Bulletin of the American Physical Society
70th Annual Gaseous Electronics Conference
Volume 62, Number 10
Monday–Friday, November 6–10, 2017; Pittsburgh, Pennsylvania
Session GT1: Poster Session I |
Hide Abstracts |
Room: Salon ABC |
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GT1.00001: Deep minimum in the Coulomb-Born TDCS for electron-impact ionization of atomic hydrogen S.J. Ward, J. B. Kent Recently, Macek {\it et al.} attributed a deep minimum in the triply differential cross section (TDCS) for electron impact ionization of helium to a vortex [1]. Vortices have been shown to be present for positron-impact ionization of atomic hydrogen [2]. Using the Coulomb-Born approximation [3] we have obtained a deep minimum in the TDCS for electron-impact ionization of atomic hydrogen for an incident energy of 76.45 eV and for the doubly symmetric coplanar geometry. At the scattering angle where there is a minimum in the TDCS, the real and imaginary parts of the transition matrix element are zero. [1] J. H.Macek, J. B. Sternberg, S. Y. Ovchinnikov and J. S. Briggs, Phys. Rev. Lett. {\bf 104}, 033201 (2010). [2] F. Navarrete and R. O. Barrachina, J. Phys. B {\bf 48}, 055201 (2015). [3] J. Botero and J. H. Macek, Phys. Rev. A {\bf 45}, 154 (1992). [Preview Abstract] |
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GT1.00002: Comprehensive out-of-plane (e, 2e) measurements on He autoionizing levels. N.L.S. Martin, B.N. Kim, C.M. Weaver, B.A. deHarak, O. Zatsarinny, K. Bartschat We report out-of-scattering-plane $(e,2e)$ measurements on helium $2\ell2\ell'$ auto\-ionizing levels for 80, 100, 120, 150, and 488 eV incident electron energies, and scattering angles 60$^\circ$, 50.8$^\circ$, 45$^\circ$, 39.2$^\circ$, and 20.5$^\circ$, respectively. The kinematics are similar in all cases: ejected electrons are detected in a plane that contains the momentum transfer direction and is perpendicular to the scattering plane, and the momentum transfer is 2.1~a.u..\footnote{B.A. deHarak, K. Bartschat, and N.L.S. Martin, Phys. Rev. Lett. {\bf 100}, 063201 (2008)} The results are presented as $(e,2e)$ angular distributions energy-integrated over each level, and are compared with our second-order theory calculated for 488 eV incident electron energy, as well as predictions based on a fully non-perturbative close-coupling model. At all energies except 80 eV, the shapes of the angular distributions, and the recoil peak intensities, are in excellent agreement with the 488 eV results for all three autoionizing levels. The reasons why this is so, for incident energies that vary by almost a factor of five, is at present unclear. [Preview Abstract] |
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GT1.00003: Introducing a phase factor for the two-electron continuum representation Lorenzo Ugo Ancarani, A.S. Zaytsev, S.A. Zaytsev We propose a numerical approach to describe three-body Coulomb continuum wave functions in the entire space. The key idea is to use an expansion on a basis set of functions whose asymptotic behavior is as close as possible to the formal one in the $\Omega_{\mathrm{0}}$ region where all interparticle distances are large. The proposed basis set contains two ingredients. First, it uses two-particle functions, named Convoluted Quasi Sturmian (CQS) [1]. While these behave asymptotically as a six-dimensional outgoing (incoming) spherical wave, they miss out an important Coulomb logarithmic phase which corresponds to the interelectronic potential; truncated expansions on CQS functions failed to converge satisfactorily with increasing basis size [1]. This brings us to the second ingredient, which consists in introducing -- from the outset -- an appropriate phase factor into the basis set. These dressed CQS functions possess then an asymptotic behavior closer to the formal one, and one then obtains a satisfactory convergence of the partial transition amplitudes on a basis set of reasonable size. Choosing a suitable phase factor, we demonstrate this numerically for the two-electron continuum that occurs, for example, in the electron-impact double ionization of helium; we consider typical experimental kinematical conditions in which two electrons escape with 10 eV each. [1] Zaytsev A S, Ancarani L U and Zaytsev S A, Eur. Phys. J. Plus 131, 48 (2016). [2] Zaytsev A S, Ancarani L U and Zaytsev S A, Eur. Phys. D, in press (2017). [Preview Abstract] |
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GT1.00004: Electron impact single ionization of ammonia. Lorenzo Ugo Ancarani, Carlos Mario Granados-Castro, Alessandro Genoni Recent (e,2e) measurements on polyatomic molecules motivated the development of theoretical methods to calculate and describe ionization cross sections in their most differential form. In this contribution, we study the electron impact single ionization of the outer valence orbital 3a$_{\mathrm{1}}$ of NH$_{\mathrm{3}}$. In a one-active electron approach, we use Generalized Sturmian Functions (GSF) [1] to expand the scattering wave function; having an appropriate asymptotic outgoing-type behavior, the basis functions are particularly efficient and allow the scattering amplitude to be extracted directly from the asymptotic behavior of the scattering solution (essentially the expansion coefficients) without the need of calculating a transition matrix element. To describe the initial state wave function, we use either the one-center wave function calculated by Moccia [2], or the one obtained by a DFT calculation. The molecular potential is either the one obtained through a static exchange approximation or the one of the DFT approach. The comparison between the two allows us to separate out the importance of the molecular structure quality from the numerical description of the molecular single continuum. We also compare our triple differential cross sections (TDCS) with the recent measurements [3]. [1] C. M. Granados-Castro and L. U. Ancarani, Eur. J. Phys. D 71, 65 (2017). [2] R. Moccia, J. Chem. Phys. 40, 2176 (1964). [3] R. El Mir et al., J. Phys. B 48, 175202 (2015). [Preview Abstract] |
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GT1.00005: Proton-helium double ionization: exploring different momentum-transfer regimes. Lorenzo Ugo Ancarani, A.I. Gomez, G. Gasaneo, M.J. Ambrosio, D.M. Mitnik We present a systematic study of fully differential cross sections (FDCS) for the double ionization of helium by fast proton impact, considering different kinematic conditions going from intermediate momentum transfers up to within the impulsive regime. Our formalism treats the projectile-target interaction up to first order, but the intra-target ones to all orders. Within this framework, we deal with a first order three-body non-homogeneous equation whose driven term depends parametrically on the momentum transfer. We solve it numerically with a Generalized Sturmian Function approach [1,2], and the ionization transition amplitude is extracted directly from the asymptotic range of the scattering wavefunction for the perturbed target. Our approach yields satisfactory agreement with the relative data measured for protons impinging with 6 MeV [3]. We explore how the binary, recoil and back-to-back structures in the FDCS change with the excess energy and momentum transfer. [1] M. J. Ambrosio et al. Phys. Rev. A 92, 042704 (2015). [2] M. J. Ambrosio et al., Eur. Phys. J. D 71, 127 (2017). [3] D. Fischer et al., Phys. Rev. Lett. 90, 243201 (2003). [Preview Abstract] |
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GT1.00006: Partial Wave Contributions in Oriented Collisions A L Harris, S Amami, T A Saxton, D H Madison We present fully differential cross sections (FDCS) for two collision processes with oriented atoms. The first collision is electron-impact ionization of oriented Mg (3p), and the second collision is electron-impact excitation-ionization of helium with an oriented final state He$^{\mathrm{+}}$(2p0) ion. Surprisingly, the theoretical functional form of the FDCS is the same for both processes, despite the fact that the only physical similarity is an oriented excited state in both processes. We use the common theoretical functional form to explore possible physical similarities between the two processes. The contributions to the FDCS of individual partial waves of the ionized electron and projectile are examined, and we show that for the ionization of oriented Mg, the FDCS are dominated by larger partial waves of the ejected electron. For the excitation-ionization process, the FDCS is dominated by the L $=$ 2 partial wave. [Preview Abstract] |
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GT1.00007: Two-Dimensional Potential Scattering using the Path Integral Technique A L Harris, T A Saxton, Z Temple We have previously developed a path integral technique for the calculation of time-dependent wave functions using a numerically exact quantum mechanical propagator. This method was applied to particles moving in one dimension, and was shown to work well for heavy particles. We have now extended our method to charged particles moving in two dimensions. Here we present numerical results that demonstrate the accuracy and efficiency of the method. We also explore the necessary numerical parameters and discuss applications to heavy-ion atomic collisions. [Preview Abstract] |
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GT1.00008: Ionization of Lithium using the HI-5 Model A L Harris, J Lyon, A Plumadore, M Bates The study of heavy-ion collisions with atoms is an increasingly active area of collision physics. We introduce the Heavy-Ion 5-Body (HI-5) model for charged particle collisions, which is only recently possible due to improvements in computing capabilities. Using our model, we present fully differential cross sections for inner and outer shell ionization of lithium using heavy-ion projectiles. Results are compared to other theoretical models, and the role of electron correlation is studied. [Preview Abstract] |
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GT1.00009: Proton collisions with water clusters studied with a screened independent atom model Tom Kirchner, Hans J\"urgen L\"udde The independent atom model purports that electron emission from molecules can be calculated by combining atomic cross sections. The simplest realization of this idea is the additivity rule according to which the molecular cross section is obtained as the sum of the atomic cross sections for all atoms that make up the molecule. Recently, we introduced a model in which the simple sum is replaced by a weighted sum. The weight factors are determined from an exact calculation of the effective area that is obtained when surrounding all atoms in the molecule by spheres representative of the atomic cross sections and projecting the resulting structure on the plane that is perpendicular to the projectile beam. The calculation is carried out using a pixel counting method [1]. In this contribution, we use this approach to study proton collisions with water clusters (H$_2$O)$_n, n$=1...10. A recent theoretical work found that at 100 keV impact energy the electron transfer cross section $\sigma_n^{\rm cap}$ for $n$=1...6 is proportional to $n^{2/3}$ [2]. By contrast, we find $\sigma_n^{\rm cap} \propto n$ at 100 keV, while at 10 keV $\sigma_n^{\rm cap} \propto n^{2/3}$ is obtained. [1] H.J. L\"udde et al, Eur. Phys. J. D 70 82 (2016). [2] A.J. Privett et al, PLoS ONE 12(4): e0174456 (2017). [Preview Abstract] |
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GT1.00010: Analysis of radiative emissions in O$^{6+}$-argon, -water, and -methane charge-exchange collisions Anthony C. K. Leung, Tom Kirchner Charge exchange between highly-charged (solar wind) ions and neutrals is the main mechanism responsible for the observed x-ray emission from comets. A recent joint experimental/theoretical work looked at these processes for O$^{6+}$ collisions with argon atoms and a variety of molecules including water and methane at impact energies which correspond to the low and high solar wind speeds [1]. In the present work we study these collision systems using the two-center basis generator method within the independent electron model [2]. For the molecular targets we used a spectral representation of the target Hamiltonian and found that a closure approximation was necessary to produce reliable total cross section results for single-, double-, and triple-electron transfer. For the single-electron transfer channel we carried out a radiative cascade analysis and compared the resulting emission spectra with the classical-trajectory Monte Carlo calculations reported in [1]. Overall, the agreement is satisfactory. [1] J. R. Machacek \textit{et al}., Astrophys. J. \textbf{809} 75 (2015). [2] A. C. K. Leung and T. Kirchner, Phys. Rev. A \textbf{95} 042703 (2017). [Preview Abstract] |
