Bulletin of the American Physical Society
2005 58th Gaseous Electronics Conference
Sunday–Thursday, October 16–20, 2005; San Jose, California
Session DM1: High Pressure Plasma I |
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Chair: Antoine Rousseau, LPTP Ecole Polytechnique Room: Doubletree Hotel Pine |
Monday, October 17, 2005 1:30PM - 1:45PM |
DM1.00001: Temporal behaviour of helium metastables and molecular nitrogen ions in a He APGD Gagik Nersisyan, Jean-Pierre van Helden, William Graham Laser-aided methods are used to characterize the temporal behaviour two of the important species, helium metastables (He$_{m}$) and N$_{2}^{+}$ ions, in the development of an atmospheric pressure glow discharge (APGD) in helium generated in a planar configuration of a dielectric barrier discharge with quartz dielectrics. The discharge modes are monitored by electrical and optical measurements and fast imaging. Under certain conditions, mainly when the impurity level is low, there is a residual discharge between the APGD pulses. The termination of this residual discharge and generation of a more typical pulse APGD happens when the impurity level is relatively high. The temporal behaviour of He$_{m}$ obtained by both optogalvanic and the laser induced fluorescence (LIF) signals is well correlated with the discharge current. The temporal variation of the N$_{2}^{+}$ ion density is also measured using LIF. When the mode of APGD with a residual discharge is generated the density between the discharge pulses is higher than during the pulses. In the typical APGD mode the N$_{2}^{+}$ ion density has a maximum which is delayed a few $\mu$s from the current peak followed by a decrease of the density to below the detection limit. [Preview Abstract] |
Monday, October 17, 2005 1:45PM - 2:00PM |
DM1.00002: Dynamics of a Homogeneous Dielectric Barrier Discharge in Xenon Excited by Short Voltage Pulses Robert Carman, Richard Mildren, Ian Falconer In a Xenon dielectric barrier discharge (DBD) lamp, the use of short pulse voltage waveforms ($<$100$_{~}$ns FWHM) can dramatically increase the electrical-VUV (172nm) conversion efficiency and VUV output, compared with conventional AC excitation. The discharge visually appears to fill the region between the electrodes more or less uniformly, rather than appearing as discrete microdischarges as seen for sinusoidal (AC) voltages. A previous modeling study of a short-pulse Xe DBD predicted that electrical breakdown of the discharge gap would be characterised by the appearance of a fast-moving ionization wave or a streamer propagating from the anode toward the cathode, strongly correlated with the spatio-temporal evolution of the visible and infrared emission from the discharge, but weakly correlated with the more intense VUV emission [1]. To investigate the dynamics of electrical breakdown under various operating conditions, streak images of the infrared emission from a cylindrical DBD lamp have been recorded using a Hamamatsu 4187 streak camera, where the spatial information is provided as a function of position across the discharge gap. \newline \newline [1] R.J. Carman and R.P. Mildren, J. Phys. D: Appl. Phys., 36, 19-33, 2003. [Preview Abstract] |
Monday, October 17, 2005 2:00PM - 2:15PM |
DM1.00003: Experimental study of an aerodynamics plasma actuator using emission spectroscopy Tsitsi Madzawa-Nussinov, Yongho Kim, Jaeyoung Park, Louis Rosocha, Vincent Ferreri, Gabriel Becerra In this paper, we report on studies of the aerodynamic plasma actuator, a special asymmetric surface discharge configuration of the dielectric barrier discharge. The configuration of the plasma actuator (one electrode exposed and a second embedded in a dielectric) employing ac power, has been proposed for flow control in aerodynamics applications$^{[1]}$. The actuator operates over a wide range of frequencies with no resonant behavior, and produces stable plasma at atmospheric pressure. The mechanisms for momentum transfer to the gas molecules are still a subject of debate. Recently, studies and simulations done at Kinema Research$^{[2]}$ suggest that due to the non-equilibrium nature of the actuator, ions contribute more to the momentum transfer than electrons. By measuring detailed emission spectra for various discharge gases such as nitrogen and air, we compare our experimental results on electron energy distribution function with simulations done at Kinema Research. We also measure flow patterns and velocities as a function of input power and gas species, and correlate these to the changes in the calculated distribution functions. [Preview Abstract] |
Monday, October 17, 2005 2:15PM - 2:45PM |
