Publications

2016

• Optimized merging of search coil and fluxgate data for MMS
  
  • Fischer David
  • Magnes Werner
  • Hagen Christian
  • Dors Ivan
  • Chutter Mark W.
  • Needell Jerry
  • Torbert Roy B.
  • Le Contel Olivier
  • Strangeway Robert J.
  • Kubin Gernot
  • Valavanoglou Aris
  • Plaschke Ferdinand
  • Nakamura R.
  • Mirioni Laurent
  • Russell Christopher T.
  • Leinweber Hannes K.
  • Bromund Kenneth R.
  • Le Guan
  • Kepko Lawrence
  • Anderson Brian J.
  • Slavin J. A.
  • Baumjohann W.
  Geoscientific Instrumentation, Methods and Data Systems, European Geosciences Union, 2016, 5, pp.521-530. The Magnetospheric Multiscale mission (MMS) targets the characterization of fine-scale current structures in the Earth's tail and magnetopause. The high speed of these structures, when traversing one of the MMS spacecraft, creates magnetic field signatures that cross the sensitive frequency bands of both search coil and fluxgate magnetometers. Higher data quality for analysis of these events can be achieved by combining data from both instrument types and using the frequency bands with best sensitivity and signal-to-noise ratio from both sensors. This can be achieved by a model-based frequency compensation approach which requires the precise knowledge of instrument gain and phase properties. We discuss relevant aspects of the instrument design and the ground calibration activities, describe the model development and explain the application on in-flight data. Finally, we show the precision of this method by comparison of in-flight data. It confirms unity gain and a time difference of less than 100 µs between the different magnetometer instruments. (10.5194/gi-5-521-2016)
  DOI : 10.5194/gi-5-521-2016
• Poynting vector and wave vector directions of equatorial chorus
  
  • Taubenschuss U.
  • Santolík O.
  • Breuillard Hugo
  • Li W.
  • Le Contel Olivier
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2016, 121 (12), pp.11,912-11,928. We present new results on wave vectors and Poynting vectors of chorus rising and falling tones on the basis of 6 years of THEMIS (Time History of Events and Macroscale Interactions during Substorms) observations. The majority of wave vectors is closely aligned with the direction of the ambient magnetic field (B<SUB>0</SUB>). Oblique wave vectors are confined to the magnetic meridional plane, pointing away from Earth. Poynting vectors are found to be almost parallel to B<SUB>0</SUB>. We show, for the first time, that slightly oblique Poynting vectors are directed away from Earth for rising tones and toward Earth for falling tones. For the majority of lower band chorus elements, the mutual orientation between Poynting vectors and wave vectors can be explained by whistler mode dispersion in a homogeneous collisionless cold plasma. Upper band chorus seems to require inclusion of collisional processes or taking into account azimuthal anisotropies in the propagation medium. The latitudinal extension of the equatorial source region can be limited to ±6<SUP>o</SUP> around the B<SUB>0</SUB> minimum or approximately ±5000 km along magnetic field lines. We find increasing Poynting flux and focusing of Poynting vectors on the B<SUB>0</SUB> direction with increasing latitude. Also, wave vectors become most often more field aligned. A smaller group of chorus generated with very oblique wave normals tends to stay close to the whistler mode resonance cone. This suggests that close to the equatorial source region (within 20<SUP>o</SUP> latitude), a wave guidance mechanism is relevant, for example, in ducts of depleted or enhanced plasma density. (10.1002/2016JA023389)
  DOI : 10.1002/2016JA023389
• Theory for the anomalous electron transport in Hall effect thrusters. II. Kinetic model
  