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GT1.00011: Electron impact ionization of Methane at intermediate energy Esam Ali, Zehra Ozer, Chuangang Ning, James Colgan, Mevlut Dogan, Don Madison We have investigated the triple differential cross sections (TDCSs) for the electron impact ionization of the 1t$_{\mathrm{1}}$ state of molecular CH$_{\mathrm{4}}$ at 250 eV for asymmetric coplanar geometry with the scattering angles of 10$^{\mathrm{o}}$, 20$^{\mathrm{o}}$, and 25$^{\mathrm{o}}$ at fixed ejected energies 30 eV and 50 eV. The experimental measurement are compared to molecular 3-boday distorted wave (M3DW), where the theory used two different calculations by using proper average (M3DW-PA) and orientation averaged molecular orbital (M3DW-OAMO) approximation. The theory predicts the shape and the structure of cross section for experiment. Overall, the M3DW-PA show better shape agreement with experiment more than OAMO calculations. [Preview Abstract] |
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GT1.00012: Theoretical and experimental study of electron impact ionization (e,2e) of the R-Carvone molecule for an intermediate incident electron energy Esam Ali, Darryl Jones, James Colgan, Chuangang Ning, Oddur Ingólfsson, Michael Brunger, Don Madison We will present preliminary results from a combined theoretical and experimental study of electron impact single ionization of the R-Carvone molecule. The study was performed for a 250 eV incident electron energy, an ejected electron energy of 20 eV, and for three fixed scattered electron angles (5$^{\mathrm{o}}$, 10$^{\mathrm{o}}$, and 15$^{\mathrm{o}})$ in asymmetric coplanar geometry. Experimental data were measured for the three unresolved outermost orbitals - the highest, next highest, and next-next highest occupied molecular orbitals (HOMO, NHOMO, and HOMO-2). The generation of fully differential cross sections for this large molecule is extremely challenging for both experimental measurements and theoretical calculations. Theoretical M3DW (molecular 3-body distorted wave) results are summed over the three unresolved states to enable the comparison with the experimental data. [Preview Abstract] |
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GT1.00013: Fully Differential Study of Dissociative Capture and Coulomb explosion in p $+$ H$_{\mathrm{2}}$ Collisions Basu Lamichhane, Madhav Dhital, Thusitha Arthanayaka, Ahmad Hasan, Krishna Koirala, Trevor Voss, Ramazi Lomsadze, Michael Schulz We measured fully differential cross sections (FDCS) for dissociation due to capture and excitation to a repulsive state as well as Coulomb explosion due to double electron capture in p$+$H$_{\mathrm{2}}$ collisions. FDCS were analyzed for various molecular orientations relative to the momentum transfer in the transverse direction (q$_{\mathrm{x}})$ as a function of projectile scattering angle ($\theta_{\mathrm{p}})$. Two orientations parallel and perpendicular to q$_{\mathrm{x}}$ were analyzed. For the latter orientation two-center interference was identified. For the dissociative case, data were obtained for a range of kinetic energy releases (KER) from 5eV to 11eV. In this region the 2p$\pi_{\mathrm{u\thinspace }}$and the 2s$\sigma_{\mathrm{g\thinspace }}$states mainly contribute to dissociation. The interference pattern observed is consistent with the 2s$\sigma_{\mathrm{g\thinspace }}$state being dominant at large $\theta _{\mathrm{p\thinspace }}$while at small $\theta_{\mathrm{p\thinspace }}$both states contributes significantly. In double capture case, KER between 13eV to 27eV were selected since here only one channel (Coulomb explosion) contributes and the KER determines the inter-nuclear separation, the phase angle should be well determined. Nevertheless, the observed interference pattern is significantly less pronounced than for dissociation. [Preview Abstract] |
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GT1.00014: Effect of Flow Shear and Curvature on Plasma Instabilities J Walls, A Patel, O Johnson, B Felber, S Sen, M Goldstein We study the effect of inhomogeneous flow on low-frequency instabilities and turbulence. The inhomogeneous flow includes both flow shear and flow curvature. The effect of flow curvature (second radial derivative of flow) is shown to have significant effect in controlling the turbulence level contrary to the usual prediction that flow shear (first radial derivative of flow) alone controls the turbulence level. The detail result of this simulation will be reported. [Preview Abstract] |
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GT1.00015: Influence of a biased electrode on the electron energy distribution function S.D. Baalrud, B. Yee, E.V. Barnat, M.M. Hopkins Positively biased electrodes can influence the electron energy distribution function (EEDF) by providing a sink for low energy electrons that would otherwise be trapped. In hot filament generated discharges, the EEDF typically consists of a cool trapped population at energies below the energy associated with ions sheaths at the chamber wall and a comparatively warm tail population associated with the filament primaries. Inserting a positively biased electrode has little influence if it is sufficiently small. However, as the electrode area approaches $\sqrt{2.3m_e/m_i}A_w$, where $A_w$ is the chamber wall area, it collects most of the total electron current exiting the plasma. This can dramatically reduce the density of the otherwise trapped population, and cause the electron temperature to increase as the distribution approaches a temperature associated with the energetic filament primaries. A global model is developed, which shows the interconnected nature of the electron temperature, density and the plasma potential. The model is compared with Langmuir probe measurements in a dc filament generated plasma [1], and with new 2D PIC simulations. [1] Barnat, Laity and Baalrud, Phys. Plasmas 21, 103512 (2014). [Preview Abstract] |
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GT1.00016: Ion flow and sheath structure near positively biased electrodes Ryan Hood, Brett Scheiner, Scott Baalrud, Matthew Hopkins, Ed Barnat, Benjamin Yee, Robert Merlino, Fred Skiff Measurements of the ion velocity distribution function and plasma potential were made near small positively biased electrodes using laser-induced fluorescence and an emissive probe [1]. The effect of dielectric material surrounding the electrode was tested and compared with a 2D particle-in-cell simulation. Both measurements and simulation reveal that if the electrode is embedded within a dielectric ring, ions are accelerated toward the electrode to approximately 0.5 times the ion sound speed before being deflected radially by the electron sheath potential barrier. The axial potential profile in this case contains a virtual cathode. In comparison, when the surrounding dielectric is removed, both the ion flow and virtual cathode are almost completely absent. These measurements suggest that the ion presheath from the negatively charged dielectric encapsulates the electron sheath of the positively biased electrode, resulting in a virtual cathode that substantially influences the local ion flow profile. [1] R. Hood, B. Scheiner, S. D. Baalrud, M. M. Hopkins, E. V. Barnat, B. T. Yee, R. L. Merlino, and F. Skiff, Phys. Plasmas 23, 113503 (2016). [Preview Abstract] |
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GT1.00017: Steady-State Properties of Low Pressure Anode Spots Brett Scheiner, Scott Baalrud, Edward Barnat, Matthew Hopkins, Benjamin Yee When a small electrode is biased sufficiently above the plasma potential, the electron impact ionization of neutral species near the electrode becomes significant. At neutral gas pressures of 1-100 mTorr, it has been previously observed that if this ionization rate is sufficiently high a double layer may form near the electrode. In some cases the double layer will move outward, separating a high-potential plasma attached to the electrode surface from the bulk plasma. This phenomenon is known as an anode spot. A model has been developed to describe the steady-state properties of anode spots. In the model, an analysis of current loss, power balance, and particle balance leads to a prediction of the anode spot size, double layer potential, and form of the sheath at the electrode. These steady-state properties are related by and vary with the energy dependence of the electron impact ionization cross section, a feature absent in prior descriptions of the anode spot. [Preview Abstract] |
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GT1.00018: A real-time model for secondary electron emission coefficients in low temperature plasmas Manaswi Daksha, Julian Schulze Low temperature plasmas are an indispensable tool in the processing of highly technical devices. However, the predictive power on the behavior of such plasmas is limited. This is, in part, due to plasma-surface interactions. In modeling such plasmas, it is important to know the electron sticking and the ion-induced secondary electron emission coefficient. Experimental determination of secondary electron emission coefficients (SEEC) is difficult at low ion energies. Therefore, there is only a few amount of metals and metal-oxides that have determined coefficients for a small set of surface conditions. A theoretical model is required to predict and explain these coefficients for a wide range of materials and conditions. Here, SEECs due to potential auger emission are calculated ab initio. They are calculated for metal-oxides and metals with varying surface conditions. These conditions include plane orientation and crystallinity. Furthermore, many gases are considered including argon and oxygen. Excellent agreement is found between experiment and theory for metals. The theory predicts the secondary electron emission to vary widely depending on the metal-oxide crystal structure and purity. This has been found to be true experimentally for magnesium oxide. [Preview Abstract] |
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GT1.00019: Experimental observations on the characteristics of an anode spot onset Edward Barnat, Brett Scheiner, Scott Baalrud, Ben Yee, Matt Hopkins Experimental observations of the characteristic features of anode spot onset and stabilization in response to a stepped voltage applied to an anode immersed in a low pressure (100 mTorr) helium afterglow are reported in this poster presentation. These observations include spatial and temporal evolution of metastable species measured by planar Laser induced fluorescence (PLIF), electron densities as measured laser-collision induced fluorescence (LCIF) and electric fields around and in the spot as measured by laser-induced fluorescence-dip (LIF-dip) spectroscopy. Oscillations observed during spot formation process are correlated to transient response of the host plasma induced by sudden loss of electron species by the spot. Experimental observations are compared with computational simulations and theory presented in a companion poster. [Preview Abstract] |
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GT1.00020: Ion extraction process from a decaying plasma by introducing an external electron source He-Ping Li, Jian Chen, Heng Guo, Dong-Jun Jiang, Ming-Sheng Zhou Ion extraction is a complex physical process with multi-particle and multi-field coupling, and is important in many fields, such as materials processing, etching and some pulsed processing with plasmas induced by an intense laser. Under such a typical pulsed processing, plasmas are usually decaying; and thus, it is indispensable to develop the novel methods to improve the extraction efficiency and shorten the extraction time. However, due to the shielding effects of the electrode sheath, the electric field cannot penetrate the whole plasma region, and only the ions in the sheath can be accelerated, which limits significantly the improvement on the ion extraction efficiency for a conventional parallel-plate ion extraction process. In this study, a novel method by introducing an external electron source is proposed to weaken the shielding effects. The modeling results show that the introduction of the external electrons can implement the loss of the plasma electrons and restrain the charge separation. Under such conditions, the conventional Child-Langmuir sheath will not form, and the ion extraction time will be shortened significantly resulting from the weakening of the shielding effects of the sheath. [Preview Abstract] |
