Publications

2012

• Shadowgraphic and optical emission spectroscopy investigation of nanosecond discharge in water
  
  • Marinov Ilya
  • Guaitella Olivier
  • Rousseau Antoine
  • Starikovskaia Svetlana
  , 2012.
• Study of a fast gas heating in a capillary nanosecond discharge. Discharge parameters and temperature increase in the afterglow
  
  • Klochko A.V.
  • Popov N.A.
  • Starikovskaia Svetlana
  , 2012.
• Time-resolved electric field measurements in 1-5 atm nanosecond surface dielectric discharge. Ignition of combustible mixtures by surface discharge
  
  • Kosarev I.N.
  • Sagulenko P.N.
  • Khorunzhenko V.I.
  • Popov N.A.
  • Starikovskaia Svetlana
  , 2012.
• Absolute Cl and Cl<SUB>2</SUB> densities in a Cl<SUB>2</SUB> ICP determined by TALIF with a new calibration method
  
  • Booth Jean-Paul
  • Sirse Nishant
  • Azamoum Yasmina
  • Chabert Pascal
  , 2012.
• A global hybrid model for Mercury's interaction with the solar wind: Case study of the dipole representation
  
  • Richer Emilie
  • Modolo Ronan
  • Chanteur Gérard
  • Hess Sebastien
  • Leblanc François
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2012, 117 (A10), pp.A10228. The interaction of the solar wind (SW) with the magnetic field of Mercury is investigated by means of a three dimensional parallelized multispecies hybrid model. A comparison between two mathematical representations of Mercury's intrinsic magnetic field is studied. The first model is an Offset Dipole (OD) having the offset and dipolar moment reported by Anderson et al. (2011). The second model is a combination of a Dipole and a Quadrupole (DQ), the total field is fitted to the offset dipolar field, for northern latitudes greater than 50°. Simulations reproduce the features which characterize Mercury's interaction with the SW, encompassing the Bow Shock (BS), the magnetosheath, the magnetotail, the "cusps" region and the neutral current sheet. Global hybrid simulations of the Hermean magnetosphere run for the OD and DQ models demonstrate that the southern parts of the magnetospheres produced by the OD and DQ models differ greatly in topology and volume meanwhile their northern parts-are quite similar. In particular the DQ model exhibits a dome of closed field lines around the south pole in contrast to the OD. Without further information on the intrinsic magnetic field of the planet in the southern region which should be provided by BepiColombo after year 2020, we can only speculate on the influence of the different magnetic topologies on the magnetospheric dynamics. (10.1029/2012JA017898)
  DOI : 10.1029/2012JA017898
• A dc-pulsed capacitively coupled planar Langmuir probe for plasma process diagnostics and monitoring
  
  • Samara V.
  • Booth Jean-Paul
  • de Marneffe J.-F.
  • Milenin A.P.
  • Brouri M.
  • Boullart W.
  Plasma Sources Science and Technology, IOP Publishing, 2012, 21, pp.065004. An improvement to the RF-biased planar Langmuir probe technique proposed by Braithwaite et al (1996 Plasma Sources Sci. Technol. 5 67) is demonstrated, and applied to the case of an industrial CCP reactor. Compared with the RF-biased probe, the new technique uses dc pulses instead of RF bursts, which provides similar results but with simpler electronics. The ion fluxes determined by both techniques are compared under the same O2/Ar plasma conditions using available literature data for the RF-biased case. The data show not only the same trends but very close absolute values of ion fluxes for all studied plasma conditions after correcting for the chamber-area difference. Furthermore, the new technique has the additional benefit of providing information on the 'electron transition region' of the IV curve, as well as allowing the resistance and capacitance of films deposited on the probe to be determined. Finally, both experimental data and numerical simulations of the IV characteristics and the film parameters are presented for different oxidizing plasmas. (10.1088/0963-0252/21/6/065004)
  DOI : 10.1088/0963-0252/21/6/065004
• Enhanced sheath heating in capacitively coupled discharges due to non-sinusoidal voltage waveforms
  
  • Lafleur Trevor
  • Boswell R.W.
  • Booth Jean-Paul
  Applied Physics Letters, American Institute of Physics, 2012, 100, pp.194101. Through the use of particle-in-cell simulations, we demonstrate that the power deposition in capacitively coupled discharges (in argon) can be increased by replacing sinusoidal waveforms with Gaussian-shaped voltage pulses (with a repetition frequency of 13.56 MHz). By changing the Gaussian pulse width, electron heating can be directly controlled, allowing for an increased plasma density and ion flux for the same gas pressure and geometrical operating conditions. Analysis of the power deposition profiles and electron distribution functions shows that enhanced electron-sheath heating is responsible for the increased power absorption. (10.1063/1.4712128)
  DOI : 10.1063/1.4712128
• Separate control of the ion flux and ion energy in capacitively coupled rf discharges using voltage waveform tailoring
  
