Bulletin of the American Physical Society
64th Annual Gaseous Electronics Conference
Volume 56, Number 15
Monday–Friday, November 14–18, 2011; Salt Lake City, Utah
Session FTP1: Poster Session I: Plasma Sources I; Plasma Modeling/Simulation I; Basic Plasma Phenomena I; Plasma Applications I; Charged Particle Collisions I; Plasma Diag. I; Control of Distribution Functions |
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Room: Exhibit Hall AB |
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FTP1.00001: PLASMA SOURCES I |
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FTP1.00002: Study of short atmospheric pressure dc glow microdischarge in air Anatoly Kudryavtsev, Eugene Bogdanov, Alexander Chirtsov, Sergey Emelin The results of experiments and simulations of short (without positive column) atmospheric pressure dc glow discharge in air are presented. We used metal steel electrodes with a gap of 5-100 microns. The experimental voltage--current characteristic's (VAC) have a constant or slightly increasing form at low gap. The most stable microdischarges were burning with a flat cathode and rounded anode, when the length of the discharge is automatically established near the minimum of the Paschen curve by changing their binding on the anode. In this case microdischarge was stable and it had growing VAC. For simulations we used 2D fluid model with kinetic description of electrons. We solved the balance equations for the vibrationally- and the electronically-excited states of a nitrogen and oxygen molecules; nitrogen and oxygen atoms; ozone molecule; and different nitrogen and oxygen ions with different plasmochemical reactions between them. Simulations predicted the main regions of the dc glow discharges including cathode and anode sheath and plasma of negative glow, Faraday dark space and transition region. Gas heating plays an important role in shaping the discharge profiles. [Preview Abstract] |
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FTP1.00003: Study of micro-EDM plasmas I.M.F. Braganca, P.A.R. Rosa, F.M. Dias, L.L. Alves Micro Electrical Discharge Machining (micro-EDM) is a plasma-assisted process for the manufacturing of micro-components in high-hardness conductive materials. The removal of material is the result of a sum of dc discharges, produced within a point to plane system of electrodes immersed in a dielectric fluid, whose electric disruption with the development of plasma-currents can be induced by imposing a threshold voltage. To better understand the interaction between the micro-plasma and the material, we have designed and build an experimental setup for the production of single-discharges, characterized by a constant voltage-current operation point. The device allows the ignition of resistive plasmas in air/water at different pulse-times ($\sim $100--3200 $\mu $s), currents ($\sim $1-20 A for $\sim $75-250 V), polarities and gap-sizes ($\sim $0,5-25 $\mu $m), and the changes in these work conditions can be correlated to the type and size of the craters produced. The micro-plasma electron density $n_{e}$ is measured using the Stark broadening of the H$_{\alpha }$ atomic line. First results give $n_{e} \quad \sim $ 10$^{16}$ -- 10$^{17}$ cm$^{3}$, in agreement with estimates obtained from an electrical circuit model of the discharge. [Preview Abstract] |
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FTP1.00004: Study of microdischarge arrays excited by DC or nanosecond pulsed discharges Virginie Martin, Gerard Bauville, Vincent Puech The spatio-temporal behavior of the optical emission of microdischarge arrays was studied through fast imaging technique. The device basically consisted of a metal/dielectric/metal sandwich drilled with many microholes, and was powered either by direct current or by nanosecond high voltage pulses. Microdischarges operating in DC mode were widely used for producing VUV emission from rare-gas excimers. However for biological applications, pulsed UV sources emitting in the range 200-280 nm, corresponding to the DNA absorption band, are required. Thus the electrical and optical characteristics of discharges operating either in pure rare-gas (argon) or in rare gas/halide mixtures (Kr/Cl$_{2})$, in which intense UV-C emissions could been achieved, were studied . It will be shown that the DC excitation induces a progressive ignition of the different micro-cavities, but the maximum number of ignited microplasmas is limited. On the other hand, nanosecond high-voltage pulses, applied at high repetition frequency, allow the simultaneous ignition of all the microcavities even in absence of ballasting resistors. [Preview Abstract] |
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FTP1.00005: Current-Voltage Measurements for DC Microplasmas with Gap Sizes Less Than 10 $\mu $m Paul Rumbach, David Go Direct current (DC) microplasmas have been of great interest to the scientific community for the past decade because of their non-equilibrium characteristics and stability at atmospheric pressures. Owing to their large surface-to-volume ratio, processes occurring at the cathode surface can play a dominant role in determining many of the thermodynamic properties of a DC microplasma. Better understanding of these processes can lead to better control of thermodynamic properties, such as the electron energy distribution function. The departure from typical Paschen pressure$\times $distance pd-scaling for breakdown in gap sizes d $<$ 5$\mu $m indicates that processes other than traditional secondary emission are producing electron current at the cathode, and ion-enhanced field emission has been identified as the main process leading to the so-called modified Paschen's curve. However, it is still unclear what other properties ion-enhanced field emission affects in addition to breakdown and its ultimate role in sustaining the microplasma. Using a classic, one-dimensional, parallel plate setup, current-voltage (iV) curves are measured for gap sizes less than 10 $\mu $m in both pure argon and nitrogen with pressures ranging from 1 to 750 torr. Distinct features of these iV curves provide insight to the different processes occurring in DC microplasmas that separate them from their meso- ($\sim $100 $\mu $ms) and macroscale counterparts ($>$ 1 mm). [Preview Abstract] |
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FTP1.00006: Measurements of atomic nitrogen distributions in a radio-frequency atmospheric-pressure plasma jet Erik Wagenaars, Kari Niemi, Deborah O'Connell, Timo Gans Radio-frequency (RF) driven atmospheric-pressure plasma jets (APPJs) are expected to have a range of new healthcare applications. To guarantee the effectiveness and safety of these devices, a thorough understanding of the physics and chemistry of these plasmas is needed. We studied an RF-APPJ in helium with small admixtures of nitrogen and/or oxygen. The low-temperature APPJ effluent contains high concentrations of reactive species such as atomic nitrogen and oxygen. The N and O radicals play a crucial role in the plasma chemistry and discharge dynamics, but are unfortunately difficult to measure experimentally. We present a two-photon absorption laser-induced fluorescence (TALIF) technique for measuring atomic nitrogen species, which uses 207 nm photons for excitation of ground-state N atoms and observes time-resolved fluorescence at 745 nm. With this diagnostic we directly measure the spatial and temporal evolution of atomic nitrogen species, and compare these to the results of a numerical model based on hydrodynamic equations with a semi-kinetic treatment of the electrons. [Preview Abstract] |
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FTP1.00007: Ultraviolet Laser Raman Scattering for Temperature Measurement in Atmospheric Air Microdischarges James Caplinger, Steven Adams, James Williamson, Jerry Clark Vibrational Raman scattering for temperature measurement within a dc microdischarge in atmospheric pressure air has been investigated using a pulsed ultraviolet laser. The Raman signal analysis method involved monitoring Q-branch signals originating from multiple N$_{2}$(X) vibrational states populated in the microdischarge. The translational temperature of N$_{2}$(X) in the microdischarge was calculated using the total Raman signal intensity calibrated with room temperature air. Also, the distribution of Q-branch intensities among vibrational states allowed for direct measurement of the vibrational temperature of N$_{2}$(X). Raman scattering results are compared to passive optical emission spectral analyses of the N$_{2}$ second positive system from which the rotational and vibrational temperatures of the N$_{2}$(C) excited state were also calculated. A comparison of the N$_{2}$(X) and N$_{2}$(C) temperatures derived from Raman scattering and emission spectroscopy, respectively, is presented. This work was supported by the Air Force Office of Scientific Research. [Preview Abstract] |
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FTP1.00008: Dispersion analysis in plasma based switchable metamaterial structures Jan Trieschmann, Thomas Mussenbrock Artificially designed materials (metamaterials) are well known for their unique possibilities of manipulating electromagnetic fields. Frequency filters, negative-refraction as well as waveguide devices have been demonstrated. As these structures are mostly implemented by statically structured materials, there has been only limited capability of switching these devices. As proposed by Sakai et al. [1] this limitation can be potentially overcome by the use of micro plasmas. We investigate the dispersion behavior of different material structures. These structures can be made of metal/dielectric elements, but most importantly switchable micro plasmas. The dispersion analysis is done by means of FDTD simulations, coupled to auxiliary differential equations for treatment of the plasma discharges. The frequency response of the structures is analyzed by short pulse excitation and subsequent Fourier transform analysis. Finally, from the obtained dispersion relation we draw the conclusion towards the transmission behavior of the structures with respect to frequency selective applications. We are able to show that micro plasmas employed as photonic crystals enable for e.g., photonic band-gap (PBG) properties along with their unique switching capability.\\[4pt] [1] O. Sakai et al., Appl. Phys. Lett. 87, 241505 (2005). [Preview Abstract] |
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FTP1.00009: The Role of Helium Metastable States in Radio-Frequency Helium-Oxygen Atmospheric Pressure Plasma Jets: Measurement and Numerical Simulation Kari Niemi, Jochen Waskoenig, Nader Sadeghi, Timo Gans, Deborah O'Connell Absolute densities of metastable He atoms were measured line-of sight integrated along the plasma channel of a capacitively-coupled radio-frequency driven atmospheric pressure plasma jet operated in helium oxygen mixtures by tunable diode-laser absorption spectroscopy. Dependencies of the He metastable density with oxygen admixtures up to 1 percent were investigated. Results are compared to a 1-d numerical simulation, which includes a semi-kinetical treatment of the electron dynamics and the complex plasma chemistry (20 species, 184 reactions), and very good agreement is found. The main formation mechanisms for the helium metastables are identified and analyzed, including their pronounced spatio-temporal dynamics. Penning ionization through helium metastables is found to be significant for plasma sustainment, while it is revealed that helium metastables are not an important energy carrying species into the jet effluent and therefore will not play a direct role in remote surface treatments. [Preview Abstract] |
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FTP1.00010: Density of metastable atoms in the plume of a low-pressure argon microplasma James Cooley, Jun Xue, Randall Urdahl Spatially-resolved measurements of the density of metastable excited atoms in the plume of an argon microplasma are presented. The microplasma device is operated at relatively low pressure, on the order of 1 Torr, and is exhausted into a vacuum. Line-integrated densities of excited argon neutrals in the exhaust plume are measured using tunable diode laser absorption spectroscopy. The density of argon metastables in both 1s$_5$ and 1s$_3$ states are measured. These line-integrated density measurements are converted to three-dimensional density maps using Abel inversion. The density of 1s$_5$ argon peaks at a value of approximately 10$^{18}$ m$^{-3}$ near the outlet orifice, while the 1s$_3$ density is roughly five times lower everywhere. It is found that, far from the face of the microplasma outlet orifice, metastable density follows an angular distribution consistent with that expected of vacuum gas expansion as predicted by classic rarified flow theory. Metastable flux is found to be conserved as the plume expands through 4 mm, suggesting an absence of de-excitation collisions or other loss processes along with a frozen velocity profile. [Preview Abstract] |
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FTP1.00011: Low-pressure glow discharge with a hollow cathode Valeriy Lisovskiy, Illia Bogodielnyi We measured the breakdown curves of a dc glow discharge with hollow cathode and flat electrodes in the gap between the electrodes L = 100 mm. At low gas pressure, the left branches of the breakdown curves for the hollow cathode and the flat electrodes are identical. At high gas pressures, the right branch of the breakdown curve of the discharge with a hollow cathode is close to the breakdown curve for the distance between the plane electrodes, equal to the gap between the edge of the plates of the hollow cathode and flat anode. Current-voltage characteristics of the hollow cathode discharge were measured. At low gas pressure discharge is in the high-voltage (electron beam) form with ascending CVC. In the gas pressure range p $>$ 0.1 Torr the discharge first burns in the glow mode. At higher current the discharge goes into the hollow cathode mode, filling the space between the plates, and it has an almost vertical CVC. The transition from a glow discharge mode into a hollow one possesses a hysteresis. At gas pressures p $\sim $ 1 Torr the hollow cathode effect disappears, since the thickness of the cathode layer is small compared with the gap between the plates of the cathode. [Preview Abstract] |
