Publications

2018

• Chemical kinetics in an atmospheric pressure helium plasma containing humidity
  
  • Schröter Sandra
  • Wijaikhum Apiwat
  • Gibson Andrew
  • West Andrew
  • Davies Helen
  • Minesi Nicolas
  • Dedrick James
  • Wagenaars Erik
  • de Oliveira Nelson
  • Nahon Laurent
  • Kushner Mark
  • Booth Jean-Paul
  • Niemi Kari
  • Gans Timo
  • O'Connell Deborah
  Physical Chemistry Chemical Physics, Royal Society of Chemistry, 2018, 20 (37), pp.24263-24286. a Atmospheric pressure plasmas are sources of biologically active oxygen and nitrogen species, which makes them potentially suitable for the use as biomedical devices. Here, experiments and simulations are combined to investigate the formation of the key reactive oxygen species, atomic oxygen (O) and hydroxyl radicals (OH), in a radio-frequency driven atmospheric pressure plasma jet operated in humidified helium. Vacuum ultraviolet high-resolution Fourier-transform absorption spectroscopy and ultraviolet broad-band absorption spectroscopy are used to measure absolute densities of O and OH. These densities increase with increasing H 2 O content in the feed gas, and approach saturation values at higher admixtures on the order of 3 Â 10 14 cm À3 for OH and 3 Â 10 13 cm À3 for O. Experimental results are used to benchmark densities obtained from zero-dimensional plasma chemical kinetics simulations, which reveal the dominant formation pathways. At low humidity content, O is formed from OH + by proton transfer to H 2 O, which also initiates the formation of large cluster ions. At higher humidity content, O is created by reactions between OH radicals, and lost by recombination with OH. OH is produced mainly from H 2 O + by proton transfer to H 2 O and by electron impact dissociation of H 2 O. It is lost by reactions with other OH molecules to form either H 2 O + O or H 2 O 2. Formation pathways change as a function of humidity content and position in the plasma channel. The understanding of the chemical kinetics of O and OH gained in this work will help in the development of plasma tailoring strategies to optimise their densities in applications. (10.1039/c8cp02473a)
  DOI : 10.1039/c8cp02473a
• Reconnexion magnétique entre le vent solaire et la magnétosphère
  
  • Rezeau Laurence
  • Belmont Gérard
  Reflets de la Physique, EDP sciences, 2018 (59), pp.20. Dans le vent solaire, plasma et champ magnétique se déplacent ensemble à grande échelle. L'interface avec la magnétosphère terrestre est une frontière fine, la magnétopause, où il peut exister des échelles suffisamment petites pour dissocier les deux mouvements. Il en résulte un phénomène nommé "reconnexion magnétique" au cours duquel le plasma est fortement accéléré le long de la frontière. La mission MMS a des points forts qui en font le meilleur outil pour étudier ce phénomène : une résolution temporelle des mesures inégalée et des satellites très proches les uns des autres (environ 10 km, de l'ordre du rayon de Larmor des électrons). (10.1051/refdp/201859020)
  DOI : 10.1051/refdp/201859020
• Introduction à la physique des plasmas
  
  • Belmont Gérard
  • Rezeau Laurence
  • Riconda C.
  • Zaslavsky A.
  , 2018. Les plasmas sont peu présents dans notre environnement immédiat et leurs propriétés sont parfois ignorées des physiciens. Il sagit pourtant de phénomènes universels quon rencontre depuis les décharges électriques jusquaux jets galactiques. Lobjectif de cet ouvrage est doffrir une introduction aux phénomènes variés qui constituent la physique des plasmas avec comme seul prérequis davoir une connaissance de la physique de base. Il présente en parallèle les fondements de la théorie des plasmas et un certain nombre dapplications aux plasmas de laboratoire ou aux plasmas naturels. Un accent particulier est mis sur lexistence des plasmas sans collision, dans lesquels le comportement collectif du milieu est dû seulement au champ électromagnétique moyen qui régit les trajectoires des particules. Ceci permet de porter un regard neuf sur des notions déjà abordées dans dautres disciplines, mais aussi de comprendre les liens qui existent entre les théories fluides, en particulier pour létude de la propagation des ondes.
• Anomalous electron transport in Hall-effect thrusters: Comparison between quasi-linear kinetic theory and particle-in-cell simulations
  
