Publications

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
• Long-lived plasma and fast quenching of N<SUB>2</SUB>(C<SUP>3</SUP>P<SUB>u</SUB>) by electrons in the afterglow of a nanosecond capillary discharge in nitrogen
  
  • Lepikhin N D
  • Klochko A.V.
  • Popov N A
  • Starikovskaia Svetlana
  Plasma Sources Science and Technology, IOP Publishing, 2016, 25 (4), pp.045003. Quenching of electronically excited nitrogen state, ##IMG## [http://ej.iop.org/images/0963-0252/25/4/045003/psstaa2269ieqn003.gif] \textN_2≤ft(\textC^3Π_u,v^\prime=0\right) , in the afterglow of nanosecond capillary discharge in pure nitrogen is studied. It is found experimentally that an additional collisional mechanism appears and dominates at high specific deposited energies leading to the anomalously fast quenching of the ##IMG## [http://ej.iop.org/images/0963-0252/25/4/045003/psstaa2269ieqn004.gif] \textN_2≤ft(\textC^3Π_u\right) in the afterglow. On the basis of obtained experimental data and of the analysis of possible quenching agents, it is concluded that the anomalously fast deactivation of the ##IMG## [http://ej.iop.org/images/0963-0252/25/4/045003/psstaa2269ieqn005.gif] \textN_2≤ft(\textC^3Π_u\right) can be explained by quenching by electrons. Long-lived plasma at time scale of hundreds nanoseconds after the end of the pulse is observed. High electron densities, about 10 14 cm &#1074;3 at 27 mbar, are sustained by reactions of associative ionization. Kinetic 1D numerical modeling and comparison of calculated results with experimentally measured electric fields in the second high-voltage pulse 250 ns after the initial pulse, and electron density measurements in the afterglow confirm the validity of the suggested mechanism. (10.1088/0963-0252/25/4/045003)
  DOI : 10.1088/0963-0252/25/4/045003
• Day-to-day variability of VTEC and ROTI in October 2012 with impact of high-speed solar wind stream on 13 October 2012
  
  • Azzouzi Ilyasse
  • Migoya-Orué Yenca
  • Coïsson Pierdavide
  • Amory-Mazaudier Christine
  • Fleury Rolland
  • Radicella Sandro
  Sun and Geosphere, BBC SWS Regional Network, 2016, 11 (1), pp.7-22. This paper presents the day-today variability of the Vertical Total Electron Content (VTEC) and the Rate of change of TEC Index (ROTI) in October 2012. We focused our attention to the impact of a high-speed solar wind stream (HSSWS) on the ionosphere in middle and low latitudes on 13 October 2012. This event was preceded by two other disturbances caused by a Coronal Mass Ejection (CME) at 05:26UT on 8 October and a HSSWS around 19:00UT on 9 October. The changes in the VTEC observed during the period between 8 and 12 October preceding the 13 October case showed a comparable response of the ionosphere in both hemispheres, varying mainly with latitude and presenting a stronger impact in the Northern hemisphere. The VTEC increased at the arrival of the CME on 8 October, then decreased, and increased again on 13 October. The solar wind speed associated with the second HSSWS reached its peak, 580 km/s around 17:00UT during the recovery phase of a geomagnetic storm started around 00:00UT on 13 October. Its impact was observed in Africa and in Eastern South America on the ROTI, an indicator of ionospheric scintillation. On 13 October, the ROTI was small over whole Africa and in Eastern South America at the moment the impact of the second HSSWS. These observations are interpreted as due to the ionospheric disturbance dynamo electric field associated with the Joule heating produced in the auroral zone by the HSSWS.
• Linear electromagnetic excitation of an asymmetric low pressure capacitive discharge with unequal sheath widths
  
