Publications

2018

• 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
• 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
• 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
• 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−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
• 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
• 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
• 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
• 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.
• 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
• 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
• Exact law for homogeneous compressible Hall magnetohydrodynamics turbulence
  
  • Andrés Nahuel
  • Galtier Sébastien
  • Sahraoui Fouad
  Physical Review E, American Physical Society (APS), 2018, 97 (1), pp.013204. We derive an exact law for three-dimensional (3D) homogeneous compressible isothermal Hall magnetohydrodynamic turbulence, without the assumption of isotropy. The Hall current is shown to introduce new flux and source terms that act at the small scales (comparable or smaller than the ion skin depth) to significantly impact the turbulence dynamics. The law provides an accurate means to estimate the energy cascade rate over a broad range of scales covering the magnetohydrodynamic inertial range and the sub-ion dispersive range in 3D numerical simulations and in in situ spacecraft observations of compressible turbulence. This work is particularly relevant to astrophysical flows in which small-scale density fluctuations cannot be ignored such as the solar wind, planetary magnetospheres, and the interstellar medium. (10.1103/PhysRevE.97.013204)
  DOI : 10.1103/PhysRevE.97.013204
• 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
• 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
• 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
• 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
• Drift-wave observation in a toroidal magnetized plasma and comparison with a modified Hasegawa-Wakatani model
  
  • Donnel Peter
  • Morel Pierre
  • Honoré Cyrille
  • Gürcan Özgür D.
  • Pisarev V.
  • Metzger C.
  • Hennequin Pascale
  Physics of Plasmas, American Institute of Physics, 2018, 25 (6), pp.062127. This paper presents the results of fluctuation measurements in a toroidal magnetized plasma, using Langmuir probes, and comparisons between the observed frequency modes and a Hasegawa-Wakatani model including curvature, adapted to the specifics of the toroidal device. More precisely, two kinds of signals are detected in the presence of an additional vertical magnetic field in the region of significant density and potential gradients. A high frequency, propagating component, corresponding to dissipative drift-waves in the curved magnetic field, is observed and the frequency and typical wavelengths are found to be in good agreement with the linear Hasegawa-Wakatani model including curvature effects. A second, low frequency component is observed at lower frequencies and is shown to correspond to large scale vertical electrostatic field structures. A significantly high level of cross correlation is observed between these two signals, with an identifiable time delay, which suggests an analogy to the time delayed quasi-periodic dynamics in predator-prey systems, and a similar phenomenon is observed between zonal flows and microturbulence in tokamaks and other magnetised plasma systems. (10.1063/1.5025141)
  DOI : 10.1063/1.5025141
• Electron Jet Detected by MMS at Dipolarization Front
  
  • Liu C. M.
  • Fu H.S.
  • Vaivads A.
  • Khotyaintsev Y. V.
  • Gershman D. J.
  • Hwang K.-J.
  • Chen Z. Z.
  • Cao D.
  • Xu Y.
  • Yang J.
  • Peng F. Z.
  • Huang S. Y.
  • Burch J. L.
  • Giles B. L.
  • Ergun R. E.
  • Russell C. T.
  • Lindqvist P.-A.
  • Le Contel Olivier
  Geophysical Research Letters, American Geophysical Union, 2018, 45 (2), pp.556-564. Using MMS high-resolution measurements, we present the first observation of fast electron jet (<fi>V</fi><SUB><fi>e</fi></SUB> 2,000 km/s) at a dipolarization front (DF) in the magnetotail plasma sheet. This jet, with scale comparable to the DF thickness ( 0.9 <fi>d</fi><SUB><fi>i</fi></SUB>), is primarily in the tangential plane to the DF current sheet and mainly undergoes the E × B drift motion; it contributes significantly to the current system at the DF, including a localized ring-current that can modify the DF topology. Associated with this fast jet, we observed a persistent normal electric field, strong lower hybrid drift waves, and strong energy conversion at the DF. Such strong energy conversion is primarily attributed to the electron-jet-driven current (E s j<SUB><fi>e</fi></SUB> &#8776; 2 E s j<SUB><fi>i</fi></SUB>), rather than the ion current suggested in previous studies. (10.1002/2017GL076509)
  DOI : 10.1002/2017GL076509
• A rotational Raman study under non-thermal conditions in a pulsed CO<SUB>2</SUB> glow discharge
  
