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 TF11: Atmospheric and High Pressure Plasmas: Streamer |
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Chair: Mujahid Zaka-ul-Islam, Bochum University Room: Virtual GEC platform |
Friday, October 8, 2021 8:00AM - 8:15AM |
TF11.00001: Self-pulsating streamer corona discharge under DC voltage Benjamin C Martell, Lee R Strobel, Arthur Dogariu, Carmen Guerra-Garcia Streamer coronae in atmospheric pressure air produced using DC voltage present a self-pulsating behavior with current pulse widths on the order of hundreds of nanoseconds and pulsation frequencies on the order of kilohertz. These burst pulsations are controlled mostly by the electrostatics. For constant applied voltage, the burst is terminated by the near-electrode accumulation of space charge and the period between bursts is driven by the timescale for charge dispersion and electric field recovery. This differs from when using pulsed DC voltage: the streamer burst is ignited and quenched by the duration of the nanosecond-duration voltage pulses. In this contribution we explore the self-pulsating characteristics of streamer corona discharges under DC voltage. First, we exploit recent advancements in laser diagnostics to measure the electric field evolution during a streamer corona burst and its afterglow, using the electric field induced second harmonic generation (E-FISH) technique. Second, we explore the impact of enhancing charge transport through wind addition. Whereas wind velocity has a negligible impact at the timescale for streamer propagation, it significantly affects the transport of space charge and hence the pulse train behavior. |
Friday, October 8, 2021 8:15AM - 8:30AM |
TF11.00002: High-voltage NS discharges interaction with blast waves Andrey Starikovskiy, Mikhail Shneider, Arthur Dogariu Streamer propagation can be blocked both in the cases of low and high gas densities in the layer if its thickness is large enough. In the case of a thin high-density layer, streamers overlap the gap both for positive and negative polarities on the high-voltage electrode. For a relatively small layer thickness, the gap exhibits selective "conductivity": a negative discharge can develop up to a low-voltage electrode, while a positive discharge stops in a low density layer. Depending on the delay time between a laser pulse and a streamer, the streamer will demonstrate different behavior. At small delay times both positive and negative polarities will not be able to propagate through the conductive plasma layer. Both negative and positive streamers will be able to propagate through the hot nonconductive gas layer immediately after plasma recombination but before gasdynamic expansion. Finally, when the low-density layer will be formed, a streamer of positive polarity will not overcome this rarified gas layer, while a streamer of negative polarity will propagate further and finally will close the discharge gap. |
Friday, October 8, 2021 8:30AM - 8:45AM |
TF11.00003: Plasma characterization of the atmospheric pressure carbon arc Nirbhav S Chopra, Yevgeny Raitses, Shurik Yatom, Jorge Munoz Burgos Atmospheric pressure anodic carbon arc discharges are a promising method for low-cost, high-volume synthesis of nanomaterials. During arc operation, carbon material is introduced into the arc by the ablation of the graphite anode [1]. The anode ablation depends on the power balance at the anode, which is influenced by whether the anode sheath is electron-repelling (negative anode sheath) or electron-attracting (positive anode sheath) [1–6]. Anodic carbon arcs exhibit a transition between low and high ablation modes; at larger arc currents the ablation rate of the anode grows nonlinearly [1,4,5]. We show the existence of a positive anode sheath in both low and high ablation modes. The electron temperature and density are determined by optical emission spectroscopy and corroborated by a Langmuir probe measurement. The plasma potential is determined with a floating probe. The floating probe potential is related to the plasma potential by assuming ions diffuse through neutrals in the probe presheath. Effects of the positive anode sheath on anode ablation rate are discussed. We also discuss a plausible explanation for the discrepancy in experimentally determined discharge voltage and discharge voltage calculated by recent models of the arc [6]. |
Friday, October 8, 2021 8:45AM - 9:15AM |
TF11.00004: On the large variability of streamer discharges Invited Speaker: Ute Ebert Streamer discharges are a basic phenomenon in electric breakdown of gases; they appear in lightning, sparks, and numerous application fields. They are 3-dimensional dynamic multiscale phenomena, with high electron energies up to possible run-away, and with growth velocities that can reach fractions of the speed of light. Our review [Nijdam, Teunissen, Ebert, PSST 29, 103001 (2020)] also summarizes open questions, and I will address results found since. First, we have studied single positive streamers in air under the same conditions both in experiments and in simulations, and we found quantitative agreement without fitting parameters. But second, positive streamers in air at fixed temperature and pressure can also have very different modes of propagation, with velocities much larger or much smaller than the electron drift velocity, accelerating, decelerating or propagating in a solitary manner. The solitary streamers propagate with constant shape and velocity after having lost the conductive connection to the electrode; this behavior matches the original definition of the stability field. But third, due to the long-range photoionization, positive streamers in air are by no means generic; in air with a stoichiometric admixture of 9.5% methane (for combustion) or in CO2 dominated gas mixtures (for high voltage engineering) positive streamer discharges behave very differently, as we illustrate with 3D MCC-PIC models for the electrons in the discharge. Fourth, we also investigate negative streamers in air, they are particular interesting in lightning due to possible electron run away, and because the radio telescope LOFAR now can detect negative streamers in thunderstorms on the meter scale that is also reached by simulations. Finally, I won’t have much time left to comment on recent model reduction approaches to complete streamer corona’s, and on processes before and after the streamer phase. Results are due to the MD-group at CWI and to the EPG-group at TU/e. |
Friday, October 8, 2021 9:15AM - 9:45AM |
TF11.00005: Streamer discharges, their initiation and electric field Invited Speaker: Tomas Hoder Streamer discharges are present in many fields of science. They are basic components of atmospheric electricity and frequently utilized sources of non-equilibrium plasmas, both in fundamental research and applications. Three cases from the physics of streamer discharges are discussed in this presentation. In a free space, the quasi-stationary phase of the streamer development is a well understood phenomenon. Nevertheless the very first stages of the initiation of the streamer in pulse driven discharges lack an experimental understanding, mostly due to the diagnostical challenges connected with the high streamer velocity and its stochastic occurence. Here, we offer an approach for such detailed diagnostics. In a similar way, the complexity and high velocity of streamer discharges developing on dielectric surfaces is the reason for unanswered questions or lack of experimental data in the field. We offer experimentally based answers to two such questions: What amplitudes can the electric field strength reach during the streamer-surface interaction? What is the initiation mechanism of long plasma filaments in surface barrier discharges? We apply the time-correlated single-photon counting-based optical emission spectroscopy to surface and coplanar barrier discharges in atmospheric air to study such phenomena. We show experimentaly that the electric field amplitude reaches values of 400 kV/cm as the positive streamer propagates directly on the surface in a coplanar discharge arrangement. Furthermore, we reveal an ultra-fast development of a remotely initiated streamer cascade in the case of surface barrier discharge operated at high overvoltage. We show that this previously unknown mechanism leads to the generation of an intense cathode spot, which is a crucial condition for plasma transition to a highly-ionized state. |
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