  • Lafleur Trevor
  • Baalrud S. D.
  • Chabert Pascal
  Physics of Plasmas, American Institute of Physics, 2016, 23 (5), pp.053503. In Paper I [T. Lafleur et al., Phys. Plasmas 23, 053502 (2016)], we demonstrated (using particle-in-cell simulations) the definite correlation between an anomalously high cross-field electron transport in Hall effect thrusters (HETs), and the presence of azimuthal electrostatic instabilities leading to enhanced electron scattering. Here, we present a kinetic theory that predicts the enhanced scattering rate and provides an electron cross-field mobility that is in good agreement with experiment. The large azimuthal electron drift velocity in HETs drives a strong instability that quickly saturates due to a combination of ion-wave trapping and wave-convection, leading to an enhanced mobility many orders of magnitude larger than that expected from classical diffusion theory. In addition to the magnetic field strength, B0, this enhanced mobility is a strong function of the plasma properties (such as the plasma density) and therefore does not, in general, follow simple 1/B20 or 1/B0 scaling laws. (10.1063/1.4948496)
  DOI : 10.1063/1.4948496
• Influence of diaphragm configuration on DC diaphragm discharge breakdown in electrolyte solution
  
  • Hlavatá L.
  • Hlochová L.
  • Kozáková Z.
  • Krčma F.
  • Guaitella Olivier
  , 2016, 768 (1), pp.012018.
• Dynamical Monte Carlo methods for plasma-surface reactions
  
  • Guerra V.
  • Marinov Daniil
  Plasma Sources Science and Technology, IOP Publishing, 2016, 25 (4), pp.045001. Different dynamical Monte Carlo algorithms to investigate molecule formation on surfaces are developed, evaluated and compared with the deterministic approach based on reaction-rate equations. These include a null event algorithm, the n-fold way/BKL algorithm and an 'hybrid' variant of the latter. NO2 formation by NO oxidation on Pyrex and O recombination on silica with the formation of O2 are taken as case studies. The influence of the grid size on the CPU calculation time and the accuracy of the results is analysed. The role of LangmuirHinsehlwood recombination involving two physisorbed atoms and the effect of back diffusion and its inclusion in a deterministic formulation are investigated and discussed. It is shown that dynamical Monte Carlo schemes are flexible, simple to implement, describe easily elementary processes that are not straightforward to include in deterministic simulations, can run very efficiently if appropriately chosen and give highly reliable results. Moreover, the present approach provides a relatively simple procedure to describe fully coupled surface and gas phase chemistries. (10.1088/0963-0252/25/4/045001)
  DOI : 10.1088/0963-0252/25/4/045001
• Time-resolved electric field measurements during and after the initialization of a kHz plasma jetfrom streamers to guided streamers
  
  • Slikboer Elmar
  • Guaitella Olivier
  • Sobota Ana
  Plasma Sources Science and Technology, IOP Publishing, 2016, 25 (3), pp.03LT04. This work presents the investigation of a 30&#8201;kHz operated atmospheric pressure plasma jet impinging a dielectric BSO-crystal, allowing time-resolved electric field measurements based on the Pockels effect. Observations indicate that from the time the voltage is applied, the plasma first develops through unstable branching before a stable periodic behavior is established. This initialization of the plasma jet suggests the importance of the build-up of leftover ionization, which creates a preferred pathway for the streamer-like discharges. After initialization the time and spatially resolved electric field of guided ionization waves induced in the crystal is obtained, showing a highly periodic charging and discharging at the surface of the crystal. When the ionization wave arrives at the crystal charge is deposited and constant electric fields are generated for approximately 14 &#956;s. Then a (back) discharge will remove the deposited charge at the surface, related to the moment when the applied voltage changes polarity and it agrees with imaging reported on in other literature. (10.1088/0963-0252/25/3/03LT04)
  DOI : 10.1088/0963-0252/25/3/03LT04
• Combined use of LIDAR and hyperspectral measurements for remote sensing of fluorescence and vertical profile of canopies
  
  • Ounis A.
  • Bach J.
  • Mahjoub A.
  • Daumard Fabrice
  • Moya I
  • Goulas Y.
  Revista de Teledetección, 2016 (45), pp.87-94. We report the development of a new LIDAR system (LASVEG) for airborne remote sensing of chlorophyll fluorescence (ChlF) and vertical profile of canopies. By combining laser-induced fluorescence (LIF), sun-induced fluorescence (SIF) and canopy height distribution, the new instrument will allow the simultaneous assessment of gross primary production (GPP), photosynthesis efficiency and above ground carbon stocks. Technical issues of the fluorescence LIDAR development are discussed and expected performances are presented. (10.4995/raet.2015.3982)
  DOI : 10.4995/raet.2015.3982
• Ionospheric and magnetic signatures of a high speed solar wind in low latitudes on 13 October 2012
  
