Publications

2012

• Shadowgraphic and optical emission spectroscopy investigation of nanosecond discharge in water
  
  • Marinov Ilya
  • Guaitella Olivier
  • Rousseau Antoine
  • Starikovskaia Svetlana
  , 2012.
• Study of a fast gas heating in a capillary nanosecond discharge. Discharge parameters and temperature increase in the afterglow
  
  • Klochko A.V.
  • Popov N.A.
  • Starikovskaia Svetlana
  , 2012.
• Time-resolved electric field measurements in 1-5 atm nanosecond surface dielectric discharge. Ignition of combustible mixtures by surface discharge
  
  • Kosarev I.N.
  • Sagulenko P.N.
  • Khorunzhenko V.I.
  • Popov N.A.
  • Starikovskaia Svetlana
  , 2012.
• Absolute Cl and Cl<SUB>2</SUB> densities in a Cl<SUB>2</SUB> ICP determined by TALIF with a new calibration method
  
  • Booth Jean-Paul
  • Sirse Nishant
  • Azamoum Yasmina
  • Chabert Pascal
  , 2012.
• Diagnostic emission and absorption spectroscopy
  
  • Roepcke J.
  • Rousseau Antoine
  • Lavrov B.P.
  • Davies P.B.
  , 2012.
• Dynamic Martian magnetosphere: Transient twist induced by a rotation of the IMF
  
  • Modolo Ronan
  • Chanteur Gérard
  • Dubinin Eduard
  Geophysical Research Letters, American Geophysical Union, 2012, 39 (1), pp.L01106. Simulation studies of the Martian environment are usually restricted to stationary situations under various steady conditions of the solar wind and solar radiation. Dynamic transients and their implications have so far attracted little attention although global simulation models can provide valuable insights to understand disagreements between simulations and in situ observations. We make use of a three dimensional multispecies hybrid simulation model to investigate the response of the Martian plasma environment to a sudden rotation of the IMF. The simulation model couples charged and neutral species via three ionisation mechanisms: the absorption of solar extreme ultraviolet radiation, the impact of solar wind electrons, and the charge exchange between ions and neutral atoms. When a rotational discontinuity conveyed by the solar wind reaches the Martian environment the bow shock adapts quickly to the new solar wind conditions in contrast to the induced magnetosphere, especially the magnetic lobes in the wake. Timescales necessary to recover a stationary state can be estimated from such simulations and have some implications for space observations especially in the use of magnetic field proxies and for organizing particle measurements made by a spacecraft like Mars Express without an onboard magnetometer. (10.1029/2011GL049895)
  DOI : 10.1029/2011GL049895
• Shell-Reduced MHD: weak and strong turbulence
  
  • Grappin Roland
  • Verdini Andrea
  , 2012, 14, pp.3856. MHD turbulence with guide field B0 is studied using the shell model for Reduced MHD, with the aim of characterizing the scaling, and anisotropy of RMHD at high Reynolds number. A basic prediction of anisotropic turbulence theory (critical balance or CB) is that, in presence of large enough B0, the 1D perpendicular energy spectrum should exhibit a k&#8869;-2 scaling characteristic of weak nonlinear coupling at large scales, followed by a break and a k&#8869;-5/3 scaling at smaller scales. Previous numerical simulations never obtained such double spectra, but instead displayed single power-laws with a monotonous increase of their index when B0 was increased. In the present work we observe for the first time the double scaling, possibly thanks to the high Reynolds number reachable in shell models. A corollary of the CB theory is that a k||-2 spectrum develops in the range with strong k&#8869;-5/3 scaling, characterizing spectral anisotropy. In our study, we find that, although the basic paradigm of the CB are verified, the parallel spectrum differs, showing an over-excitation of parallel modes, due to high-frequencies of the large perpendicular eddies. This proves on the one hand that the CB theory is well adapted to the RMHD model but on the other hand that the model is richer than previously thought.
• Comparison of a hybrid model to a global model of atmospheric pressure radio-frequency capacitive discharges
  