  • Lafleur Trevor
  • Delattre Pierre-Alexandre
  • Johnson E.V.
  • Booth Jean-Paul
  Applied Physics Letters, American Institute of Physics, 2012, 101, pp.124104. We experimentally characterize an argon plasma in a geometrically symmetric, capacitively coupled rf discharge, excited by pulse-type tailored waveforms (generated using multiple voltage harmonics). The results confirm a number of predictions made by recent particle-in-cell simulations of a similar system and demonstrate a unique form of control over the ion flux and ion energy in capacitively coupled plasmas; by increasing the number of applied harmonics (equivalent to decreasing the pulse width), it is possible to increase the plasma density and ion flux (together with the power deposition) while keeping the average ion energy on one of the electrodes low and constant. (10.1063/1.4754692)
  DOI : 10.1063/1.4754692
• Absolute atomic chlorine densities in a Cl<SUB>2</SUB> ICP determined by Two-Photon Laser Induced Fluorescence with a new calibration method
  
  • Booth Jean-Paul
  • Azamoum Yasmina
  • Sirse Nishant
  • Chabert Pascal
  Journal of Physics D: Applied Physics, IOP Publishing, 2012, 45, pp.195201. Absolute densities of chlorine atoms were determined in an inductively coupled plasma in pure chlorine gas as a function of gas pressure and RF power by two-photon laser-induced fluorescence. A new technique is proposed to put the relative two-photon laser-induced fluorescence (TALIF) measurements on an absolute scale, based on photolysis of Cl2 gas (without plasma) with a tripled Nd&#8201;:&#8201;YAG laser at 355 nm. Because the dissociation cross-section and photo-dissociation laser beam energy density are well known, the absolute densities can be determined with high accuracy. We find that the ratio of the Cl atom density normalized to the Cl2 gas density without plasma at the reactor centre increases with RF power and decreases with gas pressure, reaching 20% at 2 mTorr 500 WRF. (10.1088/0022-3727/45/19/195201)
  DOI : 10.1088/0022-3727/45/19/195201
• Coronal heating in coupled photosphere-chromosphere-coronal systems: turbulence and leakage
  
  • Verdini Andrea
  • Grappin Roland
  • Velli Marco
  Astronomy & Astrophysics - A&A, EDP Sciences, 2012, 538, pp.70. Context. Coronal loops act as resonant cavities for low-frequency fluctuations that are transmitted from the deeper layers of the solar atmosphere. These fluctuations are amplified in the corona and lead to the development of turbulence that in turn is able to dissipate the accumulated energy, thus heating the corona. However, trapping is not perfect, because some energy leaks down to the chromosphere on a long timescale, limiting the turbulent heating. Aims. We consider the combined effects of turbulence and energy leakage from the corona to the photosphere in determining the turbulent energy level and associated heating rate in models of coronal loops, which include the chromosphere and transition region. Methods. We use a piece-wise constant model for the Alfvén speed in loops and a reduced MHD-shell model to describe the interplay between turbulent dynamics in the direction perpendicular to the mean field and propagation along the field. Turbulence is sustained by incoming fluctuations that are equivalent, in the line-tied case, to forcing by the photospheric shear flows. While varying the turbulence strength, we systematically compare the average coronal energy level and dissipation in three models with increasing complexity: the classical closed model, the open corona, and the open corona including chromosphere (or three-layer model), with the last two models allowing energy leakage. Results. We find that (i) leakage always plays a role. Even for strong turbulence, the dissipation time never becomes much lower than the leakage time, at least in the three-layer model; therefore, both the energy and the dissipation levels are systematically lower than in the line-tied model; (ii) in all models, the energy level is close to the resonant prediction, i.e., assuming an effective turbulent correlation time longer than the Alfvén coronal crossing time; (iii) the heating rate is close to the value given by the ratio of photospheric energy divided by the Alfvén crossing time; (iv) the coronal spectral range is divided in two: an inertial range with 5/3 spectral slope, and a large-scale peak where nonlinear couplings are inhibited by trapped resonant modes; (v) in the realistic three-layer model, the two-component spectrum leads to a global decrease in damping equal to Kolmogorov damping reduced by a factor urms/Vac where Vac is the coronal Alfvén speed. (10.1051/0004-6361/201118046)
  DOI : 10.1051/0004-6361/201118046
• Effect of sheared flow on the growth rate and turbulence decorrelation
  