  • Migoya-Orué Yenca
  • Azzouzi Ilyasse
  • Coisson Pierdavide
  • Amory-Mazaudier Christine
  • Fleury Rolland
  • Radicella Sandro M.
  Sun and Geosphere, BBC SWS Regional Network, 2016, 11 (1), pp.23-35. This paper presents the impact of a fast solar wind on the ionosphere, in low latitudes, on 13 October 2012. On that day, the high speed solar wind reached the Earth around 16:00UT, during the recovery phase of a geomagnetic storm which started around 00:00UT. The solar wind speed was determined to be 580km/s, on the same day, around 17:00UT. Its impact was observed in low and equatorial latitudes, in Africa and in Eastern South America, on the F layer and on the geomagnetic field variations. Through the analysis of magnetic indices, ionosonde characteristics and the horizontal component of the geomagnetic field, we found that the 13 October 2012 event exhibited a local impact, affecting the observatories situated in a longitude sector between 315°E and 45°E. Particularly, the F layer in Africa (observed by the ionosonde at Ascension Island) did not present any lift, and there was a delay for approximately two hours of the ascent of the F layer in America (the ionosonde at Fortaleza). In this case, there was an evident inhibition on the development of spread F at the time of the Pre Reversal Enhancement (PRE) in Africa and Eastern America, while the ionograms of the days before and after presented clear spread F traces. The disturbances of the ionospheric equivalent electric current (Diono) deduced from the variations of the geomagnetic field at M'Bour near Dakar (Africa) and at Kourou (Eastern America) exhibited on the dayside, an anti Sq current which is signature of the influence of the Disturbance Dynamo Electric Field (DDEF).
• Global model of an iodine gridded plasma thruster
  
  • Grondein Pascaline
  • Lafleur Trevor
  • Chabert Pascal
  • Aanesland Ane
  Physics of Plasmas, American Institute of Physics, 2016, 23 (3), pp.033514. Most state-of-the-art electric space propulsion systems such as gridded and Hall effect thrusters use xenon as the propellant gas. However, xenon is very rare, expensive to produce, and used in a number of competing industrial applications. Alternatives to xenon are currently being investigated, and iodine has emerged as a potential candidate. Its lower cost and larger availability, its solid state at standard temperature and pressure, its low vapour pressure and its low ionization potential make it an attractive option. In this work, we compare the performances of a gridded ion thruster operating separately with iodine and xenon, under otherwise identical conditions using a global model. The thruster discharge properties such as neutral, ion, and electron densities and electron temperature are calculated, as well as the thruster performance parameters such as thrust, specific impulse, and system efficiencies. For similar operating conditions, representative of realistic thrusters, the model predicts similar thrust levels and performances for both iodine and xenon. The thruster efficiency is however slightly higher for iodine compared with xenon, due to its lower ionization potential. This demonstrates that iodine could be a viable alternative propellant for gridded plasma thrusters. (10.1063/1.4944882)
  DOI : 10.1063/1.4944882
• Cold ion heating at the dayside magnetopause during magnetic reconnection
  