  • Lazzaroni Claudia
  • Lieberman M.A.
  • Lichtenberg A.J.
  • Chabert Pascal
  Journal of Physics D: Applied Physics, IOP Publishing, 2012, 45, pp.495204. A one-dimensional hybrid analyticalnumerical global model of atmospheric pressure radio-frequency (rf) driven capacitive discharges, previously developed, is compared with a basic global model. A helium feed gas with small admixtures of oxygen is studied. For the hybrid model, the electrical characteristics are calculated analytically as a current-driven homogeneous discharge. The electron power balance is solved analytically to determine a time-varying Maxwellian electron temperature, which oscillates on the rf timescale. Averaging over the rf period yields effective rate coefficients for gas phase activated processes. For the basic global model, the electron temperature is constant in time and the sheath physics is neglected. For both models, the particle balance relations for all species are integrated numerically to determine the equilibrium discharge parameters. Variations of discharge parameters with composition and rf power are determined and compared. The rate coefficients for electron-activated processes are strongly temperature dependent, leading to significantly larger neutral and charged particle densities for the hybrid model. For small devices, finite sheath widths limit the operating regimes to low O2 fractions. This is captured by the hybrid model but cannot be predicted from the basic global model. (10.1088/0022-3727/45/49/495204)
  DOI : 10.1088/0022-3727/45/49/495204
• Tailored voltage waveform deposition of Microcrystalline Silicon thin films from hydrogen-diluted silane and silicon tetrafluoride: optoelectronic properties of films
  
  • Johnson E.V.
  • Pouliquen S.
  • Delattre Pierre-Alexandre
  • Booth Jean-Paul
  Japanese Journal of Applied Physics, Japan Society of Applied Physics, 2012, 51, pp.08HF01. The use of tailored voltage waveforms (TVW's) to excite a plasma for the deposition of thin films of hydrogenated microcrystalline silicon (µc-Si:H) has been shown to be an effective technique to decouple mean ion bombardment energy (IBE) from injected power. In this work, we examine the changes in material properties controlled by this technique through Raman scattering and spectroscopic ellipsometry for films deposited from H2-diluted SiH4, and we examine the electrical properties of such films using temperature dependent conductivity. As the laboratory-scale deposition system used had neither a load lock nor an oxygen filter in the H2 line, accidental O-doping was observed for the µc-Si:H films. We investigated suppression of this doping by adding varying amounts of SiF4, and using an SiF4/Ar pre-etch step to clean the reactor. This technique is shown to be effective in decreasing the accidental doping of the films, and intrinsic µc-Si:H films are produced with an activation energy of up to 0.55 eV. As well, an important difference in the amorphous-to-microcrystalline transition is observed once SiF4 is included in the gas mixture. (10.1143/JJAP.51.08HF01)
  DOI : 10.1143/JJAP.51.08HF01
• On time resolved gas temperature measurements in a pulsed dc plasma using quantum cascade laser absorption spectroscopy
  
  • Hübner M.
  • Marinov Daniil
  • Guaitella Olivier
  • Rousseau Antoine
  • Roepcke J.
  Measurement Science and Technology, IOP Publishing, 2012, 23, pp.115602. With a time resolution of 33 µs, the gas temperature in a pulsed dc air plasma admixed with 0.8% NO has been measured by quantum cascade laser absorption spectroscopy (QCLAS). For this purpose, the temperature dependent intensity ratios of two absorption structures of NO at 1900 cm&#8722;1 (5.26 µm) have been used. The QCLAS system worked in the Intra Pulse Mode with a pulse repetition frequency of 30 kHz leading to a spectrum recorded each 33 µs. In a low pressure discharge, the influence of nonlinear absorption phenomena causing strong distorted absorption structures of NO has been taken into account by a calibration routine based on tabulated line strengths. Different mean plasma currents have been applied to the discharge leading to gas temperature values ranging from about 300 K up to about 500 K. (10.1088/0957-0233/23/11/115602)
  DOI : 10.1088/0957-0233/23/11/115602
• Plasma decay in the afterglow of a high-voltage nanosecond discharge in air
  
