Publications

2018

• 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
• 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
• 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
• Anomalous electron transport in Hall-effect thrusters: Comparison between quasi-linear kinetic theory and particle-in-cell simulations
  
  • Lafleur Trevor
  • Martorelli Roberto
  • Chabert Pascal
  • Bourdon Anne
  Physics of Plasmas, American Institute of Physics, 2018, 25 (6), pp.061202. Kinetic drift instabilities have been implicated as a possible mechanism leading to anomalous electron cross-field transport in E B discharges, such as Hall-effect thrusters. Such instabilities, which are driven by the large disparity in electron and ion drift velocities, present a significant challenge to modelling efforts without resorting to time-consuming particle-in-cell (PIC) simulations. Here, we test aspects of quasi-linear kinetic theory with 2D PIC simulations with the aim of developing a self-consistent treatment of these instabilities. The specific quantities of interest are the instability growth rate (which determines the spatial and temporal evolution of the instability amplitude), and the instability-enhanced electron-ion friction force (which leads to anomalous electron transport). By using the self-consistently obtained electron distribution functions from the PIC simulations (which are in general non-Maxwellian), we find that the predictions of the quasilinear kinetic theory are in good agreement with the simulation results. By contrast, the use of Maxwellian distributions leads to a growth rate and electron-ion friction force that is around 24 times higher, and consequently significantly overestimates the electron transport. A possible method for self-consistently modelling the distribution functions without requiring PIC simulations is discussed (10.1063/1.5017626)
  DOI : 10.1063/1.5017626
• Sodium Ion Dynamics in the Magnetospheric Flanks of Mercury
  
  • Aizawa Sae
  • Delcourt Dominique C.
  • Terada N.
  Geophysical Research Letters, American Geophysical Union, 2018, 45, pp.595-601. We investigate the transport of planetary ions in the magnetospheric flanks of Mercury. In situ measurements from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging spacecraft show evidences of Kelvin-Helmholtz instability development in this region of space, due to the velocity shear between the downtail streaming flow of solar wind originating protons in the magnetosheath and the magnetospheric populations. Ions that originate from the planet exosphere and that gain access to this region of space may be transported across the magnetopause along meandering orbits. We examine this transport using single-particle trajectory calculations in model Magnetohydrodynamics simulations of the Kelvin-Helmholtz instability. We show that heavy ions of planetary origin such as Na<SUP> </SUP> may experience prominent nonadiabatic energization as they <fi>E</fi> × <fi>B</fi> drift across large-scale rolled up vortices. This energization is controlled by the characteristics of the electric field burst encountered along the particle path, the net energy change realized corresponding to the maximum <fi>E</fi> × <fi>B</fi> drift energy. This nonadiabatic energization also is responsible for prominent scattering of the particles toward the direction perpendicular to the magnetic field. (10.1002/2017GL076586)
  DOI : 10.1002/2017GL076586
• Effect of frequency on the uniformity of symmetrical RF CCP discharges
  
  • Liu Yue
  • Booth Jean-Paul
  • Chabert Pascal
  Plasma Sources Science and Technology, IOP Publishing, 2018, 27 (5), pp.055012. A 2D Cartesian electrostatic particle-in-cell/Monte Carlo collision (PIC/MCC) model presented previously (Liu et al 2018 Plasma Sources Sci. Technol. 27 025006) is used to investigate the effect of the driving frequency (over the range of 15?45 MHz) on the plasma uniformity in radio frequency (RF) capacitively coupled plasma (CCP) discharges in a geometrically symmetric reactor with a dielectric side wall in argon gas. The reactor size (12 cm electrode length, 2.5 cm gap) and driving frequency are sufficiently small that electromagnetic effects can be ignored. Previously, we showed (Liu et al 2018 Plasma Sources Sci. Technol. 27 025006) that for 15 MHz excitation, Ohmic heating of electrons by the electric field perpendicular to the electrodes is enhanced in a region in front of the dielectric side wall, leading to a maximum in electron density there. In this work we show that increasing the excitation frequency (at constant applied voltage amplitude) not only increases the overall electron heating and density but also causes a stronger, narrower peak in electron heating closer to the dielectric wall, improving the plasma uniformity along the electrodes. This heating peak comes both from enhanced perpendicular electron heating and from the appearance at high frequency of significant parallel heating. The latter is caused by the presence of a significant parallel-direction RF oscillating electric field in the corners. Whereas at the reactor center the sheaths oscillate perpendicularly to the electrodes, near the dielectric edge they move in and out of the corners and must be treated in two dimensions. (10.1088/1361-6595/aabfb4)
  DOI : 10.1088/1361-6595/aabfb4
• 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.
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• Observations of core ion cyclotron emission on ASDEX Upgrade tokamak
  
