Bulletin of the American Physical Society
71st Annual Gaseous Electronics Conference
Volume 63, Number 10
Monday–Friday, November 5–9, 2018; Portland, Oregon
Session ET1: Modeling and Simulation I |
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Chair: Natalia Babaeva, Institute for High Temperature Russian Academy of Sciences Room: Oregon Convention Center A103-A104 |
Tuesday, November 6, 2018 9:30AM - 10:00AM |
ET1.00001: Modelling of kinetic instabilities in low-temperature plasmas Invited Speaker: Trevor Lafleur Instabilities are a common phenomenon present in a wide range of different plasma devices. Such instabilities can result from macroscopic effects, such as gradients in the plasma properties, or microscopic (kinetic) effects associated with the particle distribution functions themselves. These latter instabilities are typically characterised by short-wavelengths (of the order of the Debye length) and high-frequencies (of the order of the ion plasma frequency), and can play an important role in particle transport. Modelling of kinetic instabilities is a challenge since they cannot in general be described by plasma fluid equations, and the Boltzmann or Vlasov equations often prove too difficult to solve directly. In these situations, particle-in-cell (PIC) simulations are the ``go-to'' tool, but for multi-dimensional, large-scale, or high-density problems, even these simulations can be too demanding due to strict numerical stability criteria. Using as an example electron drift instabilities in magnetised plasmas, a hybrid approach is discussed that combines elements of fluid modelling, kinetic theory, and Monte Carlo simulations. An Initial comparison with full PIC simulations offers promise for this new technique to more rapidly, and self-consistently, model kinetic instabilities. [Preview Abstract] |
Tuesday, November 6, 2018 10:00AM - 10:15AM |
ET1.00002: Elk: A New MOOSE Framework Application for Radio-Frequency Electromagnetics Casey Icenhour, Alex Lindsay, David Green, Richard Martineau, Steven Shannon A new tool in-development for general electromagnetic (EM) simulation for modeling radio-frequency (rf) systems is presented. The primary motivation for development of this tool is to leverage the flexibility and high-performance-computing capability of the Multiphysics Object-Oriented Simulation Environment (MOOSE) Framework developed by Idaho National Laboratory (INL) for complex EM problems. A MOOSE application (or MOOSE App) enables the end user to create a fully-functional simulation scenario without needing explicit knowledge of the underlying finite-element weak form implementation. MOOSE combines the libMesh library and the PetSc suite as the finite element and solver libraries, giving a robust platform for solving highly non-linear, coupled sets of PDEs such as those found in EM and plasma physics problems. Initial validation efforts have included standard waveguide and antenna benchmarks with the current focus being field validation against the well-known capacitively-coupled GEC Reference Cell (GEC-CCP). The results of this effort and progress towards coupling to the plasma fluid MOOSE App Zapdos [Lindsay \textit{et al} 2016 \textit{J. Phys. D: Appl. Phys.} \textbf{49} 235204] for cold-plasma rf wave propagation studies will be discussed. [Preview Abstract] |
Tuesday, November 6, 2018 10:15AM - 10:30AM |
ET1.00003: Developing Accurate Capacitively Coupled Plasma Models Shahid Rauf, Jun-Chieh Wang, Wei Tian, Jason Kenney Capacitively coupled plasmas (CCPs) are widely used for materials processing in the semiconductor industry. Significant progress has been made in developing 2D and 3D models of CCPs with complex chemistries. [1] In this paper, we go back to the fundamentals and investigate how to accurately capture the dynamics of low pressure CCPs in a fluid plasma model. 1D and 2D fluid models have been developed for Ar, He and N2 plasmas in the 25 -- 1000 mT pressure range. These models include continuity equation for all species, drift-diffusion approximation for electron flux, ion momentum conservation equation, electron energy conservation equation, and the Poisson equation. Fluid modeling results are compared to corresponding particle-in-cell (PIC) modeling results as well as experimental diagnostic measurements from the Gaseous Electronics Conference reference cell. [2] The fluid and PIC models utilize the same geometry and chemistry engines, and only differ in the treatment of charged species transport and chemistry. Approximations and modifications that improve the accuracy of fluid plasma models at low pressure will be discussed. [1] Agarwal et al, J. Phys. D: Appl. Phys. 50, 424001 (2017). [2] L. J. Overzet, J. Res. Natl. Inst. Stand. Technol. 100, 401 (1995). [Preview Abstract] |
Tuesday, November 6, 2018 10:30AM - 10:45AM |
