Bulletin of the American Physical Society
66th Annual Gaseous Electronics Conference
Volume 58, Number 8
Monday–Friday, September 30–October 4 2013; Princeton, New Jersey
Session TF3: Thermal Plasmas, Negative Ion Plasmas, and Dusty Plasmas |
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Chair: Brooke Stutzman, U.S. Coast Guard Academy Room: Nassau Room |
Friday, October 4, 2013 10:30AM - 10:45AM |
TF3.00001: Calculation of thermodynamic and transport properties of thermal plasmas based on the Cantera software toolkit Charles Doiron, Kai Hencken Computational fluid-dynamic simulations nowadays play a central role in the development of new gas circuit breakers. For these simulations to be reliable, a good knowledge of the pressure and temperature-dependence of the thermodynamic and transport properties of ionized gases is required. A key ingredient in the calculation of thermodynamic properties of thermal plasmas is the calculation of the chemical equilibrium composition of the gas. The general-purpose, open-source software toolkit Cantera provides most functionality required to carry out such thermodynamic calculations. In this contribution, we explain how we tailored Cantera specifically to calculate material properties of plasmas. The highly modular architecture of this framework made it possible to add support for Debye-H\"{u}ckel non-ideality corrections in the calculation of the chemical equilibrium mixture, as well as to enable the calculation of the key transport parameters needed in CFD-based electric arc simulations: electrical and thermal conductivity, viscosity, and diffusion coefficients. As an example, we discuss the thermodynamic and transport properties of mixtures of carbon dioxide and copper vapor. [Preview Abstract] |
Friday, October 4, 2013 10:45AM - 11:00AM |
TF3.00002: Simultaneous measurements of OH(A) and OH(X) radicals in microwave argon plasma assisted combustion of methane/air mixtures using optical emission spectroscopy and cavity ringdown spectroscopy Wei Wu, Chuji Wang We developed a new plasma assisted combustion system employing a continuous atmospheric argon microwave plasma jet to enhance combustion of methane/air mixtures in different fuel equivalence ratios ($\varphi )$. The combustor has three distinct reaction zones of pure plasma zone, the hybrid plasma-flame zone and pure flame zone which were well defined by their emission spectra. Optical emission spectroscopy (OES) was used to exam the excited species including OH(A) and results showed that OH(A) intensities gradually increased in plasma zone and rapidly increased in hybrid zone and then dramatically decreased to a very low level in flame zone. In addition to OES, pulsed cavity ringdown spectroscopy (CRDS) was utilized to measure the absolute number density of OH(X) in the flame zone at $\varphi =$ 0.51, 0.87, 1.10 and 1.45. Different OH(X) number densities and density profiles were observed comparing rich and lean combustions. At $\varphi $ $=$ 0.51, the OH(X, V'' $=$ 0, J'' $=$ 0.5) number density increased from 2.29 $\times $ 10$^{15}$ molecule cm$^{-3}$ at the combustor nozzle to maximum 3.13 $\times $ 10$^{5}$ molecule cm$^{-3}$ at 2 mm downstream, and then gradually decreased to the lowest detectable level of 0.12 $\times $ 10$^{15}$ molecule cm$^{-3}$ in the far downstream. [Preview Abstract] |
Friday, October 4, 2013 11:00AM - 11:15AM |
TF3.00003: Erosion of thermionic cathodes Valerian Nemchinsky Two types of the thermionic cathodes are used in industry: a) Tungsten (doped with thoria or pure) cathodes burning in a unreactive gas, and b) Thermo-chemical cathodes, such as a Hafnium cathode burning in oxygen plasma gas (mostly used plasma cutting). Both types of the cathodes experience cycle (arc on/off) erosion and constant current erosion. Available experimental data for both types of cathodes and both types of erosions (constant current and cycling) are presented and discussed. Based on the model [1,2] the constant current erosion rate is calculated. Comparison of the results of the calculations with the experimental data show reasonable agreement. Existing hypotheses on cycling erosion are also discussed. For the Tungsten cathode, it is suggested that the start erosion is mainly due to the cold cathode mode (vacuum arc mode) of the arc operation that takes place just after the arc ignition. The presented estimation doesn't contradict this hypothesis. For the Hafnium cathode, the model of the ``open can'' erosion [3] is supported by recently published observations. \\[4pt] [1] V.A. Nemchinsky J. Phys.D, 45, 135201\\[0pt] [2] V.A.Nemchinsky Plasma Chem.Plasma Proces. 33, 517\\[0pt] [3] V.A.Nemchinsky J.Phys.D. 36, 1573. [Preview Abstract] |
