Bulletin of the American Physical Society
2006 59th Annual Gaseous Electronics Conference
Tuesday–Friday, October 10–13, 2006; Columbus, Ohio
Session FPT1: Poster IA |
Hide Abstracts |
Room: Holiday Inn Salon A, 7:15pm - 9:15pm |
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FPT1.00001: MATERIAL PROCESSING |
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FPT1.00002: Passivation of the SiC gate-oxide interface using remote microwave plasmas S.F. Adams, J.D. Scofield, C.A. DeJoseph, Jr., J.M. Williamson, J.D. Umbel A well-known challenge in fabricating a SiC MOSFET switch is attaining a low density of defects on the gate oxide/SiC interface. The typical high temperature thermal oxide process leaves carbon impurities at the SiC/SiO$_2$ interface which cause high densities of defect states. The result is a decrease in channel conductivity, thus decreasing device efficiency. We have investigated two approaches to this problem involving treatment with atomic species generated by remote microwave plasma. First, a plasma passivation technique was analyzed employing atomic nitrogen to extract the carbon impurities from the interface. Second, an O$_2$ plasma was used to grow an initial highly-structured SiO$_2$ layer on the SiC surface using a low temperature slow-growth process. Results will be presented including the effects of these plasma processes on SiC MOSFET optimization along with the role that atomic nitrogen and oxygen plays in each plasma process. [Preview Abstract] |
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FPT1.00003: Plasma Treatment of Bulk Niobium Surfaces M. Raskovic, S. Popovic, L. Vuskovic, S.B. Radovanov, L. Godet In-situ plasma treatment is one of possible methods for preparation of Nb surface in superconducting radio-frequency (SRF) cavities used in linear particle accelerators. The aim is to remove Nb oxides and other poor superconductors from the bulk niobium surface and to eliminate surface roughness. The choice of the plasma technique is limited by the requirement for the discharge to fit into the relatively complex geometry of SRF cavities, which are to serve as vessels for pulsed or barrel-type reactors. For the surface treatment we used the microwave cavity discharge system with Ar/Cl2 [1] and the repetitively pulsed d.c. diode system with Ar/BF3 [2]. The preliminary studies on planar samples with both systems show results with positive influence on the surface smoothness comparing to buffered chemical polishing method, currently in use. In addition, images obtained with several surface characterization techniques show substantial reduction of feature size on the surface. The gas-phase kinetics of both discharges has been performed. Results are compared with the process diagnostics data in order to develop better understanding of the processes, the optimization strategy, and the in-situ reactor design. [1] M.Raskovic, et al., EPAC 06, Edingbourh, Scotland, June 26- 30, 2006. [2] S. Radovanov, et al., J. Appl. Phys. 98, 113307 (2005). [Preview Abstract] |
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FPT1.00004: Hafnium Oxide Film Synthesis via Laser Ablation Plasma Ion Deposition N.M. Jordan, R.M. Gilgenbach, L.M. Wang, S. Zhu, M. Atzmon, Y.Y. Lau, M.C. Jones This research investigates the feasibility of synthesizing thin films of hafnium oxide via laser ablation plasma ion deposition (LAPID).~HfO$_{2}$ is of great interest as a high dielectric constant material in the semiconductor fabrication industry. Experiments are underway to deposit and implant films of hafnium and hafnium-oxide on silicon substrates. A KrF laser (400 mJ @ 248 nm) ablates solid Hf foils in an oxygen environment or sintered pellets of hafnium-oxide in vacuum. Silicon substrates can be biased (+ or -, either pulsed or DC) by voltages up to 10 kV for ion implantation and deposition. Experiments study correlations among parameters such as laser energy, film thickness, background gas pressure, film composition, and ion energy. Ablation plasma plumes are characterized by optical emission spectroscopy. Composition and morphology of deposited films are analyzed by SEM, TEM, X-ray Energy Dispersive Spectroscopy, X-ray Photoelectron Spectroscopy, X-ray diffraction and Atomic Force Microscopy. Film deposition rates are estimated to be on the order of 0.055 nm/pulse at a laser repetition rate of 15 pulses/s, equating to 8 nm/s. [Preview Abstract] |
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FPT1.00005: Direct injection of liquids into low pressure plasmas Matthew Goeckner, Daisuke Ogawa, Richard Timmons, Lawrence Overzet, Sam Sanchez Being forced to use only gaseous precursors in plasma processing reactors is a significant and irrational limitation. Only a small minority of the molecules that could prove useful can be put into the vapor phase. On the other hand, a much greater fraction can be put into solution. We have found that by using a simple fuel injector directly coupled to a heated reactor, one can inject a variety of liquids directly into the plasma environment. A temperature controlled capillary tube can be used to accomplish the same thing. The liquids can also have a variety of solids dispersed in them: metals, dielectrics, aromatics, proteins, viruses, etc. While we have not had time yet to do detailed studies on a very wide range of liquids and dispersed solids, we do have the proof of principle. We have made films from injecting 1] ethanol, 2] hexane 3] iron nanoparticles dispersed in hexane and 4] ferrocene dissolved in benzene into capacitively coupled plasmas at approximately 50 mTorr. The details of the reactor and the films produced to date will be explained in the poster. Briefly: we use capacitively coupled plasma sources. Typical pressures are well below 1 Torr and powers below 10 Watts. The hexane films have growth rates around 10 nm/min. [Preview Abstract] |
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FPT1.00006: CAPACITIVELY COUPLED PLASMAS I |
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FPT1.00007: High Efficiency Singlet Oxygen Generator (SOG) Based on RF Discharge Olga Proshina, Oleg Braginsky, Alexander Kovalev, Dmitry Lopaev, Yury Mankelevich, Tatyana Rakhimova, Anna Vasilieva One of the main problems in a laser power increasing is the pressure scaling of SOG. It was shown in our previous studies that the SO concentration in RF discharge plasma saturates with the increase of both pressure and specific energy deposition. The new three-body mechanism of fast SO quenching by oxygen atoms has been revealed. The HgO coating of a discharge tube wall allowed us to reduce atom oxygen density in the discharge region and so to depress the role of the three-body quenching. In the present report the experimental and theoretical study of the power supply frequency and NO admixture influence on the discharge structure and the SO yield was carried out in RF discharge with HgO coating. The increase of the power frequency from 13.56 to 80 and 160 MHz allows to get the uniform spatial discharge structure at an oxygen pressures up to 30 Torr and the high singlet oxygen yields up to 15{\%}. It was shown that the simultaneous using of the NO admixture, the HgO wall coating and the high power frequency gives the effective conditions for SO excitation. The record values both the SO yield (21{\%} at p$_{O2}$=10 Torr; 17{\%} at p$_{O2}$=20 Torr) with the high energy efficiency ($\sim$ 18{\%}) were obtained at first. A 2D self-consistent model was used to study RF discharges in gas flow. Results of the simulation agree with the experimental data. [Preview Abstract] |