  • Lafleur Trevor
  • Martorelli Roberto
  • Chabert Pascal
  • Bourdon Anne
  Physics of Plasmas, American Institute of Physics, 2018, 25 (6), pp.061202. Kinetic drift instabilities have been implicated as a possible mechanism leading to anomalous electron cross-field transport in E B discharges, such as Hall-effect thrusters. Such instabilities, which are driven by the large disparity in electron and ion drift velocities, present a significant challenge to modelling efforts without resorting to time-consuming particle-in-cell (PIC) simulations. Here, we test aspects of quasi-linear kinetic theory with 2D PIC simulations with the aim of developing a self-consistent treatment of these instabilities. The specific quantities of interest are the instability growth rate (which determines the spatial and temporal evolution of the instability amplitude), and the instability-enhanced electron-ion friction force (which leads to anomalous electron transport). By using the self-consistently obtained electron distribution functions from the PIC simulations (which are in general non-Maxwellian), we find that the predictions of the quasilinear kinetic theory are in good agreement with the simulation results. By contrast, the use of Maxwellian distributions leads to a growth rate and electron-ion friction force that is around 24 times higher, and consequently significantly overestimates the electron transport. A possible method for self-consistently modelling the distribution functions without requiring PIC simulations is discussed (10.1063/1.5017626)
  DOI : 10.1063/1.5017626
• Sodium Ion Dynamics in the Magnetospheric Flanks of Mercury
  
  • Aizawa Sae
  • Delcourt Dominique C.
  • Terada N.
  Geophysical Research Letters, American Geophysical Union, 2018, 45, pp.595-601. We investigate the transport of planetary ions in the magnetospheric flanks of Mercury. In situ measurements from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging spacecraft show evidences of Kelvin-Helmholtz instability development in this region of space, due to the velocity shear between the downtail streaming flow of solar wind originating protons in the magnetosheath and the magnetospheric populations. Ions that originate from the planet exosphere and that gain access to this region of space may be transported across the magnetopause along meandering orbits. We examine this transport using single-particle trajectory calculations in model Magnetohydrodynamics simulations of the Kelvin-Helmholtz instability. We show that heavy ions of planetary origin such as Na<SUP> </SUP> may experience prominent nonadiabatic energization as they <fi>E</fi> × <fi>B</fi> drift across large-scale rolled up vortices. This energization is controlled by the characteristics of the electric field burst encountered along the particle path, the net energy change realized corresponding to the maximum <fi>E</fi> × <fi>B</fi> drift energy. This nonadiabatic energization also is responsible for prominent scattering of the particles toward the direction perpendicular to the magnetic field. (10.1002/2017GL076586)
  DOI : 10.1002/2017GL076586
• Effect of frequency on the uniformity of symmetrical RF CCP discharges
  
  • Liu Yue
  • Booth Jean-Paul
  • Chabert Pascal
  Plasma Sources Science and Technology, IOP Publishing, 2018, 27 (5), pp.055012. A 2D Cartesian electrostatic particle-in-cell/Monte Carlo collision (PIC/MCC) model presented previously (Liu et al 2018 Plasma Sources Sci. Technol. 27 025006) is used to investigate the effect of the driving frequency (over the range of 15?45 MHz) on the plasma uniformity in radio frequency (RF) capacitively coupled plasma (CCP) discharges in a geometrically symmetric reactor with a dielectric side wall in argon gas. The reactor size (12 cm electrode length, 2.5 cm gap) and driving frequency are sufficiently small that electromagnetic effects can be ignored. Previously, we showed (Liu et al 2018 Plasma Sources Sci. Technol. 27 025006) that for 15 MHz excitation, Ohmic heating of electrons by the electric field perpendicular to the electrodes is enhanced in a region in front of the dielectric side wall, leading to a maximum in electron density there. In this work we show that increasing the excitation frequency (at constant applied voltage amplitude) not only increases the overall electron heating and density but also causes a stronger, narrower peak in electron heating closer to the dielectric wall, improving the plasma uniformity along the electrodes. This heating peak comes both from enhanced perpendicular electron heating and from the appearance at high frequency of significant parallel heating. The latter is caused by the presence of a significant parallel-direction RF oscillating electric field in the corners. Whereas at the reactor center the sheaths oscillate perpendicularly to the electrodes, near the dielectric edge they move in and out of the corners and must be treated in two dimensions. (10.1088/1361-6595/aabfb4)
  DOI : 10.1088/1361-6595/aabfb4
• Observations of the Electron Jet Generated by Secondary Reconnection in the Terrestrial Magnetotail
  