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FTP1.00012: The stratification of the dc glow discharge positive column in nitrogen Valeriy Lisovskiy, Ekaterina Artushenko, Veronika Koval We have investigated the conditions of stratification of the positive column (PC) of dc glow discharge in nitrogen in the tubes with a radius of 4 mm and 27.5 mm. In every discharge tube the strata are observed in the confined areas of the current and the applied voltage over a limited range of gas pressures. The first (from the cathode end of the PC) striation is more pronounced and has a maximum length. The thickness $d$ of the striation depends weakly on the discharge current, but it decreases with increasing gas pressure. Also, the striation with high order number has a smaller thickness. The stratification of the PC obeys the similarity laws. There is observed a coincidence of the extinction curves and the regions of existence of strata measured in a variety of discharge tubes and plotted against the product \textit{pR}. Reduced strata thickness obeys the Goldstein-Wehner rule $d$/$R$ = $C$/(\textit{pR})$^{m}$. At low values \textit{pR} $<$ 1 the constants equal to $C$ = 1.17, $m$ = 0.17, and the thickness of the stratum slowly decreases with gas pressure increasing. At higher gas pressure \textit{pR} increase leads to an abrupt strata narrowing and spreading, and the constants become $C$ = 1 and $m$ = 1.7. [Preview Abstract] |
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FTP1.00013: Positive column contraction for a dc glow discharge in CF$_{4}$ Valeriy Lisovskiy, Olga Pelustka, Veronika Koval This paper studies in experiment the diffusion and contracted modes of dc glow discharge in CF$_{4}$. The existence region for the contracted mode with inter-electrode gap unchanged is found to be limited from the low-pressure side, this boundary being multi-valued. A contracted column establishes in a stratified positive column with current increasing and gas pressure fixed. However with subsequent current increase the length of the positive column decreases (with simultaneous considerable expansion of the negative glow and dark Faraday space), and contraction vanishes. At higher pressure the current increase does not lead to contraction vanishing. Similar multi-valued region exists from the narrow gap side when the inter-electrode gap changes with gas pressure fixed. [Preview Abstract] |
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FTP1.00014: Collisional -- radiative model of helium microwave discharges at atmospheric pressure M. Santos, L.L. Alves, K. Gadonna, T. Belmonte This paper presents a stationary collisional-radiative model to describe the behavior of helium microwave discharges (2.45 GHz), produced in cylindrical geometry (1 mm radius) at atmospheric pressure. The model couples the rate balance equations for the charged particles (electrons, He$^{+}$ and He$_{2}^{+}$ ions), the He(n $\le $ 6) excited states and the He$_{2}^{\ast }$ excimers, to the two-term homogeneous and stationary electron Boltzmann equation [1,2]. The latter is solved using a coherent set of electron cross sections [2], adjusted to ensure good predictions of the swarm parameters and the Townsend ionization coefficient. The model was solved for typical 5x10$^{14}$ cm$^{-3}$ electron density and 2500 K gas temperature, yielding [He$_{2}^{+}$]/[ He$^{+}$] $\sim $ 0.92 and [He$_{2}^{\ast }$]/[ He] $\sim $ 3.4x10$^{-8}$. Results show also that the He$_{2}^{+}$ ions are produced mainly from the 3-body conversion of He$^{+}$ ions and lost by the corresponding reverse reaction together with diffusion and dissociative recombination. The He$_{2}^{\ast }$ is produced by a 3-body reaction involving the 2$^{3}$P states and by the electron-stabilized recombination of He$_{2}^{+}$ and is lost by electron dissociation. [1] L.L. Alves et al, J. Phys. D 25, 1713 (1992). [2] T. Belmonte et al, J. Phys. D 40, 7343 (2007). [Preview Abstract] |
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FTP1.00015: Interpretation of EUV observations in pulsed H$_2$ and He discharges A.V. Phelps We argue that the measurements of EUV spectra from 10 kV, 2.6 J pulsed discharges in H$_2$ and/or He by Mills and Yu\footnote{R. L. Mills and Y. Lu, {\it Int. J. Hydrogen Energy} {\bf 35}, 8446 (2010).} and by Bykanov\footnote{A. Bykanov, www.blacklightpower.com/pdf/GEN3\_Harvard.pdf.} are misinterpreted by the authors. The experimental spectra show that, contrary to their model, the background (interpreted by them as continuum emission) varies considerably in shape for Ta, W, and Mo cathodes. The presence of O V and O VI lines and spectra of other than that of He show that significant material is driven from the electrodes and highly ionized by the discharge. Their measurements with Al filters with Ta and W cathodes, show that the largely unidentified spectra are not second order spectra. The claim of an optically thick plasma with Mo electrodes is inconsistent with unsuppressed lines of ionized oxygen, the absence of line reversal, and estimated metal densities and absorption coefficients. The increase in line emission with the H$_2$ to He ratio and the weak excitation when He is the fill gas suggest the importance of excitation by fast hydrogen neutrals and/or ions. For discharges in He, charge exchange collisions keep He$^+$ ion energies and excitation low. [Preview Abstract] |
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FTP1.00016: Optical emission spectroscopy study of a medium pressure Nitrogen flowing afterglow from a $\sim $1kW microwave excited plasma source Robert Carman, Peter Ha, Rod Boswell, Cormac Corr Nitrogen flowing afterglows in the medium pressure range (1-10torr) are of topical interest for applications in semiconductor film growth and biological decontamination. The spatio-temporal decay characteristics of a 2.54GHz microwave excited flowing N$_{2}$ plasma have been investigated, after a T-junction was introduced in the plasma path to optically isolate the plasma source and afterglow. The results from optical emission spectroscopy studies ($\lambda $=200-1000nm), including gas temperature estimates deduced from high resolution spectra, are compared with a simple kinetic model for key atomic and molecular nitrogen species, and are correlated to gas pressure, and gas flow rates. [Preview Abstract] |
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FTP1.00017: Physics and modeling of microwave streamers. Resonant effects and branching. B. Chaudhury, L. Papageorgiou, J.P. Boeuf, O. Pascal Breakdown in a microwave field at atmospheric pressure leads to the formation of a plasma array that moves toward the source (Chaudhury et al., Phys. Plasma 17, 123505 (2010)). When a linearly polarized microwave field is intercepted by a spherical mirror, it is possible to limit the breakdown region to a single central antinode of the field (Vikharev et al., Sov. J. Plasma Phys. 18, 554 (1992)). Breakdown in these conditions leads to the formation of a plasmoid that elongates in the direction of the field and forms a ``microwave streamer.'' On the basis of a numerical model coupling Maxwell equations with a simple description of the plasma, we describe the physics of microwave streamer formation and elongation. When the microwave field is slightly over breakdown the growth of the microwave streamer stops when its length is around one half wavelength because of resonant effects. Due to intense power deposition in the microwave streamer, gas heating and subsequent gas density drop may become important and strongly modify the structure of the microwave streamer. The simulation predicts the formation of a complex ``branching'' of the initial filament, that is qualitatively similar to the experimental observations. [Preview Abstract] |
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FTP1.00018: Spectroscopic study of CH$_{4}$ depletion in low E/N microwave discharges Do Im, Milka Nikolic, Janardan Upadhyay, Svetozar Popovic, Leposava Vuskovic Electron impact dissociation of CH$_{4}$ in plasmas has been attracting a continuous interest due to its high hydrogen content, which makes it potentially the most abundant source of hydrogen. Low E/N microwave discharges are applicable medium for oxygen-free, low temperature methane reformers and the promising candidate for the first practical application of plasma-assisted combustion. In present work we perform the optical emission spectroscopy (OES) of MW discharges in CH$_{4}$/N$_{2}$ mixtures, which has also been of interest in the planetary atmospheric studies, especially in the case of the Jupiter's satellite Titan. OES is the simplest, but also the most challenging and modeling-intensive analytical technique, mostly due to the quenching of emitters at high pressure. In present study we compare quantitative methane dissociation evidence, based on the band intensities of methylidyne (CH), cyano radical (CN) and dicarbon (C$_{2})$, and hydrogen Balmer line intensities. At low pressure, Balmer line emission proves to be useful as the CH$_{4}$ dissociation marker, but the alkyl and nytril band intensities are more reliable at higher pressures. [Preview Abstract] |
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FTP1.00019: Pulse tailoring in low-pressure radio-frequency pulsed discharges Mark Bowden, Ziad El Otell, Nicholas Braithwaite The aim of this study is investigate the effect of different pulse shapes on the properties of a low-pressure pulsed plasma. A set of differently shaped pulses were used to generate discharges in a low pressure radiofrequency discharge and measurements of electron density and optical emission spectra were used to characterise the discharge. The study was carried out in a capacitively coupled Gaseous Electronics Conference (GEC) reference reactor with gas pressure in the range of $6-70$ Pa, radiofrequency power in the range of $1-100$~W, and pulse duration in the range of $10~\mu s-100$ ms. The effect of tailored pulses on the discharge properties was investigated, with special emphasis on the development of the electron energy distribution function during the ignition phase of each pulse cycle. [Preview Abstract] |
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FTP1.00020: Analytical model of a normal mode capacitive discharge Valeriy Lisovskiy, Vladimir Yegorenkov This paper develops an analytical model describing onset conditions and characteristics for a normal mode of a low pressure capacitive discharge. The model assumes that conductivity current in the plasma volume and displacement current in near-electrode sheaths are equal as well as the ambipolar ion flux out of the plasma and drift ion flux with charge exchange in the sheaths (described by the collisional Child-Langmuir law). The normal current density is found to be proportional to gas pressure and rf field frequency squared, i.e., $J_{n}$~$\propto $~\textit{p$\omega $}$^{2}$. Calculation results match well with registered data for a number of gases. [Preview Abstract] |
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FTP1.00021: Capacitively coupled radio-frequency discharges in nitrogen at low-pressure L.L. Alves, L. Marques, C.D. Pintassilgo, G. Wattieaux, J. Berndt, L. Boufendi, E.T. Es-Sebbar, N. Carrasco, G. Cernogora This paper studies capacitively coupled radio-frequency discharges (13.56 MHz frequency) in pure nitrogen, produced within the LATMOS and the GREMI cylindrical parallel-plate reactors, surrounded by a lateral grounded grid, at 2-30 W coupled powers and 0.2-1 mbar pressures. Simulations use an hybrid code [1] that couples a 2D ($r$,$z)$ time-dependent fluid module for the charged particles and a 0D kinetic module for the nitrogen (atomic and molecular) neutral species. The coupling between these modules adopts the local mean energy approximation to define space-time dependent electron parameters for the fluid module and to work-out space-time average rates for the kinetic module. The model gives good predictions for the self-bias voltage and for the intensities of radiative transitions (average and spatially-resolved OES measurements) with the nitrogen SPS and FNS, and with the argon 811nm atomic line (present as an actinometer). Model results underestimate the experimental electron density (average resonant-cavity measurements) by a factor of 3-4. \\[4pt] [1] L. Marques et al, J. Appl. Phys. 102, 063305 (2007). [Preview Abstract] |
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FTP1.00022: Simulations of VHF capacitively coupled discharges considering wave effects Ananth Bhoj, Mustafa Megahed The influence of electromagnetic wave effects on the spatial distribution of power deposition and plasma density in plasma processing reactors has been a topic of great interest in recent years. These effects are particularly important for the operation of high frequency or large area reactors. The hydrodynamic plasma modeling platform CFD-ACE+ was improved to extend the model for capacitively coupled plasma discharges to incorporate wave effects. The approach used was to solve for the vector magnetic potential accounting separately for the contribution of the so-called electrostatic and electromagnetic fields to the total power deposition. The improved model can address arbitrary reactor geometries in 2D, axisymmetric or 3D and accepts user defined chemical reaction mechanisms relevant to the process. In this paper, results applying this model to a VHF reactor including the effects of varying rf power and frequency on the spatial distribution of the discharge are discussed. [Preview Abstract] |