  • Toledo-Redondo Sergio
  • André M.
  • Vaivads A.
  • Khotyaintsev Y. V.
  • Lavraud B.
  • Graham D. B.
  • Divin A. V.
  • Aunai Nicolas
  Geophysical Research Letters, American Geophysical Union, 2016, 43 (1), pp.58-66. Cold ions of ionospheric origin are known to be present in the magnetospheric side of the Earth's magnetopause. They can be very abundant, with densities up to 100 cm<SUP>-3</SUP>. These cold ions can mass load the magnetosphere, changing global parameters of magnetic reconnection, like the Alfvén speed or the reconnection rate. In addition they introduce a new length scale related to their gyroradius and kinetic effects which must be accounted for. We report in situ observations of cold ion heating in the separatrix owing to time and space fluctuations of the electric field. When this occurs, the cold ions are preheated before crossing the Hall electric field barrier. However, when this mechanism is not present cold ions can be observed well inside the reconnection exhaust. Our observations suggest that the perpendicular cold ion heating is stronger close to the X line owing to waves and electric field gradients linked to the reconnection process. (10.1002/2015GL067187)
  DOI : 10.1002/2015GL067187
• Cluster observations of reflected EMIC-triggered emission
  
  • Grison B.
  • Darrouzet F.
  • Santolík O.
  • Cornilleau-Wehrlin Nicole
  • Masson A.
  Geophysical Research Letters, American Geophysical Union, 2016, 43, pp.4164-4171. On 19 March 2001, the Cluster fleet recorded an electromagnetic rising tone on the nightside of the plasmasphere. The emission was found to propagate toward the Earth and toward the magnetic equator at a group velocity of about 200 km/s. The Poynting vector is mainly oblique to the background magnetic field and directed toward the Earth. The propagation angle thetak,B<SUB>0</SUB> becomes more oblique with increasing magnetic latitude. Inside each rising tone thetak,B<SUB>0</SUB> is more field aligned for higher frequencies. Comparing our results to previous ray tracing analysis we conclude that this emission is a triggered electromagnetic ion cyclotron (EMIC) wave generated at the nightside plasmapause. We detect the wave just after its reflection in the plasmasphere. The reflection makes the tone slope shallower. This process can contribute to the formation of pearl pulsations. (10.1002/2016GL069096)
  DOI : 10.1002/2016GL069096
• Theory for the anomalous electron transport in Hall effect thrusters. I. Insights from particle-in-cell simulations
  
  • Lafleur Trevor
  • Baalrud S. D.
  • Chabert Pascal
  Physics of Plasmas, American Institute of Physics, 2016, 23 (5), pp.053502. Using a 1D particle-in-cell simulation with perpendicular electric, E0, and magnetic, B0, fields, and modelling the azimuthal direction (i.e., the E0&#8201;×&#8201;B0 direction), we study the cross-field electron transport in Hall effect thrusters (HETs). For low plasma densities, the electron transport is found to be well described by classical electron-neutral collision theory, but at sufficiently high densities (representative of typical HETs), a strong instability is observed to significantly enhance the electron mobility, even in the absence of electron-neutral collisions. This instability is associated with correlated high-frequency (of the order of MHz) and short-wavelength (of the order of mm) fluctuations in both the electric field and the plasma density, which are shown to be the cause of the anomalous transport. Saturation of the instability is observed to occur due to a combination of ion-wave trapping in the E0&#8201;×&#8201;B0 direction, and convection in the E0 direction. (10.1063/1.4948495)
  DOI : 10.1063/1.4948495
• Logarithmic discretization and systematic derivation of shell models in two-dimensional turbulence
  
  • Gürcan Özgür D.
  • Morel Pierre
  • Kobayashi Sumire
  • Singh Rameswar
  • Xu S.
  • Diamond P.H.
  Physical Review E, American Physical Society (APS), 2016, 94, pp.033106. A detailed systematic derivation of a logarithmically discretized model for two-dimensional turbulence is given, starting from the basic fluid equations and proceeding with a particular form of discretization of the wave-number space. We show that it is possible to keep all or a subset of the interactions, either local or disparate scale, and recover various limiting forms of shell models used in plasma and geophysical turbulence studies. The method makes no use of the conservation laws even though it respects the underlying conservation properties of the fluid equations. It gives a family of models ranging from shell models with nonlocal interactions to anisotropic shell models depending on the way the shells are constructed. Numerical integration of the model shows that energy and enstrophy equipartition seem to dominate over the dual cascade, which is a common problem of two-dimensional shell models. (10.1103/PhysRevE.94.033106)
  DOI : 10.1103/PhysRevE.94.033106
• Signatures of complex magnetic topologies from multiple reconnection sites induced by Kelvin-Helmholtz instability
  
