Bulletin of the American Physical Society
72nd Annual Gaseous Electronics Conference
Volume 64, Number 10
Monday–Friday, October 28–November 1 2019; College Station, Texas
Session FT1: Poster Session I |
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Room: Kyle Field HOC |
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FT1.00001: Low Energy Elastic Electron Scattering from Propyne-C$_{\mathrm{3}}$H$_{\mathrm{4}}$ B Hlousek, M Zawadzki, Murtadha A Khakoo Experimental differential cross sections for electron scattering from gaseous C$_{\mathrm{3}}$H$_{\mathrm{4}}$ are presented. The measurements employed the relative flow method with a moveable aperture target gas delivery source [1], using helium [2,3] as standard. The moveable source enabled accurate determinations of background scattering [1]. The measurements were taken at incident electron energies of 1 eV to 30 eV and scattering angles of 10$^{\mathrm{o}}$ to 130$^{\mathrm{o}}$. Comparisons to any existing calculations will be made. [1] M. A. Khakoo \textit{et al}., J. Phys.B. \textbf{40}, 3601 (2007). [2] R. K. Nesbet, Phys. Rev. A \textbf{20}, 58 (1979). [3] D. F. Register et al. Phys. Rev. A \textbf{21}, 1134 (1980). [Preview Abstract] |
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FT1.00002: Study on the Effect of Laser on the Energy Deposition of ion in two-component Plasma Targets Guiqiu Wang, He Yi, Yujiao Li, Yaochuan Wang, Dajun Liu In this paper, we study the effect of laser field on the Coulomb explosion and stopping power of molecular ions in two-component plasma targets. In particular, the effect of plasma excitation on the behavior of molecular ions in intense laser field is discussed. In the absence of laser field, plasma is usually regarded as only electrons participating in the response. However, with the increase of laser field intensity, the behavior of ions becomes more and more important. Therefore, the behavior of ions shouldn't be ignored in the case of strong laser field. Their excitation in the case of strong laser field is considered, especially in the case of low-speed incident ion beam. The influence of ions in the body is very important. In this paper, we study the effects of laser field parameters and plasma parameters on the Coulomb explosion and blocking ability of molecular ions by using molecular dynamics simulation method, taking into account the dielectric function of two-component plasma. In the framework of linearized Volasov-Poisson theory, we numerically solve the equation of motion of ions. The results obtained have certain guiding significance and reference value for related experiments. [Preview Abstract] |
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FT1.00003: Production of antimatter molecular ions Mark Zammit, Michael Charlton, Svante Jonsell, James Colgan, Jeremy Savage, Dmitry Fursa, Igor Bray, Christopher Fontes, Jeffery Leiding, David Kilcrease, Peter Hakel, Eddy Timmermans Recent years have seen marked progress in the production of, and experimentation with, atomic antimatter in the form of antihydrogen, $\overline{{\rm H}}$. Now we investigate the feasibility of producing the anti-molecular hydrogen anion, $\overline{{\rm H}}_2^-$ (analogue of ${\rm H}_2^+$, consisting of two antiprotons and a positron), in the laboratory. Recently Myers [1,2] argued that spectroscopic investigations of the anti-anion can offer very sensitive tests of the CPT theorem, which is one of the primary motivations for undertaking experiments with antimatter systems. Taking into account the present day ALPHA $\overline{{\rm H}}$ trap [3], utilizing reaction rates calculated here, from the literature, and via detailed balance, key processes are identified that could lead to the anion production. The feasibility of these reactions are discussed in the context of present day and near future experimental capabilities. [1] E. G. Myers Phys. Rev. A {\bf 98}, 010101(R) (2018). [2] E. G. Myers Hyperfine Interact. {\bf 239}, 43 (2018). [3] C. Amole et al. Nuc. Inst. Meth. In Phys. Research A {\bf 735}, 319 (2014). [Preview Abstract] |
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FT1.00004: The LXCat project: a status report Wouter Graef, Jan van Dijk, Matthew Hopkins, Leanne Pitchford, Benjamin Yee LXCat is an open access website for archiving and manipulating data needed for modeling the charged particle components of low-temperature plasmas (LTP). The data include electron-neutral scattering cross sections (both as complete sets suitable for use with Boltzmann solvers, as well as total or differential cross sections), electron oscillator strengths, ion scattering cross sections, and transport and rate coefficients. LXCat hosts many databases contributed by members of the LTP community. In some cases data for the same process exist in multiple databases due to different sources or needs. While no judgment is made of the relative merit of such data, the site facilitates visitors in making their own comparisons. Related tools include mechanisms for plotting and downloading the data, and an on-line Boltzmann solver which uses complete sets of cross sections to generate transport and rate coefficients that can then be compared with experimental data or used in modeling tools. Since its inception in 2010, over 50 international volunteers have participated in this project. The organization requires work on many fronts including data contributors, site developers, and the outreach team. Those interested in sustaining this vital community resource should contact the authors. [Preview Abstract] |
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FT1.00005: Electron Scattering Time-of-Flight Studies of Electron Impact Excitation of CO, N$_{\mathrm{2}}$ and H$_{\mathrm{2}}$O M Zawadzki, M. A. Khakoo Experimental inelastic to elastic scattering ratios of electron scattering from gaseous CO, N$_{\mathrm{2}}$ and H$_{\mathrm{2}}$O are presented from near-threshold excitation incident electron energies to 30eV and for scattering angles of 20$^{\mathrm{o}}$ to 130$^{\mathrm{o}}$. The measurements were taken with a time-of-flight electron spectrometer [1]. They will be presented together with existing high resolution electrostatic electron spectrometer measurements of our laboratory and those of [2,3,4]. Comparisons to existing theoretical cross sections will also be presented [5]. [1] M. Zawadzki \textit{et al}. Phys. Rev. A \textbf{97} 050702(R) (2018). [2] J. Zobel et al., J. Phys. B, \textbf{29} 813 (1996). [3] P. W. Zetner et al., J. Phys. B, \textbf{31} 2395 (1998). [4] A. G. Middleton et al., J. Phys. B, 26 1743 (1993). [5] On-going collaboration: R-Matrix calculations of Drs. Jonathan Tennyson (UCL, London), Amar Dora (N. Orrisa University, India) and Zdenek Masin (Charles University, Prague). [Preview Abstract] |
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FT1.00006: Electron-impact vibrational excitation of molecular hydrogen Dmitry Fursa, Liam Scarlett, Jeremy Savage, Igor Bray, Mark Zammit Electron-impact vibrational excitation of molecular hydrogen in the ground electronic state is one of the most fundamental processes in electron-molecule scattering. The production of vibrationally-excited H$_2$ is of importance in modelling hydrogenic plasmas, as the cross sections for electronic excitation and dissociation have a strong dependence on the initial vibrational level. Above the electronic inelastic threshold, the dominant mechanism for vibrational excitation is electronic excitation followed by radiative cascade. Modeling this process requires a fully vibrationally-resolved description of the scattering problem. Previous calculations were performed with the impact-parameter method [Celiberto \emph{et al}, At. Data Nucl. Data Tables \textbf{77} (2001) 161], which is known to significantly overestimate cross sections. Using the CCC method, we have performed calculations of excitation-radiative-decay leading to vibrational excitation of H$_2$ [Scarlett \emph{et al}, Plasma Sources Sci. Technol. \textbf{28} (2019) 025004]. At lower energies, direct vibrational excitation is the only mechanism for producing vibrationally excited H$_2$. Here we also present vibrational close-coupling calculations of electronic-elastic vibrational excitations at low energies. [Preview Abstract] |
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FT1.00007: Free-free experiments: dressed-atom effects during inelastic electron scattering B.N. Kim, C.M. Weaver, N.L.S. Martin, B.A. DeHarak Free-free experiments investigate the absorption or emission of radiation during the collision of charged particles with atoms and molecules. The first experimental observation of dressed-atom effects -- due to the electric field of the laser -- during the elastic scattering of electrons by Xe were reported by Morimoto {\em et al}.\footnote{Y. Morimoto, R. Kanya, and K. Yamanouchi, Phys.\ Rev.\ Lett.\ {\bf 115}, 123201 (2015)} Their results were compared with an analytical expression by Zon that contains the electric dipole polarizability $\alpha$ of the target.\footnote{B. A. Zon, Sov. Phys. JETP 46(1), 65 (1977)} We are investigating dressing effects for {\em inelastic} electron scattering in the presence of a Nd:YAG laser; specifically we are investigating electron-impact excitation of the lowest excited states of He and Ar. Zon's expression is not valid for {inelastic} scattering so we have developed an equivalent inelastic expression. We will give the results of a simple calculation for dressing effects for the excited states of He, and will give a progress report on our experiments. [Preview Abstract] |
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FT1.00008: First-Principles Molecular Spectra of Air Mark Zammit, Julie Jung, Jeffery Leiding Comprehensive and highly accurate rovibronic spectral measurements of air molecules are critical to the modeling of low-temperature plasmas and air in extreme conditions. However, with the lack of experimental data, first-principles approaches are key to generating complete molecular line lists. Here, we will discuss the methodology employed for the accurate calculation of molecular rovibronic states, and present emission and equation of state results for NO and OH, which form in significant abundance in air under extreme conditions. [Preview Abstract] |
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FT1.00009: INPTDAT---a new data platform for plasma tech\-nology M. M. Becker, I. L. Paulet, St. Franke, D. O'Connell In recent years, the need for public storage of digital research data has steadily increased. Besides institutional or public data repositories like, e.g. figshare and zenodo, more and more journal publishers provide the possibility to store digital data along with journal articles. However, the findability of data in such generic repositories is rather limited and the benefit of publishing digital research data is not obvious to researchers. The new interdisciplinary data platform for plasma technology---INPTDAT aims to overcome this issue. INPTDAT uses the plasma-specific metadata schema Plasma-MDS for the annotation of research data stored in the internal database or any other public data repository. With this, relevant data become easily findable and directly accessible for researchers. This contribution demonstrates the main features of INPTDAT and shows how it could be used in the future as a central community platform for annotation and easy reuse of research data in the field of plasma technology. [Preview Abstract] |
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FT1.00010: 3D topological plasma photonic crystal with surface plasmon and Fano-resonance modes Benjamin Wang, Jesse Rodriguez, Mark Cappelli A 3D woodpile structure tunable plasma photonic crystal is designed, simulated, and experimentally characterized over the S-X band of the electromagnetic spectrum. The crystal has individually tunable elements, allowing for dynamically reconfigurable operating modes within the crystal. The photonic crystal's reconfigurability, achieved through individual discharge control of the properties of the woodpile plasma columns, allows for tuning of the interactions between both the Bragg and localized surface plasmon modes which dominate the spectrum at lower frequencies. Experiments and simulations show coupling of Bragg and surface plasmon modes through Fano resonances interactions between dimensional layers. Interesting topological effects of the 3D crystal are investigated. [Preview Abstract] |
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FT1.00011: A Switchable Magnetized Plasma Cloak Jesse Rodriguez, Ben Wang, Mark A. Cappelli Dirac-like conical dispersion with double degeneracy at the $\Gamma$ symmetry point can be exploited to cloak objects embedded in a photonic crystal. Here we describe two configurations for a switchable cloaking device that is based on transmission at such a point in a square lattice two-dimensional magnetized plasma photonic crystal. Finite difference time domain simulations are used to identify the plasma and geometric parameters for Dirac-like dispersion. The transverse electric (TE) configuration results in good closure on the transmitted phase fronts and cloaking due to wavefront reshaping. The dispersion shows the expected three-fold degenerate linear branch crossings at the Dirac-like point as seen in square lattice dielectric photonic crystals. We also explore a transverse magnetic (TM) configuration which is much more promising as the photonic crystal response in the vicinity of the Dirac Point appears to behave as a zero index material (ZIM). The required plasma conditions needed for this plasma cloak should be achievable with plasma discharges that have been used in the past to study the response of non-magnetized plasma photonic crystals with the additional requirement of a high-strength electromagnet ($\sim$0.2 T-0.6 T). [Preview Abstract] |
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FT1.00012: Current Control Capabilities in Unstable Discharge Mode. Aleksandr Mustafaev, Boris Klimenkov, Artyom Grabovsky, Victor Kuznetsov This talk continues studies of the effect of grid current control of cesium-barium vapor current modulator in the unstable mode of plasma discharge, which were presented in [1]. It is shown that the modulator in the non-stationary mode is promising not only from the point of view of limiting parameters, but also from the point of view of control efficiency. Full current modulation is provided by the forming of nonlinear plasma structures during the excitation of the electronic instability of Bursian-Pierce. It is shown that in this mode, in the interelectrode gap, a potential distribution with a virtual cathode is formed, leading to a break of the electron current. In this case, the current in the triode changes almost instantaneously, since the process of the formation of a virtual cathode proceeds over a time of the order of the electron travel time through the gap. This is especially important for the successful practical application of triode modulators. A high electric strength has been implemented, which allows to keep the triode in the locked state after a current break for a long time. The role of the grid is reduced to maintaining the locked state of the triode and ensuring high electric strength. [1] A. Mustafaev, B. Klimenkov, A. Grabovskiy, V. Kuznetsov. 71st Annual Gaseous Electronics Conference, GEC18, 5-9 November 2018. Portland, OR, USA. [Preview Abstract] |
