Bulletin of the American Physical Society
74th Annual Gaseous Electronics Conference
Volume 66, Number 7
Monday–Friday, October 4–8, 2021;
Virtual: GEC Platform
Time Zone: Central Daylight Time, USA
Session UF22: Atmospheric, High Pressure and Thermal Plasmas |
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Chair: Osamu Sakai, University of Shiga Prefecture Room: Virtual GEC platform |
Friday, October 8, 2021 10:15AM - 10:30AM |
UF22.00001: EFISH Measurements of Space Charge Waves after Streamer Corona Skye Elliott, Thomas B Coates, Arthur Dogariu, Sergey Leonov This experimental study focuses on the dynamics of volumetric charge and energy dissipation in the case of a single pin electrode streamer corona electric discharge generated in open atmosphere (P = 1 bar) with an alternating polarity high-voltage waveform, up to 100kV. Recent studies show that the volumetric electric charge deposited by the high-voltage pulse discharge greatly affects subsequent discharge parameters and morphology for surface and volumetric geometries. The initial discharge produces a wave of volumetric electric charge concomitant with a redistribution of the electric field that significantly influences the discharge pattern. The EFISH method (Electrical Field Induced Second Harmonic) was employed to perform non-intrusive measurements of the electric field magnitude and direction during, and after, a streamer corona discharge with both high temporal and spatial resolution. It was found that the volumetric charge of an initial pulse polarity occupies a zone up to 100mm from the pin electrode. The following halfcycle of the opposite polarity leads to a partial neutralization of the previous charge cloud and to the generation of a layer with a high-amplitude electric field, up to 50kV/cm. This layer prevents the propagation of the streamers at the next half-cycle. |
Friday, October 8, 2021 10:30AM - 10:45AM |
UF22.00002: Regime transitions of a pulsed nanosecond discharge during passage of a transient flame Colin A Pavan, Carmen Guerra-Garcia Repetitively pulsed nanosecond discharges are a promising way of controlling combustion processes. Whereas most works have centered on the impact of the plasma on different combustion phenomena (extension of lean blowout limits, ignition delay time reduction, static and dynamic flame stabilization, etc.), fewer studies have been devoted to the implications of having a strongly inhomogeneous environment, often unsteady in time, on the discharge characteristics. This two-way coupling is relevant since it will affect the plasma regime observed, the spatial structure of the plasma-activated zone, the total energy deposition, and the energy pathways and chemical kinetics activated by the plasma; which can be evolving at the flame dynamics timescale. In this contribution we present a relatively simple burner configuration, a rectangular cross-section quartz tapered channel, supporting a propagating laminar premixed flame. A repetitively pulsed nanosecond discharge in a dielectric barrier discharge configuration is generated at a fixed location within the burner and the temporal evolution of individual pulses is studied during the flame passage. High speed imaging, energy measurements and translational and vibrational temperature measurements are presented and discussed. |
Friday, October 8, 2021 10:45AM - 11:00AM |
UF22.00003: Coupling Strength in Atmospheric Pressure Plasmas Scott D Baalrud, Natalie Kot, Christopher H Moore A wide variety of interaction types are present in atmospheric pressure plasmas: short-range (neutral-neutral), long-range Coulomb (charge-charge), and intermediate-range (charge-neutral). In modeling such discharges, all types of interactions are usually modeled via a Boltzmann equation. This assumes that all interactions are weakly coupled in the sense that the kinetic energy greatly exceeds the potential energy. However, atmospheric and elevated pressure plasmas can reach strong coupling conditions where this assumption breaks down. Quantifying the coupling strength in a system with multiple types of interactions is challenging because screening from one type influences the strength of intraparticle interactions of another type. Here, we use molecular dynamics simulations to compute the radial distribution functions for each type of interaction over a wide range of ionization fraction at atmospheric and elevated pressures. The coupling strength of each type of interaction is quantified based on properties of the radial distribution function. The results provide a parameter space map showing where the different types of interactions are strongly coupled; motivating the need for a generalized kinetic theory to treat reaction rates and transport kinetics in these regimes. |