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GT1.00021: Locking the Plasma Potential with an Anodic Surface Matthew Hopkins, Benjamin Yee, Edward Barnat, Scott Baalrud, Brett Scheiner It is often assumed that a small positively biased electrode immersed into a bulk plasma has negligible impact on the bulk plasma properties, including the plasma potential. This is an assumption in many diagnostic devices, such as a Langmuir probe. In this poster we present a detailed study including simulations and experiments to determine the size scales when such an immersed positive interface has non-negligible impact on the plasma [1]. That is, we answer the question, “what is the largest size for an anodic surface before it influences the plasma?”. Letting $\mu = \sqrt{2.3m_e/m_i}$, we find that if the ratio of anode area ($A_A$) to grounded wall area ($A_W$) $A_A/A_W \lt 1\times\mu$, we can expect little impact on the bulk plasma, but as $A_A/A_W \to 1.7\times\mu$ we see significant influence, and at $A_A/A_W \gt 1.7\times\mu$, we expect the plasma potential to become locked to, and therefore controlled by, the anode potential. [1] Hopkins, Yee, Baalrud, Barnat, Phys. Plasmas 23, 063519 (2016). [Preview Abstract] |
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GT1.00022: Analytical model of the short argon arc Alexander Khrabry, Igor Kaganovich, Valerian Nemchinsky, Andrei Khodak In a short atmospheric-pressure arc (with several millimeters between electrodes) near-electrode non-equilibrium regions may occupy major part of the inter-electrode gap or even overlap. Therefore non-equilibrium effects in plasma such as thermal, ionization non-equilibrium, electron diffusion, thermal diffusion and effects of space-charge sheaths are important for understanding of the arc physics. An analytical model of argon arc comprising of models for near-electrode regions, arc column and a model of heat transfer in cylindrical electrodes has been developed. The model predicts arc voltages, plasma density and temperature profiles and heat fluxes to the electrodes. Parametric studies of the arc have been performed for a range of the arc current density and pressure. Analytical solutions have been compared with simulation results performed making use of non-equilibrium one-dimensional arc model. The model was validated against experimental data and verified by comparison with Ref. [1]. Good agreement between the analytical model and simulations and reasonable agreement with experimental data were obtained. [1] N. Almeida et.al, 2008, J. Phys. D: Appl. Phys. 41. [Preview Abstract] |
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GT1.00023: Properties of the electron sheath in low temperature plasmas Benjamin Yee, Brett Scheiner, Scott Baalrud, Edward Barnat, Matthew Hopkins The preponderance of sheath research has focused on ion sheaths and neglected electron sheaths in spite of their importance to Langmuir probes, microdischarges, sheath inversion, and negative ion sources. The conventional view of the electron sheath is that of a sharp transition region from the quasineutral plasma to the space charge dominated region. This view implies that only the random thermal flux of electrons crossing the electron sheath boundary is collected by the electrode. In this work, a combination of experiments, simulations, and theory is used to demonstrate that reality is considerably more complex than expected and that the physics of electron sheaths is unexpectedly rich. Advanced laser diagnostics prove the existence of a large transition region outside of the electron sheath. Simulations show that these ``electron presheaths'' are driven by pressure gradients rather than the electric field, and that these gradients originate from a loss cone-like truncation of the electron velocity distribution function. The electron flow driven by this pressure gradient can be sufficiently strong so as to excite instabilities in the sheath edge. [Preview Abstract] |
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GT1.00024: On the influence of parasitic capacitances on the ion energy bombardment in a large-area multi-frequency CCP Stefan Ries, Julian Schulze, Peter Awakowicz In this work, a large-area capacitively coupled multi-frequency plasma chamber (electrode diameter: 500 mm; gap: 35 mm) is used to investigate its capability for a better control of plasma processing in the industry. The basic idea is to use the electrical asymmetry effect (EAE) by varying the phase shift between the two lower frequencies (13.56 and 27.12 MHz) in order to control the ion energy onto the grounded substrate electrode without any effect on the high ion flux generated by 60 MHz. The ion flux and the ion energies onto the grounded substrate are measured with a retarding field analyzer. By measuring the voltage signal and using a 1D-model [1] to describe the EAE, a symmetry parameter much lower than 1 was found, which reveals a very geometrically asymmetric plasma condition. Hence the range of ion energy variation by changing the phase is much lower than it needs to be to generate remarkably changes in the film properties. Further investigations have exhibited a parasitic capacitive coupling between the powered electrode and the grounded shield that surrounds the powered electrode. In conclusion, advanced experiments to confine the plasma between both electrodes were conducted that lead to a broader ion energy variation. [1] E. Sch\"{u}ngel, et.al., Plasma Proc. Polym., 14, 1600117 (2017) [Preview Abstract] |
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GT1.00025: The effect of pressure and driving frequency on electron heating in a capacitively coupled oxygen discharge Jon Tomas Gudmundsson, David I. Snorrason, Holmfridur Hannesdottir We use the one-dimensional object-oriented particle-in-cell Monte Carlo collision code {\tt oopd1} to study the evolution of the charged particle density profiles, electron heating mechanism, and the electron energy probability function (EEPF) in a capacitively coupled oxygen discharge with pressure and driving frequency. We find that at higher pressure (50--500 mTorr) the electron heating occurs mainly in the sheath region, and detachment by the metastable singlet molecules significant has a significant influence. At a low pressure (10 mTorr) and driving frequency of 13.56 MHz, Ohmic heating in the bulk plasma (the electronegative core) dominates. However, as the driving frequency is increased the electron heating transitions to occur mainly in the sheath region. Thus at low pressure and low driving frequency, the EEPF is convex and as the driving frequency is increased the number of low energy electrons increases and the number of higher energy electrons ($>$10 eV) decreases, and the EEPF develops a concave shape or becomes bi-Maxwellian. Furthermore, we find that adding detachment by the metastable states can significantly influence the peak of the ion energy distribution for O$_2^+$-ions bombarding the powered electrode, and hence the average ion energy and ion flux. [Preview Abstract] |
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GT1.00026: Two-dimensional fluid simulation in a radio frequency capacitively coupled plasma sustained in SiH$_{\mathrm{4}}$/N$_{\mathrm{2}}$/O$_{\mathrm{2}}$ wenzhu jia, yuanhong song, younian wang In a low pressure radio frequency capacitively coupled plasma sustained in SiH$_{\mathrm{4}}$/N$_{\mathrm{2}}$/O$_{\mathrm{2}}$ gas mixture, we investigate how the dielectric layer on the bottom electrode plays it's role on the plasma characteristics by using a two-dimensional fluid model. The simulation results show that the presence of the dielectric layer could effectively suppress the non-uniformity of plasma caused by the edge effect. When the dielectric thickness increases to a certain value, the discharge will be extinguished. In addition, for the possible gas-phase precursors in SiH$_{\mathrm{4}}$/N$_{\mathrm{2}}$/O$_{\mathrm{2}}$ gas mixture, nitrogen, silicon, and oxygen-containing species are examined as a function of the pressure and composition ratio of the mixed gas. The results show that SiH$_{\mathrm{3}}$O, SiH$_{\mathrm{2}}$O, O, N and NO may be the most important deposition precursors, rather than SiN and HSiNH,etc. Moreover, the large amounts of water are formed by a number of oxygen and hydrogen-containing species presented in this gas mixture. At last, the calculated deposition rate of O, N and Si atoms are also discussed in terms of the gas pressure and composition ratio in order to predict what kind of silicon-based film can be formed. [Preview Abstract] |
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GT1.00027: Experimental investigation of standing wave effect in dual-frequency capacitively coupled argon discharges: role of low frequency source. Yong-Xin Liu, Kai Zhao, You-Nian Wang It is well known that the plasma non-uniformity caused by the standing wave effect has brought about great challenges for industrial applications. To improve the plasma uniformity, another low-frequency (LF) source was introduced, aiming to examine its effect on the radial distribution of plasma density in capacitively coupled argon plasma driven by a very-high-frequency (VHF, 100 MHz) source. The radial profiles of plasma density and spatio-temporal distributions of the electron-impact excitation rate were determined by utilizing a hairpin probe and the phase resolved optical emission spectroscopy, respectively. In this work, two typical cases [i.e., the LF and VHF sources are applied on one electrode (case I) and different electrodes (case II)] have been taken into account. Our experimental results indicate that for case I an excellent plasma uniformity can be achieved by adjusting the LF voltage amplitude or LF frequency, while the LF component was found to have a small effect on the plasma uniformity for case II. To understand the different results between these two cases, the electron excitation dynamic and the frequency coupling mechanism on each case were analyzed based on the measured spatio-temporal distributions of the electronic excitation rate. [Preview Abstract] |
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GT1.00028: Simulation of a pulse-modulated radio-frequency atmospheric pressure glow discharge in Argon-Oxygen mixture Xuechun Li, Hui Liu, Younian Wang The pulse-modulate radio-frequency atmospheric pressure glow discharges (RF- APGDs ) plasmas can achieve low temperature RF APGDs with reduced power consumption. As a new discharge form, it has been investigated for applications in trials in cancer therapy, sterilization, air pollution control, etc . And it has been confirmed that ROS(Reactive oxygen species) play a key role in the processes. Thus, the characteristics of the ROS versus various discharge parameters may be a guidance for the industrial application. In this work, we use a fluid model to simulate the plasma characteristics for pulse-modulate RF-APGDs in argon-oxygen mixture. The influences of the duty cycle of pulse-modulated on the characteristics of discharge are studied. The evolution of electron density, electron energy and various reactive species versus oxygen admixture is discussed. [Preview Abstract] |
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GT1.00029: Picosecond spectroscopy and electric field of interacting streamers on dielectric surface Tomas Hoder, Petr Synek, Mirko Cernak Surface streamers in coplanar barrier discharge in synthetic air at 30 kPa pressure were studied by time-correlated single photon counting enhanced optical emission spectroscopy and far-field microscopy enhanced intensified CCD camera. The discharge operated in a regime where two subsequent micro-discharges appeared within the same voltage half-period. During the second micro-discharge the positive surface streamers mostly follow the interface between the area of deposited charge from the previous one and the area of uncharged dielectric surface. A suppressed streamer propagating over the area of deposited surface charge was tracked and an evidence of surface streamer reconnection is hypothesized. A spatiotemporal distribution (resolution of 120 ps and 100 microns) of the reduced electric field strength was obtained for both micro-discharges from the recorded luminosities of the molecular nitrogen. The reduced electric field of positive streamers in the first micro-discharge reached 1200 Td. For the second one, the electric field values for the streamer at the interface are slightly lower than that, while for the suppressed streamers are even higher. [Preview Abstract] |