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FT1.00013: Spatial inhomogeneous distribution of high Si-H$_{\mathrm{2}}$ bond density in a-Si:H films deposited by MHPCVD. Hisayuki Hara, Yuan Hao, Kohei Abe, Daisuke Yamashita, Kunihiro Kamataki, Naho Itagaki, Kazunori Koga, Masaharu Shiratani Hydrogenated amorphous silicon (a-Si:H) solar cells are promising as a power sources for IoT devices because of its flexible features and a low production cost. t Si-H$_{\mathrm{2}}$ bond density in the films tends to correlate with light-induced degradation degree; leading to 20{\%} reduction of efficiency. The high Si-H$_{\mathrm{2}}$ bond density regions are located at random in the plane. That is one of the problems for industrial production. To decrease Si-H$_{\mathrm{2}}$ bond density and to make the better film uniformity, we study the spatial distribution of Si-H$_{\mathrm{2}}$ bond density in the plane as a parameter of substrate temperature. A-Si:H films were deposited on Si substrate by using a multi-hollow discharge plasma CVD method with a cluster-eliminating filter. Spectra of Si-H$_{\mathrm{2}}$ bond (2090cm-1) and Si-H (2000cm-1) were measured by FTIR spectrometer and from their peaks the I$_{\mathrm{SiH2}}$/I$_{\mathrm{SiH}}$ values are obtained. The spatial aperture size was 50 um x 50 um, and a total 900 points were measured in 30 rows and 30 columns (1.5mm x 1.5mm). The average value of I$_{\mathrm{SiH2}}$/I$_{\mathrm{SiH}}$ decreases from 0.23 at 170${^\circ}$ to 0.022 at 250${^\circ}$ and its uniformity becomes better as well. I will report the results with some images of distribution of Si-H$_{\mathrm{2}}$ bonds and the frequency distributions of Si-H$_{\mathrm{2}}$ bonds. [Preview Abstract] |
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FT1.00014: Characterization of high-pressure carbon dioxide glow discharge approaching supercritical conditions. Gregory Belk, Isaac Yaghi, Tanvir Farouk A plasma reactor capable of operating at supercritical conditions has been designed and fabricated. The reactor allows for the initiation of plasma discharges in different feed gases at their respective supercritical conditions to conduct the necessary diagnostics. As a test case, experiments were conducted with carbon dioxide as the feed gas for a dc power driven plasma discharge. Despite the extensive studies done on glow discharges in a variety of conditions, literature centered around characterizations of these plasmas in high-pressure environments, and more specifically for supercritical conditions, is lacking. This study aims to experimentally observe dc driven glow discharges between a pointed anode and flat cathode in carbon dioxide and to conduct the necessary characterization. Voltage-Current characteristics, current density measurements and visualizations of the discharges relative to the VI distributions were gathered for pressures beginning at 1 atm and increased up to 75 atm within the test cell. Emission spectroscopy was used to determine localized species and measure spatially averaged gas temperatures between the electrodes. We envision that the data gathered could prove vital for validation of plasma kinetics associated with gaseous carbon dioxide. [Preview Abstract] |
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FT1.00015: Rotational Non-Equilibrium of CO Excited States in Microwave Discharge CO$_2$ Plasma Shota Yamada, Yuki Morita, Atsushi Nezu, Hiroshi Akatsuka Carbon dioxide plasmas are widely studied for practical engineering. For example, they are applied to CO$_2$ laser technologies and considered as the decomposition process of CO$_2$ into CO, etc. However, in these plasmas containing CO$_2$ or CO, the excitation kinetics of electronically excited states of the CO molecule are not fully understood yet. In this study, spectroscopic characteristics of the CO Angstrom band in microwave discharge CO$_2$ plasma is investigated, and a discussion comparison the third positive system (3$^{rd}$ PS) of CO. For this purpose, vibrational temperature $T_v$ and rotational temperature $T_r$ of the CO excited states in low-pressure CO$_2$ plasma are investigated. Angstrom band spectra of CO are calculated theoretically as functions of $T_v$ and $T_r$, after which a fitting is conducted to analyze experimental results. The best theoretical fitting is obtained using two-rotational temperature, a bulk component $T_r$ = 0.04 eV with high energy tail $T_r$ = 0.17 eV, occupying 3/4 and 1/4 fraction of the number density, respectively. For the vibrational temperature $T_v \approx$ 0.4 eV is found as a unique value. From comparing these results with the CO 3$^{rd}$ PS values, it is turned out that there is a difference of 0.11 eV as to the value of $T_r$. [Preview Abstract] |
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FT1.00016: Electron kinetics in fast-pulsed discharges Luis Alves, A. Tejero-Del-Caz, V. Guerra, N. Pinhao, C.D. Pintassilgo, T. Silva This work presents a comparative study of the electron kinetics in fast-pulsed discharges produced in dry air (80{\%} N$_{\mathrm{2}}$ - 20{\%} O$_{\mathrm{2}})$, considering a quasi-stationary and a time-dependent solution of the electron Boltzmann equation (EBE), written under the classical two-term approximation. The simulations were performed using the open-source LisbOn KInetics Boltzmann solver (LoKI-B) [1,2], which handles simulations in any atomic / molecular gas mixture, considering first and second kind collisions with any target state (electronic, vibrational and rotational), characterized by any user-prescribed population. The original capabilities of LoKI-B have been extended in order to obtain the time-dependent solution of the EBE for a pulsed electric field. Noticeable deviations, between the quasi-stationary and the time-dependent calculations of the electron energy distribution function and related macroscopic coefficients, are observed below the microsecond scale, for a pulse peaking at 45 Td with rise and fall times of \textasciitilde 1$\mu $s and \textasciitilde 10$\mu $s, respectively. \newline [1] A. Tejero-del-Caz \textit{et al}, Plasmas Sources Sci. Technol. \textbf{28} (2019) 043001 \newline [2] \underline {https://github.com/IST-Lisbon/LoKI} [Preview Abstract] |
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FT1.00017: Ionization Costs in Air and Argon Plasmas Sustained by High Voltage Repetitive Nanosecond Pulses Vladlen Podolsky, Andrei Khomenko, Samuel Rowe, Sergey Macheret Previous research [Phys. Plasmas, vol. 13, no. 2, pp. 1--10, 2006] has shown that a key benefit of utilizing repetitive nanosecond pulses for the generation of plasma is low power budget, with the ionization cost per electron close to the Stoletov's minimum. This work expands on previous experiments in air and introduces new results in argon over a pressure range of 1-10 Torr, pulse repetition frequencies of 0.1 -- 30 kHz, and applied voltages of 1.5-7 kV. The electron density was measured with a 58.1 GHz microwave interferometer while the voltage and current profiles to determine the deposited energy were measured using both a back current shunt and V-I probes. The results indicate that, as expected, the ionization cost in argon is lower than that in air, and the ionization costs in both gases approach the Stoletov's minima. In argon, the measured ionization cost increases with voltage at all pressures tested, while in air, a decrease in cost occurs at higher pressures as voltage is increased. This suggests that most of the ``excess'' voltage applied falls on the cathode sheath, and the electric field in the quasineutral plasma is within a factor of 2 of the Stoletov's field. These experimental results are found to agree well with 1-D drift-diffusion modeling. [Preview Abstract] |
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FT1.00018: Nonequilibrium nitrogen excitation in NS discharge Andrey Starikovskiy, Arthur Dogariu, Jacob George, Benjamin Goldberg, Richard Miles Nanosecond pulsed discharges are now widely used as a source of a spatially homogeneous, strongly nonequilibrium plasma. To create relatively dense, highly excited plasma in a few nanoseconds, it is necessary to maintain high values ??of the reduced electric field E/n, which ensures ionization of the gas. Experimental analysis and numerical modeling shows that under conditions of pulsed periodic discharges at high values ??of the reduced electric field, it is possible to effectively populate the vibrational levels of nitrogen. The difference from discharges at low reduced fields is the change of the population mechanism. If at low electron energies the main mechanism is the direct excitation of vibrationally excited states by electron impact, then at high values ??of the field (and mean electron energy) the main mechanism is the recombination flux to high-energy levels and redistribution of this population during the VT relaxation and VV exchanges. [Preview Abstract] |
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FT1.00019: Effects of long-lived electronically excited reactive oxygen and nitrogen species in non-equilibrium gas-discharge plasma of apokamp-type. Vitaly Datsyuk, Igor Izmailov, Vadym Naumov, Vladimir Khomich, Vyacheslav Tsiolko Non-equilibrium plasma in high-voltage gas discharges of the so-called apokamp type (blue jets, red sprites) is of great interest for science and practice [1]. But, despite the advances in apokamp plasma physics, the mechanism of apokamp plasma chemistry is not very clear, in particular, concerning electronically excited reactive oxygen and nitrogen species (RONS). We tried to study this issue in more detail. Experiments were done in various oxygen-nitrogen mixtures employing electrical and optical diagnostics. Measurements showed that apokampic plasma processes are accompanied by the formation of long-lived RONS. Computational modeling by using 0D-kinetic and 1D-fluid models, including ionization, excitation, dissociation-recombination, vibrational relaxation, collisional quenching, and radiation, revealed the most probable mechanisms of plasma-chemical reactions in apokamp plasma jets. Effects of metastable RONS involving singlet oxygen $O_{2}^{\ast } (a,b)$, $O^{\ast }({ }^{1}D)$ and nitrogen $N_{2}^{\ast } (A)$, $N^{\ast }({ }^{2}D)$ were examined. The study confirms the role of long-lived RONS in apokamp plasma and indicated the way to a more efficient apokamp process. [1] E.A. Sosnin et al., JETP Lett. 103 (12):761 (2016). [Preview Abstract] |
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FT1.00020: Experimental electron density and temperature measurements following a high voltage nanosecond pulsed atmospheric spark discharge. Jared Miles, Steven Adams, Chase Murray, Ajani Ross, Kristina Lemmer, Jacob Russell Nanosecond-pulsed high-frequency discharges (NPHFD) have been shown to efficiently create high electron densities using less power than traditional DC discharges. To better understand the phenomenon caused by the high repetition rate, electron density and temperature measurements were taken following a single high voltage pulse and after multiple pulses applied at frequencies up to 300 kHz. The 10 ns duration pulses have peak voltages up to 15 kV and are applied to a 2 mm gap pin to pin discharge configuration open to atmospheric air conditions. Densities and temperatures were measured via Thomson scattering of a 532 nm laser, with evidence of electron densities on the order of 1E14 cm$^{\mathrm{-3}}$ existing 10 microseconds after the first pulse. At these relatively long times after the discharge, the electron temperature was measured to be less than 1 eV. We posit that these electrons aid in the ignition of pulse discharges that follow and allow coupling between higher repetition high voltage pulses, which have been observed in other work. Electron temperatures and densities will be presented for multiple times after the discharge in addition to data showing that the measured electrons are remnants of the nanosecond discharge and not from other sources such as photoionization. [Preview Abstract] |
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FT1.00021: Axial Ionization Modes in Hall Thruster Oleksandr Chapurin, Ivan Romadanov, Andrei Smolyakov, Yevgeny Raitses, Sarah Sadouni, Gerjan Hagelaar The axial instability in thruster channel associated with self consistent fluctuations of the electric field and ionization, commonly known as a breathing mode, and accompanied by strong oscillations of the discharge current, is one of the most violent instability in Hall thrusters. We study the physical mechanisms, criteria for the instability, including the role of boundary conditions, temperature evolution and axial resistive instabilities. The results of the fluid and hybrid simulations are compared and the reasons for the differences are investigated. [Preview Abstract] |
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FT1.00022: Paschen Curves for Pulsed Breakdown Dmitry Levko, Robert Arslanbekov, Vladimir Kolobov The influence of the voltage rise time on the Paschen curves is analyzed using kinetic and fluid models. The Paschen curves, which describe the dependence of the breakdown voltage, $U_{br}$, on the product \textit{pd} of gas pressure $p $and the characteristic length $d $between the electrodes, have minima that correspond to optimal conditions for plasma generation. It is shown that both kinetic and fluid models predict the experimentally observed shift of the curves toward higher voltages and the shift of the Paschen minima toward higher values of \textit{pd }with decreasing the voltage rise time $\tau $. On the right branch of the Paschen curves, the agreement between both models is obtained for all $\tau $. We confirm that the minimum of the Paschen curves corresponds to conditions of electron runaway. At the left branch, the electron velocity distribution function is non-local in space and also non-local in time. [Preview Abstract] |
(Author Not Attending)
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FT1.00023: OpenFOAM Implementation of Electromagnetic Field Solver for Fluid Model Applications Benjamin Marshall, Venkattraman Ayyaswamy Electromagnetic effects in plasmas are relevant to various applications from plasma-based propulsion to nanomaterial synthesis. These systems require the Maxwell's equations for wave propagation be combined with fluid model equations that describe the plasma itself. The work presented here is intended to improve our in-house finite volume (FVM) plasma code by implementing an FVM-based electromagnetic field solver. Traditionally, the preferred method for solving the Maxwell's equations has been based on the finite difference or finite element method. The current work utilizes a finite volume time domain method approach to determine the electromagnetic fields (in contrast to a potential form). Explicit discretization of the Maxwell's equations was done using various schemes derived from fluid dynamics and are compared with each other. The importance of constructing the fluxes based on the propagation of both left and right characteristics is emphasized. Results are shown for 1-D electromagnetic wave propagation as well as scattering of an incident wave by a dielectric. Results are compared to current literature. The finite volume time domain approach to solving the Maxwell's equations will greatly extend the capabilities of the solver to deal with wave-plasma interactions. [Preview Abstract] |