  • Huang S. Y.
  • Jiang K.
  • Yuan Z. G.
  • Sahraoui Fouad
  • He L. H.
  • Zhou M.
  • Fu H. S.
  • Deng X. H.
  • He J. S.
  • Cao D.
  • Yu X. D.
  • Wang D. D.
  • Burch J. L.
  • Pollock C. J.
  • Torbert R. B.
  The Astrophysical Journal, American Astronomical Society, 2018, 862 (2), pp.144. We report in situ observations of an electron jet generated by secondary reconnection within the outflow region of primary reconnection in the terrestrial magnetotail by the Magnetospheric Multiscale (MMS) mission. The MMS spacecraft first passed through the primary X-line and then crossed the electron jet in the outflow of primary reconnection. There are a series of small-scale flux ropes in the secondary reconnection region. Decoupling from the magnetic field for both ions and electrons, an intense out-of-plane current, unambiguous Hall currents, and a Hall electromagnetic field appear in the electron jet. Strong electron dissipation (), a nonzero electric field in the electron frame (), and electron crescent-like shaped distributions are detected in the center of the electron jet, implying that MMS spacecraft were likely passing through the electron diffusion region. The significant electron dissipation indicates that the electrons can be accelerated in the electron jet and the electron jet may be another important electron acceleration channel along with the electron diffusion region. (10.3847/1538-4357/aacd4c)
  DOI : 10.3847/1538-4357/aacd4c
• Comparative Study between Direct and Indirect Treatment with Cold Atmospheric Plasma on In Vitro and In Vivo Models of Wound Healing
  
  • Duchesne Constance
  • Frescaline Nadira
  • Lataillade Jean-Jacques
  • Rousseau Antoine
  Plasma Medicine, Begell House, 2018, 8 (4), pp.379-401. Cold-atmospheric plasma (CAP) produces a mixture of molecular, ionic, and radical species as well as electric field visible and ultraviolet lights. Biological effects of CAP and its therapeutic potential have been studied in disciplines such as dermatology, oncology, and dentistry. This study investigates both in vitro and in vivo effects of direct and indirect plasma treatment and their influences on wound healing. The effect of plasma treatment on cellular viability, migration, and proliferation are studied using keratinocytes, fibroblasts, and endothelial cells. Plasma is generated in a helium jet using an alternating-current 50-Hz power supply at 32 kV and 90 mW. Results show that 1-min direct CAP treatment stimulates skin cell migration; however, cellular proliferation remains unchanged. Treatment > 3 min leads to cell death. Using the same treatment parameters, notably exposure time, indirect treatment using a plasma-activated medium fails to stimulate cellular migration. A murine model of full-thickness excisional wound healing is used to study the effect of CAP on wound closure. In vivo studies demonstrate that both direct and indirect treatment do not affect acute wound closure in mice. Taken together, these results suggest that direct plasma treatment with homemade plasma devices has the potential to positively influence wound healing, but optimum parameters and suitable wound models must be identified and validated. (10.1615/PlasmaMed.2019028659)
  DOI : 10.1615/PlasmaMed.2019028659
• Validation of gyrokinetic simulations with measurements of electron temperature fluctuations and density-temperature phase angles on ASDEX Upgrade
  
  • Freethy S. J.
  • Görler T.
  • Creely A. J.
  • Conway G. D.
  • Denk S. S.
  • Happel T.
  • Koenen C.
  • Hennequin Pascale
  • White A. E.
  Physics of Plasmas, American Institute of Physics, 2018, 25 (5), pp.055903. Measurements of turbulent electron temperature fluctuation amplitudes, dTe?=T e, frequency spectra, and radial correlation lengths, LrðT e? Þ, have been performed at ASDEX Upgrade using a newly upgraded Correlation ECE diagnostic in the range of scales k? < 1:4 cm1; k r < 3:5 cm1 (k?qs < 0:28 and k rqs < 0:7). The phase angle between turbulent temperature and density fluctuations, anT, has also been measured by using an ECE radiometer coupled to a reflectometer along the same line of sight. These quantities are used simultaneously to constrain a set of ion- scale non-linear gyrokinetic turbulence simulations of the outer core (qtor ¼ 0.75) of a low density, electron heated L-mode plasma, performed using the gyrokinetic simulation code, GENE. The ion and electron temperature gradients were scanned within uncertainties. It is found that gyrokinetic simulations are able to match simultaneously the electron and ion heat flux at this radius within the experimental uncertainties. The simulations were performed based on a reference discharge for which dT e?=T e measurements were available, and L rðTe? Þ and anT were then predicted using syn- thetic diagnostics prior to measurements in a repeat discharge. While temperature fluctuation amplitudes are overestimated by >50% for all simulations within the sensitivity scans performed, good quantitative agreement is found for L rðT e? Þ and anT. A validation metric is used to quantify the level of agreement of individual simulations with experimental measurements, and the best agreement is found close to the experimental gradient values. Published by AIP Publishing. (10.1063/1.5018930)
  DOI : 10.1063/1.5018930
• Erratum: Numerical study of the influence of surface reaction probabilities on reactive species in an rf atmospheric pressure plasma containing humidity (2017 Plasma Phys. Control. Fusion 60 014035)
  
  • Schröter Sandra
  • Gibson Andrew R.
  • Kushner Mark J.
  • Gans Timo
  • O'Connell Deborah
  Plasma Physics and Controlled Fusion, IOP Publishing, 2018, 60. Not Available (10.1088/1361-6587/aa9a6b)
  DOI : 10.1088/1361-6587/aa9a6b
• A turbulent cascade model of bounce averaged gyrokinetics
  