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FPT1.00008: Behavior of ion sheath adjacent to a planar capacitive discharge operated in pulsed mode C. Gaman, S.K. Karkari, A.R. Ellingboe The dynamics of a radio-frequency sheath is important in understanding the ion-energy distribution at the substrate during a plasma process. The ion-energy depends on the mean ion-transit time through the sheath with respect to the rf-angular frequency, the rf-amplitude and the position in the sheath where the ions are created. When the radio-frequency discharge is operated in pulsed mode, the capacitive rf-fields rapidly penetrate in to bulk plasma which results in sheath expansion by exclusion of electrons from the sheath boundary. The spatial and phase-resolve behaviour of electron density has been experimentally investigated using a floating hairpin resonance probe in a hydrogen discharge, which is created in a confined symmetric parallel plate capacitively coupled radiofrequency discharge. The results show time-variation in spatial electron density as a function of rf phase during the beginning of the on-phase of the pulsed rf and relaxation of electron density in the sheath during the off-phase of the rf cycle. [Preview Abstract] |
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FPT1.00009: Investigation of a radio-frequency capacitive sheath and the effect of DC bias control on the power absorption at low pressures D. Gahan, F. Sober\'on, M.B. Hopkins Many of today's processing plasma tools are operated at low pressures to achieve high etch directivity and reduce side erosion on the wafer. At these pressures electron-neutral collisions are rare and the electrons cannot gain energy through the Ohmic heating process. Instead the heating mechanism is attributed to a stochastic process between the electrons and the sheath electric field. Theoretical models of this stochastic process include the hard wall approximation and the pressure heating effect. The former is inconsistent with electron current conservation in the sheath whilst the latter shows a difference in power absorption when the electron loss to the electrodes is considered. This paper examines the effects of electron current of a capacitive sheath by controlling this current with an additional DC bias. Experimental and particle-in-cell model results for a low pressure argon plasma are compared and presented. Results show that the electron power absorption is more effective when the electron conduction current is removed. The model also shows a high harmonic content on the sheath voltage which is attenuated by removing the electron current. These high frequency harmonics are measured in the experiment with a floating probe and their correlation with the electron current is in agreement with the model results. [Preview Abstract] |
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FPT1.00010: Neutral gas flow effect in a large area CCP plasma source TaeSang Lee, Seung-hoon Park, HoYul Baek, YongSeok Jho, Choong-Seock Chang We modified XPDP2 code to include neutral gas flow effect on CCP discharge for argon gas. Parallelized multi-grid method is used for efficient field calculation. Particle simulation is used for gas flow calculation and spatially non uniform gas distribution is obtained. Ionization, charge exchange and neutral - neutral collision effect are considered for realistic neutral gas simulation. Multi-time scale simulation is used to get steady state discharge including gas depletion by ionization. Preliminary results are obtained and compared with the results from uniform background neutral gas distribution. [Preview Abstract] |
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FPT1.00011: Analytic Model for Self-Excited Plasma Series Resonances Uwe Czarnetzki, Thomas Mussenbrock, Ralf-Peter Brinkmann Self-excited Plasma Series Resonances (PSR) are observed in capacitve discharges as high frequency oscillations superimposed on the normal RF current. This high-frequency contribution to the current is generated by a series resonance between the capacitve sheath and the inductive and ohmic bulk of the plasma. The non-linearity of the sheath leads to a complex dynamic. The effect is applied e.g. as a diagnostic technique in commercial etch reactors where analysis is performed by a numerical model. Here a simple analytical investigation is introduced. In order to solve the non-linear equations analytically, a series of approximation is necessary. Nevertheless, the basic physics is conserved and excellent agreement with numerical solutions is found. The model provides explicit and simple formula for the current waveform and the spectral range of the oscillations. In particular, the dependence on the discharge parameters is shown. Further, the model gives insight into an additional dissipation channel opened by the high frequency oscillations. With decreasing pressure the ohmic resistance of the bulk is decreasing too, while the amplitude of the PSR oscillations is growing. This results in substantially higher power dissipation. [Preview Abstract] |
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FPT1.00012: THEORY AND MODELING |
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FPT1.00013: PIC simulation of capacitive plasma with non-homogeneous boundary conditions T.A. Abu Shamaleh, M.M. Turner In earlier work, we have studied the effect of boundary non-homogeneity in a capacitive system using a lumped element circuit model. That study concentrated on what is known as the triple junction boundary configuration in the vicinity of capacitive plasma sheath. In this case, metal structures behind a dielectric wall produce disturbances in an adjacent plasma, which are suspected to cause damage to the plasma reactor wall. The investigation showed that the implementation of sheath dynamics - as opposed to a static sheath - have significant effects on the surface voltage distribution along the dielectric surface. Furthermore, quantitative differences have been observed depending on what sheath model is being implemented within the model. In the current investigation, we will be tackling the same system using the particle in cell method. The aim is to be able to investigate the detailed behaviour of a capacitive plasma in the presence of a potential disturbance at the boundary. By comparing the results of our previous and current study, we can judge which sheath theory is more representative of the plasma sheath's behaviour under such conditions, and to what extend the deviation from the expected behaviour occurs. [Preview Abstract] |