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FT1.00024: On the divergence of plasma potentials measured by cylindrical Langmuir probes and emissive probes in the presheath Greg Severn, Eugene Wackerbarth, Peixuan Li, Noah Hershkowitz It is conventional wisdom that Langmuir probes (LPs) do not work in the sheath near material boundaries, but are supposed to yield accurate measurements of plasma potentials in quasineutral plasma. Experiments that compared plasma potential measurements made by partially coated and uncoated LPs and cylindrical LPs with measurements made by emissive probes, were performed in low pressure unmagnetized argon discharges ($0.1\leq P_n \leq 1mTorr$), with electron temperatures and densities between 1 and 5 $eV$, and $ 1 \times 10^9$ and $ 1 \times 10^{10} cm^{-3}$, respectively. Presheaths were set up in the plasma using negatively biased electrodes. We used both grids and plates for the biased electrode. Results indicate that the emissive probe potential measurements (in the limit of zero emission) were more negatve than LP measurements in the presheath. In the sheath, most LP measurements did not go negative but rather became increasingly positive. Only the emissive probe measurements worked in the sheath. These divergences are thought to be caused by the inherent, diffuse, ion flow in the presheath region toward the negatively biased electrode, characteristic of sheath formation. [Preview Abstract] |
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FT1.00025: Surface flashover of machinable ceramic insulators Laura Biedermann, Ricky Tang, Joseph Howard Machinable ceramics are frequently used to provide high-voltage insulation in vacuum and low-pressure applications. Surface flashover for these insulators occurs as a multi-stage process: cathodic triple-point emission initiates secondary electron emission (SEE) from the ceramic surface. If a positive feedback loop develops, flashover occurs as Townsend breakdown of desorbed gas species. To increase the voltage hold-off strength, ceramics may be coated with a semi-conductive coating to decrease the SEE yield. Hold-off strengths of cylindrical ceramic samples are measured in a nearly-uniform electric field as a function of background gas pressure and composition. Following conditioning, these coated ceramics exhibit stable, reproducible hold-off strengths with individual flashovers occurring at random locations, suggesting, at most, limited damage to the ceramics by these flashover events. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy National Nuclear Security Administration under contract DE-NA0003525 [Preview Abstract] |
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FT1.00026: Modified floating harmonic method by analyzing the harmonic currents of a DC blocking capacitor in a floating probe Jong-In Seo, Ho-Won Lee, Chin-Wook Chung The floating harmonic method (FHM) is a diagnostic method to obtain plasma parameters by analyzing harmonic currents of driving frequency to a probe$^{\mathrm{1}}$. In the FHM, the harmonic currents are measured through a sensing resistor and a DC floating potential is maintained by a DC blocking capacitor. In this paper, the sensing resistor is eliminated by modifying FHM's measurement circuit, and the DC blocking capacitor is used for measuring the harmonic currents. Since there is no voltage drop across the sensing resistor, compensation of sheath voltage is not necessary$^{\mathrm{1}}$. In this method, plasma densities and electron temperatures are measured in an argon Inductively coupled plasma and the results are compared with those obtained from electron energy probability functions. In addition, the effect of stray currents and film deposition on the probe are also investigated. 1. M. H. Lee, S. H. Jang and C. W. Chung, Journal of Applied Physics 101 (3) (2007). [Preview Abstract] |
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FT1.00027: Electron number density measurements from the frequency shift of a plasma defect state in a one-dimensional photonic crystal David Pai, Fabio Righetti, Benjamin Wang, David Biggs, Mark Cappelli We describe the use of a plasma-functionalized vacancy defect in a one-dimensional microwave photonic crystal to experimentally measure the electron number density of glow discharges at 5 - 40 torr. The photonic crystal consists of spaced alumina plates with a built-in void defect that breaks the repeating symmetry of the layers, resulting in narrow defect transmission peaks within relatively deep bandgaps. We exploit the sensitivity of the defect transmission at 28 GHz to varying plasma density to measure electron number densities down to about 10$^{\mathrm{9}}$ cm$^{\mathrm{-3}}$. Defect energy shifts are proportional to plasma density, in reasonable agreement with theoretical predictions of photonic crystal performance. At higher discharge current densities and discharge pressure, we see a departure from the model predictions, largely attributable to the heating of the alumina structure, causing expansion and changes in the lattice parameter that counter-act the effect of the increased plasma density on the defect state frequency. [Preview Abstract] |
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FT1.00028: The characterization of reactive plasmas using frequency-domain terahertz spectroscopy. Mark Cappelli, Fabio Righetti, Karim Ouaras Terahertz (THz) spectroscopy (TS) to probe plasma chemistry is advantageous as it accesses ground state molecular transitions. Early studies were based on time-domain methods (TDTS) generating spectrally-broad pulses ranging from 0.1 -- 5 THz [1]. Experiments as early as 2003 [2] reported the use of TDTS to study dust-forming plasmas. The broad spectra makes measurements of plasma cut-off straightforward, but it is difficult to de-convolve the fine structure of molecular absorption spectra. The recent availability of continuous-wave frequency-domain (FD) THz sources with much higher spectral resolution has afforded the probing of molecular absorption features but have not yet been exploited in studies of plasma chemistry. One major benefit of FD THz spectroscopy (FDTS) compared to infrared methods is its ability to characterize both plasma chemistry as well as electron density and collision frequency. In this presentation, we provide insights into the use of FDTS as a diagnostic and demonstrate the opportunities and challenges by example measurements in a low-pressure argon-methanol RF inductively coupled plasma. [1] J. Neu and C.A. Schmuttenmeer, J. of Appl. Physics 124, 231101 (2018). [2] S. P. Jamison et al., J. Appl. Phys., vol. 93, no. 7, pp. 4334--4336 (2003). [Preview Abstract] |
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FT1.00029: Measurement of aspect ratio dependent ion energy distribution functions with a retarding field energy analyzer in RF biased plasmas Yuhua Xiao, Yao Du, Steven Shannon The control of ion energy and angular distributions (IEADs) is critically important for etching of high aspect ratio (AR) structures because the velocity vector of ions is not always perpendicular to the wafer surface. The off-normal ions are mainly a result from thermal motion, collisions during transiting across sheath, and charging effects. In this work, we measure the ion energy distribution function (IEDF) in a 13.56 MHz driven capacitively biased plasma reactor coupled to VHF or ICP driven systems for independent control of plasma density. IEDF's are measured using a commercial retarding field energy analyzer (RFEA) mounted on the biased electrode (Impedans Vertex RFEA). RFEA results are combined with hairpin probe, Langmuir probe, and OES measurements to elucidate processes that impact ion energy spectra for high aspect ratio processes. The results are further compared to fluid model and particle-in-cell (PIC) simulations. [Preview Abstract] |
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FT1.00030: Method for spectroscopic determination of sub-nanosecond electric field development in argon plasmas using a time-dependent line-ratio approach Tomas Hoder, Markus Becker, Detlef Loffhagen A time-dependent collision-radiative model and method is proposed to determine the electric field strength with sub-nanosecond resolution. This method is based on measuring emission intensities of radiative transitions of selected 4p states of atomic argon and evaluation of their ratio development by the non-steady state model. Strong dependence of ratio of selected excitation rate coefficients on E/N is used as a theoretical reference. This line-ratio method enables to reveal ultra-short local electric field variations in rapidly changing plasmas, such as nanosecond pulsed, dielectric barrier or filamentary streamer discharges. In practice, emission intensities of atomic lines can be measured with such resolution using streak and picosecond gated cameras or using time correlated single photon counting techniques. [Preview Abstract] |
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FT1.00031: Genetic-algorithm-assisted reconstruction of arbitrary EEDF of atmospheric-pressure plasma using optical emission spectroscopic measurement Thijs Van Der Gaag, Hiroshi Akatsuka Recent increased interest in non-equilibrium atmospheric pressure plasma applications in e.g. medical treatments and agriculture leads to a need for more insight in the behavior of these plasmas. Knowledge of the electron energy distribution function (EEDF) is a central element in understanding the plasma state, making it worthwhile to expand our knowledge beyond the existing EEDF models. Here, a method is developed to determine the EEDF based on optical emission spectroscopic measurement meaning that the use of probes is not needed. Under atmospheric conditions, electron-atom bremsstrahlung is considered to be the dominant source of continuum emission. A genetic algorithm is used to match a unique, arbitrary EEDF solution to the emissivity data. With realistically available OES data (300-800nm), an accurate and complete (up to 20 eV) EEDF can be obtained using this algorithm. The current state of the algorithm, validation results by comparison to EEDF models and potential applications will be discussed. [Preview Abstract] |
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FT1.00032: Electron Temperature Measurement of Atmospheric-pressure Non-equilibrium Ar Plasma by Line Intensities with CR Model and by Continuum Emissivity Hiroshi Akatsuka, Hiroshi Onishi, Fuminori Yamazaki, Atsushi Nezu Atmospheric-pressure non-equilibrium plasmas are being applied to various practical fields. The objective of this study is to examine their electron temperature $T_e$ of Ar DBD plasma with several methods of optical emission spectroscopy (OES) measurements, i.e., with line-intensity measurement and with continuum emission measurement. With the help of Ar collisional-radiative (CR) model of low-temperature argon plasma of atmospheric pressure, the relationship between $T_e$ and the excitation temperature $T_{ex}$(4p-5p) of 4p-5p levels is numerically surveyed over some ranges of the electron density and the gas temperature. It is found that $T_e$ is uniquely determined with the parameter $T_{ex}$(4p-5p) under low $T_e$ conditions. Consequently, $T_e$ of the DBD plasma is estimated to be about $0.6 - 1.0$ eV. Meanwhile, $T_e$ is also determined by the OES of continuum spectrum due to the Bremsstrahlung, where the Maxwell and Druyvesteyn electron energy distribution functions (EEDFs) are assumed for the theoretical analysis of the OES data. It is found that the latter EEDF gives reasonable results that agree well with the line-intensity OES measurement with the Ar CR model. Future possibility to find the EEDF of this kind of plasmas is briefly discussed. [Preview Abstract] |
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FT1.00033: Technique for in-situ measurements of electron density and film thickness using double curling probes. Daisuke Ogawa We have developed a technique to realize an in-situ measurement of both electron density and deposited-film thickness with the use of two curling probes. Curling probe is one of the microwave resonators, which mainly allows measuring electron density based on the microwave resonance of a curling slot antenna. A curling probe has a quartz cover separating a cavity in the probe from plasma region so that it is known that resonant frequency shifts when the film deposition occurs on the cover. We utilize the phenomenon to measure the film thickness during a deposition process. When the probe is inserted into a plasma, there are two factors to shift the resonant frequency. The first is the plasma permittivity, and the second is the dielectric constant of a deposited film. In order to separate the two frequency shifts, we use two different-sized curling probes because the attenuation of the radiation from the antenna depends on the antenna geometry and so on. Once we know the parameters specific to each probe, we can find the electron density and the film thickness simultaneously. In this presentation, we will show our theoretical background of the technique and the experiments to validate the equation. [Preview Abstract] |
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FT1.00034: Using a collisional-radiative model to validate e-Xe$^+$ cross sections calculated by the Dirac B-spline R-matrix approach Yang Wang, Yan-Fei Wang, Xi-Ming Zhu, Oleg Zatsarinny, Klaus Bartschat Experimental studies of e-Xe$^+$ collisions are difficult to carry out. Consequently, a direct comparison between cross-section data obtained theoretically and experimentally is hard to achieve. In this work, a collisional-radiative (CR) model based on e-Xe+ cross sections calculated by the Dirac B-Spline R-Matrix method is used to validate the predicted cross sections. This is achieved by comparing level density distributions predicted by the CR model and those determined experimentally. [Preview Abstract] |
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FT1.00035: Development of a 2D multi-fluid plasma model to study the anomalous electron transport in a Hall effect thruster. C. A Gonzalez, Kentaro Hara Hall Effect Thruster (HET) is an electrical propulsion device that use a cross-field configuration with and axial electric and radial magnetic fields to limit the electron motion in the azimuthal direction and use them to ionize propellant and produce thrust. We present a multi-fluid simulation of HET in two dimensions that consists on the continuity, momentum and energy equations for each plasma species, which is constituted by a mixture of neutrals, ions and electrons. We assume an electrostatic model where the coupling to the fluid equations is given by the Poisson equation and a static magnetic field. We have taken into account the collision, ionization, and excitation processes. The multi-fluid model is discretized using the HLLC approximate Riemann solver and the time evolution is computed using a third-order SSP Runge-Kutta scheme. [Preview Abstract] |
