Bulletin of the American Physical Society
2006 59th Annual Gaseous Electronics Conference
Tuesday–Friday, October 10–13, 2006; Columbus, Ohio
Session SRP2: Poster IIB |
Hide Abstracts |
Room: Holiday Inn Buckeye, 4:00pm - 5:30pm |
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SRP2.00001: PLASMA DIAGNOSTICS AND SURFACE INTERACTIONS |
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SRP2.00002: A new scheme for laser-induced fluorescence measurements in Xe II plasmas Greg Severn, Dongsoo Lee, Noah Hershkowitz We report laser-induced fluorescence (LIF) measurements in Xe II plasmas which utilize the $5p^4 (^3P_1)5d[3]_{7/2}$ metastable state. The wavelength of the excitation transition is 680.574nm in air. To our knowledge, this scheme has never been used before for LIF measurements in plasmas. The complete scheme is $5p^4 (^3P_1)5d[3]_{7/2}$ $ \rightarrow $ $5p^4 (^3P_1)6p[2] ^o_{5/2}$$ \rightarrow $ $5p^4 (^3P_1)6s[1]_{3/2} $, and the detectable photon has a $\lambda = 492.15nm $ in the rest frame, in air. The plasmas are created in a hot filament, DC discharge, with $kT_e \sim 1 eV, \: P_o \sim 1mTorr,$ and $ \: n_e \sim 10^9 cm^{-3}cm$. Preliminary measurements suggest that the metastable state is sufficiently populated to permit measurements of ion velocity distribution functions (ivdfs). We also report on LIF measurements in XeII plasmas using a scheme commonly\footnote {Hargus, Jr., W.A.; Cappelli, M.A.. Appl. Phys. B (2001), {\bf 72}, 961} used in Hall-Thruster plasmas, with excitation at 834.96 nm (air), and we assess the relative merits of the schemes. We are interested in these LIF schemes for the purpose of testing the generalized Bohm Criterion in the vicinity of sheath edge for two-ion plasmas. Proving new XeII LIF schemes for these plasmas permit measurements of the ivdfs {\em for both ions}, something never before accomplished. [Preview Abstract] |
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SRP2.00003: Electric field distribution around a biased probe immersed in an electrical discharge Ed Barnat, Greg Hebner Electric field distributions are measured around a biased probe immersed in an argon discharge. The distributions are measured as functions of probe bias, argon pressure, and distance of the probe from the ``boundary'' placed on the plasma by a powered electrode. The electric fields are symmetrically distributed around the probe when the probe is placed sufficiently far from this boundary, but become asymmetric when the sheaths around both the probe and the powered electrode began to couple. For select cases, we discuss how the space charge is distributed around the probe. We also discuss perturbations in the excited 1s$_{4}$ states that result due to the presence of the probe. In general, we note that while the measurable fields around the probe are contained in a region around the probe on the order of a Debye length ($\sim $ 1 \textit{$\lambda $}$_{Debye})$, these perturbations extend many Debye lengths ($\sim $ 10 \textit{$\lambda $}$_{Debye})$. We discuss the implication of these measurements both in terms of conventional Langmuir probes used to measure plasma parameters, as well as charged grains of dust that exhibit collective behavior leading to the formation of plasma crystals. [Preview Abstract] |
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SRP2.00004: Time resolved measurement of NO destruction using Quantum Cascade Laser in the mid-infrared L. Gatilova, A. Rousseau, S. Welzel, J. Roepcke The recent development of commercially available quantum cascade laser (QCL) in the mid infrared region offers new possibility for dynamic measurements in pulsed plasmas. Such diodes work near room temperature in pulsed mode. In the present study, we use the Q-MACS system to perform in situ time resolved measurement in a pulsed DC discharge. During each diode laser pulse (80 ns), the laser frequency is scanned over the absorption line, which gives the actual time resolution. The plasma is generated in a 50 cm long cylindrical glass tube in Ar/N2/NO = 90/10/0.9 at 133 Pa. The pulse duration and current are 1 ms and 20 mA respectively. NO line (1894.15 cm-1) is used. The detection limit is about 0.2{\%} for a 80 ns single shot time resolution. Numerical computations of the NO kinetics are compared to experimental results. Work supported by German/French exchange program PROCOPE. [Preview Abstract] |
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SRP2.00005: Measurement of dust particle size and density by a laser light scattering and extinction method Changrae Seon, Kilbyoung Chai, Hoyong Park, Yonghyun Shin, Kwanghwa Chung, Wonho Choe The measurement of dust particle density was performed using the laser light extinction method. Using two spherical mirrors, a multi-pass setup was used for lowering the measurement limit of the system. In parallel, the particle size was measured using the laser light scattering method. To self-consistently determine the time evolution of the particle size, in-situ polarization-sensitive laser light scattering was used. Polarization light intensities (incident and scattered light intensities with the same polarization) were measured at 71\r{ }. Before applying the method to the dusty plasmas, the measurement accuracy was confirmed using a distilled water solution of the size-known particles. In addition, the size-known particles were injected into the argon plasma, and the particles trapped inside the plasma were used for the accurate measurement of the light scattering angle. The measured size of the dust particles in a Ar+SiH$_{4}$ (5{\%}) 13.56 MHz capacitively-coupled plasma (160 mTorr, 150 W, 10 s after plasma on) was about 118 nm, which was also confirmed by scanning electron microscope photographs. The time evolution of the particle size and its number density was studied by both methods. [Preview Abstract] |