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FPT1.00014: Analytical solution of sheaths for cylindrical and spherical objects. Noah Hershkowitz, Lutfi Oksuz A novel exact analytical solution method is given in order to solve the space charge limited current for Poisson eqution for cylindrical and spherical geometries. Using this method Poisson equation is solved for different Cartesian, cylindrical and spherical sheaths for Child Langmuir sheath problem. The ion collections, developed for cylindrical, spherical and planar geometries showed spherical probe can collect much more current than the other geometries. The solutions are examined for collisional and collisionless cases. Analytical solutions are compared with the experimental results. [Preview Abstract] |
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FPT1.00015: Kinetic properties of particle-in-cell simulations compromised by {M}onte {C}arlo collisions M.M. Turner The particle-in-cell method with Monte Carlo collisions is frequently employed when a detailed kinetic simulation of a weakly collisional plasma is required. In such cases, one usually desires, {\em inter alia}, an accurate calculation of the particle distribution functions in velocity space. However, velocity space diffusion affects most, perhaps all, kinetic simulations to some degree, leading to numerical thermalization, and consequently distortion of the velocity distribution functions, among other undesirable effects. The rate of such thermalization can be considered a figure of merit for kinetic simulations. In this paper, we show that, contrary to previous assumption, the addition of Monte Carlo collisions to a particle-in-cell simulation seriously degrades certain properties of the simulation. In particular, the thermalization time can be reduced by as much as three orders of magnitude. We show that this effect makes obtaining a strictly converged simulation results difficult in many cases of practical interest. [Preview Abstract] |
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FPT1.00016: Using Modern C++ Idiom for the Discretisation of Sets of Coupled Transport Equations in Numerical Plasma Physics Jan van Dijk, Bart Hartgers, Joost van der Mullen Self-consistent modelling of plasma sources requires a simultaneous treatment of multiple physical phenomena. As a result plasma codes have a high degree of complexity. And with the growing interest in time-dependent modelling of non-equilibrium plasma in three dimensions, codes tend to become increasingly hard to explain-and-maintain. As a result of these trends there has been an increased interest in the software-engineering and implementation aspects of plasma modelling in our group at Eindhoven University of Technology. In this contribution we will present modern object-oriented techniques in C++ to solve an old problem: that of the discretisation of coupled linear(ized) equations involving multiple field variables on ortho-curvilinear meshes. The `LinSys' code has been tailored to the transport equations that occur in transport physics. The implementation has been made both efficient and user-friendly by using modern idiom like expression templates and template meta-programming. Live demonstrations will be given. The code is available to interested parties; please visit www.dischargemodelling.org. [Preview Abstract] |
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FPT1.00017: Modeling and experimental study of dielectric barrier discharges for mercury free flat lamps Beaudette Tristan, Guillot Philippe, Belenguer Philippe, Calegari Thierry, Therese Laurent, Auday Guillaume In this paper, a simple dielectric barrier discharge flat lamp developed by Saint-Gobain Glass is characterized. The lamp is consisting of two glass plates separated by a constant gas gap. The glass thickness is 4 mm and the gap 2 mm. The surface is 30cm x 30cm. A transparent conducting material (electrode) has been deposited on both external sides and phosphors (white emitting powders) on both internal sides of the dielectric. The lamp can be filled with rare gas mixture and can operate in a pressure range of 100-400 torr. A sinusoidal excitation voltage can be used up to 3000V in a frequency range of 10-50 kHz. In this work, we will present some results concerning a Ne-Xe 50{\%} mixture at a pressure of 188 torr and we will discuss the influence of the applied voltage (amplitude and frequency) on the consuming power, the light emission and mostly on the non-homogeneity of the discharge. Using a 2 dimensional model developed in our laboratory, the effects of the applied voltage (amplitude and frequency) and the pressure will be studied. Particularly on the distance between the streamers when the discharge is not homogeneous. Finally experimental and theoretical results will be compared. [Preview Abstract] |
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FPT1.00018: Numerical study on characteristics of neutral beam in plasma-grid-reflector system for material processing Seung-hoon Park, Yong-Seok Jho, TaeSang Lee, Choong-Seock Chang Low energy neutral beam source has been proposed as one of candidates reducing charging damage in the nano-scale etching process. The neutral beam is generated by interaction between accelerated ion from a grid which is applied hundreds voltage with a metal reflector. Whole simulation is composed of two parts, ion beam simulation and ion-reflector interaction simulation. Ion beam simulation describes ion trajectory, such as ion trajectory deflection and variation of ion energy caused by ion-ion interaction, in a grid and a reflector. Fast Multipole Method (FMM) is used for calculation of long-range interaction of ions. Ion-reflector interaction simulation is performed using molecular-dynamics for calculation ion reflection characteristics. The neutral distribution is obtained by ion-reflector simulation from ion distribution onto a reflector surface. [Preview Abstract] |
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FPT1.00019: Charging potential fluctuation induced by point particle effect in a sub-10 nm trench TaeSang Lee, YongSeok Jho, SeongSik Kim, ChoongSeock Chang Monte Carlo simulation of charging process in a sub 10nm trench shows that charging potential fluctuation increases up to the level of incident ion energy. Size dependence of charging fluctuation is observed. Trench systems with different width are selected as reference systems to see the characteristics for this phenomena. Summation formula is derived for coulomb interaction in a 2D periodic system instead of solving Poisson equation with conventional FEM or FDM method. It is observed that charging fluctuation increases as the trench size decreases. The relation between these fluctuations and ion energy distribution on the trench bottom is finally shown which may affect on etching process. [Preview Abstract] |
