Bulletin of the American Physical Society
72nd Annual Gaseous Electronics Conference
Volume 64, Number 10
Monday–Friday, October 28–November 1 2019; College Station, Texas
Session RR2: High Pressure Discharges II |
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Chair: Ute Ebert, CWI Amsterdam and Eindhoven Univ Techn Room: Century II |
Thursday, October 31, 2019 4:00PM - 4:15PM |
RR2.00001: Control of Plasma Jet Dynamics by Externally Applied Electric Fields Natalia Yu. Babaeva, George V. Naidis, Mark J. Kushner Atmospheric pressure plasma jets (APPJs), as used for biomedical applications, consists of a tube through which a noble gas mixture flows into the ambient, and which sustains and guides an ionization wave (IW). Short-pulsed voltages applied to external electrodes and synchronized to the passage of the IW can control the dynamics of the IW. Computations and experiments have shown that voltage pulses applied to a ring electrode around the axis of the IW can decrease or increase the speed of the IW depending on polarity [1,2]. In this paper, positive and negative voltage pulses applied to external electrodes are computationally are studied using the 2D \textit{nonPDPSIM} model [3]. Using a negative He APPJ into air, we show that a positive voltage pulse on the external electrodes increases the electric field in the leading edge of the IW, and increases the IW's radius and velocity. A negative voltage pulse reduces the IW electric field and decreases its radius, velocity and electron density. Consequences of multiple and staggered external electrodes will be discussed. [1] G. Naidis, J. Walsh, J. Phys. D. \textbf{46} (2013) 095203. [2] P. Olszewski et al. Plasma Src. Sci. Technol. \textbf{23} (2014) 015010 [3] S. Norberg, et al., Plasma Src. Sci. Technol$.$ \textbf{24 }(2015) 035026. [Preview Abstract] |
Thursday, October 31, 2019 4:15PM - 4:30PM |
RR2.00002: Dynamical charging of a dielectric surface exposed to a plasma jet : quantitative comparison between experiments and simulations Anne Bourdon, Pedro Viegas, Elmar Slikboer, Marlous Hofmans, Zdenek Bonaventura, Ana Sobota, Olivier Guaitella In this work, we study through a quantitative comparison between fluid modeling and experiments, the transient charging of a surface under exposure of a non-equilibrium plasma jet at atmospheric pressure. For mono-polar pulses with variable pulse duration and amplitude, the electric filed inside the target is measured. We show that the charging time (i.e. the time from impact of the ionization wave till the fall of the high voltage pulse) is crucial to understand the plasma-surface interaction. When the charging time is kept relatively short (less than 100 ns), the surface spreading of the discharge and consequently the surface charge deposition are limited. When the charging time is relatively long (up to microseconds), the increased surface spreading and charge deposition significantly change the electric field to which the target is exposed to, during the charging time, and when the applied voltage returns to zero. [Preview Abstract] |
Thursday, October 31, 2019 4:30PM - 5:00PM |
RR2.00003: Weblike chemical systems and their network topology in low-temperature reactive plasmas Invited Speaker: Osamu Sakai Chemical reactions in low-temperature plasmas for material processes are complex because such plasmas include molecule reactions leading to their resultant various radical species and enhance multiple parallel reactions via high-energy electrons. Previous studies reported to date handle their complexities with numerical calculations based on a corresponding set of the rate equations, but the calculation results frequently confuse us with unclear roles of several tens of species as well as unclear pathways of reactions. To uncover underlying processes in such complex reaction systems, a topological approach triggered by complex network science is one of the solutions for their clarification in various industrial reactors. In this report, we build up a network of chemical reactions in which nodes or vertexes are chemical species and edges are chemical reactions [1], and analyze it mainly on two different aspects. In a microscopic point of view, centrality indices of nodes developed in network science indicate roles of species (like as reactants, products, or intermediates) or their fractions for each role in an entire system [2]. In a macroscopic point of view, statistical properties of many networks in low-temperature plasmas show a scale-free-like topology that may imply robustness in the system stability. These facts indicate that a chemical system in low-temperature reactive plasmas substantially involve a kind of synthetic frameworks that are totally different from groups of elements collected randomly. [1] O. Sakai. K. Nobuto, S. Miyagi and K. Tachibana, AIP Adv. 5, 107140 (2015). [2] Y. Mizui, T. Kojima, S. Miyagi and O. Sakai, Symmetry 9, 309 (2017). [Preview Abstract] |
