Bulletin of the American Physical Society
63rd Annual Gaseous Electronics Conference and 7th International Conference on Reactive Plasmas
Volume 55, Number 7
Monday–Friday, October 4–8, 2010; Paris, France
Session BT3: Modeling and Simulation I |
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Chair: Mark Kushner, University of Michigan Room: 262 |
Tuesday, October 5, 2010 8:30AM - 9:00AM |
BT3.00001: The effect of neutral-gas depletion on the plasma density and momentum Invited Speaker: Space and laboratory plasmas can be significantly affected when ionization is so intense that the neutral-gas density is modified. Our study of the coupled dynamics of plasma and neutral-gas has predicted previously-unexpected phenomena. Such are the decrease of plasma density due to neutral-gas depletion; despite the increase in plasma production as deposited power is increased [1], and the transition from neutral-gas depletion to neutral-gas repletion as neutral-gas collisionality with ions is reduced [2]. Two new theoretical predictions related to neutral-gas depletion will be described in the talk. First, it has been recently shown that the 2D plasma transport along and across magnetic field in the presence of neutral-gas depletion may result in a hollow cylindrical profile of the plasma density, in which the plasma density has a minimum at the cylinder axis [3]. We examine further the possibility of two different steady-states of the plasma and neutral-gas in the presence of a magnetic field and neutral-gas depletion, for the same input parameters. A second issue is related to the amount of momentum carried by plasma flowing out of a plasma source, which determines the efficiency of such a source as a thruster. We have recently calculated that momentum when the plasma is collisionless [4]. Taking into account the neutral-gas dynamics, we show that the carried momentum when the plasma is collisional is larger. \\[4pt] [1] A. Fruchtman, G. Makrinich, P. Chabert, and J. M. Rax, Phys. Rev. Lett. \textbf{95}, 115002 (2005). \\[0pt] [2] A. Fruchtman, G. Makrinich, J.-L. Raimbault, L. Liard, J.-M. Rax, and P. Chabert, Phys. Plasmas \textbf{15}, 057102 (2008). \\[0pt] [3] A. Fruchtman, Phys. Plasmas \textbf{17}, 023502 (2010). \\[0pt] [4] A. Fruchtman, IEEE Trans. Plasma Sci. \textbf{36}, 403 (2008). [Preview Abstract] |
Tuesday, October 5, 2010 9:00AM - 9:15AM |
BT3.00002: Adaptive Mesh Refinement for Plasma Simulations Vladimir Kolobov, Robert Arslanbekov Many plasma problems are characterized by the presence of localized domains with large gradients of plasma parameters (streamers, filaments, ionization fronts, etc). The ability to dynamically adapt the local mesh resolution would substantially increase the accuracy and efficiency of simulations for such problems. In this paper, we will describe our current work to develop plasma simulation tool with Adaptive Mesh Refinement (AMR) using octree Cartesian mesh. We have already demonstrated such an approach for simulation of streamer development with a minimal plasma model (Poisson solver, drift-diffusion electron transport, immobile ions, and local field ionization). We used an explicit solver to compute the initial stage of streamer propagation at fast electron scale with 2D/3D simulations including curved electrode boundaries. Here we will describe new developments including ion drift, electron energy balance, and Immersed Boundary Method for improved treatment of boundary conditions with Cartesian mesh. We will illustrate new capabilities for several 2D/3D problems (streamers and high-pressure microplasmas) and describe code parallelization with dynamic load balancing among processors. New physics learned by using the new AMR code will be discussed. [Preview Abstract] |
Tuesday, October 5, 2010 9:15AM - 9:30AM |
BT3.00003: Simulation of the propagation of an air plasma discharge at atmospheric pressure in a capillary glass tube : influence of the confinement on the discharge reactivity Jaroslav Jansky, Fabien Tholin, Zdenek Bonaventura, Anne Bourdon This work presents simulations of the spatio-temporal distributions of electric field and electron density during the propagation of an air discharge in capillary tubes using a fluid model. The discharge is initiated by a positive voltage needle set inside a capillary glass tube with a variable inner radius. Pulsed applied voltage of different amplitudes and rise times are used. Depending on the applied voltage and radius of the tube, a stable discharge propagates in the tube with a homogeneous planar front or a tubular shape. As a reference, we have studied the discharge dynamics without tube and in this case, the discharge propagates with a maximum electric field of $E \sim 100$~kV/cm for a wide range of applied voltages. With a capillary glass tube, the values of the maximum electric field depend on the applied voltage and inner radius of the tube and values up to $E=500$~kV/cm have been obtained. Then, a higher reactivity of the air discharge with the capillary tube than without is expected, which is particularly interesting for applications. [Preview Abstract] |
Tuesday, October 5, 2010 9:30AM - 9:45AM |