  • Lieberman M.A.
  • Lichtenberg A.J.
  • Kawamura E.
  • Chabert Pascal
  Physics of Plasmas, American Institute of Physics, 2016, 23 (1), pp.013501. It is well-known that standing waves having radially center-high radio frequency (rf) voltage profiles exist in high frequency capacitive discharges. In this work, we determine the symmetric and antisymmetric radially propagating waves in a cylindrical capacitive discharge that is asymmetrically driven at the lower electrode by an rf voltage source. The discharge is modeled as a uniform bulk plasma which at lower frequencies has a thicker sheath at the smaller area powered electrode and a thinner sheath at the larger area grounded electrode. These are self-consistently determined at a specified density using the Child law to calculate sheath widths and the electron power balance to calculate the rf voltage. The fields and the system resonant frequencies are determined. The center-to-edge voltage ratio on the powered electrode is calculated versus frequency, and central highs are found near the resonances. The results are compared with simulations in a similar geometry using a two-dimensional hybrid fluid-analytical code, giving mainly a reasonable agreement. The analytic model may be useful for finding good operating frequencies for a given discharge geometry and power. (10.1063/1.4938204)
  DOI : 10.1063/1.4938204
• The Mass Spectrum Analyzer (MSA) on board the BepiColombo MMO
  
  • Delcourt Dominique C.
  • Saito Y.
  • Leblanc Frédéric
  • Verdeil Christophe
  • Yokota S.
  • Fraenz M.
  • Fischer H.
  • Fiethe B.
  • Katra Bruno
  • Fontaine Dominique
  • Illiano Jean-Marie
  • Berthelier Jean-Jacques
  • Krupp N.
  • Buhrke U.
  • Bubenhagen F.
  • Michalik H.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2016, 121 (7), pp.6749-6761. Observations from the MESSENGER spacecraft have considerably enhanced our understanding of the plasma environment at Mercury. In particular, measurements from the Fast Imaging Plasma Spectrometer (FIPS) provide evidences of a variety of ion species of planetary origin (He+, O+, Na+) in the northern dayside cusp and in the nightside plasma sheet. A more comprehensive view of Mercury's plasma environment will be provided by the Bepi Colombo mission that will be launched in 2018. Onboard the Bepi Colombo MMO spacecraft, the MPPE (Mercury Plasma/Particle Experiment) consortium gathers different sensors dedicated to particle measurements. Among these sensors, the Mass Spectrum Analyzer (MSA) is the instrument dedicated to plasma composition analysis. It consists of a top-hat for energy analysis followed by a Time-Of-Flight (TOF) chamber to derive the ion mass. Taking advantage of the spacecraft rotation, MSA will measure three-dimensional distribution functions in one spin (4 s), from energies characteristic of exospheric populations (in the eV range) up to plasma sheet energies (up to ~38 keV/q). A notable feature of the MSA instrument is that the TOF chamber is polarized with a linear electric field that leads to isochronous TOFs and enhanced mass resolution (typically, m/∆m ≈ 40 for ions with energies up to 13 keV/q). At Mercury, this capability is of paramount importance to thoroughly characterize the wide variety of ion species originating from the planet surface. It is thus anticipated that MSA will provide unprecedented information on ion populations in the Hermean environment and hence improve our understanding of the coupling processes at work. (10.1002/2016JA022380)
  DOI : 10.1002/2016JA022380
• Transport in the barrier billiard
  
  • Saberi Fathi S. M.
  • Ettoumi W.
  • Courbage M.
  Physical Review E, American Physical Society (APS), 2016, 93. We investigate transport properties of an ensemble of particles moving inside an infinite periodic horizontal planar barrier billiard. A particle moves among bars and elastically reflects on them. The motion is a uniform translation along the bars' axis. When the tangent of the incidence angle, alpha , is fixed and rational, the second moment of the displacement along the orthogonal axis at time n , , is either bounded or asymptotic to K n<SUP>2</SUP> , when n -->&infin; . For irrational alpha , the collision map is ergodic and has a family of weakly mixing observables, the transport is not ballistic, and autocorrelation functions decay only in time average, but may not decay for a family of irrational alpha 's. An exhaustive numerical computation shows that the transport may be superdiffusive or subdiffusive with various rates or bounded strongly depending on the values of alpha . The variety of transport behaviors sounds reminiscent of well-known behavior of conservative systems. Considering then an ensemble of particles with nonfixed alpha , the system is nonergodic and certainly not mixing and has anomalous diffusion with self-similar space-time properties. However, we verified that such a system decomposes into ergodic subdynamics breaking self-similarity. (10.1103/PhysRevE.93.062216)
  DOI : 10.1103/PhysRevE.93.062216
• Comment on "Insight into hydrogenation of graphene: Effect of hydrogen plasma chemistry" [Appl. Phys. Lett. 105, 183104 (2014)]
  
