Bulletin of the American Physical Society
67th Annual Gaseous Electronics Conference
Volume 59, Number 16
Sunday–Friday, November 2–7, 2014; Raleigh, North Carolina
Session HW1: Non-equilibrium Kinetics and Basic Plasma Physics of Low Temperature Plasmas |
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Chair: Scott Walton, NRL Room: Ballroom EF |
Wednesday, November 5, 2014 8:00AM - 8:15AM |
HW1.00001: Modeling of electron beam-generated plasmas produced in Ar/N2 mixtures Tzvetelina Petrova, Evgenia Lock, George Petrov, David Boris, Richard Fernsler, Scott Walton We discuss a non-equilibrium collisional-radiative model coupled with electron kinetics developed to study the population dynamics in electron beam-generated plasmas produced in low pressure Ar/N$_{2}$ mixtures. Generally, these plasmas are characterized by low electron temperatures (1 eV), low plasma potentials, and plasma densities in the range 10$^{9}$-10$^{11}$ cm$^{-3}$. We have shown both experimentally\footnote{D. R. Boris, G. M. Petrov, E. H. Lock, Tz. B. Petrova, R. F. Fernsler, and S. G. Walton, Plasma Sources Sci. Technol. 22 (2013) 065004.} and theoretically\footnote{G. M. Petrov, D. R. Boris, Tz. B. Petrova, E. H. Lock, R. F. Fernsler, and S. G. Walton, Plasma Sources Sci. Technol. 22 (2013) 065005.} that small admixtures of nitrogen to argon leads to changes in the electron energy distribution function (EEDF) resulting in a lowering of the electron temperature from 1.0 to 0.4 eV. The modeling results show that these changes strongly impact the production of argon excited states via changes in the collisional excitation rates. The contribution of different production and destruction mechanisms of 1s and 2p argon excited states is discussed in detail. The results of the modeling are compared with the experimentally measured EEDF, electron temperature, and the optical emission spectra in 700-850 nm range. [Preview Abstract] |
Wednesday, November 5, 2014 8:15AM - 8:30AM |
HW1.00002: Ion instability in Tonks-Langmuir model with collisions T.E. Sheridan The Tonks-Langmuir (TL) model describes a discharge with collisionless, kinetic ions and Boltzmann electrons. In the TL model, ions ``born'' throughout some volume are accelerated to the discharge walls by the self-consistent electric field in both the presheath and the sheath. That is, the TL model solves the Vlasov equation in a bounded geometry, and hence gives the full ion velocity distribution function. In this presentation, we consider the TL model in a one-dimensional planar geometry with a spatially-uniform source of warm ions. Ions are assumed to undergo ``charge exchange'' collisions with a constant collision frequency. We solve this model using a particle-in-cell (PIC) simulation. Preliminary investigations show that when the ion birth temperature is sufficiently low, and for collision frequencies which are a few percent of the ion plasma frequency, there is an ion instability in the presheath. At the same locations, the time-averaged ion distribution function displays three peaks, one of which may be associated with ions that inverse Landau damp on the waves. [Preview Abstract] |
Wednesday, November 5, 2014 8:30AM - 8:45AM |
HW1.00003: Mechanism of N$_{2}$ Dissociation and Kinetics of N($^{4}$S) Atoms in Pure Nitrogen Plasma Andrey Volynets, Dmitry Lopaev, Nikolay Popov This work deals with kinetics of the ground state nitrogen atoms N($^{4}$S) and N$_{2}$ dissociation mechanism in pure N$_{2}$ plasma. The experiment was carried out in positive column of DC glow discharge for p$=$5-50Torr, J$=$20-100mA. N($^{4}$S) balance was considered for spatially uniform conditions controlled by only two terms: source (characterized by effective production rate k$_{eff}$ ) and loss (characterized by effective loss time $\tau_{loss} )$. Analysis of k$_{eff}$ and $\tau_{loss} $ gains considerably better understanding of N$_{2}$ dissociation. N/N$_{2}$ dissociation rate as function of discharge parameters was obtained using two independent optical methods: actinometry on Ar atoms and N$_{2}$2$+$ band emission decay at discharge modulation. With N/N$_{2}$ radial profiles N atom surface loss probability $\gamma_{N}$ and then $\tau_{loss} $were estimated. $\gamma_{N}$ revealed to be dependent on N($^{4}$S) concentration and thereby discharge conditions through the sorption balance of physisorbed N atoms. Phenomenological model taking into account basic surface processes provides $\gamma_{N}$ data in good agreement with experiment. Finally, k$_{eff}$ was obtained as function of E/N and it was shown that even EEDF calculated with accounting for N$_{2}$ vibrational excitation is unable to provide observed values of k$_{eff}$. Reasons of that fact are discussed in detail. [Preview Abstract] |
Wednesday, November 5, 2014 8:45AM - 9:00AM |
HW1.00004: Modeling of vibrational kinetics in CO$_2$ dielectric barrier discharges S. Ponduri, M.M. Becker, D. Loffhagen, S. Welzel, M.C.M. van de Sanden, R. Engeln CO$_2$ reduction to CO is considered to improve the prospects of CO$_2$ recycling which in turn could mitigate the greenhouse effect and serve as energy storage. Non equilibrium plasmas were used in the past to achieve high energy efficiencies in dissociating CO$_2$. Non equilibrium distribution in asymmetric stretch modes of CO$_2$, driven by vibrational up-pumping (VV process), has been suggested as key for achieving such high energy efficiencies. In this work, a time-dependent, one dimensional fluid model taking into account balance equations for the densities of all relevant species and electron mean energy is used to investigate the kinetics of VV process in a pure CO$_2$ dielectric barrier discharge. A Treanor like distribution has been observed in CO$_2$ asymmetric modes and the rates of dissociation have been obtained from these distributions. The rates thus obtained have proved to be significantly lower than the rates of other dissociating processes such as electron impact dissociation. The effect of power in-coupling, duration of plasma and pressure on the vibrational distributions and CO production rate is also studied. [Preview Abstract] |
Wednesday, November 5, 2014 9:00AM - 9:15AM |
HW1.00005: ABSTRACT WITHDRAWN |
Wednesday, November 5, 2014 9:15AM - 9:30AM |
HW1.00006: Two-Stage Energy Thermalization Mechanism in Nanosecond Pulse Discharges in Air and Hydrogen-Air Mixtures Ivan Shkurenkov, Suzanne Lanier, Igor Adamovich, Walter Lempert Time-resolved and spatially resolved rotational temperature measurements in air and H2-air, by purely rotational Coherent Anti-Stokes Raman Spectroscopy (CARS), are presented. The experimental results demonstrate high accuracy of pure rotational psec CARS for thermometry measurements at low partial pressures of oxygen in nonequilibrium plasmas. The results are compared with modeling calculations using a state-specific master equation kinetic model of reacting hydrogen-air plasmas, showing good agreement. The results demonstrate that energy thermalization and temperature rise in these plasmas occur in two stages, (i) ``rapid'' heating, occurring on the time scale $\tau_{rapid}$ $\sim$ 0.1-1 $\mu$s$\cdot$atm, caused by collisional quenching of excited electronic states of N$_{2}$ molecules by O$_{2}$, and (ii) ``slow'' heating, on the time scale $\tau_{slow}$ $\sim$ 10-100 $\mu$s$\cdot$atm, caused primarily by N$_{2}$ vibrational relaxation by O atoms (in air) and by chemical energy release during partial oxidation of hydrogen (in H$_{2}$-air. Both energy thermalization mechanisms have major implications for plasma assisted combustion and plasma flow control. [Preview Abstract] |
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