Friday, October 4, 2013 11:15AM - 11:30AM |
TF3.00004: The Effect of Single Particle Charge Limits on Particle Charge Distributions in Dusty Plasmas Steven Girshick, Romain Le Picard There is a limit to the number of electrons that can coexist on a dust particle in a plasma. This limit depends on the particle's surface potential, electron affinity and the inter-electron Coulomb repulsion. We conducted numerical simulations that examine the effect of charge limits on steady-state particle charge distributions, as well as on the time required to reach steady state. Attachment of electrons to a cloud of nanoparticles can severely deplete the electron density and increase the ion density, causing the electron-to-ion density ratio to be much less than unity. At sufficiently high values of the density ratio, e.g. above about 0.1 for 80-nm-diameter Si particles, the charge limit strongly constrains particle charge. At lower values of the density ratio, e.g. around 0.01, particles are much less negatively charged even in the absence of a charge limit, and therefore the limit makes only a small difference. However, in this regime the charge distribution still deviates from the Gaussian form predicted by previous work that neglects charge limits. For the case of Maxwellian electron velocity distributions, we find that whether or not particle charge distributions are significantly affected by charge limits depends on the dimensionless asymmetry charging factor $p$ and on particle size. The factor $p$ in turn depends on the ratios of electron-to-ion density, temperature and mass. [Preview Abstract] |
Friday, October 4, 2013 11:30AM - 11:45AM |
TF3.00005: Plasma physical and plasma chemical aspects of nanoparticle formation in hydrocarbon plasmas Johannes Berndt, Eva Kovacevic, Ilija Stefanovic Low temperature plasmas are a breeding place for a great variety of different species, that can be used for different applications as the deposition of thin films or the the synthesis of nanoparticles and nanocomposites. However the distinctive nonequilibrium character of theses plasmas makes their understanding and their control a rather challenging task. The solution of this task is in addition hampered by the fact that decisive factors like cross sections for electron impact processes or rate coefficients for molecule-molecule reactions are very often completely unknown. In particular reactions including the walls of the plasma reactor are difficult to account for since they depend on the nature of the involved molecules and on the nature of the wall itself. This contribution deals with two simple approaches to control plasma chemical processes in a reactive low temperature plama: the variation of the diffusion length and the pulsing of the discharge. The contribution will focus on experiments performed in rf low pressure hydrocarbon plasmas with special emphasis on the influence of plasma physical and plasma chemical processes on the formation and properties of nanoparticles. [Preview Abstract] |
Friday, October 4, 2013 11:45AM - 12:00PM |
TF3.00006: Controlling Plasma Channels through Ultrashort Laser Pulse Filamentation Andrey Ionin, Leonid Seleznev, Elena Sunchugasheva A review of studies fulfilled at the Lebedev Institute in collaboration with the Moscow State University and Institute of Atmospheric Optics in Tomsk on influence of various characteristics of ultrashort laser pulse on plasma channels formed under its filamentation is presented. Filamentation of high-power laser pulses with wavefront controlled by a deformable mirror, with cross-sections spatially formed by various diaphragms and with different wavelengths was experimentally and numerically studied. An application of plasma channels formed due to filamentation of ultrashort laser pulse including a train of such pulses for triggering and guiding long electric discharges is discussed. [Preview Abstract] |
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