  • Marinov Daniil
  Applied Physics Letters, American Institute of Physics, 2016, 108. Not Available (10.1063/1.4953260)
  DOI : 10.1063/1.4953260
• 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
• 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.
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• 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).
• 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
• 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
• Transport matrix for particles and momentum in collisional drift waves turbulence in linear plasma devices
  
  • Ashourvan A.
  • Diamond P.H.
  • Gürcan Özgür D.
  Physics of Plasmas, American Institute of Physics, 2016, 23, pp.022309. The relationship between the physics of turbulent transport of particles and azimuthal momentum in a linear plasma device is investigated using a simple model with a background density gradient and zonal flows driven by turbulent stresses. Pure shear flow driven Kelvin-Helmholtz instabilities (k&#8741;=0) relax the flow and drive an outward (down gradient) flux of particles. However, instabilities at finite k&#8741; with flow enhanced pumping can locally drive an inward particle pinch. The turbulent vorticity flux consists of a turbulent viscosity term, which acts to reduce the global vorticity gradient and the residual vorticity flux term, accelerating the zonal flows from rest. Moreover, we use the positivity of the production of fluctuation potential enstrophy to obtain a constraint relation, which tightly links the vorticity transport to the particle transport. This relation can be useful in explaining the experimentally observed correlation between the presence of E×B flow shear and the measured inward particle flux in various magnetically confined plasma devices. (10.1063/1.4942420)
  DOI : 10.1063/1.4942420
• Turbulence intermittency linked to the weakly coherent mode in ASDEX Upgrade I-mode plasmas
  
  • Happel T.
  • Manz P.
  • Ryter F.
  • Hennequin Pascale
  • Hetzenecker A.
  • Conway G. D.
  • Guimarais L.
  • Honoré Cyrille
  • Stroth U.
  • Viezzer E.
  • The Asdex Upgrade Team
  Nuclear Fusion, IOP Publishing, 2016, 56 (6), pp.064004. This letter shows for the first time a pronounced increase of extremely intermittent edge density turbulence behavior inside the confinement region related to the I-mode confinement regime in the ASDEX Upgrade tokamak. With improving confinement, the perpendicular propagation velocity of density fluctuations in the plasma edge increases together with the intermittency of the observed density bursts. Furthermore, it is shown that the weakly coherent mode, a fluctuation feature generally observed in I-mode plasmas, is connected to the observed bursts. It is suggested that the large amplitude density bursts could be generated by a non-linearity similar to that in the Korteweg?de-Vries equation which includes the radial temperature gradient. (10.1088/0029-5515/56/6/064004)
  DOI : 10.1088/0029-5515/56/6/064004
• Estimating some parameters of the equatorial ionosphere electrodynamics from ionosonde data in West Africa
  
  • Grodji F.O.
  • Doumbia V.
  • Boka K.
  • Amory-Mazaudier Christine
  • Cohen Y.
  • Fleury Rolland
  Advances in Space Research, Elsevier, 2016. During the International Equatorial Electrojet Year (IEEY), an IPS-42 ionosonde located at Korhogo (9.33°N, 5.42°W, -1.88°dip-lat) and a meridian chain of 10 magnetic stations were setup in West Africa (5°West longitude). In this work, some characteristic parameters of the equatorial electrojet were estimated on the basis of the IPS-42 ionosonde data at Korhogo during the years 1993 and 1994. The study consisted of determining the zonal electric field through an estimate of the plasma vertical drift velocity. The daytime plasma vertical drift velocity was estimated from the time rates of change of the F-layer virtual height variations and a correction term that takes into account the ionization production and recombination effects. This method resulted in an improved vertical drift velocity, which was found to be comparable to the results of previous studies. The estimated vertical drift velocity was used in a semi-empirical approach which involved the IRI-2012 model for the Pedersen and Hall conductivities and the IGRF-10 model for the geomagnetic main field intensity. Thus the zonal and polarization electric fields on one hand, and the eastward Pedersen, Hall and the equatorial electrojet current densities on the other hand, were estimated. Furthermore the integrated peak current density at the EEJ center was estimated from ionosonde observations and compared with that inferred from magnetometer data. The integrated EEJ peak current densities obtained from both experiments were found to be in the same order and their seasonal variations exhibit the same trends as well. (10.1016/j.asr.2016.09.004)
  DOI : 10.1016/j.asr.2016.09.004