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SRP2.00006: LIF Measurement of Argon in Ar-Xe Plasma Sheath Boundary with Tunable Diode Laser Dongsoo Lee, Noah Hershkowitz, Greg Severn The Bohm sheath criterion in single and two-species plasma is studied with Laser-Induced Fluorescence (LIF) using a diode laser. Xenon is added to a low pressure unmagnetized dc hot filament argon discharge confined by surface multidipole magnetic fields. The Ar II transition sequence at 668.614 nm is adopted for optical pumping to detect the fluorescence from the plasma and to measure the Ar ion velocity distribution function as a function of position relative to a negatively biased boundary plate. The structures of the plasma sheath and presheath are measured by an emissive probe. The ion concentrations of the two-species in the bulk plasma are calculated from measured ion acoustic wave phase velocity. The measured phase velocity data combined with the argon LIF data is used to determine the Xe ion velocity. Results are also compared with previous experiments with Ar-He plasmas in which the Ar ions were the heavier ion species [1]. \newline [1] G.D. Severn et al, Phys. Rev. Lett., 90, 145001 (2003). [Preview Abstract] |
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SRP2.00007: Atomic oxygen and O$_{2}$(a$^{1}\Delta _{g})$ density measurements in a Micro-Cathode Sustained Discharge in oxygen and rare gases/oxygen mixtures. L. Magne, G. Bauville, P. Jeanney, B. Lacour, V. Puech This work presents first experimental investigations of atomic oxygen density and O$_{2}$(a$^{1}\Delta _{g})$ production in a Micro-Cathode Sustained Discharge (MCSD) in pure O$_{2}$ and in argon (or helium)/O$_{2}$ mixtures for a total pressure up to 130 Torr. A micro-hollow cathode discharge (MHCD), 200 micron in diameter, is used as plasma cathode for a discharge between the MHCD and a third electrode placed 8 mm away. In pure oxygen, the absolute atom density was measured by Two-photon Absorption Laser Induced Fluorescence (TALIF). It will be shown that, for a current of 1 mA and a pressure of 50 Torr, an atomic density of 3 10$^{15 }$cm$^{-3}$ is obtained near the micro-hollow cathode, and it decreases to 5 10$^{14}$ cm$^{-3}$ near the third electrode. If the MCSD is switched off while the MHCD is still on, the atom density decreases by an order of magnitude. 2D cartography of the atom distributions will be presented for different operating conditions. The density of the O$_{2}$(a$^{1}\Delta _{g})$ metastable state was evaluated from the intensity of the 1.27 $\mu $m transition measured with a calibrated InGaAs detector. It will be shown that O$_{2}$(a$^{1}\Delta _{g})$ densities up to 10$^{16}$ cm$^{-3}$ have been obtained for 10{\%} O$_{2}$ in an argon/oxygen mixture at 50 Torr. Work is in progress to determine conditions for generating higher O$_{2}$(a$^{1}\Delta _{g})$ densities. [Preview Abstract] |
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SRP2.00008: A Novel Temperature Measurement Approach for a High Pressure Dielectric Barrier Discharge Using Diode Laser Absorption Spectroscopy Robert Leiweke, Biswa Ganguly Tunable Diode-Laser Absorption Spectroscopy (TDLAS) technique based upon peak frequency shifts, $\beta $, and collision-broadened full widths at half maximum, w$_{c}$, of argon metastable 1s$_{3}\to $2p$_{2}$ and 1s$_{5}\to $2p$_{7}$ transitions, separated by 22.5 GHz, was used to measure both the gas temperature and the gas density in a short-pulse excited ($\approx $10 ns applied voltage rise time having $\approx $200 ns duration) argon DBD operating between 50-500 Torr, 1-4 kV total applied voltage, and 5 kHz repetition rate. TDLAS technique is well suited for high pressure environments having a small gas temperature rise ($\Delta $T$<$100 K) where the Doppler width component w$_{D }<<$ w$_{c}$. If there is no resonance between the absorber and the perturber and the absorbing transition terminates on a metastable state then, according to Lindholm-Foley theory, $\beta $ and w$_{c}$ scale as nT$^{0.3}$ where n is number density. Using the perfect gas law, the proportionality parameters $\beta _{o}$ (frequency shift/Torr) and $\Gamma _{o}$ (collisional broadening width/Torr) permits self-consistent measurements of both gas temperature and density. Reproducibility and accuracy of the temperature measurements were determined through the simultaneous independent measurements of these four parameters. The effects of applied voltage rise time on the power deposition and also metastable production efficiency will be reported. [Preview Abstract] |
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SRP2.00009: Cavity enhanced spectroscopy on micro spheres levitated in a plasma Ralf Basner, Gabriele Thieme, Joerg Ehlbeck, Juergen Roepcke, Holger Kersten, Jonathan P. Reid, Paul B. Davies Cavity enhanced spectroscopy has been successfully used as a diagnostic for aerosol droplets. In the present experiments the feasibility of applying this technique to solid micron sized particles levitated in an rf-plasma has been studied. A pulsed laser is used to excite whispering gallery modes in individual micro spheres leading to enhanced Raman scattering at corresponding wavelengths. The investigation of particles coated with fluorescent dye demonstrates the surface sensitivity of cavity enhanced spectroscopy. This non-invasive method gives direct access to the size and also the chemical composition of the micro spheres, and is so a very interesting tool for the characterisation of growing layers deposited onto micro-particles i.e. in molecular plasmas. For particle investigation, an asymmetric capacitively coupled rf-discharge containing two electrodes is used. The upper electrode is rf-driven. The lower adaptive electrode (AE) is divided into ca. 100 square segments which can be biased individually with a DC-voltage allowing a specific manipulation of the particle position. [Preview Abstract] |
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SRP2.00010: Spread function of real Fabry-Perot interferometer in imaging spectroscopy of inhomogeneous plasma Aleksandr Kravchenko, Lidia Luizova, Aleksei Solovev Working in the field of imaging spectroscopy of inhomogeneous plasma by spectrum line profile, we had found what additional parameters of real Fabry-Perot interferometer (FPI) impacts on its spread function. These parameters are parallelism degree and quality of polishing of the mirrors. But it is very difficult to model impact of these parameters on ideal mathematical FPI, because discreet model can describe very well alteration of the interferometer base. But, if we will integrate over surface of the mirror in this model, we will find two extra effects: different reflection angles in different points of the mirrors, caused lack of parallelism of the mirrors and wave refraction, caused differences between optical densityes of the mirror's material and of the air. It is very important do describe as minimum this three effects, impacts on spread function of the interferometer, because even 100 nanometers FPI base differences in opposite parts of the mirrors may make interferometer impossible for usage. In our last research we try to make a model of real FPI, when it uses in imaging spectroscopy equipment. [Preview Abstract] |
