Publications

2009

• Study of hydrogen plasma in the negative-ion extraction region
  
  • Svarnas P.
  • Annaratone B.M.
  • Béchu Stéphane
  • Pelletier J.
  • Bacal M.
  Plasma Sources Science and Technology, IOP Publishing, 2009, 18, pp.045010. (10.1088/0963-0252/18/4/045010)
  DOI : 10.1088/0963-0252/18/4/045010
• Auroral evidence for multiple reconnection in the magnetospheric tail plasma sheet
  
  • Treumann R. A.
  • Jaroschek C. H.
  • Pottelette Raymond
  EPL - Europhysics Letters, European Physical Society / EDP Sciences / Società Italiana di Fisica / IOP Publishing, 2009, 85, pp.49001. We present auroral evidence for multiple and, most probably, small-scale reconnection in the near-Earth magnetospheric plasma sheet current layer during auroral activity. Hall currents as the source of upward and downward field-aligned currents require the generation of the corresponding electron fluxes. The auroral spatial ordering in a multiple sequence of these fluxes requires the assumption of the existence of several ―-and possibly―- even many tailward reconnection sites. (10.1209/0295-5075/85/49001)
  DOI : 10.1209/0295-5075/85/49001
• Observations of Double Layers in Earth's Plasma Sheet
  
  • Ergun R. E.
  • Andersson L.
  • Tao J. B.
  • Angelopoulos V.
  • Bonnell J. W.
  • Mcfadden J. P.
  • Larson D. E.
  • Eriksson S.
  • Johansson T.
  • Cully C. M.
  • Newman D. N.
  • Goldman M. V.
  • Roux A.
  • Le Contel Olivier
  • Glassmeier K.-H.
  • Baumjohann W.
  Physical Review Letters, American Physical Society, 2009, 102, pp.155002. We report the first direct observations of parallel electric fields (E<SUB>||</SUB>) carried by double layers (DLs) in the plasma sheet of Earth's magnetosphere. The DL observations, made by the THEMIS spacecraft, have E<SUB>||</SUB> signals that are analogous to those reported in the auroral region. DLs are observed during bursty bulk flow events, in the current sheet, and in plasma sheet boundary layer, all during periods of strong magnetic fluctuations. These observations imply that DLs are a universal process and that strongly nonlinear and kinetic behavior is intrinsic to Earth's plasma sheet. (10.1103/PhysRevLett.102.155002)
  DOI : 10.1103/PhysRevLett.102.155002
• Kinetics of ignition of saturated hydrocarbons by nonequilibrium plasma : C<SUB>2</SUB>H<SUB>6</SUB>- to C<SUB>5</SUB>H<SUB>12</SUB>-containing mixtures
  
  • Kosarev I.N.
  • Aleksandrov N.L.
  • Kindysheva S.V.
  • Starikovskaia Svetlana
  • Starikovskii A.Yu.
  Combustion and Flame, Elsevier, 2009, 156 (1), pp.221-233. The kinetics of ignition in CnH2n 2:O2:Ar mixtures for n = 2 to 5 has been studied experimentally and numerically after a high-voltage nanosecond discharge. The ignition delay time behind a reflected shock wave was measured with and without the discharge. It was shown that the initiation of the discharge with a specific deposited energy of 1030 mJ/cm3 leads to an order of magnitude decrease in the ignition delay time. Discharge processes and following chain chemical reactions with energy release were simulated. The generation of atoms, radicals and excited and charged particles was numerically simulated using the measured time-resolved discharge current and electric field in the discharge phase. The calculated densities of the active particles were used as input data to simulate plasma-assisted ignition. The sensitivity of the results to variation in electron cross sections, reaction rates and radical composition was investigated. Good agreement was obtained between the calculated ignition delay times and the experimental data. The analysis of the simulation results showed that the effect of nonequilibrium plasma on the ignition delay is associated with faster development of chain reactions, due to atoms and radicals produced by the electron impact dissociation of molecules in the discharge phase. Finally, we studied the role of various hydrocarbon radicals in the plasma-assisted ignition of the mixtures under consideration. (10.1016/j.combustflame.2008.07.013)
  DOI : 10.1016/j.combustflame.2008.07.013
• Edge-to-center plasma density ratio in high density plasma sources
  
  • Raimbault Jean-Luc
  • Chabert Pascal
  Plasma Sources Science and Technology, IOP Publishing, 2009, 18, pp.014017. The flux of positive ions leaving a classical low-temperature plasma discharge is proportional to the plasma density at the plasmasheath edge, and the edge-to-center plasma density ratio, the so-called hl factor, normally depends only on the discharge size and the neutral gas pressure. The ion flux leaving the discharge is therefore linearly proportional to the central plasma density. The hl factor has been previously derived by solving the plasma transport equations over a large pressure range, with the assumption of constant neutral gas density within the discharge. Tonks and Langmuir derived the low pressure (collisionless) solution of this problem in 1929. More recent works have shown that the neutral gas density is no longer constant when the plasma pressure becomes comparable to the neutral gas pressure. In this paper, we solve the plasma transport equations in this new situation and we propose a new expression for the hl factor. It is shown that hl becomes a function of the central plasma density which implies that the ion flux leaving the discharge is no longer proportional to this density. This effect has to be included in particle and energy balance equations used in global models of high density plasma sources. (10.1088/0963-0252/18/1/014017)
  DOI : 10.1088/0963-0252/18/1/014017
• NO production on pyrex under, and after plasma exposure
  