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FT1.00036: Hybrid simulation of high intensity electron beam propagation through a low pressure gas cell Christopher Moore, Brandon Medina, Sidney Shields, William McDoniel, Troy Powell, Daniel Jensen, Matthew Bettencourt, Keith Cartwright, Kate Bell, Jacques Gardelle, David Hebert As part of the validation effort for Sandia's new EM PIC-DSMC plasma code EMPIRE, we simulate high intensity electron beam propagation through low pressure gas cells. Specifically, we model the CESAR and RKA beam experiments [1]. We compare the accuracy and performance of a fully kinetic PIC-DSMC scheme [2] and a hybrid fluid-kinetic scheme for modeling the electron transport through the Ar background gas. The kinetic PIC-DSMC model represents charged and neutral species as computational particles allowing for self-consistent evolution of the neutrals as the beam interacts with the Ar gas. In the hybrid scheme PIC-MCC collisions generate mass, momentum, and energy source terms for the evolution of the neutral fluid. 1. Gardelle, J. et al., ``Revisiting the propagation and focusing of a high intensity electron beam in a low-pressure gas cell'', 44th ICOPS, May 21-25, 2017. 2. Medina, B. et. al., ``EMPIRE simulation of the RKA diode into the gas cell'', PPPS 2019, June 23-28, 2019. [Preview Abstract] |
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FT1.00037: A hybrid Particle-In-Cell code for atmospheric pressure plasma jets Maximilian Klich, Ralf Peter Brinkmann, Jesper Janssen, Yue Liu, Thomas Mussenbrock To exploit the enormous potential which is inherent to non-equilibrium plasmas operated at atmospheric pressure a throughout understanding of the underlying plasma process is required. In order to contribute to the gathering of information and understanding this work introduces a hybrid code for the simulation of atmospheric pressure plasma jets. The complex chemistry of atmospheric pressure micro discharges is a key feature and from the simulations perspective the major disadvantage as well. The shear number of species leads classical Particle-In-Cell (PIC) codes to struggle with the enormous computational load. Therefore, the computation takes so long that a classical PIC scheme is not feasible in any practical sense. Furthermore, many cross sections are unknown which leads to crude assumptions or, in the worst case, an inapplicable scenario for the PIC scheme. If it is necessary to resolve as many chemical reactions as possible, a fluid model is usually preferred. However, a fluid model cannot resolve all kinetic effects which under certain conditions are the essential mechanisms of the discharge. Hence, the idea of a hybrid model is to treat electrons kinetically and heavy particles as fluid. This work presents details of the hybrid model implementation and recent results. [Preview Abstract] |
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FT1.00038: Implementing a shallow water mathematical modeling approach for simulating plasma interaction in multiphase configurations Ali Charchi Aghdam, Enrica Viparelli, Tanvir Farouk Numerous mathematical approaches have been proposed to resolve and simulate general multi-phase flow problems. Notable among them are the Volume of Fluid (VOF), the front tracking and the level-set methods. Each of these methods have their own strengths and drawbacks but they all suffer from extensive computational overhead which has limited their usage and utility in simulating plasma discharges in multiphase configuration. In this work, an attempt has been made to adopt the 1D shallow water (SW) approach; typically employed for modeling fluid flow in open channels, to model the gas liquid interface for a multiphase plasma process. The proposed model is adopted to simulate the classical cold plasma jet and its interaction with a liquid layer. A special boundary condition for the SW equations is developed from momentum balance for a selected region of the liquid which is directly affected by the jet. The SW equations are then solved for the rest of the domain to resolve the velocity and interface location. The SW method proved to be more affordable compared to the VOF methods while the results found to be in good agreement. [Preview Abstract] |
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FT1.00039: Development of reactor scale model of a batch reactor for ALD processing Evrim Solmaz, Sudharshanaraj Thiruppathiraj, Seung-Min Ryu, Laxminarayan L. Raja We report on the development of high-fidelity computational model of a chemical vapor deposition (CVD) reactor process for silicon-based atomic-layer deposition (ALD) applications. The low-pressure reactor scale process involves flow, volume chemistry, and deposition of thin film at multiple wafer surfaces. A full 3D computational representation of the reactor is developed including the multiscale geometric fidelity of the large meter-scale reactor volume and the mm-scale interwafer gap. The fluid mechanics within the reactor are described using a continuum as well as a pure particle-based (DSMC/MCC) method. A chemistry model for the hexachlorodisilane (HCD) gas precursor and nitrogen carrier gas decomposition in the reactor is developed and implemented with both continuum and particle models. The study reports on both the physics of reactor scale phenomena to identify rate limiting steps and the uniformity of the deposition process at the wafer. In addition, computational metrics of the model such as accuracy and computational times associated with the continuum and particle approaches are discussed. [Preview Abstract] |
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FT1.00040: Modeling of electrical discharges using FEniCS Aleksandar P. Jovanovic, Detlef Loffhagen, Markus M. Becker Numerical models represent a common tool for the description and analysis of physical processes in electrical discharges. The commercial software package COMSOL Multiphysics is frequently used as a modeling environment. Here, we present results of a benchmark study comparing COMSOL with FEniCS, an open-source computing platform for solving partial differential equations by the finite-element method, which provides a built-in mesh generator as well as support for parallel processing. The benchmark is based on an axisymmetric model of a positive streamer in air, which was recently used for the comparison of six simulation codes (B. Bagheri \textit{et al.}, \textit{Plasma Sources Sci.\ Technol.\ }\textbf{27} (2018) 095002). The model consists of Poisson's equation coupled with a drift-diffusion equation for electrons and a reaction equation for ions. In order to verify the newly developed FEniCS code, results are compared to the published benchmark data. To test the performance of the code, calculation times for the benchmark case using different number of cores, both for FEniCS and COMSOL are compared. Good agreement of the results and comparable performance is found. [Preview Abstract] |
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FT1.00041: Simulation Evolution of Ion Energy Distribution Uniformity in Low Pressure Plasma used in semiconductor processes Yun yang, Shawming Ma Low pressure Inductively coupled plasmas (ICPs) and Capacitively coupled plasmas (CCP) are widely used in semiconductor. Nowadays, atomic layer etchings (ALEs) and depositions (ALDs) have been studied and developed world wide and paid much more attention by using ICP and CCP tools. Processing uniformity are crucial. The uniformity processing of ALEs and ALDs was directly related to the ion energy distribution functions (IEDF) on the wafer surfaces. One challenge in plasma processing is being able to control the ion energy distributions (IEDs) from the presheath to the surface of the wafer which is necessary for maintaining the critical dimension of features and uniformities. In this study, we use 2D self-consistent fluid model, combined with electromagnetic module, and self-consistent Monte Carlo ion kinetic simulations to investigate the uniformities of the ion energy distribution on wafer surfaces employed with both biases applied to the substrate holding the wafer, and in low pressure Argon discharges. Uniformity of ion energy distribution on wafer surfaces are studied with Monte Carlo ion kinetic methods with different AC or DC biases. [Preview Abstract] |
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FT1.00042: Simulation of atmospheric pressure plasma jet with coaxial shielding gas Peng Lin, Tam Nguyen, Vincent Donnelly, Demetre Economou Atmospheric pressure plasma jets (APPJ) operated in open air are subject to changes in air conditions (e.g., humidity). A coaxial shielding gas (SG) can be used to curb air contamination and provide a controlled operating environment. A fluid model was used to simulate an APPJ with He, N$_{\mathrm{2\thinspace }}$and synthetic air as the working, shielding and ambient gas, respectively, with O$_{\mathrm{2}}$ considered the ``contaminant.'' The plasma was powered by a 13.56 sinewave at 2.25 kV peak. Base flow rates were 2 and 4.5 slm for He and N$_{\mathrm{2}}$, respectively. The shielding ratio was defined by SR $=$ (O$_{\mathrm{2}}$ concentration with SG)/( O$_{\mathrm{2}}$ concentration without SG). A lower SR reflects better shielding. SR was found to decrease with increasing SG flow rate, implying less contamination of the plasma jet. The on-axis SR showed more complex behavior as a function of distance (z) from the nozzle. SR started with a value of unity, then it dropped at z$=$2 mm, and then increased gently to SR$=$0.2 at z$=$16 mm. Further results on the effect of flow rate of the working and shielding gases are of primary interest. Simulation predictions compare favorably with experimental data from the open literature and from our own laboratory. [Preview Abstract] |
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FT1.00043: Multi-mode Striations in RF-driven He/2\%H2O Atmospheric Pressure Plasma (APP) Discharges Emi Kawamura, Michael Lieberman, Allan Lichtenberg Previous 1D particle-in-cell (PIC) simulations of 1--4mm gap, He/2\%H2O atmospheric pressure plasmas (APP's) showed bulk striations. Assuming the ionization rate coefficient $K_{iz}\propto X^q$ with $X$ the reduced field, a striation model showed that $q<0$ is a necessary condition for the instability. A local calculation yielded $q>0$, implying that nonlocal electron kinetics are required for the instability. Wider gaps can fit a wider range of wavelengths $\lambda$, resulting in multi-mode striations. Previously, we assumed one mean $q$ value for each APP, and did not calculate $q$ for each mode separately. Here, we develop a wavelength resolved striation model and apply it to PIC simulations of 4 mm gap APP's with $J=0.04-0.30$ A/cm$^2$ at 27.12 MHz. We first examine the $J=0.23$ A/cm$^2$ case and observe a mixture of unstable modes within a window of $\lambda$. At shorter $\lambda$, the modes are suppressed by diffusion. At longer $\lambda$, a transition to locality occurs where $q$ becomes less negative with increasing $\lambda$, approaching its local positive value and stabilizing the modes. The unstable modes shift to shorter $\lambda$ at higher $J$ where they are suppressed by diffusion. At lower $J$, the decrease in density with decreasing $J$ suppresses the striations. [Preview Abstract] |
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FT1.00044: Simulation and characterization of positive and negative streamers in air Hani Francisco, Behnaz Bagheri, Jannis Teunissen, Ute Ebert Streamers are propagating ionized filaments generated by electric fields, and they create paths for sparks, arcs, lightning leaders, and sprites. Their propagation is driven by a curved space charge layer at their tip, which causes local electric field enhancement. This allows streamers to extend into regions where the electric field is below the breakdown value. Streamers come in two polarities: positive and negative. In this study, we characterize positive and negative streamers in air at standard temperature and pressure subject to a homogenous background electric field below breakdown. Our goal is to understand the mechanisms and dynamics of positive and negative streamers in different parameter spaces and investigate how streamer radius and velocity respond to these parameters. The model used is a drift-diffusion-reaction model coupled with the Poisson's equation with a local field approximation. This is implemented in afivo-streamer [Teunissen and Ebert, J. Phys. D 2017], a code that features a plasma fluid model with adaptive mesh refinement, OpenMP parallelism, and geometric multigrid methods based on the afivo framework [Teunissen and Ebert, Comp. Phys. Comm. 2018]. Nonlocal photoionization is included in the simulations. [Preview Abstract] |
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FT1.00045: Simulation of streamer propagation in helium plasma jets supported by modulated voltage pulses Natalia Babaeva, George Naidis Atmospheric pressure plasma jets (APPJs) are often formed by plasma bullets -- guided streamers propagating along the jet axis [1]. Dynamics and structure of the streamers, as well as characteristics of produced plasma, are governed by a number of factors: the geometry of electrodes, the gas flow rate, the parameters of applied voltage pulses, etc. Recent experimental study of helium APPJs [2] has shown that modulation of applied voltage leads to oscillations of the streamer propagation velocity. In this talk, results on computational study of streamer dynamics in helium APPJs at application of modulated voltage pulses are presented. The effects of modulation on the streamer dynamics and on the plasma parameters (electric field, density of electrons) are considered. [1] X Lu, G V Naidis, M Laroussi and K Ostrikov, Phys. Rep. 540, 123 (2014). [2] M E Pinchuk, O M Stepanova, A M Astafiev, A V Lazukin and Zhaoquan Chen, Appl. Phys. Lett. 114, 194103 (2019). [Preview Abstract] |
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FT1.00046: Tunable negative refraction device composed of negative-permittivity plasma and negative-permeability metamaterial Osamu Sakai, Akinori Iwai, Fabio Righetti, Benjamin Wang, Mark Cappelli Negative-refractive-index devices that have been reported to date have been based on solid-state metamaterials. To overcome their limitations of fixed or very-narrowly-variable parameters, we report here on a design that incorporates gaseous plasma components, i.e., discharge tubes filled with Ar at 250 Pa, in which the permittivity is variable and rendered negative by tuning the discharge power [1], together with metamaterial supporter plates that contribute a negative permeability over a specific frequency band [2]. The experimental results within and outside of this band showed remarkable contrast. Outside the band of negative permeability, transmitted microwaves suffered from heavy damping, while recovering in transmitted amplitude with increased discharge power when the plasma contributes negative permittivity inside the negative-permeability band. In addition, strong changes in the phase of the transmitted microwaves were seen when the permeability was negative and the permittivity of plasmas was also tuned to be negative. Similar physical processes, like the abnormal recovery of the microwave amplitude and the extraordinary steepness of the phase shift are reproducible in our theoretical calculations. [1] B. Wang and M. A. Cappelli, Appl. Phys. Lett. 108, 161101 (2016). [2] Y. Nakamura, A. Iwai and O. Sakai, Plasma Sources Sci. Technol. 23, 064009 (2014). [Preview Abstract] |
