Bulletin of the American Physical Society
70th Annual Gaseous Electronics Conference
Volume 62, Number 10
Monday–Friday, November 6–10, 2017; Pittsburgh, Pennsylvania
Session MW2: Non-equilibrium Kinetics of Low-temperature Plasmas |
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Chair: Igor Adamovich, The Ohio State University Room: Duquesne |
Wednesday, November 8, 2017 1:30PM - 1:45PM |
MW2.00001: O atom kinetics in RF CCP oxygen plasma at increased pressures Andrey Volynets, Dmitry Lopaev, Olga Proshina, Tatyana Rakhimova, Alexander Rakhimov In this study, the 80 MHz symmetric CCP discharge in quartz tube was used as a source of pure O$_{2}$ plasma of increased pressures (10 to 100 Torr). This research is mainly focused on the balance of O atoms that is governed by processes of O$_{2}$ dissociation and O atom loss. The use of time-resolved actinometry technique in the modulated discharge allowed experimentally determining dissociation rate constant k$_{diss}^{O2}$ and atom loss frequency \gamma$_{loss}^{O}$. The O atom loss is connected with surface recombination at lower pressure and volume reactions at higher pressure. The variation of plasma parameters allowed varying gas temperature from ~500 K up to 1800 K and this allowed to study the O atom generation and loss mechanisms in a wide range of gas conditions. The behavior of k$_{diss}^{O2}$ at low E/N and the role of ozone in \gamma$_{loss}^{O}$ is discussed in detail. [Preview Abstract] |
Wednesday, November 8, 2017 1:45PM - 2:00PM |
MW2.00002: Vibrational kinetics of non-equilibrium CO$_{\mathrm{2}}$ plasma discharge in low-excitation regime M Grofulovic, T Silva, V Guerra, C D Pintassilgo, B L M Klarenaar, R Engeln, A S Morillo-Candas, O Guaitella The main purpose of this work is to understand in detail the vibrational energy exchanges in non-equilibrium CO$_{\mathrm{2}}$ plasmas. To that end, we develop a kinetic model that couples the electron Boltzmann equations to the rate balance equations describing the time evolution of various individual vibrational levels of CO$_{\mathrm{2}}$(X 1$\Sigma +)$. We have investigated a low excitation regime, where $\nu _{\mathrm{2}}^{\mathrm{max\thinspace }}=$ 5, $\nu _{\mathrm{3}}^{\mathrm{max\thinspace }}=$ 5 and $\nu _{\mathrm{1}}^{\mathrm{ma\thinspace x}}=$ 2, resulting in 72 vibrationally excited levels. Validation of the model was done by comparing the time-dependent densities of the aforementioned states with measurements obtained by time-resolved in situ FTIR spectroscopy in a pulsed CO$_{\mathrm{2}}$ dc discharge (at p $=$ 5 Torr, I $=$ 50 mA) and its afterglow. The calculated maintenance electric field during the pulse and the time-dependent populations are in excellent agreement with the measured values. Work is in progress to extend the study to the higher vibrational excitation. [Preview Abstract] |
Wednesday, November 8, 2017 2:00PM - 2:30PM |
MW2.00003: Kinetics of nanosecond discharges at high specific energy release Invited Speaker: Svetlana Starikovskaia Voltage pulses 5-10 kV in amplitude and a few tens of nanoseconds in duration are capable to produce highly nonequilibrium low temperature plasma in a wide pressure range, from 0.1 Torr to 15 bar. High electric fields, up to kTd, are typical for discharge front. Behind the front the electric field stays high, hundreds of Td, providing high densities of electronically excited states, high dissociation degree and so high efficiency of nanosecond discharge as a trigger for various chemically active systems. The fact that nanosecond discharges are uniform at low and moderate gas densities, and are naturally synchronized within 0.1 ns in time in the case of a multi-streamer configuration at high gas densities, is extremely attractive for laboratory-scale research. At specific deposited energies 0.5-1 eV/molecule high rate of energy relaxation from electronically excited molecules or so-called fast gas heating provides increase of gas temperature for thousands of K during tens of nanoseconds; excitation degree becomes so high that the collisions of excited species with charged, other excited and dissociated species become important, changing ``classical'' low temperature plasma kinetics developed in the assumption of a small chemical perturbation of the system. A review of plasma parameters in nanosecond discharges, from fast ionization waves (FIWs) at low pressure to filamentary nanosecond surface dielectric barrier discharges (nSDBDs) at tens of bars will be given. [Preview Abstract] |