  • Xu S.
  • Morel Pierre
  • Gürcan Özgür D.
  Physics of Plasmas, American Institute of Physics, 2018, 25 (2), pp.022304. A shell model is derived for the description of nonlinear bounce averaged gyrokinetics, which is one of the simplest kinetic descriptions in magnetized plasmas. In order to validate the numerical implementation, detailed linear evolution of the system is compared with a linear benchmark based on solving the linear dispersion relation numerically. The resulting wave number spectrum, which extends over 34 decades, is shown to have a robust general structure to model parameters, such as dissipation or the ratio of linear energy injection to nonlinear transfer. In a range of wave numbers where the nonlinear transfer term is dominant, a power law spectrum, roughly of the form k&#8722;4 , is observed for the spectral electrostatic potential energy density. The model, being fully kinetic, can be used to obtain the free energy spectra for ion and electron distribution functions as functions of E. This model constitutes the first numerical implementation of a kinetic shell model. (10.1063/1.5020145)
  DOI : 10.1063/1.5020145
• Study of Ionospheric Variability Using GNSS Observations
  
  • Jouan Taoufiq
  • Bouziani Mourad
  • Azzouzi Rachid
  • Amory-Mazaudier Christine
  Positioning, SCIRP, 2018 (9), pp.79-96. With the increasing number of applications of Global navigation satellite system, the modeling of the ionosphere is a crucial element for precise positioning. Indeed, the ionosphere delays the electromagnetic waves which pass through it and induces a delay of propagation related to the electronic density (TEC) Total Electronic Content and to the frequency of the wave. The impact of this ionospheric error often results in a poor determination of the stations position, particularly in strong solar activity. The first part of this paper focuses on a bibliographic study oriented first of all on the study of the ionosphere in relation to solar activity and secondly on the determination of the total electron content using GNSS measurements from the IGS network reference stations. Measurements were made on two permanent stations RABT, TETN. We selected years of GNSS measurements to evaluate the geomagnetic impact on the ionosphere, 2001, 2009 and 2013. A description of the ionospheric disturbances and geomagnetic storms was analyzed by determination of TEC, especially in high solar activity. The results show a strong dependence of the ionospheric activity with the geomagnetic activity. (10.4236/pos.2018.94006)
  DOI : 10.4236/pos.2018.94006
• Magnetic depression and electron transport in an ion-scale flux rope associated with Kelvin–Helmholtz waves
  
  • Tang Binbin
  • Li Wenya
  • Wang Chi
  • Dai Lei
  • Khotyaintsev Yuri
  • Lindqvist Per-Arne
  • Ergun Robert
  • Le Contel Olivier
  • Pollock Craig
  • Russell Christopher
  • Burch James
  Annales Geophysicae, European Geosciences Union, 2018, 36 (3), pp.879-889. We report an ion-scale magnetic flux rope (the size of the flux rope is ∼ 8.5 ion inertial lengths) at the trailing edge of Kelvin–Helmholtz (KH) waves observed by the Magnetospheric Multiscale (MMS) mission on 27 Septem-ber 2016, which is likely generated by multiple X-line re-connection. The currents of this flux rope are highly filamen-tary: in the central flux rope, the current flows are mainly parallel to the magnetic field, supporting a local magnetic field increase at about 7 nT, while at the edges the current filaments are predominantly along the antiparallel direction, which induce an opposing field that causes a significant magnetic depression along the axis direction (> 20 nT), meaning the overall magnetic field of this flux rope is depressed compared to the ambient magnetic field. Thus, this flux rope, accompanied by the plasma thermal pressure enhancement in the center, is referred to as a crater type. Intense lower hybrid drift waves (LHDWs) are found at the magnetospheric edge of the flux rope, and the wave potential is estimated to be ∼ 17 % of the electron temperature. Though LHDWs may be stabilized by the mechanism of electron resonance broadening , these waves could still effectively enable diffusive electron transports in the cross-field direction, corresponding to a local density dip. This indicates LHDWs could play important roles in the evolution of crater flux ropes. (10.5194/angeo-36-879-2018)
  DOI : 10.5194/angeo-36-879-2018
• Analyzing the Magnetopause Internal Structure: New Possibilities Offered by MMS Tested in a Case Study
  
