Bulletin of the American Physical Society
60th Gaseous Electronics Conference
Volume 52, Number 9
Tuesday–Friday, October 2–5, 2007; Arlington, Virginia
Session RR1: Micro and Dielectric Barrier Discharges |
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Chair: Remi Dussart, GREMI - Universite d'Orleans Room: Doubletree Crystal City Crystal Ballroom A |
Thursday, October 4, 2007 1:30PM - 2:00PM |
RR1.00001: Microcathode Sustained Discharges for the generation of DC, non-thermal plasmas at high gas pressure Invited Speaker: It is now well known that non-thermal DC plasmas can be generated and maintained in high pressure gases in small - hundreds of micron-sized - geometries. One such configuration, a MicroHollow Cathode Discharge (MHCD), orginally investigated by Schoenbach and colleagues (KH Schoenbach, et al, Plasma Sources Sci. Technol. \textbf{6}, 468 (1997)), consists of a metal/dielectric/metal sandwich through through which a central hole is pierced. The diameter of the hole and the thickness of the sandwich are each some 100's of microns. Larger volume plasmas can be generated by placing a third, positively biased electrode some distance (1 cm) away, in which case the MHCD can act as a plasma cathode. This configuration is called a MicroCathode Sustained Discharge or MCSD (RH Stark and KH Schoenbach J. Appl. Phys. \textbf{85} 2075 (1999)). This talk will focus on the properties of the MCSD - its initiation and its electrical properties - and on the properties of the plasma generated in the MCSD volume. Experimental and numerical results for discharges in rare gases and in rare gas/oxygen mixtures at pressures up to atmospheric will be used to illustrate that the plasma generated in the MCSD is similar to a positive column plasma, with a low electric field and low to moderate gas temperature. The plasma conditions in the MCSD are suitable for the generation of large densities of radical species, such as oxygen molecules in the singlet delta metastable state (G. Bauville, et al, Appl. Phys. Lett. \textbf{90}, 031501 (2007)). [Preview Abstract] |
Thursday, October 4, 2007 2:00PM - 2:30PM |
RR1.00002: Plasma-Photocatalyst Interaction for VOC Removal: Origin of the Synergy Invited Speaker: It is well known that the coupling of an atmospheric non-thermal plasma with catalytic materials lead to synergetic effects for the abatement of some volatiles organic compounds (VOC). We analyze, here, the mechanisms of such a synergy where the catalyst is a porous semi-conductor (TiO$_{2})$. Different porous materials are compared: silica fibers possibly containing SiO2 and/or TiO2 nanoparticles. The respective influence of the porosity versus the chemical type of the catalyst is investigated and the oxidizing species are identified using two complementary approaches. 1) Efficiency of the plasma-catalyst coupling in a dielectric barrier discharge (DBD) at atmospheric pressure, 2) Plasma-catalytic surface interaction in a pulsed low pressure discharge. It is shown that the VOC oxidation scales as a function of the specific injected energy and occurs mainly on the porous surface due to short-life species produced the plasma [1-3]; Time resolved and in-situ measurements using laser absorption spectroscopy and emission spectroscopy in a low-pressure experiment have shown that i) plasma-TiO2 synergy is also evidenced at low pressure[4], ii) O atoms are reversively adsorbed on porous nanoparticles of TiO2; their desorption occur during the first millisecond of a plasma pulse [5], iii) air-plasma pre-treatment of the porous material leads to an enhancement of VOC adsorption on porous TiO2 and has no influence on porous silica. \newline [1] U. Roland et al. \textit{Catalysis Today} \textbf{73} 315--323 \newline [2] F. Thevenet et al. Catal. Today 122 (2007) 186--194 \newline [3] F. Thevenet et al. I\textit{nternational Journal of Plasma Environmental Science and Technolo}gy, 1, (2007), 52-56 \newline [4] A. Rousseau et al. \textit{Appl. Phys. Let}. 87, 221501 (2005) \newline [5] Allegraud et al. J. Phys. D.~: Appl. Phys submitted. [Preview Abstract] |
Thursday, October 4, 2007 2:30PM - 2:45PM |
RR1.00003: The dynamics of light emission from micro-discharge array devices J. Wask\"onig, D. O'Connell, V. Schulz-von der Gathen, J. Winter Micro-discharges structured in arrays, of up to tens of thousands single devices, are becoming increasingly important with immense application potential. Investigations, in particular experimental, can be challenging on such discharges, however more detailed insight is essential for further development. One such array is investigated through phase and space resolved optical emission spectroscopy (PROES). Through these investigations insight into ignition and sustaining mechanisms of both the individual discharge devices and the array as a whole are obtained. It can be observed that emission is not continuous over the entire ac period, it occurs only twice in each cycle. The emission in both of these phases exhibits different signatures. Cross-talk between the individual devices can be observed through spatially resolved measurements. Funding: SFB 591, GRK 1051. [Preview Abstract] |
