Publications

2018

• Méthodes mathématiques pour la physique
  
  • Dotsenko Vladimir
  • Courtat Axel
  • Gauthier Gaétan
  , 2018, pp.704 pages. EAN − 9782100777051 Cet ouvrage regroupe en un seul volume toutes les méthodes mathématiques de base indispensables pour la physique. Chaque méthode ou définition introduite est présentée de manière formelle puis systématiquement replacée dans le contexte...
• Magnetic Reconnection at a Thin Current Sheet Separating Two Interlaced Flux Tubes at the Earth's Magnetopause
  
  • Kacem I.
  • Jacquey C.
  • Génot V.
  • Lavraud B.
  • Vernisse Y.
  • Marchaudon A.
  • Le Contel Olivier
  • Breuillard Hugo
  • Phan T. D.
  • Hasegawa H.
  • Oka M.
  • Trattner K. J.
  • Farrugia C. J.
  • Paulson K.
  • Eastwood Jonathan P.
  • Fuselier S. A.
  • Turner D. L.
  • Eriksson S.
  • Wilder F. D.
  • Russell C. T.
  • Oieroset M.
  • Burch J. L.
  • Graham D. B.
  • Sauvaud J.-A.
  • Avanov L.
  • Chandler Michael O.
  • Coffey Victoria
  • Dorelli J. C.
  • Gershman D. J.
  • Giles B. L.
  • Moore T. E.
  • Saito Y.
  • Chen L. J.
  • Penou E.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2018, 123 (3), pp.1779-1793. The occurrence of spatially and temporally variable reconnection at the Earth's magnetopause leads to the complex interaction of magnetic fields from the magnetosphere and magnetosheath. Flux transfer events (FTEs) constitute one such type of interaction. Their main characteristics are (1) an enhanced core magnetic field magnitude and (2) a bipolar magnetic field signature in the component normal to the magnetopause, reminiscent of a large-scale helicoidal flux tube magnetic configuration. However, other geometrical configurations which do not fit this classical picture have also been observed. Using high-resolution measurements from the Magnetospheric Multiscale mission, we investigate an event in the vicinity of the Earth's magnetopause on 7 November 2015. Despite signatures that, at first glance, appear consistent with a classic FTE, based on detailed geometrical and dynamical analyses as well as on topological signatures revealed by suprathermal electron properties, we demonstrate that this event is not consistent with a single, homogenous helicoidal structure. Our analysis rather suggests that it consists of the interaction of two separate sets of magnetic field lines with different connectivities. This complex three-dimensional interaction constructively conspires to produce signatures partially consistent with that of an FTE. We also show that, at the interface between the two sets of field lines, where the observed magnetic pileup occurs, a thin and strong current sheet forms with a large ion jet, which may be consistent with magnetic flux dissipation through magnetic reconnection in the interaction region. (10.1002/2017JA024537)
  DOI : 10.1002/2017JA024537
• Whistler envelope solitons. II. Interaction with non-relativistic electron beams in plasmas with density inhomogeneities
  
  • Krafft C.
  • Volokitin A. S.
  Physics of Plasmas, American Institute of Physics, 2018, 25 (10), pp.102302. This paper studies the self-consistent interactions between whistler envelope solitons and electron beams in inhomogeneous plasmas, using a Hamiltonian model of wave-particle interaction where nonlinear equations describing the dynamics of whistler and ion acoustic waves and including a beam current term are coupled with Newton equations. It allows describing the parallel propagation of narrowband whistlers interacting with arbitrary particle distributions in irregular plasmas. It is shown that the whistler envelope soliton does not exchange energy with all the resonant electrons as in the case of whistler turbulence but mostly with those moving in its close vicinity (locality condition), even if the downstream particle distribution is perturbed. During these interactions, the soliton can either damp and accelerate particles, or absorb beam energy and cause electron deceleration. If the energy exchanges are significant, the envelope is deformed; its upstream front can steepen, whereas oscillations can appear on its downstream side. Weak density inhomogeneities as the random fluctuations of the solar wind plasma have no strong impact on the interactions of the whistler soliton with the resonant particles. (10.1063/1.5041075)
  DOI : 10.1063/1.5041075
• Large-Amplitude High-Frequency Waves at Earth's Magnetopause
  
