Bulletin of the American Physical Society
73rd Annual Gaseous Electronics Virtual Conference
Volume 65, Number 10
Monday–Friday, October 5–9, 2020; Time Zone: Central Daylight Time, USA.
Session YF2: Atmospheric Pressure Plasma CharacterizationLive
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Chair: Pedro Viegas, Dutch Institute for Fundamental Energy Research |
Friday, October 9, 2020 1:00PM - 1:15PM Live |
YF2.00001: Generation and Characterization of HgBr Radical in Low Temperature Atmospheric Pressure Plasma Jets. Pubuduni A K Ekanayaka M E W, Chuji Wang Numerous ongoing studies of metal halide molecules such as HgBr radicals have been driven by their application in light source and its important roles in atmospheric mercury chemistry. Formation and characterization of HgBr radicals in two types of low temperature plasma were studied in this work. Chemical vapor of mercury bromide (HgBr$_{\mathrm{2}})$ was generated using a high temperature (\textgreater 100 $^{\mathrm{o}}$C) heating of a solid HgBr$_{\mathrm{2}}$ sample held in a pyrex tube and was introduced to a low temperature atmospheric microwave wave plasma jet (MWPJ) and a cold atmospheric pulsed plasma jet (APPJ) using He as a carrier gas. By controlling the plasma operating conditions (plasma power, applied pulse voltage, gas flow rate, etc.), we observed Hg atomic and HgBr radical emission spectra. The atomic Hg and Br were formed in both plasma jets; but HgBr radicals were formed only in the cold plasma jet. Optical emission spectra of Hg and HgBr were obtained vertically along the axis of the plasma jet to validate their formation in the plasma. The strongest band in the vibronic spectrum was observed at 502 nm, which belongs to the electronic system$({V}'=0-\to {V}'')B^{2}\Sigma_{1/2}^{+} \to {\rm X}^{2}\Sigma _{1/2}^{+} $ of HgBr radical. We speculate that the plasma thermal dissociation and electron impact dissociation of HgBr$_{\mathrm{2}}$ molecules are responsible for the generation of HgBr radicals and that the high temperature of MWPJ (400-800 K) further dissociates HgBr radicals into Hg and Br atoms, so that no HgBr was observed in the MWPJ. [Preview Abstract] |
Friday, October 9, 2020 1:15PM - 1:30PM Live |
YF2.00002: Optical characteristics of a gas discharge in mixtures of sulfur vapor with inert gases Svetlana Avtaeva, Andriy Heneral The discharge in mixtures of inert gas with sulfur vapors is an effective source of radiation spectrum, which is similar to solar in the wavelength range of 280-600 nm due to strong emission of S2 molecules. This paper presents optical properties of the pulsed-periodic discharge (the pulse $\le $10 kV with duration of several $\mu $s and repetition frequency of 10 kHz) in mixtures of argon with sulfur vapour in the wavelength range of 300-700 nm. In this wavelength range strong bands of S2 molecules are observed in the discharge radiation along with Ar and S lines. Radiation of S2 bands dominates at argon pressure less than 30 Torr. The radiation efficiency of sulfur dimer bands rises with increase in temperature of gas-discharge tube walls. Kinetics of excited sulfur molecules in the discharge is studied using a global model. Time profiles of plasma species densities under various Ar-S2 mixture compositions during voltage pulses were calculated. It is shown, that densities of S2 excited molecules fast increases at the voltage pulse beginning and reach maximum after about 2 $\mu $s, strong radiation of S2 excited molecules is characteristic for this time. [Preview Abstract] |
Friday, October 9, 2020 1:30PM - 1:45PM Live |
