Bulletin of the American Physical Society
67th Annual Gaseous Electronics Conference
Volume 59, Number 16
Sunday–Friday, November 2–7, 2014; Raleigh, North Carolina
Session SF2: Thermal and Microwave Plasmas |
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Chair: Venkatt Ayyaswamy, University of California Merced Room: State C |
Friday, November 7, 2014 8:30AM - 8:45AM |
SF2.00001: Experimental Characterization of Magnetogasdynamic Phenomena in Ultra-High Velocity Pulsed Plasma Jets Keith Loebner, Benjamin Wang, Mark Cappelli The formation and propagation of high velocity plasma jets in a pulsed, coaxial, deflagration-type discharge is examined experimentally. A sensitive, miniaturized, immersed probe array is used to map out magnetic flux density and associated radial current density as a function of time and axial position. This array is also used to probe the magnetic field gradient across the exit of the accelerator and in the jet formation region. Sensitive interferometry via a continuous-wave helium-neon laser source is used to probe the structure of the plasma jet over multiple chords and axial locations. A two dimensional plasma density gradient profile at an instant in time during jet formation is compiled via Shack-Hartmann wavefront sensor analysis. The qualitative characteristics of rarefaction and/or shock wave formation as a function of chamber back-pressure is examined via fast-framing ICCD imaging. These measurements are compared to existing resistive MHD simulations of the coaxial deflagration accelerator and the ensuing rarefaction jet that is expelled from the electrode assembly. The physical mechanisms governing the behavior of the discharge and the formation of these high energy density plasma jets are proposed and validated against both theoretical models and numerically simulated behavior. [Preview Abstract] |
Friday, November 7, 2014 8:45AM - 9:00AM |
SF2.00002: Plasma diagnostics of non-equilibrium atmospheric plasma jets Alexey Shashurin, David Scott, Michael Keidar, Mikhail Shneider Intensive development and biomedical application of non-equilibrium atmospheric plasma jet (NEAPJ) facilitates rapid growth of the plasma medicine field. The NEAPJ facility utilized at the George Washington University (GWU) demonstrated efficacy for treatment of various cancer types (lung, bladder, breast, head, neck, brain and skin). In this work we review recent advances of the research conducted at GWU concerned with the development of NEAPJ diagnostics including Rayleigh Microwave Scattering setup, method of streamer scattering on DC potential, Rogowski coils, ICCD camera and optical emission spectroscopy. These tools allow conducting temporally-resolved measurements of plasma density, electrical potential, charge and size of the streamer head, electrical currents flowing though the jet, ionization front propagation speed etc. Transient dynamics of plasma and discharge parameters will be considered and physical processes involved in the discharge will be analyzed including streamer breakdown, electrical coupling of the streamer tip with discharge electrodes, factors determining NEAPJ length, cross-sectional shape and propagation path etc. [Preview Abstract] |
Friday, November 7, 2014 9:00AM - 9:30AM |
SF2.00003: Dynamic Contraction of the Positive Column of a Self-Sustained Glow Discharge in Molecular Gas Flow Invited Speaker: Mikhail Shneider Contraction of the gas discharge, when current contracts from a significant volume of weakly ionized plasma into a thin arc channel, was attracted attention of scientists for more than a century. Studies of the contraction (also called constriction) mechanisms, besides carrying interesting science, are of practical importance, especially when contraction should be prevented. A set of time-dependent two-dimensional equations for the non-equilibrium weakly-ionized nitrogen / air plasma is formulated. The process is described by a set of time-dependent continuity equations for the electrons, positive and negative ions; gas and vibrational temperature; by taking into account the convective heat and plasma losses by the transverse flux. Transition from the uniform to contracted state was analyzed. It was shown that such transition experiences a hysteresis, and that the critical current of the transition increases when the pressure (gas density) drops. Possible coexistence of the contracted and uniform state of the plasma in the discharge where the current flows along the density gradient of the background gas was discussed. In this talk the problems related to the dynamic contraction of the current channel inside a quasineutral positive column of a self-sustained glow discharge in molecular gas in a rectangular duct with convection cooling will be discussed. Study presented in this talk was stimulated by the fact that there are large number of experiments on the dynamic contraction of a glow discharge in nitrogen and air flows and a many of possible applications. Similar processes play a role in the powerful gas-discharge lasers. In addition, the problem of dynamic contraction in the large volume of non-equilibrium weakly ionized plasma is closely related to the problem of streamer to leader transitions in lightning and blue jets.\\[4pt] [1] M. N. Shneider, M. S. Mokrov, and G. M. Milikh, Dynamic contraction of the positive column of a self-sustained glow discharge in molecular gas, Physics of Plasmas 19, 033512 (2012)\\[0pt] [2] M. N. Shneider, M. S. Mokrov, and G. M. Milikh, Dynamic Contraction of the Positive Column of a Self-Sustained Glow Discharge in Air Flow, Physics of Plasmas 21, 032122 (2014)\\[0pt] [3] G. M. Milikh, M.N. Shneider, and M. S. Mokrov, Model of Blue Jet Formation and Propagation in the Nonuniform Atmosphere, JGR (2014) (submitted) [Preview Abstract] |
Friday, November 7, 2014 9:30AM - 9:45AM |