  • Rezeau Laurence
  • Belmont Gérard
  • Manuzzo Roberto
  • Aunai Nicolas
  • Dargent Jérémy
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2018, 123 (1), pp.227-241. We explore the structure of the magnetopause using a crossing observed by the Magnetospheric Multiscale (MMS) spacecraft on 16 October 2015. Several methods (minimum variance analysis, BV method, and constant velocity analysis) are first applied to compute the normal to the magnetopause considered as a whole. The different results obtained are not identical, and we show that the whole boundary is not stationary and not planar, so that basic assumptions of these methods are not well satisfied. We then analyze more finely the internal structure for investigating the departures from planarity. Using the basic mathematical definition of what is a one‐dimensional physical problem, we introduce a new single spacecraft method, called LNA (local normal analysis) for determining the varying normal, and we compare the results so obtained with those coming from the multispacecraft minimum directional derivative (MDD) tool developed by Shi et al. (2005). This last method gives the dimensionality of the magnetic variations from multipoint measurements and also allows estimating the direction of the local normal when the variations are locally 1‐D. This study shows that the magnetopause does include approximate one‐dimensional substructures but also two‐ and three‐dimensional structures. It also shows that the dimensionality of the magnetic variations can differ from the variations of other fields so that, at some places, the magnetic field can have a 1‐D structure although all the plasma variations do not verify the properties of a global one‐dimensional problem. A generalization of the MDD tool is proposed. (10.1002/2017JA024526)
  DOI : 10.1002/2017JA024526
• Plasma-activation of tap water using DBD for agronomy applications: Identification and quantification of long lifetime chemical species and production/consumption mechanisms
  
  • Judée Florian
  • Simon Stéphane
  • Bailly Christophe
  • Dufour Thierry
  Water Research, IWA Publishing/Elsevier, 2018, 133, pp.47-59. Cold atmospheric plasmas are weakly ionized gases that can be generated in ambient air. They produce energetic species (e.g. electrons, metastables) as well as reactive oxygen species, reactive nitrogen species, UV radiations and local electric field. Their interaction with a liquid such as tap water can hence change its chemical composition. The resulting " plasma-activated liquid " can meet many applications, including medicine and agriculture. Consequently, a complete experimental set of analytical techniques dedicated to the characterization of long lifetime chemical species has been implemented to characterize tap water treated using cold atmospheric plasma process and intended to agronomy applications. For that purpose, colorimetry and acid titrations are performed, considering acid-base equilibria, pH and temperature variations induced during plasma activation. 16 species are quantified and monitored: hydroxide and hydronium ions, ammonia and ammonium ions, orthophosphates, carbonate ions, nitrite and nitrate ions and hydrogen peroxide. The related consumption/production mechanisms are discussed. In parallel, a chemical model of electrical conductivity based on Kohlrausch's law has been developed to simulate the electrical conductivity of the plasma-activated tap water (PATW). Comparing its predictions with experimental measurements leads to a narrow fitting, hence supporting the self-sufficiency of the experimental set, i.e. the fact that all long lifetime radicals of interest present in PATW are characterized. Finally, to evaluate the potential of cold atmospheric plasmas for agriculture applications, tap water has been daily plasma-treated to irrigate lentils seeds. Then, seedlings lengths have been measured and compared with untreated tap water, showing an increase as high as 34.0% and 128.4% after 3 days and 6 days of activation respectively. The interaction mechanisms between plasma and tap water are discussed as well as their positive synergy on agronomic results. (10.1016/j.watres.2017.12.035)
  DOI : 10.1016/j.watres.2017.12.035
• Fast gas heating of nanosecond pulsed surface dielectric barrier discharge: spatial distribution and fractional contribution from kinetics
  
  • Zhu Yifei
  • Starikovskaia Svetlana
  Plasma Sources Science and Technology, IOP Publishing, 2018, 27. The effect of heat release in reactions with charged and electronically excited species, or so-called fast gas heating (FGH), in nanosecond surface dielectric barrier discharge (nSDBD) in atmospheric pressure air is studied. Two-dimensional numerical simulations based on the PArallel Streamer Solver with KinEtics code are conducted. The code is based on the direct coupling of a self-consistent fluid model with detailed kinetics, an efficient photoionization model, and Euler equations. The choice of local field approximation for nSDBD modeling with simplified kinetics is discussed. The reduced electric field and the electron density are examined at both polarities for identical high-voltage pulses 24 kV in amplitude on a high-voltage electrode and 20 ns full width at half maximum. The distribution of the FGH energy and the resulting gas temperature field are studied and compared with findings in the literature. The input of different reactions to the appearance of hydrodynamic perturbations is analyzed. (10.1088/1361-6595/aaf40d)
  DOI : 10.1088/1361-6595/aaf40d
• Reply to Comment on `The case for in situ resource utilisation for oxygen production on Mars by non-equilibrium plasmas
  
  • Guerra Vasco
  • Silva Tiago
  • Ogloblina Polina
  • Grofulovic Marija
  • Terraz Loann
  • Lino da Silva Mário
  • Pintassilgo Carlos D.
  • Alves Luís L.
  • Guaitella Olivier
  Plasma Sources Science and Technology, IOP Publishing, 2018, 27. Not Available (10.1088/1361-6595/aaa570)
  DOI : 10.1088/1361-6595/aaa570
• Numerical study of the influence of surface reaction probabilities on reactive species in an rf atmospheric pressure plasma containing humidity
  