  • Vernisse Y.
  • Lavraud B.
  • Eriksson S.
  • Gershman D. J.
  • Dorelli J. C.
  • Pollock C.
  • Giles B. L.
  • Aunai Nicolas
  • Avanov L.
  • Burch J. L.
  • Chandler Michael O.
  • Coffey Victoria
  • Dargent Jérémy
  • Ergun R. E.
  • Farrugia C. J.
  • Génot V.
  • Graham D. B.
  • Hasegawa H.
  • Jacquey C.
  • Kacem I.
  • Khotyaintsev Y. V.
  • Li W.
  • Magnes W.
  • Marchaudon A.
  • Moore T. E.
  • Paterson W. R.
  • Penou E.
  • Phan T. D.
  • Retinò Alessandro
  • Russell C. T.
  • Saito Y.
  • Sauvaud J.-A.
  • Torbert R.
  • Wilder F. D.
  • Yokota S.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2016, 121 (10), pp.9926-9939. The Magnetospheric Multiscale mission has demonstrated the frequent presence of reconnection exhausts at thin current sheets within Kelvin-Helmholtz (KH) waves at the flank magnetopause. Motivated by these recent observations, we performed a statistical analysis of the boundary layers on the magnetosheath side of all KH current sheets on 8 September 2015. We show 86% consistency between the exhaust flows and particle leakage in the magnetosheath boundary layers but further highlight the very frequent presence of additional boundary layer signatures that do not come from the locally observed reconnection exhausts. These additional electron and ion boundary layers, of various durations and at various positions with respect to the leading and trailing boundaries of the KH waves, signal connections to reconnection sites at other locations. Based on the directionality and extent of these layers, we provide an interpretation whereby complex magnetic topologies can arise within KH waves from the combination of reconnection in the equatorial plane and at midlatitudes in the Southern and Northern Hemispheres, where additional reconnection sites are expected to be triggered by the three-dimensional field lines interweaving induced by the KH waves at the flanks (owing to differential flow and magnetic field shear with latitude). The present event demonstrates that the three-dimensional development of KH waves can induce plasma entry (through reconnection at both midlatitude and equatorial regions) already sunward of the terminator where the instability remains in its linear stage. (10.1002/2016JA023051)
  DOI : 10.1002/2016JA023051
• First results of the magnetospheric multiscale mission (MMS)
  
  • Le Contel Olivier
  • Lavraud B.
  • Retinò Alessandro
  • Jacquey C.
  • Breuillard Hugo
  • Vernisse Y.
  • Chasapis A.
  • Aunai N.
  • Dargent Jérémy
  • Chust Thomas
  • Rezeau Laurence
  • Mirioni Laurent
  • Kacem I.
  • Génot V.
  • Penou E.
  • Sauvaud J.-A.
  • Leroy Paul
  • Alison Dominique
  • Coillot Christophe
  • Aoustin C.
  • Le Comte E.
  • Rouzaud J.
  French report to COSPAR, 2016.
• Langmuir turbulence driven by beams in solar wind plasmas with long wavelength density fluctuations
  
  • Krafft C.
  • Volokitin A.
  AIP Conference Proceedings, American Institute of Physics, 2016, 1720 (1), pp.040008. The self-consistent evolution of Langmuir turbulence generated by electron beams in solar wind plasmas with density inhomogeneities is calculated by numerical simulations based on a 1D Hamiltonian model. It is shown, owing to numerical simulations performed with parameters relevant to type III solar bursts' conditions at 1 AU, that the presence of long-wavelength random density fluctuations of sufficiently large average level crucially modifies the well-known process of beam interaction with Langmuir waves in homogeneous plasmas. (10.1063/1.4943819)
  DOI : 10.1063/1.4943819
• Poynting vector behaviour during the resonance scattering of a plane electromagnetic wave by a gyrotropic cylinder
  
