Bulletin of the American Physical Society
71st Annual Gaseous Electronics Conference
Volume 63, Number 10
Monday–Friday, November 5–9, 2018; Portland, Oregon
Session TF1: High Pressure Discharges III 
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Chair: Tanvir Farouk, University of South Carolina Room: Oregon Convention Center A103A104 
Friday, November 9, 2018 9:30AM  9:45AM 
TF1.00001: Towards robust explicit models for streamer discharges Jannis Teunissen, Ute Ebert Computer simulations are an important tool to study and understand the behavior of streamer discharges. Such simulations can computationally be quite costly, because a highresolution mesh is required to accurately model the growth of streamers. In recent years, the use of adaptive mesh refinement (AMR) and parallelized simulations codes have made it possible to study the evolution of multiple streamers in 3D. However, a problem that often arises with explicit time step methods  which are the most efficient  is that very small time steps are required for numerical stability. Two challenging cases will be presented: a positive streamer that stops to grow in a low background field, and a positive streamer reaching a dielectric surface. Model adaptations to allow for larger time steps and more robustness will be discussed. [Preview Abstract] 
Friday, November 9, 2018 9:45AM  10:00AM 
TF1.00002: ABSTRACT WITHDRAWN 
Friday, November 9, 2018 10:00AM  10:15AM 
TF1.00003: Fluid modeling of streamer inception and propagation in singlefilament dielectric barrier discharges M. M. Becker, H. H\"{o}ft, M. Kettlitz, D. Loffhagen A singlefilament dielectric barrier discharge (DBD) at atmospheric pressure (0.1\,vol\% O$_2$ in N$_2$) is investigated with special focus on the inception and propagation of the positive streamer for different preionization levels. The DBD has a gap width of 1\,mm and is driven by a 10\,kV voltage pulse with a rise time of about 45\,ns. The preionization can be adapted, e.g., by the width of the highvoltage pulse. The numerical analysis is based on a spatially twodimensional axisymmetric fluid model using the local mean energy approximation for the determination of the electron transport coefficients as well as the rate coefficients for elastic and various inelastic collisions. Besides Poisson's equation, balance equations for electrons, heavy particle species and surface charges accumulated on the dielectric surfaces are included. The modeling results are in fair agreement with electrical measurements and provide detailed insights into the Townsend prephase, streamerdriven breakdown and subsequent transient glowphase. It was found that the combined effect of volume and surface charges induces a distortion of the electric field in the prephase and results in a reduction of the streamer propagation velocity for preionization levels $\gg 10^{10}\,\mathrm{cm}^{3}$. [Preview Abstract] 
Friday, November 9, 2018 10:15AM  10:30AM 
TF1.00004: Modeling of surface plasma discharge induced by spoof surface plasmon polariton in high pressure Yunho Kim, Laxminarayan raja Spoof Surface Plasmon Polariton (SSPP) is an electromagnetic wave strongly confined near the surface of a corrugated metal surface (metasurface) filled with dielectric materials. Our group previously studied how the SSPP excited in microwave regime can be used to generate a uniformly elongated argon plasma with electron number density on the order of 1.0x10$^{\mathrm{19}}$m$^{\mathrm{3}}$ or higher. The conduction channel formation among the periodic elements (metaldielectric) is well studied for the operating pressure around 10 Torr, but both physical and numerical difficulties associated with high pressure discharges in 100 \textasciitilde 760 Torr were encountered. Less diffusivity and mobility of electrons in higher pressure hinder the formation of uniformly elongated conduction channel, which we address in this work. Possible solutions to the problem such as adding a dielectric layer on the metasurface and its reflection spectrum are discussed to understand the resonant behaviors the metamaterial. A selfconsistent model for the description of plasma coupled with Maxwell's equations is used in this numerical study. Transients of plasmawave interactions at varying pressures are presented to provide the details of the microwave generated plasma. [Preview Abstract] 
Friday, November 9, 2018 10:30AM  10:45AM 
