Bulletin of the American Physical Society
60th Gaseous Electronics Conference
Volume 52, Number 9
Tuesday–Friday, October 2–5, 2007; Arlington, Virginia
Session CT2: High Pressure Arcs |
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Chair: Joachim Heberlein, University of Minnesota Room: Doubletree Crystal City Crystal Ballroom B |
Tuesday, October 2, 2007 10:00AM - 10:15AM |
CT2.00001: Generation and Properties of Plasmas in Contact with Ionic Liquids Rikizo Hatakeyama, Kazuhiko Baba, Toshiro Kaneko Recently, much attention is paid to the plasmas in contact with liquids for potential applications in the material synthesis fields. We have focused on sheath electric fields in gas-liquid interfacial regions because the electric fields are effective for the control of ion behavior in both gaseous and liquid phases on the synthesis process. Here, ionic liquids are regarded as the liquids introduced into the plasma because of their greatly interesting characteristics such as their composition consisting of only positive and negative ions and extremely low vapor pressure. In this work, a plasma in contact with ionic liquids is generated in the range of low gas and atmospheric pressures. The plasma ion irradiation to ionic liquids is realized through the formation of the sheath electric field. As a result, the ion irradiation causes a remarkable change of the ionic liquid color and has effects on the plasma parameters in gas phase such as an increase in the electron density. The chemical and physical reactions induced by irradiating the plasma ion are expected to contribute to the novel material synthesis. [Preview Abstract] |
Tuesday, October 2, 2007 10:15AM - 10:30AM |
CT2.00002: Spatiotemporal behavior of a dielectric capillary atmospheric pressure plasma jet Brian Sands, Biswa Ganguly, Kunihide Tachibana We have studied an atmospheric pressure plasma jet utilizing time- and space-resolved emission spectroscopy by flowing helium/argon gas mixtures through a cylindrical glass capillary energized using a $\Delta $t$_{rise}$ $\sim$ 15 ns high voltage pulse. Emission measurements from Ar 2p$_{1}$--1s$_{2}$ were acquired from both the inner capillary DBD and the outer plasma jet. Just outside the capillary, the jet emission was found to occur up to 20 ns before the emission from the DBD and also exhibited a temporal variation with axial distance of 10$^{5}$ m/s. These observations preclude both direct photo-excitation and heavy particle collisional excitation from the DBD as the primary mechanism for external plasma jet formation as the former is expected to be nearly instantaneous and the latter is too slow to account for our measurements. This suggests that the outer plasma jet is not directly coupled to the interior DBD and is more likely the result of a corona discharge set up by surface charging at the capillary edge. Additional results from varying discharge conditions such as driving voltage, repetition rate, and gas mixture ratios will be presented. [Preview Abstract] |
Tuesday, October 2, 2007 10:30AM - 10:45AM |
CT2.00003: Microwave Plasma Torches Driven by Surface Waves Julio Henriques, Elena Tatarova, Edgar Felizardo, Francisco Dias, Carlos Ferreira Plasma torches driven by surface waves at atmospheric pressure were studied by optical emission spectroscopy. The relative intensity of OH rotational bands and the broadening of H Balmer lines were measured. The microwave (2.45 GHz) plasma torches were created in a cylindrical fused silica tube (R = 7.5 mm) in air and N$_{2}$-Ar, with powers in the range 200-2000 W and flows of 500-10000 sccm. Due to the axial gas flow an afterglow is formed beyond the discharge zone. The measured SW wave number and attenuation coefficient axial changes follow the SW dispersion law. The small variation of the gas temperature along the main part of the plasma column (4000-3000 K) is followed by a sharp drop (down to 1000 K) in the afterglow. The large difference between the gas and the wall temperatures (T$_{W} \quad \sim $ 500 K) is indicative of strong radial variations in the plasma quantities. ``Hot'' O atoms (with $\sim $ 1.7 eV) were detected in the air torch. Acknowledgment: This study was funded by FCT/FEDER in the framework of the project ``Ecological Plasma Engineering Laboratory'' POCI/FIS/61679/2004. [Preview Abstract] |
Tuesday, October 2, 2007 10:45AM - 11:00AM |
CT2.00004: Atmospheric Pressure Plasma Jet (APPJ) and Dielectric Barrier Atmospheric Pressure Glow Discharge (DB-APGD) in Comparison S. Reuter, V. Schulz-von der Gathen, H.F. D{\"o}bele In this work two prominent types of low temperature atmospheric pressure plasma sources are compared. First, a plane-parallel 13.56 MHz RF-excited atmospheric pressure plasma jet (APPJ) operated with 2 m3/h helium feed gas containing 0.5 {\%} molecular oxygen is investigated. Its stainless steel electrodes' area measures 8 x 4 cm2 and the discharge gap is 1.1 mm. The effluent leaving the discharge through the jet's nozzle contains very few charged particles and a high oxygen radical density in the order of 1016 cm-3. By covering both electrodes with a dielectric, the APPJ is then modified to a dielectric barrier atmospheric pressure glow discharge (DB-APGD). The homogeneity of the respective discharges is investigated by phase-resolved optical emission intensity measurements as well as by voltage and current signal measurements. The atomic oxygen generation efficiency of both plasma sources is determined (according to [1, 2]) by measuring the absolute atomic oxygen ground state density in the effluent by two-photon absorption laser induced fluorescence (TALIF) measurements. [1] K. Niemi, V. Schulz-von der Gathen, H.F. D\"{o}bele, Plasma Sources Sci. Tech. 14 (2005), 375; [2] K. Niemi, S. Reuter, V. Schulz-von der Gathen, H.F. D\"{o}bele, Proceedings of the 17th ESCAMPIG (2004), 157. [Preview Abstract] |
