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 DT24: Modeling of Plasma Chemistry |
Hide Abstracts |
Chair: Xiaopu Li, Applied Materials Inc Room: Virtual GEC platform |
Tuesday, October 5, 2021 10:15AM - 10:30AM |
DT24.00001: 2D Modeling of Dynamic Contraction in Chemically Reactive Non-equilibrium Plasma Flow Hongtao Zhong, Xingqian Mao, Mikhail Shneider, Yiguang Ju Dynamic contraction in weakly ionized plasma has attracted attention for decades. It occurs when a homogeneous volumetric plasma transits into a filamentary channel. This process is critical for plasma applications including gas lasers, plasma-assisted ignition, and fuel reforming. In this work, a time-dependent two-dimensional plasma model is formulated by considering detailed plasma kinetics, chemical kinetics, transport models, and electrical circuit. The diffusion-drift approximation is applied for charged species. The near-electrode sheaths are not considered and the plasma is assumed quasi-neutral. By perturbing the steady-state plasma column, a filament is propagating from one electrode to another. The contraction is shown to be not only dominated by the well-known thermal-ionization mechanism but also by chemical heat release/absorption and chemical kinetics. The work integrates the modeling of the weakly ionized plasma and chemical kinetics, which is of practical interest for plasma-assisted chemical processing. |
Tuesday, October 5, 2021 10:30AM - 10:45AM |
DT24.00002: Chemical Model Reduction for Negative Hydrogen Ion Density Predictions Using Global Sensitivity Analysis Simone Venturi, Tiernan Casey, Wei Yang, Igor Kaganovich Negative hydrogen ion sources (NHIS) are the preferred mode of plasma heating in tokamak devices for nuclear fusion. Accurate predictions of the H- density are crucial for the design of such machines. This work exploits state-of-the-art statistical and data science tools developed for machine learning and uncertainty quantification to improve the predictive capabilities of the Global Model for NHIS by W. Yang et al. To achieve high fidelity in reproducing the important kinetics features, this model involves detailed pathways composed of hundreds of reactions. While increased complexity represents a benefit in terms of completeness, the resulting augmentation of model capacity requires parameter calibration through sufficient validation data, which are not always available. With this constraint in mind, this study relies on an efficient framework consisting of: i) global sensitivity analysis (GSA) enabled by polynomial chaos expansions to inform the construction of reduced-order models that omit the uninformative reactions, and ii) solution of an inverse problem via Bayesian inference to update the most influential chemical reactions from experimental data. The analysis suggests that reducing the NHIS mechanism from more than 1300 reactions to only 35 provides accuracy within ±10% for the prediction of H- number density. Such a low-dimensional pathway is dominated by H2+e dissociation, associative detachment, wall recombination, and dissociative electron attachment. |
Tuesday, October 5, 2021 10:45AM - 11:00AM |
DT24.00003: Refined Optimization of a Uranium Oxide Reaction Mechanism Using Plasma Flow Reactor Measurements Mikhail S Finko, Davide Curreli, Batikan Koroglu, Kate E Rodriguez, Timothy P Rose, Harry B Radousky, Kim Knight As part of a continued effort to study formation of metal oxides in rapidly cooling atmospheric plasmas, we present a refined stochastic optimization of a uranium oxide reaction mechanism using optical emission measurements from a plasma flow reactor (PFR). This work builds on a previously presented Monte Carlo Genetic Algorithm approach by utilizing an expanded dataset from a modified PFR setup and analyzing the resulting reaction mechanism in detail. The PFR modifications allow for finer unobstructed axial measurements of atomic and molecular emission, providing a well resolved time history of oxide formation. In addition, a wider range of oxygen fugacities are explored to better constrain the sensitivity of reaction channels to oxygen conditions. The newly calibrated reaction mechanism is compared against a previously published mechanism and dominant reaction pathways are identified via standard sensitivity analysis and mechanism reduction methods. |
Tuesday, October 5, 2021 11:00AM - 11:15AM |
DT24.00004: Investigation of CO2 Conversion in a High-Power Inductively Coupled Plasma Source by Global Modeling Hendrik Burghaus, Sebastian Wilczek, Thomas Mussenbrock, Stefanos Fasoulas, Georg Herdrich Identifying and understanding the main pathways of carbon dioxide dissociation is an important step towards efficient plasma-based CO2 conversion. Here, the step-wise vibrational excitation by electron impact, found in non-equilibrium plasmas, has shown great potential. At the Institute of Space Systems (IRS), the capability of the inductively coupled plasma source IPG4 (Inductive Plasma Generator 4) for effective carbon dioxide dissociation is under investigation. IPG4 is a high-power (160kW) plasma source operating at reduced pressure (2600Pa). In this work, the kinetic model globalKin is used to analyze the CO2 conversion efficiency of the plasma source IPG4. The simulation code is developed by Prof. Mark Kushner from the University of Michigan. The built-in plug-flow model of globalKin allows for a one-dimensional analysis of the reaction kinetics in the CO2 plasma. The role of vibrational excitation in carbon dioxide dissociation is studied. Moreover, the effect of dilution with argon and nitrogen on the reaction kinetics is examined. |