BT3.00004: Negative corona current pulse modelling in air at atmospheric pressure Delphine Bessi\`eres, Jean Paillol When a sufficiently high negative voltage is applied to the point of a point - plane electrode system in air at atmospheric pressure, current pulses are observed in the external circuit. These pulses are mainly discerned by a very short rise time of 1.5 ns. The negative corona ignition and development take place in the vicinity of the cathode and electron emission plays a crucial role : an accurate numerical description of a sharp cathode which is able to take electron emission into account is a real challenge. This paper proposed a numerical technique based on non-orthogonal meshing which enables to cope with these two problems. A discussion is proposed about the different emission mechanisms able to ignite and to sustain the discharge. Photo-emission and positive ion bombardment are introduced in the calculations as well as field emission. A satisfactory agreement is obtained when compared to experimental data already published by the authors. The paper focuses on the modelling of the first negative corona current pulse, and more precisely, on the mechanisms influencing the rise time of this pulse. The paper aims at giving a contribution to solve the theoretical problem of the mechanism of negative corona ignition in interesting conditions for applications. [Preview Abstract] |
Tuesday, October 5, 2010 9:45AM - 10:00AM |
BT3.00005: About positive streamer corona inception near a curved electrode Sergey Pancheshnyi Inception of first discharge is often a key question for pulsed discharge applications rapidly developing last time. Fine control of a short (for example, nanosecond) discharge requires detailed understanding of inception phenomena. It is known that ignition voltage of a DC or low-frequency AC corona in air is well described by Peek's law that assumes single-avalanche triggering. This inception voltage doesn't depend on polarity and secondary emission processes. In contrast, pulsed corona inception conditions differ significantly for both polarities that means a completely different mechanism of inception. In this case, a multi avalanche mechanism is typically responsible for streamer inception. In the present paper, a detailed model of first positive corona inception near a curved electrode is presented. Collisional detachment of electrons from negative ions in electric field, avalanche development and drift of ions of both polarities are the main processes taken into consideration. The entire frequency range (from DC to sub-nanosecond voltage pulses) is analyzed and compared with available experimental results. Inception probability as a function of voltage amplitude and voltage duration is calculated for various levels of background negative ion densities. The presented results were obtained in simple rod-plain gas discharge geometry but this model is applicable for other geometries as well. [Preview Abstract] |
Tuesday, October 5, 2010 10:00AM - 10:15AM |
BT3.00006: The electro-negative character of He/O$_{2}$ cold atmospheric pressure plasmas Jochen Waskoenig, Timo Gans Cold radio-frequency (RF) driven atmospheric pressure plasmas in helium with a small admixture of oxygen can produce large number densities of reactive oxygen species, which is of particular interest for sensitive surface treatments, e.g. in bio-medicine. 1-D numerical simulations reveal that the sheath and electron dynamics are significantly influenced by comparatively high densities of negative ions. The latter can not respond instantaneously to the rapidly changing RF electric field and are confined to the time averaged plasma bulk. In the plasma center the quasi-neutrality condition is fulfilled by both, electrons and negative ions, while at times of sheath collapse this condition has to be fulfilled by electrons exclusively. Therefore, maximum electron density is observed in close vicinity of the electrodes, rather than in the plasma center as for electro-positive plasmas. The negative ion density scales with the mean electron energy and is independent of the electron density. Hence, it decreases with power, whereas the electron density increases. This results in a decrease of the electro-negativity towards higher input powers. [Preview Abstract] |
Tuesday, October 5, 2010 10:15AM - 10:30AM |
BT3.00007: Liquid Droplets in Atmospheric Pressure Plasmas Muhammad Iqbal, Miles Turner Atmospheric pressure plasmas have many applications, ranging from industrial processes to medical treatments. The behaviour of such droplets, once immersed in the plasma, may be important. For example, in chemical vapour deposition, which is the immediate motivation for the present work, it may be desirable for droplets to evaporate into the plasma, and most undesirable for partially evaporated droplets to reach the substrate. In this paper, we will discuss the behaviour of liquid droplets in the atmospheric pressure plasmas environment, with a focus on particles with radii in the micron range. We will consider charging of the droplets by interaction with electrons and ions, transport of droplets through the plasma, and evaporation of the droplets during their passage. We note that although charging and transport of small bodies has been studied extensively in connection with dusty plasmas, and the regime of concern to us has some distinctive features, which we will discuss. The focus of this discussion will be on models to describe droplet charging, which necessarily differ from those usually used for dusty plasma, on describing the rate of evaporation, which is in the regime of the nonequilibrium Langmuir-Knudson law, and on the implications for describing droplet transport. [Preview Abstract] |
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