Friday, October 8, 2021 11:00AM - 11:15AM Not Participating |
UF22.00004: Investigation of Non-equilbrium Effects in Plasma Jets Alessandro Munafo, Sanjeev Kumar, Nagi N Mansour, Marco Panesi Plasma jets are found in many technological applications such as medicine, arc welding, plasma cutting, waste treatment, nanopowder fabrication and in inductively coupled plasma (ICP) facilities to test thermal protection materials for reentry vehicles. In many circumstances, plasma jets are modeled assuming Local Thermodynamic Equilibrium (LTE). The argument in support of this hypothesis is that operating conditions (e.g. pressure) are such that collisions between free-electrons and heavy-particles (e.g. atoms and molecules) are frequent enough to ensure that LTE prevails. However, these assumptions cannot be justified a priory and should be confirmed by simulations accounting for Non-LTE (NLTE) effects, an understanding of which is also crucial for design and correct interpretation of experiments. |
Friday, October 8, 2021 11:15AM - 11:30AM |
UF22.00005: Study on the conditions to obtain a diffuse nanosecond positive ionization wave in a point-to-plane geometry in atmospheric pressure air Anne Bourdon, Francois Pechereau, fabien tholin, Zdenek Bonaventura Recently, attention has been attracted to 2D axisymmetric diffuse positive discharges with radii of several millimeters produced by high overvoltages applied with nanosecond voltage fronts on point-to-plane geometries. In addition, to better understand the physics of these discharges, different diagnostics have been used to measure the time evolution of the electric field in several locations in the gap. |
Friday, October 8, 2021 11:30AM - 11:45AM |
UF22.00006: Streamer Evolution Dynamics under Repetitive Nanosecond Pulses in Gas Gap and along Dielectric Surface: Effects of Residual Space and Surface Charges Zheng Zhao, Zhifeng Dai, Zongze Huang, Anbang Sun, Jiangtao Li Streamer discharges in gas gap and along dielectric surface driven by repetitive nanosecond pulses have been implemented in many advanced low-temperature plasma applications. Streamer discharges driven by repetitive nanosecond pulses probably exhibit complicated evolution features, where the streamer-to-spark transition is a representative scenario. However, evolution mechanisms of streamer discharge have not been fully revealed. Streamer evolution characteristics and dynamics under repetitive nanosecond pulses in gas gap and along dielectric surface were compared. |
Friday, October 8, 2021 11:45AM - 12:00PM |
UF22.00007: Thermalization Between Electrons and Heavy Species in CO2 Microwave Plasmas Revealed by Thomson Scattering Alex W van de Steeg, Luca Vialetto, Pedro Viegas, Ana F Silva, Ashley J Hughes, Omar Biondo, Paola Diomede, M.C.M. van de Sanden, Gerard J Van Rooij Thomson scattering has been implemented for the first time in CO2 microwave plasma to study electron properties. Resolving the Thomson spectra has been enabled by (i) attenuation of Rayleigh scattered light using a volume Bragg grating and (ii) a disentangling of the Raman and Thomson signatures, made possible by the high gas temperatures (4000-7000 K) and large degree of dissociation. The plasma contracts with pressure, which is accompanied by an increasing gas temperature and decreasing electron temperature. At low pressures (<100 mbar) electron temperatures are found between 1 and 2 eV with gas temperatures <0.5 eV. At pressures above approximately 150 mbar, electron and gas temperatures equilibrate at ~0.6 eV (or ~7000 K). Electron density and ionization fraction increase as electron temperature decreases. Radial profiles of electron density and atomic oxygen emission (3s5S0 <- 3p5P) overlap for contracted conditions, but not in the transient regime between diffuse and contracted plasma; here electron density has a wider profile than oxygen emission, a result of optical contraction. Initial analysis, using 1D fluid modeling, indicates C+O associative ionization is the main mechanism providing ionization at the high gas temperatures, albeit with C fractions <1%. This mechanism explains the simultaneous increase in ionization fraction and decrease in electron temperature. These results are at odds with the current picture of non-equilibrium in moderate pressure CO2 microwave plasma. |
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