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 KW2: Microdischarges II |
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Chair: Teresa Delosarcos, Ruhr University Room: Ballroom II |
Wednesday, October 2, 2013 1:30PM - 2:00PM |
KW2.00001: Interactions Between Small Arrays of Atmospheric Pressure Micro-Plasma Jets: Gas Dynamic, Radiation and Electrostatic Interactions Invited Speaker: Natalia Babaeva Atmospheric pressure plasma jets are widely used devices for biomedical applications. A typical plasma jet consists of a tube through which noble gas or its mixture with a molecular gas flows. The noble gas creates a channel into the ambient air which is eventually dispersed by interdiffusion with the air. Plasma plumes are formed by the propagation of ionization waves (IWs) through the tubes and then through the noble gas phase channel. The IW typically propagates until the mole fraction of the ambient air in the channel increases above a critical values which requires a larger E/N to propagate the IW. By grouping several jets together to form an array of jets, one can in principle increase the area treated by the plume. If the jets are sufficiently far apart, the IWs and resulting plasma plumes are independent. As the spacing between the jets decreases, the plasma jets begin to mutually interact. In this talk, we discuss results from a computational investigation of small arrays of He/O$_{2}$ micro-plasma jets propagating into ambient air. The model used in this work, \textit{nonPDPSIM}, is a plasma hydrodynamics model in which continuity, momentum and energy equations are solved for charged and neutral species with solution of Poisson's equation for the electric potential. Navier-Stokes equations are solved for the gas dynamics and radiation transport is addressed using a propagator method. We found that as the spacing between the jets decreases, the He channels from the individual jets tend to merge. The IWs from each channel also merge into regions having the highest He mole fraction and so lowest E/N to sustain the IW. The proximity of the IWs enable other forms of interaction. If the IWs are of the same polarity, electrostatic forces can warp the paths of the IWs. If in sufficient proximity, the photoionization from one IW can influence its neighbors. The synchronization of the voltage pulses of adjacent IWs can also influence its neighbors. With synchronized pulses, adjacent IWs can simultaneously travel along their common single stream or their separate helium channels. If the voltages pulses are not synchronized, adjacent IWs may be extinguished or enhanced, depending on the timing and polarity of its neighbors. [Preview Abstract] |
Wednesday, October 2, 2013 2:00PM - 2:15PM |
KW2.00002: Modeling the excitation dynamics of micro structured atmospheric pressure plasma arrays Alexander Wollny, Ralf Peter Brinkmann Micro structured atmospheric pressure plasma arrays have been developed by J.G. Eden and co-workers as efficient light sources [1]. In essence, this device forms an array of dielectric barrier discharges: a silicon wafer with a matrix of cavities is covered by dielectrics. The counter electrode grid is embedded in the dielectrics. It is driven by alternating voltage at a frequency of 10-100 kHz in argon at atmospheric pressure. To the naked eye these devices appear to glow homogeneously. However, phase resolved optical emission spectroscopy performed by V.~Schulz-von~der~Gathen and co-workers [2] revealed strong dynamics. The model presented here addresses each cavity independently: cavities are described by a one dimensional drift model. Interactions, mainly driven by photon transport, are treated in a separate model that couples back to the individual cavity models. This allows us to investigate the individual discharge as well as the experimentally observed ionization wave propagation. Both will be addressed in this work.\\[.5em] [1] J.G. Eden, et al., {\it J. Phys. D: Appl. Phys.} {\bf38} 1644 (2005)\\[0em] [2] H. Boettner, et al., {\it J. Phys. D: Appl. Phys.} {\bf43} 124010 (2010) [Preview Abstract] |
Wednesday, October 2, 2013 2:15PM - 2:30PM |
KW2.00003: Bulk heating of electrons in capacitive radio frequency atmospheric pressure microplasmas Torben Hemke, Denis Eremin, Thomas Mussenbrock, Aranka Derzsi, Zoltan Donko, Kristian Dittmann, Juergen Meichsner, Julian Schulze Electron heating and ionization dynamics in capacitively coupled radio frequency atmospheric pressure microplasmas operated in helium are investigated by particle-in-cell simulations and semi-analytical modeling. A strong heating of electrons and ionization in the plasma bulk due to high bulk electric fields are observed at distinct times within the RF period. Based on the model the electric field is identified to be a drift field caused by a low electrical conductivity due to the high electron-neutral collision frequency at atmospheric pressure. Thus, the ionization is mainly caused by ohmic heating in this ``$\Omega $-mode.'' The phase of strongest bulk electric field and ionization is affected by the driving voltage amplitude, which determines the resistivity of the discharge via its effect on the plasma density. At high voltage amplitudes the ionization peaks at the sheath edges due to a decrease of the ion density towards the electrodes. Significant analogies to electronegative low-pressure macroscopic discharges operated in the drift-ambipolar mode are found, where similar mechanisms induced by a high electronegativity instead of a high collision frequency have been identified. [Preview Abstract] |
Wednesday, October 2, 2013 2:30PM - 2:45PM |
KW2.00004: Modeling of the filamentary plasma generated in an rf plasma jet at atmospheric pressure F. Sigeneger, J. Sch\"afer, R. Foest, K.-D. Weltmann, D. Loffhagen The argon plasma occurring in an rf plasma jet at atmospheric pressure is investigated by a two-dimensional fluid model. The jet consists of two concentric capillaries and two ring-shaped electrodes which are twisted around the outer capillary with a gap of 4\,mm. The plasma is sustained by an rf voltage at 27.12 MHz which is supplied to the upper electrode. The lower electrode is grounded. The axisymmetric model comprises continuity equations for electrons and the most important argon species, the electron energy balance equation, Poisson's equation and an equation for the surface charges at the walls of the capillaries. Furthermore, the heat balance equation is solved to determine the temperature of the gas. The transport properties of electrons and the collision rate coefficients have been determined by solving the electron Boltzmann equation as functions of the electron mean energy and of the ionization degree. The results show a distinct separation between the bulk plasma in the center between the inner and outer capillaries and the sheath regions in front of the electrodes. [Preview Abstract] |
Wednesday, October 2, 2013 2:45PM - 3:00PM |
KW2.00005: Evaluation of RF Micro-Discharge Regimes in the Performance of Evanescent-Mode Cavity Resonators Abbas Semnani, Dimitrios Peroulis A number of different RF discharge mechanisms may be important in gas breakdown including ionization, secondary electron emission, and field emission.\footnote{A. Semnani et al. Appl. Phys. Lett., \textbf{102}, 174102 (2013)} However, the impact of each of these mechanisms is a strong function of frequency.\footnote{C. E. Muehe, DTIC Document, (1965)} Consequently, estimating power handling in microwave devices needs to carefully consider the operating frequency. In this paper, we study the frequency-dependent impact of these mechanisms in two evanescent-mode cavity resonators\footnote{K. Chen et al. International Microw. Symp., (2013)} operating at 1 GHz and 50 GHz. The key characteristic of these resonators, unlike typical cavities, is that the resonant electric field is primarily concentrated in a relatively small volume. The smallest dimension of this volume is referred to as critical gap and typically is in the order of a few $\mu$m. The two resonators in this study have the same critical gap size of $19~\mu $m which results in the same gas critical frequency of 6.3 GHz in atmospheric pressure. Plasma simulation results as well as the electromagnetic simulations considering plasma are presented and compared for both cases which operate in different discharge mechanisms. [Preview Abstract] |
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