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FTP1.00023: 2D PIC/MC simulations of electrical asymmetry effect in capacitive coupled plasma Quan-Zhi Zhang, Wei Jiang, You-Nian Wang Recently a so-called electrical asymmetry effect (EAE), which could achieve high-degree separate control of ion flux and energy in dual-frequency capacitively coupled plasmas, was discovered theoretically by Heil et al. and was confirmed by experiments and theory/numerical simulations later on. However, since there always is a bigger grounded surface area for experiment devices, which reduces the geometrical symmetry, and all the simulations were limited to 1D before, it is, thus, worth studying the EAE when coupling the electrically and geometrically asymmetric discharges theoretically. Here, we perform 2D PIC/MC simulations, which can include both electrically and geometrically asymmetric factors. The EAE on plasma parameters, such as dc self-bias voltage, density profiles, ion energy distribution and power absorption of electron have been examined for different pressures and geometry conditions. [Preview Abstract] |
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FTP1.00024: Theoretical Investigation of Transport properties of Ar-He thermal Plasma at High Pressure Rohit Sharma, Kuldip Singh Transport properties of Ar-He thermal plasma mixture has been studied in temperature range from 5000 to 30000K at high pressure in local thermodynamic equilibrium (LTE) and non-LTE conditions for different values of non-equilibrium parameter $\theta $ =T$_{e}$/T$_{h}$ . Computations of electron transport properties and their higher-order contribution has been carried out by using the Chapman-Enskog method. The effect of non-equilibrium parameter $\theta $ =T$_{e}$/T$_{h}$ and electronic excitation has been investigated for the electrical conductivity, electron thermal conductivity and electron diffusion. It has been observed that both the electronic excitation and non-equilibrium parameter $\theta $ considerably affect these properties. [Preview Abstract] |
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FTP1.00025: Time resolved measurements of electron and heavy particle kinetics in a short pulse excited helium DBD Feng Liu, George Huang, Biswa Ganguly A fast rise time ($\le $20 ns) high voltage pulse excited DBD in helium has been investigated in the pressure range from 10 up to 100 Torr. Time resolved emission intensities of helium (3$^{3}$S-2$^{3}$P), (3$^{3}$D -2$^{3}$P), and He$_{2 }$(d$^{3}\Sigma _{u} - b^{3}\Pi _{g})$ along with 1083 nm diode laser absorption by metastable state (2$^{3}$S-2$^{3}$P) have been measured. The influence of different applied voltages and pressures on the atomic helium metastable production and emission intensities was investigated. We observed two temporal peaks in both the 1083 nm laser absorption spectrum and also in the He$_{2}$ emission, as opposed to a single temporal peak in the atomic helium transitions corresponding to the peak current value of the DBD. The second temporal peaks in the dimer emission as well as in the laser absorption spectrum occur in the afterglow. These excited states are presumably formed through helium dimer kinetics. A comparison of time resolved measurements of discharge current, atomic and dimer emission intensities along with the laser absorption of 2$^{3}$S-2$^{3}$P state will be used to determine the relative efficiency of atomic helium metastable production by direct electron impact versus through dimer kinetics of as functions of pressure and applied voltage. [Preview Abstract] |
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FTP1.00026: Laser electric field measurement in open-air dielectric barrier discharges Tsuyohito Ito, Tatsuya Kanazawa, Satoshi Hamaguchi Electric field induced coherent Raman scattering (E-CRS) measurement is a promising technique for measuring electric field in high-pressure environments. In this study, the discharge initiation mechanism of nanosecond dielectric barrier discharges (DBDs) in open air has been examined with time dependent measurement of the discharge electric field by E-CRS. Two pulsed ns laser beams (532 nm and 607 nm) are employed. In the presence of nitrogen molecules the two laser beams together with the electric field induce a coherent IR signal at a wavelength of 4.29 $\mu $m and the normal coherent anti-Stokes Raman scattering (CARS) signal at 473 nm. The ratio of these two signals (IR and CARS) is a function of the electric field strength, so that the magnitude of the electric field can be estimated. Our experimental observations have revealed that, in the pre-breakdown phase of a nanosecond DBD discharge, the externally applied fast-rising electric field is strongly enhanced near the cathode due to large accumulation of space charge, which then strongly enhances ionization near the cathode. This process is essentially different from the well-known Townsend mechanism for slower discharges. [Preview Abstract] |
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FTP1.00027: Spectrally filtered ICCD-camera imaging of dielectric barrier discharge plasma jet using two crossed gas flows Keiichiro Urabe, Brian Sands, Osamu Sakai, Biswa Ganguly Temporally resolved imaging using an intensified charge-coupled device (ICCD) camera is one of the most effective ways for investigation of discharge behaviors in atmospheric-pressure plasmas. In a plasma jet using a dielectric barrier discharge (DBD) configuration with two crossed gas flows of pure He and Ar/acetone mixture, we have observed plasma jet propagations and transient glow discharge formation in the helium flow channel, and also a secondary discharge was ignited in the Ar/acetone flow channel when the applied voltage was in a falling slope. A transition point of the discharge between the He and Ar/acetone flows moved toward the upstream side. In order to analyze excited species formation in more detail, interference filters were used to identify discharge emissions from each excited species. From imaging results, by the spectrally filtered ICCD-camera, it was revealed that the transition point's movement was probably caused by the change of gas composition in the Ar/acetone flow, which was most likely due to the decomposition of acetone molecules by the collision with Ar metastable atoms. This effect was monitored from the time delayed C$_{2}$ Swan band emission. [Preview Abstract] |
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FTP1.00028: Quenching of electronically excited states of molecular nitrogen in nanosecond repetitive pulsed discharges in atmospheric pressure air Moon Soo Bak, Mark A. Cappelli Temporally and spectrally resolved emission measurements of the N$_{2}$ C-B transition, and thermocouple measurements along the post-discharge region have been carried out to investigate the quenching of electronically excited states of molecular nitrogen produced in nanosecond repetitive pulsed discharges in air. To investigate kinetics in detail, 2-D kinetic simulations of this air plasma have been conducted. In the simulation, the plasma parameters such as initial electron number density, peak reduced electric field, and discharge diameters are determined by matching the simulated gas temperature to the measured temperatures. The simulation reveals that a significant amount of atomic oxygen is produced through dissociative quenching of electronically excited nitrogen by molecular oxygen. [Preview Abstract] |
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FTP1.00029: Investigation of deposited material in an atmospheric pressure DC corona discharge in artificial air containing a trace of benzene, toluene or xylene Seiji Sakai, Kohki Satoh, Hidenori Itoh A trace of benzene, toluene or xylene, which is contained in artificial air, is decomposed using an atmospheric pressure DC corona discharge, and the characteristics of deposited material during the decomposition are analyzed by infrared absorption spectroscopy. The absorptions of substituted benzene, O=C-O, C=O and C-H groups are found in the transmittance spectra, and there is no significant difference in the absorption of the substituted benzene regardless of the kinds of gases. However, the absorptions of O=C-O, C=O and C-H groups increase in toluene and xylene decomposition. Further, the decomposition rates of toluene and xylene are higher than that of benzene, therefore, it is probable that the aromatic ring of toluene and xylene is easily cleaved by the discharge as compared with benzene, and that the cleaved fragments contribute to the deposition of O=C-O, C=O and C-H groups. [Preview Abstract] |
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FTP1.00030: Peculiarities of local nitrogen SPS spectra emitted from streamer head Yuri Shcherbakov, Leonid Nekhamkin We present results on spectroscopic studies of filamentary streamer discharge in short air gap in stage of primary streamer propagation. We have found that the mid-resolved nitrogen second positive system (SPS) spectra emitted from the primary streamer head changes essentially in form within some nanoseconds as compared to typical one. Namely, main peak near the band head formed by the P-branches of Pi3-to-Pi3 transition turns into a widened twin-peak hump, relative intensities of each sub-peaks change in time resulting finally in a quite usual one-peak form; with inessential modification of smooth short-wave part of the SPS-band as whole. For interpretation of this phenomenon we have considered: 1) dynamic breaking of the spin-axis coupling of the Pi3-states resulting in an appearance of Pi3(a)-to-Pi3(b)- and Pi3(b)-to-Pi3(b)-transitions additionally to a standard Pi3(a)-to-Pi3(a)-transition; 2) instrumental factors, including non-even illumination of the monochromator entrance slit due to very strong gradient of all physical parameters within streamer head; 3) Zeeman and Stark-effects. Stark-effect and instrumental peculiarities are supposed to be most adequate reasons for the phenomenon. [Preview Abstract] |
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FTP1.00031: Phenol decomposition by pulsed-plasma exposure in oxygen and argon atmosphere Kohki Satoh, Haruki Shiota, Hideyuki Itabashi, Hidenori Itoh Phenol in an aqueous solution is decomposed by the exposure of pulsed-discharge plasma, and by-products are investigated by gas chromatograph mass spectrometry. When Ar is used as a background gas, catechol, hydroquinone and 4-hydroxy-2-cyclohexene-1-on are produced, and no O$_{3}$ is produced; therefore, OH radicals generated in the plasma can initiate the decomposition of phenol, and 4-hydroxy-2-cyclohexene-1-on can be produced. Further, 4-hydroxy-2-cyclohexene-1-on can be converted into catechol and hydroquinone. When O$_{2}$ is used as a background gas, catechol, hydroquinone, formic acid, maleic acid, succinic acid and 4,6-dihydroxy-2,4-hexadienoic acid are produced. Therefore, phenol is probably decomposed into 4,6-dihydroxy-2,4-hexadienoic acid by 1,3-dipolar addition reaction with O$_{3}$, and 4,6-dihydroxy-2,4-hexadienoic acid can be decomposed into maleic acid and succinic acid by 1,3-dipolar addition reaction with O$_{3}$. Oxalic acid is possibly another by-product from 4,6-dihydroxy-2,4-hexadienoic acid, since formic acid, which is produced from oxalic acid, is detected. [Preview Abstract] |
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FTP1.00032: PLASMA MODELING AND SIMULATION I |
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FTP1.00033: C-R model for Ar plasmas Allan Stauffer, Reetesh Gangwar, Lalita Sharma, Rajesh Srivastava We have used a collisional-radiative model to calculate the population densities of the various 3p$^{5}$4s and 3p$^{5}$4p fine-structure levels in both CCP and ICP low temperature Ar discharge plasmas. This model included cross sections for the excitation of various fine-structure levels of Ar calculated with our Relativistic Distorted-Wave approximation. These calculations included distinct Dirac-Fock target wave functions for each fine-structure level and the projectile electron distorted waves were obtained from the continuum Dirac equations. Cross sections for excitation to the 3p$^{5}$4s, 3p$^{5}$4p, 3p$^{5}$3d, 3p$^{5}$5s and 3p$^{5}$5p levels from both the ground state and 3p$^{5}$4s levels were included. We have compared our results with recent OES measurements [1] as well as calculations using cross sections derived from the simple Drawin formula. Our results are in good agreement with the measurements especially for the CCP plasma. \\[4pt] [1] Xi-Ming Zhu and Yi-Kang Pu, J. Phys. D: Appl. Phys. \textbf{43}, 015204 (2010). [Preview Abstract] |
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FTP1.00034: Electron Transport in Ar/H2 Mixtures Vladimir Stojanovi\'c, \v{Z}eljka Nikitovi\'c, Zoran Lj. Petrovi\'c In this work we present transport coefficients for electrons in Ar/H2 mixtures for the conditions used in plasma assisted technologies for semiconductor production. We used numerical solution of Boltzman equation analysis obtained by program ELENDIF and Monte Carlo technique. For the conditions of very high electric fields is shown contribution of backscattered electrons of Ha emission for stainless steel and graphite anode surface. [Preview Abstract] |
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FTP1.00035: Computational simulation of finite Langmuir probe characteristics in low-temperature plasma with magnetic field of arbitrary orientation and magnitude Vojtech Hruby, Rudolf Hrach Langmuir probes are used to measure parameters of various types of plasma. Usually, the analysis of the probe characteristics are based on simplified theories, which cannot cover all configurations of the plasma and the probe. In the case of magnetized plasma, the measurement with a Langmuir probe is sensitive to the orientation of the probe to the magnetic field. Besides the theoretical approach, the computational simulations provide still better insight into these complex problems. In our contribution, we present a computational study of a cylindrical Langmuir probe diagnostics in a low-temperature plasma with an external homogeneous magnetic field. The model is fully three-dimensional, so that a general direction of the magnetic field, finite dimensions of the probe and processes on the dielectric holder of the probe could be included in the study. The presented numerical results comprise current-voltage characteristics and visualizations of sheath in the vicinity of the probe for various magnetic field magnitudes and directions. [Preview Abstract] |