  • Schröter Sandra
  • Gibson Andrew R.
  • Kushner Mark J.
  • Gans Timo
  • O'Connell Deborah
  Plasma Physics and Controlled Fusion, IOP Publishing, 2018, 60. The quantification and control of reactive species (RS) in atmospheric pressure plasmas (APPs) is of great interest for their technological applications, in particular in biomedicine. Of key importance in simulating the densities of these species are fundamental data on their production and destruction. In particular, data concerning particle-surface reaction probabilities in APPs are scarce, with most of these probabilities measured in low-pressure systems. In this work, the role of surface reaction probabilities, gamma, of reactive neutral species (H, O and OH) on neutral particle densities in a He-H<SUB>2</SUB>O radio-frequency micro APP jet (COST-mu APPJ) are investigated using a global model. It is found that the choice of gamma, particularly for low-mass species having large diffusivities, such as H, can change computed species densities significantly. The importance of gamma even at elevated pressures offers potential for tailoring the RS composition of atmospheric pressure microplasmas by choosing different wall materials or plasma geometries. (10.1088/1361-6587/aa8fe9)
  DOI : 10.1088/1361-6587/aa8fe9
• New Insights into the Nature of Turbulence in the Earth's Magnetosheath Using Magnetospheric MultiScale Mission Data
  
  • Breuillard Hugo
  • Matteini L.
  • Argall M. R.
  • Sahraoui Fouad
  • Andriopoulou M.
  • Le Contel Olivier
  • Retinò Alessandro
  • Mirioni Laurent
  • Huang S. Y.
  • Gershman D. J.
  • Ergun R. E.
  • Wilder F. D.
  • Goodrich K. A.
  • Ahmadi N.
  • Yordanova E.
  • Vaivads A.
  • Turner D. L.
  • Khotyaintsev Y. V.
  • Graham D. B.
  • Lindqvist P.-A.
  • Chasapis A.
  • Burch J. L.
  • Torbert R. B.
  • Russell C. T.
  • Magnes W.
  • Strangeway R. J.
  • Plaschke F.
  • Moore T. E.
  • Giles B. L.
  • Paterson W. R.
  • Pollock C. J.
  • Lavraud B.
  • Fuselier S. A.
  • Cohen I. J.
  The Astrophysical Journal, American Astronomical Society, 2018, 859, pp.127. The Earth's magnetosheath, which is characterized by highly turbulent fluctuations, is usually divided into two regions of different properties as a function of the angle between the interplanetary magnetic field and the shock normal. In this study, we make use of high-time resolution instruments on board the Magnetospheric MultiScale spacecraft to determine and compare the properties of subsolar magnetosheath turbulence in both regions, i.e., downstream of the quasi-parallel and quasi-perpendicular bow shocks. In particular, we take advantage of the unprecedented temporal resolution of the Fast Plasma Investigation instrument to show the density fluctuations down to sub-ion scales for the first time. We show that the nature of turbulence is highly compressible down to electron scales, particularly in the quasi-parallel magnetosheath. In this region, the magnetic turbulence also shows an inertial (Kolmogorov-like) range, indicating that the fluctuations are not formed locally, in contrast with the quasi-perpendicular magnetosheath. We also show that the electromagnetic turbulence is dominated by electric fluctuations at sub-ion scales (f &gt; 1 Hz) and that magnetic and electric spectra steepen at the largest-electron scale. The latter indicates a change in the nature of turbulence at electron scales. Finally, we show that the electric fluctuations around the electron gyrofrequency are mostly parallel in the quasi-perpendicular magnetosheath, where intense whistlers are observed. This result suggests that energy dissipation, plasma heating, and acceleration might be driven by intense electrostatic parallel structures/waves, which can be linked to whistler waves. (10.3847/1538-4357/aabae8)
  DOI : 10.3847/1538-4357/aabae8
• Plasma-catalytic mineralization of toluene adsorbed on CeO<SUB>2</SUB>
  
