Publications

2009

• 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
• 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
• 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
• 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.
• Unveiling the nature of phase transitions in the Vlasov limit for a system with longrange interactions
  
  • Firpo Marie-Christine
  , 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 ∼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
• 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
• 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
• 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
• 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
• 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
• Production of molecules on surface under plasma exposure: Example of NO on pyrex
  
  • Marinov Daniil
  • Guaitella Olivier
  • Rousseau Antoine
  , 2009.
• Solar-geomagnetic activity and Aa indices toward a standard classification
  
  • Ouattara Frédéric Martial
  • Amory-Mazaudier Christine
  Journal of Atmospheric and Solar-Terrestrial Physics, Elsevier, 2009, 71, pp.1736-1748. Legrand and Simon [1989. Solar cycle and geomagnetic activity: a review for geophysicists. Part I. The contributions to geomagnetic activity of shock waves and of the solar wind. Annales Geophysicae 7(6), 565-578] classified one century (1868-1978) of geomagnetic activity, using the Mayaud's Aa index, in four classes related to solar activity: (1) the magnetic quiet activity due to slow solar wind flowing around the magnetosphere, (2) the recurrent activity related to high wind speed solar wind, (3) the fluctuating activity related to fluctuating solar wind and (4) the shock activity due to shock events (CME). In this paper, we use this classification to analyse the solar-geomagnetic activity from 1978 to 2005. We found that during the last three decades the level of geomagnetic quiet activity estimated by Aa indices is decreasing: 2003 is the year of the smallest level of quiet geomagnetic activity since 1868. We compare Legrand and Simon's classification with new in situ solar wind data [Richardson, I.G., Cliver, E.W., Cane, H.V., 2000. Sources of geomagnetic activity over the solar cycle: relative importance of coronal mass ejections, high-speed streams, and slow solar wind. Journal of Geophysical research 105(A8), 18,200-18,213; Richardson, I.G., Cane, H.V., 2002. Sources of geomagnetic activity during nearly three solar cycles (1972-2000). Journal of Geophysical Research 107(A8), 1187] and find a rather good agreement. The differences are only due to minor definitions of the extent of the classes. An attempt is made at defining a more precise standard classification of solar phenomena and at defining time scales of these to understand more precisely the geomagnetic signatures of solar activity. (10.1016/j.jastp.2008.05.001)
  DOI : 10.1016/j.jastp.2008.05.001
• Landau and non-Landau linear damping: Physics of the dissipation
  
  • Chust Thomas
  • Belmont Gérard
  • Mottez Fabrice
  • Hess S.
  Physics of Plasmas, American Institute of Physics, 2009, 16, pp.2104. For linear Langmuir waves, it is well known that the energy exchanges generally lead to a continuous dissipation, on average, from the electric form to the kinetic one. Many papers have estimated these exchanges and indeed shown that the classical Landau value gamma<SUB>L</SUB>, characterizing the electric field damping, can be derived from this estimation. The paper comes back to this demonstration and its implicit assumption of ``forgetting the initial conditions.'' The limits of the usual energy calculations have become much apparent recently when non-Landau solutions, decreasing with damping rates smaller than gamma<SUB>L</SUB>, have been evidenced [Belmont et al., Phys. Plasmas 15, 052310 (2008)]. Taking advantage of the explicit form provided in this paper for the perturbed distribution function, the dissipation process is revisited here in a more general way. It is shown that the energy calculations, when complete (i.e., when the role of the initial conditions is not excluded by the very hypotheses of the calculations), are indeed in full agreement with the existence of non-Landau solutions; Landau damping, by the way, appears as a particular mode of dissipation, in which the ballistic transport of the initial plasma perturbation leads to negligible effects. Two approaches are presented for this demonstration, Eulerian and Lagrangian, the first one starting from the Vlasov equation and the second from the dynamics of the individual particles. The specific role of the so-called resonant particles is investigated in both formalisms, which provides complementary pictures of the microphysics involved in the energy transfers between field and particles for Landau as well as for non-Landau solutions. (10.1063/1.3205896)
  DOI : 10.1063/1.3205896
• Introduction to several papers on special section of 'The Time varying Sun
  
  • Amory-Mazaudier Christine
  • Gregori G.
  • Schroder W.
  Journal of Atmospheric and Solar-Terrestrial Physics, Elsevier, 2009, 17-18, pp.1681-1682. The Sun is at the origin of life on the Earth, and it influences all the Earth's environment, human life, climate, geomagnetism as well as many new technologies systems as for example navigation system. This is why the time varying sun deserves to a trans-disciplinary approach of many topics. In the following 8 papers, we will consider the sun itself its relation with the earth (geomagnetism and climate). (...)
• New insights on Titan's plasma-driven Schumann resonance inferred from Huygens and Cassini data
  
  • Béghin Christian
  • Canu Patrick
  • Karkoschka E.
  • Sotin C.
  • Bertucci C.
  • Kurth W.S.
  • Berthelier Jean-Jacques
  • Grard R.
  • Hamelin Michel
  • Schwingenschuh K.
  • Simões Fernando
  Planetary and Space Science, Elsevier, 2009, 57 (14-15), pp.1872-1888. (10.1016/j.pss.2009.04.006)
  DOI : 10.1016/j.pss.2009.04.006
• Validating a quasi-linear transport model versus nonlinear simulations
  