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FTP1.00036: Modeling of electron behaviors under microwave electric field in methane and air pre-mixture gas plasma assisted combustion Haruaki Akashi, K. Sasaki, T. Yoshinaga Recently, plasma-assisted combustion [1] has been focused on for achieving more efficient combustion way of fossil fuels, reducing pollutants and so on. Shinohara et al [2] has reported that the flame length of methane and air premixed burner shortened by irradiating microwave power without increase of gas temperature. This suggests that electrons heated by microwave electric field assist the combustion. They also measured emission from 2nd Positive Band System (2nd PBS) of nitrogen during the irradiation. To clarify this mechanism, electron behavior under microwave power should be examined. To obtain electron transport parameters, electron Monte Carlo simulations in methane and air mixture gas have been done. A simple model has been developed to simulate inside the flame. To make this model simple, some assumptions are made. The electrons diffuse from the combustion plasma region. And the electrons quickly reach their equilibrium state. And it is found that the simulated emission from 2nd PBS agrees with the experimental result.\\[0pt] [1] V.Bychkov et al., IEEE Trans. Plasma Sci.,37,12 2280-2285(2009)\\[0pt] [2] K.Shinohara et al, J.Phys.D:Appl.Phys., 42, 182008 (1-7) (2009). [Preview Abstract] |
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FTP1.00037: Simulation of atmospheric pressure microplasma in Ar on the basis of heat transfer Masanori Yamasaki, Takashi Yagisawa, Tetsuya Tatsumi, Toshiaki Makabe In a decade, atmospheric pressure microplasmas have been applied to wide range of fields based on the characteristics of high plasma density. The underlying mechanism for sustaining a stable glow discharge, however, is not well understood. In this study, the microplasma characteristics at atmospheric pressure are numerically investigated, particularly focusing on a heat transfer in the whole system. We consider a capacitively coupled plasma with the characteristic size of several hundred micrometers, driven by radio frequency (13.56 MHz) in a cylindrical reactor under atmospheric pressure of pure Ar. A plasma fluid model is coupled with a neutral gas dynamics model including the temperature and flow in gas phase. A wall heating caused by energetic ions and metastables coming from the plasma is also incorporated in the model. Under a constant gas pressure, the local depletion of a neutral gas density occurs due to a gas heating, simply shown by ideal gas law. The influence of the local gas density on the structure of the microplasma will be mainly discussed in a periodic steady state. [Preview Abstract] |
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FTP1.00038: Particle-in-cell simulation using parallel techniques N. Hanzlikova, H. Leggate, M.M. Turner Particle-in-cell simulation is an accurate but computationally expensive approach to modelling low-temperature plasma. Consequently, implementations of this method should preferably make efficient use of computer resources. In modern hardware, such resources typically include a high degree of parallelism, using facilities such as vectorisation and multi-threading. Capabilities of this kind appear in both general purpose processors and in more specialised hardware such as graphical processing units. In principle, very large improvements in performance can be achieved by exploiting such hardware. This paper discusses particle-in-cell implementation using features of this kind. We will show that accelerations in excess of an order of magnitude are quite easily achieved, and that considerably greater performance is likely to be achieved with specialized hardware. [Preview Abstract] |
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FTP1.00039: Hydrocarbons Global Model Using MATLAB Robert L. Bates, Lawrence Overzet, Matthew Goeckner, David Urrabazo Jr. We are developing a Global Model written in MATLAB which utilizes a built in nonlinear numeric solver (FSOLVE) to estimate the densities of the various (dominant) species and the electron temperature as a function of power. We are comparing our output to the published model results of Kokkoris et al. in c-C4F8 and SF6 for validation [1,2]. The purpose is to allow us to develop a global model of discharge chemistry in hydrocarbon plasmas. As a result, we are also acquiring a rate constant set for Methanol (CH3OH) and Ethanol (C2H5OH) discharges. These models are desired for comparison to both deep silicon etch studies and to studies of misty plasmas (wherein liquid droplets of various solvents are injected into low pressure plasmas). Discussion of the model results for c-C4F8, SF6 and CH3OH will be presented. We expect to compare to FTIR measurements made in the mGEC reactor. We will also include discussion of computational techniques discovered during the development of the model. \\[4pt] [1] G. Kokkoris, et al., 2008, J. Phys D, 42, 055209. \\[0pt] [2] G. Kokkoris, et al., 2008, J. Phys D, 41, 195211. [Preview Abstract] |
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FTP1.00040: Kinetic Description of the Impedance Probe Jens Oberrath, Martin Lapke, Thomas Mussenbrock, Ralf Peter Brinkmann Active plasma resonance spectroscopy is a well known diagnostic method. Many concepts of this method are theoretically investigated and realized as a diagnostic tool, one of which is the impedance probe (IP). The application of such a probe in plasmas with pressures of a few Pa raises the question whether kinetic effects have to be taken into account or not. To address this question a kinetic model is necessary. A general kinetic model for an electrostatic concept of active plasma spectroscopy was presented by R.P. Brinkmann [1] and can be used to describe the multipole resonance probe (MRP) [2]. In principle the IP is interpretable as a special case of the MRP in lower order. Thus, we are able to describe the IP by the kinetic model of the MRP. Based on this model we derive a solution to investigate the influence of kinetic effects to the resonance behavior of the IP.\\[4pt] [1] R.P. Brinkmann, Bulletin of the APS {\bf 54} no. 12, BM 4 (2009)\\[0pt] [2] M. Lapke et al., Appl. Phys. Lett. {\bf 93}, 051502 (2008) [Preview Abstract] |
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FTP1.00041: Model of a small surface wave plasma source at atmospheric pressure J. Henriques, A. Ivanov, Zh. Kiss'ovski, E. Tatarova, C.M. Ferreira Environmental and industrial applications of microwave discharges at atmospheric pressure such as detoxification of hazardous gases, surface activation and air monitoring require the development of new plasma sources with specific qualities [1]. This study presents a two-dimensional model of a small portable Ar microwave plasma source [1] based on a surface wave sustained discharge at 2.45 GHz. This novel source creates a dense plasma in a high permittivity ceramic capillary with stable parameters at atmospheric pressure both in continuous and pulsed regimes. The self-consistent model includes the dispersion relation of the azimuthally symmetric surface mode propagating along a non-contracted cylindrical plasma column in a ceramic tube (inner diameter of 1 mm) surrounded by air and a metal screen. Furthermore, the electron Boltzmann equation under the local approximation is solved together with the heavy particle balance equations. The gas temperature as experimentally obtained is taken into account. The radial and axial distributions of the mean electron energy and plasma density are obtained and compared with results obtained by probe diagnostics and optical emission spectroscopy. \\[0pt] [1] Kiss'ovski Zh, Kolev M, Ivanov A, Lishev St, Koleva I 2009 \textit{J Phys. D: Appl. Phy}s., \textbf{42, }182 004 [Preview Abstract] |
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FTP1.00042: Effects of the instability enhanced friction on relative ion densities in a two-ion species low-temperature plasma Mirko Vukovic The instability enhanced friction theory of Baalrud \& Hegna (Phys. Plasmas 18, 023505 (2011)) predicts that for comparable ion densities the ions nearly reach a common velocity near the sheath edge in a low temperature plasma. The theory was experimentally confirmed by Yip, Hershkowitz, \& Severn (Phys. Rev. Letters 104, 225003 (2010)). We will explore the effects of the theory on relative ion densities in a numerical simulation of an Ar/Xe plasma. Results for a 0D plasma model (Lieberman, Lichtenberg, Principles of Plasma Discharges and Materials Processing, 2005) will be presented. [Preview Abstract] |
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FTP1.00043: Numerical analysis of inductive and capacitive coupling in radio-frequency micro discharges Yoshinori Takao, Koji Eriguchi, Kouichi Ono A numerical study of radio-frequency Ar micro discharges has been performed including both inductive and capacitive coupling of the source coil to the plasma. We employ a two-dimensional axisymmetric particle-in-cell with Monte Carlo collisions (PIC-MCC) method. The plasma chamber is 2.5 mm in radius and 4 mm in height with a flat spiral coil on top of the source or a helical coil on the cylindrical wall. The particle simulation was conducted at the Ar pressure of 500 mTorr, rf frequency of 450 MHz, and total power deposition in the plasma of 5 mW. The peak electron density and temperature obtained in the discharge were $7.5 \times 10^{10}$ cm$^{-3}$ and 3.4 eV, respectively, under the condition where only inductive coupling was taken into account. Including capacitive coupling in the model resulted in different spatial distributions, where the peak density was a little away from the coil, although almost the same values of the peak electron density and temperature were obtained. [Preview Abstract] |
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FTP1.00044: Monte Carlo simulations of breakdown in radio-frequency discharges Marija Savic, Marija Radmilovic-Radjenovic, Zoran Lj. Petrovic The mechanism of gas breakdown in radio-frequency electric fields represents a topic of fundamental and practical importance in the field of low-temperature plasma physics and applications. Although, a number of groups have performed experimental, modeling and theoretical studies in this area, many aspects are insufficiently explored even at the present day. This work represents the investigation of the effect of the various parameters (pressure, gap size, frequency, {\ldots}.) on the breakdown voltage in rf argon discharges. Calculations were performed by using a Monte Carlo code with simulation conditions based on the experimental conditions. The obtained simulation results are in a good agreement with the available experimental data. We have analyzed double valued breakdown curves, the role of drift, diffusion and ionization in achieving balance of charged particles and the role of ions on the breakdown in rf regime. [Preview Abstract] |
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FTP1.00045: Kinetic Modeling of the Advanced Plasma Source Benjamin Schroeder, Ralf Peter Brinkmann, Jens Harhausen, Andreas Ohl Plasma ion assisted-deposition (PIAD) is a well-established technology for the creation of high quality coatings on mirrors, lenses, and other optical devices. This paper investigates the Advanced Plasma Source (APS), a plasma beam source employed for PIAD. A field enhanced glow discharge generates a radially expanding plasma flow with an ion energy of about 80 - 120\,eV. Charge exchange collions with the neutral background gas (pressure 0.1\,Pa and below) produce a cold secondary plasma which expands as well. A hybrid model is developed which consists of a drift-kinetic description of the magnetized electrons, coupled to a simplified Boltzmann equation for the primary ions and fluid-dynamic representation of the secondary ions. All results compare well to experiments conducted at a commercial APS system. [Preview Abstract] |
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FTP1.00046: The effect of collision frequency on the electric field distribution in a high frequency capacitive discharge Hyunjoo Kang, Wooyoung Choi, Boram Lee, ChinWook Chung The electric field distribution in a high frequency capacitive discharge was investigated by solving Maxwell's equations. It was found that electric field distribution is governed by two current sources: displacement currents and conduction currents. When the displacement current is dominant, the electric field distribution has a convex shape while it has a concave shape in case of high conduction current. In a radio frequency capacitive discharge, there are the two current components which are correlated with plasma density and collision frequency. From our calculation, we found that when collision frequency is comparable with plasma frequency, it can change the electric field distribution significantly from the concave shape to the convex shape and vice versa. Therefore, it can be one of control knobs for uniform electric field distribution. [Preview Abstract] |
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FTP1.00047: BASIC PLASMA PHYSICS PHENOMENA I |