  • Gürcan Özgür D.
  Physical Review Letters, American Physical Society, 2012, 109, pp.155006. The effect of a large scale flow shear on a linearly unstable turbulent system is considered. A cubic equation describing the effective growth rate is obtained, which is shown to reduce to well-known forms in weak and strong shear limits. A shear suppression rule is derived which corresponds to the point where the effective growth rate becomes negative. The effect of flow shear on nonlinear mode coupling of drift or Rossby waves is also considered, and it is shown that the resonance manifold shrinks and weakens as the vortices are sheared. This leads to a reduction of the efficiency of three-wave interactions. Tilted eddies can then only couple to the large scale sheared flows, because the resonance condition for that interaction is trivially satisfied. It is argued that this leads to absorbtion of the sheared vortices by large scale flow structures. Studying the form of the effective growth rate for weak shear, it was shown that in addition to reducing the overall growth rate, a weak flow shear also reduces the wave number where the fluctuations are most unstable. (10.1103/PhysRevLett.109.155006)
  DOI : 10.1103/PhysRevLett.109.155006
• Analysis of symmetry breaking mechanisms and the role of turbulence self-regulation in intrinsic rotation
  
  • Kwon J.M.
  • Yi Sukyoung
  • Rhee T.
  • Diamond P.H.
  • Miki K.
  • Hahm T.S.
  • Kim J.Y.
  • Gürcan Özgür D.
  • Mcdevitt C.J.
  Nuclear Fusion, IOP Publishing, 2012, 52, pp.013004. We present analyses of mechanisms which convert radial inhomogeneity to broken k||-symmetry and thus produce turbulence driven intrinsic rotation in tokamak plasmas. By performing gyrokinetic simulations of ITG turbulence, we explore the many origins of broken k||-symmetry in the fluctuation spectrum and identify both E × B shear and the radial gradient of turbulence intensitya ubiquitous radial inhomogeneity in tokamak plasmasas important k||-symmetry breaking mechanisms. By studying and comparing the correlations between residual stress, E × B shearing, fluctuation intensity and its radial gradient, we investigate the dynamics of residual stress generation by various symmetry breaking mechanisms and explore the implication of the self-regulating dynamics of fluctuation intensity and E × B shearing for intrinsic rotation generation. Several scalings for intrinsic rotation are reported and are linked to investigations of underlying local dynamics. It is found that stronger intrinsic rotation is generated for higher values of ion temperature gradient, safety factor and weaker magnetic shear. These trends are broadly consistent with the intrinsic rotation scaling found from experimentthe so-called Rice scaling. (10.1088/0029-5515/52/1/013004)
  DOI : 10.1088/0029-5515/52/1/013004
• Detection of Small-Scale Structures in the Dissipation Regime of Solar-Wind Turbulence
  
  • Perri S.
  • Goldstein M. L.
  • Dorelli J. C.
  • Sahraoui Fouad
  Physical Review Letters, American Physical Society, 2012, 109 (19), pp.191101. Recent observations of the solar wind have pointed out the existence of a cascade of magnetic energy from the scale of the proton Larmor radius &#961;p down to the electron Larmor radius &#961;e scale. In this Letter we study the spatial properties of magnetic field fluctuations in the solar wind and find that at small scales the magnetic field does not resemble a sea of homogeneous fluctuations, but rather a two-dimensional plane containing thin current sheets and discontinuities with spatial sizes ranging from l&#8819;&#961;p down to &#961;e and below. These isolated structures may be manifestations of intermittency that localize sites of turbulent dissipation. Studying the relationship between turbulent dissipation, reconnection, and intermittency is crucial for understanding the dynamics of laboratory and astrophysical plasmas. (10.1103/PhysRevLett.109.191101)
  DOI : 10.1103/PhysRevLett.109.191101
• Source location of falling tone chorus
  