TF1.00005: Resonant element microwave plasma source. Barton Lane, Peter Ventzek, Amit Bhakta We present here a new concept for plasma generation which employs the near fields from resonant metal structures to sustain a plasma. These structures are embedded in ceramic using a lamination technology and thus allow compatibility with corrosive chemistries. The structures can be viewed as LC circuits which a number of resonances corresponding to different electric field eigenmodes. These correspond to different polarizations of the fields which penetrate into the plasma region. The frequency band determines the approximate scale of the resonant structures and we present a proof of concept experiment in the microwave band. The inductive part of the structure corresponds to the portion of the standing wave fields where the magnetic field is the strongest. We position this near the plasma so that the changing magnetic fields penetrate into the plasma region. The microwave currents are arranged to be parallel to the alumina  plasma interface so that the induced electric fields are parallel to the plasma sheath. For the microwave frequency band the structures had dimensions of approximately 10 mm and produced plasmas of a similar size. [Preview Abstract] 
Friday, November 9, 2018 10:45AM  11:00AM 
TF1.00006: Revisiting the positive DC corona discharge theory: beyond Peek's and Townsend's law Nicolas Monrolin, Olivier Praud, Franck Plouraboue The classical positive Corona Discharge (CD) theory in cylindrical axisymmetric configuration is revisited in order to find analytically the influence of gas properties and thermodynamic conditions on the corona current. The matched asymptotic expansion of Durbin \& Turyn of a simplified but selfconsistent problem is performed and explicit analytical solutions are derived. The mathematical derivation permits to express a new positive DC corona currentvoltage characteristic, either choosing dimensionless or dimensional formulation. In dimensional variables, the currentvoltage law and the corona inception voltage explicitly depends on electrodes size and on physical gas properties such as ionization and photoionization parameters. The analytical predictions are successfully confronted with experiments and with Peek's and Townsend's laws. An analytical expression of the corona inception voltage $\varphi_{on}$ is proposed, which depends on known values of the physical parameters without adjustable parameters. As a proof of consistency, the classical Townsend currentvoltage law $I=C\varphi(\varphi\varphi_{on})$ is retrieved by linearizing the nondimensional analytical solution. A brief parametric study showcases the interest of this analytical current model especially for exploring small corona wires or considering various thermodynamic conditions. [Preview Abstract] 
Friday, November 9, 2018 11:00AM  11:30AM 
TF1.00007: Machine learning plasmasurface interface for coupling sputtering and transport simulations Invited Speaker: Jan Trieschmann For consistent sputtering and transport simulations, the coupling of the model components has to be established bridging the intrinsic time and length scales of both plasma and surface. Their direct coupling is infeasible as the scales of the systems span several orders of magnitudes. As a means of mitigation, a plasmasurface interface based on artificial neural networks is suggested. A multilayer perceptron network has been trained on data of Ar sputtering an AlTi composite target. The set of input data has been obtained using TRIDYN developed by Moeller and Eckstein [1]. It is demonstrated that the trained network can be successfully exploited to predict the energy distributions and angular distributions of sputtered and reflected particles for arbitrary energy distributions of impinging particles. It is finally argued that such machine learning model interfaces may be generally applied to various coupling problems, e.g., for the direct linkage between the discharge of an atmospheric plasma jet and an exposed liquid or solid surface.\\ \\$[1]$ W. Moeller, W. Eckstein, Nucl. Instr. and Meth. B2, 814 (1984)\\ \\Contributions by Florian Kr\"uger, Tobias Gergs, and Thomas Mussenbrock as well as funding by the DFG in the frame of SFBTR 87 are kindly acknowledged. [Preview Abstract] 
Friday, November 9, 2018 11:30AM  11:45AM 
TF1.00008: 3D simulations of streamer branching in air Behnaz Bagheri, Jannis Teunissen, Ute Ebert Streamer discharges form the first stage of electric breakdown of air and other gases. They are rapidly growing ionized filaments driven by strong enhancement of the electric field at their tips. Here we simulate branching of positive streamers in air in full three dimensions. We use afivostreamer [Teunissen, Ebert, J. Phys. D (2017)], which is an open source plasma fluid code based on the afivo framework [Teunissen, Ebert, accepted for Comp. Phys. Comm. (2018)] with adaptive mesh refinement, OpenMP parallelism and geometric multigrid methods for solving the Poisson equation. We use the driftdiffusionreactionmodel in local field approximation and implement the nonlocal photoionization either in continuum approximation or through a Monte Carlo approach. We find major differences in streamer branching between the continuum and the stochastic model for photoionization, and between simulations with or without cylindrical symmetry. We simulate streamer branching in full 3D with stochastic photons and discuss how branching depends on air density. [Preview Abstract] 