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FTP1.00048: The Effects of a Highly Secondary Electron Emissive Boundary on the Plasma Potential and Electron Energy Distribution J.P. Sheehan, Noah Hershkowitz In a multi-dipole chamber with a thin layer of dielectric coating the wall, the plasma potential is observed to be negative with respect to the grounded wall in the tens of volts. The dielectric affects the plasma potential in two ways: by charging negative on the surface in contact with the plasma and by emitting significant numbers of secondary electrons. The secondary electron emission coefficient due to electrons (the ratio of secondary electron current to incident electron current) is larger than 1 and at low enough densities a virtual cathode can be observed near the wall. The potential structure of the virtual cathode is affected primarily by the electron temperature and the energy of the ionizing electrons (tens of eV). The secondary electrons enter the bulk plasma and enhance the high energy tail of the electron energy distribution function. [Preview Abstract] |
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FTP1.00049: Self-consistent simulation of high-frequency driven plasma sheaths Mohammed Shihab, Denis Eremin, Thomas Mussenbrock, Ralf Peter Brinkmann Low pressure capacitively coupled plasmas are widely used in plasma processing and microelectronics industry. Understanding the dynamics of the boundary sheath is a fundamental problem. It controls the energy and angular distribution of ions bombarding the electrode, which in turn affects the surface reaction rate and the profile of microscopic features. In this contribution, we investigate the dynamics of plasma boundary sheaths by means of a kinetic self-consistent model, which is able to resolve the ion dynamics. Asymmetric sheath dynamics is observed for the intermediate RF regime, i.e., in the regime where the ion plasma frequency is equal to the driving frequency. The ion inertia causes an additional phase difference between the expansion and the contraction phase of the plasma sheath and an asymmetry for the ion energy distribution bimodal shape. A comparison with experimental results and particle in cell simulations is performed. [Preview Abstract] |
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FTP1.00050: Energetic electrons in Ne/Ar inductively-coupled plasmas L.E. Aneskavich, John B. Boffard, R.O. Jung, Chun C. Lin, A.E. Wendt Electron energy distribution functions (EEDF) have been monitored in neon/argon 13.56 MHz inductively-coupled plasmas (ICPs) with electrical (Langmuir) probes and optical diagnostics. Good agreement is observed between probes and emission modeling of the argon optical emission spectra (OES), with both showing a nonequilibrium EEDF with depletion of energetic electrons relative to a Maxwellian. In plasmas with high neon concentration, however, an analysis of neon OES results is consistent with the presence of an additional even higher energy electron population, beyond the detection limits of our Langmuir probe system. In addition, phase-resolved OES (PR-OES) reveals that select Ne lines have a 13.56 MHz modulation that increases in amplitude under the same plasma conditions. We explore possible physical mechanisms influencing this phenomenon, including 1) penetration of ICP fields to the OES line of sight (skin depth), 2) stochastic heating and secondary emission of electrons associated with capacitive coupling to the plasma by the ICP antenna, and 3) production of energetic electrons by the plasma series resonance. [Preview Abstract] |
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FTP1.00051: Time Resolved Simulation and Measurement of Violet Emission Spectra Early in an Ar Pulsed rf Inductively Coupled Plasma During Metastable Build-Up Steven Adams, Charles DeJoseph, Jr., Vladimir Demidov, Jared Miles, Jordan Sawyer The temporal evolution of metastable Ar within a pulsed rf inductively coupled plasma (ICP) source has been measured by tunable diode laser absorption spectroscopy (TDLAS) and combined with time-resolved Langmuir probe measurements of the EEDF and optical cross sections to simulate the evolution of the violet emission spectrum from a 5 mTorr Ar discharge. Measurements were conducted in a diffuse plasma region, 12 cm away from the rf window. Here the metastable density was found to build relatively slowly, from near zero at the beginning of the rf pulse to a maximum density over several hundred microseconds. Experimental optical emission spectra in the 410-430 nm range were found to be in good agreement with the simulations over all times. Certain emission line ratios with unique dependences on direct and step-wise excitation were shown to be good indicators of the metastable evolution. This work was supported by the Air Force Office of Scientific Research. [Preview Abstract] |
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FTP1.00052: Plasma decay in air excited by high-voltage nanosecond discharge Nikolay Aleksandrov, Eugeny Anokhin, Svetlana Kindusheva, Artem Kirpichnikov, Ilya Kosarev, Maryia Nudnova, Svetlana Starikovskaia, Andrey Starikovskiy Plasma decay in air after a high-voltage nanosecond discharge has been studied experimentally and numerically at room temperature for pressures between 1 and 10 Torr. Time-resolved electron density was measured by a microwave interferometer for initial electron densities in the range (2 -- 3)$\times $10$^{12}$ cm$^{-3}$. Discharge non-uniformity was investigated by optical methods. The balance equations for charged particles and electron temperature were numerically solved to describe the temporal evolution of the densities of electrons and ions in the discharge afterglow. It was shown that the loss of electrons is governed by dissociative and three-body recombination with O$_{2}^{+}$ ions under the conditions considered. Good agreement between the calculated and measured electron density histories could be obtained only when increasing the rate of three-body recombination by an order of magnitude and when changing the dependence of the recombination rate on electron temperature. This could testify that the well-known mechanism of three-body recombination of atomic ions changes in the case of molecular ions. [Preview Abstract] |
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FTP1.00053: Interaction between liquid droplets and atmospheric pressure discharge M.M. Iqbal, M.M. Turner We present a multi-dimensional model for two-phase flow. The two phases are liquid and plasma, described by a two-dimensional time-dependent fluid model and a stochastic liquid droplet model. We describe the evolution of major parameters, such as temperature and radial and axial velocities of liquid droplets. The behaviour of liquid droplets in atmospheric pressure discharge are discussed in detail by considering collision mechanisms, such as grazing, coalescence, and distortion of liquid droplets during transport in helium gas. The temporal distributions of droplet counts are compared before and after collisions, which provides insight into the effect of droplet collisions on the characteristics of atmospheric pressure discharges. The evolution of spatial profiles of charge carriers are examined as liquid droplets evaporate. The effect of material evaporated from liquid droplets on the plasma characteristics is appreciable. [Preview Abstract] |
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FTP1.00054: Experimental Determination of Paschen Curve and First Townsend Coefficient of Nitrogen Plasma Discharge Sabah Wais In the present work, an experimental study is performed to determine the first Townsend coefficient and Paschen curve for N$_{2}$ gas chamber using a parallel plate geometrical configuration. Paschen curve coefficients are derived by exponential fitting of first Townsend coefficients data of plasma discharge. The experimental data is acquired at different working pressure and various electrode gap separations. Furthermore, the amplification process of the gas gain in non-uniform electric field is realized. [Preview Abstract] |
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FTP1.00055: 2D Plasma Density Distributions and Plasma Vortex Motion in Low-Pressure Gas Discharges Sergey Dvinin Plasma density distribution in a 2D nonuniform positive column of a low-pressure gas discharge is studied in the hydrodynamic approximation with allowance for ion inertia. Hodograph transformation [1] taking into account plasma vortex motion was used to solve system of equation. The vortex motion can be caused by drift of ions, neutral gas flow through the discharge chamber and a complex chemical nature of plasma. Influence of the listed effects on spatial distribution of charged particles density and electric field, necessary for discharge maintenance, is considered. The solution is presented in the form of a number on the predetermined system of functions. Asymptotic solutions near the coordinate origin and near the critical surface are considered. It is shown that, for potential plasma flows, the flow velocity component normal to the plasma boundary is equal to the ion acoustic velocity. The results obtained can be used to analyze the processes in low-pressure plasmochemical reactors.\\[4pt] [1] E. V. Berlin, S. A. Dvinin, V. V. Mikheev et al, Plasma Physics Reports, 30, No. 12, 1043 (2004). [Preview Abstract] |
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FTP1.00056: PLASMA APPLICATIONS I |
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FTP1.00057: ABSTRACT HAS BEEN MOVED TO QRP1.00017 |
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FTP1.00058: Dielectric Barrier Discharge control on an unstarting supersonic flow Seong-kyun Im, Hyungrok Do, Moonsoo Bak, Mark Cappelli The control of unstarting supersonic model inlet flow using Dielectric Barrier Discharge (DBD) is experimentally demonstrated at Mach 4.7 flow condition. Planar Laser Rayleigh Scattering (PLRS) technique is utilized to visualize important flow features, such as boundary layers and shockwaves, at low static temperature ($\sim $60K) and pressure ($\sim $1kPa) freestream condition. The unstart which is initiated by jet injection in three different model inlet flow, a laminar boundary layer, tripped boundary layer without actuation, and tripped boundary layer with actuation, is demonstrated with PLRS technique. The delay of unstart process is observed through the DBD actuation of the tripped boundary layer when a single DBD actuator pair is oriented parallel to the freestream flow, generates spanwise disturbances. However, this actuation on unstart process is limited to a region of actuation. [Preview Abstract] |
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FTP1.00059: The characteristics of a Hall plasma discharge ion accelerator operating on molecular nitrogen Keith Loebner, Eunsun Cha, Nicolas Gascon, Mark Cappelli Generally, ionization and acceleration efficiencies are low in Hall ion sources operating on low molecular weight gases. The reasons for such low efficiencies include energy losses into internal molecular modes (including dissociation) as well as short residence times within the discharge itself due to the high neutral molecular speeds. In this study, we have designed and fabricated a Hall discharge with an extended channel and magnetic field distribution to promote longer residency. The design was motivated by hybrid simulations of the discharge with the desire to optimize ion current. Preliminary operation confirms that unlike operation on pure heavy monatomic gases such as krypton, the discharge currents are significantly higher at comparable discharge voltage. The discharge characteristics and ion current are compared to hybrid fluid/PIC simulations which use a parameterized electron transport model driven by azimuthal shear in the electron fluid. [Preview Abstract] |
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FTP1.00060: Time Synchronized Optical Diagnostics of a Diverging Cusped Field Ion Accelerator Natalia MacDonald, Keith Loebner, Mark Cappelli The Diverging Cusped Field Thruster (DCFT) - a plasma discharge ion accelerator, is an innovative alternative to a conventional low-power Hall Thruster. The DCFT employs permanent magnets of alternating polarity to create a cusped magnetic field profile that mitigates the transport of high energy ions toward channel walls, thereby reducing the effects of erosion. This discharge tends to operate in two modes: a low-current, quiescent mode, and a high-current mode characterized by strong periodic oscillations in the discharge current. While time-averaged diagnostics are adequate for the low-current mode of operation, diagnostic intervals longer that the period of the discharge oscillations prevent them from resolving the dynamics seen in the high-current mode. We report on the development of spectroscopic emission and laser-induced fluorescence (Doppler-based) velocimetry that is synchronized in time to the periodic discharge current. This diagnostic is not unique to these thrusters, and may be useful in the studies of other quasi-periodic plasma devices. [Preview Abstract] |
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FTP1.00061: Numeric and experimental study of a microwave resonant cavity as a cathode for space propulsion Laurent Liard, Yu Zhu, Gerjan Hagelaar Resonant microwave cavity as a plasma source has shown recently [1] some exciting experimental results, including dense electronic density and low plasma potential in a xenon plasma. Nevertheless, physical causes of these interesting properties are not totally understood. We present in this poster a microwave cavity designed in our laboratory for a 2.45 GHz resonance. The prototype is characterized by its S parameters and its plasma by Langmuir probes measurements. The cavity is also modelized by a 2-D fluid model named Cavimo [2], which couples plasma and microwave interaction. The matching system is discussed to optimize the plasma creation and select the excited microwave mode. By a parametric study (power, pressure, condition of electron extraction) performed at the same time on the code and the prototype, the physical causes of the particualr properties of the plasma are discussed.\\[4pt] [1] K. Diamant IEEE Trans. On Plasma Sci. p1558 2009\\[0pt] [2] G. Hagelaar et al.,J. Phys. D : Appl. Phys vol. 42 p194019 2009 [Preview Abstract] |