  • Es'Kin V. A.
  • Ivoninsky A. V.
  • Kudrin A. V.
  • Krafft C.
  Physica Scripta, IOP Publishing, 2016, 91 (1), pp.015502. The energy-flow structure during the resonance scattering of a normally incident plane electromagnetic H wave by a gyrotropic cylinder is studied. The main attention is focused on the bifurcations of the time-averaged Poynting vector field at the surface and volume plasmon resonances in the case where the cylinder is aligned with a gyrotropy axis. The behaviour of the Poynting vector field in this case is compared with that observed during the scattering by an isotropic cylinder, and significant differences in the energy-flow structures in the two cases are revealed. Conditions are found under which the maximum magnitude of the Poynting vector at the boundary of a gyrotropic cylinder turns out to be much greater than that at the boundary of an isotropic scatterer of the same shape and size. (10.1088/0031-8949/91/1/015502)
  DOI : 10.1088/0031-8949/91/1/015502
• A comparative experimental kinetic study of spontaneous and plasma-assisted cool flames in a rapid compression machine
  
  • Vanhove G.
  • Boumehdi M.-A.
  • Shcherbanev S.A.
  • Fenard Y.
  • Desgroux Pascale
  • Starikovskaia Svetlana
  Proceedings of the Combustion Institute, Elsevier, 2016. Plasma-assisted cool flames of n- heptane were generated in the combustion chamber of a rapid compression machine coupled with a nanosecond dielectric barrier discharge, at a pressure of 1.5 bar and temperature T = 650 K. Increasing of the voltage pulse amplitude at the electrode resulted in a transition from no reactivity to induced cool flame and then to fast ignition. Sampling of the reacting mixture was performed at selected times during the experiments to draw mole fraction profiles of the fuel and major low temperature stable intermediates, showing a gradual increase in the mole fraction of these species after the discharge. Comparison with a spontaneous cool flame case at a slightly higher pressure shows that no new species are formed in the plasma-assisted case, and that after the initiation of reactivity by the discharge at the nanosecond timescale, the distribution and relative importance of the main reaction pathways is conserved at the millisecond timescale. Differences in the shape of the mole fraction and light emission profiles however suggest that the plasma-assisted cool flame is propagative. (10.1016/j.proci.2016.09.007)
  DOI : 10.1016/j.proci.2016.09.007
• Magnetospheric Multiscale observations of large-amplitude, parallel, electrostatic waves associated with magnetic reconnection at the magnetopause
  
  • Ergun R. E.
  • Holmes J. C.
  • Goodrich K. A.
  • Wilder F. D.
  • Stawarz J. E.
  • Eriksson S.
  • Newman D. L.
  • Schwartz S. J.
  • Goldman M. V.
  • Sturner A. P.
  • Malaspina D. M.
  • Usanova M. E.
  • Torbert R. B.
  • Argall M.
  • Lindqvist P.-A.
  • Khotyaintsev Y. V.
  • Burch J. L.
  • Strangeway R. J.
  • Russell C. T.
  • Pollock C. J.
  • Giles B. L.
  • Dorelli J. J. C.
  • Avanov L.
  • Hesse Michael
  • Chen L. J.
  • Lavraud B.
  • Le Contel Olivier
  • Retinò Alessandro
  • Phan T. D.
  • Eastwood Jonathan P.
  • Oieroset M.
  • Drake J. F.
  • Shay M. A.
  • Cassak P. A.
  • Nakamura R.
  • Zhou M.
  • Ashour-Abdalla M.
  • André M.
  Geophysical Research Letters, American Geophysical Union, 2016, 43 (11), pp.5626-5634. We report observations from the Magnetospheric Multiscale satellites of large-amplitude, parallel, electrostatic waves associated with magnetic reconnection at the Earth's magnetopause. The observed waves have parallel electric fields (E<SUB>||</SUB>) with amplitudes on the order of 100 mV/m and display nonlinear characteristics that suggest a possible net E<SUB>||</SUB>. These waves are observed within the ion diffusion region and adjacent to (within several electron skin depths) the electron diffusion region. They are in or near the magnetosphere side current layer. Simulation results support that the strong electrostatic linear and nonlinear wave activities appear to be driven by a two stream instability, which is a consequence of mixing cold (<10 eV) plasma in the magnetosphere with warm (~100 eV) plasma from the magnetosheath on a freshly reconnected magnetic field line. The frequent observation of these waves suggests that cold plasma is often present near the magnetopause. (10.1002/2016GL068992)
  DOI : 10.1002/2016GL068992
• Exact scaling laws for helical three-dimensional two-fluid turbulent plasmas
  
