Bulletin of the American Physical Society
74th Annual Gaseous Electronics Conference
Volume 66, Number 7
Monday–Friday, October 4–8, 2021;
Virtual: GEC Platform
Time Zone: Central Daylight Time, USA
Session JW64: Computational Methods I |
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Chair: Davide Curreli, University of Illinois Room: Virtual GEC platform |
Wednesday, October 6, 2021 2:00PM - 2:15PM |
JW64.00001: Computational Modeling of Laser Induced Breakdown in Gases Alessandro Munafo, Andrea Alberti, Marco Panesi The first observations of Laser Induced Breakdown (LIB) in gases go back were reported by Maker in the 1960s. In those experiments it was observed that, gases which are normally transparent to optical radiation, could be transformed in plasmas by focusing a laser beam onto a small volume. When the operating conditions (e.g. pressure) ensure that the process is collision-dominated, plasma formation occurs in two-steps: creation of priming electrons via Multi Photon Ionization (MPI) and cascade ionization initiated and sustained by energy absorption in inverse Bremsstrahlung interactions. |
Wednesday, October 6, 2021 2:15PM - 2:30PM |
JW64.00002: Numerical Investigation of the Interaction of an Expanding Plasma Plume with Ambient Gas using Direct Kinetic Simulations Wai Hong Ronald Chan, Alexander R Vazsonyi, Iain D Boyd The interaction of a laser pulse with a material surface induces the formation of a plasma plume that expands away from the surface. Understanding laser ablation is key to enhancing the efficiency and performance of pulsed laser deposition, laser propulsion, inertial confinement fusion, and laser-induced breakdown spectroscopy. Such plumes split and sharpen upon interacting with a background gas of intermediate pressure, and a definitive mechanistic explanation remains an active area of research. The highly transient process is amenable to direct numerical simulation, which can probe plume–gas interactions and provide detailed physical insights inaccessible by other means. This requires the adoption of appropriate numerical methods and models. Most studies have employed particle kinetic methods, such as the direct simulation Monte Carlo method, which are subject to statistical noise and are suboptimal for transient flows. Direct kinetic methods solve the Boltzmann equation in an Eulerian fashion and more accurately resolve time-evolving flows. In this work, a direct kinetic solver is used to simulate a two-species mixture as a model problem for laser-induced plume expansion. A weakly ionized plume is initially concentrated at one end of the simulation domain and allowed to expand into ambient low-pressure gas of a distinct species. The roles of key parameters such as the plume–gas pressure ratio and the degree of ionization are investigated, along with sensitivity to underlying collision models. |
Wednesday, October 6, 2021 2:30PM - 2:45PM |
JW64.00003: Numerical Simulation of Electrostatic Discharge with Energy Distributions Distorted by Electric Field Philip D Flammer, John W Rose, Claudia A Schrama, Sarah Hinnegan, Forrest Doherty, Jonathan Mace, Charles G Durfee Electron energies drive many processes in electrostatic discharges: ionization rates, collisional relaxation rates, secondary emission, etc. Especially in the initial phases, the energy delivered to electrons by direct acceleration from the electric field can be just as important as the thermal energies. In these cases, the velocity distribution for the electrons is not a Maxwell-Boltzmann distribution, but skewed along the axis of the electric field. Ideally, one would use the Boltzmann equation to solve for these dynamics, but this is often not practical when modeling realistic problems. |
Wednesday, October 6, 2021 2:45PM - 3:00PM |
JW64.00004: High-order moment models for low pressure discharges Alejandro Alvarez Laguna, Benjamin Esteves, Louis Reboul, Anne Bourdon, Pascal Chabert We introduce a novel electron fluid model based on the resolution of higher-moment equations that aims at extending the validity of the fluid equations for transitional collisional regimes between the continuum and the kinetic descriptions. In addition to mass, momentum, and energy conservation equations, the model explicitly solves for the evolution of the heat flux vector and the contracted fourth moment to capture perturbations in the skewness and the kurtosis of the electron distribution function. We use the model to study an argon inductively coupled discharge in the low-pressure range (p < 100 mTorr). We will discuss the closure of the system of equations with Grad’s method and considering a full Boltzmann collisional operator, as opposed to the commonly used Krook operator simplification. The new equations show new effects in the mass and energy transport that are consequence of the dependency of the transport coefficients on the kurtosis of the electron distribution function. Numerical simulations of the new system of equations will be compared to particle in cell simulations as well as to experimental measurements of the electron quantities in low-pressure ICP discharges. |
Wednesday, October 6, 2021 3:00PM - 3:15PM |
JW64.00005: Three-dimensional numerical simulation of branching structure in surface dielectric-barrier-discharge Hideto Tamura, Shintaro Sato, Naofumi Ohnishi Surface dielectric-barrier-discharge (DBD) has been studied to improve the insulating performance of electric devices. In some experiments, spanwise non-uniform branching structures of the streamer have been observed. In this study, we conducted three-dimensional numerical simulation of the surface DBD with a small protrusion of exposed electrode using a plasma fluid model. The branching structures are successfully obtained when a step-like positive voltage is applied, and the surface charge distribution of the streamer is similar to the experimental result. Simulations considering various size of the protrusion and sub-atmospheric pressure conditions are conducted to investigate three-dimensional discharge structure of the surface DBD. The size of protrusion affects the width in the spanwise direction of the branching structure that is formed from the electrode edge. The branched streamers propagate over a long distance in spanwise direction for the case of the larger protrusion. Under sub-atmospheric pressure conditions, the width in the spanwise distribution of the branching structure becomes wider than that for the atmospheric pressure conditions. Elaborate comparisons of branching structures under each condition and important factors that affect the branching structure such as grid convergence will be discussed in the full paper. |
Wednesday, October 6, 2021 3:15PM - 3:30PM |
JW64.00006: Asymptotic preserving finite-volume method for fluid models in low-temperature partially-magnetized plasma applications involving instabilities. Louis Reboul, Alejandro Alvarez Laguna, Pascal Chabert, Anne Bourdon, Thierry Magin, Marc Massot Multi-fluid plasma models are able to represent the scale disparity between the different species within plasmas while being theoretically less expensive than kinetic approaches. In a previous work, we have demonstrated the capability of advanced finite-volume methods for electrostatic multi-fluid models to simulate the onset and physics of instabilities in magnetized partially-ionized plasma at low pressure in the presence of sheaths. Nevertheless, stability constraints, which typically imply that the time step must be lower than the inverse of the electron plasma frequency and that the mesh size should be below the Debye length, are extremely restrictive and prevent finite-volume method from significantly outperforming PIC methods in terms of computational cost. We propose a so-called asymptotic preserving scheme that remains stable even when these conditions are not met. As a result, this approach allows for a significant reduction of the simulation time and fully benefits from the potential of fluid methods. The results are compared to reference PIC simulation obtained via the LPPic code and other fluid models found in the literature. |
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