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FTP1.00062: The Effects of Plasma Shield on the Radar Cross Section of a Generic Missile in UHF Band Shen Shou Max Chung RF Stealth is the dominant technology in today's military aircraft, and most is achieved by shape design with a few reductions achieved by RAM, but most of these effects are only valid in X band. With the popularity of UHF radar again rising, the possibility of detecting a stealth object has increased due to resonance effect, and this is difficult to decrease with previous means due to the long wavelength. A plasma shield generated in front of an object may be suitable to alter the RCS in specific band without physically changing its shape. We examine the RCS of a generic missile in UHF band, and compared it with one with a cone-shape plasma generated in front of the missile. We find the plasma effectively changes the RCS of the missile, though not necessarily smaller. The RCS of the missile with the plasma shield is now dominated by the plasma instead of the missile. The RCS is a function of the size, shape, and density of the plasma shield. For higher frequency signals like the X band radar, it can still penetrate the plasma, and sees the original RCS of the missile. Due to the relatively lower UHF frequency, the plasma density needed is lower than one in X band and thus more practical to achieve. [Preview Abstract] |
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FTP1.00063: Time resolved PLIF and CRD diagnostics of OH radicals in the afterglow of plasma discharge in hydrocarbon mixtures Liang Wu, Jamie Lane, Nicholas Cernansky, David Miller, Alexander Fridman, Andrey Starikovskiy Two types of diagnostic techniques have been used to investigate the OH radical dynamics in the afterglow of a pulsed nanosecond discharge. The time resolved Planar Laser Induced Fluorescence (PLIF) imaging and Cavity Ring-Down (CRD) techniques provide the information of spatial distribution and absolute concentration of OH, respectively. Experiments were carried out using a lean methane/air mixture ($\phi $=0.1) at atmospheric pressure for temperatures of 300~K and 500~K. The nanosecond pulsed discharge was formed in a pin to pin electrode system. PLIF imaging indicated uniform OH radical dynamics along the discharge channel, and CRD spectroscopy showed a long life time ($>$200 $\mu $s) for [OH] at 500~K. This life time is not predicted by any existing kinetic models. The absolute [OH] from CRD was consistent with our previous [OH] measurements using Laser Induced Fluorescence (LIF). Comparison of OH radical emission dynamics with discharge emission dynamics from excited nitrogen revealed a close similarity in spatial distribution and allowed clarification of the mechanisms of atomic oxygen formation. [Preview Abstract] |
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FTP1.00064: Laser flash-photolysis and gas discharge in N2O-containing mixture: kinetic mechanism Ilya Kosarev, Nikolay Popov, Svetlana Starikovskaia, Andrey Starikovskiy The paper is devoted to further experimental and theoretical analysis of ignition by ArF laser flash-photolysis and nanosecond discharge in N2O-containing mixture has been done. Additional experiments have been made to assure that laser emission is distributed uniformly throughout the cross-section. The series of experiments was proposed and carried out to check validity of O($^{1}$D) determination in experiments on plasma assisted ignition initiated by flash-photolysis. In these experiments, ozone density in the given mixture (mixture composition and kinetics has been preliminary analyzed) was measured using UV light absorption in Hartley band. Good coincidence between experimental data and results of calculations have been obtained Temporal behavior of energy input, electric field and electric current has been measured and analyzed. These data are considered as initial conditions for numerical modeling of the discharge in O2:N2O:H2:Ar = 0.3:1:3:5 mixture. Ion-molecular reactions and reactions of active species production in Ar:H2:O2:N2O mixture were analyzed. The set of reactions to describe chemical transformation in the system due to the discharge action has been selected. [Preview Abstract] |
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FTP1.00065: Localized and distributed behavior of nanosecond pulse-periodic discharge in air Andrey Nikipelov, Ilya Popov, Sergey Pancheshnyi, Andrey Starikovskiy Three different regimes of nanosecond pulse-periodic discharge development in different geometries were investigated with nanosecond temporal resolution: streamer corona, localized nanosecond spark and distributed spark. Kinetic and gasdynamic effects that control the transition from streamer to spark discharge were demonstrated. Significant radial inhomogeneity of streamer channels parameters (electrons and excited particle density, specific energy release) leads to decreased plasma channel diameters for each following pulse in a sequence. This self-focusing of the plasma channel leads to the local overheating and ionization of the gas and provokes the breakdown of the gap. Transition from localized to distributed (rotating) spark can be achieved increasing the repetition rate of pulses. Distributed spark demonstrates the highest efficiency for plasma-assisted applications compared to localized spark and streamer corona. [Preview Abstract] |
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FTP1.00066: Enhancement of hydrogen trapping by heavier ion bombardment in silicon (111) surfaces Cedric Thomas, Kazuhiro Karahashi, Thierry Angot, Satoshi Hamaguchi Hydrogen content in a silicon substrate is an important parameter in plasma processing of silicon. With the use of ion and neutrals beams, plasma can be experimentally simulated and thus specific effects of each ionic/neutral species can be studied and compared to those in plasma experiments. In this study, with temperature programmed desorption, properties of hydrogen trapping in silicon during argon and hydrogen ion implantation have been studied. Especially focused are the effects of damages generated by heavier ion bombardment that increases hydrogen trapping in the substrate. It has been found that the amount of hydrogen trapped in silicon is much larger in the case of simultaneous injection of argon and hydrogen ions than the case of injection of hydrogen ions only. Damage induced trapping of hydrogen in silicon discussed here may have some resemblance with hydrogen trapping in amorphous carbon observed during chemical sputtering of amorphous carbon materials used for the first wall of a thermonuclear fusion reactor. [Preview Abstract] |
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FTP1.00067: Vacuum ultraviolet argon excimer laser excited by optical-field-induced ionized electrons produced in an argon-filled hollow fiber Shoichi Kubodera, Masanori Kaku, Masahito Katto Short-wavelength lasers in the vacuum ultraviolet (VUV) spectral region between 100 and 200 nm have not yet been developed to the same degree as visible and infrared lasers. We have demonstrated the production of argon excimers via an optical-field-induced ionization (OFI) process by using a high-intensity infrared laser. We here report optical amplification of argon excimers at the wavelength of 126 nm by producing an extended OFI plasma inside an argon-filled hollow fiber with an inner diameter of 250 microns with a length of 5.0 cm. A gain-length product of 4.3 through the use of single-pass amplification with VUV optics was observed, indicating a small signal gain coefficient of 0.86 cm$^{-1}$ with an uncertainty of 0.03. It was found that the hollow fiber served to extend the OFI plasma length and to guide the excitation of the infrared laser and the produced VUV emissions at 126 nm, but did not affect the OFI plasma conditions to produce argon excimer molecules. [Preview Abstract] |
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FTP1.00068: Study on decreasing ignition voltage of mercury-free HID lamps for automotive headlamps Tadao Uetsuki, Takahumi Ota, Masaya Shido, Toshiaki Tsuda, Yukio Onoda Recently the HID lamps for automotive headlamps have gradually changed from the mercury containing HID lamps to the mercury-free. Filling gas pressure of the mercury-free HID lamps is much higher than that of the mercury containing, because luminous flux and run-up speed of the mercury-free HID lamps are much lower than that of the mercury containing if filling gas pressure is the same. High filling gas pressure also leads to high ignition voltage of the mercury-free HID lamps and it makes their ballast (include ignition circuit) bigger and heavier to keep reliability of the ignition. Therefore it is important to decrease ignition voltage of the mercury-free HID lamps. We studied influence of outer filling gas type and pressure on ignition voltage. As the result, we found that they have strong influence on ignition voltage, for instance nitrogen is a very effective gas for decreasing ignition voltage. We also found that a streamer path of ignition tends to be longer as ignition voltage decreases. In this study we discuss these measurement results. [Preview Abstract] |
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FTP1.00069: Effect of the superposition of a dielectric barrier discharge onto a premixed gas burner flame Kazunori Zaima, Noriharu Takada, Koichi Sasaki We are investigating combustion control with the help of nonequilibrium plasma. In this work, we examined the effect of dielectric barrier discharge (DBD) on a premixed burner flame with CH$_4$/O$_2$/Ar gas mixture. The premixed burner flame was covered with a quartz tube. A copper electrode was attached on the outside of the quartz tube, and it was connected to a high-voltage power supply. DBD inside the quartz tube was obtained between the copper electrode and the grounded nozzle of the burner which was placed at the bottom of the quartz tube. We clearly observed that the flame length was shortened by superposing DBD onto the bottom part of the flame. The shortened flame length indicates the enhancement of the burning velocity. We measured the optical emission spectra from the bottom region of the flame. As a result, we observed clear line emissions from Ar, which were never observed from the flame without DBD. We evaluated the rotational temperatures of OH and CH radicals by spectral fitting. As a result, the rotational temperature of CH was not changed, and the rotational temperature of OH was decreased by the superposition of DBD. According to these results, it is considered that the enhancement of the burning velocity is not caused by gas heating. New reaction pathways are suggested. [Preview Abstract] |
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FTP1.00070: Nonlinear Oscillations of Gas Bubbles and Their Impact on Plasma Breakdown in Water Bradley Sommers, John Foster We investigate the effects of a time varying electric field on air bubbles submerged in water. For a sufficiently strong field, a large electrical stress acting on the liquid-gas boundary can deform the volume and shape of the bubble. This deformation may drastically alter the internal pressure and polarization of the bubble, thus easing the conditions for streamer formation within the gas volume. This type of enhancement could have a broad impact on the viability of liquid plasma technologies, which tend to suffer from high voltage requirements. Bubbles with 0.5-3 mm diameter are trapped in the node of a 26.5 kHz underwater acoustic field while either alternating or pulsed voltage signals of 5-20 kV are applied across their diameter. Bubble response is captured using a high speed camera (10,000 fps), along with a high sensitivity hydrophone. The response is documented over a wide range of factors, including bubble size, field frequency, and field strength. The observed deformations of the bubble shape are then used to predict changes to the reduced field (E/N) within the bubble volume. [Preview Abstract] |
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FTP1.00071: Surface energy modification for biomedical material by corona streamer plasma processing to mitigate bacterial adhesion Ibrahim Alhamarneh, Patrick Pedrow Bacterial adhesion initiates biofouling of biomedical material but the processes can be reduced by adjusting the material's surface energy. The surface of surgical-grade 316L stainless steel (316L SS) had its hydrophilic property enhanced by processing in a corona streamer plasma reactor using atmospheric pressure Ar mixed with O$_{2}$. Reactor excitation was 60 Hz ac high-voltage ($\le $ 10 kV RMS) applied to a multi-needle-to-grounded-torus electrode configuration. Applied voltage and streamer current pulses were monitored with a broadband sensor system. When Ar/O$_{2}$ plasma was used, the surface energy was enhanced more than with Ar plasma alone. Composition of the surface before and after plasma treatment was characterized by XPS. As the hydrophilicity of the treated surface increased so did percent of oxygen on the surface thus we concluded that reduction in contact angle was mainly due to new oxygen-containing functionalities. FTIR was used to identify oxygen containing groups on the surface. The aging effect that accompanies surface free energy adjustments was also observed. [Preview Abstract] |
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FTP1.00072: CHARGED PARTICLE COLLISIONS I |
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FTP1.00073: Electron Impact Induced Break-Up of Aligned H$_{2}$: Molecular Frame (e, 2e) Studies Alexander Dorn, Xueguang Ren, Thomas Pflueger, Arne Senftleben, Joachim Ullrich, Shenyue Xu, James Colgan, Mitch Pindzola In electron impact ionization details of the collision dynamics should depend on the alignment of the target molecule with respect to the incoming projectile. Here we present experimental and theoretical results for ionization of molecular hydrogen (H$_{2})$ by slow (54 eV) electron impact. Experimentally, the alignment of the H$_{2}$ molecule is determined by the post-collisional dissociation of the molecular ion. Therefore, fully differential cross sections for fixed in space molecular axis can be presented which indeed show strong alignment dependence. In comparison with non-perturbative time dependent close coupling calculations (TDCC) these results give detailed insight into the multi-centre ionization dynamics. [Preview Abstract] |