Tuesday, October 2, 2007 11:00AM - 11:15AM |
CT2.00005: Investigation of a gas discharge switch based on a Lorentz drift M. Iberler, A. Fedjuschenko, J. Jacoby, J. Otto, T. Rienecker, Ch. Teske Fast switches are very important tools for pulsed power applications. Basically, there are two complete different principles used to realise a high power switch. One is based on the use of semiconductors, where as the other is based on a triggered breakdown in gases or in vacuum. This contribution gives an introduction in a new kind of gas discharge switch, which consists of a coaxial electrode geometry. The insulated electrode acts initially as an anode, whereas the coaxially arranged electrode is used as cathode. This switch device is called, based on its underlying effect, as Lorentz Drift Switch (LDS). The Lorentz Drift Switch discharge is a low low pressure gas discharge, which is positioned on the left branch of a breakdown voltage curve, similarly to the Paschen curve. Using an external triggering the gas breakdown is initiated and forms a conductive plasma sheath which closes the external electric circuit. The main circuit consists of a capacity as an energy storage system in connections with the switch. To determine the working point of the switch the Paschen break down voltage of the electrode systems was determined. Further investigations were accomplished to improve the understanding of the voltage and current behaviour depending on the loading parameter like the maximum voltage and the external capacity. [Preview Abstract] |
Tuesday, October 2, 2007 11:15AM - 11:30AM |
CT2.00006: Instability Analysis of Formation of Multiple Arc Anode Attachments Guang Yang, Joachim Heberlein To understand the origin of the multiple arc-anode attachments and the origin of the restrike behavior in the anode region of high intensity arcs, linear stability analyses of a non-uniform singly-ionized argon plasma and of the arc-anode interface are performed. The short characteristic times of such anode phenomena allow significant simplification and linearization of the governing equations, from which dispersion relations of the plasma are obtained. According to the calculations, we propose that the electron overheating instability and the anode evaporation-ionization instability are responsible for the formation of these anode phenomena. The electron overheating instability, which generates an electron temperature run-away situation, is excited by small-amplitude fluctuations in the plasma with specific combination of current flow, electric field, electron temperature and electron density. The vaporation-ionization instability, which leads to current run-away in a small area, is encouraged by large electric fields accelerating electrons towards the anode. The regions of these instabilities are identified with our experimental measurements. The results show that the multiple arc-anode attachments form in the fringes of the arc, and that the restrike behavior starts from flow instabilities, which bring high electron temperature cloud to the anode surface. Observations to the anode surface confirm the analysis results. [Preview Abstract] |
Tuesday, October 2, 2007 11:30AM - 11:45AM |
CT2.00007: Discharge dynamics in a micro-plasma jet T. Gans, L. Schaper, N. Knake, K. Niemi, V. Schulz-von der Gathen, J. Winter Micro-plasmas operated at ambient pressure with dimensions of the confining geometry in the order of a few ten micrometers to a millimetre bear enormous potential for technological applications. However, fundamental discharge phenomena and energy transport mechanisms in these discharges are only rudimentary understood. The atmospheric pressure plasma jet (APPJ) is a homogeneous non-equilibrium discharge. A specially designed radio-frequency (rf) $\mu$-APPJ provides excellent optical diagnostic access to the discharge volume and the interface to the effluent region. The discharge dynamics and energy transport mechanisms from the discharge core to the effluent region are investigated using phase resolved optical emission spectroscopy (PROES) and two-photon laser induced fluorescence spectroscopy (TALIF). PROES measurements give detailed insight into the dynamics of electrons sustaining the discharge. The TALIF measurements provide spatial profiles of absolutely calibrated atomic oxygen densities. [Preview Abstract] |
Tuesday, October 2, 2007 11:45AM - 12:00PM |
CT2.00008: Student Excellence Award Finalist: Comparison between Non-Equilibrium and Equilibrium Modeling Results of an Arc Plasma Torch Juan Trelles, Joachim Heberlein, Emil Pfender The strong plasma -- cold-flow interaction, added to the intense cooling of the electrodes, suggests that thermal non-equilibrium effects could be important inside arc plasma torches. These effects can modify significantly the energy balance within the torch and subsequently affect the arc dynamics. In this research, a two-temperature non-equilibrium and a local thermodynamic equilibrium model are developed and applied to the three-dimensional and time-dependent simulation of the flow inside a plasma torch. The equations in both models are approximated numerically by a multi-scale finite element method. The results show large non-equilibrium regions near the plasma -- cold-flow interaction region and close to the anode surface. Furthermore, marked differences between the non-equilibrium and equilibrium results in the arc dynamics, and in the magnitudes of the voltage drop, and outlet temperatures and velocities are observed. The non-equilibrium results show improved agreement with experimental observations, and clearly indicate the necessity for considering non-equilibrium effects in the description of plasma processing systems were strong plasma -- cold-flow interactions are present. [Preview Abstract] |
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