  • Jia Zixian
  • Wang Xianjie
  • Foucher Emeric
  • Thevenet Frederic
  • Rousseau Antoine
  Catalysts, MDPI, 2018, 8 (8), pp.303. In the context of coupling nonthermal plasmas with catalytic materials, CeO2 is used as adsorbent for toluene and combined with plasma for toluene oxidation. Two configurations are addressed for the regeneration of toluene saturated CeO2: (i) in plasma-catalysis (IPC); and (ii) post plasma-catalysis (PPC). As an advanced oxidation technique, the performances of toluene mineralization by the plasma-catalytic systems are evaluated and compared through the formation of CO2. First, the adsorption of 100 ppm of toluene onto CeO2 is characterized in detail. Total, reversible and irreversible adsorbed fractions are quantified. Specific attention is paid to the influence of relative humidity (RH): (i) on the adsorption of toluene on CeO2; and (ii) on the formation of ozone in IPC and PPC reactors. Then, the mineralization yield and the mineralization efficiency of adsorbed toluene are defined and investigated as a function of the specific input energy (SIE). Under these conditions, IPC and PPC reactors are compared. Interestingly, the highest mineralization yield and efficiency are achieved using the in-situ configuration operated with the lowest SIE, that is, lean conditions of ozone. Based on these results, the specific impact of RH on the IPC treatment of toluene adsorbed on CeO2 is addressed. Taking into account the impact of RH on toluene adsorption and ozone production, it is evidenced that the mineralization of toluene adsorbed on CeO2 is directly controlled by the amount of ozone produced by the discharge and decomposed on the surface of the coupling material. Results highlight the key role of ozone in the mineralization process and the possible detrimental effect of moisture. (10.3390/catal8080303)
  DOI : 10.3390/catal8080303
• Plasmaspheric Plumes and EMIC Rising Tone Emissions
  
  • Grison B.
  • Hanzelka M.
  • Breuillard Hugo
  • Darrouzet F.
  • Santolík O.
  • Cornilleau-Wehrlin Nicole
  • Dandouras I.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2018, 123 (11), pp.9443-9452. Due to its polar orbit Cluster spacecraft crossed plasmaspheric plumes out of the magnetic equatorial plane. We study the occurrence of broadband, narrowband, and rising tone emissions in the plume vicinity, below the local proton gyrofrequency. Based on a database of 935 Cluster plumes crossings, reduced to 189 unique plumes, we find that broadband activity is the most common case. We confirm result from a previous study showing that plume vicinity is not a preferred place for observing narrowband emissions. Rising tones are the less frequently observed of these three kinds of emissions. Nevertheless, ElectroMagnetic Ion Cyclotron (EMIC) rising tone occurrence rate is high compared to the narrowband one: Tones are seen in six of 30 plume events (20%) when narrowband emissions are observed. Rising tones are observed at absolute magnetic latitudes larger than 17° and up to 35° . We detail the 16 August 2005 plume crossing when a rising tone is observed. Results of a ray tracing analysis agree with a tone triggering process taking place above 15° of magnetic latitude. (10.1029/2018JA025796)
  DOI : 10.1029/2018JA025796
• Generation of Electron Whistler Waves at the Mirror Mode Magnetic Holes: MMS Observations and PIC Simulation
  
  • Ahmadi N.
  • Wilder F. D.
  • Ergun R. E.
  • Argall M.
  • Usanova M. E.
  • Breuillard Hugo
  • Malaspina D.
  • Paulson K.
  • Germaschewski K.
  • Eriksson S.
  • Goodrich K. A.
  • Torbert R.
  • Le Contel Olivier
  • Strangeway R. J.
  • Russell C. T.
  • Burch J. L.
  • Giles B. L.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2018, 123, pp.6383-6393. The Magnetospheric Multiscale mission has observed electron whistler waves at the center and at the edges of magnetic holes in the dayside magnetosheath. The magnetic holes are nonlinear mirror structures since their magnitude is anticorrelated with particle density. In this article, we examine the growth mechanisms of these whistler waves and their interaction with the host magnetic hole. In the observations, as magnetic holes develop and get deeper, an electron population gets trapped and develops a temperature anisotropy favorable for whistler waves to be generated. In addition, the decrease in magnetic field magnitude and the increase in density reduce the electron resonance energy, which promotes the electron cyclotron resonance. To investigate this process, we used expanding box particle-in-cell simulations to produce the mirror instability, which then evolve into magnetic holes. The simulation shows that whistler waves can be generated at the center and edges of magnetic holes, which reproduces the primary features of the MMS observations. The simulation shows that the electron temperature anisotropy develops in the center of the magnetic hole once the mirror instability reaches its nonlinear stage of evolution. The plasma is then unstable to whistler waves at the minimum of the magnetic field structures. In the saturation regime of mirror instability, when magnetic holes are developed, the electron temperature anisotropy appears at the edges of the holes and electron distributions become more isotropic at the magnetic field minimum. At the edges, the expansion of magnetic holes decelerates the electrons, which leads to temperature anisotropies. (10.1029/2018JA025452)
  DOI : 10.1029/2018JA025452
• Excitation and relaxation of the asymmetric stretch mode of CO<SUB>2</SUB> in a pulsed glow discharge
  