  • Klarenaar Bart
  • Grovulović Marija
  • Morillo-Candas Ana-Sofia
  • Bekerom D C M van Den
  • Damen Mark
  • Sanden Richard van De
  • Guaitella Olivier
  • Engeln Richard
  Plasma Sources Science and Technology, IOP Publishing, 2018, 27 (4), pp.045009. The implementation of in situ rotational Raman spectroscopy is realized for a pulsed glow discharge in CO2 in the mbar range and is used to study the rotational temperature and molecular number densities of CO2, CO, and O2. The polarizability anisotropy of these molecules is required for extracting number densities from the recorded spectra and is determined for incident photons of 532 nm. The spatiotemporally-resolved measurements are performed in the same reactor and at equal discharge conditions (510 ms onoff cycle, 50 mA plasma current, 6.7 mbar pressure) as in recently published work employing in situ Fourier transform infrared (FTIR) spectroscopy. The rotational temperature ranges from 394 to 809 K from start to end of the discharge pulse and is constant over the length of the reactor. The discharge is demonstrated to be spatially uniform in gas composition, with a CO2 conversion factor of 0.15 ± 0.02. Rotational temperatures and molecular composition agree well with the FTIR results, while the spatial uniformity confirms the assumption made for the FTIR analysis of a homogeneous medium over the line-of-sight of absorption. Furthermore, the rotational Raman spectra of CO2 are related to vibrational temperatures through the vibrationally averaged nuclear spin degeneracy, which is expressed in the intensity ratio between even and odd numbered Raman peaks. The elevation of the odd averaged degeneracy above thermal conditions agrees well with the elevation of vibrational temperatures of CO2, acquired in the FTIR study. (10.1088/1361-6595/aabab6)
  DOI : 10.1088/1361-6595/aabab6
• Self-organized patterns by a DC pin liquid anode discharge in ambient air: Effect of liquid types on formation
  
  • Zhang Shiqiang
  • Dufour Thierry
  Physics of Plasmas, American Institute of Physics, 2018, 25 (7), pp.073502. A pin liquid anode DC discharge is generated in open air without any additional gas feeding to form self-organized patterns (SOPs) on various liquid interfaces. Axially resolved emission spectra of the whole discharge reveal that the self-organized patterns are formed below a dark region and are visible mainly due to the N2 (C 3 -B 3 ) transitions. The high energy N2 (C) level is mainly excited by the impact of electrons heated by the local increased electric field at the interface. For the first time, the effect of the liquid type on the SOP formation is presented. With almost the same other discharge conditions, the formed SOPs are significantly different from HCl and H2SO4 liquid anodes. The SOP difference is repeated when the discharge current and gap distance change for both liquid anodes. The variations of SOP size and discretization as a function of discharge current and gap distance are discussed and confirm that different SOPs are formed by the HCl liquid anode from tap water or the H2SO4 liquid anode. A possible explanation is brought up to explain the dependence of SOPs on the liquid type. (10.1063/1.5030099)
  DOI : 10.1063/1.5030099
• Logarithmically discretized model of bounce averaged gyrokinetics and its implications on tokamak turbulence
  
  • Xu S.
  • Morel Pierre
  • Gürcan Özgür D.
  Physics of Plasmas, American Institute of Physics, 2018, 25 (10), pp.102306. A logarithmically discretized model, which consists of writing the system in log polar coordinates in wave-number domain and reducing the nonlinear interactions to a sum over neighboring scales that satisfy the triad conditions, is proposed for bounce averaged gyrokinetics, where the energy dependence is kept over a semi-regular grid that allows quadrature calculations in order to guarantee quasi-neutrality. The resulting model is a cheaper implementation of nonlinear multi-scale physics involving trapped electron modes, trapped ion modes, and zonal flows, which can handle anisotropy. The resulting wave-number spectrum is anisotropic at large scales, where the energy injection is clearly anisotropic, but is isotropised rapidly, leading generally towards an isotropic k&#8722;4 spectrum for spectral potential energy density for fully kinetic system and a k&#8722;5 spectrum for the system with one adiabatic species. Zonal flow damping, which is necessary for reaching a steady state in this model, plays an important role along with electron adiabaticity. Interesting dynamics akin to predator-prey evolution is observed among zonal flows and similarly large scale but radially elongated structures. (10.1063/1.5049681)
  DOI : 10.1063/1.5049681
• Living on mars: how to produce oxygen and fuel to get home
  