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FT1.00047: Ionization Instabilities in Bounded and Infinite Microwave Plasma Sergey Dvinin, Oleg Sinkevich Ionization instability takes place in much kind of discharges. It can be initiated by kinetic [1] and electrodynamic [2] processes. The evolution of the instability from a local source for an infinite [3, 4], and bounded plasma sheet [2] when plasma is excited by a plane wave (at arbitrary incident angle) or by a surface wave is considered. It is shown that electrodynamic instability can take place in cases where at least two electrodynamic modes can propagate in the medium, and one of which can be excited in a resonant manner. In an unbounded medium, the instability will always convective, while in a bounded plasma, absolute instability is possible if the dimensions exceed an integer number of half-waves of the resonant mode. In the cylindrical geometry, perturbations with a violation of the azimuthal symmetry of the plasma are observed at higher electron densities due to a lower critical number value. Phenomenological models of the nonlinear stage of instabilities development are proposed. The possibility of observing of this type of instability in low-pressure plasma reactors is discussed. For a spatially limited system, the results of the calculations show good agreement with experiment. $^{\mathrm{1}}$B.S. Kerner\textbf{, }V.V. Osipov\textbf{. }Autosolinons. Springer-science$+$Business Media B.V. 1994, 671 p. $^{\mathrm{\mathbf{2}}}$S. Dvinin et al. Sov. Phys.: Fizika Plazmy, 9, 1983, 1297. $^{\mathrm{3}}$D.L. Bobroff, H.A. Haus. J. Apple. phys., 1967, \textbf{38}, ¹1, p. 390. $^{\mathrm{4}}$A. Bers. Handbook of Plasma Physics vol. 1. Ed. A.A. Galeev and R.N. Sudan, North-Holland Publishing Company, 1983, 451--517. [Preview Abstract] |
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FT1.00048: Striations in DC Driven Discharges in Nitrogen Malik Tahiyat, Tanvir Farouk, Shamia Hoque A striated positive column was observed when low pressure dc discharge experiments were performed in nitrogen operating at 0.7 Torr with an inter-electrode spacing of 15.5 cm. Visualization of the discharge showed that as discharge current was raised from 0.5 to 14.8 mA, number of striations decreased and thickness of negative glow region increased. 1-D simulations of the experiments were conducted employing a fluid model with detailed nitrogen kinetics, incorporating multiple levels of vibrational and electronic excitations. Predictions from the model were found to qualitatively agree with experimental observations of the striated positive column and the dependence of the number of striations on discharge current. Perturbation analysis of chemical kinetics identified the vibrational excitation reactions to be the most sensitive to the striation behavior. Sensitivity analysis further indicated that as vibrational cross sections were increased and decreased, magnitude of intensity of each striated segment intensified and subsided respectively. A detailed analysis of the kinetics reveals that the onset of striations results from the delayed initiation of the ionization reaction due to the predominance of vibrational reactions at lower electron temperatures and vice versa. [Preview Abstract] |
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FT1.00049: Influence of voltage pulse duration on ignition of glow discharge in air V.A. Lisovskiy, P.P. Platonov, S.V. Dudin The effect of the duty cycle coefficient on the pulsed discharge ignition in air has been studied in experiment. It has been found that the highest breakdown voltage values are required for igniting the discharge with short pulses possessing moderate values of the duty cycle coefficient D. On increasing the pulse duration the strongest changes of the breakdown voltage are observed at low gas pressure to the left of the breakdown curve minimum. With the D quantity growing and the gas pressure fixed the breakdown voltage first decreases and then it experiences saturation that corresponds to the breakdown in the constant (not pulsed) electric field (D $=$ 1). In the region to the right of the breakdown curve the range of the breakdown voltage variation against the duty cycle narrows. [Preview Abstract] |
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FT1.00050: Subnanosecond breakdown and higher pulse repletion rate in plasma device combining an open and capillary discharges. Experiment and simulation. Irina Schweigert, Petr Bokhan, Dmitry Zakrevsky Results of experimental and theoretical studies of the switching characteristics of plasma devices consisting of open discharge and capillary one are presented. The open pulse discharge is used as a plasma source, and the capillary discharge provides a quick decay of plasma and recovery of electrical resistivity in the inter-pulse period. A capillary tube placed outside is connected to the chamber of the open discharge. This tube with the anode inside made from Al2O3 has 5 cm length and 0.1-0.5 cm diameter. In the experiment and calculation, two cases of the external capillary discharge were considered with a) floating tube wall potential and b) the wall covering with potential equal to the anode one. The simulations of the plasma device were performed with the combined kinetic (with PIC MCC method) and fluid approaches. The results of study show that the latter case exhibits better characteristics, the breakdown time t\textless 0.4 ns, $f=$100kHz, $U=$30kV, helium pressure $p_{He}=$3.5Torr. [Preview Abstract] |
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FT1.00051: Effect of transverse magnetic field on electron temperature distribution between parallel plate capacitive discharge Shikha Binwal, Yashashri Patil, Shantanu Kumar Karkari, Lekha Nair A symmetric parallel plate capacitive discharge, operated at 13.56 MHz in push-pull configuration is presented. Spatial electron temperature distribution is obtained using RF compensated Langmuir probe. In the un-magnetized case, one usually finds uniform temperature between the plates, while the temperature peaks sharply near the sheaths. However when transverse magnetic field is introduced, the local electron heating near the sheath is found to spread over a significant distance resulting in a gradual increase in electron temperature from the center towards the sheath edge. Thus the average temperature in the center is also found to be enhanced as compared with un-magnetized case. Also a contrasting effect on the average electron temperature is observed with background pressure. The above observation has been depicted using COMSOL Multiphysics® software. A qualitative model is given to explain the above effects introduced by the external magnetic field. [Preview Abstract] |
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FT1.00052: Features of Electromagnetic Field Excitation in a Capacitive RF Discharge Sergey Dvinin, Oleg Sinkevich, Davlat Solikhov, Zafari Kodirzoda A low-pressure capacitive RF discharge ($\nu $\textless \textless $\omega )$ with large electrodes, excited by an electromagnetic field, is considered. Under these conditions, the discharge is supported by surface waves propagating along three-layered structure metal -- sheath -- plasma -- sheath -- metal [1] and evanescent waves. The features of field representation as series of surface and higher order evanescent waves in multilayer structures containing regions with positive and negative permittivities are discussed. It is shown that the resonances of a long line in such a discharge are significantly modified due to the excitation of evanescent modes (an example is the geometric resonance of the plasma and sheath [3]), and, at high frequencies, plasma and empty waveguide evanescent modes (surface waves) excited at the lateral plasma boundary. The features of the natural waves, connected with asymmetry of sheathes and the inhomogeneity of the plasma density distribution in the radial and axial directions are considered. The results of analytical calculations are compared with the numerical impedance and spatial field structure calculation using the Comsol Multiphysics. $^{\mathrm{1}}$M.A. Lieberman, J.P. Booth, P. Chabert et al. Plasma Sources Sci. technol., 2002, 11, 283. $^{\mathrm{2}}$P.Chabert. J. Phys. D: Appl. Phys., 2007, \textbf{40}, R63. $^{\mathrm{3}}$J.$^{\mathrm{\thinspace }}$Taillet American Journal of Physics, 1969, 37, 423. [Preview Abstract] |
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FT1.00053: Observation of Nonlinear Standing Waves Excited by Plasma-Series-Resonance-Enhanced Harmonics in Capacitive Discharges Kai Zhao, De-Qi Wen, Yong-Xin Liu, Michael A. Lieberman, Demetre J. Economou, You-Nian Wang It is well-recognized that in a very high frequency (VHF) capacitive discharge, standing wave effects come into play that compromise the plasma uniformity. Here we present the first experimental evidence of nonlinear standing waves excited by plasma-series-resonance-enhanced harmonics in low pressure, VHF, parallel plate, capacitively coupled plasmas. Spatial structures of the harmonics of the magnetic field, measured by a magnetic probe, are in very good agreement with simulations based on a nonlinear electromagnetics model. At relatively low pressure, the nonlinear sheath motion generates high-order harmonics that can be strongly enhanced near the series resonance frequencies. Satisfying certain conditions, such nonlinear harmonics induce radial standing waves, with voltage and current maxima on axis, causing center-high plasma density. Excitation of higher harmonics is suppressed at higher pressures, due to more frequent electron momentum transfer collision with the background gas, resulting in improved plasma uniformity. [Preview Abstract] |
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FT1.00054: Experimental confirmation of transitions in the discharge operation mode in low-pressure capacitively coupled Ne plasmas Benedek Horváth, Aranka Derzsi, Julian Schulze, Peter Hartmann, Ihor Korolov, Zoltan Donko In this work, the electron power absorption and ionization dynamics in low-pressure discharges operated in Ne are studied and a detailed comparison of simulated and experimental results is provided in a wide parameter regime. 1d3v PIC/MCC simulations and PROES measurements are performed at different driving frequencies, pressures and voltage amplitudes in a geometrically symmetric CCP reactor. Both in simulations and experiments, a transition of the discharge operation mode from $\alpha $ to $\gamma $ is found by increasing the voltage amplitude at a fixed frequency and pressure, as well as by increasing the pressure at a fixed frequency and voltage amplitude. However, the simulations and the experiments suggest different voltage amplitudes/pressures at which the transition happens. This study reveals the applicability of PROES (which provides the spatio-temporal distribution of the excitation dynamics of the Ne 2p1 state) to probe the discharge operation mode (which is determined by the spatio-temporal distribution of the ionization dynamics) under various discharge conditions. [Preview Abstract] |
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FT1.00055: Properties of low-pressure rf capacitive discharge in acetylene V.A. Lisovskiy, S.V. Dudin, P.P. Platonov, S.I. Bogatyrenko, A.A. Minenkov We measured breakdown and extinction curves of radio-frequency discharge in acetylene as well as dependences of active current, power and gas pressure on the discharge burning time, and also optical emission spectra. The experiments were carried out in the range of acetylene pressure of 0.02 - 10 Torr at a distance between the electrodes of 20 mm. It was found that in the region of low acetylene pressures (to the left of the minimum of the breakdown curve), the discharge can cover only a part of the electrode surface. Immediately after the ignition of the discharge, due to the intense deposition of the polymer film and the formation of dust particles in the plasma volume, the gas pressure decreases sharply (by the factor of 2--5), while the active current and power increase and then reach saturation. In the discharge with intense polymerization, the lines of atomic and molecular hydrogen dominate in the emission spectrum of the discharge. The film deposited on the surface of the electrodes and the tube walls, as well as the dust particles formed, are amorphous, the maximum peak of XRD spectrum is observed at 2$\theta \quad =$ 18\textdegree , and the light absorption by the deposited films is highest at 440 nm wavelength. [Preview Abstract] |
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FT1.00056: Experimental and computational investigations of the electrode gap length effect on capacitively coupled radio frequency oxygen discharges Hyo-Chang Lee, K. H. You, J. Schulze, A. Derzsi, Z. Donko, H. J. Yeom, J. H. Kim, D. J. Seong Geometrically symmetric capacitively coupled oxygen plasmas are studied via experiments and Particle-in-Cell/Monte Carlo collision simulations [1]. The experiments reveal that the central electron density increases with an increased electrode gap, while the time averaged optical emission of atomic oxygen lines decreases. The simulations show that the electron density increases due to a mode transition from the Drift-Ambipolar-mode to the alpha-mode induced by increasing the electrode gap. This mode transition is due to a drastic change of the electronegativity and the mean electron energy. The observed mode transition is also found to cause a complex non-monotonic dependence of the O2 ion flux to the electrodes as a function of the electrode gap. These fundamental results are correlated with measurements of the etch rate of amorphous carbon layers at different gap distances. [1] Phys. Plasmas 26, 013503 (2019) [Preview Abstract] |
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FT1.00057: Multiple diagnostics of a large-area very-high frequency capacitively coupled oxygen discharge Zi-Xuan Su, Dao-Man Han, Yong-Xin Liu, You-Nian Wang The large-area very-high-frequency capacitively coupled plasmas, as a powerful tool for materials processing, has been widely used in semiconductor industry. Though a higher driving frequency and a larger electrode area can significantly improve output, accompanied electromagnetic effects have been the limitation for plasma material processing uniformity. In our work, the effect of electromagnetic effects on capacitively coupled oxygen discharge has been studied in a large-area cylindrical reactor driven with different very high frequencies. A fiber Bragg grating probe, a floating double probe and a hairpin probe were employed to measure the radial profiles of neutral gas temperature, relative O$_{\mathrm{2}}^{\mathrm{+\thinspace }}$ion density and electron density, respectively. Through the comprehensive diagnostics, the influences of the pressure and RF power on the plasma uniformity and some important plasma parameters were compared at various external control parameters. [Preview Abstract] |