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GT1.00030: Ignition voltage of atmospheric-pressure dielectric barrier discharges in argon with admixtures of HMDSO and TMS D. Loffhagen, M. M. Becker, J. Philipp, A. K. Czerny, C.-P. Klages Hexamethyldisiloxane (HMDSO) and tetramethylsilane (TMS) are frequently used as monomers in dielectric barrier discharges (DBD) for the deposition of silicon-organic films. Already small admixtures of few ppm of these monomers to the carrier gas lead to drastic changes of the discharge characteristics due to Penning ionization processes. In the present contribution, the impact of HMDSO and TMS on the ignition behavior of an atmospheric-pressure DBD in argon is analyzed experimentally and by means of numerical modeling. Rate coefficients for Penning ionization and quenching due to collisions of excited argon atoms with HMDSO and TMS, respectively, are specified by an experimental validation of results of a time-dependent, spatially one-dimensional fluid model. The experimentally observed decrease of the ignition voltage with increasing monomer admixture in the range from 0 to 200\,ppm by about 60\% can be reproduced with very good agreement by the validated model. [Preview Abstract] |
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GT1.00031: Thermal and energetic study of nanosecond sparks for application to plasma-assisted combustion Nicolas Minesi, Sergey Stepanyan, Erwan Pannier, Gabi-Daniel Stancu, Christophe Laux Nanosecond Repetitively Pulsed (NRP) discharges are widely used for ignition and stabilization of lean combustible mixtures because of their interesting chemical, thermal and hydrodynamic effects. While the chemical and thermal effects have been extensively studied, the hydrodynamic effects have received much less attention. Yet, they provide a unique means to increase the combustion velocity by redistributing active species and heat over a large volume of gas. The aim of the present work is to understand the mechanism of hydrodynamic coupling in NRP discharges in order to maximize its effects. Parametric studies were performed in atmospheric pressure air with electrodes in pin-to-pin geometry. Time-resolved Schlieren diagnostics, optical emission spectroscopy (OES), and electrical measurements at different frequencies (0-100 kHz) have been conducted to study the dependence of the hydrodynamic effects on the energy deposited per pulse, the inter-electrode space, and the pulse repetition frequency, both in quiescent and flowing air. The potential of these discharges for combustion of lean mixtures or flow control will be discussed. [Preview Abstract] |
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GT1.00032: Effect of accumulated charges desorption in atmospheric pressure oxygen dielectric barrier discharge Haruaki Akashi, Tomokazu Yoshinaga Recently, atmospheric dielectric barrier discharges (DBDs) are widely applied to various fields, such as ozone generation, bio-medical field and so on. But less attentions on the mechanisms of accumulated charges behaviors between discharge space and dielectric surfaces. Golubovskii et al[1], simulated Atmospheric Pressure Townsend Discharges using one dimensional fluid model with considering the effect of the charge detachments. Recently, Itoh et al[2] also mentioned about desorption from dielectrics in DBDs. In the present paper, simulation with considering accumulated charges desorption by the electric field has been done using two dimensional fluid model[3]. The effect of electron desorption from the dielectrics affect significantly on the electron density distributions in the vicinity of the dielectrics. In the bulk region, less effect on the electron density distributions can be seen. And the charges accumulated on the dielectrics increase in positive on both dielectrics. As a result, the assumed condition of desorption would be inappropriate.[1] Y.B.Golubovskii, et al, J.Phys. D: Appl.Phys. 35, pp.751-761 (2002) [2] H.Itoh et al, ESCAMPIG XXIII, Bratislava, Slovakia, p.192 (2016)[3] G.Takahashi and H.Akashi, IEEE Trans. PS-39, 11, pp.234-235 (2011) [Preview Abstract] |
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GT1.00033: Investigation of Discharge Processes in a High-Pressure Pulsed Arc Discharge Environment for Model Verification. Ricky Tang, Andrew Fierro, Edward Barnat, Matthew Hopkins Characteristics of a plasma generated in an arc discharge are investigated. In a discharge, various processes contribute to overall characteristics. Electron chemistry and photonic processes each play a role in establishing the discharge environment based on background pressure and gas species involved. Photonic processes have been incorporated into a PIC-DSMC plasma modeling code, showing effects of including these processes on the discharge current and generating simulated photo-emission spectra. A high-pressure arc discharge experiment was set up to validate model prediction and attempt to elucidate mechanisms of charged species interaction during discharge and in the post-arc environment. Photodetectors and optical emission spectroscopy are used to probe the plasmas and characterize their spectral responses. Discharges generated with inert and reactive gases (nitrogen and air) are studied. Furthermore, differentially-charged species in the post-arc environment interact via local electric field, resulting in current flow. Model can simulate/isolate various processes, and discharge behavior can be inferred by measuring dI/dt and compared with predicted observables, showing FFT components associated with this localized current flow due to charged species interaction. [Preview Abstract] |
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GT1.00034: Equilibrium plasma formation in coaxial plasma accelerators Vivek Subramaniam, Laxminarayan Raja Coaxial plasma accelerators are electromagnetic acceleration devices that utilize the Lorentz force generated by self-induced magnetic fields to accelerate high density thermal plasmas to large velocities (10Km/s). The deflagration mode of accelerator operation is achieved by introducing a neutral gas puff into an evacuated coaxial inter-electrode volume that is stood off to a high potential (5 kV). The neutral gas breaks down to form a two-temperature non-equilibrium plasma that rapidly thermalizes to produce an arc. In this work, a computational model based on the self-consistent, multi-species continuum description of the plasma is used to study the neutral gas breakdown and the incipient stages of the thermalization process. The non-equilibrium plasma model is used to obtain a timescale associated with the temperature equilibration process. The plasma model is subsequently coupled with a Navier-Stokes based flow model to yield an effective length over which the plasma equilibrates as it expands into the initially evacuated inter-electrode volume. The objective of this study is to self-consistently obtain an inlet temperature boundary condition and an effective accelerator length for a MHD model that is used to describe the equilibrium plasma as it accelerates under the effect of the Lorentz force. [Preview Abstract] |
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GT1.00035: Kinetic effects during the interaction between high density microplasma and electromagnetic wave Dmitry Levko, Laxminarayan Raja The interaction between a high-density microplasma and high-power electromagnetic wave is studied by one-dimensional Particle-in-Cell Monte Carlo collisions model coupled with the Maxwell's equations. We find the value of the amplitude of the wave field above which a fully ionized plasma is generated on the picosecond time scale. This fully ionized plasma is obtained only in the skin layer while the ionization degree of the plasma bulk is \textasciitilde 20{\%}. The simulation results show that such non-homogeneous distribution of plasma and gas density influences significantly the heating of plasma electrons and time evolution of the electron energy distribution function. [Preview Abstract] |
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GT1.00036: Study of a micro hollow cathode discharge in Ar/N$_{\mathrm{2}}$ used for boron nitride synthesis. Claudia Lazzaroni, Salima Kasri, Xavier Aubert, Guillaume Lombardi, Alexandre Tallaire, Jocelyn Achard, Nader Sadeghi A microplasma is generated in the 400 micron diameter micro hole of a molybdenum-alumina-molybdenum sandwich (MHCD type) at several hundreds of Torr in argon (Ar) with an admixture of nitrogen (N$_{\mathrm{2}})$. MHCDs allow high electron densities and therefore we expect to reach high dissociation degree of nitrogen which is particularly suited for nitride deposition given the high bond energy of molecular nitrogen. A global model of the discharge, that combines the particle and the energy balance equations, is presented. The model is run until the steady state is reached and we obtain the plasma parameters that are the species densities and the electron temperature. A particular focus is given to the electron density and the atomic nitrogen density, a key parameter for the deposition and growth of nitride films. The model predictions are compared to experiments performed during the normal regime, when the plasma is not only confined in the hole but also expands on the cathode backside. Emission spectroscopy is used to infer the electronic density in the micro-hole via the Stark broadening of the H$_{\mathrm{\beta }}$ line. A parametric study is done varying the current, the gas pressure and the N$_{\mathrm{2}}$ fraction in Ar. [Preview Abstract] |
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GT1.00037: Modelling of an RF plasma jet at atmospheric pressure using complementary approaches Florian Sigeneger, Jan Sch\"afer, R\"udiger Foest, Detlef Loffhagen Different model approaches have been used to investigate various aspects of a non-thermal RF plasma jet operating in argon at atmospheric pressure. The jet consists of two concentric capillaries and two cylindrical electrodes driven by an RF voltage at 27.12 MHz. The studies concern the generation of a filamentary plasma in the active volume investigated by a phase-resolved single filament model and the interaction of the plasma with the gas flow and with precursor molecules additionally injected for the deposition of thin films. The latter is studied by a period-averaged axially symmetric model of the plasma jet including the effluent which is directed to a substrate. Further studies refer to the phenomena of self-organization observed e.g. in the regular azimuthal rotation of filaments. The relation between the inclination of the filaments and the azimuthal gas velocity component has been revealed by a three-dimensional hydrodynamic model of gas flow and heating using the heating profile from the the single filament model. [Preview Abstract] |
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GT1.00038: Nonlinear Hydrodynamic Effects in Dense Microplasmas Dylan Pederson, Konstantinos Kourtzanidis, Laxminarayan Raja Nonlinear behavior in plasma interactions with GHz electromagnetic waves arises from nonlinearities in the electron momentum equation, among other sources. In systems where there may be a high local electric field amplification (resonators), dense microplasmas of size much smaller than the wavelength are formed near regions of high fields. In a typical Finite-Difference Time-Domain simulation, a plasma is modeled as a (linear) Drude material, which does not capture the nonlinear polarization terms of a plasma. In this work we couple the nonlinear electron momentum equation to electromagnetic simulation in order to explore nonlinear behavior. [Preview Abstract] |
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GT1.00039: Numerical modeling of microwave driven surface discharge induced by resonantly exciting spoof surface plasmon polariton. Yunho Kim, Laxminarayan Raja Spoof Surface Plasmon Polariton (SSPP) is an electromagnetic wave strongly confined near the surface of a corrugated metal surface (meta-surface) filled with dielectric materials. Strong resonances from each corrugated structure couple with one another to produce highly localized wave structures with wavelength much lesser than the incident wave. The electric field amplification of the microwave at the interface of the meta-surface is used to initiate the plasma breakdown of pure argon gas at 10 Torr. A self-consistent model for the description of plasma coupled with Maxwell's equations is used in this numerical study. By carefully choosing the dimensions of each periodic structure with the use of the dispersion relations for SSPP, a uniformly elongated argon plasma is obtained near the meta-surface where electron number density reaches around 1.0*${10}^{19}m^{-3}$. It is found that the nature of SSPP strongly depends on the dimensions of the meta-surface, the dielectric permittivity, and frequency which therefore determine the plasma profile. [Preview Abstract] |
