Bulletin of the American Physical Society
69th Annual Gaseous Electronics Conference
Volume 61, Number 9
Monday–Friday, October 10–14, 2016; Bochum, Germany
Session JW3: Atmospheric Plasma Jets and Sources IFocus
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Chair: Amanda Lietz, Univ of Michigan Room: 2b |
Wednesday, October 12, 2016 8:30AM - 9:00AM |
JW3.00001: Attraction of positive streamers to surfaces and free electrons Invited Speaker: Sander Nijdam Positive streamers require two ingredients to propagate: a sufficiently high external electric field and a constant supply of (free) electrons in front of the developing streamer head. In air, the electrons are usually provided by photo-ionization, producing free electrons in all directions around the streamer head. However, in cases with reduced photo-ionization, for example in pure gasses, the local external field direction does not necessarily coincide with the direction of sufficient electron density. One way to create such a condition is by using a laser beam to ionize a path. Depending on parameters this can lead to a guided streamer moving almost perpendicular to the field direction. Alternatively, a preceding discharge can have left a specific electron distribution and thereby guide the path of following discharges. This effect is very important for pulsed plasma jets or plasma bullets in pure nitrogen. We have studied this by looking at the development of the discharge during the first few pulses after ignition. Finally, a dielectric surface close to the streamer path can have a large influence on both the electric field distribution, as well as the electron density distribution and thereby can lead to specific paths that the streamer follows or avoids. [Preview Abstract] |
Wednesday, October 12, 2016 9:00AM - 9:15AM |
JW3.00002: Screening in humid air plasmas Anatoly Filippov, Ivan Derbenev, Nikolay Dyatko, Sergey Kurkin Low temperature air plasmas containing H$_2$O molecules are of high importance for atmospheric phenomena, climate control, biomedical applications, surface processing, and purification of air and water. Humid air plasma created by an external ionization source is a good model of the troposphere where ions are produced by the galactic cosmic rays and decay products of air and soil radioactive elements such as Rn$^{222}$. The present paper is devoted to study the ionic composition and the screening in an ionized humid air at atmospheric pressure and room temperature. The ionization rate is varied in the range of $10^1-10^{18}$~cm$^{-3}$s$^{-1}$. The humid air with $0-1.5$\% water admixture that corresponds to the relative humidity of $0-67$\% at the air temperature equal to $20^{\circ}$C is considered. The ionic composition is determined on the analysis of more than a hundred processes. The system of 41 non-steady state particle number balance equations is solved using the 4$^{th}$ order Runge-Kutta method. The screening of dust particle charge in the ionized humid air are studied within the diffusion-drift approach. The screening constants are well approximated by the inverse Debye length and characteristic lengths of recombination and attachment processes. [Preview Abstract] |
Wednesday, October 12, 2016 9:15AM - 9:30AM |
JW3.00003: (Student Award Finalist) Gas flow phenomena in atmospheric-pressure plasma jets impinging on solid and liquid substrates investigated using numerical modelling and Schlieren imaging Adam Obrusnik, Marco Boselli, Emanuele Simoncelli, Augusto Stancampiano, Matteo Gherardi, Lenka Zajickova, Vittorio Colombo Neutral gas dynamics, i.e. the gas flow, gas mixing and heat transfer, play an important role in medical and other applications of helium atmospheric-pressure plasma jets (APPJs), as they determine the transport of plasma-generated active species to the substrate that is being treated. To capture the full complexity of this problem numerically, the buoyant Navier-Stokes equations (either laminar or with an appropriate turbulence model) must be solved together with multicomponent diffusion equations and the heat equation. In this contribution, we present the results of a combined experimental-numerical approach. The gas flow in three different plasma sources impinging on a flat surface, solid or liquid, is captured using high-speed Schlieren imaging. Special attention was dedicated to the onset of turbulence and the changes in the flow behaviour when a liquid substrate is used. By combining the experiments with numerical simulations of the flow (laminar and large-eddy simulation turbulent model), we analyze the role of three different types of plasmas on the gas flow and identify the phenomena that are likely responsible for the changes observed. [Preview Abstract] |
Wednesday, October 12, 2016 9:30AM - 9:45AM |
JW3.00004: Cooling and Laser-Induced Fluorescence of Electronically-Excited He$_2$ in a Supersonic Microcavity Plasma Jet Rui Su, Andrey Mironov, Thomas Houlahan, Jr., J. Gary Eden Laser-induced fluorescence (LIF) resulting from transitions between different electronic states of helium dimers generated within a microcavity plasma jet was studied with rotational resolution. In particular, the d$^3\Sigma^+_u$, e$^3\Pi_g$ and f$^3\Sigma^+_u$ states, all having electronic energies above 24 eV, are populated by a microplasma in 4 bar of helium gas and rotationally cooled through supersonic expansion. Analysis of two dimensional maps (spectrograms) of dimer emission spectra as a function of distance from the nozzle orifice indicates collisional coupling during the expansion between the lowest rotational levels of the e$^3\Pi_g$, f$^3\Sigma^+_u$ states and high rotational levels (around N=11) of the d$^3\Sigma^+_u$ state (all of which are in the v = 0 vibrational state). In an attempt to verify the coupling, a scanning dye laser (centered near 596 nm) pumps the b$^3\Pi_g$ $\rightarrow$ f$^3\Sigma^+_u$ transition of the molecule several hundred micrometers downstream of the nozzle. As a result, the emission intensities of relevant rotational lines are observed to be enhanced. This research shows the potential of utilizing microcavity plasma jets as a tool to study and manipulate the collisional dynamics of highly-excited diatomic molecules. [Preview Abstract] |
Wednesday, October 12, 2016 9:45AM - 10:00AM |
JW3.00005: Characterization of atmospheric nanosecond discharge under highly inhomogeneous and transient electric field in air/water mixture Karim Ouaras, Pierre Tardiveau, Lionel Magne, Pascal Jeanney, Blandine Bournonville We report the studies of a centimeter range pin-to-plane nanosecond repetitively discharge (\textless 30 ns and 10 Hz) in standard conditions of pressure and temperature under very high positive voltage pulses (20 to 100 kV). In these typical conditions, plasma exhibit unusual diffuse and large structure. This kind of discharge is not well understood and in first approach, it requires (i) a description of plasma dynamic and (ii) behavior under relevant context (environmental issues \textellipsis ) using pertinent gas (humid air). Thus, we will first present sub-nanosecond imaging of the discharge obtained for typical conditions of stabilized plasma. Then we will focus on determination of rotational and vibrational temperature (OES) and preliminary results concerning the production and evolution of OH radical in temporal post-discharge in air/water mixture (PLIF). Theses spectroscopic measurements are undertaken as function of most influent parameters, $i.e.$ voltage pulses features (amplitude, rise time and length) and water concentration. [Preview Abstract] |
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