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FTP1.00074: Two- and Three-Photon Double Ionization of Lithium at FLASH Alexander Dorn, Michael Schuricke, Gopi Veeravalli, Ganjun Zhu, Christian Dornes, Katharina Joachimsmeyer, Joachim Ullrich With the advent of free electron lasers studies on non-linear few-photon - few-electron reactions in the VUV and EUV regime have become possible. Here we investigate how two or three photons interact with the three electrons in lithium. Therefore, a dedicated apparatus was built combining a many-particle momentum spectrometer (reaction microscope, REMI) and a cold and dense lithium gas target which is provided by magneto-optically trap (MOT). The recoil ion momentum distributions obtained reveal detailed information on the different single and multiple ionization reaction pathways. During beam times at the Hamburg Free electron Laser FLASH a number of resonant and non-resonant, basic two- and three-photon, single and double ionization reactions have been investigated at different photon energies. [Preview Abstract] |
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FTP1.00075: Relativistic Many-Body Approach to Calculating Radiation and Autoionization Probabilities, Electron Collision Strengths For Multicharged Ions in a Plasma: Debae Approximation Alexander Glushkov, Andrey Loboda, Ludmila Nikola We present the uniform energy approach, formally based on the gauge-invariant relativistic many-body perturbation theory for the calculation of the radiative and autoionization probabilities, electron collision strengths and rate coefficients in a multicharged ions (in a collisionally pumped plasma). An account for the plasma medium influence is carried out within a Debae shielding approach. The aim is to study, in a uniform manner, elementary processes responsible for emission-line formation in a plasma. The energy shift due to the collision is arisen at first in the second PT order in the form of integral on the scattered electron energy. The cross-section is linked with imaginary part of the scattering energy shift. The electron collision excitation cross-sections and rate coefficients for some plasma Ne-, Ar-like multicharged ions are calculated within relativistic energy approach. We present the results of calculation the autoionization resonances energies and widths in heavy He-like multicharged ions and rare-earth atoms of Gd and Tm. To test the results of calculations we compare the obtained data for some Ne-like ions with other authors' calculations and available experimental data for a wide range of plasma conditions. [Preview Abstract] |
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FTP1.00076: Two-photon double ionization of lithium Gregory Armstrong, James Colgan The advent of free-electron laser technology has generated significant interest in the study of few-photon reactions at VUV and EUV wavelengths. Pioneering experimental measurements of recoil-ion momentum distributions for two-photon double ionization of lithium are currently underway at the Hamburg FLASH facility, augmenting previous measurements for helium and neon [1,2]. The time-dependent close-coupling (TDCC) method employed in this work is capable of treating single, double and triple photoionization of a three-electron system in full dimensionality [3]. However, the current work focuses on double ionization, and so a `frozen core' approach is used to treat the inner 1s electron. This work provides the first TDCC calculations to date of two-photon double ionization of lithium. This work also aims to extend the analysis of symmetrized amplitudes, previously invoked for double photoionization [4], to two-photon double ionization of a general two-electron atom. \\[4pt] [1] A. Rudenko {\em et al.}, 2008 {\emph{Phys.Rev.Lett.}} {\bf 101} 073003\\[0pt] [2] M. Kurka {\em et al.}, 2010 {\emph{New J. Phys.}} {\bf 12} 073035\\[0pt] [3] J. Colgan, M. S. Pindzola and F. Robicheaux, 2004 {\emph{Phys.Rev.Lett.}} {\bf 93} 053201\\[0pt] [4] A. S. Kheifets {\em et al.}, 2010 {\emph{Phys.Rev.A}} {\bf 82} 023403 [Preview Abstract] |
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FTP1.00077: Dynamical orientation effects in atomic ionization by impact of protons and positrons Daniel Fregenal, Ra\'ul Barrachina, Guillermo Bernardi, Sergio Su\'arez, Juan Fiol Recent results in ionization collisions with positrons and protons showed that just above the two-body threshold, for electron velocities close to the final projectile's velocity, the electron-projectile continuum dipole is narrowly oriented along the direction of motion of its centre-of-mass, with the negative charge pointing towards the residual target. Although a forward-backward asymmetry in the vicinity of the two-body threshold has been studied many year ago in ion impact ionization collisions, that was by far a much milder effect that left no fingerprint on the cusp position. Our results show that the phenomena is present for ionization by impact of both protons and positrons. In this communication, through measurements on H$^{+}$ + He and calculations we analyze in detail this effect that can be linked to a dynamical alignment of the two-body subsystem in the continuum. [Preview Abstract] |
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FTP1.00078: Kinetic and fluid equation treatments of non-equilibrium electron and positron transport in dense gases and liquids R.D. White, R.E. Robson, G. Boyle, W. Tattersall, S. Dujko, Z. Lj. Petrovic New frontiers in science and technology have generated a fresh wave of interest in understanding the fundamental physics of electron and positron transport processes in dense, structured and soft condensed materials. This paper focuses on the adaptation of gas phase scattering cross-sections to study the transport of electron and positron in dense systems where the effects of coherent scattering, and hence material structure, become important. In particular we focus on non-equilibrium situations where the electrons and positrons are driven out of equilibrium by an applied electric field, using a recently developed multi-term solution of a generalized Boltzmann's equation. The explicit effects of the material structure on the transport properties will be quantified. A fluid model derived from the generalized Boltzmann equation has furnished generalisations of Wannier energy relation and Einstein relations to account for the structure of the material. The accuracy and applicability of these relations will also be highlighted using various model and real systems. A scheme for the direct calculation of transport coefficients in dense gas/liquid systems from those in the dilute gas limit will also be presented. [Preview Abstract] |
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FTP1.00079: Evaluation of Cross Section for Electron Collisions with SF6 and BCl3 Mi Young Song, Deuk-Chul Kwon, Won-Seok Jhang, Jun-Hyung Park, Sung-Ha Hwang, Yeong-Kyeong Kang, Jung-Sik Yoon Electron-impact cross sections for SF6 and BCl3, including their radicals, are important in developing plasma processing. Low-energy electron collision data for these gases are sparse and only the limited cross section data are available. We interest to evaluate of cross section including various processes such as elastic and inelastic processes for electron collisions with SF6 and BCl3, including their radicals. The research objective is to provide a more complete data set for electron collisions with SF6 and BCl3, their radicals than those published before. We collected cross section data through journal, report, web database and reviewed available cross section data using critical evaluation rule. Through this processes, we determined a set of recommended values of cross section, as far as possible. The literature has been surveyed through early 2011. [Preview Abstract] |
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FTP1.00080: Mass and isotopic effects in the Li-Li$^{+}$ collision Moncef Bouledroua, Fouzia Bouchelaghem We suggest in this work to deal with the ion-atom collision. More precisely, the transport coefficients, the temperature-dependant mobilities, and the charge-transfer phenomena are examined quatum-mechanically. Also is examined the mass and isotopic effects and their behaviour with temperature. To do so, the interatomic potentials are constructed and then injected in the radial wave equation to determine the phase shifts. [Preview Abstract] |
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FTP1.00081: Effective charge fraction for ions bombarding SiC Juana Gervasoni, Leonardo Bianco, JuanCarlos Furnari One of the main problems in the interaction of charged particles with solids is the transfer of charged among them. The purpose of this work is to use the Bohr's adiabatic criterion [1] to study the ion-stripping process in a collision event, taking into account the projectile electronic structure [2]. We analyze the effective charge fraction for different incident ions on silicon carbidecomposites, a new material that is being intensively investigated due to it presents many advantages for use in devices that involve working in extreme conditions as radiation damage [3]. \\[4pt] [1] J. L. Gervasoni and S. Cruz -Gimenez. Radiation Physics and Chemistry \underline {48}, 433-436 (1996). \\[0pt] [2] S. A. Serebrinsky, J. L. Gervasoni, J. P. Abriata and V. H. Ponce. Journal of Materials Science \underline {33}, 167-171 (1998) \\[0pt] [3] I. Shibahara. Radiation Effects {\&} Defects in Solids, vol. 144, (1998) pp. 233-250. [Preview Abstract] |
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FTP1.00082: Young-type oscillations in the autoionizing He$^{2+}$ + H$_2$ double capture collision: A new challenge for theoreticians R.O. Barrachina, B.S. Frankland, J.-Y. Chesnel, F. Fremont We study the Young-type process, He$^{2+}$ + H$_2$ $\rightarrow$ He$^{**}$(2l nl', n $\geq$ 2) + 2 H$^{+}$, where the autoionizing Helium outgoing projectile plays the role of the source of a single electron, while the two residual protons provide a double-center interferometer. The autoionization lines are found to oscillate with the angle in the range 90-170 degrees, in agreement with previous expectations. However, as shown in this communication, our experimental results do not agree with the available theoretical models in some key issues. For instance, the loci of the oscillations in momentum space do not coincide in theory and experiment, except in the neighborhood of the backward direction. Some hints on the possible origin for these disagreements will be discussed in detail at the conference. [Preview Abstract] |
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FTP1.00083: PLASMA DIAGNOSTICS TECHNIQUES I |
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FTP1.00084: Time resolved measurement of charged particle distributions at electrodes in rf and pulsed plasma discharges David Gahan, Paul Scullin, Boris Dolinaj, Donal O Sullivan, Mike Hopkins Retarding field energy analyzers (RFEAs) are commonly used to measure the ion energy distribution function (IEDF) in plasma reactors. When deployed on grounded surfaces the RFEA design can be relatively simple due to the absence of large voltages. At biased surfaces the RFEA design is more complex. Filtering techniques need to be implemented to ensure the RFEA floats at the substrate holder potential. In cases where the discharge and/or substrate holder are driven with a pulsed bias the time resolved IEDFs through the pulse cycle are desirable. Time resolved measurements at a pulsed bias surface are more complicated, mainly because of the need to incorporate low pass filters with high input impedance to allow the RFEA to float at the bias potential. Here, we present a summary of the time resolved measurement capabilities of a RFEA in pulsed plasmas. Time resolved energy distributions of charged species are measured at the grounded electrode in capacitively coupled plasmas. The time resolved IEDFs at a biased electrode are also measured. The RFEA body is allowed to float at the bias potential using low pass filters and a novel technique is implemented to allow time resolution of the IEDF during the bias period. Time resolution of 100ns, at frequencies up to 500 kHz is demonstrated. [Preview Abstract] |
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FTP1.00085: Doppler-free spectra of Balmer-$\alpha$ line of atomic hydrogen measured by saturation spectroscopy in a linear magnetized plasma source Koichi Sasaki, Renge Asakawa, Motoshi Goto, Nader Sadeghi The resolution of conventional laser absorption spectroscopy is limited by Doppler broadening. Saturation spectroscopy is a technique to obtain a Doppler-free resolution, and is widely used in fundamental spectroscopy. However, applications of saturation spectroscopy to plasma diagnostics are rather limited. In this work, we developed a system of saturation spectroscopy at the Balmer-$\alpha$ line of atomic hydrogen with the intention of applying it to diagnostics of the Large Helical Device at the National Institute for Fusion Science. A probe beam ($<1$ mW) and a pump beam ($<200$ mW) were injected into a hydrogen plasma produced in a linear magnetized plasma source from the counter axial directions. We observed many dip components in the absorption spectrum of the probe beam. The dips were assigned to fine-structure components of the Balmer-$\alpha$ line with Zeeman splitting and their cross-over signals. The saturated absorption spectrum had broadband components in addition to the dips. We examined the depths of the dip and broadband components as functions of the pump laser power, the discharge power, and the discharge pressure. [Preview Abstract] |