  • Ochoukov R.
  • Bobkov V.
  • Chapman B.
  • Dendy R.
  • Dunne M.
  • Faugel H.
  • García Muñoz M.
  • Geiger B.
  • Hennequin Pascale
  • Mcclements K. G.
  • Moseev D.
  • Nielsen S.
  • Rasmussen J.
  • Schneider P.
  • Weiland M.
  • Noterdaeme J.-M.
  Review of Scientific Instruments, American Institute of Physics, 2018, 89 (10), pp.10J101. The B-dot probe diagnostic suite on the ASDEX Upgrade tokamak has recently been upgraded with a new 125 MHz, 14 bit resolution digitizer to study ion cyclotron emission (ICE). While classic edge emission from the low field side plasma is often observed, we also measure waves originating from the core with fast fusion protons or beam injected deuterons being a possible emission driver. Comparing the measured frequency values with ion cyclotron harmonics present in the plasma places the origin of this emission on the magnetic axis, with the fundamental hydrogen/second deuterium cyclotron harmonic matching the observed values. The actual values range from ∼27 MHz at the on-axis toroidal field BT = -1.79 T to ∼40 MHz at BT = -2.62 T. When the magnetic axis position evolves during this emission, the measured frequency values track the changes in the estimated on-axis cyclotron frequency values. Core ICE is usually a transient event lasting ∼100 ms during the neutral beam startup phase. However, in some cases, core emission occurs in steady-state plasmas and lasts for longer than 1 s. These observations suggest an attractive possibility of using a non-perturbing ICE-based diagnostic to passively monitor fusion alpha particles at the location of their birth in the plasma core, in deuterium-tritium burning devices such as ITER and DEMO. (10.1063/1.5035180)
  DOI : 10.1063/1.5035180
• 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
• 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
• Imaging axial and radial electric field components in dielectric targets under plasma exposure
  
  • Slikboer Elmar
  • Sobota Ana
  • Guaitella Olivier
  • Garcia-Caurel Enric
  Journal of Physics D: Applied Physics, IOP Publishing, 2018, 51 (11), pp.115203. Mueller polarimetry is used to investigate the behavior of an electro optic target (BSO crystal) under exposure of guided ionization waves produced by an atmospheric pressure plasma jet. For the first time, this optical technique is time resolved to obtain the complete Mueller matrix of the sample right before and after the impact of the discharges. By analyzing the induced birefringence, the spatial profiles and local values are obtained of both the electric field and temperature in the sample. Electric fields are generated due to deposited surface charges and a temperature profile is present, due to the heat transferred by the plasma jet. The study of electric field dynamics and local temperature increase at the target, due to the plasma jet is important for biomedical applications, as well as surface functionalization. This work shows how Mueller polarimetry can be used as a novel diagnostic to simultaneously acquire the spatial distribution and local values of both the electric field and temperature, by coupling the external source of anisotropy to the measured induced birefringence via the symmetry point group of the examined material. (10.1088/1361-6463/aaad99)
  DOI : 10.1088/1361-6463/aaad99
• Recent advances in the modeling and computer simulations of non-equilibrium plasma discharges
  
  • Raja Laxminarayan L
  • Bourdon Anne
  • Ventzek Peter L G
  Journal of Physics D: Applied Physics, IOP Publishing, 2018, 51 (15), pp.150202. The mathematical modeling and computer simulation of low-temperature plasmas is gradually such a level of maturity that these simulation tools can be used not just for improving scientific understanding but also as computer-aided engineering design tools in an industrial setting. These models necessarily involve the description of multiple physical phenomena occurring over a range of times and lengths, thereby complicating their numerical implementation and solution. This special issue presents 12 invited contributions that present recent developments in the field of modeling and simulation of low-temperature plasma discharges. This editorial introduces these papers by providing an overview of the context in which these papers are presented. (10.1088/1361-6463/aab1b9)
  DOI : 10.1088/1361-6463/aab1b9