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GT1.00040: Development of a Cascade Arc Discharge for an Atmosphere-vacuum Interface. Shinichi Namba, Yuuki Iwamoto, Megumi Ueda, Takuma Endo, Naoki Tamura In order to demonstrate a high-performance plasma window as a vacuum interface, a compact and low-cost wall-stabilized arc (cascade arc) discharge apparatus has been developed. The device diameter was 120 mm, a length of 100 mm and its weight of \textless 15 kg, which had a 3.2mm-CeW cathode, eight intermediate electrodes, and a CuW anode to generate the plasma channel with an opening of 3 mm. Absolute pressures in the discharge and expansion sections were measured to examine the performance as the plasma window. Visible emission spectroscopy to determine the plasma parameters has been carried out as well. At Ar discharge of 50 A, the gas pressure significantly decreased from 100 kPa to 0.1 kPa between the discharge channel. Spectral analysis indicated that the plasma had an electron temperature of \textgreater 1 eV and a density of 2.4×10$^{\mathrm{16}}$ cm$^{\mathrm{-3\thinspace }}$at 50 A at the anode exit. By installing a higher-power water pump and cooling tower, providing a pressure of 10 atm at a flow rate of 15 L/min, we will increase the discharge current up to 100 A to obtain much hot, dense arc plasmas. [Preview Abstract] |
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GT1.00041: ABSTRACT WITHDRAWN |
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GT1.00042: Experimental and Theoretical Study of the Carbon Arc: from Plasma to Nanomaterial Synthesis Vladislav Vekselman, Alexander Khrabry, Brentley Stratton, Igor Kaganovich, Yevgeny Raitses A carbon arc for nanomaterial synthesis was comprehensively studied using spectroscopic techniques and modeled by specially modified computationally fluid dynamic (CFD) code ANSYS. The arc was operated at near atmospheric pressure of He background gas. Under these conditions, the carbon arc plasma is generated and sustained by ablation of the graphite anode. The same process generates carbon feedstock for carbon nanomaterials synthesis. We performed experimental study and CFD modeling to fully characterize plasma and carbon composition in the synthesis region that is important for understanding of synthesis of carbon nanomaterials by the arc method. This study revealed dimensions of the hot arc core and a cooler region of the arc periphery where synthesis of nanostructures occurs. Measurements and simulations show that the main component in the synthesis region is C$_{\mathrm{2}}$, which is a key precursor for synthesis of carbon nanostructures. Measurements of the voltage drop in the arc confirms hypothesis that the enhanced ablation occur due to transition of the anode sheath from electron-repelling at low arc currents to electron-attractive at high currents. [Preview Abstract] |
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GT1.00043: ABSTRACT WITHDRAWN |
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GT1.00044: Production of electrical discharges in acoustic cavitation bubbles K. Sasaki, N. Takada, Y. Hayashi, M. Goto We produced electrical discharges in acoustic cavitation bubbles with the intension of enhancing the reactivity of sonochemical processes. Acoustic cavitation bubbles were generated in a rectangular vessel which was filled with water by applying an ultrasonic power at a frequency of 27 kHz. The efficient generation of cavitation bubbles was possible with the help of a punching metal plate$^1$. Glowlike discharges were observed in cavitation bubbles which were attached on the bottom surface of the cylindrical high-voltage electrode. Bright optical emission was observed in the expanding period of cavitation bubbles, while we also observed electrical discharges even in the shrinking phase. The discharge was possible until 3.7 $\mu$s before the collapse of cavitation bubbles. If lifetimes longer than 3.7 $\mu$s are expected for discharge-produced reactive species, the species composition inside the collapsed cavitation bubbles with the discharge may be different from that without the discharge. The discharge in the cavitation bubbles may be helpful to enhance the reactivity of sonochemistry processes. \par \noindent $^1$Y. Iwata, N. Takada, and K. Sasaki, Appl. Phys. Express \textbf{6}, 127301 (2013). [Preview Abstract] |
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GT1.00045: Formation of Metal-Composite Nanoparticles by Laser Ablation under Supercritical CO$_{\mathrm{2}}$ Mardiansyah Mardis, Wahyu Diono, Noriharu Takada, Hideki Kanda, Motonobu Goto Gold (Au), silver (Ag), titanium (Ti) and iron (Fe) nanoparticles were produced by pulsed laser ablation (PLA) of a metal plate in supercritical CO$_{\mathrm{2}}$. Metal plate was placed in the center of high pressure chamber and ablated by using Nd: YAG laser with 532 nm and 1064 nm of wavelength. The experiments were performed at temperatures of 31$^{\mathrm{o}}$C-80$^{\mathrm{o}}$C and pressures of 5-15 MPa with irradiation time of 15 minutes. The generated particles were analyzed by using field emission scanning electron microscopy (FE-SEM), scanning transmission electron microscopy (STEM), transmission electron microscopy (TEM) system equipped with energy dispersive X-ray spectroscopy (EDS). The results showed that the generated particles are spherical in shape with average diameter 5-100 nm. Besides, based on EDS results, the generated particles consists of carbon, oxygen and metal which provide the evidence of reaction between metal target and solution (CO$_{\mathrm{2}})$. Moreover, the influence of CO$_{\mathrm{2}}$ by changing the temperatures and pressures were also studied and the possible mechanisms of particles formation are discussed. This provides useful insight for the synthesis of composite nanoparticles which can be applied in several fields, such as catalysis and photonics. [Preview Abstract] |
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GT1.00046: The impact of solution chemistry on the absorption spectra of plasma-generated solvated electrons in aqueous solutions Hernan E. Delgado, Paul Rumbach, David M. Bartels, David B. Go In this work, we use a low-temperature atmospheric plasma as a cathode in an electrochemical cell to generate solvated electrons, and a total internal reflection absorption spectroscopy (TIRAS) technique to measure their optical absorbance at different wavelengths. Solvated electrons are a species of great interest because of their ability to drive a variety of chemical reactions at the plasma-liquid interface. Historically, their absorption spectrum and thermodynamic properties in aqueous solutions have been studied extensively with pulse radiolysis. However, while radiation generates solvated electrons in the bulk from the solvent molecules, solvated electrons from plasma-liquid interactions form near the interface, which can lead to different behavior. For example, we have observed significant differences in the plasma-generated (e$^{\mathrm{-}})_{\mathrm{aq}}$ optical absorption spectrum, including a shift of the spectrum toward the blue and a suppression of the Lorentzian tail on the high-energy side. We will present further study of these spectra in different solutions with varying salt (sodium perchlorate) concentrations in order to understand the interfacial behavior of plasma-solvated electrons. [Preview Abstract] |
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GT1.00047: Resonance induced striations in electronegative capacitively coupled radio-frequency plasmas Edmund Schuengel, Yong-Xin Liu, Ihor Korolov, Zoltan Donko, Julian Schulze, You-Nian Wang The eigenfrequency of capacitively coupled radio-frequency plasmas in electronegative gases may locally match the frequency of the applied voltage. Such a resonance leads to a spatial modulation of the electric field, the densities of positive and negative ions, the energy gain of electrons, and the optical emission intensity in the plasma bulk region. Accordingly, self-organized striation patterns emerge. We investigate these striations and the physical mechanisms behind them in capacitive discharges in CF{\$}\textunderscore 4{\$} by a combination of Phase Resolved Optical Emission Spectroscopy measurements and outcomes of PIC/MCC simulations for various neutral gas pressures, electrode gaps, and applied voltage frequencies and amplitudes. The distance between the striations is found to decrease as a function of pressure. Furthermore, the discharge modes and mode transitions depending on the global control parameters are mapped in a phase diagram. [Preview Abstract] |
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GT1.00048: Forming of long nanosecond pulses with the rectangular envelope in a compact active microwave pulse compressor. Vladislav Igumnov, Stanislav Gorev, Sergey Artemenko The paper presents the results of research of a compact, compared to the length of the emitted wave train, active microwave compression systems. This system allow for generating high power microwave pulses with the duration from \textasciitilde 10 ns to \textasciitilde 100 ns and a rectangular pulse shape. The variant of the compression system is based on an oversized cylindrical cavity, which generates TE0mn (m, n\textgreater 1) type oscillations and is composed of a set of (m-1) circular waveguide sections. The sections are embedded coaxially into the cavity volume. The sections have the same diameter as that of the boundaries of radial variant of working mode oscillation and also have a length of half wave less than the working wavelength of the cavity. They fixed at the input and output of the end of the cavity wall. Thus, a set of waveguide sections forms a slow-wave structure, which increased travel time of wave into the volume of a cavity. The energy output device for the cavity is designed as an interference microwave switch based on the H-tee. It was shown experimentally that such compressors form nearly rectangular shaped microwave pulses. The power of the output pulse is comparable to the power of the waves in the classical microwave compression systems. [Preview Abstract] |
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GT1.00049: Construction of a multidipole cylindrical chamber, MAXIMUS, with magnetic X-point configuration and investigation of its plasma properties Yegeon Lim, Daeho Kwon, Won Jun Lee, Bo Sung Kim, Young-chul Ghim We have constructed a low temperature DC plasma source with a cylindrical (60cm radial and 200cm axial) multidipole chamber, `MAgnetic X-point sIMUlator System (MAXIMUS)', whose base pressure is \textasciitilde 10$^{\mathrm{-6}}$ Torr. DC plasmas are generated by a number of hot tungsten filaments which can be biased up to -200 V with respect to the grounded chamber. By applying approximately 50A of current to the filaments, we obtain plasma density of the order of 10$^{\mathrm{9}}$ cm$^{\mathrm{-3}}$ with the electron temperature of \textasciitilde 1 eV measured by a single Langmuir probe. A set of axial copper tube through the chamber creates an axially homogeneous magnetic X-point. This configuration allows us to investigate effects of X-point to the surrounding plasmas. In this work, we present basic properties of plasmas in MAXIMUS and how we can control them. [Preview Abstract] |
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GT1.00050: Influence of Initial Conditions On Discharge-Pumped XUV Laser Beam. Jiri Schmidt, Karel Kolacek, Jaroslav Straus, Oleksandr Frolov This work reports on recent results of the experimental device CAPEX working as an XUV laser source that is pumped by a fast capillary discharge. On this device we observed lasing at 46.9 nm (Ne-like Ar line). The initial conditions (such as pre-pulse current amplitude and duration, filling argon pressure in the capillary) play a key role on the laser beam characteristics (e.g. on the laser beam profile, and on the laser pulse energy). The external pre-pulse driver operates independently on the main capillary current. The pre-pulse current amplitude can be varied in the range from 5 A up to hundreds of A, and its duration (the pre-pulse beginning to the main current onset) can be adjusted from 3 ?s up to hundreds of ?s. We have found a significant influence of these initial conditions on the laser beam profile and on the laser pulse energy. Of course, the initial pressure of argon inside the capillary has a substantial effect on the laser beam as well. These measurements have been performed for three groups of the main capillary current amplitudes (\textasciitilde 12 kA, \textasciitilde 19 kA, \textasciitilde 26 kA). In summary, this paper gives a systematic survey of laser beam profiles and laser pulse energies in dependence on capillary-discharge initial conditions varying in much broader ranges than ever before. [Preview Abstract] |