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FTP1.00086: Development of Picosecond Electric Field Measurement by Coherent Four Wave Mixing Walter Lempert, Ben Goldberg, Sean O'Byrne, Igor Adamovich The development of a four wave mixing based, sub-nanosecond temporal resolution optical diagnostic for determination of electric field is presented. The method utilizes a high pressure hydrogen stimulated Raman shifting cell to produce a pump/Stokes beam pair from an input approximately 30 picosecond laser pulse at 532 nm. When the pump/Stokes beam pair is focused into a hydrogen containing discharge a coherent IR beam is generated at the wavelength corresponding to the fundamental hydrogen vibrational mode, 2.4 microns, the intensity of which is proportional to the square of the external field component parallel to the polarization of the input laser beams. Initial results have demonstrated field resolution of a few hundred volts/cm at 1 bar hydrogen pressure. The temporal resolution is limited by the relaxation time of the coherence induced by the pump/Stokes beam pair, the functional dependence of which upon pressure will be presented, along with characterization of the efficiency of the Raman shifting cell and a comparison of the sensitivity obtained using three different IR detectors. [Preview Abstract] |
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FTP1.00087: Transition flow of binary gas mixtures through small sampling orifices Rainer Johnsen, Mirko Vukovic Low-temperature plasma experiments often sample the gas mixture through a small orifice into a differentially-pumped mass spectrometer or other instruments. ~If gas mixture flow through the orifice is either in the molecular regime or in the transition regime between molecular and hydrodynamic flow, the relative concentrations of the gases in the mass spectrometer can differ significantly from that in the plasma chamber. The degree to which this occurs is poorly known from theory or experiment.~ We present results of ion-drift-tube measurements, in which ion-molecule reactions are used to determine the variation of the number density of a minority molecular gas as a function of the flow rate of a lighter or heavier atomic carrier gas. We find that the concentration of a heavier minority gas declines strongly with increasing carrier gas flow, while the effect is less pronounced when the minority gas is composed of molecules lighter than the carrier gas atoms. A semi-empirical formula, written in terms of the rare-faction parameter (essentially the reciprocal of the ``Knudsen number''), reproduces observations fairly well and may be a useful estimating tool. ~We are trying to develop more rigorous Monte Carlo computer code to the gas mixture flow through the orifice. [Preview Abstract] |
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FTP1.00088: Process Diagnostics and Monitoring Using the Multipole Resonance Probe (MRP) J. Harhausen, P. Awakowicz, R.P. Brinkmann, R. Foest, M. Lapke, T. Musch, T. Mussenbrock, J. Oberrath, A. Ohl, I. Rolfes, Ch. Schulz, R. Storch, T. Styrnoll In this contribution we present the application of the MRP in an industrial plasma ion assisted deposition (PIAD) chamber (Leybold optics SYRUS-pro). The MRP is a novel plasma diagnostic which is suitable for an industrial environment - which means that the proposed method is robust, calibration free, and economical, and can be used for ideal and reactive plasmas alike [1]. In order to employ the MRP as \emph{process diagnostics} we mounted the probe on a manipulator to obtain spatially resolved information on the electron density and temperature. As \emph{monitoring tool} the MRP is installed at a fixed position. Even during the deposition process it provides stable measurement results while other diagnostic methods, e.g. the Langmuir probe, may suffer from dielectric coatings.\\[4pt] [1] Lapke et. al., Appl. Phys. Lett. {\bf 93}, 051502 (2008) [Preview Abstract] |
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FTP1.00089: Investigation on Electric Field Excitation type MWR Probe Emi Kumazaki A plane-type microwave resonator (MWR) probe has been developed for electron density monitoring with less disturbance to the plasma. In a conventional case, the resonator was excited by MW magnetic field where the complex connection of the frequency-swept MW source was necessary. In this study, an electric-field-excited resonator was investigated to simplify the probe structure, and this excitation configuration was applied to a multi-resonance MWR probe for measurements of electron density and electron temperature. The probe has two slot resonators of 34 mm and 39 mm in length which are formed in a 0.1-mm-thick 28 mm square plane conductor. To excite the two resonators, only one MW-applied small rod conductor was used for one of the resonators. FDTD simulation revealed that even in such an excitation configuration, both the resonators were excited at different two frequencies of 1.88 GHz and 1.68 GHz similarly to the conventional magnetic field excitation. The resonance frequencies almost coincided with calculated ones under an assumption that the slot length is equal to a quarter wavelength of electromagnetic wave propagating the slot. These results suggested the electric field excitation enabling simple probe structure is useful for the multi-resonance MWR probe. [Preview Abstract] |
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FTP1.00090: Data Processing from Micro-Plasma Gas Analytical Sensor Alexander Mustafaev, Alexander Tsyganov Theoretical consideration of signal formation at micro-plasma gas analyzer based on Collisional Electron Spectroscopy (CES) and experimental results on CES sensor are presented. It is demonstrated that a diffusion path confinement for characteristic electrons provides a possibility to measure electrons energy distribution function (EEDF) and to find characteristic spectra of species at high (up to atmospheric) gas pressure. Simple micro-plasma CES sensor of two plane parallel electrode configuration with current-voltage measurement in afterglow discharge may be operated in two possible modes. The first mode presumes application of classic 2-nd derivative of current-voltage curve to select characteristic peaks in electron energy spectra of the species to be detected. In the case of a deeper collisional dissipation of characteristic peaks, a 3-rd derivative may be used. Said derivatives were obtained by differentiating of a spline providing least-squares approximation of current-voltage curve. Model and experimental electron energy spectra of pair \textit{He} metastables collisions in dependence of inter-electrode gap are discussed. [Preview Abstract] |
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FTP1.00091: Mass spectrometry of metastable species during plasma processing J.A. Rees, S. Davies, C.L. Greenwood, D.L. Seymour Among the techniques in common use for mass spectrometric studies of processing plasmas, the so-called ``threshold ionisation'' (TI) method for examining the neutral species generated in a plasma has been particularly useful. In the past, the technique has been applied using source pressures in the mass spectrometer of about 10$^{-6}$Torr. With the current availability of particle detectors which can be operated at much higher pressures, it is of interest to examine possible extensions of the TI technique. The present data for mass spectrometer pressures of up to 4.10$^{-4}$Torr, using gas mixtures which include rare gases, show clearly the generation of long-lived metastable atoms of the inert gases in both the source of the mass spectrometer and in the plasmas. For gases such as oxygen, generation of metastable species in the mass spectrometer source is also observed. The interpretation of the experimental threshold ionisation data is discussed. The measurements suggest new avenues of research for both gas analysis and plasma diagnostics for gases having long-lived, metastable states. [Preview Abstract] |
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FTP1.00092: Experimental Study on a Radial Uniformity in 2f-CCP Based on the Density Distribution of Metastable Ar(1s$_5$) by Way of an OES Takashi Yagisawa, Tomihito Ohba, Toshiaki Makabe The use of different frequencies to a two-frequency capacitively coupled plasma (2f-CCP) realizes an independent control between of a high density plasma generation by VHF electrode and of a high-energy ion impact onto a wafer by LF bias. Metastables with a long lifetime in gas phase make large contributions to the maintenance of high density plasma through multistep ionizations. Density distribution of non-emissive metastable can be optically measured by a careful choice of emission lines consisting of upper resonant state and lower short- and long-lived state [1]. In this paper, our discussion will be devoted on the radial uniformity in front of the wafer in the 2f-CCP driven by VHF and LF sources in Ar at 100 mTorr, based on the density distribution of metastable atom Ar(1s$_5$) measured by optical emission spectroscopy (OES). With increasing the voltage amplitude of LF bias, the area of metastable production moves from the center of the reactor to the edge of the electrode, resulting in the non-uniform density profile of Ar(1s$_5$). \\[4pt] [1] T. Ohba and T. Makabe, Appl. Phys. Lett. {\bf 96}, 11150 (2010). [Preview Abstract] |
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FTP1.00093: ABSTRACT WITHDRAWN |
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FTP1.00094: CONTROL OF DISTRIBUTION FUNCTIONS |
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FTP1.00095: Kr ion Laser-Induced Fluorescence using a tunable diode laser near 729nm Greg Severn, Tim Welsh, Noah Hershkowitz We are working to produce an ion flow diagnostic for Kr II ions using diode laser based laser-induced fluorescence (LIF). We have found an atomic energy level scheme that is accessible to diode lasers: $^{4}D_{7/2} \rightarrow$ $^{4}P_{5/2}^0 \rightarrow$ $^{4}P_{5/2}$. Excitation is nominally at 729 nm, and the detected photon is nominally at 473 nm. The metastable state, $^{4}D_{7/2}$, should be the one most populated in the low temperature plasma discharges that we will create for these experiments ($T_e \sim 1 eV, T_i \sim 1/40 eV, n_i \sim 10^9 cm^{-3}$). The extended cavity diode laser is in the Littrow configuration (Sacher-Lasertechnik TEC-100-0730-20). LIF measurements of molecular iodine will be made simultaneously and will be compared with the molecular iodine absorption spectrum measurements of Gerstenkorn \& Chevillard for absolute wavelength calibration. Successful completion of these experiments will provide a new ion velocity diagnostic for Kr ions which will aid in at least 3 basic plasma science experiments: 1) Hall Thruster ion plume measurements, 2) sheath formation in the case of multiple ion species plasmas (with 3 ion species), and 3) studies of the comparison between ion velocities of metastable state rare gas ions and known ground state ion mobilities. [Preview Abstract] |
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FTP1.00096: Simulating Electron Scattering in Cold-Cathode Discharges Alexander V. Khrabrov, Igor D. Kaganovich Accurate representation of anisotropic scattering in collisions is required for particle simulations of plasmas with energetic ($10^2$-$10^3$ eV) electrons, especially in weakly collisional regimes. A high-voltage glow discharge in helium is a good example. Electron multiplication in the cathode layer occurs with only a few ionizing collisions per each primary electron. Thus the flux of energetic electrons, which provide ionization in the negative glow, depends on the structure of the strongly anisotropic electron velocity distribution in the cathode fall. To simulate the discharge kinetics, defined by non-local transport and non-Maxwellian distributions, one needs to correctly represent the angular scattering of electrons on atoms within a large energy range. In simulations, the scattering should adequately reproduce the macroscopic transport properties and also allow rapid sampling of the probability distribution. An important condition for the model differential cross-section is that it should yield the correct value of the transport (momentum-transfer) cross section as a function of electron energy. We present a practical approximation of energy-dependent scattering in helium for energies between 0.01 and 1000 eV, with correct asymptotic behavior at higher energies. [Preview Abstract] |
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FTP1.00097: An Industry Viewpoint on Electron Energy Distribution Function Control Peter Ventzek It is trite to note that plasmas play a key role in industrial technology. Lighting, laser, film coating and now medical technology require plasma science for their sustenance. One field stands out by virtue of its economic girth and impact. Semiconductor manufacturing and process science enabling its decades of innovation owe significant debt to progress in low temperature plasma science. Today, technology requires atomic level control from plasmas. Mere layers of atoms delineate good and bad device performance. While plasma sources meet nanoscale specifications over 100s cm scale dimensions, achieving atomic level control from plasmas is hindered by the absence of direct control of species velocity distribution functions. EEDF control translates to precise control of species flux and velocities at surfaces adjacent to the plasma. Electron energy distribution function (eedf) control is a challenge that, if successfully met, will have a huge impact on nanoscale device manufacturing. This lunchtime talk will attempt to provide context to the research advances presented at this Workshop. Touched on will be areas of new opportunity and the risks associated with missing these opportunities. [Preview Abstract] |
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