Publications

2009

Kelvin-Helmholtz waves at the Earth's magnetopause: Multiscale development and associated reconnection
- Hasegawa H.
- Retinò Alessandro
- Vaivads A.
- Khotyaintsev Y. V.
- André M.
- Nakamura T. K. M.
- Teh W.-L.
- Sonnerup B. U. Ö.
- Schwartz S. J.
- Seki Y.
- Fujimoto M.
- Saito Y.
- Rème H.
- Canu Patrick
Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2009, 114, pp.12207. We examine traversals on 20 November 2001 of the equatorial magnetopause boundary layer simultaneously at 1500 magnetic local time (MLT) by the Geotail spacecraft and at 1900 MLT by the Cluster spacecraft, which detected rolled-up MHD-scale vortices generated by the Kelvin-Helmholtz instability (KHI) under prolonged northward interplanetary magnetic field conditions. Our purpose is to address the excitation process of the KHI, MHD-scale and ion-scale structures of the vortices, and the formation mechanism of the low-latitude boundary layer (LLBL). The observed KH wavelength (>4 × 104 km) is considerably longer than predicted by the linear theory from the thickness (1000 km) of the dayside velocity shear layer. Our analyses suggest that the KHI excitation is facilitated by combined effects of the formation of the LLBL presumably through high-latitude magnetopause reconnection and compressional magnetosheath fluctuations on the dayside, and that breakup and/or coalescence of the vortices are beginning around 1900 MLT. Current layers of thickness a few times ion inertia length 100 km and of magnetic shear 60° existed at the trailing edges of the vortices. Identified in one such current sheet were signatures of local reconnection: Alfvénic outflow jet within a bifurcated current sheet, nonzero magnetic field component normal to the sheet, and field-aligned beam of accelerated electrons. Because of its incipient nature, however, this reconnection process is unlikely to lead to the observed dusk-flank LLBL. It is thus inferred that the flank LLBL resulted from other mechanisms, namely, diffusion and/or remote reconnection unidentified by Cluster. (10.1029/2009JA014042)
DOI : 10.1029/2009JA014042
Turbulence in the TORE SUPRA Tokamak: Measurements and Validation of Nonlinear Simulations
- Casati A.
- Gerbaud T.
- Hennequin P.
- Heuraux Stéphane
Physical Review Letters, American Physical Society, 2009, 102, pp.165005. Turbulence measurements in TORE SUPRA tokamak plasmas have been quantitatively compared to predictions by nonlinear gyrokinetic simulations. For the first time, numerical results simultaneously match within experimental uncertainty (a) the magnitude of effective heat diffusivity, (b) rms values of density fluctuations, and (c) wave-number spectra in both the directions perpendicular to the magnetic field. Moreover, the nonlinear simulations help to revise as an instrumental effect the apparent experimental evidence of strong turbulence anisotropy at spatial scales of the order of ion-sound Larmor radius.
What can we learn from HF signal scattered from a discrete arc?
- Seran Elena
- Godefroy Michel
- Kauristie K.
- Cerisier Jean-Claude
- Berthelier Jean-Jacques
- Lester M.
- Sarri L.-E.
Annales Geophysicae, European Geosciences Union, 2009, 27 (5), pp.1887-1896. We present observations of a discrete southward propagating arc which appeared in the mid-night sector at latitudes equatorward of main substorm activity. The arc observations were made simultaneously by the ALFA (Auroral Light Fine Analysis) optical camera, the SuperDARN-CUTLASS HF radar and the Demeter satellite during a coordinated multi-instrumental campaign conducted at the KEOPS/ESRANGE site in December 2006. The SuperDARN HF signal which is often lost in the regions of strong electron precipitation yields in our case clear backscatter from an isolated arc of weak intensity. Consequently we are able to study arc dynamics, the formation of meso-scale irregularities of the electron density along the arc, compare the arc motion with the convection of surrounding plasma and discuss the contribution of ionospheric ions in the arc erosion and its propagation. (10.5194/angeo-27-1887-2009)
DOI : 10.5194/angeo-27-1887-2009
Capture of solar wind alpha-particles by the Martian atmosphere
- Chanteur Gérard
- Dubinin E.