  • Graham D. B.
  • Vaivads A.
  • Khotyaintsev Y. V.
  • André M.
  • Le Contel Olivier
  • Malaspina D. M.
  • Lindqvist P.-A.
  • Wilder F. D.
  • Ergun R. E.
  • Gershman D. J.
  • Giles B. L.
  • Magnes W.
  • Russell C. T.
  • Burch J. L.
  • Torbert R. B.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2018, 123 (4), pp.2630-2657. Large-amplitude waves near the electron plasma frequency are found by the Magnetospheric Multiscale (MMS) mission near Earth's magnetopause. The waves are identified as Langmuir and upper hybrid (UH) waves, with wave vectors either close to parallel or close to perpendicular to the background magnetic field. The waves are found all along the magnetopause equatorial plane, including both flanks and close to the subsolar point. The waves reach very large amplitudes, up to 1 V m-1, and are thus among the most intense electric fields observed at Earth's magnetopause. In the magnetosphere and on the magnetospheric side of the magnetopause the waves are predominantly UH waves although Langmuir waves are also found. When the plasma is very weakly magnetized only Langmuir waves are likely to be found. Both Langmuir and UH waves are shown to have electromagnetic components, which are consistent with predictions from kinetic wave theory. These results show that the magnetopause and magnetosphere are often unstable to intense wave activity near the electron plasma frequency. These waves provide a possible source of radio emission at the magnetopause. (10.1002/2017JA025034)
  DOI : 10.1002/2017JA025034
• Non-adiabatic energization and transport of planetary ions in the magnetospheric flanks of Mercury
  
  • Aizawa S.
  • Delcourt Dominique
  • Terada N.
  • Kasaba Y.
  • Katoh Y.
  , 2018, 2018, pp.pp. 10. We investigate the acceleration and transport of planetary ions within Kelvin-Helmholtz (KH) vortices that develop in the magnetospheric flanks of Mercury, using single-particle trajectory calculations in a field model obtained from MHD simulations. Due to the presence of heavy ions of planetary origin (e.g., O+, Na+, and K+) following ionization of exospheric neutrals and the complicated field structure during the KH vortex development, the scale of electric field variation may be comparable with ion gyration motion. Therefore ions may experience non-adiabatic energization as they drift across the magnetopause. In this study, we consider realistic configurations for both dawn and dusk magnetospheric flanks, and we focus on the effect of the spatial and temporal variations of the electric field magnitude and orientation along the ion path on the ion dynamics. We show that the intensification rather than the change of orientation is responsible for large non-adiabatic energization of heavy ions of planetary origin. This energization systematically occurs for ions with low initial energies in the direction perpendicular to the magnetic field, the energy gain being of the order of the energy corresponding to the maximum ExB drift speed, ɛ<SUB>max</SUB>, in a like manner to a pickup ion process. It is also found that ions that have initial energies comparable to ɛ<SUB>max </SUB>may be decelerated depending upon gyration phase. We find that ions with initial perpendicular energies much larger than ɛ<SUB>max </SUB>are little affected along the ion path through KH vortices. By comparing dynamical regimesin the dawn versus dusk regions, and also by considering different IMF directions, we show that the ion transport across the magnetopause is controlled by the orientation of the magnetosheath electric field and that the rate of energization depends upon the scale of KH vortices versus Larmor radii.
• Plasma non-uniformity in a symmetric radiofrequency capacitively-coupled reactor with dielectric side-wall: a two dimensional particle-in-cell/Monte Carlo collision simulation
  