  • Marinov Daniil
  • Guaitella Olivier
  • Rousseau Antoine
  , 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.
• 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
• 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<SUB>&#8869;e</SUB>/T<SUB>||e</SUB>>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<SUB>||e</SUB> (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
• 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
• On the long term change in the geomagnetic activity during the 20th century
  
  • Ouattara F.
  • Amory-Mazaudier Christine
  • Menvielle Michel
  • Simon P.
  • Legrand J.-P.
  Annales Geophysicae, European Geosciences Union, 2009, 27 (5), pp.2045-2051. The analysis of the aa index series presented in this paper clearly shows that during the last century (1900 to 2000) the number of quiet days (Aa<20 nT) drastically di- minished from a mean annual value greater than 270 days per year at the end of the nineteenth century to a mean value of 160 quiet days per year one hundred years later. This de- crease is mainly due to the decrease of the number of very quiet days (Aa<13 nT). We show that the so-evidenced de- crease in the number of quiet days cannot be accounted for by drift in the aa baseline resulting in a systematic underes- timation of aa during the first quarter of the century: a 2– 3 nT overestimation in the aa increase during the 20th cen- tury would lead to a 20–40% overestimation in the decrease of the number of quiet days during the same period. The quiet days and very quiet days correspond to periods during which the Earth encounters slow solar wind streams flowing in the heliosheet during the period where the solar magnetic field has a dipolar geometry. Therefore, the ob- served change in the number of quiet days is the signature of a long term evolution of the solar coronal field topology. It may be interpreted in terms of an increase in the magnitude of the solar dipole, the associated decrease of the heliosheet thickness accounting for the observed decrease in the number of quiet days. (10.5194/angeo-27-2045-2009)
  DOI : 10.5194/angeo-27-2045-2009
• Nonlinear electron acoustic structures generated on the high-potential side of a double layer
  
  • Pottelette Raymond
  • Berthomier Matthieu
  Nonlinear Processes in Geophysics, European Geosciences Union (EGU), 2009, 16, pp.373-380. High-time resolution measurements of the electron distribution function performed in the auroral upward current region reveals a large asymmetry between the low- and high-potential sides of a double-layer. The latter side is characterized by a large enhancement of a locally trapped electron population which corresponds to a significant part (~up to 30%) of the total electron density. As compared to the background hot electron population, this trapped component has a very cold temperature in the direction parallel to the static magnetic field. Accordingly, the differential drift between the trapped and background hot electron populations generates high frequency electron acoustic waves in a direction quasi-parallel to the magnetic field. The density of the trapped electron population can be deduced from the frequency where the electron acoustic spectrum maximizes. In the auroral midcavity region, the electron acoustic waves may be modulated by an additional turbulence generated in the ion acoustic range thanks to the presence of a pre-accelerated ion beam located on the high-potential side of the double layer. Electron holes characterized by bipolar pulses in the electric field are sometimes detected in correlation with these electron acoustic wave packets. (10.5194/npg-16-373-2009)
  DOI : 10.5194/npg-16-373-2009
• West African equatorial ionospheric parameters climatology based on Ouagadougou ionosonde station data from June 1966 to February 1998
  
  • Ouattara F.
  • Amory-Mazaudier Christine
  • Fleury Rolland
  • Lassudrie Duchesne Patrick
  • Vila P.
  • Petitdidier Monique
  Annales Geophysicae, European Geosciences Union, 2009, 27 (6), pp.2503-2514. This study is the first which gives the climatology of West African equatorial ionosphere by using Ouagadougou station through three solar cycles. It has permitted to show the complete morphology of ionosphere parameters by analyzing yearly variation, solar cycle and geomagnetic activity, seasonal evolution and diurnal development. This work shows that almost all ionospheric parameters have 11-year solar cycle evolution. Seasonal variation shows that only foF2 exhibits annual, winter and semiannual anomaly. foF2 seasonal variation has permitted us to identify and characterize solar events effects on F2 layer in this area. In fact (1) during quiet geomagnetic condition foF2 presents winter and semiannual anomalies asymmetric peaks in March/April and October. (2) The absence of winter anomaly and the presence of equinoctial peaks are the most visible effects of fluctuating activity in foF2 seasonal time profiles. (3) Solar wind shock activity does not modify the profile of foF2 but increases ionization. (4) The absence of asymmetry peaks, the location of the peaks in March and October and the increase of ionization characterize recurrent storm activity. F1 layers shows increasing trend from cycle 20 to cycle 21. Moreover, E layer parameters seasonal variations exhibit complex structure. It seems impossible to detect fluctuating activity effect in E layer parameters seasonal variations but shock activity and wind stream activity act to decrease E layer ionization. It can be seen from Es layer parameters seasonal variations that wind stream activity effect is fairly independent of solar cycle. E and Es layers critical frequencies and virtual heights diurnal variations let us see the effects of the greenhouse gases in these layers. (10.5194/angeo-27-2503-2009)
  DOI : 10.5194/angeo-27-2503-2009
• 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
• 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.
• Dielectric Barrier Discharge (DBD) and Zeolite Coupling: Butane case
  
  • Youssef Joseph
  • Bouamra K.
  • Makarov M.
  • Guaitella Olivier
  • Rousseau Antoine
  , 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.
• 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 &#8764;k&#8722;5/3 at MHD scales, a &#8764;k&#8722;2.8 power law at ion scales, and an exponential &#8764;exp&#65279;[&#8722;&#8730;k&#961;e] at scales k&#961;e&#8764;[0.1,1], where &#961;e 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
• 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
• 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 B<SUB>z</SUB> 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
• Unveiling the nature of phase transitions in the Vlasov limit for a system with longrange interactions
  
  • Firpo Marie-Christine
  , 2009.
• 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