  • Aleksandrov N.L.
  • Anokhin E.M.
  • Kindysheva S.V.
  • Kirpichnikov A.A.
  • Kosarev I.N.
  • Nudnova M.M.
  • Starikovskaia Svetlana
  • Starikovskii A.Yu.
  Fizika Plazmy / Plasma Physics Reports, MAIK Nauka/Interperiodica, 2012, 38 (2), pp.179-186. The decay of air plasma produced by a high-voltage nanosecond discharge at room temperature and gas pressures in the range of 110 Torr was studied experimentally and theoretically. The time dependence of the electron density was measured with a microwave interferometer. The initial electron density was about 10¹2 cm3. The discharge homogeneity was monitored using optical methods. The dynamics of the charged particle densities in the discharge afterglow was simulated by numerically solving the balance equations for electron and ions and the equation for the electron temperature. It was shown that, under these experimental conditions, plasma electrons are mainly lost due to dissociative and three-body recombination with ions. Agreement between the measured and calculated electron densities was achieved only when the rate constant of the three-body electronion recombination was increased by one order of magnitude and the temperature dependence of this rate constant was modified. This indicates that the mechanism for three- body recombination of molecular ions differs from that of the well-studied mechanism of atomic ion recombination. (10.1134/S1063780X12010011)
  DOI : 10.1134/S1063780X12010011
• Electric and magnetic contributions to spatial diffusion in collisionless plasmas
  
  • Smets Roch
  • Belmont Gérard
  • Aunai Nicolas
  Physics of Plasmas, American Institute of Physics, 2012, 19, pp.102309. We investigate the role played by the different self-consistent fluctuations for particle diffusion in a magnetized plasma. We focus especially on the contribution of the electric fluctuations and how it combines with the (already investigated) magnetic fluctuations and with the velocity fluctuations. For that issue, we compute with a hybrid code the value of the diffusion coefficient perpendicular to the mean magnetic field and its dependence on the particle velocity. This study is restricted to small to intermediate level of electromagnetic fluctuations and focuses on particle velocities on the order of few times the Alfvén speed. We briefly discuss the consequences for cosmic ray modulation and for the penetration of thermal solar wind particles in the Earth magnetosphere. (10.1063/1.4762845)
  DOI : 10.1063/1.4762845
• Electron and wave characteristics observed by the THEMIS satellites near the magnetic equator during a pulsating aurora
  
  • Nakajima A.
  • Shiokawa K.
  • Sakaguchi K.
  • Miyoshi Y.
  • Lee S.
  • Angelopoulos V.
  • Le Contel Olivier
  • Mcfadden J. P.
  • Bonnell J. W.
  • Fornacon K.-H.
  • Donovan E.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2012, 117, pp.3219. Based on conjugate ground and THEMIS satellite observations, we show electron spectra and wave characteristics near the magnetic equatorial plane during a pulsating aurora event on the high latitude side of the auroral oval. The pulsating aurora was observed by a 30-Hz sampled all-sky imager (ASI) at Gillam (56.4°N, 265.4°E), Canada, at 0840-0910 UT on 8 January 2008. The auroral intensity pulsation at the possible THEMIS D (THD) footprints had frequency peaks at 0.1-0.2 Hz. The footprint of THD was in the poleward part of the proton aurora observed by a meridian-scanning photometer. After auroral pulsation began at 0842 UT, both THD and THEMIS E which was near THD in the mid-tail at 11.6-11.8 R<SUB>E</SUB>, observed enhanced field-aligned electron fluxes at energies of 1-10 keV. However, the amplitudes of whistler mode waves and electrostatic cyclotron harmonics (ECH) waves observed by THD with the highest sampling rate of 8 kHz were not significant, showing a marked contrast to the recent report of clear correlation between whistler mode waves and auroral pulsations observed at 5-9 R<SUB>E</SUB>. We suggest that the observed field-aligned electrons, which are probably caused by Fermi-type acceleration associated with earthward plasma flow in the mid-tail plasma sheet, are modulated by some wave processes to cause pulsating auroras. (10.1029/2011JA017066)
  DOI : 10.1029/2011JA017066
• The impact of the ITER-like wall at JET on disruptions
  