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FT1.00058: Two-dimensional particle-in-cell simulation for the control of the standing wave effect in a dual-frequency capacitively coupled plasmas Chang Ho Kim, Hae June Lee The high driving frequency of a capacitively coupled plasma (CCP) is helpful to achieve a high plasma density, but the plasma non-uniformity caused by the standing wave effect is a significant drawback especially for a large scale wafer. It was experimentally reported that the addition of a low-frequency source is helpful for the mitigation of the standing wave effect [1], but the underlying kinetic effects are not fully understood yet. In this study, a two-dimensional GPU-based PIC simulation is utilized for the investigation of the mitigation of the standing wave effect by low-frequency driving power. The standing wave effect in the electrostatic PIC simulation is mimicked with the addition of the electron acceleration by the analytic standing wave solution with the Darwin model for electromagnetic plasma simulation. With the addition of the low-frequency driving power, the transport and heating of electrons show different behaviors for the non-local and the local kinetics. [1] K. Zhao, Y.-X. Liu, K. Kawamura, D.-Q. Wen, M. A. Lieberman, and Y.-N. Wang, Plasma Sources. Sci. Technol. \textbf{27}, 055017 (2018). [Preview Abstract] |
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FT1.00059: Two-dimensional particle-in-cell simulation of hollow cathode discharges in the showerhead of capacitively coupled plasmas Heesung Park, Hae June Lee The plasma property in a capacitively coupled deposition reactor with the hollow cathode (HC) showerhead has been investigated using a 2D PIC simulation with the variation of the hole size, the secondary electron emission (SEE) coefficient, the edge shape of the hole, and the applied DC bias. The SEE from the HC wall plays an important role in the increase of the plasma density, which is sensitive to the ratio of the hole size to the electron collisional mean free path. With the DC bias, the electron density shows different behaviors inside and outside of the HC. When the hole size is large enough, there are two electron density peaks in the HC and at the outer bulk plasma. The former is caused by the ionization enhanced by the SEE inside of the HC, and the latter is by the ionization near the substrate. Regardless of the hole size, the average electron density in the bulk plasma region increases with the positive DC bias while the negative DC bias decreases it. However, the electron density in the bulk HC region shows a complex mechanism, which is affected by the ionization rate as well as particle transport. Not only the ion Ohmic heating at the edge but also the electron Ohmic heating at the entrance of the hole are reduced with the reduced electric fields at the round edges. [Preview Abstract] |
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FT1.00060: Electron energy probability function measurement in a 2 MHz and 13.56 MHz dual frequency capacitive argon discharge. Bum-Seok Kim, Kyung-Hyun Kim, Nae-il Lee, Chin-Wook Chung Electron energy probability functions (EEPFs) are measured to obtain plasma parameters in a dual frequency capacitive argon discharge. 2 MHz and 13.56 MHz dual frequency powers are applied simultaneously to a powered electrode. For reliable measurement, a RF choke filter is used to minimize RF perturbations due to the RF harmonics and the intermodulation frequencies. As the 2 MHz power increases, the population of low energy electrons decreases while the population of high energy electrons little changes. Therefore, the plasma density decreases and the electron temperature increases. As the 13.56 MHz power increases, the population of low energy electrons is almost constant while the population of high energy electrons increases. Thus, the plasma density and electron temperature increase. From the measurement, the change in the EEPFs in the dual frequency operation shows independent control of the electron temperature and plasma density. [Preview Abstract] |
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FT1.00061: The effect of inhomogeneous ohmic heating on the electron energy probability functions in an oxygen capacitively coupled plasma. Ho-won Lee, Chin-Wook Chung Electron energy probability functions (EEPFs) are measured in an oxygen capacitively coupled plasma (CCP) using a Langmuir probe depending on the distance from the power electrode to the ground electrode in the CCP. Plasma densities and electron temperatures are obtained from the EEPFs. A choke filter is used to minimize a RF perturbation. The EEPF is changed from a Maxwellian distribution to a bi-Maxwellian distribution from the powered electrode. This seems to occur because the electric fields generated by the powered electrode does not penetrate through the center. The collisional heating is efficient by the strong electric fields near the powered electrode, while the collisional heating is inefficient far from the powered electrode. This shows the effect of inhomogeneous ohmic heating on the EEPFs in CCPs. [Preview Abstract] |
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FT1.00062: Improvement of power transfer efficiency in a capacitively coupled plasma You He, Yeong-Min Lim, Chin-Wook Chung In capacitively coupled plasma (CCP), the plasma resistance between electrodes is inversely proportional to the electron density. At low densities, the plasma resistance can be larger greater than the system resistance including power losses in an impedance matcher and a power feed line, than the power transfer efficiency is high. However, at high densities, the power transfer efficiency is low because the plasma resistance is smaller than the system resistance. To improve the power transfer efficiency, an inductor is connected to the CCP in parallel. This inductor increases the resistance of the chamber and improves the power transfer efficiency. The plasma density is increased compared to that of without the inductor. The resistance of the inductor should be much smaller than the plasma resistance so that the transmitted power is mostly applied to the plasma. [Preview Abstract] |
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FT1.00063: Experimental and Numerical Studies of Coherent and Chaotic Azimuthal Disturbances in a Magnetron Discharge Mark Cappelli, Andrea Marcovati Studies of instabilities in magnetron discharges (0.1-10 MHz) is an active area of research due to the important role they play in many technologies (Hall effect thrusters, magnetron sputtering, and Penning discharges). Our study focuses on a magnetron discharge confined between two parallel electrodes within a toroidal region of E x B field, under conditions where only the electrons are magnetized. A segmented anode is used to measure the cross-field current from which Fourier analyses give the power density spectrum of the fluctuations. In a highly obstructed discharge, the instabilities appear to be quite coherent, exhibiting a range of principal azimuthal modes depending on the gas mixture and discharge voltage. Under some conditions, the spectrum shows evidence of three-wave mixing suggesting nonlinear mode interactions. A linear model appears to capture the growth of coherent structures in the linear regime, but the development of a nonlinear model is necessary to understand the behavior seen between modes. We show through a sensitivity analysis that the transit time of the non-magnetized ions plays an important role in the growth of the instability. [Preview Abstract] |
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FT1.00064: Response of Average Electron Velocity Vector under AC Electric and DC Magnetic Fields in a Constant-Collision-Frequency Model Hirotake Sugawara In order to study fundamental features of electron transport in magnetized plasmas, the average electron velocity $\bf V$ in gas under uniform AC electric and DC magnetic fields, $\bf E$ and $\bf B$, crossed at a right angle is theoretically derived assuming a constant collision frequency $\nu$. When ${\bf E}=(0,-E\sin\omega_Et,0)$ and ${\bf B}=(0,0,B)$, the analytical solution of ${\bf V}=(V_x,V_y,V_z)$ in periodical steady state is $V_x=[2a\nu\omega_E\omega_B/\Omega]\cos\omega_Et+[a\omega_B(\omega_E^2-\omega_B^2-\nu^2)/\Omega]\sin\omega_Et$, $V_y=[a\nu(\omega_E^2+\omega_B^2+\nu^2)/\Omega]\sin\omega_Et-[a\omega_E(\omega_E^2-\omega_B^2+\nu^2)/\Omega]\cos\omega_Et$ and $V_z=0$. Here, $a=eE/m$, $\omega_B=eB/m$, $\Omega=[(\omega_E+\omega_B)^2+\nu^2][(\omega_E-\omega_B)^2+\nu^2]$, and $e$ and $m$ are the electronic charge and mass. Although this model ignores the dependence of the collisions on electron energy, it is a merit that basic $\bf V$ responses at various $E$ and $B$ are predictable from the solution. $\bf V$ draws an ellipse in the $V_xV_y$-plane synchronously to $\bf E$ and the tilt of its major axis represents the time-averaged Hall deflection angle of $\bf V$. This depiction is informative to understand the electron swarm response under AC $\bf E$ and DC $\bf B$ fields. [Preview Abstract] |
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FT1.00065: Measurement of anomalous resistivity in a magnetic nozzle Shadrach Hepner, Benjamin Jorns Magnetic nozzles consist of expanding magnetic fields used to accelerate a plasma for use in in-space propulsion. The question of electron transport in magnetic nozzles is important to understanding how the plasma escapes the field geometry, which is vital for thrust generation. This work investigates the role of instabilities in cross-field electron transport in an expanding magnetic field with applications to propulsion and processing. To investigate the influence of instabilities, we first position a B-dot probe downstream and measure the total induced magnetic field from the plasma during startup. Measuring in the radial and axial directions, integrating over time, and applying Ampere’s law yields a measurement of azimuthal current density. We then measure plasma potential and pressure with a Langmuir probe, which yields ideal azimuthal current from the gradients and provides the classical resistivity. Comparing the ideal current to that measured with the B-dot probe, we find the total resistivity and subtract the classical value to determine the anomalous effect. We then compare the results to the resistivity predicted with nonlinear wave theory and show that the magnitude of this anomalous effect corresponds to that induced by previously measured instabilities. [Preview Abstract] |
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FT1.00066: Control of plasma parameters in capacitively coupled plasmas operated in reactive gases via the Magnetic Asymmetry Effect Birk Berger, Moritz Oberberg, Dennis Engel, Christian Woelfel, Denis Eremin, Jan Lunze, Ralf Peter Brinkmann, Peter Awakowicz, Julian Schulze A major aspect of application-oriented research of capacitively coupled plasmas (CCPs) is to investigate and control particle flux energy distributions to the powered and grounded electrode. One way to facilitate this control is to make the discharge symmetry and, hence, the DC self-bias controllable by external parameters.\\ Recently, the effects of applying a magnetic field with an axial asymmetry, referred to as the Magnetic Asymmetry Effect, have been investigated in theoretical and experimental works. The results shown in this contribution were obtained in a geometrically asymmetric CCP driven at 13.56 MHz at pressures of up to a few Pa with a magnetron-like magnetic field configuration at the powered electrode. Introducing oxygen to the discharge is found to affect the DC self-bias, the ion energy distributions at the grounded electrode, and the RF current measured at the center of the grounded electrode. This effect is strongly dependent on the used magnetic field strength. [Preview Abstract] |
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FT1.00067: Fluid modeling of plasmas magnetized by electromagnetic waves Dylan Pederson, Laxminarayan Raja Strong electromagnetic resonance in cavity resonators and similar devices can lead to many configurations of resonant field enhancement. Some resonant modes lead to strongly enhanced electric fields, but there also exist modes in which the magnetic field enhancement dominates. The typical fluid model of gas breakdown and electromagnetic interaction does not account for magnetic fields, which can lead to significant differences between observed and numerically computed breakdown thresholds, as well as differences in post-breakdown plasma evolution. Starting from an expansion of the Boltzmann equation for charged particles, we develop an analytical model that captures how strong oscillating magnetic fields can affect the plasma evolution even for overdense plasmas. Certain parameter regimes are shown to have unexpected diffusion and drift behavior. We develop a breakdown model that incorporates the effects of both static and oscillating magnetic field energy deposition to electrons. The fluid model parameters are compared to swarm behavior in a particle-in-cell (PIC) computation. The resulting fluid model is used in conjunction with a finite-difference time-domain (FDTD) method to evaluate gas breakdown and plasma behavior in a magnetically resonant cavity. [Preview Abstract] |
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FT1.00068: Extensible Algorithmic Generation of Molecular Electron-Impact Cross-Section Data from DFT Information for Simple Organic Molecules Steven Marcinko, Davide Curreli Medical and industrial atmospheric pressure plasma discharges frequently involve complex electrochemical reaction networks with large organic molecules. Modeling of these networks which may contain thousands of species and hundreds of thousands of reactions is infeasible by manual methods, and so must be handled algorithmically. In this work, a preliminary software framework for handling large plasma-chemistry problems is presented. The framework currently generates usable electron-impact cross-section datasets for species within the reaction network using the open-source DFT software NWChem, and automatically assembles the corresponding plasma-chemistry network using the CRANE (https://github.com/lcpp-org/crane) open-source software. We show an example on how to create a reaction network for ethylene, a small well-studied organic molecule, and extend the same algorithmic approach to isopropyl alcohol. Comparisons to experimental cross-sections and prior computational work on ethylene is discussed. We also explore computational scaling to larger molecules and reaction networks, including the effects of adding additional reaction mechanisms or levels of theory. [Preview Abstract] |