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SRP2.00011: A Spatial Heterodyne Spectrometer for Plasma Spectroscopy J.E. Lawler, Z. Labby, F. L. Roesler, J. Harlander Spatial Heterodyne Spectrometer (SHS) designs will revolutionize interferometric spectroscopy in the VUV. Advantages of interferometric spectrometers include: (1) a very high spectral resolving power with a large etendue, (2) excellent absolute wavenumber accuracy, (3) extremely broad spectral coverage, and (4) high data collection rates. Interferograms from a conventional Fourier transform spectrometer (Michelson interferometer) are recorded as a function of time using a single channel detector while moving a mirror. Interferograms from an SHS are spread in space across a detector array. The lack of moving parts means that an SHS is compatible with low duty cycle, transient sources common in the VUV. Our SHS has a CaF$_{2}$ beamsplitter and a matched pair of very coarse (23.2 groove/mm) echelle gratings blazed for 63.5\r{ }. Key mechanical components have temperature compensated designs and many parts, including the entire optical bread board, are made of Invar for long term phase stability. The 96 mm wide gratings are compatible with a theoretical limit-of-resolution of 0.058 cm$^{-1}$ (inverse maximum path difference of 2 x 9.6 cm x sin 63.5\r{ }) using a symmetric interferogram. The quality of interferograms recorded with a low resolution test camera indicated that the optics and mountings is satisfactory. First results with the full resolution 4 Mega-pixel VUV compatible CCD camera will be reported. [Preview Abstract] |
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SRP2.00012: Determining Plasma Conditions from Experimental Spectral Data Using Pegasys Nicolas Pereyra, Joseph MacFarlane, Pamela Woodruff, Igor Golovkin, Ping Wang PEGASYS is a software tool used in the analyses of experimental spectra. Operating on an imported experimental spectrum, PEGASYS supports continuum background subtraction, wavelength calibration, and fitting to spectral lines. In addition, PEGASYS computes the best fit of an experimental spectrum to PrismSPECT results, thereby finding temperatures and densities most representative of the plasma. PrismSPECT is a collisional-radiative spectral analysis code designed to simulate the atomic and radiative properties of LTE and non-LTE plasmas spanning a wide range of conditions. For a grid of user-specified plasma conditions, PrismSPECT computes spectral properties (emission and absorption), ionization fractions, atomic level populations, atomic transition rates, and line intensities and ratios. In designing PEGASYS and PrismSPECT, a strong emphasis has been placed on ease of use. It features a user-friendly, graphical interface for setting up problems, monitoring the progress of simulations, and viewing results. Recent enhancements to PEGASYS, including line identification and curve fitting, will be discussed. [Preview Abstract] |
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SRP2.00013: Electron-Beam Produced Air Plasma: Optical and Electrical Diagnostics Robert Vidmar, Kenneth Stalder, Megan Seeley High energy electron impact excitation is used to stimulate optical emissions that quantify the measurement of electron beam current. A 100 keV 10-ma electron beam source is used to produce air plasma in a test cell at a pressure between 1 mTorr and 760 Torr. Optical emissions originating from the N$_{2}$ 2$^{nd}$ positive line at 337.1 nm and the N$_{2}^{+}$ 1$^{st}$ negative line at 391.4 nm are observed. Details on calibration using signals from an isolated transmission window and a Faraday plate are discussed. Results using this technique and other electrical signal are presented. [Preview Abstract] |
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SRP2.00014: In-situ characterization of oxygen plasma surface etching/modification by Infrared-Visible Sum Frequency spectroscopy Darcie Farrow, Edward Barnat, Paul Miller, Greg Hebner Unlike many other techniques used to characterize surfaces under plasma exposure, Infrared-visible sum frequency (IVSF) generation is a surface specific probe molecular vibrations that can be carried in situ to follow molecular interactions and plasma initiated chemistry at the interface in quasi real time. We present an in-situ characterization of octadecyltrimethoxysilane monolayers and common industrial polymers (polypropylene, polyethylene, polystyrene) on Quartz in the presence of a DC oxygen plasma and an atmospheric pressure glow discharge using IVSF. Analysis is based on hydrocarbon lines in the IVSF spectra as a function of plasma exposure time, voltage and oxygen pressure. This test system will be used to demonstrate the unique advantages and limitations of IVSF as an in situ surface diagnostic in plasma systems. This work was supported by the Division of Material Sciences, BES, Office of Science, U. S. Department of Energy and Sandia National Laboratories, a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
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SRP2.00015: Space and phase resolved electron energy distribution functions in an industrial dual-frequency capacitively coupled radio-frequency discharge Julian Schulze, Timo Gans, Deborah O'Connell, Uwe Czarnetzki, Bert Ellingboe, Miles Turner The excitation dynamics in a confined dual-frequency plane parallel CCRF discharge (Exelan, Lam Research Inc.), operated at 1.94 MHz and 27.12 MHz is investigated by phase resolved optical emission spectroscopy. The emission from different rare gas lines in a He-O2 plasma with small rare gas admixtures is measured during one low frequency RF-cycle resolving the dynamics within every high frequency cycle with one dimensional spatial resolution along the discharge axis. In a detailed analysis a time dependent model, based on rate equations, is developed, that describes the dynamics of the population density of excited levels. Electron impact excitation out of the ground state, quenching, reabsorption and cascades are taken into account. Based on this model and the comparison of the excitation of various rare gas states, with different excitation thresholds, time and space resolved electron temperature and propagation velocity of the high energetic, directed electrons, heated at the sheath edge, are determined. These parameters reveal the time and space resolved electron energy distribution function. [Preview Abstract] |