  • de Vries P. C.
  • Arnoux G.
  • Huber A.
  • Flanagan J.
  • Lehnen M.
  • Riccardo V.
  • Reux C.
  • Jachmich S.
  • Lowry C.
  • Calabro G.
  • Frigione D.
  • Tsalas M.
  • Hartmann N.
  • Brezinsek S.
  • Clever M.
  • Douai D.
  • Groth M.
  • Hender T. C.
  • Hodille E.
  • Joffrin E.
  • Kruezi U.
  • Matthews G. F.
  • Morris J.
  • Neu R.
  • Philipps V.
  • Sergienko G.
  • Sertoli M.
  Plasma Physics and Controlled Fusion, IOP Publishing, 2012, 12, pp.124032. The new full-metal ITER-like wall (ILW) at JET was found to have a profound impact on the physics of disruptions. The main difference is a significantly lower fraction (by up to a factor of 5) of energy radiated during the disruption process, yielding higher plasma temperatures after the thermal quench and thus longer current quench times. Thus, a larger fraction of the total energy was conducted to the wall resulting in larger heat loads. Active mitigation by means of massive gas injection became a necessity to avoid beryllium melting already at moderate levels of thermal and magnetic energy (i.e. already at plasma currents of 2 MA). A slower current quench, however, reduced the risk of runaway generation. Another beneficial effect of the ILW is that disruptions have a negligible impact on the formation and performance of the subsequent discharge.Culham Sci Ctr, CCFE EURATOM Assoc, Abingdon OX14 3DB, Oxon, England.EURATOM, Forschungszentrum Julich, Inst Energie & Klimatforsch IEK 4, D-52425 Julich, Germany.Ecole Polytech, CNRS, F-91128 Palaiseau, France.ERM KMS, Assoc Euratom Etat Belge Belg Staat, Brussels, Belgium.Commiss European Communities, B-1049 Brussels, Belgium.Assoc Euratom ENEA Fus, I-00044 Rome, Italy.CEA, IRFM, F-13108 St Paul Les Durance, France.Aalto Univ, Assoc EURATOM Tekes, Espoo, Finland.Ecole Cent Lyon, F-69134 Ecully, France.EURATOM, Max Planck Inst Plasmaphys, D-85748 Garching, Germany.JET EFDA Culham Sci Ctr, Abingdon OX15 3DB, Oxon, England.contract of Association between EURATOM and FOM and was carried outwithin the framework of the European Fusion Development Agreement. Theviews and opinions expressed herein do not necessarily reflect those ofthe European Commission. (10.1088/0741-3335/54/12/124032)
  DOI : 10.1088/0741-3335/54/12/124032
• Control of the ion flux and ion energy in CCP discharges using non-sinusoidal voltage waveforms
  
  • Lafleur Trevor
  • Booth Jean-Paul
  Journal of Physics D: Applied Physics, IOP Publishing, 2012, 45, pp.395203. Using particle-in-cell simulations we perform a characterization of the ion flux and ion energy in a capacitively coupled rf plasma reactor excited with non-sinusoidal voltage waveforms. The waveforms used are positive Gaussian type pulses (with a repetition frequency of 13.56 MHz), and as the pulse width is decreased, three main effects are identified that are not present in typical symmetric sinusoidal discharges: (1) the ion flux (and plasma density) rapidly increases, (2) as the pressure increases a significant asymmetry in the ion fluxes to the powered and grounded electrodes develops and (3) the average ion energy on the grounded electrode cannot be made arbitrarily small, but in fact remains essentially constant (together with the bias voltage) for the pressures investigated (20500 mTorr). Effects (1) and (3) potentially offer a new form of control in these types of rf discharges, where the ion flux can be increased while keeping the average ion energy on the grounded electrode constant. This is in contrast with the opposite control mechanism recently identified in Donkó et al (2009 J. Phys. D: Appl. Phys. 42 025205), where by changing the phase angle between applied voltage harmonics the ion flux can be kept constant while the ion energy (and bias voltage) varies. (10.1088/0022-3727/45/39/395203)
  DOI : 10.1088/0022-3727/45/39/395203
• Model of a low-pressure radio-frequency inductive discharge in Ar/O<SUB>2</SUB> used for plasma spray deposition
  