  • Guerra V.
  • Silva Tiago
  • Guaitella Olivier
  Europhysics News, EDP Sciences, 2018, 49 (3), pp.15-18. Sending a manned mission to Mars is one of the next major steps in space exploration. Creating a breathable environment, however, is a substantial challenge. A sustainable oxygen supply on the red planet can be achieved by converting carbon dioxide directly from the Martian atmosphere. A new solution to do so is on the way: plasma technology. (10.1051/epn/2018302)
  DOI : 10.1051/epn/2018302
• Observations of Whistler Waves Correlated with Electron-scale Coherent Structures in the Magnetosheath Turbulent Plasma
  
  • Huang S. Y.
  • Sahraoui Fouad
  • Yuan Z. G.
  • Le Contel Olivier
  • Breuillard Hugo
  • He J. S.
  • Zhao J. S.
  • Fu H.S.
  • Zhou M.
  • Deng X. H.
  • Wang X. Y.
  • Du J. W.
  • Yu X. D.
  • Wang D. D.
  • Pollock C. J.
  • Torbert R. B.
  • Burch J. L.
  The Astrophysical Journal, American Astronomical Society, 2018, 861. A new type of electron-scale coherent structure, referred to as electron vortex magnetic holes, was identified recently in the Earth's magnetosheath turbulent plasma. These electron-scale magnetic holes are characterized by magnetic field strength depression, electron density enhancement, temperature and temperature anisotropy increase (a significant increase in perpendicular temperature and a decrease in parallel temperature), and an electron vortex formed by the trapped electrons. The strong increase of electron temperature indicates that these magnetic holes have a strong connection with the energization of electrons. Here, using high time resolution in situ measurements from the MMS mission, it is further shown that electron-scale whistler waves coexist with electron-scale magnetic holes. These whistler waves were found not propagating from remote regions, but generated locally due to electron temperature anisotropy (T <SUB>e&#8869;</SUB>/T <SUB>e||</SUB>) inside the magnetic holes. This study provides new insights into the electron-scale plasma dynamics in turbulent plasmas. (10.3847/1538-4357/aac831)
  DOI : 10.3847/1538-4357/aac831
• Higher-Order Turbulence Statistics in the Earth's Magnetosheath and the Solar Wind Using Magnetospheric Multiscale Observations
  
  • Chhiber R.
  • Chasapis A.
  • Bandyopadhyay R.
  • Parashar T. N.
  • Matthaeus W. H.
  • Maruca B. A.
  • Moore T. E.
  • Burch J. L.
  • Torbert R. B.
  • Russell C. T.
  • Le Contel Olivier
  • Argall M. R.
  • Fischer D.
  • Mirioni Laurent
  • Strangeway R. J.
  • Pollock C. J.
  • Giles B. L.
  • Gershman D. J.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2018, 123 (12), pp.9941-9954. High-resolution multispacecraft magnetic field measurements from the Magnetospheric Multiscale mission's flux-gate magnetometer are employed to examine statistical properties of plasma turbulence in the terrestrial magnetosheath and in the solar wind. Quantities examined include wave number spectra; structure functions of order two, four, and six; probability density functions of increments; and scale-dependent kurtoses of the magnetic field. We evaluate the Taylor frozen-in approximation by comparing single-spacecraft time series analysis with direct multispacecraft measurements, including evidence based on comparison of probability distribution functions. The statistics studied span spatial scales from the inertial range down to proton and electron scales. We find agreement of spectral estimates using three different methods, and evidence of intermittent turbulence in both magnetosheath and solar wind; however, evidence for subproton-scale coherent structures, seen in the magnetosheath, is not found in the solar wind. (10.1029/2018JA025768)
  DOI : 10.1029/2018JA025768