  • Klarenaar Bart
  • Morillo-Candas Ana-Sofia
  • Grofulovic Marija
  • Sanden Richard van De
  • Engeln Richard
  • Guaitella Olivier
  Plasma Sources Science and Technology, IOP Publishing, 2018, 28, pp.035011. The excitation and relaxation of the vibrations of CO₂ as well as the reduction of CO₂ to CO are studied in a pulsed glow discharge. Two diagnostics are employed, being (1) time-resolved <i>in situ</i> Fourier transform infrared (FTIR) spectroscopy and (2) spatiotemporally resolved <i>in situ</i> rotational Raman spectroscopy. Experiments are conducted within a pressure range of 1.3-6.7 mbar and a current range of 10-50 mA. In the afterglow, the rate of exponential decay from the asymmetric stretch temperature (<i>T</i>₃) to the rotational temperature (<i>T</i>_rot) is found to be only dependent on <i>T</i>_rot, in the conditions under study. The decay rate <i>&#961;</i>_{<i>T</i>₃-<i>T</i>_rot} follows the relation <i>&#961;</i>_{<i>T</i>₃-<i>T</i>_rot} = 388 s^-1 exp((<i>T</i>_rot - 273 K)/(154 K)). Pressure and varying concentrations of CO and (presumably) atomic oxygen did not show to be of significant influence. In the active part of the discharge the excitation of <i>T</i>₃ showed to be positively related to current and negatively to pressure. However, the contribution of current to vibrational excitation is ambiguous: the conversion of CO₂ and therefore the fraction of CO in the discharge, is found to be strongly dependent on the current, with a conversion factor of 0.05 to 0.18 for 10 mA to 50 mA, while CO can contribute to the excitation through near-resonant collisions. A clear relation between the elevation of <i>T</i>₃ and the dissociation of CO₂ could not be confirmed, though conversion peaks are observed in the near afterglow, which motivate future experiments on vibrational ladder-climbing directly after termination of the discharge. (10.1088/1361-6595/aada5e)
  DOI : 10.1088/1361-6595/aada5e
• Kinetic study of low-temperature CO<SUB>2</SUB> plasmas under non-equilibrium conditions. I. Relaxation of vibrational energy
  
  • Silva Tiago
  • Grofulovic Marija
  • Klarenaar Bart
  • Morillo-Candas Ana-Sofia
  • Guaitella Olivier
  • Engeln Richard
  • Pintassilgo C.D.
  • Guerra V.
  Plasma Sources Science and Technology, IOP Publishing, 2018, 27 (1), pp.015019. A kinetic model to describe the time evolution of ~ 70 individual CO2(X-1 Sigma( )) vibrational levels during the afterglow of a pulsed DC glow discharge is developed in order to contribute towards the understanding of vibrational energy transfer in CO2 plasmas. The results of the simulations are compared against in situ Fourier Transform Infrared spectroscopy data obtained in a pulsed dc glow discharge and its afterglow at pressures of a few Torr and discharge currents around 50 mA. The very good agreement between the model predictions and the experimental results shows a validation of the kinetic scheme considered and the corresponding V-T and V-V rate coefficients. In this sense, it establishes a reaction mechanism for the vibrational kinetics of these CO2 energy levels and delivers a firm basis to understand the vibrational relaxation in CO2 plasmas. It is shown that first-order perturbation theories, namely Schwartz-Slawsky-Herzfeld (SSH) and Sharma-Brau (SB) methods, provide a good description of CO2 vibrations under low excitation regimes. (10.1088/1361-6595/aaa56a)
  DOI : 10.1088/1361-6595/aaa56a
• Numerical study on the time evolutions of the electric field in helium plasma jets with positive and negative polarities
  
  • Viegas Pedro
  • Pechereau François
  • Bourdon Anne
  Plasma Sources Science and Technology, IOP Publishing, 2018, 27, pp.025007. This paper presents 2D simulations of atmospheric pressure discharges in helium with N2 and O2 admixtures, propagating in a dielectric tube between a point electrode and a grounded metallic target. For both positive and negative polarities, the propagation of the first ionization front is shown to correspond to a peak of the absolute value of the axial electric field inside the tube, but also outside the tube. After the impact on the metallic target, a rebound front is shown to propagate from the target to the point electrode. This rebound front is 23 times faster than the first ionization front. Close to the high voltage point, this rebound front corresponds to a second peak of the absolute value of the axial electric field. Close to the target, as the first ionization and rebound fronts are close in time, only one peak is observed. The dynamics of the absolute value of the radial component of electric field outside the tube is shown to present an increase during the first ionization front propagation and a fast decrease corresponding to the propagation of the rebound front. These time evolutions of the electric field components are in agreement with experiments. Finally, we have shown that the density of metastable He * in 99% He1% N2 and 99% He1% O2 atmospheric pressure discharges are very close. Close to the grounded target, the peak density of reactive species is significantly increased due to the synergy between the first ionization and rebound fronts, as observed in experiments. Similar results are obtained for both voltage polarities, but the peak density of metastable He* close to the target is shown to be two times less in negative polarity than in positive polarity. (10.1088/1361-6595/aaa7d4)
  DOI : 10.1088/1361-6595/aaa7d4