DM1.00004: Modeling of nitrogen atmospheric pressure discharges Invited Speaker: Recently, dielectric barrier discharges at atmospheric pressure have been widely applied to ozone production, surface treatment, gas cleaning and so on. Two forms of discharges can be seen at this condition; filamentary discharges and homogeneous discharges. The former discharge form has been applied to ozone productions for years. Recently, latter form of discharge has been investigated for applying to efficient surface treatment processes. At atmospheric pressure, it is known that filamentary discharges are normally formed, however, their discharge characteristics are not clearly understood. Moreover, homogeneous barrier discharge characteristics are not known neither. The homogeneous barrier discharges are obtained in helium, nitrogen and other gases. And there are two types of discharges, Townsend discharge and glow discharge. For efficient surface treatment processes, atmospheric pressure glow discharge (APGD) in nitrogen is necessary. To investigate APGD in nitrogen, two dimensional fluid model has been developed. The discharge characteristics of high pressure barrier discharges in simple gas system have been simulated. As a result, homogeneous barrier discharges have been obtained and discharge developments are simulated clearly. Applying electric field uniformly between the gap and the slight photoionization are key points to obtain homogeneous barrier discharges. For further study, more complicated gas system will be considered in the model. [Preview Abstract] |
Monday, October 17, 2005 2:45PM - 3:00PM |
DM1.00005: High Pressure NEQ Plasma Formation by Non-Self-Sustained Repetitively Pulsed Discharges Walter Lempert, Adam Hicks, Munetake Nishihara, Seth Norberg, J. William Rich, Igor Adamovich We describe generation of large volume ($\sim $ 1-2 cm dimension) stable, high pressure non-equilibrium plasmas, utilizing non-self sustained repetitive high voltage pulsing. Ionization is created by means of $\sim $ 10 KV -- 10 nsec duration pulses, repeated at 100 kHz repetition rate. In between the high voltage pulses, the plasma is sustained by application of a relatively low DC or RF field, in which the reduced electric field, E/n, is selected to optimize energy loading into desired molecular degrees of freedom. Detailed measurements of i-V characteristics, plasma lifetime, and heavy species temperature will be presented, along with recent results documenting creation of large ($\sim $5{\%} or more) fractional excitation of O$_{2}$ into the metastable ``single delta'' electronic state, which is the upper lasing level for the oxygen -- iodine laser. Demonstration of turbulent supersonic boundary layer control using Lorentz forces will also be presented. [Preview Abstract] |
Monday, October 17, 2005 3:00PM - 3:15PM |
DM1.00006: Air-Plasma Test Cell, Electron-Beam Source, and Measurements of Electron Density and Ozone Concentration Robert Vidmar, Kenneth Stalder, Megan Seeley An experimental facility at the University of Nevada, Reno, has recently been completed and initial testing is underway. A description of the facility for generation of air plasma from sea level to 300,000 ft, the electron-gun source, and two diagnostics will be discussed. The test cell has a volume of 400 liter, provisioning for electrodes to provide a sustaining electric field, and additional ports for future diagnostics. The ionization source consists of a pulsed 100 kV 10-20 mA electron beam and a thin-foil transmission window. The source provides plasma generation for approximately 1 ms and the diagnostics have sufficient bandwidth to resolve microsecond time dependencies. Electron concentration is measured using RF absorption and phase shift at X-band. Ozone concentration is measured by means of absorption at 254 nm in a White's cell. Results on initial measurements and plans for additional diagnostics to quantify other species will be discussed. This material is based on research sponsored by the Air Force Research Laboratory, under agreement numbers FA9550-041-1-0015 and FA9550-04-1-0444. [Preview Abstract] |
Monday, October 17, 2005 3:15PM - 3:30PM |
DM1.00007: A comparison of lifted jet diffusion flame stabilization using corona, dielectric barrier, and repetitively- pulsed plasma discharges Wookyung Kim, Hyungrok Do, Godfrey Mungal, Mark Cappelli Three different types of discharges are applied to a lifted jet diffusion flame in coflow, and their abilities regarding flame stabilization enhancement are compared. First, a single-electrode corona discharge is obtained between a crown shaped platinum electrode and the flame base. It is observed that the flame is maintained at 20{\%} higher coflow speed. Also, it is shown that the discharge direction is self-adjusting with varying electrode position. Second, an asymmetric dielectric barrier discharge is implemented and results in increased flame stabilization; here a flame stably resides at up to 50{\%} higher coflow speed. In addition, the nonthermal aspect of the DBD is verified by a spectral line analysis and simulation of the nitrogen 2$^{nd}$ positive system. Finally, an ultra short pulse generator (pulse width of $\sim $ 10ns), is used in an opposed platinum electrode configuration. This approach further enhances the stability limit by nearly ten-fold. As discussed in the presentation, the degree of nonequilibrium of this pulsed discharge is found to be higher than the DBD. [Preview Abstract] |
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