(Author Not Attending)

TF1.00009: Dynamic ionization feedback in nonlinear, partially ionized plasma simulations. Alasdair Wilson, Declan Diver We present results from numerical simulations of partially ionized plasmas using a nonlinear finite difference GasMHD Interactions Code (GMIC), capable of utilising GPU accelerators. We incorporate the physics of Alfven ionization along with elastic and inelastic moment coupling and thermal recombination to show behaviour which manifest in a twofluid treatment of a partially ionized plasma that are not present when either species is considered separately. All such plasmas show a hybrid response to wave propagation and plasmas in a critical regime are shown to be somewhat resistant to recombination, with up to 25\% of a rapid recombination event being undone by selfinduced flows. In addition, by considering a dynamic 3dimensional atmosphere representing a tidally locked gas giant an equilibrium background ionization fraction much higher than estimated by e.g. Saha can be obtained. This method has allowed a dynamic calculation of the ionization fraction of a “Hot Jupiter” style gas giant to reach $10^{4}$ in some regions of the atmosphere, this ionization fraction is sufficient for coupling of the magnetic field to the fluid. [Preview Abstract] 
Friday, November 9, 2018 12:00PM  12:15PM 
TF1.00010: Parametric Modeling and Measurements of Pulsed Source and Bias Plasmas Peter Ventzek, Z. Chen, Y. Fukunaga, K. Suzuki, R.R. Upadhyay, L.L. Raja, M. Sekine, A. Ranjan Pulsed plasmas for materials processing take many forms including gas, source and bias pulsing. Born as a solution for plasma damage control, variations on pulsed plasmas are used for control of selectivity, profile and critical dimension variations. Atomic layer etching for precision etch relies on plasma pulsing to discriminate volatile layer formation and removal phases. Integral to the performance of pulsed plasmas is the ion energy and angular distribution functions (IEADF) and the “radical to ion flux ratio”. This presentation will describe the influence of key plasma parameters (source, bias and relevant pulse frequencies, plasma source configuration) on IEADFs. We focus on bias and relevant pulse frequencies and plasma source configuration. A challenge is simulation of a sufficient number of pulse periods to include sufficient species transit times at higher pressures. A further challenge is obtaining sufficient particle statistics to represent the wide range of energies and flux over an entire pulse cycle. We employ VizGlowTM, a finite volume based solver, to simulate a generic plasma and VizGrain, a companion test particle solver to describe pulsed plasmas and their IEADFs. Measurements of IEADFs on a test plasma platform are compared with the simulation results. [Preview Abstract] 
Friday, November 9, 2018 12:15PM  12:30PM 
TF1.00011: Modeling of the transport phenomena for an atmosphericpressure argon jet plasma in contact with a liquid I. L. Semenov, T. von Woedtke, K.D. Weltmann, D. Loffhagen Plasmaactivated liquids have gained increasing interest for biomedical applications. Currently, atmosphericpressure plasma jets are the most common plasma sources applied for the treatment of liquids. Recent numerical studies [1,2] have shown that the transport of reactive species from the plasma jet into the liquid is noticeably affected by the liquid convection and the transport phenomena in the gasliquid boundary layer. However, a detailed theoretical analysis of this layer is still lacking. In this work we present a comprehensive twodimensional numerical model of the momentum, heat and mass transport processes for an argon jet plasma at atmospheric pressure in contact with a liquid. The primary focus is on the description of the transport phenomena near the gasliquid interface. We show that an accurate numerical treatment of the velocity boundary layer is required to reproduce the experimentally observed flow pattern in the liquid phase. In addition, the impact of the gas flow rate and the distance between jet and liquid on the transport of reactive species into aqueous solutions is discussed. [1] A. Lindsay {\it et al.}, J. Phys. D: Appl. Phys. {\bf 48}, 424007 (2015). [2] C. C. W. Verlackt {\it et al.}, Phys. Chem. Chem. Phys. {\bf 20}, 6845 (2018). [Preview Abstract] 
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