  • Kurita S.
  • Misawa H.
  • Cully C. M.
  • Le Contel Olivier
  • Angelopoulos V.
  Geophysical Research Letters, American Geophysical Union, 2012, 39, pp.22102. Chorus is characterized by its fine structures consisting of rising or falling tones believed to result from nonlinear wave-particle interactions. However, previous studies have showed that the intensity and propagation characteristics of rising and falling tone chorus are quite different, suggesting that their generation processes might be different. In this paper, the propagation direction of falling tone chorus is statistically investigated to identify its source region based on the Poynting vector measurement with THEMIS. The result shows that the falling tone chorus propagates from the magnetic equator to higher latitude both in the northern and southern hemispheres, in the same way as rising tone chorus. Our result shows that the magnetic equator is the common source location for both rising and falling tone chorus. The result emphasizes that the different properties between rising and falling tone chorus originate from their generation mechanism rather than source region. (10.1029/2012GL053929)
  DOI : 10.1029/2012GL053929
• Inductance and near fields of a loop antenna in a cold magnetoplasma in the whistler frequency band
  
  • Korobkov S. V.
  • Kostrov A. V.
  • Gushchin M. E.
  • Zaboronkova T. M.
  • Krafft C.
  Physics of Plasmas, American Institute of Physics, 2012, 19, pp.093301. The influence of a magnetoplasma on the inductance of a circular loop antenna oriented perpendicular to the ambient static magnetic field and operated in the whistler frequency band is studied. Based on a strict electrodynamic approach, the analytical treatment of the antenna reactance is performed for a uniform rf current distribution along the antenna wire. Calculations are made for plasma parameters and operating frequencies typical for active ionospheric experiments and laboratory rf (helicon) sources of dense magnetized plasmas. It is shown that the plasma influence on the inductance of the loop antenna remains relatively weak, even for antennas with dimensions close to half of the longitudinal whistler wavelength, when the rf field distribution in the antenna near zone is strongly different from that in vacuum. The theoretical predictions are confirmed by measurements performed on the large KROT plasma device. The results obtained are of crucial importance for the preparation of active ionospheric experiments and for the matching of loop antennas used in laboratory rf sources of dense magnetized plasmas. (10.1063/1.4745611)
  DOI : 10.1063/1.4745611
• A hemispherical retarding field energy analyzer to characterize spatially and angularly extended electron beams
  
  • Cipriani Fabrice
  • Leblanc Frédéric
  • Illiano Jean-Marie
  • Berthelier Jean-Jacques
  European Physical Journal: Applied Physics, EDP Sciences, 2012, 60 (2), pp.21002 (7 p.). We have designed and built a hemispherical retarding field energy analyzer in order to facilitate characterization of large area electron emitters (typically field emitter arrays with active areas up to 1 cm2) with large angular aperture. A complete numerical model of the analyzer has been built, including perturbations due to secondary particles, in order to determine the analyzer performances. The analyzer energy resolution is better than 100 meV for an energy range up to 120 eV. The analyzer has a global field of view of 112° and allows measurements of the energy distribution of the beam as a function of the emission angle, as well as measurements of the beam intensity profile along any section of the beam. We have successfully used the analyzer to characterize the electron beam emitted by 1 cm2 Mo microtips-based field emitter arrays. (10.1051/epjap/2012120011)
  DOI : 10.1051/epjap/2012120011
• The impact of the ITER-like wall at JET on disruptions
  