Thursday, October 4, 2007 2:45PM - 3:00PM |
RR1.00004: Plasma Confinement in Glass Microcavities: Dependence of Plasma Properties on Microcavity Geometry. S.H. Sung, A.G. Berger, J.-Y. Kim, S.-J. Park, J.G. Eden Arrays of glass microcavities having diameters of 50-200 $\mu $m and controllable geometries have been successfully fabricated by micropowder blasting techniques. Anisotropic or isotropic microcavities, including cavities with ellipsoidal geometry have been fabricated in large scale arrays with high resolution and various shapes of microcavities were prepared precisely. Arrays having as much as 1000 microcavities were fabricated on 400 $\mu $m thick soda lime glasses and a pair of these glasses was aligned and sealed to form a closed microdischarge cell. The cross-sectional microcavity shape in the discharge cell is designed from the calculation of electric field distribution. Powered by electrodes located outside the microcavity with ac frequencies of 20-100 kHz, the stable, uniform discharges and confinement of plasma in entire microcavity was observed at 300-800 Torr of noble gases. From the spatially-resolved measurement of emission from a microcavity, the device has better plasma confinement and increased emission intensity in higher gas pressures. Discharge performance in various gas or gas mixtures and its dependence on microcavity geometry will be discussed. [Preview Abstract] |
Thursday, October 4, 2007 3:00PM - 3:15PM |
RR1.00005: Student Excellence Award Finalist: Self organization of streamers in a surface DBD: evidence of collective breakdowns K. Allegraud, N. Leick, O. Guaitella, A. Rousseau Surface dielectric barrier discharges (DBD) are mainly investigated for airflow control. In this paper, surface processes controlling the filament development are studied. Recent results have shown that in a cylindrical DBD, most of the energy is transferred via few large amplitude current peaks called collective effects [1]. To get further in the study of this phenomenon, electrical measurements and CCD imaging have been performed on a surface discharge, were the plasma filaments are generated onto the dielectric surface. The plasma is generated via several nearby (but distinct) filaments occurring simultaneously, the current peak duration being a few tens of nanoseconds. The current peak amplitude is proportional to the number of filaments, with a value of about 40 mA/filament. The filament length depends on the applied and breakdown voltages, independently from the current amplitude. The self-organization of the streamer breakdown in adjacent patterns is due to the simultaneous triggering of individual filaments via a collective effect. We suggest that the origin of such a self triggering is due to the photo-desorption of electrons from the surface by a first filament. These electrons then initiate the neighbouring filaments, and all the filaments contribute to the whole charge transfer. [1] O. Guaitella et .al, Phys. D.: Appl. Phys. 39(2006) [Preview Abstract] |
Thursday, October 4, 2007 3:15PM - 3:30PM |
RR1.00006: Experimental observations and simulations of single and double barrier DBD plasma actuators Alan Hoskinson, Young-Chul Kim, Noah Hershkowitz When operated in air, a surface-mounted dielectric barrier discharge (DBD) induces flow in the gas just above its surface. In recent years, interest has grown in using these discharges as aerodynamic actuators. We present the results of our experimental and computational studies of how variations in discharge geometry effect both the plasma and the induced electro-hydrodynamic (EHD) force. Our studies primarily focus on double barrier actuators (both electrodes insulated), but make comparisons to single barrier actuators (one electrode insulated). Pitot tube measurements of the induced air flow show the velocity reaches a plateau several kilovolts above the turn-on voltage, and shows only weak variations with the degree of asymmetry between the two electrodes. To explain this behavior, we present time-resolved optical emission measurements of the plasma volume while varying the diameter of one of the electrodes. We also report the results of fluid simulations of discharges with various electrode sizes. [Preview Abstract] |
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