Bulletin of the American Physical Society
61st Annual Gaseous Electronics Conference
Volume 53, Number 10
Monday–Friday, October 13–17, 2008; Dallas, Texas
Session CT1: Microhollow Cathode Discharges |
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Chair: K. Nordheden, The University of Kansas Room: Salon E |
Tuesday, October 14, 2008 10:00AM - 10:15AM |
CT1.00001: Absolute atomic oxygen density measurements in core and effluent of a micro scaled atmospheric pressure plasma jet Volker Schulz-von der Gathen, Nikolas Knake, Stephan Reuter, Kari Niemi The micro atmospheric pressure plasma jet ($\mu$APPJ) is a capacitively coupled rf discharge (13.56 MHz, $\sim$15 W transceiver power) developed, in particular, for optical diagnostics. The discharge is operated at a helium flow of about 1.4 slm with an admixture of oxygen ($\sim$0.5 vol.-\%). In the effluent spatially resolved density distributions of the ground state oxygen atoms have been measured by two-photon absorption laser-induced fluorescence spectroscopy. After calibration by comparative measurements on xenon maximum densities of 2 x 10$^{14}$cm$^{-3}$ have been measured. Variation of the admixture of molecular oxygen between 0 and 2 vol.-\% reveals a maximum of the reactive oxygen species yield inside the effluent at 0.6 vol.-\%. Varying the power a saturation of the oxygen density is observed beyond about 15 W. First spatially resolved investigations within the discharge core yielded dissociation degrees of more than 20\%. While the admixture variation also results in an optimum atom production similar to the effluent, a power variation revealed significant deviations within the core region of the discharge. [Preview Abstract] |
Tuesday, October 14, 2008 10:15AM - 10:30AM |
CT1.00002: Coupling of imaging and emission spectroscopy for microplasmas studies Claudia Lazzaroni, Nader Sadeghi, Antoine Rousseau A microplasma is generated in the microhole of a metal-dielectric-metal sandwich at medium pressure in pure argon. The gas pressure ranges from 30 to 300Torr; the hole diameter from 100 to 400 $\mu $m. The aim of our experiment is to study the radial dependence of the mechanism of atoms excitation and of the electronic density inside the microhollow cathode discharge. Imaging of the emission from the microplasma is performed with a spatial resolution of 2$\mu $m. The electron density is estimated from the Stark broadening of the H$_{\beta }$-line. The radial distribution of the emission intensities of an Ar atomic line and an Ar$^{+}$ ionic line are used for the excitation study. Ar and Ar$^{+}$ lines are excited in the cathode sheath edge by beam electrons accelerated within the sheath. These two excitations show the decay of the energy of electrons in negative glow. The Ar line presents also production of excited atoms by recombination of argon ions with electrons at the center of the micro-hole. Work is in progress to evaluate the contribution of the static electric field on the stark broadening. [Preview Abstract] |
Tuesday, October 14, 2008 10:30AM - 10:45AM |
CT1.00003: Atmospheric pressure microdischarges utilizing nanoporous dielectric electrodes Jin Hoon Cho, Woong Moo Lee, Cameron Moore, George Collins We report the generation of microplasmas that use electrodes with nanoporous dielectric surfaces. The electrodes used in the dielectric barrier discharge are made of aluminum rods or plates covered with nanoporous alumina films, $\sim $80 $\mu $m thick and mean pore diameters being $\sim $40 nm. The alumina nanoporous film was grown onto Al rod via an electrochemical etching process. The microplasma was sustained using $\sim $10W of AC power at 10$\sim $30 kHz, with a gap of 100$\sim $500 $\mu $m between the rod, tube and plate shaped electrodes. The typical driving voltage and the electron density are $\sim $1200V and 10$^{11}\sim $10$^{12 }$cm$^{-3}$, respectively while the temperature at the discharge region is in the range of 310-350 K. This type of dielectric barrier discharge effectively generates low temperature uniform microplasmas that can be used for a variety of applications, including UV generation, surface treatment, biomedical treatment, and plasma chemical synthesis. [Preview Abstract] |
Tuesday, October 14, 2008 10:45AM - 11:00AM |
CT1.00004: GEC Student Award for Excellence Finalist: Laser Diagnostics of High Pressure Microdischarge Plasmas Sergey Belostotskiy, Vincent Donnelly, Demetre Economou, Nader Sadeghi Laser diagnostics were performed in the positive column of a high pressure (100s of Torr) parallel-plate DC microdischarge operating in argon or nitrogen. For 50 mA current and over the range of 300 -- 700 Torr, Laser Thomson Scattering yielded T$_{e}$ = 0.9 $\pm $ 0.3 eV and n$_{e}$ = (6 $\pm$ 3)\textbullet 10$^{13}$ cm$^{-3}$, in agreement with a mathematical model. Rotational Raman spectroscopy was performed for a set of N$_{2}$ pressures (400 -- 600 Torr) to measure the gas temperature. T$_{g}$ changed from 450 $\pm $ 40 K at 5 mA to 740 $\pm $ 40 K at 30 mA, and was nearly independent of pressure, within experimental error. Finally, spatially resolved diode laser absorption spectroscopy was used to measure the density of argon metastables. The metastable number density peaked at the plasma-sheath ($\sim $ 10$^{14}$ cm$^{-3})$ interface in agreement with simulation. The gas temperature was also extracted from the Doppler width of the absorption profile. [Preview Abstract] |
