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 UF3: Modeling and Simulation V |
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Chair: Oleksandr Marchuk, Juelich Room: Century III |
Friday, November 1, 2019 10:00AM - 10:15AM |
UF3.00001: Development of a Two Fluid Model for Low-Temperature Magnetized Plasmas Rupali Sahu, Kentaro Hara A two fluid model of plasma is developed to study low temperature magnetized plasmas. For the first test case, a quasi-neutral plasma between two walls is modeled under applied electric and magnetic fields. Source terms due to ionization are designed to compensate the ion diffusion toward the wall and to achieve steady state. Moments of Maxwellian distribution are calculated, which we call kinetic fluxes for the boundary conditions. Inclusion of ion momentum transfer collisions displayed variations in plasma sheath properties in close agreement with analytical trends. It was also observed that an applied transverse magnetic field could eliminate a classical sheath formation in some cases. Two fluid model is used to model discharge plasma of Hall effect thrusters. We will assess the two-fluid model in comparison with a quasi-neutral drift-diffusion model to evaluate the effects of the terms neglected in the drift-diffusion approximation. [Preview Abstract] |
Friday, November 1, 2019 10:15AM - 10:30AM |
UF3.00002: Modeling of hot cathode DC magnetized plasma source Alexandre Likhanskii, Alexander Perel, John Koo, Jay Scheuer, Shahid Rauf Hot cathode magnetized ion sources are widely used in ion implantation for the semiconductor industry. A typical ion source consists of a source chamber, biased hot cathode, biased electron repeller and extraction slit. A magnetic field confines the plasma\textbf{,} achieving plasma densities of 1e11 - 1e12 per cm3 at a few mTorr of gas pressure. By adjusting ion source parameters, one can obtain desired ion extraction current and ion spectrum. Despite such sources have been used for decades, their detailed understanding is still unclear. In the paper, we will present the results of numerical investigations of the ion source physics using two codes -- AMAT's in-house hybrid plasma code CRTRS and commercial Particle-In-Cell (PIC) code Vorpal. CRTRS solves momentum equation for ions and splits electrons into two populations, bulk and beam electrons. Transport for bulk and beam electrons is solved using drift-diffusion approximation and Monte-Carlo collision formulation correspondingly. PIC code treats ions and electrons as particles and solves equation of motion and Monte-Carlo collisions with background gas. Specifically, we will analyze plasma diffusion across magnetic field in PIC simulations and discuss adjustments to the diffusion model in hybrid codes. [Preview Abstract] |
Friday, November 1, 2019 10:30AM - 10:45AM |
UF3.00003: Application of Rejection-Sampling Theory to Particle Injection in PIC/VSIM Simulations Daniel Main, John Cary, Tom Jenkins, Nate Crossette, Sergey Averkin A particle injection boundary condition for PIC simulations representing an infinite plasma beyond a boundary has been implemented in VSIM and is presented here. This boundary condition allows the simulation of a small part of a much larger physical plasma. Our particular application is to determine the interaction of a plasma with a material wall, which requires injection of new particles at the opposite boundary. Because the computational boundary is physically artificial, one goal of this work is to eliminate the formation of sheaths at the injection boundary (since no sheath would form in the physical situation). Therefore, all particles moving toward the boundary are absorbed while the emitted particles are a drifting population which mimics the population already present. To smoothly transition the emitted particles into the simulation domain in VSIM, the incoming particles at the wall correspond to a uniform, thermal plasma with some drift corresponding to the losses at the wall. In this presentation, we discuss a novel method of introducing new particles at a boundary chosen from the correct flux-conserving probability distribution function using Rejection Sampling theory. We show that by emitting particles correctly at the boundary, and by choosing a particular value for the drift velocity, the build-up of sheaths at the boundary can be minimized. [Preview Abstract] |
Friday, November 1, 2019 10:45AM - 11:00AM |
UF3.00004: Laser induced plasma in hydrogen-air mixtures. Albina Tropina, Mikhail Shneider Dual-pulse laser ignition in hydrogen-air mixtures at atmospheric pressure conditions was studied numerically. A two dimensional three-temperature plasma model was developed, which includes transport equations for neutral components of the mixture, electrons, molecular and atomic hydrogen ions in the ground state combined with equations for the electronic, vibrational and translational temperatures and Navier --Stokes equations for the compressible gas. Analysis of different kinetic schemes and ignition delay time dependence on the initial ionization level have been carried out, taking into account a multi-photon ionization of hydrogen molecules by the first ultraviolet laser pulse, avalanche ionization by the second near-infrared laser pulse and formation of excited states of oxygen. The results allow us to understand the role of chemistry, hydrodynamics phenomenon, vibrational non-equilibrium and energy exchange mechanisms in facilitating ignition by the dual-pulse laser in the hydrogen-air mixture. [Preview Abstract] |
Friday, November 1, 2019 11:00AM - 11:15AM |