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SRP2.00016: Comparison of excitation temperature and electron temperature in low pressure argon plasmas Hoyong Park, Junkyu Rhee, Junghee Kim, Jongsub Lee, Seonghun Lee, Shinjae You, Hongyoung Chang, Wonho Choe Compared to other active diagnostic methods, the optical emission spectroscopy (OES) method using an emission spectrum from the plasmas has a benefit of non-intrusive, in-situ monitoring of the plasmas. In this work, a study was performed to investigate the relation between the excitation temperature (obtained by OES) and the electron temperature (obtained by a Langmuir probe) in low pressure argon plasmas. In order to compare the two temperatures for various experimental conditions, argon pressure and input power were independently varied. The collection optics consisted of an optical fiber and a bi-convex lens was used for a comparison between the local values of the two temperatures. The results so far achieved in capacitively-coupled argon plasmas of which electron energy probability function was bi-Maxwellian showed that the excitation temperature had the same tendency with the high energy part of the electron temperature as the rf power and the pressure were increased. From the results, the measured excitation temperature can be used as an indicator of electron temperature variation, which may be applicable to the plasmas where non-intrusive diagnostic methods are required such as in large area plasmas for LCD plasma processes. [Preview Abstract] |
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SRP2.00017: Gas temperature measurements in a microcathode sustained discharge in oxygen V. Puech, J.F. Lagrange, N. Sadeghi, M. Touzeau, G. Bauville, B. Lacour Microcathode sustained discharges (MCSD) produced between a microhollow cathode discharge (MHCD) and a third electrode offer the possibility to produce high density plasmas at low E/N values. Such discharges in oxygen could be attractive for efficient production of singlet O$_{2}$ if the gas temperature remains low. The temperature of a discharge in oxygen at 50 Torr and for currents up to 2 mA and E/N of 25 Td was measured through a spectroscopic investigation of the plasma emission. The spatial distribution of the O$_{2}$(b$^{1}\Sigma )$ and O(5p) was measured. These species have a very different behaviour: O(5p) is mainly produced inside the hole of the 0.2 mm diameter MHCD and its density decreases by two orders of magnitude over a distance of 3 mm. On the other hand, the O$_{2}$(b$^{1}\Sigma )$ production by the MHCD is very low, and this state is mainly produced in the MCSD, with a smooth density gradient in the interelectrode gap. The gas temperature was determined in the MCSD from the high resolution spectra of the atmospheric band at 760 nm, while the gas temperature inside the hole of the MHCD was measured through the rotational spectra of the 337 nm 2$^{nd}$ positive band of nitrogen, introduced at low concentration in the discharge. In our experimental conditions, the gas temperature in the MHCD is lower than 650 K and less than 400 K in the MCSD. [Preview Abstract] |
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SRP2.00018: Radical Production in a Short-Pulse Excited, Flowing Gas Atmospheric Pressure Dielectric Barrier Discharge J.M. Williamson, P. Bletzinger, D.D. Trump, B.N. Ganguly The production of plasma-chemical radicals in a short-pulse excited atmospheric pressure Ar / H$_{2}$O or He / H$_{2}$O dielectric barrier discharge as a function of gas flow rate and H$_{2}$O concentration was investigated. The plasma emission of excited Ar, He, OH, and N$_{2}^{+}$at 750, 706, 308,and 391 nm, respectively, were recorded for various flow conditions and H$_{2}$O concentrations as well as applied voltage. The change in plasma emission with different conditions was measured either by temporally integrated dispersed emission with a spectrometer/CCD or temporally resolved, wavelength selected emission with a spectrometer/gated PMT. The OH radical production increased with applied voltage and also with small additions of water but the emission was greatly reduced with higher water concentrations. The temporally-resolved OH and N$_{2}^{+}$ emission was delayed with respect to the excited Ar and He emission due to the heavy particle production of OH and N$_{2}^{+}$. The radical production as function of applied voltage, gas flow rate, and gas mixture will be presented. [Preview Abstract] |
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SRP2.00019: Monte Carlo simulation of the profiles of H$\alpha $ emission in hydrogen Townsend discharges at high E/N Zoran Petrovic, Vladimir Stojanovic Our goal is to calculate H$\alpha $ emission from Townsend discharge in pure hydrogen between two parallel electrodes. Monte Carlo simulation technique was used to follow electrons and heavy particles for the conditions of high electric field ($E)$ to gas density ($N)$ ratios $E/N$... We used simple cross section sets for heavy particles, as provided by A.V. Phelps, where fast H atoms were produced by charge transfer collisions of H$^{+}$, H$_{2}^{+}$, H$_{3}^{+}$ with H$_{2}$ and with the surface. After collisions we followed trajectories of all reaction fragments until their neutralization or thermalizaton down to the H$\alpha $ excitation energy... As a result, for the conditions of experiment, we obtained spatially resolved emission profiles and end on Doppler broadened profiles. Agreement of Monte Carlo with experimental results supported prediction that the main excitation channel of H$\alpha $ emission proceeds via fast H atoms. [Preview Abstract] |