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FPT1.00020: 2D electromagnetic modeling of a microwave plasma torch R. Alvarez, L.L. Alves This work models the 2D electromagnetic field distribution, produced within a metallic reactor by a microwave driven Axial Injection Plasma Torch. The coaxial torch imposes a TEM mode to excite the device, which leads to the development of a symmetric TM mode inside the cylindrical reactor. Maxwell's equations were discretized on a variable grid, featuring smaller cells near the torch tip (around which the plasma density is higher) and at the reactor walls. Special attention was given to boundary conditions. At the reactor axis, symmetry considerations impose a zero value for the azimuthal component of the magnetic field. The reactor walls were assumed to be perfect conductors, thus leading to zero tangential electric fields. Finally, at the excitation boundary, the incident field was set equal to the theoretical solution inside a coaxial wave-guide, with a first-order Absorbing Boundary Condition imposed to the reflected field component. The resulting linear system was solved using a Gauss-Seidel algorithm combined with a Successive Over-Relaxation iterative method. Solutions were obtained by imposing a spatial distribution of the plasma permittivity, obtained from the experimental observations of the electron density profile within the device. In the future, the electromagnetic code is to be coupled with a transport model for charged particles, in view of the self-consistent description of this microwave plasma torch. [Preview Abstract] |
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FPT1.00021: OODR-LIF experiments on N$_{2}$(A$^{3}\Sigma $u$^{ +})$ in volume and in surface atmospheric pressure DBDs Santolo De Benedictis, Paolo F. Ambrico, Giorgio Dilecce, Milan Simek A calibrated optical double resonance laser induced fluorescence, OODR-LIF, has been used to measure N$_{2}$(A$^{3}\Sigma _{u}^{+})$ metastable density at high pressure in the voltage cycle of volume and surface atmospheric DBDs. OODR{\_}LIF excitation-detection scheme is: N$_{2}$(A$^{3}\Sigma _{u}^{+}$, v) + h$\nu _{L1 }\to $ N$_{2}$(B$^{3}\Pi _{g}$, v') + h$\nu _{L2 }\to $ N$_{2}$(C$^{3}\Pi _{g}$, v'') $\to \quad _{ }$ N$_{2}$(C$^{3}\Pi _{g}$, v'')+ h$\nu _{E }$. The two exciting photons (\textit{red-}$\nu _{L1}$ and\textit{ UV-}$\nu _{L2})$ are generated by two independently tunable and synchronized lasers. In volume DBD, N$_{2}$(A) is measured in the discharge gap ( d=1.5 mm, voltage 10 kV$_{pp}$ at 1.8 kHz) pulsed at T$_{ON}$=5ms and T$_{OFF}$=10ms. In surface DBD, N$_{2}$(A) is measured in the gas layer over a comb electrode deposited over a ceramic plate back covered by a metallic large background electrode. The current and the applied voltage are monitored by a digitizing oscilloscope. The measured time-resolved emissions of N$_{2}$ SPS and NO-$\gamma $ bands allows exploring the correlations between emissions, LIF and discharge current and implementing a calibration of OODR-LIF. The measured density is about 10$^{13}$cm$^{-3}$ in volume DBD while lower in a surface DBD. [Preview Abstract] |
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FPT1.00022: ELECTRON AND PHOTON COLLISIONS |
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FPT1.00023: Electron Impact Excitation of the Electronic States of Water Penny Thorn, N. Diakomichalis, M.J. Brunger, L. Campbell, P.J.O. Teubner, H. Kato, C. Makochekanwa, M. Hoshino, H. Tanaka We report differential and integral cross sections for excitation of the lowest lying $^3$B$_1$, $^1$B$_1$, $^3$A$_1$ and $^1$A$_1$ electronic states of water. The energy range of these measurements is 15-50eV and the angular range of the DCS measurements is 10-90$^\circ$. From these DCS the corresponding ICS is calculated using a molecular phase shift analysis technique. Where possible, comparison is made to the results of available theory. One of the main objectives of this study is to perform statistical equilibrium calculations to determine if the origin of the OH Meinel bands in our atmosphere are due to electron driven processes. [Preview Abstract] |
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FPT1.00024: Photoionization Angular Distributions for the Hydrogen Molecular Ion. Ola Al-Hagan, J.L. Peacher, D.H. Madison Walter and Briggs [ \textit{J. Phys. B: At. Mol. Opt. Phys. }\textbf{32, }2487 (1999)] used a perturbation method to calculate the single photoionization of the molecular hydrogen ion. They used an ansatz ``2C'' wave function and they presented results for the angular distribution of the photoionized electron. More recently Rescigno et al. [\textit{Phys. Rev}. $A$ \textbf{72}, 052709 (2005)] have carried out a non-perturbative calculation for the same process. They used a numerical grid-based method combined with exterior complex scaling. Their results show that the photoelectron distribution follows the direction of photon polarization, while the simpler perturbative ``2C'' model of Walter and Briggs predicts alignment along the molecular axis. We will present our perturbative results for this process in order to determine the source of the difference between the angular distributions obtained by the other two calculations. [Preview Abstract] |
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FPT1.00025: Electron Excitation out of the Metastable Levels of Ar into Levels of the $3p^55p$ R.O. Jung, John B. Boffard, L.W. Anderson, Chun C. Lin We have measured electron-impact excitation cross sections out of the two metastable levels of the $3p^54s$ configuration into the levels of the $3p^55p$ configuration of Ar by observing fluorescence from the decay of these levels (390-470~nm). Metastable atoms are produced in a hollow cathode discharge. After exiting the discharge, the atoms are excited by a variable energy electron beam and the resulting fluorescence from the decay of excited levels is detected by a PMT. To determine cross sections out of each metastable level ($^3P_0$ and $^3P_2$) separately, a Ti:Sapphire laser (pumped by an Ar$^+$ laser) is used to depopulate the target atoms in the $J=2$ metastable level. We find that the cross sections have peak magnitudes between $10^{-17}$ and $10^{-16}$~cm$^2$. These cross sections are one to two orders of magnitude smaller than the corresponding metastable excitation cross sections into $3p^54p$ levels\footnote{G. A. Piech \emph{et al}, Phys. Rev. Lett. \textbf{81}, 309 (1998).}, but are still two orders of magnitude larger than the $3p^55p$ excitation cross sections from the ground state.\footnote{T.~Weber \emph{et al}, Phys. Rev. A \textbf{68}, 032719 (2003).} [Preview Abstract] |
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FPT1.00026: Cross sections for simultaneous ionization/excitation of argon John B. Boffard, Chun C. Lin Optical emissions from $3p^44p$ argon ion levels (420-490~nm) are widely used in plasma diagnostics. Cross sections for electron-impact from the ground state have been studied extensively since the 1960's for levels involved in argon-ion laser emissions. Much less work, however, has been performed on measuring cross sections for other excited levels. We present measurements for simultaneous ionization/excitation cross sections into virtually all of the levels of the $3p^44p$, $3p^44d$, and $3p^45s$ configurations, and a number of additional higher levels. Emission cross sections from 300-900~nm were measured using a monochromator/PMT combination, whereas near-IR transitions in the range 850-1500~nm were measured using a FTS/Ge detector combination. [Preview Abstract] |
