Bulletin of the American Physical Society
69th Annual Gaseous Electronics Conference
Volume 61, Number 9
Monday–Friday, October 10–14, 2016; Bochum, Germany
Session QR3: Streamer and Breakdown ProcessesFocus
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Chair: Natalia Babaeva, Joint Institute for High Temperatures, RAS Room: 2b |
Thursday, October 13, 2016 8:30AM - 9:00AM |
QR3.00001: Fluid and hybrid models for streamers Invited Speaker: Zden\v{e}k Bonaventura Streamers are contracted ionizing waves with self-generated field enhancement that propagate into a low-ionized medium exposed to high electric field leaving filamentary trails of plasma behind. The widely used model to study streamer dynamics is based on drift-diffusion equations for electrons and ions, assuming local field approximation, coupled with Poisson's equation. For problems where presence of energetic electrons become important a fluid approach needs to be extended by a particle model, accompanied also with Monte Carlo Collision technique, that takes care of motion of these electrons. A combined fluid-particle approach is used to study an influence of surface emission processes on a fast-pulsed dielectric barrier discharge in air at atmospheric pressure. It is found that fluid-only model predicts substantially faster reignition dynamics compared to coupled fluid--particle model. Furthermore, a hybrid model can be created in which the population of electrons is divided in the energy space into two distinct groups: (1) low energy `bulk' electrons that are treated with fluid model, and (2) high energy `beam' electrons, followed as particles. The hybrid model is then capable not only to deal with streamer discharges in laboratory conditions, but also allows us to study electron acceleration in streamer zone of lighting leaders. There, the production of fast electrons from streamers is investigated, since these (runaway) electrons act as seeds for the relativistic runaway electron avalanche (RREA) mechanism, important for high-energy atmospheric physics phenomena. Results suggest that high energy electrons effect the streamer propagation, namely the velocity, the peak electric field, and thus also the production rate of runaway electrons. [Preview Abstract] |
Thursday, October 13, 2016 9:00AM - 9:15AM |
QR3.00002: Magnetic field effects on the propagation of positive streamers Anbang Sun, Jannis Teunissen, Ute Ebert We investigate how strong magnetic fields affect the propagation of positive streamer discharges. Because such discharges grow opposite to the electron drift direction, they require a source of electrons ahead of them. Here we focus on air, in which photoionization supplies such free electrons isotropically around the streamer head. Using a 3D particle model, we investigate how strong transverse magnetic fields alter the trajectory, ionization rate and energy of these source electrons, leading to streamer branching in the plane spanned by E and B. [Preview Abstract] |
Thursday, October 13, 2016 9:15AM - 9:30AM |
QR3.00003: Two-Dimensional Electron Density Measurement of Positive Streamer Discharge in Atmospheric-Pressure Air Yuki Inada, Ryo Ono, Akiko Kumada, Kunihiko Hidaka, Mitsuaki Maeyama The electron density of streamer discharges propagating in atmospheric-pressure air is crucially important for systematic understanding of the production mechanisms of reactive species utilized in wide ranging applications such as medical treatment, plasma-assisted ignition and combustion, ozone production and environmental pollutant processing. However, electron density measurement during the propagation of the atmospheric-pressure streamers is extremely difficult by using the conventional localized type measurement systems due to the streamer initiation jitters and the irreproducibility in the discharge paths. In order to overcome the difficulties, single-shot two-dimensional electron density measurement was conducted by using a Shack-Hartmann type laser wavefront sensor. The Shack-Hartmann sensor with a temporal resolution of 2 ns was applied to pulsed positive streamer discharges generated in an air gap between pin-to-plate electrodes. The electron density a few ns after the streamer initiation was 7*10$^{\mathrm{21}}$m$^{\mathrm{-3}}$ and uniformly distributed along the streamer channel. The electron density and its distribution profile were compared with a previous study simulating similar streamers, demonstrating good agreement. [Preview Abstract] |
Thursday, October 13, 2016 9:30AM - 9:45AM |