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FT1.00069: Impact of Surface Flashover on Coated Ceramics Ricky Tang, Laura Biedermann, Joseph Howard, Ronald Goeke, Cherrelle Thomas, Paul Clem Machinable ceramics are frequently used to provide high-voltage insulation in vacuum and low-pressure applications, and surface flashover of these insulators can be detrimental. To increase the voltage hold-off strength, often a semi-conductive coating is utilized to decrease the secondary electron emission (SEE) yield of the material and increase the charge bleed-off time constant, thereby reducing charge build-up on the ceramic surface leading to breakdown. In our experiments, hold-off strengths of cylindrical ceramic samples are measured in a nearly-uniform electric field as a function of coating formulation and background gas pressure and composition. The different formulation alters the surface chemistry of the resulting material. The samples are modified to produce a preferential direction of flashover in a repeated location to enable imaging of the flashover process, as well as investigating the spectral composition of the resulting plasma using a photodiode detector. Additionally, a preferential breakdown location allows microscopy surface analysis of ``as-received'' and ``pulsed'' samples by comparing the coated surface before and after flashover under various background conditions. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy National Nuclear Security Administration under contract DE-NA0003525. [Preview Abstract] |
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FT1.00070: Diagnostics of chemical composition of ``plasma acid'' generated in water using oxygen DBD plasma Danil Dobrynin, Ryan Robinson, Alexander Fridman Plasma treated water has been studied recently by many groups due to its typically high oxidative properties that are interesting for a number applications, including biomedicine and agriculture. In the case of air-plasma treatments, water becomes acidic due to generation of nitric and nitrous acids, while oxidative properties are due to ROS and RNS, including \textbullet OH, \textbullet O, H2O2, NO3-, ONOO-. Here, we report on identification of acidity source of oxygen DBD treated water, sometimes referred as ``plasma acid'', with strong but temporary oxidizing properties. The conjugate base of this oxygen plasma-produced acid remained unidentified. The results presented here suggest that ``plasma acid'' contains unstable O2- and O3- as possible anion species. [Preview Abstract] |
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FT1.00071: Application of underwater discharge shock wave to wood beating process as a pretreatment of enzymatic saccharification for cellulosic ethanol production Fumiyoshi Tochikubo, Ryo Oohata, Yusuke Nakagawa, Satoshi Uchida Cellulosic ethanol is expected as a renewable biomass fuel alternative to petroleum fuel. The cellulosic ethanol is obtained by saccharifying cellulose and fermenting the produced sugar. However, wood saccharification is not easy since wood is physically and chemically robust due to the hydrogen bond existing between cellulose polymers. Various wood saccharification methods have been studied. Although enzymatic saccharification has little environmental impact, its saccharification rate is slow. Therefore, the pretreatment is generally added to increase the surface area of wood for efficient enzyme reaction. In this work, we applied underwater discharge shock wave to wood powder in order to break the hydrogen bond between cellulose polymers. Underwater discharge shockwave was generated by applying a pulsed high voltage through spark switch to pin-to-pin electrodes in wood-powder disperse water. When the wood powder was irradiated with the shock wave, the volume of wood powder was increased. The increase of powder volume strongly suggests that water molecules penetrate between cellulose polymers as a result of wood beating. The wood powder treated by the shock wave was applied to enzymatic saccharification. We confirmed the increase of saccharification rate by enzyme. [Preview Abstract] |
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FT1.00072: Proof of concept for irradiation breakdown if PFOS via electron beam Ruilian Gao, Robert Rodi, John Lassalle, Corinne Kowald, Mingbao Feng, Suresh Pillai, David Staack Perfluorooctanesulfonic acid, known as PFOS, is a suspected carcinogen found in global waters and soils. It is very difficult to breakdown as a result of the carbon-fluorine bonds. Toxicity and bioaccumulation of PFOS have been verified by several studies. Rising concerns and inadequate solutions led to the belief that electron beam treatment may be a cost effective and efficient way to destroy PFOS in water. This study uses 10 MeV, 15kW electron beam to process aqueous PFOS solution spiked to concentrations of 10 \textmu g/L, sand samples spiked to concentration of 20mg/kg, and field samples from Texas, Michigan, Pennsylvania. Previous research shows that NaOH, NaHCO3, and NaNO3 aid in the breakdown of PFOS at low doses. Preliminary results show a greater than 48.6{\%} PFOS level breakdown for water samples without laboratory additives under the ebeam at 500 and 2000 kGy absorbed dose, and that additives are detrimental in the reduction of PFOS at higher doses. Irradiated sand samples, without additives, show greater than 99{\%} PFOS breakdown at the doses of 500 and 2000 kGy. This research adds upon previous work and hopes to introduce insight on the topic including single run high dosing, additive testing, and condensation recovery. [Preview Abstract] |
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FT1.00073: Remediation of Petroleum Impacted Soils with Electron Beam Irradiation John Lassalle, Chris Campbell, Abismael Diaz, David Staack, Thomas Hoelen, Paul Bireta, Deyuan Kong, Gabriel Sabadell Soil contamination by crude oil presents a global environmental threat. Existing remediation techniques such as incineration and bioremediation are not always practical. Hydrocarbons from approximately C16-C40 are relatively recalcitrant in soil but still mobile enough for exposure to organisms through direct contact or groundwater. Hydrocarbons lighter than C40 constitute Total Petroleum Hydrocarbons, an index of contamination levels. The high-power-density heating and radicals generated by electron beam irradiation show potential for remediation of petroleum impacted soils. Experiments were conducted using a 10 MeV, 15 kW electron beam to investigate the remediation process. These experiments demonstrated radiation chemistry effects unique to the irradiation process, as well as other attributes of the treatment. Treatment of soil samples with a 3 MeV electron beam at currents from 14.4-28.5 mA has shown reductions to below 1{\%} TPH at the high power densities required for the technology to be practical at site scales. Dose rates for these experiments varied from 10-80 kW/kg, with penetration depths of approximately 2.5 cm for the 10 MeV beam and 0.9 cm for the 3 MeV beam. Experiments have also been conducted to demonstrate TPH reductions in heavily impacted sludge (TPH \textgreater 10{\%}). [Preview Abstract] |
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FT1.00074: High Energy Electron Beam Irradiation of Hydrocarbons with Different Saturation Degree Kunpeng Wang, David Staack Saturation degree of hydrocarbons indicates the hydrogen deficiency of a hydrocarbon inside its molecule and have been widely used in chemistry field. It affects the physicochemical properties of a molecule such as its molecular geometry, average chemical bond strength as well as electron density distribution. Effect of saturation degree (SatuDe) of a hydrocarbon molecule on its stability under high energy electron beam irradiation was studied. A high energy electron beam (10 MeV, LINAC) was used to irradiate hydrocarbons samples in a batch reactor submerged in a water bath in a temperature range of 5-20 $^{\mathrm{o}}$C. Hydrocarbon samples were selected to represent saturated alkanes, alkanes with ring structure, aromatics, aromatics with branch of different length and polyaromatics. For example, SatuDe values for saturated alkanes (group 1) is equal to 1. Group 2 which includes alkenes and saturated alkanes with ring structures has a SatuDe values between 0.7-0.9. Group 3 are represented by benzene and toluene which are aromatics hydrocarbons. SatuDe values for them are in the range of 0.3-0.5. During experiments, specific energy input (SEI) to all samples was controlled by controlling the irradiation time. SEI was in the range of 350-450 kJ/kg. Analysis by GC-FID and TGA showed that original compounds in each sample were converted to new compounds which depends on the saturation degree of the sample. High satuDe gave high total conversion and favor conversion to light compounds. Low satuDe samples showed low conversion and favor conversion to heavy compounds such as polymerized species. [Preview Abstract] |
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FT1.00075: Microwave plasma reactor for CO$_2$ decomposition Stefan Merli, Irina Kistner, Frederic Buck, Thomas Schiestel, Andreas Schulz, Matthias Walker, Günter Tovar Since electricity from renewable sources of energy is subject to fluctuations, energy storage plays a crucial role to create a reliable grid system. The CO$_2$ conversion into syngas or higher hydrocarbons via a plasma assisted gas conversion powered by renewable energy is a promising approach towards energy storage. To make this power to gas concept applicable it is important to improve its energy and conversion efficiency. Therefore, a modular microwave plasma unit for CO$_2$ conversion has been set up and investigated. This plasma torch enables a self-ignition and stable operation of the CO$_2$ plasma over a wide range of parameters. The electric field distribution and the gas flow inside the plasma torch were modeled with an FEM simulation to optimize the configuration. Another important point is the separation of oxygen from the CO$_2$ plasma to obtain pure CO for the syngas. For this purpose a tubular reactor was constructed, which is connected to the plasma torch and that contains a ceramic capillary, which acts as a permeation membrane for the oxygen. The oxygen permeation was investigated for a variety of capillary material compositions to identify the best operating conditions for the conversion of CO$_2$. [Preview Abstract] |
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FT1.00076: Nitrogen fixation by plasma processing Cezar Gaman, Gary J. Lanigan, Miles M. Turner In another presentation at this meeting, we show that a plasma process can in principle accomplish nitrogen fixation (or, more specifically, nitric oxide synthesis) with an energy efficiency of approximately 20~\%. However, energy efficiency appears as fundamentally in conflict with yield (understood as molar conversion efficiency). In this presentation we discuss the experimental conditions required to achieve both high efficiency and high yield. This essentially requires highly efficient excitation of vibrationally excited states of nitrogen in conjunction with several other conditions. For preference, these conditions must be achieved in a way consistent with processing large quantities of material, since the outcome of the process, nitrate fertiliser, is required in industrially large amounts. [Preview Abstract] |
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FT1.00077: Energy distribution function on high power impulse magnetron sputtering Masayuki Nakamura, Keigo Takeda, Akinori Oda, Hiroyuki Kousaka, Takayuki Ohta High power impulse magnetron sputtering (HiPIMS) is the pulse sputtering to produce the high energy ions. A pulsed high voltage of several tens $\mu $s is applied to the target at a frequency as low as several hundred Hz. The peak power density is 100 times larger than that of dcMS under same average power density, so that an ionization of sputtered species is promoted and the production of high energy ions is realized. Sputtered ion and gas ion produced in the plasma are incident on the film and influence the crystal structure of the film. Therefore, it is essential to analyze and control their energy and ion-to-neutral flux ratio. In this study, we measured ion energy distribution function (IEDF) by energy-resolved mass spectrometry. In the case of C-HiPIMS, the IEDF of Ar ion composed of bi-Maxwell velocity distribution function with low and high temperatures. On the other hand, that of C ion was composed of Maxwell velocity distribution function with high temperature. In the case of reactive TiN-HiPIMS, the energy tail of N ion extends toward 80 eV as well as Ti ion with increasing input voltage. These differences would be explained by the production process ions in HiPIMS. [Preview Abstract] |
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FT1.00078: Production of stable Zn-O2 mixture plasma for ZnO transparent conductive film Naoyuki Sato, Takashi Ikehata Our goal is to construct the multi-ion-plating method by arraying each PC controlled point source for the large-area fast coating of the oxide materials. One point source introducing Zn vapor to O2 ICP ( Inductively Coupled Plasma ) is relatively controlled well over the sheet resistance Rs of 10 ops (ohm/square) order for ZnO transparent conductive film, however, at 1 ops order there is crucial problem for the poor reproducibility including of the thin film peeling-off. To overcome it, we look for the more optimum synthesis condition by moving continuously the ICP coil and the Zn oven with respect to the substrate position during the deposition. This configuration can vary the exited state for Zn, O, O2 and their amount, resulting in the extension of control window to be able to draw much lower Rs. After we consider the life-time of the excited particles, their mean-free-paths, and the coil induced electric-field between the oven top and the film growth surface, we can set the adequate position-relation to obtain the excellent opto-electrical property of ZnO thin film at high deposition rate over 1000 nm/min. We report how to generate the mixture plasma stably and the improvement state to elevate the appearance of 1 ops order film with keeping the visible-NIR transparency. [Preview Abstract] |
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FT1.00079: Charge neutralization in electronegative rf power pulsed plasmas Alex Press, Keith Hernandez, Matthew Goeckner, Lawrence Overzet It has been noted that in electronegative plasmas, rf power pulsing can allow for etch feature charge neutralization. The main mechanism is thought to be formation of an ion-ion plasma which allows negative ions to reach the bottom of the features being etched and neutralize positive charge build up. However, charge neutralization is observed when rf power pulse frequency is too high for a fully ion-ion plasma to form and negative ions to reach the surface. In these cases, although a fully ion-ion plasma may not form, the electron population will be decreased at the end of the rf power off time, and positive current will have time to reduce the total charge on the surface. When power is reapplied, its positive magnitude may be great enough to cause the sheath to invert for a short time, causing an anisotropic distribution to interact with the surface reaching the bottom of etch features. Another explanation is the total surface charge has been reduced to a point where the local feature charges dominate enough space around them that they "capture" a large enough portion of the electrons reaching the surface when power is applied to cause some charge neutralization. In this presentation, current and voltage results pointing to this sort of charge neutralization will be presented. [Preview Abstract] |
