Bulletin of the American Physical Society
2005 58th Gaseous Electronics Conference
Sunday–Thursday, October 16–20, 2005; San Jose, California
Session LT2: High Pressure Plasmas II |
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Chair: Biswa Ganguly, Air Force Research Laboratory Room: Doubletree Hotel Cedar |
Tuesday, October 18, 2005 1:30PM - 2:00PM |
LT2.00001: Microcavity Discharge Devices and Arrays: A Photonic Platform for Photodetectors, Optical Amplifiers and Displays Invited Speaker: Microcavity plasma is the term associated with the spatial confinement of a nonequilibrium plasma to a cavity having a characteristic dimension below nominally 500 $\mu $m. Recently, fabrication techniques developed largely by the semiconductor and MEMs communities have been adapted to realize a family of microcavity plasma (microplasma) devices with cross-sectional dimensions as small as (10 $\mu $m)$^{2}$. Fabricated in a wide range of materials platforms, including Si, ceramics, and metal/dielectric multilayer structures, these devices exhibit a number of intriguing properties. These include: 1) the ability to operate on a continuous basis at pressures of one atmosphere and above, 2) specific power loadings of at least tens of kW-cm$^{-3}$, and 3) microcavity volumes of nanoliters or picoliters. This talk will summarize the properties of microcavity plasmas with characteristic dimensions in the 10-150 $\mu $m range, and operating at gas pressures up to $\sim $1200 Torr. Emphasis will be placed on the scientific opportunities afforded by: 1) the access provided by microcavity plasmas to a new region of parameter space, and 2) the ability to now interface a low temperature plasma with an electronic or optical material. Several examples of photonic structures and their applications will be presented, including the recent development of arrays of 250,000 (500 $\times $ 500) inverted pyramid microcavity devices fabricated in silicon. Having an active area of 25 cm$^{2}$, this array has been operated in both the rare gases and Ar/N$_{2}$ mixtures, and yields luminous efficacies $>$5 lumens/W when coupled with a commercial green phosphor (Mn:Zn$_{2}$SiO$_{4})$. Ceramic microchips offering a microplasma gain length of 1-2 cm have also been developed and gain on the 460.3 nm transition of Xe$^{+}$ has been observed. Applications of microplasmas in biomedical diagnostics and optics will also be discussed. [Preview Abstract] |
Tuesday, October 18, 2005 2:00PM - 2:15PM |
LT2.00002: Combination of atmospheric pressure dielectric barrier discharge and photocatalysis for C$_{2}$H$_{2}$ oxidation Frederic Thevenet, Chantal Guillard, Olivier Guaitella, Antoine Rousseau Non-thermal plasma and photocatalysis have attracted attention as energy-saving methods for VOCs destruction. TiO$_{2}$ photocatalysts are porous semiconductors activated by UV radiations. They are known for their ability to oxidize organic molecules with high CO$_{2}$ selectivity. It was shown recently that the coupling of dielectric barrier discharges (DBD) with photocatalysis improves oxidation efficiency and reduces undesirable by-products. Experiments were carried out in a closed DBD reactor containing photocatalytic surface, with C$_{2}$H$_{2}$ as a test molecule. First, TiO$_{2}$ influence on DBD deposited energy was investigated, as well as ageing of TiO$_{2}$ under DBD conditions. Then, air cleaning efficiency of coupling was investigated. Introduction of higher specific energy and addition of UV radiations increase the synergistic effect. Selectivity is clearly enhanced. The CO amount is reduced in presence of TiO$_ {2}$. CO$_{2}$ formation is improved. Experimental data were fitted by kinetics models. Constants were calculated and reaction mechanisms are reported. Understanding of plasma-TiO$_{2}$ synergy has been improved by in situ and time resolved laser absorption experiment in the mid infrared region [Preview Abstract] |
Tuesday, October 18, 2005 2:15PM - 2:30PM |
LT2.00003: Hydrogasification of Coal using Atmospheric Pressure Microwave Plasma Yongho Kim, Hans Ziock, Louis Rosocha, Graydon Anderson, Don Coates, Gabriel Becerra, Elijah Martin, Vincent Ferreri, Jaeyoung Park, Tsitsi Madzawa-Nussinov A clean coal technology is a newly highlighted research field because coal is America's largest domestic energy source and coal can be gasified to methane or hydrogen. However, the coal gasification process has encountered technical barriers because no reliable sulfur-tolerant chemical catalysts exist. Los Alamos National Laboratory has proposed a plasma catalyzed coal gasification concept, where plasma turns coal and reactant gases into highly reactive free radicals and excited species, which are believed to promote gasification reactions. We have developed an atmospheric pressure microwave plasma system using a 2.45 GHz magnetron. In this paper, we report the preliminary results on the hydrogasification of coal (C + 2H$_{2}$ $\diamondsuit $ CH$_{4})$. Stable plasma conditions will be explored with pulverized coal powders, as functions of hydrogen flow, and applied power. UV/IR spectroscopic measurements will be carried out to characterize the plasma properties and correlate these to hydrogasification reactivity. [Preview Abstract] |
