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
• 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
• 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
• 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
• 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.
• 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
• 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
• 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&#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
• 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
• 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
• 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
• 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
• 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
• Electron Energization at a Reconnecting Magnetosheath Current Sheet
  
  • Eriksson Elin
  • Vaivads Andris
  • Graham Daniel B.
  • Divin Andrey
  • Khotyaintsev Yu. V.
  • Yordanova Emiliya
  • André Mats
  • Giles Barbara L.
  • Pollock Craig J.
  • Russell Christopher T.
  • Le Contel O.
  • Torbert Roy B.
  • Ergun Robert E.
  • Lindqvist Per-Arne
  • Burch James L.
  Geophysical Research Letters, American Geophysical Union, 2018, 45, pp.8081-8090. We present observations of electron energization within a sub-ion-scale magnetosheath current sheet (CS). A number of signatures indicate ongoing reconnection, including the thickness of the CS (&tilde;0.7 ion inertial length), nonzero normal magnetic field, Hall magnetic fields with electrons carrying the Hall currents, and electron heating. We observe localized electron acceleration and heating parallel to the magnetic field at the edges of the CS. Electrostatic waves observed in these regions have low phase velocity and small wave potentials and thus cannot provide the observed acceleration and heating. Instead, we find that the electrons are accelerated by a parallel potential within the separatrix regions. Similar acceleration has been reported based on magnetopause and magnetotail observations. Thus, despite the different plasma conditions in magnetosheath, magnetopause, and magnetotail, the acceleration mechanism and corresponding heating of electrons is similar. (10.1029/2018GL078660)
  DOI : 10.1029/2018GL078660
• Investigation of a plasma--target interaction through electric field characterization examining surface and volume charge contributions: modeling and experiment
  
  • Viegas Pedro
  • Slikboer Elmar
  • Obrusník Adam
  • Bonaventura Zdenek
  • Sobota Ana
  • Garcia-Caurel Enric
  • Guaitella Olivier
  • Bourdon Anne
  Plasma Sources Science and Technology, IOP Publishing, 2018, 27. Numerical simulations and experiments are performed to better understand the interaction between a pulsed helium plasma jet and a dielectric target. The focus of this work lies on the volume and surface charge influence on the electric field distribution. Experimentally, the electric field due to surface charges is measured inside an electro-optic target under exposure of a plasma jet, using the optical technique called Mueller polarimetry. For the first time, the time-resolved spatial distributions of both the axial and radial components of electric field inside the target are obtained simultaneously. A 2D fluid model is used in a complementary way to the experiments in order to study separately the contribution of volume charges and surface charges to the spatio-temporal evolutions of the electric field during the plasma--surface interaction. The experimental investigation shows that the average axial and radial components of electric field inside the dielectric target, only due to surface charges, are lower than generally reported for electric field values in the plasma plume. Thanks to the phenomenological comparison with experiments, simulations show that during the plasma--surface interaction two effects sequentially determine the electric field inside the target: firstly, a relatively high electric field is observed due to the proximity of the ionization front; afterwards, in longer timescales, lower electric fields are induced due to the contribution of both leftover volume charges close to the target and surface charges deposited on its surface. The experimental technique provides a unique way to examine this second phase of the plasma--surface interaction. (10.1088/1361-6595/aadcc0)
  DOI : 10.1088/1361-6595/aadcc0
• Study of Ionospheric Variability Using GNSS Observations
  
  • Taoufiq Jouan
  • Mourad Bouziani
  • Rachid Azzouzi
  • Amory-Mazaudier Christine
  Positioning, SCIRP, 2018, 09 (04), pp.79-96. <div><p>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 station's 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.</p></div> (10.4236/pos.2018.94006)
  DOI : 10.4236/pos.2018.94006
• 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
• 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
• Optical actinometry of O-atoms in pulsed nanosecond capillary discharge: peculiarities of kinetics at high specific deposited energy
  
  • Zhu Yifei
  • Lepikhin N D
  • Orel Inna
  • Salmon A.
  • Klochko A.V.
  • Starikovskaia Svetlana
  Plasma Sources Science and Technology, IOP Publishing, 2018. Density of O-atoms was studied in capillary nanosecond discharge in air with 5.3% additions of Ar at 28.5 mbar. Time-resolved electrical current, longitudinal electric fifield, optical emission of O(3p3P), Ar(2p1) and their ratio, and emission of N2(C)were measured. A kinetic scheme describing consistent behavior of the set of the experimental data was developed. The main processes responsible for population and decay of the species of interest were selected on the basis of sensitivity and rate analysis. The electric fifield was taken as input data; all other experimentally obtained signals were modeled; experimental data and results of calculations are in good agreement. The role of the reactions between excited, charged species and electrons in early afterglow for pulsed discharges at high reduced electric fifields and high specifific deposited energy was discussed. Density of O atoms in the ground state was calculated. It was concluded that Ar-based traditional actinometry demands an advanced kinetic modeling in the case of the nanosecond discharge with a high specifific energy deposition. (10.1088/1361-6595/aac95f)
  DOI : 10.1088/1361-6595/aac95f