ET1.00004: Computational Modeling and Simulation of a Resonant Plasma Source Rochan Upadhyay, Peter Ventzek, Laxminarayan Raja, Alok Ranjan Electrical resonance can be exploited to extend low temperature, unmagnetized plasma sources beyond their usual limits. Electrical resonance in a cavity can be achieved by different antenna configurations, one such is described by Niazi et. al. (Plasma Sources Sci. Technol.,3,1994), who use a coil wrapped around a tube. The resonator typically has a configuration dependent resonant frequency and a high quality factor that allows gas heating by strong electric fields producing a high density plasma suitable for material processing. Due to the dependence of the resonance on the precise geometrical and material properties of the chamber, a full three dimensional computational modeling of the plasma electromagnetic wave coupling is necessary. In this study we simulate the plasma in a resonant cavity using a quasi-neutral plasma model that is solved together with the Maxwell Equations in 3D. We distinguish the frequency response of the system with and without plasma. Simulations reveal spatial plasma distributions that are largely governed by electron heating by the electric field that in turn is determined by the structure of the coil. We present dependence of plasma on pressure and power. Comparisons with literature results, including those of Niazi et. al., are also presented. [Preview Abstract] |
Tuesday, November 6, 2018 10:45AM - 11:00AM |
ET1.00005: Electromagnetic Effect on Plasmas in Rectangular Very High Frequency Capacitively Coupled Plasma Source Kallol Bera, Shahid Rauf, Ken Collins Capacitively coupled plasmas have been used in both etching and deposition processes in the semiconductor industry. In this study, we investigate very high frequency plasma behavior in a rectangular parallel plate capacitively coupled plasma reactor. Our plasma model includes the Maxwell equations using finite difference time domain (FDTD) formulation. Plasma current source for the Ampere's law is computed using the plasma characteristics. The plasma transport equations and the Maxwell equations are solved explicitly in time. Ar plasma at moderate pressure (a few Torr) has been simulated at 60 and 120 MHz. In this reactor, the plasma is formed in the gap between the top powered electrode and the bottom return electrode, both of which are rectangular in shape. The RF feed to the powered electrode is located at the center of the reactor. The RF return path along the outer electrode is separated from the powered electrode by a dielectric. Plasma uniformity is found to be primarily determined by the electric field distribution in the sheath/pre-sheath region. The electric field distribution, and hence plasma distribution, depend on geometric parameters, such as shape of the electrode and gap between the electrodes, and operating parameters, such as pressure, power and frequencies. [Preview Abstract] |
Tuesday, November 6, 2018 11:00AM - 11:15AM |
ET1.00006: The effects of secondary electrons on the discharge characteristics and control of particle properties in low-pressure capacitively coupled plasmas Aranka Derzsi, Benedek Horvath, Katharina Noesges, Sebastian Wilczek, Zoltan Donko, Julian Schulze In particle-based simulation studies of low-pressure capacitively coupled plasmas (CCPs), the assumption of a constant ion induced secondary electron emission (SEE) coefficient is typical; this coefficient is independent of the incident particle energy and angle, the electrode material and its surface conditions. The emission of SEs by electron impact and by other plasma species is typically neglected in such simulations. Recent studies emphasize the importance of the realistic description of the SEE in simulations of low-pressure CCPs, as largely different results can be obtained for the same discharge conditions based on different (simple or realistic) descriptions of the various SEE processes. In this work, we perform a systematic investigation of the effects of implementing realistic energy- and material-dependent SE yields for heavy particles and electrons in PIC/MCC simulations of low-pressure CCPs on the plasma parameters and control of ion properties at the electrodes. The simulations cover discharge conditions that are relevant for plasma processing applications of surfaces. [Preview Abstract] |
Tuesday, November 6, 2018 11:15AM - 11:30AM |
ET1.00007: Implementing a model for material dependent secondary electron emission coefficients in PIC/MCC simulations of capacitive RF plasmas Manaswi Daksha, Aranka Derzsi, Zoltan Donko, Julian Schulze Ion induced secondary electron emission coefficients ($\gamma$) are a pivotal parameter utilized in Particle-in-Cell/ Monte Carlo collision (PIC/MCC) simulations to mimic realistic plasma-surface interactions. However, $\gamma$ is usually implemented in a rudimentary way, e.g. as an arbitrary constant. Experimental and theoretical studies have, however, suggested that it is significantly influenced by the surface material, its crystallinity, the impinging ion properties, etc. Therefore, we use an ab-initio model based on Hagstrum’s theory to calculate realistic $\gamma$-coefficients, which are then included in PIC/MCC simulations. To demonstrate the effect of material dependent $\gamma$ on modeling results, simulations of 13.56 MHz, single frequency argon and helium capacitive discharges are carried out based on different models for $\gamma$. We find that, depending on the material simulated, the plasma properties will change dramatically, if realistic surface coefficients are used. Thus, we conclude that a realistic material dependent implementation of $\gamma$ is required to obtain realistic simulation results. [Preview Abstract] |
Tuesday, November 6, 2018 11:30AM - 11:45AM |