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GT1.00051: Characterization of a Flow-Through Low Temperature RF Plasma Reactor for Nanomaterial Synthesis Necip Uner, Elijah Thimsen Flow-through low temperature plasmas are being increasingly studied in the laboratory, especially for producing nanomaterials. Low temperature radio frequency (RF) plasmas have been very successful for synthesizing crystalline and monodisperse semiconductor nanocrystals. Although used by many groups worldwide, thorough characterization of the reactor itself is largely missing from the literature. The flow-through reactor used in this study was a simple and easy-to-build capacitively coupled RF design comprised of a glass tube with two ring electrodes wrapped outside of the tube. Using a Langmuir double probe, electron temperature and ion density were measured as a function of axial position, input RF power, and pressure. Neutral gas temperatures were determined using a fluorescence decay temperature probe. The reactor was found to have a distinct distribution of ion density and gas temperature along its central axis. Gas temperatures were found to be significantly higher than room temperature at moderate applied RF powers. Along with a complete set of plasma parameters as a function of axial position, calculated nanoparticle temperature histories and the energy efficiency of the reactor will also be presented. [Preview Abstract] |
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GT1.00052: Neutral Flow Coupling in Helicon Plasmas Earl Scime, Zachary Short, Miguel Henrizquez, Jacob McLaughlin, Luke Neal, Derek Thompson Neutral particle distributions are critical to the study of plasma boundary interactions, where ion-neutral collisions, e.g. via charge exchange, may modify energetic particle populations impacting the boundary surface. Neutral particle behavior at absorbing boundaries thus underlies a number of important plasma physics issues, such as wall loading in fusion devices and anomalous erosion in Hall thruster channels. Neutral velocity distribution functions (NVDFs) are often measured using laser-induced fluorescence (LIF). Our standard LIF scheme excites the 1s4 non-metastable state of neutral argon with 667.913 nm photons from a tunable diode laser. The subsequent decay emission at 750.590 nm is recorded synchronously with injection laser frequency. The signal-to-noise of this LIF scheme is poor. Here we present NVDF measurements using a recently developed scheme for neutral argon LIF at 706.92 nm (exciting from the 1s5 to the 2p3 state). Emission is observed at 738.60 nm (from the 2p3 state to the 1s4 state). The light source for this LIF scheme is a high-power, tunable dye laser. The NVDF measurements are compared to three-dimensional ion flow field measurements performed at the same locations in a helicon plasma source. [Preview Abstract] |
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GT1.00053: Laser Induced Fluorescence for Singly Ionized Atomic Iodine Thomas Steinberger, Earl Scime While xenon is the standard propellant for a wide range of plasma thrusters, xenon is expensive and xenon propellant systems require heavy compressed gas tanks, pressure regulators, and other bulky hardware. Iodine has similar mass and is much easier to acquire than xenon. Iodine’s natural state of matter at room temperature is solid and is easily sublimated to gas with a simple heating element. This advantage for iodine is also a significant challenge when developing gas handling systems for iodine. Another challenge for iodine thrusters is a lack of well-defined spectroscopic diagnostics for single ionized iodine, specifically, a lack of a demonstrated laser induced fluorescence (LIF) scheme. We present emission spectroscopy measurements of iodine ion emission from the $6p^5P_3-5d^5D^o_4$ transition at 695.878 nm and the $6p^5 P_3-6s^5 S_2^o$ transition at 516.12 nm as a function of pressure and microwave power for a microwave excited iodine plasma in a sealed quartz cell at a pressure of 1 mTorr. The $5d^5 D_4^o$ state is metastable and was identified by Hargus et al. [48th AIAA Joint Propulsion, 2012] as a strong candidate for an iodine ion LIF scheme. We will also present preliminary LIF measurements using a tunable dye laser operating at 695.878 nm and new chamber design. [Preview Abstract] |
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GT1.00054: Non-invasive plasma diagnostics using oxygen optical emissions John Boffard, Nathaniel Ly, Chun C. Lin, Amy Wendt The optimization and control of technological plasmas is facilitated by measurements of plasma properties. Non-invasive diagnostics based on optical emission spectroscopy (OES) rely on the prediction of recorded spectral features, using an emission model accounting for processes related to the excitation and de-excitation of photon-emitting species. Here we implement an emission model for low-pressure oxygen plasmas. We have measured the emission spectra of low pressure oxygen inductively coupled plasmas in the 350-900~nm wavelength range, yielding both atomic~O lines and a few O$_2^+$ molecular ion bands. The model takes the intensities as inputs, returning values of dissociation fraction, and electron density and temperature, which we benchmark against O$_2$/Ar actinometry and Langmuir probe measurements, respectively. Trends (pressure: 1-30 mTorr, RF power: 100-2000 W) reveal that the O$_2^+$ emissions have a complicated dependence on the electron density. The dominant excitation mechanism shifts from simultaneous ionization-excitation of O$_2$ molecules at very low plasma densities to excitation of ground state O$_2^+$ ions at higher densities, for which it is also found that electron-induced quenching suppresses emissions from long-lived radiative levels. [Preview Abstract] |
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GT1.00055: Noninvasive measurement of plasma parameters via the reactor substrates Ji-Hwan Park, Chin-Wook Chung Noninvasive electrical plasma monitoring method is proposed. When a small sinusoidal voltage is applied between a bias electrode and a grounded substrate in an inductively coupled plasma reactor, the current flows through a closed circuit via the plasma. This current consists of the harmonic components due to the nonlinearity of the sheath. The plasma density and electron temperature can be obtained by using double probe harmonic current analysis. Because this method uses existing reactor substrates, noninvasive electrical measurement is possible without probe insertion. The measurement principle, experimental results, and the comparative analysis with a conventional electrical method are presented. [Preview Abstract] |
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GT1.00056: Plasma diagnostic method by using charged capacitor voltage Moo-Young Lee, Kyung-Hyun Kim, Chin-Wook Chung New plasma diagnostic method based on measuring charged capacitor voltage is proposed to obtain plasma density and electron temperature. When two square voltages which have different amplitudes are applied to a probe tip, the voltages of a capacitor connected to the probe vary due to current flowing through probe sheath. To obtain relations with plasma parameters and capacitor voltage, equivalent circuit containing nonlinear sheath and capacitor is adopted. The electron temperature and plasma density were obtained from the ratio of voltage variation during the same time based on those relations. The results are well agreement with those obtained from floating harmonic method. [Preview Abstract] |
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GT1.00057: Measurement of ion energy distributions using a capillary plate with a high-aspect ratio Jun-Hyeon Moon, Kyung-Hyun Kim, Kwan-Yong Kim, Chin-Wook Chung An energy analyzer using a capillary plate with high-aspect ratio is proposed to measure the ion energy distribution (IED). The capillary plate replaces the role of the grid of the conventional retarding field energy analyzer and has several advantages at the same time. As using the capillary plate, the electrons are repelled by electron shading effect due to the difference in mobility of ions and electrons and the measured IED at the bottom of the capillary plate will be closer to the value at the bottom of the contact hole in etch process. In our experiment, the effect of electron repelling by the capillary plate (L/D = 40) is confirmed by measured I – V characteristic curve and COMSOL simulation. The IED is measured under various discharge conditions. [Preview Abstract] |
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GT1.00058: Generation and optical diagnostics of pulse-modulated microwave plasma in high-pressure argon Kenichi Inoue, Noritaka Sakakibara, Jaeho Kim, Tsuyohito Ito, Kazuo Terashima High electron density plasma in high-density media provides highly reactive environments. Such plasma could be useful for developing rapid materials processing as well as synthesizing non-equilibrium materials. To achieve high-density plasma in high-pressure argon up to 1.0 MPa, we apply pulse-modulated microwave in this study. Because of the electron confinement, microwave plasma generally reaches high electron density. Pulse modulation is expected to enhance non-equilibrium properties and to provide further controllability of the processes, e.g. keeping low temperature and suppressing heat damages to materials. The pulse-modulated microwave plasmas were generated at the pressures of 0.1-1.0 MPa with the pulse frequency of 100-1000 Hz. The spatio-temporal structure of the plasmas was investigated via high-speed-camera analysis; confirming the pulse-modulated generation of plasma in 1 mm space at 0.1 MPa. Optical emission spectroscopy and near-infrared laser heterodyne interferometry were performed; indicating that the electron densities were in the order of 10$^{\mathrm{23}}$ m$^{\mathrm{-3}}$. [Preview Abstract] |
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GT1.00059: Mobility of Ar$^(+)$ IN Ar/C$F_4$ Zeljka Nikitovic, Vladimir Stojanovic, Zoran Raspopovic, Zoran Lj. Petrovic In this paper we present a cross section sets for Ar$^(+)$ in Ar/C$F_4$ where existing experimentally obtained data are selected and extrapolated. Monte Carlo code is applied to accurately calculate transport coefficients in hydrodynamic regime. We discuss new data for Ar$^(+)$ ions in Ar/C$F_4$ where flux and bulk values of reduced mobility are given as a function of reduced electric field E/N (E-electric field, N-gas density). [Preview Abstract] |
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GT1.00060: Striations due to Kinetic Instability in Water Containing Atmospheric Pressure Plasmas E. Kawamura, M.A. Lieberman, A.J. Lichtenberg Narrow gap atmospheric pressure plasmas (APPs) have wide ranging energy and biomedical applications. Common feedstock gases are helium and argon with trace H2O vapor. Discharge control for applications requires stability, but kinetic particle-in-cell (PIC) simulations of rf or dc driven narrow gap (1--4 mm) helium or argon APPs with trace H2O vapor show an ionization instability resulting in striations (spatial oscillations) in the bulk plasma. These striations are due to non-local electron kinetics and would not be observed in commonly used APP fluid simulations. We develop a striation theory which agrees well with the PIC results. Discharges with lower ion mobility $\mu_i$ and higher $K_{\rm rec}n_0$ tend to be more unstable, where $K_{\rm rec}$ is the electron-ion recombination rate coefficent and $n_0$ is the bulk plasma density. Water-containing APPs tend to form high mass positive ion clusters with high $K_{\rm rec}$ and are thus more likely to exhibit striations. APPs with argon rather than helium feed stock gas are more unstable due to the reduced (stabilizing) $\mu_i$ in the heavier gas. Water-containing APPs operated at a low frequency of 50 kHz introduce a new phenomenon of time-varying $n_0$, which leads to a time-varying instability. [Preview Abstract] |
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GT1.00061: How boundary conditions affect the plasma properties in CCRF discharges? Anbang Sun, Markus Becker, Detlef Loffhagen PIC/MCC methods are commonly used for the simulation of CCRF discharges. Various boundary conditions (BCs) have been used to describe the interaction of particles with the electrode surfaces. However, well-founded explanations and investigations of the influence of those BCs are very rare. In the present contribution, our 1d3v PIC/MCC code is applied to analyze the quantitative impact of electron BCs on the properties of CCRF discharges. It is shown that for the lowest gas pressure considered, the secondary electron emission (SEE) coefficient and the electron reflection coefficient have a similar impact on the plasma parameters. With increasing gas pressure, the discharge switches from alpha to gamma mode and the emission of secondary electrons becomes the dominant boundary effect. At the highest pressure of 80 Pa, the SEE strongly affects the plasma parameters while the electron reflection coefficient has almost no effect. *The work was supported by EU PlasmaShape project (no 316216), by State Key Laboratory of Electrical Insulation and Power Equipment (no EIPE17311) of Xi'an Jiaotong University and by the German Research Foundation within CRC TRR24. [Preview Abstract] |