(Author Not Attending)
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MW2.00004: Influence of superelastic collisions on discharge properties: A self-consistent approach Gianpiero Colonna A fundamental aspect in modeling a gas discharge is to determine the rate coefficients of electron-induced processes. An accurate approach is to solve the Boltzmann equation in the two-term approximation to calculate the electron energy distribution function (eedf), that, together with the cross sections, allows the calculation of the rates. To simplify the calculation, under the assumption that eedf relaxes much faster than the gas composition, the rate coefficients can be related only to the local electric field. This approach cannot consider the contribution of the superelastic collisions in affecting the eedf. In participating to the Round Robin activity for the verification of different plasma kinetic codes, strong effects of superelastic collisions on the plasma properties have been observed, when a self--consistent coupling of free electron and level kinetics has been considered, even in the simple argon discharge, including ionization/recombination and excitation/de-excitation of the metastable state. Effects of superelastic collisions are very important not only in the post-discharge conditions, but also in the presence of high electric field, considering both power density or $E/N$ as input. [Preview Abstract] |
Wednesday, November 8, 2017 2:45PM - 3:00PM |
MW2.00005: Interactions between thermodynamic and chemical non-equilibrium states in an arc plasma He-Ping Li, Heng Guo, Jian Chen Since the power input rate is usually higher than the energy exchange rate between the sub-systems of electrons and heavy particles in low temperature plasmas, the electron temperature typically exceeds that of heavy particles, which makes the plasmas deviate from local thermodynamic or even local chemical equilibrium state. It is indispensable to investigate the complicated fundamental processes in a non-equilibrium plasma system with the aid of numerical simulations so as to optimize the discharge operating parameters. In this study, a full non-equilibrium physical-mathematical model is employed to simulate the non-equilibrium transportation processes in a free-burning argon arc, which is regarded as a model system for arc plasmas. Based on the two-dimensional non-equilibrium modeling, the complex interactions between the electron and heavy-species sub-systems are investigated. The modeling results show that, on one hand, the collisions between electrons and heavy particles influence directly the energy and mass transfer processes between these two sub-systems; while on the other hand, there exists an interaction between the non-uniform spatial temperature distributions of electrons and heavy particles, which has never been reported in previous publications. [Preview Abstract] |
Wednesday, November 8, 2017 3:00PM - 3:15PM |
MW2.00006: Abstract Withdrawn
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Wednesday, November 8, 2017 3:15PM - 3:30PM |
MW2.00007: Theoretical study of scaling law for electron kinetics in field emission-driven microplasmas in the pre-breakdown regime Xi Tan, David B. Go For microplasmas with a characteristic length less than 10 microns, field emission can be an important process that affects Townsend pre-breakdown regime. In this regime the electron kinetics fail to scale with the reduced electric field E/p (or E/N) due to some population of the electrons behaving ballistically or near-ballistically. This non-collisionality has been considered in a pseudo-analytical expression for the electron energy distribution (EED) that shows that the EED scales with three independent parameters -- pd (collisionality), V (voltage drop across gap) and E/p. As a result the reaction rate coefficients also scale with these parameters. The model is validated using 1D particle-in-cell/Monte Carlo collision (PIC/MCC) simulations. The theory provides new scaling in pre-breakdown field emission-driven microplasmas, and a relatively simple model for identifying operating conditions for plasma chemical processes, encouraging new ideas for controlling plasma chemistry at microscales. [Preview Abstract] |
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