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FPT1.00027: Monte Carlo simulation of 337.1 nm and 391.4 nm emission due to the electron thermalization in Nitrogen. Zoran Petrovic, Vladimir Stojanovic Electron thermalization in nitrogen is studied by Monte Carlo simulations for electron energies from 20 eV to 10 keV. The purpose of this work is to clarify the origin of electron excitation of Second Positive System (2P) corresponding to C$^{3}\Pi _{u}$-B$^{3}\Pi _{g}$ transition at energies much higher than ionization the threshold. Such emission occurs when cosmic ray induced particles are thermalized in the atmosphere and may be used to detect very high energy elementary particles. Spatially resolved emission profiles are calculated at pressures of 1 Torr and 760 Torr. Relaxation of the electron energy is followed. At the same time anisotropic scattering for elastic and inelastic collisions, and energy partitioning in ionization events are included in the model. We proved that secondary electrons significantly affect the emission of 2$^{+}$ emission band while their effect on 1$^{-}$ emission band is minimal. For 337.1 nm emission, we find that below 30 eV, single collisions of secondary electrons with gas are main the source of excitation while number of multiple electron collisions with gas significantly increase with energy. For electron energies up to 10 keV, single collisions of secondary electrons dominate in excitation of 391.4 nm emission. [Preview Abstract] |
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FPT1.00028: Photodetachment Spectroscopy of Ce$^{-}$ N.D. Gibson, C.W. Walter, K.A. Starr, C.M. Janczak, P. Andersson Tunable infrared and visible laser photodetachment spectroscopy has been performed on Ce$^{-}$ using a crossed laser-ion beam apparatus. The relative photodetachment cross section for neutral production was measured over the photon energy range 0.5 eV -- 2.6 eV. The spectrum shows several continuum threshold features and reveals five narrow peaks associated with negative ion resonances. The present measurements will be compared to recent theoretical [1] and experimental [2] results which are in significant disagreement on fundamental physical quantities such as the electron affinity of Ce and the ground state configuration of Ce$^{-}$. \newline \newline [1] S.M. O'Malley and D.R. Beck, \textit{Phys. Rev. A} \textbf{61}, 034501 (2000); X. Cao and M. Dolg, \textit{Phys. Rev. A} \textbf{69}, 042508 (2004). \newline [2] V.T. Davis and J.S. Thompson, \textit{Phys. Rev. Lett.} \textbf{88}, 073003 (2002). [Preview Abstract] |
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FPT1.00029: Electron Scattering by Deoxyribose and Related Molecules Carl Winstead, Vincent McKoy Interactions between slow electrons and DNA are now known to be a cause of genetic damage, but the mechanisms that lead to DNA strand breaks remain a subject of investigation. Studies of electron collisions with DNA subunits in the gas phase may help to elucidate those mechanisms. In the present work, we apply the Schwinger multichannel method, an {\it ab initio} computational procedure, to compute elastic electron scattering cross sections for 2-deoxyribose, the sugar found in the DNA backbone, and for some related molecules. For deoxyribose, the calculations indicate the presence of shape resonances in two distinct energy ranges. When a phosphate group is added, these ranges merge into a single broad maximum. [Preview Abstract] |
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FPT1.00030: Electron Impact Excitation Collision Strengths For Ni XI. Nupur Verma, Alok Jha, Man Mohan In recent years, there has been considerable interest in the study of interaction of electrons and photons with ionized atoms, particularly with the iron group elements. Nickel is an important impurity in modern fusion research devices, especially in those where the vessel walls are constructed largely of high- nickel-content alloys (e.g. The Joint European Torus). We have used the R-matrix method to calculate electron impact collision strengths from the ground state to the first 16 fine-structure levels of argon--like Ni XI. The relativistic effects are incorporated in the Breit Pauli approximation by including one body mass correction, Darwin, and spin-orbit interaction terms in the scattering equations. Configuration interaction wave functions are used to represent the lowest 9 LS-coupled target states. The low energy region is dominated by closed channel (or Feshbach) resonances which perturb the otherwise smoothly varying background collision strength. The effective collision strengths are determined by integrating the collision strengths over a Maxwellian distribution of electron energies. Results are presented for the effective collision strengths for a wide temperature range. Our results are the only collision strengths and rate coefficients available for this ion. We believe that the data calculated in this work will be useful in solar, astrophysical and laser applications. [Preview Abstract] |
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FPT1.00031: High-precision calculations for electron collisions with krypton and xenon. Oleg Zatsarinny, Klaus Bartschat We extended our earlier work on electron collisions with Ne~[1] and Ar~[2] to the heavier noble gas targets Kr and Xe. In our $B$-Spline $R$-matrix method~[3,4], relativistic effects are accounted for through the most important terms of the Breit-Pauli hamiltonian in the inner region of the $R$-matrix box. Several sets of non-orthogonal valence orbitals were employed to account for the strong term dependence in the one-electron orbitals. Using non-orthogonal basis sets avoids the need for pseudo-orbitals to improve upon the target description and reduces pseudo-resonance problems. The agreement between our predictions and experiment~[5] is much better than that obtained in previous calculations based on the standard $R$-matrix approach with strictly orthogonal orbitals, particularly in details such as resonance positions and widths. Our new results for excitation from both the ground and the metastable states are believed to represent a significant improvement of the current database for electron collisions with heavy noble gases. \par\noindent [1] O. Zatsarinny and K. Bartschat, J. Phys. B {\bf 37} (2004) 2173. \par\noindent [2] O. Zatsarinny and K. Bartschat, J. Phys. B {\bf 37} (2004) 4693. \par\noindent [3] O. Zatsarinny and C. Froese Fischer, J. Phys. B {\bf 33} (2000) 313. \par\noindent [4] O. Zatsarinny, Comp. Phys. Commun. {\bf 174} (2006) 274. \par\noindent [5] S.J. Buckman and C.W. Clark, Rev. Mod. Phys. {\bf 66} (1994) 539. [Preview Abstract] |