SF2.00004: Pulsed laser measurement of temperature and conductivity of a decaying arc channel Patrick Stoller, Emmanouil Panousis, Jan Carstensen, Valeria Teppati When a high voltage circuit breaker interrupts alternating current, the arc established between its contacts is axially blown by a transonic gas flow until it is extinguished at a current-zero crossing. Improvement of circuit breaker design to achieve higher short circuit current ratings or more compact equipment relies on an understanding of the processes involved in cooling and interruption of the arc. At present, current, voltage, and pressure measurements together with CFD simulations give only limited insight into how the arc is cooled---mainly via convection and radiation---and finally is interrupted via turbulent mixing. Measurement of the density, temperature, and conductivity of the arc embedded in a gas-flow would permit validation of the CFD simulations and allow direct quantitative determination of important parameters such as the arc and boundary layer width and temperature. We have developed a Speckle imaging technique that permits determination of these parameters via measurement of the refractive index. A pulsed, nanosecond laser is used to interrogate the arc and surrounding flow. The short pulse length permits visualization of turbulent flow features and prevents smearing of time varying features of the flow and the arc that may occur if a continuous wave laser is used. We present and compare to CFD simulations measurements of the temperature, density, and conductivity of axially blown arcs. Based on these results we examine the dependence of the arc width on blowing conditions. [Preview Abstract] |
Friday, November 7, 2014 9:45AM - 10:00AM |
SF2.00005: Pseudo-continuous meter-scale microwave plasma production under atmospheric pressure Hirotaka Toyoda, Haruka Suzuki, Suguru Nakano, Hitoshi Itoh, Makoto Sekine, Masaru Hori Atmospheric pressure plasmas (APP) have been given much attention because of its cost benefit and a variety of possibilities for industrial applications such as large area processing. We have been studying production of a pseudo-continuous meter-scale 2.45 GHz microwave APP source which consists of a loop-structure waveguide antenna and a circulator. Plasma is produced inside a meter-length slot of the waveguide and pseudo-continuous plasma is realized by fast movement of small (a few mm in length) plasmas along the slot. In this study, plasma behavior is investigated by a high-speed camera and an ICCD camera to give insight into the mechanism of the plasma movement. In emission intensity profile along the slot from a single plasma, asymmetric structure and higher emission intensity was observed in the vicinity of the plasma edge of the microwave downstream side, suggesting the plasma movement was induced by the asymmetric ionization rate in the single plasma. Origin of such asymmetric structure was investigated using a simulation of three-dimensional electromagnetic field. [Preview Abstract] |
Friday, November 7, 2014 10:00AM - 10:15AM |
SF2.00006: CO$_{2}$ dissociation in vortex-stabilised microwave plasmas S. Welzel, W.A. Bongers, M.F. Graswinckel, M.C.M. van de Sanden Plasma-assisted gas conversion techniques are widely considered as efficient building blocks in a future energy infrastructure which will be based on intermittent, renewable electricity sources. CO$_{2}$ dissociation in high-frequency plasmas is of particular interest in carbon capture and utilisation process chains for the production of CO$_{2}$-neutral fuels. In order to achieve efficient plasma processes of high throughput specifically designed gas flow and power injection regimes are required. In this contribution vortex-stabilised microwave plasmas in undiluted CO$_{2}$ were studied in a pressure range from 170 to 1000 mbar at up to 1 kW (forward) injected power, respectively. The CO$_{2}$ depletion was measured downstream, e.g. by means of mass spectrometry. Although the system configuration was entirely not optimised, energy efficiencies of nearly 40{\%}, i.e. close to the thermal dissociation limit, and conversion efficiencies of up to 23{\%} were achieved. Additionally, spatially-resolved emission spectroscopy was applied to map the axial and radial distribution of excited atomic (C, O) and molecular (CO, C$_{2})$ species along with their rotational temperatures. [Preview Abstract] |
Friday, November 7, 2014 10:15AM - 10:30AM |
SF2.00007: Experimental observation of electron density bifurcation in plasma-metamaterial composites in microwave range Osamu Sakai, Yoshihiro Nakamura, Akinori Iwai Metamaterials, which are composed of designed microstructures and show extraordinary electromagnetic responses, match plasmas so well, and high-power microwaves induce bifurcation phenomena in this plasma-metamaterial composite. Since dielectric constant or permittivity of plasmas varies from positive to negative values at microwave frequencies, the composite with negative permeability becomes a reconfigurable negative refractive index material [1]. Furthermore, as indicated by our recent report [2,3], this composite shows strong nonlinear properties. Bifurcation of permittivity (or electron density) was predicted by a theory [2], and we have verified it in our recent experiments; using double split ring resonators whose array showed negative permeability at 2.45 GHz, clear bifurcation with hysteresis was observed in electron density evolutions with input power \textless 300 W. This result implies that this composite is a nonlinear microwave metamaterial.\\[4pt] [1] O. Sakai et al., Plasma Sources Sci. Technol. 13, 013001 (2013).\\[0pt] [2] O. Sakai, Journal of Applied Physics 109, 084914 (2011).\\[0pt] [3] Y. Nakamura and O. Sakai, Jpn. J. Appl. Phys. 53, 03DB04 (2014). [Preview Abstract] |
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