- Modolo Ronan
- Fraenz M.
Geophysical Research Letters, American Geophysical Union, 2009, 36 (23), pp.L23105. Integration along He++ test-particle trajectories in the self-consistent electromagnetic fields generated by three-dimensional hybrid simulations of the solar wind/Mars interaction is used to evaluate the removal of solar wind α-particles due to charge-exchange processes with neutral species of the Martian exosphere. The total removal rate of solar wind He++ ions, transformed into either singly ionised or neutral helium, is equal to 6.7 × 1023 s−1, which corresponds approximately to 30% of the flux of solar α-particles through the planetary cross-section. The deposition rate of helium neutral atoms, created by double electronic capture on exospheric oxygen, impacting the exobase, and penetrating below where it can be trapped, is about 1.5 × 1023 s−1. That means an important contribution of the solar wind source to the helium balance of the Martian atmosphere. The implantation of the solar helium into the Martian atmosphere shows an asymmetry related to the orientation of the motional electric field of the solar wind, −VSW × BIMF. (10.1029/2009GL040235)
DOI : 10.1029/2009GL040235
Time resolved quantum cascade laser absorption spectroscopy on NO containing pulsed DC discharges
- Welzel S.
- Guaitella Olivier
- Pintassilgo C.D.
- Rousseau Antoine
- Roepcke J.
, 2009.
A comment on the paper 'Solar activity and its influence on climate' Author C. de Jager Published in Netherlands Journal of Geosciences-Geologie en Mijnbouw, 87-3, pp 207213, 3 2008
- Amory-Mazaudier Christine
- Legrand J.P.
NETHERLANDS JOURNAL OF GEOSCIENCES-GEOLOGIE EN MIJNBOUW, 2009, [88-3] 177, pp.[88-3] 177. The purpose of this comment is not to criticize the results obtained by Dr C. de Jager, and we agree for example with his prediction of the next sunspot cycle amplitude - 68 with σ= 17.
Dispersion relations of electron density fluctuations in a Hall thruster plasma, observed by collective light scattering
- Tsikata Sedina
- Lemoine N.
- Pisarev V.
- Grésillon D.
Physics of Plasmas, American Institute of Physics, 2009, 16, pp.033506. Kinetic models and numerical simulations of E×B plasma discharges predict microfluctuations at the scales of the electron cyclotron drift radius and the ion plasma frequency. With the help of a specially designed collective scattering device, the first experimental observations of small-scale electron density fluctuations inside the plasma volume are obtained, and observed in the expected ranges of spatial and time scales. The anisotropy, dispersion relations, form factor, amplitude, and spatial distribution of these electron density fluctuations are described and compared to theoretical expectations. (10.1063/1.3093261)
DOI : 10.1063/1.3093261
Toroidal Rotation Driven by the Polarization Drift
- Mcdevitt C.J.
- Diamond P.H.
- Gürcan Özgür D.
- Hahm T.S.
Physical Review Letters, American Physical Society, 2009, 103, pp.205003. Starting from a phase space conserving gyrokinetic formulation, a systematic derivation of parallel momentum conservation uncovers a novel mechanism by which microturbulence may drive intrinsic rotation. This mechanism, which appears in the gyrokinetic formulation through the parallel nonlinearity, emerges due to charge separation induced by the polarization drift. The derivation and physical discussion of this mechanism will be pursued throughout this Letter. (10.1103/PhysRevLett.103.205003)
DOI : 10.1103/PhysRevLett.103.205003
International Heliophysical Year: GPS Network in Africa
- Amory-Mazaudier Christine
- Basu S.
- Bock Olivier
- Combrink A.
- Groves K.
- Fuller Rowell T.