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FPT1.00032: Elastic scattering of electrons from the heavy noble gases A.D. Stauffer, R.P. McEachran Since the cross sections for elastic scattering of electrons from the noble gases are much larger than the excitation cross section, elastic scattering plays a dominant role in the diffusion of electrons through these gases. In order to study the spread of an electron cloud in a gas, differential cross sections are required. For the heavier noble gases such as krypton and xenon, the relativistic j-j coupling formulation provides a more accurate description of these atoms than the usual LS coupling scheme. We have developed an optical potential approach to elastic scattering within this formulation which takes account of the open inelastic channels within a single channel potential scattering approximation. This yields more accurate cross sections, particularly for large angle scattering which play a large role in the spread of electrons within a gas. We will present detailed results for differential cross sections in comparixon with recent experiments which have measured differential scattering cross sections over the whole angular range. Our ultimate goal is to produce sufficient data to provide an accurate basis for modeling studies. [Preview Abstract] |
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FPT1.00033: Excitation of atmospheric species by electron impact. Charles P. Malone, Paul V. Johnson, J. William McConkey, Murtadha A. Khakoo, Joseph M. Ajello, Isik Kanik Electron collisions with neutral atomic and molecular targets, such as O, H$_{2}$, and N$_{2}$, have been investigated. Resulting fluorescence was probed using various monochromator-detector combinations. Line and band intensities were investigated as a function of wavelength and incident electron energy. In addition, electron energy-loss spectroscopy (EELS) was utilized such that differential cross sections (DCSs) and integral cross sections (ICSs) were obtained. The emission cross sections, DCSs, and ICSs, for these atmospheric species will be presented. [Preview Abstract] |
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FPT1.00034: Electron Impact Excitation of Molecular Nitrogen Murtadha A. Khakoo, Shiyang Wang, Charles P. Malone, Paul V. Johnson, Isik Kanik We present differential cross-sections for electron impact excitation of the N$_{2}$ b,c,o $^{1}\Pi _{u}$ and b$'$,c$'$ $^{1}\Sigma _{g}^{+}$ from the X$^{1}\Sigma _{g}^{+}$ ground state at 17.5eV, 20eV, 30eV, 50eV and 100eV for scattering angles from 5$^{\circ}$ to 130$^{\circ}$. The DCSs were obtained by unfolding the energy loss spectrum of N$_{2}$ taking into account Rydberg-valence mixing between these levels. These DCSs constitute the first systematic study of the high-lying states of N$_{2}$ of importance in plasma and astrophysics applications. [Preview Abstract] |
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FPT1.00035: Excitation of the Resonance Lines of Copper and Silver by Electron Impact Bernhard Stumpf We present a summary of our experimental investigations of the copper resonance lines 4P-4S (324.8, 327.4 nm) and silver resonance lines 5P-5S (328.1, 338.3 nm) excited by electrons with energies from threshold (3.8 eV) to 1000 eV. Linear polarizations and excitation cross sections have been measured for the unresolved copper resonance lines and for the resolved silver resonance lines. Systematic experimental errors like instrumental polarization, finite solid angle of observation, and radiation trapping have been carefully studied and corrected. Relative experimental cross sections are normalized at an energy of 1000 eV with respect to first Born theory. We compare our experimental data with theoretical calculations using the close-coupling method and the relativistic distorted-wave approximation. [Preview Abstract] |
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FPT1.00036: Benchmark Measurements and Theory for Electronic Excitation of He by Electron Impact M. Lange, J. Matsumoto, J.C. Lower, S.J. Buckman, K. Bartschat, O. Zatsarinny, I. Bray, D. Fursa We present measurements and calculations of near-threshold electron impact excitation of the n=2 and n=3 levels of the He atom. The measurements have been performed using a new differential, position sensitive, time-of-flight technique. The theoretical calculations include the R-matrix with pseudostates, B-Spline R-Matrix and convergent close coupling approaches. The agreement between experiment and theory is very good and leads us to propose some benchmark cross sections for several energies and angles for these excited states. [Preview Abstract] |
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FPT1.00037: Accelerate the transition of radioisotopes or unwanted weapons-grade $^{239}$Pu into stable nuclei with a system of high frequency modulation for a net energy gain Eugene Pamfiloff A process of high frequency stimulation of nucleons can be utilized for the accelerated fission, decay or controlled transition of unstable isotopes. For example $^{238}$U could be persuaded to transition promptly into $^{206}$Pb, where portions of the total mass difference of 29873.802 MeV per nucleus becomes available energy. The proposals of this paper describe an effective system for nuclei stimulation configured to accelerate such a series of 14 transitions over several milliseconds, instead of 4.47 x 10$^{9}$ years. Positive ions or ionized capsules of fuel suspended by magnetic fields and subjected to the system of correlated frequency modulation of multiple beam lines, tailored to the specific target, will emit sufficient energy to stimulate subsequent targets. The system can be applied to all radioisotopes, including $^{232}$Th, nuclear waste product isotopes such as $^{239}$Pu, and a variety of other suitable unstable or stable nuclei. Through the proposed confinement system and application of high frequency stimulation in the 10$^{22}$ to 10$^{24}$ Hz regime, the change in rest mass can be applied to both the fragmentation of subsequent, periodically injected targets, and the production of heat, making a continuous supply of energy possible. The system allows the particle fragmentation process to be brought into the laboratory and provides potential solutions to the safe disposal of fissile material. [Preview Abstract] |
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FPT1.00038: POST-DEADLINE |
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FPT1.00039: Flow Velocity Measurement with Mach Probe and Laser-Induced Fluorescence in the Un-magnetized Ar Plasma Hyun-Jong Woo, Kyu-Sun Chung, Taihyeop Lho The Mach probe (MP), composed of two opposite-directional electric probes, is generally used for the measurement of plasma flow velocity in edge of magnetic fusion devices, space propulsion systems, processing plasmas, sheath and pre-sheath regions. Although several un-magnetized MP theories are available, they have not been completely calibrated and should be checked by comparative (or simultaneous) measurement with another diagnostic tools such as laser-induced fluorescence or optical emission spectroscopy. Most of the previous calibrations have been done in the low Mach number (say, less than 0.5), where the existing theories predict the very similar numbers, so that the validity of the calibration is still in doubt. In this work, the plasma flow velocity is measured via MP and LIF in un-magnetized Ar plasma generated by LaB$_6$ cathode, one of two sources of Diversified Plasma Simulator (DiPS). For meaningful comparison of MP and LIF, we increase the plasma flow velocity over the $0.5C_s$, where $C_s$ is the ion sound velocity, by generating a steep density gradient from diverging magnetic field and measure the flow velocity flat magnetic field near the diverging magnetic field. Although magnetic field are applied in plasma, the ion gyro-radius is still less than the probe radius. Hence, the MP results is analyzed by un-magnetized probe theories and these are compared to LIF results. [Preview Abstract] |