  • Liu Yue
  • Booth Jean-Paul
  • Chabert Pascal
  Plasma Sources Science and Technology, IOP Publishing, 2018, 27 (2), pp.025006. A Cartesian-coordinate two-dimensional electrostatic particle-in-cell/Monte Carlo collision (PIC/MCC) plasma simulation code is presented, including a new treatment of charge balance at dielectric boundaries. It is used to simulate an Ar plasma in a symmetric radiofrequency capacitively-coupled parallel-plate reactor with a thick (3.5 cm) dielectric side-wall. The reactor size (12 cm electrode width, 2.5 cm electrode spacing) and frequency (15 MHz) are such that electromagnetic effects can be ignored. The dielectric side-wall effectively shields the plasma from the enhanced electric field at the powered-grounded electrode junction, which has previously been shown to produce locally enhanced plasma density (Dalvie et al 1993 Appl. Phys. Lett. 62 3207?9; Overzet and Hopkins 1993 Appl. Phys. Lett. 63 2484?6; Boeuf and Pitchford 1995 Phys. Rev. E 51 1376?90). Nevertheless, enhanced electron heating is observed in a region adjacent to the dielectric boundary, leading to maxima in ionization rate, plasma density and ion flux to the electrodes in this region, and not at the reactor centre as would otherwise be expected. The axially-integrated electron power deposition peaks closer to the dielectric edge than the electron density. The electron heating components are derived from the PIC/MCC simulations and show that this enhanced electron heating results from increased Ohmic heating in the axial direction as the electron density decreases towards the side-wall. We investigated the validity of different analytical formulas to estimate the Ohmic heating by comparing them to the PIC results. The widespread assumption that a time-averaged momentum transfer frequency, v m , can be used to estimate the momentum change can cause large errors, since it neglects both phase and amplitude information. Furthermore, the classical relationship between the total electron current and the electric field must be used with caution, particularly close to the dielectric edge where the (neglected) pressure gradient term becomes significant. (10.1088/1361-6595/aaa86e)
  DOI : 10.1088/1361-6595/aaa86e
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• Multiscale Currents Observed by MMS in the Flow Braking Region
  
  • Nakamura R.
  • Varsani Ali
  • Genestreti Kevin J.
  • Le Contel Olivier
  • Nakamura T. K. M.
  • Baumjohann W.
  • Nagai Tsugunobu
  • Artemyev A. V.
  • Birn Joachim
  • Sergeev Victor A.
  • Apatenkov Sergey
  • Ergun Robert E.
  • Fuselier Stephen A.
  • Gershman D. J.
  • Giles Barbara J.
  • Khotyaintsev Y. V.
  • Lindqvist Per-Arne
  • Magnes Werner
  • Mauk Barry
  • Petrukovich Anatoli
  • Russell Christopher T.
  • Stawarz J. E.
  • Strangeway Robert J.
  • Anderson Brian
  • Burch James L.
  • Bromund Ken R.
  • Cohen Ian
  • Fischer David
  • Jaynes Allison
  • Kepko Laurence
  • Le Guan
  • Plaschke Ferdinand
  • Reeves Geoff
  • Singer Howard J.
  • Slavin J. A.
  • Torbert Roy B.
  • Turner Drew L.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2018, 123 (2), pp.1260-1278. We present characteristics of current layers in the off-equatorial near-Earth plasma sheet boundary observed with high time-resolution measurements from the Magnetospheric Multiscale mission during an intense substorm associated with multiple dipolarizations. The four Magnetospheric Multiscale spacecraft, separated by distances of about 50 km, were located in the southern hemisphere in the dusk portion of a substorm current wedge. They observed fast flow disturbances (up to about 500 km/s), most intense in the dawn-dusk direction. Field-aligned currents were observed initially within the expanding plasma sheet, where the flow and field disturbances showed the distinct pattern expected in the braking region of localized flows. Subsequently, intense thin field-aligned current layers were detected at the inner boundary of equatorward moving flux tubes together with Earthward streaming hot ions. Intense Hall current layers were found adjacent to the field-aligned currents. In particular, we found a Hall current structure in the vicinity of the Earthward streaming ion jet that consisted of mixed ion components, that is, hot unmagnetized ions, cold E × B drifting ions, and magnetized electrons. Our observations show that both the near-Earth plasma jet diversion and the thin Hall current layers formed around the reconnection jet boundary are the sites where diversion of the perpendicular currents take place that contribute to the observed field-aligned current pattern as predicted by simulations of reconnection jets. Hence, multiscale structure of flow braking is preserved in the field-aligned currents in the off-equatorial plasma sheet and is also translated to ionosphere to become a part of the substorm field-aligned current system. (10.1002/2017JA024686)
  DOI : 10.1002/2017JA024686
• Turbulence and microprocesses in inhomogeneous solar wind plasmas
  
