Bulletin of the American Physical Society
61st Annual Gaseous Electronics Conference
Volume 53, Number 10
Monday–Friday, October 13–17, 2008; Dallas, Texas
Session GW3: Lasers, Breakdowns and Sparks |
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Chair: Z.Lj. Petrovic, Institute of Physics Belgrade Room: Addison Room |
Wednesday, October 15, 2008 8:00AM - 8:15AM |
GW3.00001: Applicability of Generalized Peek's Law to Scaling of Corona Onset Voltages in Electropositive Gases Yan-Ming Li We have developed the steady state positive corona model with the ionization zone physics in the point-plane configuration. The geometry is axisymmetric, consisting of a pointed anode of small tip radius and a planar cathode. The model solves the Poisson equation, drift dominated electron and the positive ion transport equations with the nonlinear Townsend ionization source terms, to give the complete electric field, electron and positive ion density distributions. The corona plasma properties can be determined as function of discharge current, ranging from the pico-ampere up to a milli-ampere. The calculated voltage-current characteristics obeyed the Townsend equation, agreeing with the general experimental observations. The model is applied to different electropositive gases, argon, xenon, nitrogen and mercury. Corona onset potentials are determined based on the discharge voltages at very low currents. Extensive parametric study for argon positive corona with varying anode tip radius, gap distance and gas pressure has been completed. All the simulated corona onset voltages are very well described by the generalized Peek's Law [1]. At sufficiently high current in the range of 0.1 mA, discharge filament is formed near the anode tip. [1] Peek F. W., Dielectric Phenomena in High Voltage Engineering, McGraw Hill, New York (1929). [Preview Abstract] |
Wednesday, October 15, 2008 8:15AM - 8:30AM |
GW3.00002: Modeling of the propagation of streamers in methane-air mixtures using the 3-group SP$_{3}$ photoionization model N.Y. Liu, V.P. Pasko, A. Bourdon, S. Celestin, P. Segur, E. Marode Non-thermal plasma assisted ignition and combustion receives increasing attention recently [e.g., Starikovskaia, J. Phys. D, 39, R265, 2006]. Experimental and numerical work has shown that the application of transient plasma discharges (including the stages of streamer propagation and streamer-to-spark transition) in the ignition of propane-air or methane-air mixtures significantly reduces the ignition delay time [e.g., Pancheshnyi et al., IEEE Trans. Plasma Sci., 34, 2478, 2006; Naidis, J. Phys. D, 40, 4525, 2007]. In this work, we study the propagation of streamers in methane-air mixtures. We have recently developed a photoionization model based on radiative transfer theory, called 3-group SP$_{3}$ model, for the simulation of streamer discharges in air [Bourdon et al., Plasma Sources Sci. Technol. 16, 656, 2007; Liu et al., Appl. Phys. Lett., 91, 211501, 2007]. In this talk, we show it is straightforward to apply the 3-goup SP$_{3}$ model to the simulation of streamers in methane-air mixtures. We report the modeling results on the propagation of streamers in methane-air mixtures and the associated heating of the gas mixtures. We also discuss the effects of addition of methane to air on the dynamics of the streamer. [Preview Abstract] |
Wednesday, October 15, 2008 8:30AM - 8:45AM |
GW3.00003: Optical Breakdown Based on Resonant Enhanced Multi-Photon Ionization and Electron Avalanche Ionization in Gas Mixtures Mikhail Shneider, Zhili Zhang, Richard Miles We present the results of the experimental and theoretical study of a new kind of optical breakdown in gases with ionization amplification by the combination of Resonant Enhanced Multi-Photon Ionization (REMPI) and subsequent avalanche ionization. As an example, the Ar:Xe mixture was studied. Coherent microwave Rayleigh scattering (radar REMPI) was used to measure REMPI and avalanche ionization. It was shown that REMPI ionization of a relatively small density component (Ar) can catalyze the avalanche ionization process in a buffer gas (Xe) by the use of a laser beam at very low intensity. Theoretical plasma dynamic model verifies the finding. Based on the presented results, several important applications are possible. First, it can improve the detection sensitivity of Radar REMPI. Second, it suggests that plasma generation can be achieved at reduced gas densities or laser beam intensities. Here we can suggest the following two methods: 1. Long laser pulse: The pulse front generates REMPI and subsequent pulse initiates avalanche ionization and Joule heating. 2. Two subsequent laser pulses: A short laser pulse tuned on a REMPI of mixture component generates weakly ionized REMPI plasma and a long off-resonant laser pulse for the avalanche ionization and Joule heating. [Preview Abstract] |