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FPT1.00040: Why is the Mach probe formula expressed as $R = J_{up}/J_{dn} = \text{exp} [KM_\infty]$? Kyu-Sun Chung Normalized drift velocity of the flowing plasmas can be deduced by a Mach probe, which has two directional probes at opposite sides. The relation between the ratio($R$) of the upstream ion saturation current density($J_{up}$) to the downstream($J_{dn}$) and the normalized drift velocity ($M_\infty=V_d/\sqrt{T_e/m_i}$) of plasma has generally been fitted into an exponential form as $R = J_{up}/J_{dn} = \text {exp} [KM_\infty]$, where $K$ is a calibration factor depending upon the magnetic flux density, collisionality, viscosity, and ion temperature of plasmas. Without going into detailed theories for various conditions of plasmas and probes, a simple explanation is given in terms of decaying current density in the downstream region. Existing theories and experiments of Mach probes in magnetized and unmagentized flowing plasmas are summarized along with key physics and comments. [Preview Abstract] |
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FPT1.00041: Measurements of the density of metastable helium atoms in dielectric barrier discharges Ali El-Astal, Gagik Nersisyan, Tom Morrow, William Graham Measurements of the density of metastable helium atoms in dielectric barrier discharges operating in glow discharge mode are reported. The measurements were made in two systems using three different approaches. One DBD was created in air with helium flowing in the inter-electrode gap, in the other the DBD was in a vacuum chamber in static pure helium with some impurities present. In the first system a multi-pass absorption technique at 388.865 nm was used, the lack of any absorption signal over a path length of 25 cm indicated an upper limit of the metastable density in this system of 2x10$^{10}$ cm$^{-3 [1]}$. In the second system the time dependence of the helium metastable density using laser collisional-induced fluorescence established that the maximum density in this system was in the range 0.5 to 2.5 x10$^{10}$ cm$^{-3}$ and from the time dependence the metastable density at the next breakdown was estimated to be about 10$^{4}$. When the glass plates in the latter system were replaced by optical quality quartz, helium metastable absorption can be seen as an optogalvanic effect on the measured discharge current, indicating a higher metastable density in this case. [1]G Nersisyan, T Morrow, WG Graham Appl. Phys. Lett. \textbf{85}, 1487 (2004). [Preview Abstract] |
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FPT1.00042: Study of the non-local electron kinetics in rare gas and reactive plasmas Gordon K. Grubert, Detlef Loffhagen The development of a time- and space-dependent hybrid model for the analysis and self-consistent modelling of capacitively coupled rf discharges between plane electrodes is in progress. This model includes the coupled solution of hydrodynamic equations for the charge carriers and neutral species in the plasma, an equation system for the external electrical circuit, the Poisson equation determining the internal electric field, and the time-dependent, spatially inhomogeneous Boltzmann equation providing transport and rate coefficients of the electrons. In the current presentation the kinetic behaviour of the electrons in axially inhomogeneous discharges in rare and molecular gases is discussed on the basis of the space-dependent electron Boltzmann equation. The analysis is performed by using the multi-term approximation of an expansion of the electron velocity distribution function in Legendre polynomials. Main details of an improved technique for solving the partial differential equation system resulting from the substitution of this expansion into the kinetic equation are represented. Results of the velocity distribution and relevant macroscopic properties of the electrons are reported and the impact of the spatial variation of the electric field is discussed.\\ The work is supported by DFG Sonderforschungsbereich/Transregio 24. [Preview Abstract] |
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FPT1.00043: Electron Impact Ionization of Atoms and Ions B.C. Saha, A.K. Basak Electron impact ionization cross sections are at the heart of many active fields ranging from astro- to medical- physics. These applications require cross sections for a wide range of species as a function of projectile energies. This demand, however, is very hard to fulfill neither by experiments nor \textit{ab initio }calculations. Various analytical and semi-classical models are commonly used to generate such a vast ionization cross sections. We recently applied a modified version [1] of the Bell et. al. equations [2] including both the ionic and relativistic corrections. We will show in this presentation how to generalize the much-needed MBELL parameters for treating the orbital quantum numbers \textit{nl} dependency; comparing our results with experimental findings tests the accuracy of this procedure; very good agreements are obtained even in relativistic energies. Details will be presented at the meeting. \newline [1] A. K. F. Haque, M. A. Uddin, A. K. Basak, K. R. Karim and B. C. Saha, Phys. Rev. A73, 052703 (2006). \newline [2] K. L. Bell, H. B. Gilbody, J. G. Hughes, A. E. Kingston, and F. J. Smith, J. Phys. Chem. Ref. Data 12, 891 (1983). [Preview Abstract] |
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FPT1.00044: Optical and electrical characteristics of hollow-needle to plate atmospheric-pressure discharge in nitrogen Milan Simek, Jiri Schmidt, Stanislav Pekarek, Josef Khun We have studied basic optical and electrical characteristics of the DC hollow needle to plate electrical discharge enhanced by the gas flow through the needle. Substantial advantage of this arrangement is that all gas supplied to the discharge passes through the discharge zone and therefore it is affected by plasma chemical processes. Depending on the energy dissipated between electrodes, we previously observed two basic discharge regimes: a) DC corona and b) DC corona superimposed with pulsed filamentary streamers [1]. In this work, we have analyzed radiation induced by filamentary streamers. In addition to nitrogen emissions driven by electron impact processes we have detected emission induced by specific energy transfer processes [2]. We have also determined mean repetition frequency of filamentary streamers (0.1-15 kHz) for the needle-to-plane gap and for the nitrogen flow through the needle ranging between 2-6 mm and 1-10 slm, respectively. [1] M. Simek and S.Pekarek, GEC 2005, Bul. Am. Phys. Soc. 50, 29, (2005) ; [2] M. Simek at al, Pure Appl. Chem. 78, 1213, (2006). [Preview Abstract] |