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SRP2.00020: Decomposition of N-Isopropylacrylamide in low-pressure helium plasma Horacio Martinez, Yamilet Rodriguez-Lazcano Emission spectroscopy was applied to observe decomposed species of N-Isopropylacrylamide (N-iPAAm) exposed to He plasma, which was generated by AC discharge at the pressure of 3.0 Torr. In the diagnosis measurement, several emission peaks assigned to the H$_{\alpha }$ and H$_{\beta }$ atomic lines, CH$_{3}$O, CN (B$^{2}\Sigma $-X$^{2}\Pi )$, CH (A$^{2}\Delta $-X$^{2}\Pi )$, and C$_{3}$H$_{5}$, CN, CHO, CH$_{2}$O and C$_{4}$H$_{2}^{+}$ transitions were observed and measured at various discharge times. The present results shows the presence of C$_{4}$H$_{2}$ and C$_{4}$H$_{2}^{+}$ which is not present in great concentration in the simulation done by Herrebout et al (IEEE Transactions on Plasma Science 31 (2003) 659), who used a one-dimensional fluid model for an RF acetylene discharge. The time dependence of the emission intensities was also investigated. When the discharge time of He plasma was increased, the emission intensities of the observed transitions also increased and then gradually decreased. [Preview Abstract] |
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SRP2.00021: HIGH PRESSURE, LIGHTING, AND CHEMISTRY |
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SRP2.00022: Low-pressure indium-bromide discharges for sustainable lighting Peter Vankan, Piet Antonis, Ariel de Graaf Lighting up today's world requires massive amounts of energy: 20{\%} of the world's electricity consumption is used for lighting, which illustrates nicely that energy efficiency is a key issue in sustainable lighting. Of all light produced, roughly half comes from low-pressure mercury vapour lamps. These lamps are limited to around 110~lm/W due to the Stokes-losses in the phosphor conversion. Therefore, to make a more energy efficient lamp, the mercury has to be replaced by another filling. This contribution will present a discharge based on indium-bromide that emits mainly in the UVA and visible region instead of the UVC, which strongly reduces the Stokes-losses and therefore offers the potential of a high energy efficiency. On top of that, the indium-bromide discharges are mercury-free, which gives an extra impulse for sustainable lighting. In this contribution we will show the indium-bromide discharge efficiency as a function of filling pressure and type of starting gas, diameter and coldest spot temperature. A maximum discharge efficiency of around 50{\%} has been reached in a capacitively coupled lamp. [Preview Abstract] |
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SRP2.00023: Modelling Metal-Halide Lamps with Plasimo Jan van Dijk, Bart Hartgers, Mark Beks, Wouter Brok, Joost van der Mullen After a general introduction of the plasma simulation model Plasimo, being developed at Eindhoven University of Technology, we will discuss its application to the modelling of metal-halide lamps. The underlying model is based on a quite complete description of the plasma. It involves non-equilibrium plasma chemistry, the barycentric flow field, the gas temperature, spectrally and spatially resolved radiation transport and the electro-magnetic field. Special attention will be paid to the elemental diffusion sub-model, a non-equilibrium description of the plasma composition that is able to reproduce the process of elemental de-mixing. This convection-driven phenomenon is responsible for axial inhomogeneities in light output. This effect has been studied under various gravity conditions both on earth and in the International Space Station (ISS). A comparison with these experiments will be made. Plasimo (including the source code) is in principle available for fellow researchers. Interested parties are invited to contact the author or visit the Plasimo website, http://www.dischargemodelling.org. [Preview Abstract] |
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SRP2.00024: Characterization of a cascaded arc - an extremely bright light source Daniel Schram, R. Zijlmans, J. Goudsmits, R. Engeln The need for a high intensity light source in spectroscopic applications like cavity enhanced absorption spectroscopy and spectroscopic ellipsometry is obvious, because it potentially leads to more accurate measurements in terms of signal to noise ratio. In this contribution we present an intense and stable broadband light source, a cascaded arc, and a thorough characterization of its light output and modulation possibilities. The light output is spectrally characterized in terms of absolute spectral radiance, which is determined by calibrating the used spectrometers with a tungsten bandlamp, which exhibits a known spectral light output. Furthermore we show the use of an extremely fast, flexible and surprisingly accurate modelling scheme, called: Flexible Approximate Simulation of a Thermal plasma (F.A.S.T.), to investigate the optimal geometry of the arc channel. The agreement between calculated and measured continuum emission is excellent: they show both an appreciable improvement in brightness of the source when the source channel is profiled. [Preview Abstract] |
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SRP2.00025: Striations in a low pressure RF-driven argon plasma W.J.M. Brok, H.C.J. Mulders, W.W. Stoffels In experiments we observed spatially periodic modulations of the light emitted by an argon plasma in a tube of 30 cm length and 2.5 cm radius. The plasma is capacitively excited by RF electrodes positioned towards the ends of the tube. The argon pressure is approximately 2 Torr. We studied the space and phase dependence of the light emitted by the spheroidally shaped striations. Temporal phase-shifts within one striation were clearly visible. Furthermore, a simple model of the electric field modulation inside the tube was used in conjunction with a Monte Carlo model in order to study the electron kinetics in the tube. The excitation rates resulting from this model are compared with the measurements. [Preview Abstract] |