  • Lazzaroni Claudia
  • Baba K.
  • Nikravech M.
  • Chabert Pascal
  Journal of Physics D: Applied Physics, IOP Publishing, 2012, 45, pp.485207. A global (volume-averaged) model of a low-pressure radio-frequency (RF) inductive discharge used for nanostructured zinc oxide thin film deposition, the so-called spray-plasma device, is proposed. The plasma reactor is fed with an admixture of argon and oxygen and the pressure is typically several tens of mTorr. In the first step of the modelling, the injector and the substrate holder are not taken into account, and therefore zinc-containing species are not considered. The global model is based on the numerical integration of the particle balance equations and the electronic power balance equation. The model is first run until the steady state is reached to determine the equilibrium discharge parameters that are the species densities and the electron temperature. A parametric study is carried out varying the gas pressure, the RF power and the O2 fraction in the reactor. A parameter of great importance for the deposition process is the flux of the reactive species on the substrate holder and the model allows a fast exploration of this parameter. For continuous plasmas, the ratio of the reactive species flux to the total positive ion flux can be controlled varying the three basic parameters cited before (pressure, power and dilution). In the last part of the paper, we also investigate pulsed plasmas and the effect of the duty cycle variations on the neutral/ion flux ratio. (10.1088/0022-3727/45/48/485207)
  DOI : 10.1088/0022-3727/45/48/485207
• On application of quantum cascade lasers for plasma diagnostics : A Review
  
  • Röpcke J.
  • Davies P.B.
  • Lang N.
  • Rousseau Antoine
  • Welzel S.
  Journal of Physics D: Applied Physics, IOP Publishing, 2012, 45, pp.423001. Over the past few years mid-infrared absorption spectroscopy based on quantum cascade lasers operating over the region from 3 to 12 µm and called quantum cascade laser absorption spectroscopy or QCLAS has progressed considerably as a powerful diagnostic technique for in situ studies of the fundamental physics and chemistry of molecular plasmas. The increasing interest in processing plasmas containing hydrocarbons, fluorocarbons, nitrogen oxides and organo-silicon compounds has led to further applications of QCLAS because most of these compounds and their decomposition products are infrared active. QCLAS provides a means of determining the absolute concentrations of the ground states of stable and transient molecular species at time resolutions below a microsecond, which is of particular importance for the investigation of reaction kinetics and dynamics. Information about gas temperature and population densities can also be derived from QCLAS measurements. Since plasmas with molecular feed gases are used in many applications such as thin film deposition, semiconductor processing, surface activation and cleaning, and materials and waste treatment, this has stimulated the adaptation of QCLAS techniques to industrial requirements including the development of new diagnostic equipment. The recent availability of external cavity (EC) QCLs offers a further new option for multi-component detection. The aim of this paper is fourfold: (i) to briefly review spectroscopic issues arising from applying pulsed QCLs, (ii) to report on recent achievements in our understanding of molecular phenomena in plasmas and at surfaces, (iii) to describe the current status of industrial process monitoring in the mid-infrared and (iv) to discuss the potential of advanced instrumentation based on EC-QCLs for plasma diagnostics. (10.1088/0022-3727/45/42/423001)
  DOI : 10.1088/0022-3727/45/42/423001
• Hydrogenated microcrystalline silicon thin films deposited by RF-PECVD under low ion bombardment energy using voltage waveform tailoring
  
  • Johnson E.V.
  • Pouliquen S.
  • Delattre Pierre-Alexandre
  • Booth Jean-Paul
  Journal of Non-Crystalline Solids, Elsevier, 2012, 358 (17), pp.1974-1977. We present experimental results for hydrogenated amorphous and microcrystalline silicon (a-Si:H and &#956;c-Si:H) thin films deposited by PECVD while using a voltage waveform tailoring (VWT) technique to create an electrical asymmetry in the reactor. VWT dramatically modifies the mean ion bombardment energy (IBE) during growth, and we show that for a constant peak-to-peak excitation voltage (VPP), waveforms resembling peaks or valleys result in very different material properties. Using Raman scattering spectroscopy, we show that the crystallinity of the material depends strongly on the IBE, as controlled by VWT. A detailed examination of the Raman scattering spectra reveals that the narrow peak at 520 cm&#8722; 1 is disproportionately enhanced by lowering the IBE through the VWT technique. We examine this effect for a range of process parameters, varying the pressure, hydrogensilane dilution ratio, and total flow of H2. In addition, the Sisingle bondHX bonding in silicon thin films deposited using VWT is characterised for the first time, showing that the hydrogen bonding character is changed by the IBE. These results demonstrate the potential for VWT in controlling the IBE during thin film growth, thus ensuring that application-appropriate film densities and crystallinities are achieved, independent of the injected RF power. (10.1016/j.jnoncrysol.2012.01.014)
  DOI : 10.1016/j.jnoncrysol.2012.01.014
• Inductance and near fields of a loop antenna in a cold magnetoplasma in the whistler frequency band
  