- Lassudrie-Duchesne Patrick
- Petitdidier Monique
- Yizengaw E.
Earth, Moon, and Planets, Springer Verlag, 2009, 104 (1-4), pp.263-270. The main scientific objectives of the International Heliophysical Year are to discover and study all the physical processes coupling the Earth to the Sun. During the IHY a number of scientific instruments are being deployed all over the world. This brief report presents the scientific objectives, the GPS receiver network over Africa and the long lasting research planned for the next decades in Africa (10.1007/s11038-008-9273-8)
DOI : 10.1007/s11038-008-9273-8
Quasi-parallel whistler mode waves observed by THEMIS during near-earth dipolarizations
- Le Contel Olivier
- Roux A.
- Jacquey C.
- Robert Patrick
- Berthomier Matthieu
- Chust Thomas
- Grison B.
- Angelopoulos V.
- Sibeck David G.
- Chaston C. C.
- Cully C. M.
- Ergun B.
- Glassmeier K.-H.
- Auster U.
- Mcfadden J. P.
- Carlson C. W.
- Larson D. E.
- Bonnell J. W.
- Mende S. B.
- Russell C. T.
- Donovan E.
- Mann I. R.
- Singer H.
Annales Geophysicae, European Geosciences Union, 2009, 27, pp.2259-2275. We report on quasi-parallel whistler emissions detected by the near-earth satellites of the THEMIS mission before, during, and after local dipolarization. These emissions are associated with an electron temperature anisotropy alpha=T⊥e/T||e>1 consistent with the linear theory of whistler mode anisotropy instability. When the whistler mode emissions are observed the measured electron anisotropy varies inversely with beta||e (the ratio of the electron parallel pressure to the magnetic pressure) as predicted by Gary and Wang (1996). Narrow band whistler emissions correspond to the small alpha existing before dipolarization whereas the broad band emissions correspond to large alpha observed during and after dipolarization. The energy in the whistler mode is leaving the current sheet and is propagating along the background magnetic field, towards the Earth. A simple time-independent description based on the Liouville's theorem indicates that the electron temperature anisotropy decreases with the distance along the magnetic field from the equator. Once this variation of alpha is taken into account, the linear theory predicts an equatorial origin for the whistler mode. The linear theory is also consistent with the observed bandwidth of wave emissions. Yet, the anisotropy required to be fully consistent with the observations is somewhat larger than the measured one. Although the discrepancy remains within the instrumental error bars, this could be due to time-dependent effects which have been neglected. The possible role of the whistler waves in the substorm process is discussed. (10.5194/angeo-27-2259-2009)
DOI : 10.5194/angeo-27-2259-2009
Slow Solar Wind From Open Regions with Strong Low-Coronal Heating
- Wang Y-M
- Ko Y-K
- Grappin Roland
The Astrophysical Journal, American Astronomical Society, 2009, 691 (1), pp.760--769. By comparing solar wind data taken by the Advanced Composition Explorer during 1998-2007 with extrapolations of the observed photospheric magnetic field, we verify that high O7 /O6 and Fe/O ratios are associated with low wind speeds, large expansion factors, strong footpoint fields, and high mass and energy flux densities at the coronal base. As demonstrated by model calculations, these correlations are consistent with the idea that the bulk of the slow wind originates from regions of rapidly diverging open flux, where the coronal heating is concentrated at low heights. We identify two main components of the slow wind, one emanating from small coronal holes near active regions and characterized by particularly strong low-coronal heating, the other coming from just inside the polar-hole boundaries and characterized by weaker low-coronal heating and intermediate O7 /O6 and Fe/O ratios. (10.1088/0004-637X/691/1/760)
DOI : 10.1088/0004-637X/691/1/760
Role of internal plasma sources in planetary magnetospheres
- Moore T. E.
- Fok M.-C. H.
- Delcourt Dominique
, 2009.