  • Andrés Nahuel
  • Galtier Sébastien
  • Sahraoui Fouad
  Physical Review E, American Physical Society (APS), 2016, 94 (6), pp.063206. We derive exact scaling laws for a three-dimensional incompressible helical two-fluid plasma, without the assumption of isotropy. For each ideal invariant of the two-fluid model, i.e., the total energy, the electron helicity, and the proton helicity, we derive simple scaling laws in terms of two-point increment correlation functions expressed in terms of the velocity field of each species and the magnetic field. These variables are appropriate for comparison with direct numerical simulation data and with in situ measurements in the near-Earth space over a broad range of spatial scales. Finally, using the exact scaling laws and dimensional analysis we predict the magnetic energy and electron helicity spectra for different ranges of scales. (10.1103/PhysRevE.94.063206)
  DOI : 10.1103/PhysRevE.94.063206
• In situ observations of flux rope at the separatrix region of magnetic reconnection
  
  • Pang Y.
  • Wang D. D.
  • Huang S. Y.
  • Retinò Alessandro
  • Phan T. D.
  • Daughton W.
  • Vaivads A.
  • Karimabadi H.
  • Zhou M.
  • Sahraoui Fouad
  • Li G. L.
  • Yuan Z. G.
  • Deng X. H.
  • Fu H.S.
  • Fu S. Y.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2016, 121 (1), pp.205-213. We present the first in situ observations of a small-scale flux rope locally formed at the separatrix region of magnetic reconnection without large guide field. Bidirectional electron beams (cold and hot beams) and density cavity accompanied by intense wave activity substantiate the crossing of the separatrix region. Density compression and one parallel electron beam are detected inside the flux rope. We suggest that this flux rope is locally generated at the separatrix region due to the tearing instability within the separatrix current layer. This observation sheds new light on the 3-D picture of magnetic reconnection in space plasma. (10.1002/2015JA021468)
  DOI : 10.1002/2015JA021468
• Mars-solar wind interaction: LatHyS, an improved parallel 3-D multispecies hybrid model
  
  • Modolo Ronan
  • Hess Sebastien
  • Mancini Marco
  • Leblanc François
  • Chaufray Jean-Yves
  • Brain David
  • Leclercq Ludivine
  • Esteban Hernandez Rosa
  • Chanteur Gérard
  • Weill Philippe
  • González-Galindo Francisco
  • Forget François
  • Yagi Manabu
  • Mazelle Christian
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2016, 121 (7), pp.6378–6399. In order to better represent Mars-Solar wind interaction, we present an unprecedented model achieving spatial resolution down to 50 km, a so far unexplored resolution for global kinetic models of the Martian ionized environment. Such resolution approaches the ionospheric plasma scale height. In practice, the model is derived from a first version described in Modolo et al. [2005]. An important effort of parallelization has been conducted and is presented here. A better description of the ionosphere was also implemented including ionospheric chemistry, electrical conductivities and a drag force modelling the ion-neutral collisions in the ionosphere. This new version of the code, named LatHyS (Latmos Hybrid Simulation), is here used to characterize the impact of various spatial resolutions on simulation results. In addition, and following a global model challenge effort [Brain et al., 2010], we present the results of simulation run for three cases which allows addressing the effect of the supra-thermal corona and of the solar EUV activity on the magnetospheric plasma boundaries and on the global escape. Simulation results showed that global patterns are relatively similar for the different spatial resolution runs but finest grid runs provide a better representation of the ionosphere and display more details of the planetary plasma dynamic. Simulation results suggest that a significant fraction of escaping O+ ions is originated from below 1200 km altitude. (10.1002/2015JA022324)
  DOI : 10.1002/2015JA022324
• Electron density measurements in highly electronegative plasmas
  
