Bulletin of the American Physical Society
70th Annual Gaseous Electronics Conference
Volume 62, Number 10
Monday–Friday, November 6–10, 2017; Pittsburgh, Pennsylvania
Session ET2: Modeling and Simulation I |
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Chair: Jannis Teunissen, University of Leuven - KU Leuven Room: Duquesne |
Tuesday, November 7, 2017 10:00AM - 10:15AM |
ET2.00001: PIC-DSMC Model For Breakdown In Voids Laura Biedermann, Chris Moore, Christian Turner High-voltage components such as transformers, gas vacuum switches, wide-bandgap power electronics, and power LEDs may be externally coated with polymer encapsulants to prevent surface flashover and high voltage breakdown. These epoxies and silicon resin encapsulants may be poured into a mold or dispensed as a liquid encapsulant to surround the component. During the thermal/vacuum cure process, potentially-damaging air voids may be introduced in the epoxy from entrapped air or partial delamination. Such microscopic voids can be an initiation point for high-voltage breakdown. We have developed atmospheric air models for breakdown [1] within such atmospheric voids as are found in encapsulated transformers. Plasma development and voltage collapse are simulated using an electrostatic particle-in-cell (PIC) code that models particle-particle collisions using the direct simulation Monte Carlo (DSMC) method. We model the breakdown of $\sim$25-$\mu$m voids including surface charging and plasma-surface interactions such as photoemission, sputtering, and SEE. These models show under what conditions (voltage, location) voids can induce high voltage breakdown. [1] C.H. Moore, \textit{et al.}, ICOPS 2016 [Preview Abstract] |
Tuesday, November 7, 2017 10:15AM - 10:30AM |
ET2.00002: Student Excellence Award Finalist: Gas Breakdown: Across Length Scales and Frequency Amanda Loveless, Adam Darr, Allen Garner Paschen's law (PL), based on the Townsend avalanche criterion, is a well-established condition for gas breakdown. Reducing gap sizes to microscale leads to deviations from PL that are hypothesized to arise due to ion enhanced field emission. We summarize a matched asymptotic analysis that quantifies the transition from field emission to Townsend avalanche to the classical PL. As device miniaturization further drives dimensions to nanoscale, the impact of surface roughness on field emission and length scales on the order of the electron mean free path will further alter the gas breakdown condition. We couple the one-dimensional Schr\"{o}dinger equation to the microscale breakdown equation to estimate the conditions at which quantum effects become dominant. Finally, we assess the impact of frequency on gas breakdown, showing the transition of breakdown predictions from DC to RF to microwave conditions and deriving universal, analytic equations that demonstrate the relative insensitivity of the right-hand side of Paschen's curve to frequency. Implications of the results and the ultimate connection to microwave breakdown and other breakdown regimes, such as space-charge limited and streamers, will be discussed. [Preview Abstract] |
Tuesday, November 7, 2017 10:30AM - 11:00AM |
ET2.00003: Modeling and Simulation of Lightning Related Transient Luminous Events at High Altitude in the Earth's Atmosphere Invited Speaker: Victor Pasko Transient luminous events are large-scale optical events occurring at high altitude in the Earth’s atmosphere, which are directly related to the electrical activity in underlying thunderstorms. Several different types of transient luminous events have been documented and classified. These include relatively slow-moving fountains of blue light, known as `blue jets', that emanate from the top of thunderclouds up to an altitude of 40 km; `sprites' that develop at the base of the ionosphere and move rapidly downwards at speeds up to 10,000 km/s; `elves', which are lightning induced flashes that can spread over 300 km laterally, and upward moving `gigantic jets', which establish a direct path of electrical contact between thundercloud tops and the lower ionosphere. This presentation focuses of the modeling efforts at Penn State directed on interpretation of morphological electrical gas discharge features observed in sprite events. After a brief review of similarity properties of electrical discharges as a function of gas pressure, we introduce parameters typically used for quantitative description of electron avalanches and discuss importance of space charge effects on different spatial scales, including sprite halos (exhibiting 10s of km transverse extents) and sprite streamers (requiring sub-meter resolution for accurate description). A special emphasis is placed on interpretation of initiation and development of sprite streamers captured in high-speed video observations and critical review of the recent modeling efforts related to these observations. [Preview Abstract] |
Tuesday, November 7, 2017 11:00AM - 11:15AM |