Wednesday, October 15, 2008 8:45AM - 9:00AM |
GW3.00004: Scaling of an Electric Discharge Excited Oxygen-Iodine Laser John Bruzzese, Munetake Nishihara, Walter Lempert, J. William Rich, Igor Adamovich Electric discharge excited oxygen-iodine laser apparatus has been scaled to increase the electric discharge volume and power, the laser mixture flow rate, and the gain path in the M=3 laser cavity. Specifically, singlet delta oxygen (SDO) generator discharge power has been increased at least up to 3.5 kW, laser mixture flow rate up to 0.5 mole/sec, and gain path up to 10 cm. Steady-state run time of the new scaled-up laser apparatus at these conditions is up to 10 sec. Two different discharge configurations have been used to generate singlet delta oxygen, crossed nanosecond pulser / transverse DC sustainer discharge and capacitively coupled transverse RF discharge. Flow temperature downstream of the discharge, singlet delta oxygen yield, and laser gain have been measured in a wide range of discharge powers, nitric oxide mole fraction in the main oxygen-helium flow, and oxygen percentage in the mixture, at discharge pressures ranging from 60 to 90 torr. The results demonstrate that SDO yield increases with the discharge power for both discharge configurations, although highest yields achieved so far remain low, 3.6-3.7{\%}, due to fairly low energy loading per oxygen molecule in the discharge. Small signal gain measured in the M=3 cavity of the new laser apparatus is up to 0.116{\%}/cm (2.3{\%} gain per single pass), at the flow temperature of T=125 K. [Preview Abstract] |
Wednesday, October 15, 2008 9:00AM - 9:15AM |
GW3.00005: Laser emission at $\lambda $ = 337.1 and $\lambda $ = 357.7 nm of $N_{2}$ molecules in inductively coupled plasma Alexander Razhev, Dmitry Churkin Pulsed inductively coupled plasma for inversion population formation on electronic transitions of neutral atoms and molecules of gases was used. UV inductive $N_{2}$ laser at $\lambda $ = 337.1 nm and $\lambda $ = 357.7 nm has been created. The system for formation of the pulsed inductive discharge of the cylindrical form in gases was described. Results of an experimental investigations of spectral, temporal and energy parameters of spontaneous and laser radiation of the inductive $N_{2}$ laser operated in pure nitrogen and gas mixtures of $N_{2}$ with$_{ }$\textit{NF}$_{3}$ and \textit{SF}$_{6}$ are presented. The generation only at $\lambda $ = 337.1 nm, corresponding to the (0 - 0) band of the second positive system of $C^{3}$\textit{$\Pi $}$_{u}$\textit{$\to $B}$^{3}$\textit{$\Pi $}$_{g}$ transition of nitrogen molecules was obtained in pure nitrogen pumped by inductive discharge. The generation at $\lambda $ = 337.1 nm and $\lambda $ = 357.7 nm was obtained in gas mixtures of $N_{2}$ with \textit{NF}$_{3}$ and \textit{SF}$_{6}$. Under optimal conditions the behavior of $\lambda $ = 337.1 nm to $\lambda $ = 357.7 nm intensities was approximately as 10:1. Total mixture pressure was varied in a range 0.1 - 3 Torr. The maximal generation energy of 4.5 mJ at pulse duration (FWHM) 15$\pm $1 ns was achieved. Laser beam had a ring shape with external diameter about 42 mm and the thickness of 1.0 - 1.5 mm. Inductive $N_{2}$ laser could operate with pulse repetition rate up to 50 Hz. The present work has been supported by RFBR, Grant {\#} 06-02-16149-a. [Preview Abstract] |
Wednesday, October 15, 2008 9:15AM - 9:30AM |
GW3.00006: Influence of nitrogen oxides on singlet delta oxygen production in pulsed discharge for electric discharge oxygen-iodine laser Andrey Ionin, Yurii Klimachev, Andrey Kozlov, Andrey Kotkov, Igor Kochetov, Anatoly Napartovich, Oleg Rulev, Leonid Seleznev, Dmitry Sinitsyn, Nikolay Vagin, Nikolay Yurushev Influence of nitrogen oxides NO and NO2 on specific input energy (SIE) and time behavior of singlet delta oxygen (SDO) luminescence excited by pulsed e-beam sustained discharge in oxygen was experimentally and theoretically studied. NO and NO2 addition into oxygen results in a small increase and a decrease of SIE, respectively. Addition of 0.1-0.3 percent of nitrogen oxides was experimentally and theoretically demonstrated to result in notable enhancement of SDO lifetime, which is related to a decrease of atomic oxygen concentration in afterglow. For getting high SDO concentration at gas pressure 30-60 Torr for the time interval less than 0.5 s one needs to add not less than 0.2 percent of nitrogen oxides into oxygen. Temperature dependence of relaxation constant for SDO quenching by unexcited oxygen was estimated by using experimental data on time behavior of SDO luminescence. [Preview Abstract] |
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