  • Korobkov S. V.
  • Kostrov A. V.
  • Gushchin M. E.
  • Zaboronkova T. M.
  • Krafft C.
  Physics of Plasmas, American Institute of Physics, 2012, 19, pp.093301. The influence of a magnetoplasma on the inductance of a circular loop antenna oriented perpendicular to the ambient static magnetic field and operated in the whistler frequency band is studied. Based on a strict electrodynamic approach, the analytical treatment of the antenna reactance is performed for a uniform rf current distribution along the antenna wire. Calculations are made for plasma parameters and operating frequencies typical for active ionospheric experiments and laboratory rf (helicon) sources of dense magnetized plasmas. It is shown that the plasma influence on the inductance of the loop antenna remains relatively weak, even for antennas with dimensions close to half of the longitudinal whistler wavelength, when the rf field distribution in the antenna near zone is strongly different from that in vacuum. The theoretical predictions are confirmed by measurements performed on the large KROT plasma device. The results obtained are of crucial importance for the preparation of active ionospheric experiments and for the matching of loop antennas used in laboratory rf sources of dense magnetized plasmas. (10.1063/1.4745611)
  DOI : 10.1063/1.4745611
• Observations of turbulence within reconnection jet in the presence of guide field
  
  • Huang S. Y.
  • Zhou M.
  • Sahraoui Fouad
  • Vaivads A.
  • Deng X. H.
  • André M.
  • He J. S.
  • Fu H.S.
  • Li H. M.
  • Yuan Z. G.
  • Wang D. D.
  Geophysical Research Letters, American Geophysical Union, 2012, 39, pp.L11104. We present the first comprehensive observations of turbulence properties within high speed reconnection jet in the plasma sheet with moderate guide field. The power spectral density index is about &#8722;1.73 in the inertial range, and follows the value of &#8722;2.86 in the ion dissipation range. The turbulence is strongly anisotropic in the wave-vector space with the major power having its wave-vector highly oblique to the ambient magnetic field, suggesting that the turbulence is quasi-2D. The measured dispersion relations obtained using the k-filtering technique are compared with theory and are found to be consistent with the Alfvén-Whistler mode. In addition, both Probability Distribution Functions and flatness results show that the turbulence in the reconnection jet is intermittent (multifractal) at scales less than the proton gyroradius/inertial lengths. The estimated electric field provided by anomalous resistivity caused by turbulence is about 3 mV/m, which is close to the typical reconnection electric field in the magnetotail. (10.1029/2012GL052210)
  DOI : 10.1029/2012GL052210
• Determination of TEC by using pseudo range at Koudougou station in Burkina Faso
  
  • Ouattara Frédéric Martial
  • Zoundi C.
  • Amory-Mazaudier Christine
  • Fleury Rolland
  • Lassudrie Duchesne P.
  Journal des sciences, Université Cheikh Anta Diop, 2012, 11 (1), pp.12-19. ...
• New Insight into Short-wavelength Solar Wind Fluctuations from Vlasov Theory
  
  • Sahraoui Fouad
  • Belmont Gérard
  • Goldstein M. L.
  The Astrophysical Journal, American Astronomical Society, 2012, 748, pp.100. The nature of solar wind (SW) turbulence below the proton gyroscale is a topic that is being investigated extensively nowadays, both theoretically and observationally. Although recent observations gave evidence of the dominance of kinetic Alfvén waves (KAWs) at sub-ion scales with omega < omega<SUB>ci</SUB>, other studies suggest that the KAW mode cannot carry the turbulence cascade down to electron scales and that the whistler mode (i.e., omega > omega<SUB>ci</SUB>) is more relevant. Here, we study key properties of the short-wavelength plasma modes under limited, but realistic, SW conditions, typically beta<SUB> i </SUB> >~ beta<SUB> e </SUB> ~ 1 and for high oblique angles of propagation 80° <= Theta<SUB> kB </SUB> < 90° as observed from the Cluster spacecraft data. The linear properties of the plasma modes under these conditions are poorly known, which contrasts with the well-documented cold plasma limit and/or moderate oblique angles of propagation (Theta<SUB> kB </SUB> < 80°). Based on linear solutions of the Vlasov kinetic theory, we discuss the relevance of each plasma mode (fast, Bernstein, KAW, whistler) in carrying the energy cascade down to electron scales. We show, in particular, that the shear Alfvén mode (known in the magnetohydrodynamic limit) extends at scales krho<SUB> i </SUB> >~ 1 to frequencies either larger or smaller than omega<SUB>ci</SUB>, depending on the anisotropy k <SUB>par</SUB>/k <SUB></SUB>. This extension into small scales is more readily called whistler (omega > omega<SUB>ci</SUB>) or KAW (omega < omega<SUB>ci</SUB>), although the mode is essentially the same. This contrasts with the well-accepted idea that the whistler branch always develops as a continuation at high frequencies of the fast magnetosonic mode. We show, furthermore, that the whistler branch is more damped than the KAW one, which makes the latter the more relevant candidate to carry the energy cascade down to electron scales. We discuss how these new findings may facilitate resolution of the controversy concerning the nature of the small-scale turbulence, and we discuss the implications for present and future spacecraft wave measurements in the SW. (10.1088/0004-637X/748/2/100)
  DOI : 10.1088/0004-637X/748/2/100
• The International Research Group in geophysics, Europa Africa : a laboratory without borders in the Earth Science and Environment
  