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GT1.00062: Effect of runaway electrons on discharge breakdown in air at atmospheric pressure: simulation study Zdenek Bonaventura, Olivier Chanrion, Anne Bourdon, Torsten Neubert Thanks to development of both power supplies and diagnostic techniques, a number of experiments have been performed to study the discharges obtained using high voltage pulses with sub-nanosecond rise fronts. We use a 2D axisymmetric beam-bulk hybrid model, which describes cold electrons with a fluid model and high energy electrons with a particle model, to study discharge breakdown appearing in a negative point-to-plane gap submitted to very high voltage pulse. The results show the effect of high energy electrons on discharge development. While overtaking the discharge front, the high energy electrons pre-ionize the gas ahead and leave a trace of secondary seed electrons that in turn facilitate discharge propagation. Characteristics of fast electrons generated in the region of enhanced electric field ahead of the discharge propagating front are studied in detail. [Preview Abstract] |
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GT1.00063: Plasma chemistry round robin Leanne Pitchford In response to the need for a community-wide activity on the assessment of plasma chemical kinetics in commonly used gases, a round robin exercise was proposed during the discussion session on LXCat at GEC 2016. A call for participation was then circulated and 12 teams responded. Participants were asked to calculate electron temperature and species concentrations using a 0D model of their choice. It was decided to start with a one-level system and a given set of cross sections and to compare predicted densities of species and transport parameters. Results were centralized and distributed anonymously to all participants who then had the opportunity to refine their calculations. After several rounds, good, but not perfect, agreement has been obtained using either a given E/N or a given power as the parameter, and assuming either Maxwellian or non-Maxwellian electron distribution. The round robin is now beginning comparisons in N2/O2 mixtures.\\ \\In collaboration with G. Colonna, CNR-Nanotec, Italy, M. Turner, Dublin City Univ., Ireland, M. Becker, D. Loffhagen, F. Sigeneger, INP Germany, F. Gordillo, A. Luque, Inst. Of Astrophysics of Andalusia, Spain, F. Iza, F. Montazersadgh, Loughborough Univ., UK, J van Dijk, W. Graef, G. Kroesen, D. Mihailova, Eindhoven Univ. of Technology, Netherlands, A. Bogaerts, S. Heijkers, Univ of Artwerp, Belguim, L. Alves, M. Castela, V. Guerra, M. Lino da Silva, L. Marques, N. Pinhao, C. Pintassilgo, A. Tejero, Univ. of Lisbon, Portugal, T. Kozak, Univ. of West Bohemia, Czech Republic, A. Derzsi, Z. Donko, P. Hartmann, K. Kutasi, Wigner Research Centre for Physics, Hungary, S. Pancheshnyi, ABB Switzerland [Preview Abstract] |
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GT1.00064: Convergence of fluid and kinetic models in the high pressure limit Miles M. Turner, Sean Kelly, Ann Bourdon Kinetic models (such as particle-in-cell simulations) are usually accepted as offering an fundamentally accurate description of low-temperature plasmas, albeit at high computational cost. Fluid models are far more economical, but less accurate. A common strategy for supplying electron transport and rate constants to a fluid model is to solve a fluid energy transport equation, and use the mean energy so computed to interpolate data obtained from a solution of the Boltzmann equation, often using the two-term spherical harmonic expansion. The fluid approach and the kinetic approach should then converge at sufficiently high pressure, where the local field approximation applies. In this work we compare the fluid and kinetic approaches for a capacitively-coupled discharge in helium over a wide range of pressures. We find that a regime of convergence is difficult to find, and perhaps does not exist under conditions where a uniform glow discharge occurs experimentally. We conclude that, in this case, the uncertainty introduced by the fluid model formulation is likely comparable with the uncertainty associated with basic data. Consequently, the basic fluid model formulation is a factor limiting the predictive capability of many present plasma simulations. [Preview Abstract] |
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GT1.00065: Computational Modeling of Nb Magnetron Sputtering in an SRF Chamber using PIC-MCC Thomas Jenkins, James McGugan, Scott Bartlett, Scott Kruger, Christine Roark, Jonathan Smith, David Smithe, Peter Stoltz, Yi Xie A 2D axisymmetric simulation model for a cylindrical, coaxial magnetron sputtering device is presented. The model was built to simulate niobium sputtering in superconducting radio frequency cavities, in tandem with an experiment being conducted at Fermi National Accelerator Laboratory. The simulation model uses Particle-in-Cell and Finite-Difference algorithms, and is performed using the VSim software [C. Nieter and J. R. Cary, J. Comp. Phys. {\bf 196}, 448 (2004)]. The simulation is fully self-consistent and includes an external feedback circuit, secondary electron emission, sputtering emission, and background neutral gas collisions. The magnetic field is solved within the simulation. The erosion profile, deposition profile, and detailed plasma parameters are obtained. [Preview Abstract] |
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GT1.00066: Development of Three-Dimensional Kinetic Codes for Modeling of a Plasma Switch Andrew Powis, Johan Carlsson, Igor Kaganovich The plasma switch is a proposed alternative mechanism for performing AC to DC (or visa-versa) power conversion within a compact and robust device. Accurate three-dimensional kinetic models for the discharge are critical towards understanding the fundamental physics and improving device performance. To this end we have updated the commercially available Partice-in-Cell, Monte-Carlo-collision (PIC-MCC) code, Large Scale Plasma (LSP) [1] for applications to low-temperature (electrostatic) plasma devices such as the plasma switch. Improvements include an updated circuit model and updated collision models [2]. Furthermore we have updated the Poisson's equation solver to take advantage of state-of-the-art direct and iterative techniques. By taking advantage of massively parallel architectures, these improvements allow us to perform self-consistent kinetic simulations of large scale systems within reasonable time frames. We foresee a wide range of applications for this code beyond the plasma switch such as plasma micro-discharges and sputtering-magnetrons. [1] Welch, D. R., et al. "Integrated simulation of the generation and transport of proton beams from laser-target interaction."~Physics of Plasmas~13.6 (2006): 063105. [2] Carlsson, J., et al., "Validation and benchmarking of two particle-in-cell codes for a glow discharge."~Plasma Sources Science and Technology~26.1 (2016): 014003. [Preview Abstract] |
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GT1.00067: Subnanosecond breakdown development in high-voltage pulse discharge. Main mechanisms. Irina Schweigert, Andrey Alexandrov, Pavel Gugin, Maxim Lavrukhin, Petr Bokhan, Dmitry Zakrevsky A subnanosecond breakdown in high-voltage pulse discharge may be a key tool for superfast commutation of high power devices. The breakdown in mid-high pressure in helium was studied in experiment and in particle-in-cell Monte Carlo collision simulations. The complex kinetic model was developed, based on kinetic simulation of discharge plasma, including dynamics of electrons, ions and fast helium atoms, produced by ions scattering. Attention was paid to electron emission processes from cathode: photoemission by Doppler-shifted resonant photons, produced in excitation processes with fast atoms; electron emission by ions and fast atoms bombardment; and the secondary electron emission (SEE) by hot electrons from bulk plasma. The simulations show that the fast atoms are the main reason of emission growth at the early stage of breakdown, but at the final stage, when the voltage on plasma gap drops, the SEE is responsible for subnanosecond rate of current growth. The influence of SEE yield for three types of cathode material (titanium, SiC, and CuAlMg-alloy) was tested. By changing the pulse voltage amplitude and gas pressure, the area of existence of subnanosecond breakdown is identified. [Preview Abstract] |
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GT1.00068: Effect of electron energy distribution function on formation of graphene nanocrystallites during electron-irradiation-induced carbon film growth process in an ECR Plasma Wencong Chen, Xi Zhang, Dongfeng Diao Recently, a low-energy electron irradiation technique was developed to deposit graphene-nanocrystallites-embedded carbon (GNEC) films which manifests unique tribological, magnetic and optoelectronic properties. However, the role played by low-energy electrons in this process remains unclear. During the electron irradiation process, substrates are positively biased and electrons produced in the plasma are accelerated to irradiate the deposited GNEC films. In this work, electron energy distribution function on the substrate surface during the electron-irradiation-induced carbon film growth process in an ECR (Electron Cyclotron Resonance) plasma is measured with a retarding field energy analyzer (RFEA). The deposition temperature is probed by an infrared thermometer. A Langmuir probe is used to monitor the plasma potential and calibrate the current sensitivity of the RFEA. It is found that the size and concentration of graphene nanocrystallites strongly depend on the irradiation electron energy and the electron flux but not the temperature, which indicates that the electron excitation effect of the covalent bonds dominate the formation process of these nanocrystallites. This finding sheds light on the interaction between the plasma and carbon materials. [Preview Abstract] |
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GT1.00069: Computational Study of RailPAc Arc-Root Jets Miles Gray, Laxminarayan Raja A computational study was conducted on a magnetohydrodynamic plasma actuator called the rail plasma actuator (RailPAc). The actuator consists of two parallel, 6 in long, copper rails flush mounted on an insulating ceramic plate. When a current pulse (~1kA) at ~100V is supplied, an electrical arc is generated and driven along the rails by the Lorentz force generated from the interaction of the arc current with the self-induced magnetic field of the arc-electrode system. The motion of the arc induces flow in the surrounding air through compression and entrainment. This induced flow may be used to reattach flow over an aerodynamic surface. An equilibrium arc model is used to simulate the propagation of the RailPAc plasma and compliments previous experimental work focused on physical characterization of the arc. Particular focus is made on the complex interaction of macroscopic jet flows generated by the arc roots with the plasma column which has been shown in the past to be critical to reliable operation of the RailPAc actuator. Implications of these interactions on actuation efficacy and actuator design are discussed. [Preview Abstract] |
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GT1.00070: Non-linear response of Hall thruster plasma to modulation of the discharge voltage. Yevgeny Raitses, Ivan Romadanov, Andrei Smolyakov For cylindrical Hall thrusters, naturally occurred breathing oscillations have a characteristic frequency of \textasciitilde 13 kHz. The external modulation of the anode potential was applied to make this mode coherent. To determine the driving frequency, a set of natural frequencies was defined from the Fourier transform of the discharge current and the ion current in the plume. By varying driving frequency in the range of 5-20 kHz and monitoring the power spectra of the currents, we found that the coupling of the driving frequency to the intrinsic breathing mode is at frequency of this mode \textasciitilde 13 kHz rather than at the driving frequency. More than that, with the increase of the driving voltage, there is a non-linear response of the discharge current and the ion current as well as a shift of the breathing mode to lower frequencies. We will discuss this interesting non-linear behavior of breathing oscillations in response to driving signal. [Preview Abstract] |