YF2.00003: A 3-D Computation of the Microwave Emission Spectrum of the Cold Atmospheric Helium Plasma Jet Yi Liu, Li Lin, Micheal Keidar As a source of the reactive species, electromagnetic emissions, and acoustic waves, the cold atmospheric plasma jet (CAPJ) is currently widely and intensively used for biomedicine, material processing, and environmental science. One of the most critical applications is the cancer treatment induced by CAPJ chemistry. Recent studies show that microwave emissions from a CAPJ may also lead to the apoptosis of cells, which is a new point of view of plasma medicine. To reveal the microwave emission spectrum of the CAPJ and its treatment mechanism, a helium CAPJ and its 3-D radiation field were simulated. The electromagnetic radiation field is a superposition of three components. The first one is the bulk current emission. The movement of net charge distribution in each simulation grid provides a current which is considered as a linear wire antenna. The second one is the plasma oscillation emission, where the thermal electron motion and particle collisions are considered. The third one is the Bremsstrahlung emission due to the e-e collisions and e-ion collisions. As a result, the spectrum of the 3-D CAPJ radiation field is obtained, which is highly informative to future research on the physical effects of CAPJ treatments. [Preview Abstract] |
Friday, October 9, 2020 1:45PM - 2:00PM Live |
YF2.00004: Spatially and temporally resolved electron temperature and number density measurements in 100-kHz nanosecond pulse burst discharges using laser Thomson scattering. Yue Wu, Richard Miles, Christopher Limbach In order to better understand plasma transport, plasma chemistry, and energy efficiency in nanosecond repetitively pulsed (NRP) discharges, spatially and temporally resolved studies of plasma afterglows in argon with additions of carbon dioxide and water vapor have been investigated using laser Thomson scattering, laser Rayleigh scattering, and optical emission spectroscopy. Bursts of 6-ns, 14-kV pulses at 100-kHz rate (10 pulses per burst at 30 Hz) are produced in a pin-to-sphere discharge geometry at a pressure of 80 Torr. Electron temperature, electron number density, and active species have been measured within the first microsecond. Meanwhile, gas temperature has been monitored after the first microsecond with Rayleigh scattering. Selected pulses (i.e. 1$^{\mathrm{st}}$, 2$^{\mathrm{nd}}$, 5$^{\mathrm{th}}$, and 10$^{\mathrm{th}}$ pulse) in each burst have been investigated in more detail. Both the dissociation of species and the increase of gas temperature played important roles in the plasma chemistry, energy deposition, and electron lifetime. The investigation on NPB discharges provides valuable insight into the nature of NRP discharges and shows fundamental differences from other nanosecond discharges operating in single-shot or low frequency mode. [Preview Abstract] |
Friday, October 9, 2020 2:00PM - 2:15PM Live |
YF2.00005: Characterization of an RF cold atmospheric pressure plasma jet for use with open channel microfluidics test bed Josh Morsell, Steven Shannon One major challenge in the field of atmospheric pressure plasmas is understanding the plasma interaction with complex, multi-phase interfaces. To study this, an open channel microfluidics test bed has been developed as a controllable surface for characterizing atmospheric plasma sources and their interactions with multiphase interfaces. The 120 microchannels on each bed are 100um wide with a 100um pitch. Each pair of channels is gathered in reservoirs and allows for a spatial resolution of 400um. The source characterized in this work is an RF cold atmospheric pressure plasma jet modified from a source being developed at the University of Minnesota. The source consists of a needle electrode inside a quartz tube with a grounded cuff at its end. Multiple gas channels allow for feed and shielding gas as required. Power is delivered via a tunable matching network and 13.56MHz power supply driven by a function generator for pulsing. Source characterization will consist of spatially resolved OES methods as well as electrical characterization through VI probe and directional couplers. The microchannel spatial measurements will be used as comparison to OES and as initial work to understand plasma interaction with complex, multi-phase interfaces. [Preview Abstract] |
Friday, October 9, 2020 2:15PM - 2:30PM Live |
