Bulletin of the American Physical Society
75th Annual Gaseous Electronics Conference
Volume 67, Number 9
Monday–Friday, October 3–7, 2022;
Sendai International Center, Sendai, Japan
The session times in this program are intended for Japan Standard Time zone in Tokyo, Japan (GMT+9)
Session IR1: Plasma Liquid Interaction I |
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Chair: Wohno Choe, KAIST, Korea Room: Sendai International Center Sakura 2 |
Thursday, October 6, 2022 8:00AM - 8:15AM |
IR1.00001: Analysis of Key Factor of Higher Hydrogen Peroxide Production Performance of Diaphragm Discharge Plasma Based on Time-Resolved Observation Taichi Watanabe, Shungo Zen, Nozomi Takeuchi We have found that the diaphragm discharge plasma generates hydrogen peroxide (H2O2) at a markedly different rate and efficiency under different conditions of solution conductivity and applied voltage waveform. We can build some hypotheses on this characteristic, but its cause is not clear mainly because details of the discharge formation mechanism are unknown. In this paper, to elucidate the plasma generation process and the factor affecting the H2O2 generation rate and efficiency, we conducted time-resolved optical emission spectrum (OES) measurements on 10-parallel diaphragm discharge plasma. The electron temperature was much lower than the threshold energy of dissociation of water molecules, which starts reactions to generate H2O2. On the other hand, the rotation temperature of hydroxyl radical, an indicator of gas temperature, fluctuated around the threshold temperature of thermal dissociation of water molecules 3000–4000 K. The results of this study strongly suggest that thermal energy, rather than electrons, is responsible for the dissociation of water molecules and thus the formation of hydrogen peroxide. Furthermore, based on these results, we discuss the state of the discharge region and the mechanism of plasma formation and H2O2 production. |
Thursday, October 6, 2022 8:15AM - 8:30AM |
IR1.00002: Analysis of OH Emission Spectra Using Deep Learning Shuhei Takamatsu, Kenichi Inoue, Hitoshi Muneoka, Tsuyohito Ito, Kazuo Terashima Plasmas in liquids have attractive features both of plasma and liquid, such as high reactivity and solubility. However, such reaction fields including phase transitions are more complicated than conventional gaseous plasma fields. Thus we need to improve diagnostics and analysis methods. Deep learning is a well-known method for analyzing and generalizing some complicated data and extensively studied in various areas. As for the plasma diagnostics, several studies have been reported, including analysis to extract internal parameters from optical emission spectra. In this study, we also apply deep learning to OH optical emission spectra with the purpose to analyze the plasma in liquid reaction fields more effectively. Using more than million theoretical spectra, we make a deep learning model to train the relationship between emission spectra and various parameters not only OH rotational temperatures, but also apparatus functions. The trained model were tested for estimating each parameter from the experimental spectra. The interesting point with this model is that we do not need to know the apparatus function for finding rotational energy distribution, which we assume here in bi-Maxwellian distribution. Further details and discussion about various errors will be presented. |
Thursday, October 6, 2022 8:30AM - 8:45AM |
IR1.00003: Ultrafast x-ray phase contrast imaging of pulsed plasma initiation in water and hydrocarbons Mirza R Akhter, Christopher S Campbell, Kamel Fezzaa, Samuel J Clark, Zhehui Wang, David Staack Plasma breakdown in liquids poses a complex multiphase environment which challenges conventional imaging techniques. During the breakdown process, emitted bright light saturates camera sensors used in optical imaging mode, which is not the case in x-ray phase contrast imaging (PCI). This work focuses on ultrafast x-ray PCI of nanosecond-pulsed plasma discharge breakdown in distilled water and heptane, for double electrode geometries. A pulsed power circuit was used (+15kV, 50mJ) in conjunction with a laser-triggered (Nd:YAG, 532nm, 30 mJ/pulse) air spark gap switch in order to reduce jitter, facilitating time-dependent diagnostics. Preliminary results show propagating streamers which connect to form a conducting channel through the liquid, which would typically be obscured by optical emission. Streamer propagation speed is estimated to be >5 km/s. A Fresnel-Kirchhoff diffraction model was constructed and used to estimate the specific gravity and density of the plasma channels. Plasma breakdown in heptane was imaged for complete and incomplete breakdown modes by varying the breakdown voltage. Ultrafast imaging results are presented, highlighting their utility for revealing nanosecond-timescale multiphase plasma environments typically obscured by strong broadband optical emission. |