Thursday, October 31, 2019 5:00PM - 5:15PM |
RR2.00004: Abstract moved to Poster Session MW1.00090 |
Thursday, October 31, 2019 5:15PM - 5:30PM |
RR2.00005: Zero Dimensional Model for the Investigation of Dielectric Barrier Discharges in Humid Air Anthony Ezeabasili, Youfan He, Kemaneci Efe This investigation is about applying a nanosecond power to a dielectric barrier discharge in humid air at atmospheric pressure.A number of 53 species and 624 reactions were considered in describing the chemistry of the system. The model involves two dependent discharge (comprising of charged and fast neutral species) and after glow (slow neutrals) regions solved on different time scales given the varied lifetime of the species in the considered regions. The particle and electron energy balance equations are the salient equations which are solved dependently under the time varying power in the system. The model gives further insight into the chemical dynamics of the species. This is because the electron energy is accounted for by the energy balance equation. It could also be calculated from conventional electron energy distribution function that Boltzmann solvers can easily be used for. The model finds good agreement with proven experimental results on the density of species within the plasma region and in the effluent gas regime and thus a powerful tool in plasma simulation. [Preview Abstract] |
Thursday, October 31, 2019 5:30PM - 5:45PM |
RR2.00006: Fractional abundance of negative ions in dc glow discharge in contact with solution K. Sasaki, R. Hosoda, N. Shirai, F. Tochikubo We examined negative ion species in a dc helium glow discharge produced in the air. The detection of negative ions was based on laser photodetachment. We injected tunable laser pulses into the discharge. The laser pulse produced electrons from negative ions by photodetachment, which resulted in the pulsed increase in the discharge current. The experimental results indicate a linear relationship between the increase in the discharge current and the amount of electrons produced by photodetachment. We obtained the knowledge on negative ion species by scanning the laser wavelength around the photodetachment threshold. The dominant negative ion was O$^-$ when the plasma was produced between a needle anode and a planar metal cathode, and a small amount of O$_2^-$ and OH$^-$ was observed. We observed significant increase in the OH$^-$ density by changing the cathode to an electrolyte solution. The O$^-$ density also increased in the electrolyte-cathode discharge. According to the cross-section data, it is speculated that the major production process of OH$^-$ is dissociative electron attachment to H$_2$O$_2$. In addition, we detected Cl$^-$ when the cathode was an NaCl solution. [Preview Abstract] |
Thursday, October 31, 2019 5:45PM - 6:00PM |
RR2.00007: Density Effects in the Collision and Reaction Rate Coefficients of Atmospheric Pressure Plasmas Scott Baalrud Computation of collision and reaction rate coefficients are usually based on a dilute gas concept in which cross sections for binary interactions (either computed or measured) are used in a Boltzmann kinetic description to obtain the relevant rates. However, partially ionized plasmas at atmospheric and elevated pressures are sufficiently dense that the concept of binary collisions can break down. Interactions in this regime can be described as strongly correlated because the potential energy is comparable to the kinetic energy. Many-body effects become important in this regime. This presentation describes a new generalization of the Boltzmann equation that is suitable for these conditions, modeling interactions of neutrals, charge-neutral interactions and Coulomb collisions. The kinetic theory is derived from a new closure of the BBGKY hierarchy that expands about equilibrium instead of in terms of the strength of interactions. The result shows that particles interact via a mean force that includes many-body correlations. Validation of the theory has been obtained by comparison with experiments and molecular dynamics simulations for Coulomb collisions. Progress toward application to charge-neutral interactions in partially ionized plasmas will also be discussed. [Preview Abstract] |
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