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 RR42: Plasma-liquid Interaction III |
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Chair: Mikhail Shneider, Princeton University Room: Virtual GEC platform |
Thursday, October 7, 2021 2:00PM - 2:15PM |
RR42.00001: In situ detection of atomic oxygen in liquids using TALIF Katharina Stapelmann, Brayden G Myers, Arthur Dogariu Recently, there has been an emerging realization of the importance of atomic oxygen in plasma-induced chemistry, particularly in the aqueous phase. Unlike many reactive species generated by plasmas, atomic oxygen is not found in biological systems in nature, so its effects remain largely unknown. However, several studies have alluded to its potential, documenting atomic oxygen’s central role in deactivating multiple cancer cell lines, cleaving DNA, and thoroughly degrading a variety of organics. Quantifying solvated O atoms, critical for isolating its effects, has proven exceedingly difficult as chemical probes used for its detection suffer from a number of shortcomings. Here we show that aqueous O can be measured directly by employing two-photon absorption laser induced fluorescence (TALIF) with a femtosecond laser. We demonstrate that given a sufficiently fast laser pulse, solvated O atoms can be excited without appreciable heating of the liquid and at a requisite efficiency for detection of a fluorescence signal despite the highly collisional aqueous environment. These measurements establish the proof of concept for an experimental technique to directly quantify atomic oxygen in liquid without the need for inherently problematic chemical probes. |
Thursday, October 7, 2021 2:15PM - 2:30PM |
RR42.00002: On the OH density distribution in an atmospheric pressure plasma interacted with liquid cathode Yuanfu Yue, Santosh Kondeti, Nader Sadeghi, Peter Bruggeman The interaction of plasmas with liquids enables the generation of a broad spectrum of reactive species in the liquid phase mediated by a significant amount of species and energy transfer at the gas-liquid interface. |
Thursday, October 7, 2021 2:30PM - 2:45PM |
RR42.00003: Time Resolved Plasma Characterization by Optical Emission Spectroscopy in a Nanosecond Pulsed Plasma Gas-Liquid Reactor Radha Krishna Murthy Bulusu, Robert J Wandell, Shurik Yatom, Bruce R Locke Time resolved optical emission spectroscopy (OES) was used to determine electron density and excitation temperature as functions of pulse width and pulse frequency in a nanosecond pulsed plasma gas-liquid flow reactor with argon (Ar) and deionized liquid water. The plasma characteristics were obtained by analysis of H-Balmer lines. The pulse frequency was varied between 5kHz – 100kHz using a custom-made power supply (Airity Technologies, LLC). The peak electron density in a single pulse varies between 1.8×1017 cm-3 - 4.8×1017 cm-3 with frequency. The peak electron density was observed at 20kHz. After voltage breakdown and the increase in current, the electron density rises quickly and exponentially decays over a single pulse. The electron decay is longer than the current decay (40 ns), and the decay time constant for electron density varies between 110ns-1 – 140ns-1 with frequency and these results will be used to analyze the recombination mechanisms in our plasma. |
Thursday, October 7, 2021 2:45PM - 3:00PM |
RR42.00004: Electrostrictive Cavitation under Nanosecond Pulsed Electric Field Xuewei Zhang, Mikhail Shneider Plasma discharge in water under nanosecond pulsed electric field has received extensive research attention in the last decade. Previous work has demonstrated that the physical mechanism of the breadkown initiation is cavitation due to electrostriction in strong imhomogeneous fields. The first electrons are released into the cavities and then undergo multiplication, eventually leading to the initial plasma discharge channel. However, the unknown characterisctics of the cavitation zone, e.g., cavity size and density, prohibit a clear delineation of the electron processes at the initial stage of the nanosecond breakdown. This work aims to explore the electrostrictive cavitation dynamics to extract key features of the cavitation zone which sets stage for the electron processes. In the literature, most of the discussions of cavitation have been focused on the kinetics following the Zeldovich-Fisher model. In this work, we extend the kinetic model to a dynamic one by including (a) the cavity growth after formation, i.e., the Rayleigh bubble equation; and (b) the "feedback" to the negative pressure due to cavity formation and growth. The preliminary numerical calculations indicate that this dynamic model results in the saturation of cavitation and a spectrum of cavity sizes. The results of this work will be used in the subsequent work to test alternative models to clarify the electron processes. |
Thursday, October 7, 2021 3:00PM - 3:15PM |
RR42.00005: Machine learning approach for plasma image processing: application to plasma-on-water characterization Valentin Boutrouche, Tymon Nieduzak, Juan Trelles Machine Learning (ML) is a set of computational tools particularly suited for the analysis and classification of large datasets. ML has been widely applied to image processing for application such as pattern recognition (e.g., face detection) and image segmentation (e.g., medical imaging, object detection). Digital cameras are one of the most versatile experimental diagnostics instrument. Optical images recorded during plasma experiments are often used to describe the shape and size of the discharge. A generic ML approach for plasma image processing has been developed using MATLAB Machine Learning Toolbox, and applied to image segmentation from plasma-on-water experiments on a pin-to-plate setup. The segmentation identifies and quantifies zones of interests in the discharge (plasma column, plasma-water interface, etc.). The segmentation data is then used for the three-dimensional reconstruction of the discharge. The ML approach can be extended to incorporate other types of data (e.g. voltage signals), which makes it a promising approach to current enhance plasma diagnostics approaches. |
Thursday, October 7, 2021 3:15PM - 3:30PM |
RR42.00006: Experimental observation of liquid phase short-lived reactive species by advection system in contact with atmospheric pressure plasma Kazuki Takeda, Shota Sasaki, Keisuke Takashima, Toshiro Kaneko Novel applications of non-equilibrium atmospheric pressure plasmas (APPs) in a liquid or in contact with a liquid have been found in the life science field (e.g., biology, medicine, agriculture). These applications employ APP as a source to deliver the reactive oxygen and nitrogen species (RONS) to the liquid phase. However, much of the RONS chemistry at the plasma-liquid interface has not been understood, notably liquid-phase OH radical (OHaq) has hardly been characterized in experiments due to their high reactivity and non-uniformity at the interface. To break through this problem, we built an APP system with a high-speed liquid flow (over 10 m/s) through plasma, which gives an OHaq advection system. This advection system revealed very rapid OHaq decay within approximately 0.5 ms after the plasma exposure and an acceleration of the OHaq decay with the 0.5% N2 admixture to helium. In the presentation, the detail OHaq detection process by the advection system including the measurement accuracy will be discussed quantitatively. |
Thursday, October 7, 2021 3:30PM - 3:45PM |
RR42.00007: Detection of aqueous H2O2 and NO3- at plasma-water interface by in situ Raman spectroscopy David Pai Using a light sheet technique, in situ Raman microspectroscopy has been applied to investigate the liquid side of the plasma-water interface with micrometer depth resolution [1]. During plasma operation, simultaneous measurements were performed to track the Raman spectra of the –OO stretch mode of H2O2, symmetric stretch (v1) of NO3-, and –OH bend of water. The light sheet was positioned just below a glow discharge was generated in atmospheric-pressure air facing a water cathode. Far from the interface region, aqueous NO3- was produced at a rate of 48 µM/minute, but the aqueous H2O2 concentration stabilized at about 5 mM. When approaching the interface to within several tens of microns, the concentrations of both species increase. These measurements reveal the existence of an interfacial layer of excess NO3- concentration extending 28 µm in depth, although this determination is subject to some interpretation due to the presence of the meniscus. Interfacial layers of such depth have been modeled for transient species such as OH but not for NO3-, a stable product of plasma-activated water. |
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