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FT1.00080: Atmospheric pressure pulsed discharge plasma using slug flow systems in glass column and its application for dye degradation Motoki Yamada, Wahyu Diono, Hideki Kanda, Motonobu Goto Non-equilibrium pulsed discharge plasma using a gas/liquid slug flow in glass column is applied to waste water treatment containing Methylene Blue (MB). The reactor was comprised of 4 rows glass column bundled by copper foils that attached on the outside surface of the column. Also, the foils were used as high-voltage electrodes totally in 5 parallels. As the ground electrodes, copper foils were attached on the column at distant of 25 mm from high-voltage electrodes in the same way. By flowing the solution and gas simultaneously in the slug flow system, the interval of produced bubbles could be controlled and adjusted each flow rate. After the slug flow became steady, an electrical discharge was introduced into the system by using AC power supply with a bipolar pulsed output voltage, generating plasma in bubbles between electrodes. The output voltage is 9kV at 10 kHz repetition. The reaction was conducted totally in 120 min, and the degradation ratio was measured every 20 minute. As a result, over 90{\%} of MB were degraded in all of the gas species (oxygen, argon, and helium). Especially in the case of oxygen, mostly all of the MB were degraded within 120 min. This implies that many kinds of active species originated from oxygen plasma worked effectively. [Preview Abstract] |
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FT1.00081: Electromagnetic response of a limited-size two dimensional plasma grating formed by cw laser pumping. Fabio Righetti, Mark A. Cappelli Incorporating a plasma into metamaterial and photonic crystal devices is advantageous, in particular because of its tunability. A variation in the plasma density results in a modification of the dielectric constant of the gaseous component enabling the tunability of its electromagnetic response. In our previous work we show tunable bandgaps and resonantly enhanced extinction in a device constructed from an array of discharge lamps that include a quartz envelope [1]. To overcome the limitations of a periodic device composed by both plasmas and dielectrics, we propose the use of a cw laser to generate unconfined plasma filaments in cesium vapor with peak plasma densities in excess of 10$^{\mathrm{14}}$cm$^{\mathrm{-3}}$. The lattice periodicity is obtain by focusing the laser through a microlens array. We describe the transmission of normal incidence electromagnetic waves at low terahertz frequencies, from 50 GHz to 0.6 THz. Spectroscopic measurements provide detailed information on the plasma density profile. Numerical simulations are carried out to investigate the behavior of the system and compare these to experimental results. [1] F. Righetti, B. Wang and M. A. Cappelli, Physics of Plasmas 25, 124502 (2018). [Preview Abstract] |
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FT1.00082: On the penetration of reactive oxygen and nitrogen species generated by a plasma jet into and through mice skin with/without stratum corneum XinPei Lu In this paper, reactive oxygen and nitrogen species (RONS) generated by a plasma jet penetrating through and left in the skin after the plasma treatment are measured, and the effects of stratum corneum (SC) on the penetration of the RONS are also investigated. It is found that the RONS generated by the plasma jet can penetrate through the skin, and that the penetration of some of the RONS could be enhanced significantly by tape stripping the SC layer of the skin. Further investigation find that the typical ROS species, including OH, $^{\mathrm{1}}$O$_{\mathrm{2}}$, O$_{\mathrm{3}}$ and H$_{\mathrm{2}}$O$_{\mathrm{2}}$, can’t penetrate through the mice skin at all no matter whether the SC layer of the skin is present or not, where the thickness of the mice skin is about 200-300$\mu $m. Finally, it is found that high concentrations of long-lived RONS (H$_{\mathrm{2}}$O$_{\mathrm{2}}$, NO$_{\mathrm{2}}^{\mathrm{-}}$ and NO$_{\mathrm{3}}^{\mathrm{-}})$ are left in the skin after the plasma treatment, which means that the plasma treatment could have long-time scale therapy effect. [Preview Abstract] |
(Author Not Attending)
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FT1.00083: Optical emission spectroscopy of plasma-catalytic CO$_{\mathrm{2}}$ methanation Akihisa Yamamoto, Masashi Ideguchi, Susumu Toko, Kazunori Koga, Masaharu Shiratani CO2 methanation has been proposed to generate rocket propellant fuel in Mars exploration[1]. We aim to establish CO2 methanation process using plasma and catalyst. In our previous study, we have proposed the model that CO2 is excited and decomposed in the gas phase and the methane is generated on the catalyst surface[2]. In order to clarify the reaction processes more in detail, correlation between the emission intensity of plasma and the CH4 yield was investigated. The experiments were performed under various conditions at a pressure of 3.5 to 8.0 Torr, with discharge power of 20 to 100 W,t he electrodes of SUS, Cu and Ru/TiO2 and the total flow rate of below 21 sccm. The CH4 yield increases with the highest emission intensity of CO angstrom bands during the methanation process. This result implies that the increase of high energy levels of CO promotes CH4 methanation. [1] G. Sanders, ``Current NASA Plans For Mars In Situ Resource Utilization,'' no. 281, 2018.[2] S. Toko, et al. Sci. Adv. Mater., 10 (2018) 1087. [Preview Abstract] |
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FT1.00084: Experimental study of plasma parameters and discharge instabilities in 500W Hall effect thruster Victor Désangles, Sergey Shcherbanev, Thomas Charoy, Pascal Chabert, Anne Bourdon Hall-Thrusters (HT) are known from the 60's and are now routinely used for spacecrafts propulsion. Nevertheless, some key physical phenomena happening inside the engine channel are still to be understood and it puts a curb on the development of low-power HT. An effort is currently made towards the development of predictive models based on PIC simulations. These works have demonstrated the importance of oscillatory effects such as the electron cyclotron drift instability (ECDI) in the axial anomalous transport of electrons. Nevertheless, quantitative studies of these fluctuations are still to be done. We propose to develop experiments both to validate the above mentioned PIC simulations and to characterize the instabilities at play. Our study is carried out on a 500W PPS-type HT in Argon and Xenon with a cathode made of a 0.25 mm diameter W/Th (1\%) filament. The discharge biasing is varied from 80 to 400~V and the gas flow rate between 1.0 and 3 mg/s. The plasma parameters are analyzed in the plume of the thruster using Langmuir probes and emission spectroscopy (OES) coupled with a collisional-radiative model (CRM) . The electron energy distribution function used in the CRM is compared to the one obtained using the PIC code. [Preview Abstract] |
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FT1.00085: Ionization and acceleration of molecular constituents in a Hall thruster operating with xenon/air and xenon/nitrogen mixtures. Mark Cappelli, Antonio Gurciullo, Andrea Lucca Fabris The ion plume of a 70-mm diameter Hall Effect Thruster operated on mixtures of xenon/nitrogen and xenon/air is investigated by means of a Wien filter (E x B probe). The dependence of the velocities of the plume ions on the operating parameters of the thruster (anode voltage, anode power, mass flow rate and magnetic field) is explored. The most probable ion acceleration voltages, the ion current and density fractions of the multi-propellant, multi-species ion beam, are computed from the Wien filter spectra through a dedicated post-processing analysis. The knowledge of these properties is fundamental for understanding the contribution of each ion species to the propulsive performance metrics of the thruster when operated on these molecular gas mixtures. One finding that will be discussed in this poster is that the constituent air ions in an air/Xe mixture appear to form at a higher potential than that at which ions of Xe are formed, suggesting perhaps that additional metastable kinetics may be playing a role in their formation. [Preview Abstract] |
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FT1.00086: Kinetic simulation of ignition in micro-cathode vacuum thruster model Irina Schweigert, Michael Keidar The miniature pulse thrusters with vacuum arc developed by George Washington University are a promising type of thruster already used in several missions (see, for example [1]). In this work, in 2D3V PIC MCC simulations, the ignition of discharge in the simplified model of micro-cathode vacuum arc thruster was studied for the setup and conditions of the experiment [2]. In our kinetic simulations, as in the experiment, the model thruster consists of rectangular metal cathode (Ti) and anode (Cu) with 4 cm length and 0.5 cm thickness placed on alumina ceramic substrate. In simulations, the surface condition of alumina is set in terms of secondary electron emission yield. The effects of variations of the gap between electrodes, gas pressure and magnetic field strength on the model thruster operation are analyzed. [1]. Hurley S, Teel G, Lukas J, Haque S, Keidar M, Dinelli C and Kang J 2016 Trans. Japan Soc. Aeronaut. Space Sci. Aerosp. Technol. Japan 14 Pb157--Pb163 [2]. D B Zolotukhin and M Keidar 2018 \textit{Plasma Sources Sci. Technol. }\textbf{27 }074001 [Preview Abstract] |
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FT1.00087: Electrical Characterization of An Atmospheric Pressure Plasma Jet Sushil KC, Deepak Subedi, Rajendra Shrestha In this work, a non-thermal plasma jet has been generated with capillary tube having external diameter 4.0 mm and thickness 1.0 mm. An Argon gas has been used as a working gas. The electrical characteristics of this device like instantaneous power, and discharge current have been measured. The effects of applied voltage on the dissipated power of the device have been investigated. The current is measured with the current probe whereas the voltage is measured from the locally fabricated voltage divider having ratio 1201:1. The electron density has been found out using power balance method. In addition, the power consumption during the discharge has also been studied with the help of T.C Manley Method i.e. Lissajous Figures. The calculated power consumption has been compared with other manual as well as I-V plots. \textbf{Keywords:} Discharge current, electron density, power balance method, Lissajous figures, plasma jet. [Preview Abstract] |
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FT1.00088: OpenGPS: An OpenFOAM solver for simulation of low temperature plasmas. Luis Marques, Alexandre Silva Predictability in plasma science and engineering based on fundamental modelling has been considered a requirement for progress in the field of low temperature plasmas (LTP). While several in-house and commercial simulation codes exist for this purpose, a common opensource framework that can be developed by the community will likely accelerate the impact of computational studies in LTP. In this regard, we present our initial effort to develop a friendly, versatile, general plasma solver for LTP simulation based on OpenFOAM, an open-source CFD simulation suite that relies on the Finite Volume Method. The solver implements a time-dependent fluid type model to describe charged particle transport in electric discharges in argon, consisting in continuity and the momentum transfer equations for electrons and Ar$+$ ion, the electron mean energy transport equation, and Poisson's equation for the electric potential. The space-time map of the electron transport and rate coefficients are obtained from the electron mean energy profile, using the local mean energy approximation. In this work we will present preliminary simulation results of DC and RF discharges in argon and discuss the future outlook for the solver suite. [Preview Abstract] |
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FT1.00089: Efficiency of methylene blue in water purification using atmospheric plasma jet under varying conditions Marisa Thompson, Ryan Gott, Kunning Xu Globally 2.5 billion people are unable to access clean water. Advanced oxidation processes (AOP’s), an accepted method of water purification, use hydroxide radicals (OH) to break down pollutants, but many AOP’s employ harsh chemicals and are expensive. Low temperature, atmospheric pressure plasma (LTAPP) presents novel methods of creating AOP’s to purify water. LTAPP provides a cheaper, greener method of purification because it can create plasma from ambient air and does not use chemical consumables such as ozone, hydrogen peroxide, or chlorine that need constant renewal. Thus the only cost associated with LTAPP purification is the cost of electricity to generate the plasma. The research presented studied the effects of different voltages, pulse widths, frequencies, and stand-off distances (SOD, distance from the edge of the plasma tube to the surface of the water) on water purification. Methylene blue dye (a known pollutant) in water was run at a set of standard conditions and tests were then run at conditions above and below standard conditions. The results of this research are presented in this work as an examination of total carbon content and a comparison of reduced methylene blue concentration and spectrometer measurements as a function of different plasma jet parameters. [Preview Abstract] |
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FT1.00090: Study on the Dynamics and Stabilities of Motions of the Trojan Asteroids Richard Kyung, Juwon Moon Trojan asteroids are small celestial bodies that share the stable orbits of planets or large moons. They move ahead or behind the main body to near one of its Lagrangian points. The study of Trojan asteroids is one of the popular fields of astronomical dynamics. The three-body problem in astronomical mechanics studies Lagrange points and the stabilities and motions around these points. In this paper, based on the equations of motion around Lagrange points, simulations of orbit of Trojan asteroids system were performed using the equations of the dynamics of Trojan and computer analysis. The 2D and 3D display were obtained in either inertial frame or rotating frame. Modifications of the parameters and initialization were made to change the binary system and compare the output of trajectories for different cases. [Preview Abstract] |
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