Unveiling the nature of phase transitions in the Vlasov limit for a system with longrange interactions
- Firpo Marie-Christine
, 2009.
Magnetotail after Geotail, Interball and Cluster: Thin current sheets, fine structure, force balance and stability
- Zelenyi L. M.
- Malova H. V.
- Artemyev A. V.
- Popov V. Y.
- Petrukovich A. A.
- Delcourt Dominique
- Bykov V.
, 2009, pp.121-170. We present a short review devoted to some scientific achievements in the physics of Earths magnetotail current sheets based on results of Geotail, Interball and Cluster missions. The structure and dynamics of very thin current sheets (TCSs) that are often observed at the night side of the Earths magnetosphere are discussed in details. The development of theoretical ideas and models, stimulated by numerous experimental findings in the terrestrial (and other) magnetospheres, outlined to formulate the state of the art in this field of physics in the pre-THEMIS era.
On the minimal set of plasma parameters to determine the dispersion law of electron whistler waves
- Lundin B. V.
- Krafft C.
Fizika Plazmy / Plasma Physics Reports, MAIK Nauka/Interperiodica, 2009, 35 (6), pp.502-509. The minimal sufficient set of plasma parameters is presented to describe the dispersion properties of electron whistler waves (helicons) in a wide frequency range above the ion cutoff frequency, provided that the wave frequency is significantly lower than the electron plasma frequency. When the gyrofrequency of the lightest ions is much higher than those of heavier ions, it is sufficient to know the relative content of the lightest ions, the highest ion cutoff frequency, the lower hybrid resonance frequency, and the electron gyro- and plasma frequencies. In this case, the frequency of electron whistler waves is determined by the upper root of the biquadratic equation derived, whereas the lower root corresponds to a resonant mode with its refractive index increasing when the frequency tends toward the highest ion gyrofrequency from below. The developed approach is also efficient in plasmas containing a substantial amount of negative ions and/or heavy dust particulates. The accuracy of the approximate solution of the total cold plasma dispersion relation is illustrated graphically. (10.1134/S1063780X09060075)
DOI : 10.1134/S1063780X09060075
Universality of Solar-Wind Turbulent Spectrum from MHD to Electron Scales
- Alexandrova Olga
- Saur J.
- Lacombe C.
- Mangeney Anne
- Mitchell J.
- Schwartz S. J.
- Robert Patrick
Physical Review Letters, American Physical Society, 2009, 103, pp.165003. To investigate the universality of magnetic turbulence in space plasmas, we analyze seven time periods in the free solar wind under different plasma conditions. Three instruments on Cluster spacecraft operating in different frequency ranges give us the possibility to resolve spectra up to 300 Hz. We show that the spectra form a quasiuniversal spectrum following the Kolmogorovs law ∼k−5/3 at MHD scales, a ∼k−2.8 power law at ion scales, and an exponential ∼exp[−√kρe] at scales kρe∼[0.1,1], where ρe is the electron gyroradius. This is the first observation of an exponential magnetic spectrum in space plasmas that may indicate the onset of dissipation. We distinguish for the first time between the role of different spatial kinetic plasma scales and show that the electron Larmor radius plays the role of a dissipation scale in space plasma turbulence. (10.1103/PhysRevLett.103.165003)
DOI : 10.1103/PhysRevLett.103.165003
Magnetosheath excursion and the relevant transport process at the magnetopause
- Cai C. L.
- Dandouras I.
- Rème H.
- Cao J.B.
- Zhou G.C.
- Shen C.
- Parks G. K.
