and dissipation properties of the electrons, as the density, the particle and energy fluxes and the power transfer rates to the gas particles in electron collisions, is elaborated and interpreted. Moreover, the influence of a variation of the active plasma conditions and of the spread of the field decay region on the resultant transition behavior of the electron gas is evaluated. A particular finding is that the spatial field decay is generally accompanied by a large density increase in order to allow the continuation of the electron flux by a pure diffusion process in the adjacent remote plasma. This finding could be completely confirmed by the almost perfect coincidence of corresponding results obtained by two independent kinetic approaches.     

Effect of small admixtures of N<Subscript>2</Subscript>, H<Subscript>2</Subscript> or O<Subscript>2</Subscript> on the electron drift velocity in argon: experimental measurements and calculations

The electron drift velocity in argon with admixtures of up to 2% of nitrogen, hydrogen or oxygen is measured in a pulsed Townsend system for reduced electric fields ranging from 0.1 Td to 2.5 Td. The results are compared with those obtained by Monte Carlo simulations and from the solution of the electron Boltzmann equation using two different solution techniques: a multiterm method based on Legendre polynomial expansion of the angular dependence of the velocity distribution function and the S _n method applied to a density gradient expansion representation of the distribution function. An almost perfect agreement between the results of the three numerical methods and, in general, very good agreement between the experimental and the calculated results is obtained. Measurements in Ar-O₂ mixtures were limited by electron attachment to oxygen molecules, which contributes to the measured drift velocity. As a result of this attachment contribution, the bulk drift velocity becomes larger than the flux drift velocity if attachment is more probable for electrons with energy below the mean value and smaller in the opposite case. Attachment also contributes to the negative differential conductivity observed in Ar-O₂ mixtures.     

Unified Non-equilibrium Modelling of Tungsten-Inert Gas Microarcs in Atmospheric Pressure Argon

Plasma Chemistry and Plasma Processing - Analysis of the plasma parameters of a tungsten-inert gas microarc with a length of 0.4&nbsp;mm is carried out by means of a unified one-dimensional...