Tuesday, October 5, 2021 11:15AM - 11:30AM |
DT24.00005: CO2 dissociation in a microwave plasma torch: efficiency evaluation and comparison with other plasma sources Natalia Y Babaeva, George V Naidis, Dmitry V Tereshonok, Timofey V Chernishev, Luka S Volkov, Sebastian Wilczek, Yue Liu, Thomas Mussenbrock The idea of re-using CO2 and transforming it into valuable chemicals has been gaining increasing interest in recent years. Plasma-assisted CO2 dissociation offers one possible solution to this problem. In this contribution, we report on the results from a 2-dimensional computational investigation of the CO2 conversion to CO and oxygen in an atmospheric pressure microwave (MW) plasma torch device. The mixtures of CO2 with Ar and other gases are considered. The parameters that are varied is MW power, CO2 and CO2/Ar flow rates. The optimal operation conditions for CO2 dissociation as a function of these and other parameters are investigated. The achieved energy efficiency is evaluated and compared with available information for other plasma sources. In this study, the two-dimensional nonPDPSIM modeling platform was used which was developed in the group of Prof. Mark J. Kushner (University of Michigan). |
Tuesday, October 5, 2021 11:30AM - 11:45AM |
DT24.00006: The influence of key vibrational states on plasma modelling Sebastian Mohr, Harindranath Ambalampitiya, Martin Hanicinec, He Su, Jonathan Tennyson Vibrational states play an important role in molecular plasmas; they induce gas phase reactions not available for ground state neutrals as well as surface reactions [1] or contribute to gas heating via V-T relaxation. Furthermore, the vibrational excitation process itself affects the electron kinetics and contributes to collisional energy losses. Therefore, cross-sectional data for vibrational excitation is needed to accurately simulate molecular plasmas. |
Tuesday, October 5, 2021 11:45AM - 12:00PM |
DT24.00007: Two dimensional simulations of the vibrational state distributions in low pressure hydrogen plasmas with an isothermal neutral gas and gas temperature gradients Gregory J Smith, Paola Diomede, Andrew Gibson, Scott J Doyle, Vasco Guerra, Mark J Kushner, Timo Gans, James P Dedrick Low pressure hydrogen plasmas are of interest in fundamental plasma phenomena and applications including surface processing and negative ion beams. As negative ions form in the plasma volume through dissociative attachment of vibrationally excited hydrogen molecules, it is important to understand their response to gas temperature gradients, known to form at high power densities. In this study, two dimensional fluid-kinetic simulations using the Hybrid Plasma Equipment Model, including a new reaction set that accounts for gas temperature dependencies in determining heavy particle reaction rates with all of the vibrational levels of the ground electronic state, are used to study the influence of these temperature gradients. The results demonstrate that the incorporation of spatially resolved gas temperatures has a significant impact on the distribution of atomic hydrogen and the vibrational states, but has a relatively smaller impact on the negative ions. These results are important for future studies of low pressure hydrogen plasmas in technological plasma sources that generate spatial gas temperature gradients. |
Tuesday, October 5, 2021 12:00PM - 12:15PM |
DT24.00008: Student Excellence Award Finalist: Insight into chemistry and transport in CO2 microwave discharges through comparisons between simulations and experiments Luca Vialetto, Pedro Viegas, Alex W van de Steeg, Gerard J Van Rooij, Savino Longo, Jan Van Dijk, Paola Diomede In the past few years, a lot of attention has been devoted to the study of CO2 dissociation by means of microwave (MW) discharges. Nevertheless, mechanisms underlying this kind of discharge are not well understood and only a synergy between experiments and models can help to shed a light on them. A fully native 1-D radial fluid model has been developed to simulate a CO2 MW discharge operated at DIFFER. The model is coupled to a Monte Carlo Flux code for electron kinetics. Model results are validated against spatially-resolved measurements of the main neutral species and electron number density, gas and electron temperature, obtained by advanced laser scattering diagnostics at DIFFER. It is found that (i) radial mass and heat transport are fundamental to predict values of product formation (CO and O), (ii) detailed charged particles kinetics provides a better understanding of the contraction phenomenon in CO2 plasmas, and (iii) a non-Boltzmann electron energy distribution function explains counter-intuitive electron temperature measurements by Thomson scattering. The excellent agreement between experiments and simulations allows one to clarify the role of different transport and chemical processes in determining plasma composition and electron properties. |
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