Thursday, October 6, 2022 8:45AM - 9:00AM |
IR1.00004: Electrical Properties of Plasma Formation in Organic Solution and the Structure of the Resulting Carbon Material Niu Jiangqi, Chayanaphat Chokradjaroen, Nagahiro Saito Solution plasma process (SPP) enables several unique reactions at the interfaces, and it is worth noting that a widespread application in carbon nanomaterials with different various allotropes was achieved. Detailed plasma parameters of different interfaces such as plasma potential profile, electron density, electron temperature and heavy active particle distribution are important parameters in the plasma processes. In this study, a modified Langmuir probe method was proposed to measure physical parameters at different locations in the solution plasma under pin-to-pin electrode structure system. The electron temperature mappings of spatial distribution including plasma, plasma-gas, gas-liquid phase of SPP obtained from benzene, toluene, phenol and aniline, respectively, were diagnosed. The proposed plasma-metal junction, plasma-solution junction and the electric double-layer concept clarified the distribution structure and energy characteristics of the active particles in the solution plasma. The important effect of the electron temperature gradient from plasma-phase to interface of a specific quenching-like process on carbon growth, i.e., a larger quenching temperature induced will synthesize multilayer large-size carbon products. |
Thursday, October 6, 2022 9:00AM - 9:15AM |
IR1.00005: Imaging Electric Breakdown over the Rise and Fall of ns Pulses in Water and Free-flowing Bubbles Nicholas L Sponsel, Sophia Gershman, Maria J Herrera Quesada, Jacob T Mast, Katharina Stapelmann Gas bubbles in water have been a target of extensive study for plasma discharges in liquid environments. The initiation mechanism of electric discharge in liquids was contested between the ‘bubble model’ and the ‘direct impact ionization model’ early on, debating whether a vapor phase must form prior to discharge [1]. Recently, a theoretical model of electrostrictive cavitation leading to nanovoids has been developed to account for the initiation of electric breakdown in liquids with fast rise-times of the applied voltage in inhomogeneous electric fields [2]. We show experimentally that even in the presence of a macroscopic bubble, discharge is first observed at the sharp tip of a positive electrode, within the first 4-8 ns of a 20 kV nanosecond pulse. Imaging of the electric breakdown was carried out over the 30 ns “half-wave” of the pulse and beyond with 2-10 ns image gate-widths to maximize temporal resolution. The short rise-time of the applied voltage, and the time it takes for the discharge to bridge the gap between the tip of the sharp electrode and the apex of the bubble, suggest the cavitation mechanism for discharge initiation and propagation in the water. |
Thursday, October 6, 2022 9:15AM - 9:30AM |
IR1.00006: Plasmas-in-lquids heating in a mm-sized bubbles multiphase thermochemical rearctor Ahmed M Hala Energy production that is based on plasma-in-liquid multiphase reactions is an emerging and active area of research in the plasma science. For example, and as in the early days of testing fusion energy production, there were successful proof-in-principal devices that were based on plasma-in-liquid interactions. In this paper, a description of the design of a multiphase thermochemical reactor shows the efficient coupling of modern high power sub-Terahertz radiation sources heating to many forms of liquid & liquid solutions mm-sized bubbles to generate dense and hot plasma-in-liquid in the reactor. Furthermore, new compact and high magnetic field intensity elements that are based on commercially available superconducting technologies are properly configured in this reactor column design, and they support the feasibility of this energy production construct. In addition, the role of external heating elements in initiating the overall reaction process and in assisting to control it is highlighted. This overall design, while simplified by description, is scalable. However, it will be shown that actual experimental testing is to be carried out only after a careful analysis that includes design-of-experiment techniques. |
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