Bulletin of the American Physical Society
2006 59th Annual Gaseous Electronics Conference
Tuesday–Friday, October 10–13, 2006; Columbus, Ohio
Session GW2: High Pressure Discharges I |
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Chair: William Graham, Queens University Belfast Room: Holiday Inn Salon B |
Wednesday, October 11, 2006 8:00AM - 8:30AM |
GW2.00001: Energy transport and instabilities in high pressure plasmas Invited Speaker: While electric arc plasmas can be considered to be in local thermal equilibrium, any interaction of the arc with its surroundings will result in a non-equilibrium boundary layer. Two such non-equilibrium boundary layers will be considered. One is the interaction of an arc with a solid surface, i.e. what happens to the energy and current transfer if you have extremely steep gradients, and when diffusion processes dominate. Contradictory evidence and theories exist for such a situation. Recent Langmuir probe and Thomson scattering measurements have provided some insight and support qualitatively some previous modeling predictions. However, it may be questioned if a continuum approach is still valid when temperature gradients of 10$^{5}$ K/mm exist. The other boundary layer is encountered when a high velocity plasma jet is surrounded by a cold gas. The steep gradients in density and viscosity between the plasma jet and its surroundings result in fluid dynamic instabilities, enhanced by upstream arc instabilities. These instabilities result in entrainment of cold surrounding gas in form of larger bubbles, requiring a description of a jet consisting of two immiscible fluids. Approaches will be described for controlling these instabilities for an application like plasma spraying where the residence time of the particles is in the same order of magnitude as the period of the instability. [Preview Abstract] |
Wednesday, October 11, 2006 8:30AM - 9:00AM |
GW2.00002: Characterization of Atmospheric Pressure Dielectric Barrier Discharges for Environmental Applications Invited Speaker: Two types of atmospheric pressure glow discharge (APGD) schemes, i.e., a conventional parallel-plate type and a microplasma-integrated type, are compared from viewpoints of those plasma parameters and other physicochemical characteristics. In the former type, the discharge tends to constrict showing filamentary appearance as the current density increases. The tendency becomes noticeable when electronegative gases such as O$_{2}$ and H$_{2}$O are included. Therefore, in the glow mode the electron density cannot exceed the order of 10$^{11}$ cm$^{3}$, as measured by a mm-wave transmission technique, even though an elaborate method to control the voltage waveform is performed. The mechanisms concerning with the filamentation will be argued based on the variation of the accumulated charge density on the dielectrics from the spatially resolved measurement by a Pockels-effect method. On the centrally, the latter type with such a structure composed of stacked metal-mesh covered with dielectrics has been proved to be promising for stable operation at higher plasma density in the order of 10$^{12}$ to 10$^{13}$ cm$^{-3}$ even with admixtures of O$_{2}$ and H$_{2}$O. This is of much advantage for many environmental uses in the effective production of oxidizing precursors such as O, OH and O$_{3}$. In order to effuse the plasma out of the mesh-electrode holes, the effect of gas flow has been studied, and the modified structure enabling higher flow velocity is going to be tested together with the optimization of the operating frequency and the voltage waveform. The results of laser spectroscopic diagnostics of those radicals and ions such as N$_{2}^{+}$ will be explained at the conference. [Preview Abstract] |
Wednesday, October 11, 2006 9:00AM - 9:15AM |
GW2.00003: Plasma properties in microcathode sustained discharges in oxygen containing mixtures -- comparisons of experiments and models G. Bauville, J.F. Lagrange, L. Magne, V. Puech, E. Munoz-Serrano, L.C. Pitchford, N. Sadeghi, M. Touzeau In this communication, we will summarize results of a joint experimental/modeling project whose purpose is to evaluate the feasibility of generating high yields of singlet delta (1D) metastable oxygen molecules in a microcathode sustained discharge (MCSD), a discharge configuration in which a microhollow cathode discharge is used as a plasma cathode with a third electrode being placed 0.5-1 cm away. From electrical and optical measurements and from modeling (presented in more detail in companion posters at this conference), we deduce the gas temperature, the [ O] density profile, the spatial distribution of O2(singlet sigma), the spatial distribution of the O3, and the yield of O2(1D) as determined from IR emission at points downstream from the discharge. These quantities are compared with results from a 2D quasi-neutral model. The baseline conditions are 10{\%} O2 in Ar at a total pressure of 50 torr, discharge currents on the order of 1 mA, and for a 200 micron microhollow cathode discharge diameter. This communication will focus on the intercomparison of results from the different diagnostics and from the model. [Preview Abstract] |
Wednesday, October 11, 2006 9:15AM - 9:30AM |
GW2.00004: Simulations of nitrogen glow discharge phenomena for high-speed flow control Thomas Deconinck, Shankar Mahadevan, Laxminarayan Raja Plasma actuators offer a promising opportunity for high-speed flow control applications. The forcing of the flow occurs through three primary mechanisms: electrohydrodynamic forcing or ion drag, dilatation effects related to gas heating, and magnetohydrodynamic forcing in the presence of magnetic fields. In order to gain a physical understanding of these factors, we developped a detailed computational model for the plasma and bulk flow. The model is based on a two-dimensional, self-consistent, multi-species continuum description of the plasma. We use a two-temperature chemical kinetics model that includes the following species: e$^{-}$, N$_{2}^{+}$, N$^{+}$, N, and N$_{2}$. In this work, a surface plasma actuator with two bare-electrodes on a single plane is considered. The imposed background flow-field simulates a boundary layer with an external velocity of 700 m/s. Results include maps of charge density, temperature and electric potential profiles. For a pressure of 5 Torr and an applied voltage of 2500 V, the sheath region in front of the cathode is about 5 mm thick. The peak electron number density reaches $\sim $1e16 m\^{}(-3) in the bulk plasma. The number density of N$_{2}^{+}$ is found to be dominant in the discharge, about two orders of magnitude higher than that of N$^{+}$. Relative contributions of the body forces will be explored for different operating conditions. [Preview Abstract] |
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