  • Amory-Mazaudier Christine
  Journal of Life Sciences, 2012, 6, pp.336-342. ...
• Coupling between whistler waves and slow-mode solitary waves
  
  • Tenerani Anna
  • Califano F.
  • Pegoraro F.
  • Le Contel Olivier
  Physics of Plasmas, American Institute of Physics, 2012, 19, pp.052103. The interplay between electron- and ion-scale phenomena is of general interest for both laboratory and space plasma physics. In this paper, we investigate the linear coupling between whistler waves and slow magnetosonic solitons through two-fluid numerical simulations. Whistler waves can be trapped in the presence of inhomogeneous external fields such as a density hump or hole where they can propagate for times much longer than their characteristic time scale, as shown by laboratory experiments and space measurements. Space measurements have detected whistler waves also in correspondence to magnetic holes, i.e., to density humps with magnetic field minima extending on ion-scales. This raises the interesting question of how ion-scale structures can couple to whistler waves. Slow magnetosonic solitons share some of the main features of a magnetic hole. Using the ducting properties of an inhomogeneous plasma as a guide, we present a numerical study of whistler waves that are trapped and transported inside propagating slow magnetosonic solitons. (10.1063/1.4717764)
  DOI : 10.1063/1.4717764
• Thin current sheets in the presence of a guiding magnetic field in Earth's magnetosphere
  
  • Malova H. V.
  • Popov V. Y.
  • Mingalev O. V.
  • Mingalev I. V.
  • Melnik M. N.
  • Artemyev A. V.
  • Petrukovich A. A.
  • Delcourt Dominique C.
  • Shen C.
  • Zelenyi L. M.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2012, 117, pp.4212. A self-consistent theory of relatively thin anisotropic current sheets (TCS) in collisionless plasma is developed, taking into account the presence of a guiding field B<SUB>y</SUB> (all notations are used in the GSM coordinate system). TCS configurations with a finite value of guiding field B<SUB>y</SUB> are often observed in Earth's magnetotail and are typical for Earth's magnetopause. A characteristic signature of such configurations is the existence of a magnetic field component along the direction of TCS current. A general case is considered in this paper with global sheared magnetic field B<SUB>y</SUB> = const. Analytical and numerical (particle-in-cell) models for such plasma equilibria are analyzed and compared with each other as well as with Cluster observations. It is shown that, in contrast to the case with B<SUB>y</SUB> = 0, the character of ``particle-current sheet'' interaction is drastically changed in the case of a global magnetic shear. Specifically, serpentine-like parts of ion trajectories in the neutral plane become more tortuous, leading to a thicker current sheet. The reflection coefficient of particles coming from northern and southern sources also becomes asymmetric and depends upon the value of the B<SUB>y</SUB> component. As a result, the degree of asymmetry of magnetic field, plasma, and current density profiles appears characteristic of current sheets with a constant B<SUB>y</SUB>. In addition, in the presence of nonzero guiding field, the curvature current of electrons in the center of the current sheet decreases, yielding an effective thickening of the sheet. Implications of these results for current sheets in Earth's magnetosphere are discussed. (10.1029/2011JA017359)
  DOI : 10.1029/2011JA017359