ET2.00004: Striation Characteristics in Radio-Frequency Capacitively Coupled Discharges under Different Conditions Kallol Bera, Shahid Rauf, John Forster, Ken Collins In radio-frequency (RF) capacitively coupled discharges, striations with spatial periodic structure have been observed. Thermoelectric effect that reduces electron energy diffusion has been proposed$^{\mathrm{1}}$ as a mechanism generating the periodic structure. The thermoelectric coefficient is calculated using Bolsig$+^{\mathrm{2}}$, and incorporated in our fluid plasma model. Two- and three-dimensional modeling of RF capacitive discharge is first done without thermoelectric effect. The charged species densities are then randomly perturbed, and the growth or decay of different modes with time is observed. Multiple peaks in electron density are formed in an almost periodic manner. The result shows that N$_{\mathrm{2}}$ plasma with weaker thermoelectric effect is more stable than Ar plasma. With increase in secondary electron emission from the electrodes, plasma peaks intensify. Magnetic field increases plasma peaks at lower pressure. For a design with multiple steps on the electrode, distance between plasma peaks is modified. In addition, the striation characteristics are modified by pressure, electrode spacing, rf power and rf pulsing. Compared to two-dimensional model, plasma peaks are stronger in three-dimensional model. $^{\mathrm{1}}$Mackey et. al, Appl Math Lett, 2005 $^{\mathrm{2}}$Hagelaar and Pitchford, Plasma Sources Sci. Technol., 2005 [Preview Abstract] |
Tuesday, November 7, 2017 11:15AM - 11:30AM |
ET2.00005: Student Excellence Award Finalist: Differences between Cartesian and spherical 1d3v Particle-In-Cell simulations Sebastian Wilczek, Jan Trieschmann, Julian Schulze, Ralf Peter Brinkmann, Zoltan Donko, Thomas Mussenbrock 1d3v Particle-In-Cell (PIC) simulations of capacitively coupled radio frequency (CCRF) discharges are usually considered to be symmetric, which implies a Cartesian grid is used. However, in most CCRF systems the driven electrode is smaller compared to the grounded electrode (grounded chamber walls have to be taken into account). In such a situation, different current fluxes at both electrodes can be observed and a DC self-bias develops. The plasma boundary sheaths at the driven and grounded electrode exhibit different dynamics (e.g. sheath potential and sheath size). Especially in very asymmetric scenarios, most of the RF power is coupled into the plasma at the smaller driven electrode. In order to investigate such an asymmetric electrode configuration within 1d3v PIC simulations, a spherical grid is implemented. In this work, the differences between symmetric and asymmetric 1d3v PIC simulations of CCRF discharges are investigated. Particularly, the electron power gain and loss mechanisms (e.g. nonlinear electron resonance heating, power gain due to secondary electrons, ambipolar heating) are studied for different discharge conditions. [Preview Abstract] |
Tuesday, November 7, 2017 11:30AM - 11:45AM |
ET2.00006: Electric field rebound of He plasma jets with positive and negative polarities on metal and dielectric targets Pedro Viegas, Adam Obrusnik, Zdenek Bonaventura, Anne Bourdon In this work, simulations performed with a 2D fluid discharge model coupled with detailed kinetic schemes and flow calculations address the study of the dynamics of a helium plasma discharge with N$_{2}$ or O$_{2}$ admixtures propagating in a dielectric tube. At the exit of the tube, the discharge propagates as a free jet or interacts with a metallic or dielectric target, grounded or at a floating potential. The spatial distribution of the gas mixture at the exit of the tube is previously obtained through the flow calculation of helium flowing through the tube into the outside air. After the arrival of the ionization front at a target, the interaction is shown to be dependent on the features of the target and a rebound of electric field in both positive and negative polarities is observed in some cases. We focus on the calculation of electric field associated to plasma propagation in the tube and in the plasma plume, to gas-mixing at the end of the tube, to the interaction with the target and to the rebound, in different conditions (electrode inside or outside the tube, location of the target) for both positive and negative polarities. The characteristics of the electric field rebound and its dependence on the presence of target and on the type of target are studied in detail. [Preview Abstract] |
Tuesday, November 7, 2017 11:45AM - 12:00PM |
ET2.00007: Kinetic, Unstructured Finite Element PIC-DSMC Simulation of Ultra-Fast Pin-to-Plane Discharge in Air Christopher Moore, Andrew Fierro, Jean-Michel Pouvesle, Eric Robert, Anne Bourdon, Roy Jorgenson, Ashish Jindal, Matthew Hopkins Recently, highly reproducible breakdown experiments in air at atmospheric pressure, leading to large volume homogeneous plasmas, have been performed in a 1.5 cm gap, pin-to-plane geometry with \textasciitilde 2 ns rise-time [1]. The present work compares temporally resolved experimental results for the electric field and electron density to kinetic simulations using an unstructured finite element Particle-In-Cell code that models the collisions via Direct Simulation Monte Carlo. The model includes electron-neutral elastic, excitation, ionization, and attachment collisions; ion and photon induced electron emission from surfaces; ion-neutral collisions; and self-absorption, photoionization, and photodissociation. The model tracks excited state neutrals which can be quenched through collisions with the background gas and surfaces or spontaneously emit a photon (isotropically) and transition to a lower state. [1] J-M. Pouvesle, et al. ``Experimental Study of an Ultra-Fast Atmospheric Pressure Discharge in a Pin-to-Plate Geometry'', ICOPS 2017. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA0003525. [Preview Abstract] |
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