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SRP2.00026: Wall Effects on Electron Beam Generated Plasmas. Darrin Leonhardt, Scott Walton, Richard Fernsler Electron beam generated plasmas have been shown to possess intriguing characteristics for plasma processing applications such as low electron temperatures, high plasma densities and the capability to ionize all gases uniformly and in proportion to their relative concentrations. In this work, we discuss the effects of large versus small ionization-to-chamber volume ratios; i.e. what happens to the steady-state plasma as the system volume is decreased around the electron beam? At first glance, the presence of walls appears inconsequential. However, even in a modulated system, the walls affect the electron temperature as well as the magnitude and distribution of the plasma densities. Time resolved data from in situ diagnostics (electrostatic probes and mass spectrometry) and theoretical expressions will be compared for various configurations of the chamber volume with fixed ionization regions. [Preview Abstract] |
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SRP2.00027: Generation of Negative Ions in Pulsed Boron Trifluoride Glow Discharge Ludovic Godet, Svetlana Radovanov, Jay Scheuer, Gilles Cartry, Christoph Cardinaud In earlier studies (1, 2) of boron trifluoride pulsed discharges significant dependence of the plasma parameters upon the negative ion formation was observed. In these plasmas negative ions can reach relatively high densities 2-5 10$^{9 }$cm$^{-3 }$which are comparable to the electron density. We have measured the ion energy distributions of positive and negative ions under various discharge conditions. The influence of negative ions on transport properties of charged particles, plasma parameters and structure of the sheath will be discussed. The role of heavy molecular ions in the process of ion-ion recombination is evaluated. \newline \newline [1]. S.Radovanov, et al., JAP, 98, 113307, 2005. \newline [2]. Ludovic Godet Thesis, 2006, University of Nantes, France. [Preview Abstract] |
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SRP2.00028: Cold Jet Plasma Studies by Cavity Ring Down Absorption Spectroscopy (CRDS) Patrick Dupr\'{e}, Shenghai Wu, Terry Miller Reactive intermediates are of crucial importance both for combustion and atmospheric chemistry. We have set up a cold radical plasma source based on a pulsed slit jet supersonic expansion (5 cm long) and a transverse DC discharge. This source is inserted inside a CRDS cavity running in the near and mid infra-red ranges (the high resolution laser source is described in the second paper). We will present results obtained in the rotational temperature range of 15 to 30~K on various species including the metastable nitrogen (transition: $B\,^{3}\Pi_{g}(v'=2)\leftarrow A\,^{3}\Sigma_{u}^{+}(v''=4)$), hydroxyl radical (first overtone), methyl radical (fundamental transition of the antisymmetric CH stretch mode) and preliminary results on the weak $\widetilde{A}-\widetilde{X}$ transition of methyl peroxy (${\rm CH}_{3}{\rm O}_{2})$. Density number of certain of these unstable species can reach $\sim4\times10^{14}/{\rm cm}^{3}$ inside the throat.% \footnote{S.~Wu, P. Dupr\'e and T.A.~Miller, Phys. Chem. Chem. Phys. 2006, 8, 1682% } Sensitivities better than $40\,{\rm ppb}/{\rm pass}/\sqrt{{\rm Hz}}$ have been reached. [Preview Abstract] |
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SRP2.00029: High efficiency for dioxin dehalogenazation using an electron source with a carbon nanotube Michiteru Yamaura, Shigeaki Uchida, Chiyoe Yamanaka We propose the application of an electron source with a carbon nanotube (CNT) for the dehalogenation of dioxin [1]. The dioxin consists of some amount of chlorine. As the chlorine content is increased, a highly poisonous dioxin is produced. It is clarified that a lot of electrons supply around the chlorine is treated on dioxin by dehalogenation due to the electron affinity of chlorine is very strong. Moreover, the dehalogenation treats on the dioxin without producing toxic by-products. To date, it has been confirmed that o-chlorophenol further the procession materials of dioxin is dehalogenated by utilizing electrons generated around a non-equilibrium plasma. However, a rate of approximately 50{\%} is not expected to be found for the dehalogenation because the number of electrons supplied by the non-equilibrium plasma is low. It is well-known that the CNTs have a high aspect ratio, high mechanical strength, and good chemical stability. Hence, the rate of dehalogenation drastically increases due to the abundant supply of electrons when a CNT electron source is used. The dehalogenation of o-chlorophelol with high or low concentration using the CNT electron sources and the characterizations of the CNT will be discussed. *A part of this work is supported by a Grant-in Aid for Young Scientists (B) Research of the Ministry of Education, Science, Sport and Culture, Japan. [1] M.Yamaura, and S.Uchida Japanese patent pending to be submitted in 1 June 2006. [Preview Abstract] |
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SRP2.00030: Decomposition of Volatile Organic Compounds under Low-Energy Pulsed-Electron Beam Irradiation Masato Watanabe, Asuna Fukamachi, Akitoshi Okino, Eiki Hotta, Kwang-Cheol Ko Development of treatment system of gaseous pollutants including some toxic substances, such as nitrogen oxides (NOx) and volatile organic compounds (VOCs), is one of the important technological research subjects. It is well known that the non-thermal plasma processes using electrical discharge or electron beam are effective for the environmental pollutant removal. Especially, the electron beam can efficiently remove pollutant, because a lot of radicals which are useful to remove pollutant can be easily produced by high-energy electrons. In present study, decomposition of VOCs under electron beam irradiation was experimentally investigated in order to examine the kinetics of the process and to characterize the reaction product distribution. The experiments were carried out using a compact 100 kV secondary emission electron gun (SEEG). SEEG is based on ion induced secondary emission phenomena, uses a thin tungsten wire pulsed glow discharge device as a wire ion plasma source. Benzene and toluene were selected as representative VOC compounds. The experimental results indicate better benzene and toluene removal efficiencies and the SEEG represents a promising technology for the treatment of VOCs. [Preview Abstract] |