  • Casati A.
  • Bourdelle C.
  • Garbet X.
  • Imbeaux Frédéric
  • Candy J.
  • Clairet F.
  • Dif-Pradalier Guilhem
  • Falchetto G.
  • Gerbaud T.
  • Grandgirard Virginie
  • Gürcan Özgür D.
  • Hennequin Pascale
  • Kinsey J.
  • Ottaviani M.
  • Sabot R.
  • Sarazin Y.
  • Vermare Laure
  • Waltz R. E.
  Nuclear Fusion, IOP Publishing, 2009, 49, pp.085012. In order to gain reliable predictions on turbulent fluxes in tokamak plasmas, physics based transport models are required. Nonlinear gyrokinetic electromagnetic simulations for all species are still too costly in terms of computing time. On the other hand, interestingly, the quasi-linear approximation seems to retain the relevant physics for fairly reproducing both experimental results and nonlinear gyrokinetic simulations. Quasi-linear fluxes are made of two parts: (1) the quasi-linear response of the transported quantities and (2) the saturated fluctuating electrostatic potential. The first one is shown to follow well nonlinear numerical predictions; the second one is based on both nonlinear simulations and turbulence measurements. The resulting quasi-linear fluxes computed by QuaLiKiz (Bourdelle et al 2007 Phys. Plasmas 14 112501) are shown to agree with the nonlinear predictions when varying various dimensionless parameters, such as the temperature gradients, the ion to electron temperature ratio, the dimensionless collisionality, the effective charge and ranging from ion temperature gradient to trapped electron modes turbulence. (10.1088/0029-5515/49/8/085012)
  DOI : 10.1088/0029-5515/49/8/085012
• Ignition with Low-Temperature Plasma : Kinetic Mechanism and Experimental Verification
  
  • Starikovskaia Svetlana
  • Aleksandrov N.L.
  • Kosarev I.N.
  • Kindysheva S.V.
  • Starikovskii A.Yu.
  High Energy Chemistry, 2009, 43 (3), pp.213-218. The results of experiments and calculations performed at the Laboratory of Physics of Nonequilibrium Systems, Moscow Institute of Physics and Technology from 1996 to 2008 to demonstrate the efficiency of low-temperature plasma in initiation of combustion of gas mixtures over a wide range of initial conditions are surveyed. In the studies reviewed, a method for quantitative analysis of kinetic processes during ignition of combustible gas mixtures by nonequilibrium plasma was developed. (10.1134/S0018143909030096)
  DOI : 10.1134/S0018143909030096
• Fluid model of an electronegative discharge with magnetized electrons and unmagnetized ions
  
  • Leray Gary
  • Chabert Pascal
  • Lichtenberg A.J.
  • Lieberman M.A.
  Journal of Physics D: Applied Physics, IOP Publishing, 2009, 42, pp.194020. A fluid model is developed to determine the cross-field equilibrium densities and fluxes in a finite-size electronegative discharge with magnetized electrons and unmagnetized positive and negative ions. A two-dimensional rectangular geometry with a uniform axial magnetic field is considered. After averaging over the axial losses, the fluid equations, including ion inertia terms, are integrated numerically along the transverse direction to determine the equilibrium quantities, for the boundary condition of vanishing electron density and flux at a transverse insulating wall. This yields equilibrium solutions with equal flows of positive and negative ions to the transverse wall, and with equal positive ion and electron flows to the axial walls. An analytical model is developed for this case, neglecting ion inertia, and is used to determine the scaling of the discharge equilibrium with discharge parameters and to optimize the ion fluxes. The model and the numerical integrations are in reasonable agreement. (10.1088/0022-3727/42/19/194020)
  DOI : 10.1088/0022-3727/42/19/194020
• Dynamics and waves near multiple magnetic null points in reconnection diffusion region
  
  • Deng X. H.
  • Zhou M.
  • Li S. Y.
  • Baumjohann W.
  • André M.
  • Cornilleau-Wehrlin Nicole
  • Santolík O.
  • Pontin D. I.
  • Rème H.
  • Lucek E.
  • Fazakerley A.
  • Décréau Pierrette
  • Daly P.
  • Nakamura R.
  • Tang R. X.
  • Hu Y. H.
  • Pang Y.
  • Büchner J.
  • Zhao H.
  • Vaivads A.
  • Pickett J. S.
  • Ng C. S.
  • Lin X.
  • Fu S. Y.
  • Yuan Z. G.
  • Su Z. W.
  • Wang J. F.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2009, 114 (A7), pp.A07216. Identifying the magnetic structure in the region where the magnetic field lines break and how reconnection happens is crucial to improving our understanding of three-dimensional reconnection. Here we show the in situ observation of magnetic null structures in the diffusion region, the dynamics, and the associated waves. Possible spiral null pair has been identified near the diffusion region. There is a close relation among the null points, the bipolar signature of the Z component of the magnetic field, and enhancement of the flux of energetic electrons up to 100 keV. Near the null structures, whistler-mode waves were identified by both the polarity and the power law of the spectrum of electric and magnetic fields. It is found that the angle between the fans of the nulls is quite close to the theoretically estimated maximum value of the group-velocity cone angle for the whistler wave regime of reconnection. (10.1029/2008JA013197)
  DOI : 10.1029/2008JA013197
• Nature des transitions de phase hors-équilibre dans un système avec interactions à longue portée
  
  • Firpo Marie-Christine
  , 2009. Papier sélectionné comme communication flash dans la session "Systèmes complexes : la physique statistique a perdu léquilibre . . . ".