Tuesday, October 14, 2008 11:00AM - 11:30AM |
CT1.00005: Generation of microplasma ensemble and its functional interaction with electromagnetic waves Invited Speaker: Various patterns and structures of microplasma arrays were generated, and interactions between microplasmas and electromagnetic waves were investigated both for control of waves by microplasma ensembles and for production of microplasmas by waves. Using bipolar-voltage power supply with frequencies from several kHz to several MHz and insulated wires, several types of microplasmas were generated at atmospheric pressure with their electron density ranging from 10$^{12}$ to 10$^{13}$ cm$^{-3}$. They serve as equivalent dielectrics or metals according to their electron plasma frequency ranging from several GHz to several tens of GHz, with respect to the frequency of a propagating electromagnetic wave. When we installed such microplasmas forming a functional array in the propagation region of electromagnetic waves, microplasma arrays exhibited several types of performance; photonic crystals with band gaps, plasmonic waveguides, and metamaterials with extraordinary macroscopic permittivity and/or permeability. One of the significant advantages arising from use of microplasmas in a wave controller is their dynamic and tunable manner by changing external parameters such as generation power and working gas pressure. Especially rapid change of spatial generation patterns gives rise to transformation into another functional device. Another advantage is a role of complex functions arising from dispersion relations with frequency-dependent loss, which will lead to simultaneous and independent control of phase and attenuation of electromagnetic waves. [Preview Abstract] |
Tuesday, October 14, 2008 11:30AM - 11:45AM |
CT1.00006: Modeling of Mode Transition Behavior in Argon Microhollow Cathode Discharges Thomas Deconinck, Laxminarayan Raja Microhollow cathode discharges (MHCD) can be generated in a simple geometry comprising a cathode/dielectric/anode sandwich structure into which a blind or through hole is drilled. These microdischarges operate at a relatively high pressure of $\sim $10s-100s Torr with a hole dimension of $\sim $10s-100s $\mu $m. In this study, a fluid model with an argon chemistry is used to help clarify physical mechanisms occurring in a MHCD. The plasma is described using a self-consistent, multi-species, multi-temperature formulation. A variable secondary emission coefficient that depends on the local value of the electric field at the solid surface is used in our model. Computational results are compared to experiments performed in a similar set-up [1]. At low currents (I $< \quad \sim $0.3 mA), the discharge operates in the abnormal regime and is localized within the cylindrical hollow cathode. At higher current, the discharge expands over the outer surface of the cathode and operates in the normal regime. The differential resistivity of the discharge in this normal regime depends critically on the variable secondary electron emission model used in this study. [1] X. Aubert et al\textit{, Plasma Sources Sci. Technol}., 16 (2007), 23-32. [Preview Abstract] |
Tuesday, October 14, 2008 11:45AM - 12:00PM |
CT1.00007: Ignition of parallel Micro Hollow Cathode Discharges in He without ballasts Thierry Dufour, Monali Mandra, Matthew Goeckner, Philippe Lefaucheux, Pierre Ranson, Jeong-Bong Lee, R\'emi Dussart, Lawrence Overzet Microplasmas are of interest for many different applications including medical, micro TAS, plasma treatment{\ldots} The purpose of our study is to switch on and control several microdischarges mounted in parallel on a single chip, without ballasting them individually. Microcavities used in our experiments are Ni:Al$_{2}$O$_{3}$:Ni sandwich structures. Holes are 80-180 $\mu $m diameter. DC microplasmas are created in He gas without flow with a pressure from 200 to 1000 Torr. A maximum power of 7 watts can be injected into one microdischarge. The area of the plasma spread on the cathode side is determined using an ICCD camera. A current density as high as around 10 mA/mm$^{2}$ could be evaluated. Abnormal glow regime can be obtained by limiting the cathode surface. By this way, it is possible to switch on all the microplasmas without using individual ballasts. We will also present results of microplasmas ignited in gas flow crossing the cavities and show the flow affects the microplasmas and their V-I curve. [Preview Abstract] |
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