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GT1.00071: Background pressure effects on Hall thruster discharge plasma using a full particle simulation Kentaro Hara, Shinatora Cho Facility effects play an important role when testing space propulsion devices in laboratory, which can be problematic because measurements in laboratory may significantly differ from how the device would operate in space. It has been often observed experimentally that the thruster performance, namely, specific impulse, thrust, and efficiency, increases as the background pressure in vacuum chamber increases. In this talk, we present a two-dimensional particle-in-cell simulation with Monte Carlo collision algorithm to model the discharge plasma of a Hall thruster in the presence of ingested neutral atoms from the vacuum chamber. A half-Maxwellian at room temperature is assumed for the ingested neutral atom flow. Numerical results show that ionization and acceleration regions are pushed upstream as the background pressure increases. This suggests that the distribution function of the ingested flow, i.e., non-Maxwellian distribution of the neutral atoms, affects the discharge plasma. [Preview Abstract] |
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GT1.00072: Promotion of angiogenesis using Atmospheric Pressure Plasma Derived FGF-2/VEGF Chihiro Kobayashi, Toshiya Yoshikawa, Akira Mori, Takamichi Hirata Atmospheric pressure plasma is applied in the medical field for coagulation, sterilization, and treatment for diabetic gangrene. Direct plasma irradiation has recently been reported to promote wound healing. The aim of the present study was to clarify the mechanism by which wound healing is promoted by plasma irradiation. Therefore we focused to the nitric oxide (NO) and growth factors, which is a key component of the healing mechanism. Using an in vitro model, we investigated the effect of the atmospheric pressure plasma irradiation to mice embryonic fibroblast cell line (NIH3T3 cell) and porcine aortic endothelial cells (POAEC). We investigated expression analysis with focus on factors related to angiogenesis it was found that the transient overexpression of b-FGF and VEGF are observed after the plasma irradiation. Furthermore, in order to investigate the function of nitric oxide syntheses (NOS), we conducted an inhibition experiment using a NOS inhibitor. These data suggest that direct plasma irradiation involving ion/radical may promote endogenous NO and b-FGF/VEGF and it promotes angiogenesis activation. [Preview Abstract] |
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GT1.00073: Direct Near Infrared Imaging of Brain Surface Blood Vessel Using Indocyanine Green Angiography Takamsa Tamura, Sayaka Matsuda, Seira Shigekuni, Risaco Tanaka, Chihiro Tsutsui, Takamichi Hirata A three major disease (cancer, apoplexy, and acute myocardial infarction) becomes a serious problem in various foreign countries of the world. Especially, hypoxic-ischemic encephalopathy (HIE) caused by cardiac infarction, arrest cardiac, and suffocation, etc. is a type of brain damage that occurs when the brain doesn't receive enough oxygen and blood. From the above-mentioned background, we performed direct imaging by indocyanine green (ICG) angiography of rat's cerebral blood vessel. The contrast medium: ICG is a water-soluble, tricarbocyanine dye used in medical diagnostics. It is used for determining cardiac output, hepatic function, and liver blood flow, and for ophthalmic angiography. ICG in the blood is excited near infrared ray (NIR), generates fluorescence of 800 - 850 nm. The excitation of ICG used 780 nm Infrared (IR) LED array light source. Fluorescence is made an image with near-infrared (NIR) cooled CMOS camera system and long wavelength pass filter installed in the video zoom microscope. As a result, it was proven to be able to measure the behavior of the cerebral blood vessel by noncontact by using light in the near-infrared area that had the living body permeability [Preview Abstract] |
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GT1.00074: Study of Atmospheric-pressure plasmas administration methods for Hypoxic-Ischemic Encephalopathy model rat Sayaka Matsuda, Takamasa Tamura, Risaco Tanaka, Seira Shigekuni, Cihiro Kobayashi, Takamichi Hirata, Masaya Watada, Akira Mori In recent years, atmospheric-pressure plasmas are applied in various fields and also develop in the medical applications. Although the mechanism of action remains unclear, new biomedical applications of plasma have been found. Experiments using atmospheric pressure plasmas confirmed several effects such as burn healing with angiogenesis, the increasing of SpO2 and improvement of circulatory function. Therefore, we have been focusing treatment of Hypoxic Ischemic Encephalopathy (HIE) by using the atmospheric-pressure plasma. HIE caused by the discontinuation of blood supplied means that a part of the brain is necrotized and a brain function is impaired. Cause of HIE is various, for example, respiratory failure and circulatory failure, neonatal asphyxia. There is no fundamental therapy for HIE except for symptomatic therapy as of now. Because of preservation and recovery of brain functions can be expected by the action of plasma, as a study on HIE treatment using atmospheric-pressure plasma, we consider and report on a method of administrating atmospheric-pressure plasma to HIE model rat at first. [Preview Abstract] |
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GT1.00075: Evaluation of characteristics of Multi-purpose Atmospheric Pressure Plasma Device Seira Shigekuni, Risaco Tanaka, Takamasa Tamura, Sayaka Matsuda, Chihiro Kobayashi, Takamichi Hirata The atmospheric pressure plasma (APP) doesn't stop at the industrial field, and application is also developed in the medical field. But commercialization is precedent to plasma medical equipment only by empirical fact, and there're many indefinite points in a mechanism of revival in biomedical tissue. In generally, the flow of APP source includes active oxygen species (ROS) such as ozone (O$_{\mathrm{3}})$, hydroxyl radical (OH), hydrogen peroxide (H$_{\mathrm{2}}$O$_{\mathrm{2}})$, nitric oxide (NO), nitrite (NO$_{\mathrm{2}})$, and active nitrogen species (RNS), etc. generated around the plasma flow. In view of the above background, in this research, we are developing a prototype and evaluation of an atmospheric pressure plasma source for the purpose of controlling radical species. Previous experiments confirmed that it is possible to easily change the plasma product by controlling the plasma parameters. In this presentation we will report on the consideration of the power supply unit. [Preview Abstract] |
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GT1.00076: Healing mechanism clarification of plasma irradiated wound by quantification and detection of superoxide dismutase (SOD) activity Risaco Tanaka, Seira Shigekuni, Sayaka Matsuda, Takamasa Tamura, Chihiro Kobayashi, Akira Mori, Takamichi Hirata Plasma medicine is currently applied in clinical settings, in many cases, without any explanation for its mechanism. This study therefore aims to elucidate the mechanism of healing by plasma irradiation in burn injury, by focusing on plasma wound healing. In preceding studies, it has been reported that atmospheric pressure plasma generates reactive oxygen species (ROS) and that mild oxidative stress promotes cell proliferation, which suggests that oxidative stress may play a major role in the mechanism in which plasma irradiation promotes healing burn injury. Based on these, we first measured superoxide dismutase (SOD) activity, an oxidative stress marker, at burn injury sites that were artificially created on the back of rats. We now report the results of comparative investigation of differences in SOD activity in case of non-treatment and plasma irradiation. In particular, we focused on the change in SOD activity over time. From the result, it is suggested that SOD activity of \textit{in vivo} changes in proportion to the time course. [Preview Abstract] |
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GT1.00077: DNA damage and its mechanism induced by cisplatin and 10 eV electron collision Yeunsoo Park, Young Rock Choi, Youghyun Kim, Dae Chul Kim Low energy electrons (LEE, especially below 10 eV) can generate strand breaks on DNA via energy resonance mechanism named dissociative electron attachment (DEA). Interestingly, this indirect damage is a considerable yield compared to direct damage by high energy quanta ionization. To better understand of LEE roles on DNA damage in plasma and radiation fields, it needs to investigate experimental and theoretical studies at the molecular level. Definitely, it needs diverse interaction data between LEEs and biomolecules to interpret damage mechanism. We have tried to investigate DNA damage induced by single and synergistic effects of cisplatin and 10 eV electron. All dried DNA samples were irradiated by 10 eV electrons under ultra-high vacuum. And then, the samples were analyzed by high-performance liquid chromatography-tandem mass spectrometry. We compared the yields of different types of DNA damage such as strand break, base release and modification. We also suggested the possible mechanisms of DNA damage originated by cisplatin bonding and LEE collision based on current experimental findings. Finally, we expect that this study can help to find out the cause of cancer or genetic diseases and a novel therapy for them. [Preview Abstract] |
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GT1.00078: Effects of atmospheric-pressure plasma irradiation on germination and growth of radish sprouts Shinji Yoshimura, Hiroshi Kasahara Positive effects of atmospheric-pressure non-equilibrium plasma irradiation on plant seeds have recently been studied worldwide, and enhancement of seed germination and seedling growth has been reported by many research groups. However, there are wide varieties of the reported effects, which may be attributable to the difference of plasma parameter, plant seed species and growth environment. This study aims to investigate the effects of plasma irradiation onto plant seeds and to provide a new set of results under a controlled growth environment. We chose radish sprouts seeds ({\textit Raphanus sativus} L.) as test plant seeds because of their short growth period and adequate amount of preceding research reports. We used two types of atmospheric pressure discharge devices (NU-Global, PN-110+TPN-20, HUMAP-WSAP-50) with helium or argon as feed gas. The plasma-treated seeds were cultivated in a plant growth chamber (incubator) with temperature and relative humidity control. Comparison of the germination and growth rate as well as the average plant length of plasma-treated seeds with those of non-treated control seeds will be presented. [Preview Abstract] |
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GT1.00079: On the calculation of vibrational-vibrational rates of CO$_2$ Jesper Janssen, Jan Van Dijk, Jos Suijker The increase of the CO$_2$ concentration in the air and the accompanying climate change has driven the need to limit the CO$_2$ output. One of the possible ways is to convert CO$_2$ back into fossil fuels using plasmas. The conversion of CO$_2$ to CO is a crucial step. The most energy efficient path to dissociation uses vibrational pumping. The vibrational-vibrational reactions are poorly understood. Numerical models use empirical scaling relations whose accuracy is unknown. The aim of this project is to calculate the vibrational-vibrational rates. The number of dimensions of the system is too large to calculate the potential energy surface using ab initio methods for all possible orientations. Therefore an analytical potential surface is constructed based on Z\'u\~niga et al and Bartolomei et al. This potential is used to evaluate several trajectories of two colliding CO$_2$ molecules. By varying the initial conditions and by sampling several trajectories, the reaction rates can be deduced. In a later stage of the project the improved reaction rates will be used to simulate the microwave reactor using PLASIMO. This model will couple equations for momentum, continuity, Te, Th and electromagnetics self-consistently. The model will be used to optimize the reactor. [Preview Abstract] |
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GT1.00080: Effect of Radio Frequency Waves on Plasma Instabilities {\&} Turbulences J Melendez, I Durojaiye, K Trivedi, E Nti, S Sen We study the effect of Radio Frequency Waves on low-frequency instabilities and turbulences. No ponderomotive force induced flow generation is considered. In spite of this the effect of RF waves is shown to have significant effect in controlling the turbulence level contrary to the usual prediction that ponderomotive force induced flow shear (first radial derivative of flow) alone controls the turbulence level. This has a crucial role in the fusion energy generation. [Preview Abstract] |
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