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SRP2.00031: Dynamics of ionization fronts during high-pressure gas breakdown. Dmitry Nikandrov, Lev Tsendin, Robert Arslanbekov, Vladimir Kolobov Dynamics of gas breakdown is important for numerous high-pressure plasma applications. This paper presents an analytical theory and numerical simulations of the high-pressure gas breakdown. The problem of discharge evolution after applying an external voltage $U(t) $is divided into two sub-problems. The first sub-problem deals with the \textit{proforce} anode front initiated by the electrons present in the gap before the voltage was applied. An analytical solution for the ionization front dynamics is obtained by neglecting electron diffusion and assuming small variation of the electric field compared to the density variation. Expressions for the electron and ion densities, drift velocities, and the electric field are obtained. At the evolution stage, when $U(t) $is decreasing, the formation of an \textit{antiforce} cathode-directed ionization front is possible$. $The second problem treats the evolution of the \textit{antiforce} (cathode directed) ionization front, which is initiated by the electrons generated upstream with respect to the electron drift. The situation, in which these electrons are emitted from the cathode, is analyzed. When the field perturbation becomes significant, the plasma region is formed, and the plasma boundary moves towards the cathode. The numerical and analytical solutions are in good agreement. [Preview Abstract] |
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SRP2.00032: $\gamma$ action of metastable atom in Ar micro gap Susumu Suzuki, Haruo Itoh To separate $\gamma $ process that consisted of $\gamma $i, $\gamma $m and$\gamma $p, Monte Carlo simulation (MCS) was performed[1] for the preparation. Generated numbers of ion, metastable atom and photon were calculated, and the feedback effect of those particles was investigated. It was ensured that the ratio of the ion returned to the cathode occupies 71{\%} among the sum of those particles. Therefore, it was considered that main action of $\gamma $ was $\gamma $i by the ion returning to the cathode. However, it is evident that the metastable Ar having the long lifetime and high potential energy higher than 10 eV occupies 11{\%} among the three kinds of particle. Therefore it is necessary to consider about the attribution of metastable atom for $\gamma $ action. Rate of metastable Ar that arrives to the cathode is calculated from the solution of the diffusion equation[2] that can take account of the reflection of metastable Ar on the surface of electrodes. The diffusion coefficient of metastable Ar[3] and the collisional quenching rate coefficient[3] of metastable Ar by Ar in ground state are used for the estimation. The reflection coefficient[2] of metastable Ar at the electrodes is calculated as 0 using a boundary condition of the third kind. Approximately 30{\%} of the metastable Ar enters the cathode. Therefore, the influence on the current by the $\gamma $ action of the metastable Ar is small, but it can not be neglected. [1] S.Suzuki and H.Itoh: submitted to Jpn. J. Appl. Phys. [2] S.Suzuki, H.Itoh, N.Ikuta and H.Sekizawa: J. Phys. D, \textbf{25} (1992) 1568-1573. [3] A.H.Futch and F.A.Grant: Phys.Rev., \textbf{104 }(1956) 356-361. [Preview Abstract] |
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SRP2.00033: Study of a Filamentary Dielectric Barrier Discharge in Air at Atmospheric Pressure Sebastien Celestin, Barbar Zeghondy, Olivier Guaitella, Anne Bourdon, Antoine Rousseau Dielectric Barrier Discharges (DBD) at atmospheric pressure have many applications, for instance ozone production, surface treatment, and waste gas treatment. Generally, such a discharge is filamentary but it can be diffuse under particular conditions. Understanding the formation of the filament, which is an ionization wave or so-called ``streamer'', is very hard theoretically, numerically, and experimentally. This is due, first, to the non-linearity of the equations concerned, and second, because of the scaling in space and time of this phenomenon: a streamer has a radius on the order of a few microns, and propagates through distances of several centimeters in a few nanoseconds. In this study we will present the results obtained in experiments and in simulations for a plane-to-plane DBD. We electrically characterized this device and have observed collective effects that are still poorly understood. A point-to-plane DBD has also been studied for producing a much more localized discharge. In parallel with the experimental study we have developed a numerical model based on the Immersed Boundary Method (IBM) to introduce an electrode having a complex geometry into a structured Cartesian mesh. The first results of the code will be discussed. [Preview Abstract] |
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SRP2.00034: Study of UV efficiency of a plasma display panel in Ne/Xe/He mixtures HoYul Baek, TaeSang Lee, YongSeok Jho, ChoongSeock Chang Plasma display panel is a mature technology with a substantial market. In this work, there is considerable interest in improving UV efficiency in PDP by optimizing gas mixture. For this, we develop 2D particle-in-cell/monte-carlo collsions(PIC/MCC) code. Using 2D PIC/MCC code, we carry out simulations of UV efficiency of a PDP in Ne/Xe/He mixtures, and find a gas mixture for high UV efficiency. Also, we study about mechanism of the striations, which occurs on the dielectric surface of the anode at simulations using PIC code. [Preview Abstract] |