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FPT1.00045: A Tunable, High Energy, Fourier Transform Limited Laser Source for Spectroscopy Applications Patrick Dupr\'{e}, Terry Miller We have constructed a Ti:Sa pulsed amplifier and used its beam for mainly infra-red radiation generation either by Scattering Raman Stimulated (SRS) or by Difference Frequency Mixing (DFM). The IR radiation is used to probe cold-jet radical plasmas by CRDS (see the paper devoted to the radical generation). The master (seed) source is a CW high resolution tunable ring Ti:Sa laser injected inside the amplifier which consists of an unstable resonator (slave cavity) including a GRM profile output coupler. The tuning of the slave cavity is accomplished by using the Ramp-Lock-and-Fire (RLF) technique consisting of matching (usually) on resonance the cavity length through the end mirror mounted on an actuator before firing the frequency doubled 20~Hz Nd:YAG pump laser. The implementation of the RLF technique is under the full control of a Digital Signal Processor (DSP). Energy up to 100~mJ and spectral linewidths in the range of 10--30 MHz (FWHM) have been obtained. The detailed functioning of the system will be shown as well as the features of the generated radiation showing the near Fourier transform limited pulse behavior. A model for the amplifier will also be discussed. [Preview Abstract] |
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FPT1.00046: Surface modification of substrates for bacteria and cell culture. Tom Baede, Raymond Sladek, Eva Stoffels The plasma needle is a medical device that consists of a tungsten wire placed in a tube through which helium flows. A RF voltage frequency of 13.05 MHz is applied to the wire to produce the plasma. The device has a non-thermal effect and is therefore suited for both organic and inorganic surfaces. It was designed to manipulate tissues, but can also be used to modify the bacterial adhesion properties of material surfaces. The surface modification has a number of applications, most notably cell culture and the preventive treatment of caries. The research consists of two sets of experiments. In the first experiments the effect of the plasma treatment on the wettability was studied by means of contact angle measurements. The wettability quantifies the hydrophilic behavior of a surface. Plasma treatment with the plasma needle significantly increased the wettability of the studied materials. The persistence of the wettability change was also examined. For some materials the effect was only temporary. Bacteria are very particular about the surfaces they adhere to and the wettability of the surface plays an important role in their preference. The next set of experiments dealt with the effect of plasma treatment on bacterial adhesion. This effect was measured by comparing the growth rates of E. coli and S. mutans bacteria that were cultured on both plasma and non-treated surfaces. The effect appears to be species specific. [Preview Abstract] |
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FPT1.00047: The effect of microwave and pulse corona discharges on hydrocarbons partial oxidation, combustion and detonation initiation Alexander Babaritskii, Maxim Deminsky, Viktor Jivotov, Dmitrii Medvedev, Sergey Korobtsev, Roman Smirnov, Grigory Konovalov, Mikhail Krotov, Marina Strelkova, Boris Potapkin We present experimental and theoretical results on application of microwave plasmas for stimulation of partial oxidation processes for hydrogen rich gas production from gas and liquid hydrocarbons. Said results ranging from investigation of plasma catalysis mechanism, kinetics and energy balance to plasma reactor design and heat management issues. It is appeared that relatively small plasma energy deposition (0.1eV per outcome H2, or CO molecule) under certain range of plasma parameters leads to the significant acceleration of partial oxidation processes and this effect can be used for compact on board plasma reformer development. The paper includes test results of 10 st.m3/h plasma reformer. Experimental and theoretical results devoted to MW plasma and pulse corona discharge application for combustion and detonation initiation are discussed as well. [Preview Abstract] |
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FPT1.00048: Addressable Silicon Microplasma Arrays: Discharge Properties for Pixelized Microcavities having a Multi-Electrode Geometry P. Tchertchian, S.-H. Sung, T.L. Kim, S.-J. Park, J.G. Eden The demonstration of large array of microcavity plasma devices in Si has provided new platform for the efficient light sources and high resolution displays. Device structures with vertically stacked multilayers allow opportunities to modify the device geometry to meet specific requirements of addressability or to obtain microplasma array with high spatial resolution. In this paper, we report the performance of addressable Si microplasma arrays having multiple electrodes with various geometric configurations. Each microcavity is driven by two or three thin layer electrodes which are individually patterned and embedded in the multilayer structure. We have fabricated 20 x 20 and 50 x 50 arrays of inverted pyramidal Si microcavities having (50 $\mu$m)$^2$ and (100 $\mu$m)$^2$ emitting apertures and all of the microplasma operate at atmospheric pressure with various molecular ultraviolet emitters. Stable glow discharges are observed in mixtures of atomic or molecular gases, such as Xe in Ne and D$_2$, H$_2$O in Ar, excited by AC (sinusoidal) or bipolar voltage waveform. Discharge characteristics and the spatial profiles of microplasma emission are dependent on the discharge electrode configurations and the power addressing function. The (100 $\mu$m)$^2$ microcavity device exhibits a higher UV emission intensity and efficiency than the (50 $\mu$m)$^2$ device under identical operating conditions. [Preview Abstract] |
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FPT1.00049: Confinement of Plasmas in Microcavities with Diamond or Circular Cross Sections and Driven by Al$_2$O$_3$ Encapsulated Electrodes K.S. Kim, J.D. Readle, T.M. Spinka, L.Z. Hua, S.-J. Park, J.G. Eden Arrays of Al/Al$_2$O$_3$/glass microplasma devices with microcavities having diamond or circular cross-sectional geometries have been fabricated and operated in atomic and molecular gas mixtures at atmospheric pressure. Microcavities of the device are fabricated in only one of two electrodes, and the thickness of the completed device is less than 200 $\mu$m. Spatially-resolved emission from the microcavity is investigated in the microcavity devices having diameters between 50 $\mu$m and 500 $\mu$m by optical microscopy. Optical micrographs show the operation of the microplasma in two well-defined modes. One of these is evident at higher current densities at which we observe microplasmas centered in microcavities, each having a near-cylindrical cross-sectional geometry regardless of the shape of the microcavity. Also the diameter of the microplasma decreased with rising rare gas pressure to $\sim$20\% of the characteristics microcavity dimension. Details of discharge performance and its relation to microcavity shape, dimensions and electric field distribution will be discussed. [Preview Abstract] |
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