Publications

2009

Titan's ionosphere in the magnetosheath : Cassini RPWS results during the T32 flyby
- Garnier P.
- Wahlund J.-E.
- Rosenqvist L.
- Modolo Ronan
- Agren K.
- Sergis N.
- Canu Patrick
- Andre M.
- Gurnett D.A.
- Kurth W.S.
- Krimigis S.M.
- Coates A.
- Dougherty M.
- Waite J.H
Annales Geophysicae, European Geosciences Union, 2009, 27 (11), pp.4257-4272. The Cassini mission has provided much information about the Titan environment, with numerous low altitude encounters with the moon being always inside the magnetosphere. The only encounter taking place outside the magnetopause, in the magnetosheath, occurred the 13 June 2007 (T32 flyby). This paper is dedicated to the analysis of the Radio and Plasma Wave investigation data during this specific encounter, in particular with the Langmuir probe, providing a detailed picture of the cold plasma environment and of Titan's ionosphere with these unique plasma conditions. The various pressure terms were also calculated during the flyby. The comparison with the T30 flyby, whose geometry was very similar to the T32 encounter but where Titan was immersed in the kronian magnetosphere, reveals that the evolution of the incident plasma has a significant influence on the structure of the ionosphere, with in particular a change of the exo-ionospheric shape. The electrical conductivities are given along the trajectory of the spacecraft and the discovery of a polar plasma cavity is reported. (10.5194/angeo-27-4257-2009)
DOI : 10.5194/angeo-27-4257-2009
Electric propulsion using ion-ion plasmas
- Aanesland Ane
- Meige A.
- Chabert Pascal
Journal of Physics: Conference Series, IOP Science, 2009, 162, pp.012009. Recently, we have proposed to use both positive and negative ions for thrust in an electromagnetic space propulsion system. This concept is called PEGASES for Plasma Propulsion with Electronegative GASES and has been patented by the Ecole Polytechnique in France in 2007. The basic idea is to create a stratified plasma with an electron free (ion-ion plasma) region at the periphery of a highly ionized plasma core such that both positive and negative ions can be extracted and accelerated to provide thrust. As the extracted beam is globally neutral there is no need for a downstream neutralizer. The recombination of positive and negative ions is very efficient and will result in a fast recombination downstream of the thruster and hence there is no creation of a plasma plume downstream. The first PEGASES prototype, designed in 2007, has recently been installed in a small vacuum chamber for preliminary tests in our laboratory and the first results have been presented in several conferences. This paper reviews important work that has been used in the process of designing the first PEGASES prototype. (10.1088/1742-6596/162/1/012009)
DOI : 10.1088/1742-6596/162/1/012009
Plasma sheet circulation pathways
- Moore T. E.
- Fok M.-C. H.
- Delcourt Dominique
- Slinker Steve P.
- Damiano P.
, 2009.
Cascade models in plasma turbulence: The role of sheared flows
- Gürcan Özgür D.
- Garbet X.
- Hennequin Pascale
- Diamond P.H.
- Casati A.
, 2009 (oral).
A novel mechanism for exciting intrinsic toroidal rotation
- Mcdevitt C.J.
- Diamond P.H.
- Gürcan Özgür D.
- Hahm T.S.
Physics of Plasmas, American Institute of Physics, 2009, 16, pp.052302. Beginning from a phase space conserving gyrokinetic formulation, a systematic derivation of parallel momentum conservation uncovers two physically distinct mechanisms by which microturbulence may drive intrinsic rotation. The first mechanism, which emanates from E×B convection of parallel momentum, has already been analyzed [ O. D. Gurcan et al., Phys. Plasmas 14, 042306 (2007) ; R. R. Dominguez and G. M. Staebler, Phys. Fluids B 5, 3876 (1993) ] and was shown to follow from radial electric field shear induced symmetry breaking of the spectrally averaged parallel wave number. Thus, this mechanism is most likely active in regions with steep pressure gradients or strong poloidal flow shear. The second mechanism uncovered, which appears in the gyrokinetic formulation through the parallel nonlinearity, emerges due to charge separation induced by the polarization drift. This novel means of driving intrinsic rotation, while nominally higher order in an expansion of the mode frequency divided by the ion cyclotron frequency, does not depend on radial electric field shear. Thus, while the magnitude of the former mechanism is strongly reduced in regions of weak radial electric field shear, this mechanism remains unabated and is thus likely relevant in complementary regimes. (10.1063/1.3122048)
DOI : 10.1063/1.3122048
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
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
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.
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
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
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
Dielectric Barrier Discharge (DBD) and Zeolite Coupling: Butane case
- Youssef Joseph
- Bouamra K.
- Makarov M.
- Guaitella Olivier
- Rousseau Antoine
, 2009.
Time resolved shadow imaging of a pulsed corona in water
- Ceccato P H
- 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.
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
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
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 studies on pulsed DC discharges using QCL
- Welzel S.
- Guaitella Olivier
- Lazzaroni Claudia
- Gatilova Lina
- Rousseau Antoine
- Roepcke J.
, 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
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
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
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.

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