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1. Effect of Temperature and Water Droplets on Production of Prodigious Hydrogen Oxides by Electrical Discharges

   https://doi.org/10.1029/2023JD039362  

   Jenkins, J. M.; Brune, W. H. (October 2023, Journal of Geophysical Research: Atmospheres)

   Abstract Recently, electrical discharges have been identified as a potentially significant source of the atmosphere's most important oxidant, the hydroxyl radical. Measurements of hydroxyl, the closely related hydroperoxyl radical, and the nitrogen oxides from sparks and subvisible discharges were made in the laboratory under different environmental and electrical conditions representing those found in the troposphere. However, there were still several conditions not yet investigated that could impact hydroxyl and hydroperoxyl production in electrical discharges. In this study, the production of electrically generated hydroxyl and hydroperoxyl (LHO_x) and nitrogen oxides (LNO_x) was measured under three new conditions not tested previously, including lower pressure, different temperatures, and the presence of cloud droplet‐sized water droplets. In spark discharges, LHO_xwas mostly independent of pressure, increased with increasing temperature, and was unaffected by the water droplets. LNO_xgeneration was independent of temperature from −10 to 40°C and the presence of water droplets, but increased 1.5‐fold with decreasing pressure. LNO_xgeneration was also found to be sensitive to changes in spark intensity and air flow in the laboratory setup. Increasing temperature also made it more likely that a discharge was visible instead of subvisible, but did not impact LHO_xproduction in subvisible discharges. Even under these new conditions, the laboratory results agree with results of LHO_xfrom a field campaign, demonstrating the relevance of the laboratory experiments to the atmosphere. 

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2. Contrasting Chlorine Chemistry on Volcanic and Wildfire Aerosols in the Southern Mid‐Latitude Lower Stratosphere

   https://doi.org/10.1029/2024GL110412  

   Wang, Peidong; Solomon, Susan (September 2024, Geophysical Research Letters)

   Abstract Volcanic eruptions and wildfires can impact stratospheric chemistry. We apply tracer‐tracer correlations to satellite data from Atmospheric Chemistry Experiment—Fourier Transform Spectrometer and the Halogen Occultation Experiment at 68 hPa to consistently compare the chemical impact on HCl after multiple wildfires and volcanic eruptions of different magnitudes. The 2020 Australian New Year (ANY) fire displayed an order of magnitude less stratospheric aerosol extinction than the 1991 Pinatubo eruption, but showed similar large changes in mid‐latitude lower stratosphere HCl. While the mid‐latitude aerosol loadings from the 2015 Calbuco and 2022 Hunga volcanic eruptions were similar to the ANY fire, little impact on HCl occurred. The 2009 Australian Black Saturday fire and 2021 smoke remaining from 2020 yield small HCl changes, at the edge of the detection method. These observed contrasts across events highlight greater reactivity for smoke versus volcanic aerosols at warm temperatures. 

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3. Electrical breakdown dynamics in an argon bubble submerged in conductive liquid for nanosecond pulsed discharges

   https://doi.org/10.1088/1361-6463/acfb1b  

   L Sponsel, Nicholas; Gershman, Sophia; Stapelmann, Katharina (September 2023, Journal of Physics D: Applied Physics)

   Abstract This study delves into the dynamics of cold atmospheric plasma and their interaction within conductive solutions under the unique conditions of nanosecond pulsed discharges (22 kV peak voltage, 10 ns FWHM, 4.5 kV ns⁻¹rate-of-rise). The research focuses on the electrical response, breakdown, and discharge propagation in an argon bubble, submerged in a NaCl solution of varying conductivity. Full or partial discharges were observed at conductivities of 1.5µS cm⁻¹(deionized water) to 1.6 mS cm⁻¹, but no breakdown was observed at 11.0 mS cm⁻¹when reducing the electrode gap. It is demonstrated that at higher conductivity electric breakdown is observed only when the gas bubble comes into direct contact with the electrode and multiple emission nodes were observed at different timescales. These nodes expanded in the central region of the bubble over timescales longer than the initial high-voltage pulse. This work offers a temporal resolution of 2 ns exposure times over the first 30 ns of the initial voltage pulse, and insight into plasma formation over decaying reflected voltage oscillations over 200 ns. 

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4. Target sensitivity study of density transition-injected electrons in laser wakefield accelerators

   https://doi.org/10.1103/PhysRevAccelBeams.27.111301  

   Cobo, C C; Arran, C; Bourgeois, N; Calvin, L; Carderelli, J; Cavanagh, N; Colgan, C; Dann, S_J D; Fitzgarrald, R; Gerstmayr, E; et al (November 2024, Physical Review Accelerators and Beams)

   While plasma-based accelerators have the potential to positively impact a broad range of research topics, a route to application will only be possible through improved understanding of their stability. We present experimental results of a laser wakefield accelerator in the nonlinear regime in a helium gas jet target with a density transition produced by a razor blade in the flow. Modifications to the target setup are correlated with variations in the plasma density profile diagnosed via interferometry and the shot-to-shot variations of the density profile for nominally equal conditions are characterized. Through an in-depth sensitivity study using particle-in-cell simulations, the effects of changes in the plasma density profile on the accelerated electron beams are investigated. The results suggest that blade motion is more detrimental to stability than gas pressure fluctuations, and that early focusing of the laser may reduce the deleterious effects of such density fluctuations. Published by the American Physical Society2024 

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5. A multiphase simulation study of electrochemical discharge machining of glass

   https://doi.org/10.1007/s00170-019-04318-5  

   Kolhekar, Ketaki; Sundaram, Murali (September 2019, The International Journal of Advanced Manufacturing Technology)

   Micromachining of glass has gained importance due to numerous applications of glass in microfluidics, optics, electronics, and biotechnology industry. Electrochemical discharge machining (ECDM) is an emerging nontraditional process which has the potential for micromachining of glass with minimal surface damages. Material removal during the machining of glass by ECDM involves thermal machining by electrical discharges between the tool and the gas film. The energy of these discharges is influenced by the gas film characteristics and affects the machining results. In this study, a combined approach of finite element simulation and experimentation is used to study the ECDM process to understand the impact of gas film characteristics on the overcut in machining. The multiphase simulation setup incorporates a combined electrochemical system of glass and electrolyte. The changes in the gas film characteristics due to the variations in the level of electrolyte and the corresponding changes in the overcut are studied. It was observed that the gas film thickness increased with an increase in the level of electrolyte and the gas film stability showed an opposite trend. This resulted in an increase in the overcut in the machining with the increase in the level of electrolyte. This trend observed in the simulation was validated with experimentation. 

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