- Fontaine Dominique
Annales Geophysicae, European Geosciences Union, 2009, 27, pp.2997-3005. A large-amplitude excursion of the magnetosheath (MS) in quiet solar wind conditions on 17 March 2004 was recorded simultaneously by the Cluster and TC-1 spacecraft. During this period, the IMF Bz was entirely northward. The coherence between the bow shock motion and magnetopause (MP) motion is revealed and the excursion velocities of the bow shock motion are analyzed. In addition, the relevant plasma transport phenomenon in the form of flux fluctuations below the ion gyrofrequency at the MP is exposed and is interpreted as manifestation of the drift instability. Correlated observations on charge accumulation and electrostatic potential perturbation are recorded by electron measurements in high energy regime, and also the eventual cross-field vortex motion in the nonlinear stage and the consequential mass exchange are exhibited. The present investigation gives some new insight into the MS plasma transport mechanism across the subsolar MP region in quiet solar wind conditions during a period of northward IMF. (10.5194/angeo-27-2997-2009)
DOI : 10.5194/angeo-27-2997-2009
Competitive effects of an axial magnetic field and of neutral gas depletion in a positive column
- Liard Laurent
- Raimbault Jean-Luc
- Chabert Pascal
Physics of Plasmas, American Institute of Physics, 2009, 16, pp.053507. Neutral gas dynamics has been incorporated in plasma transport equations in recent studies of nonmagnetized plasma discharge equilibrium. It was found that when the plasma density increases, the neutral gas density becomes depleted in the discharge center, leading to plasma deconfinement. Consequently, larger electron temperature, flatter plasma density profiles, and larger edge-to-center plasma density ratios were observed. In this paper, we investigate the effect of adding a static axial magnetic field to the discharge. We find that at fixed plasma density at the center, the magnetic field reduces the calculated neutral depletion and all the associated effects. Nevertheless, the action of the magnetic field is less pronounced if one keeps the power deposited into the discharge fixed instead. This is because at fixed power, the plasma density increases with the magnetic field. (10.1063/1.3139262)
DOI : 10.1063/1.3139262
Velocity distribution function of sputtered Ga atoms during inductively-coupled Ar plasma treatment of a GaAs surface
- Despiau-Pujo Emilie
- Chabert Pascal
- Ramos R.
- Cunge G.
- Sadeghi N.
Journal of Vacuum Science & Technology A, American Vacuum Society, 2009, 27, pp.356-361. A GaN laser diode at 403.3 nm is used to measure the velocity distribution function (vdf) of Ga atoms sputtered from a radio-frequency biased GaAs substrate in a low pressure inductively coupled plasma (ICP) argon discharge. To investigate both perpendicular (Vz normal to wafer) and longitudinal (Vx parallel to wafer) velocity components, laser induced fluorescence (LIF) measurements are performed in the z direction and atomic absorption spectroscopy (AAS) in the x direction. The longitudinal vdf of Ga sputtered atoms is very close to a Lorentzian function with Vx comprised between 0 and 7500 m/s, while the perpendicular velocities Vz can reach 10000 m/s. Experimental results are compared to molecular dynamics (MD) simulations of Ar+ ion sputtering of GaAs under 200 eV bombardment. MD predictions and experiments are in fairly good agreement, which confirms the existence of products sputtered from the surface with kinetic energies larger than 10 eV. In etching processes dominated by physical bombardment, these energetic atoms could alter passivation layers on sidewalls and be responsible for defects observed in nanodevices. The best fit of the Doppler-broadened LIF and AAS profiles with the vdfs predicted by sputtering theory allows one to estimate the surface binding energy of Ga atoms in GaAs, Eb, to be around 3 eV. (10.1116/1.3081967)
DOI : 10.1116/1.3081967
Disk formation during collapse of magnetized protostellar cores
- Hennebelle Patrick
- Ciardi Andrea
Astronomy & Astrophysics - A&A, EDP Sciences, 2009, 506, pp.L29-L32. Context: In the context of star and planet formation, understanding the formation of disks is of fundamental importance. Aims: Previous studies found that the magnetic field has a very strong impact on the collapse of a prestellar cloud, by possibly suppressing the formation of a disk even for relatively modest values of the magnetic intensity. Since observations infer that cores have a substantial level of magnetization, this raises the question of how disks form. However, most studies have been restricted to the case in which the initial angle, alpha, between the magnetic field and the rotation axis equals 0°. Here we explore and analyse the influence of non aligned configurations on disk formation. Methods: We perform 3D ideal MHD, AMR numerical simulations for various values of mu, the ratio of the mass-to-flux to the critical mass-to-flux, and various values of alpha. Results: We find that disks form more easily as alpha increases from 0 to 90°. We propose that as the magnetized pseudo-disks become thicker with increasing alpha, the magnetic braking efficiency is lowered. We also find that even small values of alpha (~=10-20°) show significant differences with the aligned case. Conclusions: Within the framework of ideal MHD, and for our choice of initial conditions, centrifugally supported disks cannot form for values of mu smaller than ~=3 when the magnetic field and the rotation axis are perpendicular, and smaller than about ~=5-10 when they are perfectly aligned. (10.1051/0004-6361/200913008)
DOI : 10.1051/0004-6361/200913008
Mechanism of ignition by non-equilibrium plasma
- Aleksandrov N.L.