  • Krafft C.
  • Volokitin A.
  • Gauthier Gaétan
  , 2018. The random density fluctuations observed in the solar wind plasma crucially influence on the Langmuir wave turbulence generated by energetic electron beams ejected during solar bursts. Those are powerful phenomena consisting of a chain of successive processes leading ultimately to strong electromagnetic emissions. The small-scale processes governing the interactions between the waves, the beams and the inhomogeneous plasmas need to be studied to explain such macroscopic phenomena. Moreover, the complexity induced by the plasma irregularities requires to find new approaches and modelling. Therefore theoretical and numerical tools were built to describe the Langmuir wave turbulence and the beams dynamics in inhomogeneous plasmas, in the form of a self-consistent Hamiltonian model including a fluid description for the plasma and a kinetic approach for the beam. On this basis, numerical simulations were performed in order to shed light on the impact of the density fluctuations on the beam dynamics, the electromagnetic wave radiation, the generation of Langmuir wave turbulence, the waves coupling and decay phenomena involving Langmuir and low frequency waves, the acceleration of beam electrons, their diffusion mechanisms, the modulation of the Langmuir waveforms and the statistical properties of the radiated fields distributions.
• 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
• 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
• 8th International Workshop on Plasma Spectroscopy (IPS)
  
  • Guaitella Olivier
  • Morillo-Candas Ana-Sofia
  • Klarenaar Bart
  • Engeln Richard
  • Silva Tiago
  • Guerra V.
  , 2018.
• Electromagnetic Wave Emissions from a Turbulent Plasma with Density Fluctuations
  
  • Volokitin A. S.
  • Krafft Catherine
  The Astrophysical Journal, American Astronomical Society, 2018, 868. In the solar wind, Langmuir turbulence can generate electromagnetic waves at the fundamental plasma frequency omega <SUB> p </SUB>. This process can likely result from either linear wave transformations on the ambient random density inhomogeneities or resonant three-wave interactions involving Langmuir waves and ion acoustic oscillations. In the presence of sufficiently intense plasma density fluctuations of scales much larger than the Langmuir wavelengths, the first mechanism may be more efficient than the second one. A new approach to calculate the electromagnetic wave emissions by Langmuir wave turbulence in plasmas with background density fluctuations is developed. The evolution of the Langmuir turbulence is studied by numerically solving the Zakharov equations in such a two-dimensional plasma. The dynamics of the spatial distributions of the electric currents with frequencies close to omega <SUB> p </SUB> is calculated, as well as their emission into electromagnetic waves. The efficiency of this radiation is determined as a function of the level of the Langmuir turbulence, the characteristics of the density fluctuations, the background plasma temperature, the position of the satellite receiver, and the durations of the source's emissions and spacecraft's observations. The results obtained by the theoretical modeling and numerical simulations are successfully compared with space observations of electromagnetic waves radiated during Type III solar radio bursts. (10.3847/1538-4357/aae7cc)
  DOI : 10.3847/1538-4357/aae7cc
• 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
• 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
• 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
• Turbulence in space plasmas and beyond
  
  • Galtier Sébastien
  Journal of Physics A: Mathematical and General (1975 - 2006), IOP Publishing, 2018, 51, pp.293001. Most of the visible matter in the Universe is in the form of highly turbulent plasmas. For a long time the turbulent character of astrophysical fluids has been neglected and not well understood. One reason for this is the extremely complicated physics involved in astrophysical processes ranging from the machinery of stars, solar and stellar winds, accretion disks to interstellar clouds and galaxies. The other reason is that turbulence constitutes in itself a difficult subject where most of the fundamental results belongs to the incompressible hydrodynamics. Nevertheless, significant theoretical progress has been made during the last years to incorporate some ingredients like compressibility or small-scale plasma physics which are fundamental in astrophysics. This paper reviews some of these results with a strong focus on space plasmas (solar wind, solar corona). Turbulence in interstellar clouds (supersonic flows) and cosmology (space-time fluctuations) are also briefly mentioned. (10.1088/1751-8121/aac4c7)
  DOI : 10.1088/1751-8121/aac4c7