ET1.00008: Embedded boundary fluid simulations of complex-geometry plasma discharges with structured adaptive mesh refinement Robert Marskar I present results on the development and use of a scalable two- and three-dimensional computer code for low temperature plasma simulations in complex geometries that feature both insulators and electrodes. Our approach is based on the Chombo library, and uses embedded boundary (EB) finite volume discretizations of fluid plasma models on adaptive Cartesian grids, extended to multi-material cases that also account for charging of dielectric surfaces. I discuss cut-cell geometry generation, temporal and spatial discretizations, and implementation of these into Chombo. Our use of AMR provides a scalable platform for performing 3D fluid simulations of filamentary plasmas in realistic geometries at moderate pressures and comparatively large scale. Simulation examples that demonstrate this capability up to many thousands of CPU cores are presented. I also discuss computational bottlenecks and challenges related to large scale HPC simulations, and remark on possible optimization strategies for emergent architectures that display increasing degrees of inhomogeneity, decreasing memory-to-CPU ratios, and wider vector units. [Preview Abstract] |
Tuesday, November 6, 2018 11:45AM - 12:00PM |
ET1.00009: 3D unsteady model of arc heater plasma flow using the ARC Heater Simulator (ARCHeS) Jeremie Meurisse, Alejandro Alvarez Laguna, Nagi Mansour Arc jets are unique facilities used to evaluate the performance of Thermal Protection Systems (TPS) for hypersonic vehicles. They produce a high pressure and high enthalpy plasma flow to simulate the extreme heat encountered during atmospheric entry. The constricted arc heater part of an arc jet increases the test gas temperature by Joule heating. This study details the development of the three-dimensional unsteady plasma flow analysis tool, ARCHeS (ARC Heater Simulator). Coupled Navier-Stokes, radiative transfer and Maxwell equations yield current density, magnetism, radiation and flow field solutions. Results from plasma flow simulations performed using 1200 processors will be presented. The present work constitutes the first demonstration of an unsteady three-dimensional plasma flow simulation of a high pressure and high enthalpy arc heater that captures kink instabilities of the electric arc. It is found that the arc attachment is mainly driven by upstream arc instabilities. Analysis of the electric arc dynamics will provide better intuitive understanding of the complex behavior of plasma flow observed in arc jets. Massive parallel simulation capability is inherited in ARCHeS from its OpenFOAM framework, making such studies possible. [Preview Abstract] |
Tuesday, November 6, 2018 12:00PM - 12:15PM |
ET1.00010: Two-dimensional non-equilibrium plasma model for dual-pulse laser ignition. Rajib Mahamud, Albina A. Tropina, Mikhail N. Shneider, Richard B. Miles Dual-pulse laser ignition mechanism uses an ultraviolet (UV) pulse with low pulse energy to create initial ionization and a subsequent deposition of energy by a near-infrared (NIR) pulse that allows avoiding any optical breakdown and minimization of energy requirements. Decoupling of the UV preionization (without breakdown) pulse from the second energy deposition pulse allows tailoring the laser plasma parameters such as electron number density and temperature, ion number density and size of the initial ignition kernel. In this study a two dimensional mathematical model is presented for dual-pulse laser ignition technique that self-consistently integrates Navier-stokes, three energy states (electronic, vibrational, and neutral), Poisson equation, plasma species and GRI-Mech 3.0 mechanism. The two-dimensional multiphysics model allows to understand the role of chemistry and energy exchange mechanisms on the hydrodynamics of dual-pulse laser ignition and flame propagation. The results also suggest that the initial flame kernel growth and ignition delay time are affected by the energy exchange mechanism between internal degrees of freedom, the laser intensity and initial electron density from the first UV pulse. [Preview Abstract] |
Tuesday, November 6, 2018 12:15PM - 12:30PM |
ET1.00011: Particle-in-Cell Modeling of Laser Thomson Scattering in Low-Density Plasmas at Elevated Laser Intensities Andrew Powis, Mikhail Shneider Incoherent Thomson scattering is a non-intrusive technique commonly used for measuring local plasma density. Within low-density, low-temperature plasma's and for sufficient laser intensity, the laser may perturb the local electron density via the ponderomotive force, causing the diagnostic to become intrusive and leading to erroneous results. This effect is explored both theoretically and numerically via kinetic simulations of a quasi-neutral plasma. Results demonstrate that experimentalists should take care when attempting to apply laser Thomson scattering to the measurement of low density plasmas, and where possible avoid boosting the signal by increasing laser intensity. Shneider, Mikhail N. "Ponderomotive perturbations of low density low-temperature plasma under laser Thomson scattering diagnostics." Physics of Plasmas 24.10 (2017): 100701. Powis, Andrew T., and Mikhail N. Shneider. "Particle-in-cell modeling of laser Thomson scattering in low-density plasmas at elevated laser intensities." Physics of Plasmas 25.5 (2018): 053513. [Preview Abstract] |
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