- Kindysheva S.V.
- Kosarev I.N.
- Starikovskaia Svetlana
- Starikovskii A.Yu.
Proceedings of the Combustion Institute, Elsevier, 2009, 32 (1), pp.205-212. The kinetics of ignition in stoichiometric CnH2n 2:O2:Ar mixtures with 90% dilution for n = 15 has been studied experimentally and numerically under the action of a high-voltage nanosecond discharge. It was shown that the initiation of the discharge by a high-voltage pulse 115 kV in amplitude with a specific deposited energy of 1030 mJ/cm3 leads to more than an order of magnitude decrease in the ignition delay time. The generation of atoms, radicals and excited and charged particles by the discharge was numerically described. The role of different atoms and radicals (O, H and CnH2n 1) was analyzed. The temporal evolution of the densities of intermediate components in the plasma assisted ignition was discussed. (10.1016/j.proci.2008.06.124)
DOI : 10.1016/j.proci.2008.06.124
Simulation of the ignition of a methane-air mixture by a high-voltage nanosecond discharge
- Aleksandrov N.L.
- Kindysheva S.V.
- Kukaev E. N.
- Starikovskaia Svetlana
- Starikovskii A.Yu.
Fizika Plazmy / Plasma Physics Reports, MAIK Nauka/Interperiodica, 2009, 35 (10), pp.867-882. The ignition dynamics of a CH4: O2: N2: Ar = 1: 4: 15: 80 mixture by a high-voltage nanosecond discharge is simulated numerically with allowance for experimental data on the dynamics of the discharge current and discharge electric field. The calculated induction time agrees well with experimental data. It is shown that active particles produced in the discharge at a relatively low deposited energy can reduce the induction time by two orders of magnitude. Comparison of simulation results for mixtures with and without nitrogen shows that addition of nitrogen to the mixture leads to a decrease in the average electron energy in the discharge and gives rise to new mechanisms for accumulation of oxygen atoms due to the excitation of nitrogen electronic states and their subsequent quenching in collisions with oxygen molecules. Acceleration of the discharge-initiated ignition is caused by a faster initiation of chain reactions due to the production of active particles, first of all oxygen atoms, in the discharge. (10.1134/S1063780X09100109)
DOI : 10.1134/S1063780X09100109
Time resolved shadow imaging of a pulsed corona in water
- Ceccato P H
- Guaitella Olivier
- Rousseau Antoine
, 2009.
Time resolved studies on pulsed DC discharges using QCL
- Welzel S.
- Guaitella Olivier
- Lazzaroni Claudia
- Gatilova Lina
- Rousseau Antoine
- Roepcke J.
, 2009.
Quantum Cascade Laser Absorption Spectroscopy Study on the Influence of Plasma Stimulated Surface Adsorptions to the NO Destruction Kinetics
- Hübner M.
- Guaitella Olivier
- Rousseau Antoine
- Welzel S.
- Roepcke J.
, 2009.

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