UF3.00005: Electron Beam Driven Plasmas in O$_{\mathrm{2}}$: Modeling and Diagnostics Shahid Rauf, David R. Boris, Scott G. Walton Electron beam driven plasmas are well-known for their low electron temperature ($T_{e})$, which leads to low plasma potential. These plasmas have been demonstrated as ideal sources for high-precision plasma processing applications such as atomic layer etching and functionalization of 2-dimensional materials (e.g., Graphene). Several diagnostic techniques were used to characterize magnetized electron beam plasmas in O$_{\mathrm{2}}$. These diagnostics allowed measurements of spatially-resolved electron density, electron temperature and ion flux for a range of pressures, beam currents, magnetic fields and beam electron energies. As expected $T_{e}$ was low (\textless 0.3 eV) in these plasmas. There were however some surprises, such as a O$^{\mathrm{+}}$ flux being higher compared to O$_{\mathrm{2}}^{\mathrm{+}}$ flux. This paper focuses on 2-dimensional modeling of the O$_{\mathrm{2}}$ electron beam driven plasma with detailed comparison to experiments. The simulations utilized a hybrid plasma model with bulk electrons and ions treated as a fluid and a Monte Carlo model for the beam electrons. We will discuss the enhancements in the O$_{\mathrm{2}}$ plasma chemistry that allowed the model to capture most experimental observations. This work is partially supported by the Naval Research Laboratory base program. [Preview Abstract] |
Friday, November 1, 2019 11:15AM - 11:30AM |
UF3.00006: Application of a least-square weighted residual method based global model to simulations of material processing plasmas Sergey Averkin, Thomas Jenkins Global models are widely used for quick estimation of volume-averaged plasma parameters (number densities of plasma components, or electron temperatures) in partially-ionized plasmas. Such plasma discharges may contain thousands of species and hundreds of thousands of chemical reactions that are relevant to material processing. A major drawback of global models is the lack of spatial resolution, which can be critical in some cases. However, fluid simulations with the necessary spatial resolution are computationally limited (even in 1D) to relatively simple cases using fewer reactive species and chemical reactions. To fill this gap we have developed a novel formulation of global model equations that allows us to estimate the spatial variation of plasma parameters in 1D, with computational costs that are comparable to conventional global models. The model uses a rational functional representation of various plasma properties; profiles are reconstructed using least-square weighted residual methods that minimize the L$^{\mathrm{2}}$ norm of the residual of 1-D multi-fluid equations. Optimal fitting parameters can thus be obtained for all plasma components. In this work we present an application of the method to chlorine plasma, which has many practical applications for material processing. [Preview Abstract] |
Friday, November 1, 2019 11:30AM - 11:45AM |
UF3.00007: Intensity Distribution in the Focal Area of Ionizing Dual Gaussian Laser Pulses in Air Matthew R. New-Tolley, Mikhail N. Shneider, Richard B. Miles The localized energy deposition which accompanies dual laser pulse sequences has been proposed for use in remote sensing and efficient combustion systems. The presence of the plasma region created by the first ‘pre-ionizing’ pulse allows energy from the second laser to be efficiently deposited in a specific location. Previous experiments and fluid simulations have made clear that the relative position of the beam waists dictate which fluid structures will dominate the motion of the surrounding fluid following the laser pulse. These studies however, manually selected the location of the beam waist and did not account for the distortion of the beams by the plasma region. In this study we simulate the application of a pre-ionizing UV nano-second laser pulse followed by a second higher-energy IR pulse. Each laser pulse is temporally discretized, and a split step Fourier code applied to calculate the local intensity at each grid point. The local intensity is used to calculate the rate coefficients of multiphoton and avalanche ionization processes. The modified gas composition is then used to recalculate the refractive index at each grid point. This study looks at the effect of the plasma region on the near-focus intensity distribution of the laser pulses. [Preview Abstract] |
Friday, November 1, 2019 11:45AM - 12:00PM |
UF3.00008: Multi-physics modeling of combustion ignition from an elongated plasma kernel generated by microwave driven metasurface. Yunho Kim, Laxminarayan Raja We present the multi-physics modeling of combustion ignition phenomena in a hydrogen-air mixture initiated by a microwave surface plasma discharges. The surface plasma is generated over a resonant metamaterial structure that provides sufficient field intensification to breakdown and sustain a discharge under relatively high-pressure conditions of 10's to 100's Torr. Specifically, a surface electromagnetic (EM) wave mode known as the Spoof Surface Plasmon Polariton (SSPP) is excited to yield a hybrid resonance that is characteristic of the coupling of cavity and surface EM wave modes. Motivated by the need for a large, volumetric ignition kernel for applications in combustion ignition, we numerically demonstrate the volumetric surface plasma discharge enabled by the use of this particular EM wave mode in a high pressure operating regime. We discuss the transients evolution of an order 16 mm long plasma kernel and subsequent ignition kernel formation. High density combustion enhancing radical species (O, H, OH) are produced throughout the bulk plasma, which leads to successful ignition. [Preview Abstract] |
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