YF2.00006: Optical diagnostics of nanosecond capillary discharge in pure CO2 at high values of deposited energy and reduced electric field. Georgy Pokrovskiy, Olivier Guaitella, Ana Sofia Morillo-Candas, Elena Filimonova, Svetlana Starikovskaia Optical and electrical diagnostics of nanosecond discharge ignited in pure CO$_{\mathrm{2}}$ at moderate (10-20 mbar) pressures was performed. The reduced electric fields of 250-300 Td and the electric current of 130 A were registered after the passing front of the fast ionization wave. The absolute downstream densities of CO$_{\mathrm{2}}$ dissociation products were measured by FTIR. The values of CO$_{\mathrm{2}}$ dissociation fraction of 20{\%} at single pulse regime and 90{\%} at 300 Hz repetition rate have been obtained. The gas temperature measurements were performed by the means of OES in~CO$_{\mathrm{2}}$:N$_{\mathrm{2}}$ mixtures. The following values of the gas temperature were derived: 450 K, 1700 K and 2000 K in 1st, 2nd and the 3rd pulses separated by 200 ns. Numerical modelling of the discharge has shown that the vibrational kinetics is not dominant in the case of high electric fields. Instead, excitation of electronic levels of CO$_{\mathrm{2}}$ with their consequent dissociation onto CO and O and dissociative recombination of electrons with CO$_{\mathrm{2}}^{\mathrm{+}}$ ions play the leading role. The sensitivity and the rate analysis of the kinetic scheme have been done. [Preview Abstract] |
Friday, October 9, 2020 2:30PM - 2:45PM Live |
YF2.00007: Spatially-resolved Optical Emission Spectroscopy Measurements of Free Plasma Jets Formed off the Surface of a Piezoelectric Transformer Jinyu Yang, Seong-kyun Im, David Go Spatially resolved optical emission spectroscopy (OES) was performed to characterize the chemical composition of a plasma jet originating from the surface of a piezoelectric transformer (PT). A PT is a non-centrosymmetric crystal that converts low-voltage AC input to high-voltage AC output through an innate electromechanical coupling. When a PT is actuated by input of \textasciitilde 20 V$_{\mathrm{rms}}$, high-voltage gain at the distal end can be several orders of magnitude, leading to a free plasma jet without flowing a guiding gas. In this work, spatially resolved OES measurements were conducted along the PT-driven plasma jet using a spectrometer with a wavelength resolution of 0.06 nm. Results reveal the chemical composition of the plasma jet and how it evolves as the jet extends into open air. Notably, as the jet propagates into the open air, the emission intensity of the nitrogen second positive system stays almost constant in the first 5 mm and then starts to decrease monotonically as the jet propagates away from the PT. The emission spectrum can still be observed until 15 mm from the PT's surface, which is comparable to many conventional plasma jets and the visible length of the free plasma jet. [Preview Abstract] |
Friday, October 9, 2020 2:45PM - 3:00PM Live |
YF2.00008: Electron parameters between high voltage pulses in nanosecond repetitively pulsed discharges. Jared Miles, Chase Murray, Steven Adams Electron parameters are extremely important in nanosecond repetitively pulsed discharges (NRPD's). This work focuses on a burst of multiple pulses applied at high frequencies (\textgreater 100 kHz) in an atmospheric air pin to pin discharge, and the electron activity occurring between pulses. Recently, electrons have been measured long after the voltage drops to zero, up to 20 \textmu s after the initial nanosecond voltage pulse. In atmospheric air conditions, the electron density should quickly reduce to zero, yet certain conditions resulting from NRPD's are contributing to the greatly reducing the decay rate. Hydrodynamic effects have been observed which greatly reduce the gas density after the first pulse, thus affecting the decay rate. Here, emission spectroscopy is performed to see evidence of different reactions occurring between pulses that could contribute to the electron production, thus contributing to the decay rate. Electron density and temperature measurements taken via Thomson scattering will also be discussed, and the electron decay rate will be calculated from the experimental measurements. [Preview Abstract] |
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