Tuesday, October 18, 2005 2:30PM - 2:45PM |
LT2.00004: Measurement of plasma properties in a cutting arc John Peters, Joachim Heberlein, Jon Lindsay Plasma cutting utilizes a highly constricted arc to melt the material being processed. The processed material, or work-piece, serves as the anode, and arc constriction between the torch cathode and anode is attained using a small diameter nozzle together with a high velocity gas flow. This gas flow also assists in the cutting process by removing the molten material from the work-piece. The performance of the cutting system is related to the properties of the plasma jet. Temperature, electron density and the velocity of the jet are the properties used to characterize the plasma arc. Spectroscopic methods are used to measure radial and axial distributions of the temperature and electron density within the arc using several calculation methods as well as several emitting species. From these measurements the axial pressure variations due to the expansion of the under-expanded plasma jet are estimated. The validity of the assumption of LTE in different regions of the arc is also discussed. Finally, the effects of selected cutting process inputs such as current, flow rate and nozzle diameter on the plasma jet properties are evaluated. [Preview Abstract] |
Tuesday, October 18, 2005 2:45PM - 3:00PM |
LT2.00005: A 2-Temperature Model for High Pressure High Temperature Thermal Plasmas Ning Zhou The high pressure thermal plasmas due to its high temperature and high ionization degree, are generally modeled using equilibrium assumptions. As the results, many variables can be expressed as the functions of thermodynamic states. And in particular, the electric conductivity is measured and curve-fitted as the function of temperature, pressure for the given gas mixture. This model is attractive for its simplicity, but it neglects some important aspects of physics and is subject to the accuracy of the measured coefficients. A fluid model for high pressure high temperature thermal plasmas such as arc discharge, is therefore proposed. In this model, the thermal non-equilibrium effect is considered by solving the temperatures for electron and gas, respectively. The plasma chemical kinetics is modeled by the finite-rate reactions and the electron transport coefficients (mobility, diffusivity and electric conductivity) are calculated according to the electron collisions with heavy particles. Quasi-neutrality is assumed for the bulk of plasma and sheath model is employed to account for the near electrode phenomena. This model is validated for arc discharges at near equilibrium conditions, and the comparison with the equilibrium model is discussed. [Preview Abstract] |
Tuesday, October 18, 2005 3:00PM - 3:15PM |
LT2.00006: Simulations of 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: bulk heating of the flow, electrostatic forcing and Lorentz forcing (in the presence of external magnetic fields). In typical experiments with plasma actuators, several of these forces act simultaneously. By developing detailed computational models for the plasma and bulk flow we hope to gain a better understanding of each of these factors. The plasma model we are using is based on a two-dimensional, self-consistent, multi-species continuum description of the plasma. A surface plasma actuator with two electrodes on a single plane is considered. A DC plasma is generated between the two exposed electrodes to produce body forces that perturb the flow. Results include maps of charge density, temperature and electric potential profiles. For an argon plasma at a pressure of 5 Torr and an applied voltage of 100 V, the sheath region in front of the cathode is about 1 mm thick. In this region where electrohydrodynamic effects are dominant, the electrostatic body force is $\sim $100 N/m$^{3}$. For a magnetic flux density of 1 Tesla and in a region $\sim $1cm thick above the electrodes, the resulting Lorentz force is $\sim $10 N/m$^{3}$. Relative contributions of the body forces as a function of geometry and operating conditions will be explored in this study. [Preview Abstract] |
Tuesday, October 18, 2005 3:15PM - 3:30PM |
LT2.00007: An efficient algorithm for axisymmetrical 2D fluid Zoran Ristivojevi\'c, Zoran Petrovi\'c We have developed an efficient algorithm for steady axisymmetrical 2D fluid equations. The algorithm employs multigrid method as well as standard implicit discretization schemes for systems of partial differential equations. Linearity of multigrid method with respect to the number of grid points allowed us to use $256\times 256$ grid, where we could achieve solutions in several minutes. Time limitations due to nonlinearity of the system are partially avoided by using multi level grids. In other words the initial solution on $256\times 256$ grid was the extrapolated, steady solution from $128\times 128$ grid which allowed using ``long'' integration time steps. The fluid solver is used as the basis for hybrid codes for DC discharges. [Preview Abstract] |
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