  • Rafalskyi D.V.
  • Lafleur Trevor
  • Aanesland Ane
  Plasma Sources Science and Technology, IOP Publishing, 2016, 25 (4), pp.047001. In this paper we present experimental measurements of the electron density in very electronegative ionion ArSF 6 plasmas where previous investigations using Langmuir probes have observed electronegativities of up to 5000. The electron density is measured using a short matched dipole probe technique that provides a tolerance better than&#8201;&#8201;±2 · 10 13 m &#8722;3 . The results demonstrate that the electron density in the low pressure plasma source (which contains a magnetic filter) can be reduced to around 2.7 · 10 13 m &#8722;3 with a corresponding plasma electronegativity of about 4000; close to that from fluid simulation predictions. The highest electronegativity, and lowest electron density, is achieved with a pure SF 6 plasma, while adding only 6% SF 6 to Ar allows the electronegativity to be increased from 0 to a few hundred with a corresponding decrease in the electron density by more than a thousand. The impedance probe based on a short matched dipole appears to be a practical diagnostic that can be used for independent measurements of the electron density in very electronegative plasmas, and opens up the possibility to further investigate and optimize electronegative plasma sources. (10.1088/0963-0252/25/4/047001)
  DOI : 10.1088/0963-0252/25/4/047001
• The Baseline Th17 Lymphocytes Level Is a Predictive Marker of Good Response to Biologics in Rheumatoid Arthritis
  
  • Salomon Sarah
  • Guignant Caroline
  • Morel Pierre
  • Gubler Brigitte
  • Fardellone Patrice
  • Marolleau Jean-Pierre
  • Goeb Vincent
  Arthritis & rheumatology, Wiley, 2016, 68 (10).
• Tailored voltage waveform capacitively coupled plasmas in electronegative gases: frequency dependence of asymmetry effects
  
  • Schüngel E.
  • Korolov Ihor
  • Bruneau Bastien
  • Derzsi A.
  • Johnson E.V.
  • O'Connell D.
  • Gans T.
  • Booth Jean-Paul
  • Donkó Z.
  • Schulze J.
  Journal of Physics D: Applied Physics, IOP Publishing, 2016, 49 (26), pp.265203. Capacitively coupled radio frequency plasmas operated in an electronegative gas (CF 4 ) and driven by voltage waveforms composed of four consecutive harmonics are investigated for different fundamental driving frequencies using PIC/MCC simulations and an analytical model. As has been observed previously for electropositive gases, the application of peak-shaped waveforms (that are characterized by a strong amplitude asymmetry) results in the development of a DC self-bias due to the electrical asymmetry effect (EAE), which increases the energy of ions arriving at the powered electrode. In contrast to the electropositive case (Korolov et al 2012 J. Phys. D: Appl. Phys . 45 465202) the absolute value of the DC self-bias is found to increase as the fundamental frequency is reduced in this electronegative discharge, providing an increased range over which the DC self-bias can be controlled. The analytical model reveals that this increased DC self-bias is caused by changes in the spatial profile and the mean value of the net charge density in the grounded electrode sheath. The spatio-temporally resolved simulation data show that as the frequency is reduced the grounded electrode sheath region becomes electronegative. The presence of negative ions in this sheath leads to very different dynamics of the power absorption of electrons, which in turn enhances the local electronegativity and plasma density via ionization and attachment processes. The ion flux to the grounded electrode (where the ion energy is lowest) can be up to twice that to the powered electrode. At the same time, while the mean ion energies at both electrodes are quite different, their ratio remains approximately constant for all base frequencies studied here. (10.1088/0022-3727/49/26/265203)
  DOI : 10.1088/0022-3727/49/26/265203