QR3.00004: Mechanism of bullet-to-streamer transition in water surface incident helium atmospheric pressure plasma jet (APPJ) Sung-Young Yoon, Gon-Ho Kim, Su-jeong Kim, Byeongjun Bae, Seong Bong Kim, Seungmin Ryu, Suk Jae Yoo The mechanism of bullet to streamer transition of helium-APPJ bullet on the electrolyte surface was investigated. The APPJ was discharged in pin-to-ring DBD reactor system with helium gas by applying the ac-driven voltage at a frequency of 10 kHz. The water evaporation was controlled via saline temperature. The temporal- and 2-dimensional spatially- resolved plasma properties are monitored by optical diagnostics. During the APPJ bullet propagation from reactor to electrolyte surface, the transition of bullet from streamer was recognized from the high speed image, hydrogen beta emission line, and bullet propagation speed. The He metastable species density profiles from the tunable diode laser absorption spectroscopy (TDLAS) showed the metastable lost the energy near electrolyte surface. It is found that the bullet transited to streamer when the water fraction reached to \textasciitilde 29{\%}. This can be fascinating result to study the plasma physics liquid surface, non-fixed boundary. [Preview Abstract] |
Thursday, October 13, 2016 9:45AM - 10:00AM |
QR3.00005: Distinctive features of kinetics of plasma at high specific energy deposition Nikita Lepikhin, Nikolay Popov, Svetlana Starikovskaia A nanosecond capillary discharge in pure nitrogen at moderate pressures is used as an experimental tool for plasma kinetics studies at conditions of high specific deposited energy up to 1~eV/molecule. Experimental observations based on electrical (back current shunts, capacitive probe) and spectroscopic measurements (quenching rates; translational, rotational and vibrational temperature measurements) demonstrate that high specific deposited energy, at electric fields of 200-300~Td, can significantly change gas kinetics in the discharge and in the afterglow. The numerical calculations in 1D axially symmetric geometry using experimental data as input parameters show that changes in the plasma kinetics are caused by extremely high excitation degree: up to 10{\%} of molecular nitrogen is electronically excited at present conditions. Distinctive features of kinetics of plasma at high specific energy deposition as well as details of the experimental technique and numerical calculations will be present. The work was partially supported by French National Agency, ANR (PLASMAFLAME Project, 2011 BS09 025 01), AOARD AFOSR, FA2386-13-1-4064 grant (Program Officer Prof. Chiping Li), LabEx Plas@Par and Linked International Laboratory LIA KaPPA (France-Russia). [Preview Abstract] |
Thursday, October 13, 2016 10:00AM - 10:15AM |
QR3.00006: Parameters of Runaway Electron Beams at a Subnanosecond Breakdown of Gases at Atmospheric Pressure Victor Tarasenko The generation of runaway electrons in gases at atmospheric pressure is a fundamental physical phenomenon. The aim of this work is to determine the main parameters of runaway electron beams at a subnanosecond breakdown of gases at atmospheric pressure from experiments performed with the highest currently achieved time resolution. Studies were performed with five experimental setups and three generators of nanosecond pulses with the duration of the voltage pulse front from 0.1 to 1 ns and the amplitude of the voltage pulse in the incident wave from 40 to 200 kV. It has been proven that the duration of the current pulse of the runaway electron beam detected behind the foil of the gas diode in air and other gases at atmospheric pressure was \textasciitilde 100 ps. It has been shown that the use of a collimator with a hole with a diameter of 1 mm or smaller, short interelectrode gaps, and cathodes with a small area of a sharp edge makes it possible to separate a fraction of runaway electrons of the beam and to detect pulses with a FWHM of about 25 ps. The number of electrons detected behind the anode foil was correspond to a current amplitude of the runaway electron beam of 100 A. [Preview Abstract] |
Thursday, October 13, 2016 10:15AM - 10:30AM |
QR3.00007: Experimental study of plume induced by nanosecond repetitively pulsed spark microdischarges in air at atmospheric pressure. Thomas Orriere, Nicolas Benard, Eric Moreau, David Pai Nanosecond repetitively pulsed (NRP) spark discharges have been widely studied due to their high chemical reactivity, low gas temperature, and high ionization efficiency. They are useful in many research areas: nanomaterials synthesis, combustion, and aerodynamic flow control. In all of these fields, particular attention has been devoted to chemical species transport and/or hydrodynamic and thermal effects for applications. The aim of this study is to generate an electro-thermal plume by combining an NRP spark microdischarge in a pin-to-pin configuration with a third DC-biased electrode placed a few centimeters away. First, electrical characterization and optical emission spectroscopy were performed to reveal important plasma processes. Second, particle image velocimetry was combined with schlieren photography to investigate the main characteristics of the generated flow. Heating processes are measured by using the N$_{\mathrm{2}}$(C$\to $B) (0,2) and (1,3) vibrational bands, and effects due to the confinement of the discharge are described. Moreover, the presence of atomic ions N$^{\mathrm{+}}$ and O$^{\mathrm{+}}$ is discussed. Finally, the electro-thermal plume structure is characterized by a flow velocity around 1.8 m.s$^{\mathrm{-1}}$, and the thermal kernel has a spheroidal shape. [Preview Abstract] |
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