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SRP2.00035: Dynamics of Statistical Fluctuations in Low-Current Microdischarges. Vladimir Khudik, Alex Shvydky, Constantine Theodosiou According to the Paschen's similarity law, when the product of the gas pressure and the system dimension is kept constant, pd = const, discharges in small and large systems exhibit the similar behavior. However, the influence of fluctuations (as well as nonlinear processes such as, for example, stepwise ionization and radiation trapping) on the discharge dynamics in systems with different dimensions is different: Their level is higher in smaller systems, so that statistical fluctuations change dramatically the discharge behavior in microdischarges operating in Townsend regime. We present a simple model that incorporates all main processes which cause fluctuations and that allows to describe analytically their dynamics. Close analogy to an oscillator driven by a random force is revealed. In this analogy, the voltage across the discharge gap is related to a generalized coordinate, the number of ions in subsequent generations is related to a generalized momentum, and fluctuations in the number of ions (i.e. fluctuations in the generalized momentum) play, in essence, role of the random force. In the same manner as a random force, fluctuations pump ``energy'' in natural oscillations of the discharge current. Without dissipation they grow in time which eventually leads to disruption of the discharge. Dissipation suppresses fluctuations and limits them at some level. [Preview Abstract] |
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SRP2.00036: Double Electric Layer in Stationary Shock Structures of a Supersonic Flowing Afterglow D.J. Drake, J. Upadyay, S. Popovic, L. Vuskovic Mutual interaction between an acoustic shock wave and weakly ionized gas produces many effects that have been studied in recent years [1]. This interaction is manifested as plasma-induced shock dispersion and acceleration, shock wave induced double electric layer, localized increase of electron temperature and density, or enhancement of optical emission. A comprehensive review of this research and its significance for high-speed aerodynamics is given in Ref. [2]. We have performed experiments in a microwave flowing afterglow system and observed the enhancement of optical radiation in the interaction of a stationary shock wave with weakly ionized argon at 100-600 Pa. The enhancement of optical radiation coincided with the calculated standoff distance of the detached shockwave. We studied the stationary shock structures, mainly using the 4p excited state populations of argon, which were measured using absolute emission spectroscopy. Oblique shock parameters were evaluated exactly for the given model geometry, which were usually spherical. We will present results at the conference. \newline [1] S. Popovic, L. Vu\v{s}kovic, Phys. Plasmas \textbf{6} (1999) 1448. \newline [2] P. Bletzinger, B. N. Ganguly, D. Van Wie, A. Garscadden, J. Phys. D: App. Phys.\textbf{ 38} (2005) R33. [Preview Abstract] |
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SRP2.00037: O atom number density measurements in repetitively pulsed plasmas by two photon laser induced fluorescence Mruthunjaya Uddi, Naibo Jiang, Kraig Frederickson, Yvette Zuzeek, Igor Adamovich, Walter Lempert We present measurements of atomic oxygen number density in high pressure, non-equilibrium plasmas created by a high repetition rate (50 kKz) -- short (20 nsec) pulse duration discharge. Measurements are performed using two photon absorption laser induced fluorescence (TALIF). Atomic oxygen mole fractions are presented as a function of time after plasma initiation in oxygen/helium, air, and air/methane mixtures at pressures of approximately 60-100 torr. Two approaches will be described for absolute number density calibration, comparison with two photon xenon spectra, and chemical titration with NO$_{2}$. Diagnostic issues relevant to short pulse plasmas, in particular mitigation of electromagnetic interference, will be described in detail. [Preview Abstract] |
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SRP2.00038: Optimization of Dielectric Barrier Discharge Plasma Actuators at Atmospheric and Subatmospheric Pressures Alexander Likhanskii, Mikhail Shneider, Sergey Macheret, Richard Miles Asymmetric dielectric barrier discharge (DBD) plasma actuators are known to be effective in aerodynamic control. We describe a comprehensive kinetic model for asymmetric DBD actuators in air. Application of the model shows that charging of the dielectric surface plays a crucial role, acting as a harpoon. The tangential force on the gas is shown to be directed downstream in both cathode and anode half-cycles. Inefficiency of gas acceleration is due to the motion of positive ions toward the exposed electrode in the cathode half-cycle. A near-optimal voltage waveform is proposed, consisting in high repetition rate short pulses of negative voltage in combination with positive dc bias applied to the exposed electrode. Computations show that repetitive-pulse waveform can induce gas velocities similar to those in conventional sine-voltage DBD actuators at considerably lower voltages and smaller plasma sizes. Increasing the peak pulsed voltage should increase the wall jet velocity by an order of magnitude. However, at some threshold voltage the reverse (backward-directed) breakdown occurs. A modified voltage waveform is proposed and studied that would prevent the reverse breakdown. Results of modeling for low-pressure operation are also presented. [Preview Abstract] |
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SRP2.00039: Plasma expansion and invasion in the shock measured by diode laser fluorescence D.C. Schram, O. Gabriel, P. Colsters, P. Vankan, R. Engeln Expansion from a remote thermal plasma source, for plasma processing, is first supersonic, with density and temperature dropping due to rarefaction and adiabatic cooling. The plasma then over-expands and forms a valley before it passes a stationary shock front, after which subsonic expansion occurs. If in the over-expanded region the plasma is rarefied it becomes possible that atoms or molecules from outside enter the valley, and gets scattered into the supersonic expansion, therewith effectively mixing gas from outside. This process of ``invasion'' has been analyzed in detail by LIF with a diode laser on argon 1s5 metastable, with measurements both parallel and perpendicular to the expansion. Acceleration, rarefaction and cooling in the first expansion are in agreement with predictions. In the valley two distributions are observed: the fast, cold supersonic and a slower hotter one coming from outside the barrel shock. This invasion is as strong as the original flux from the source. Also some measurements are shown on O metastable indicating invasion of O2 molecules in the expansion of Ar plasma. [Preview Abstract] |
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