  • de Vries P. C.
  • Arnoux G.
  • Huber A.
  • Flanagan J.
  • Lehnen M.
  • Riccardo V.
  • Reux C.
  • Jachmich S.
  • Lowry C.
  • Calabro G.
  • Frigione D.
  • Tsalas M.
  • Hartmann N.
  • Brezinsek S.
  • Clever M.
  • Douai D.
  • Groth M.
  • Hender T. C.
  • Hodille E.
  • Joffrin E.
  • Kruezi U.
  • Matthews G. F.
  • Morris J.
  • Neu R.
  • Philipps V.
  • Sergienko G.
  • Sertoli M.
  Plasma Physics and Controlled Fusion, IOP Publishing, 2012, 12, pp.124032. The new full-metal ITER-like wall (ILW) at JET was found to have a profound impact on the physics of disruptions. The main difference is a significantly lower fraction (by up to a factor of 5) of energy radiated during the disruption process, yielding higher plasma temperatures after the thermal quench and thus longer current quench times. Thus, a larger fraction of the total energy was conducted to the wall resulting in larger heat loads. Active mitigation by means of massive gas injection became a necessity to avoid beryllium melting already at moderate levels of thermal and magnetic energy (i.e. already at plasma currents of 2 MA). A slower current quench, however, reduced the risk of runaway generation. Another beneficial effect of the ILW is that disruptions have a negligible impact on the formation and performance of the subsequent discharge.Culham Sci Ctr, CCFE EURATOM Assoc, Abingdon OX14 3DB, Oxon, England.EURATOM, Forschungszentrum Julich, Inst Energie & Klimatforsch IEK 4, D-52425 Julich, Germany.Ecole Polytech, CNRS, F-91128 Palaiseau, France.ERM KMS, Assoc Euratom Etat Belge Belg Staat, Brussels, Belgium.Commiss European Communities, B-1049 Brussels, Belgium.Assoc Euratom ENEA Fus, I-00044 Rome, Italy.CEA, IRFM, F-13108 St Paul Les Durance, France.Aalto Univ, Assoc EURATOM Tekes, Espoo, Finland.Ecole Cent Lyon, F-69134 Ecully, France.EURATOM, Max Planck Inst Plasmaphys, D-85748 Garching, Germany.JET EFDA Culham Sci Ctr, Abingdon OX15 3DB, Oxon, England.contract of Association between EURATOM and FOM and was carried outwithin the framework of the European Fusion Development Agreement. Theviews and opinions expressed herein do not necessarily reflect those ofthe European Commission. (10.1088/0741-3335/54/12/124032)
  DOI : 10.1088/0741-3335/54/12/124032
• Solar wind charge exchange X-ray emission from Mars.
  
  • Koutroumpa Dimitra
  • Modolo Ronan
  • Chanteur Gérard
  • Chaufray Jean-Yves
  • Kharchenko V.
  • Lallement Rosine
  Astronomy & Astrophysics - A&A, EDP Sciences, 2012, 545, pp.A153. We study the soft X-ray emission induced by charge exchange (CX) collisions between solar-wind, highly charged ions and neutral atoms of the Martian exosphere. A 3D multi species hybrid simulation model with improved spatial resolution (130 km) is used to describe the interaction between the solar wind and the Martian neutrals. We calculated velocity and density distributions of the solar wind plasma in the Martian environment with realistic planetary ions description, using spherically symmetric exospheric H and O profiles. Following that, a 3D test-particle model was developed to compute the X-ray emission produced by CX collisions between neutrals and solar wind minor ions. The model results are compared to XMM-Newton observations of Mars. We calculate projected X-ray emission maps for the XMM-Newton observing conditions and demonstrate how the X-ray emission reflects the Martian electromagnetic structure in accordance with the observed X-ray images. Our maps confirm that X-ray images are a powerful tool for the study of solar wind - planetary interfaces. However, the simulation results reveal several quantitative discrepancies compared to the observations. Typical solar wind and neutral coronae conditions corresponding to the 2003 observation period of Mars cannot reproduce the high luminosity or the corresponding very extended halo observed with XMM-Newton. Potential explanations of these discrepancies are discussed. (10.1051/0004-6361/201219720)
  DOI : 10.1051/0004-6361/201219720
• On application of quantum cascade lasers for plasma diagnostics : A Review
  
  • Röpcke J.
  • Davies P.B.
  • Lang N.
  • Rousseau Antoine
  • Welzel S.
  Journal of Physics D: Applied Physics, IOP Publishing, 2012, 45, pp.423001. Over the past few years mid-infrared absorption spectroscopy based on quantum cascade lasers operating over the region from 3 to 12 µm and called quantum cascade laser absorption spectroscopy or QCLAS has progressed considerably as a powerful diagnostic technique for in situ studies of the fundamental physics and chemistry of molecular plasmas. The increasing interest in processing plasmas containing hydrocarbons, fluorocarbons, nitrogen oxides and organo-silicon compounds has led to further applications of QCLAS because most of these compounds and their decomposition products are infrared active. QCLAS provides a means of determining the absolute concentrations of the ground states of stable and transient molecular species at time resolutions below a microsecond, which is of particular importance for the investigation of reaction kinetics and dynamics. Information about gas temperature and population densities can also be derived from QCLAS measurements. Since plasmas with molecular feed gases are used in many applications such as thin film deposition, semiconductor processing, surface activation and cleaning, and materials and waste treatment, this has stimulated the adaptation of QCLAS techniques to industrial requirements including the development of new diagnostic equipment. The recent availability of external cavity (EC) QCLs offers a further new option for multi-component detection. The aim of this paper is fourfold: (i) to briefly review spectroscopic issues arising from applying pulsed QCLs, (ii) to report on recent achievements in our understanding of molecular phenomena in plasmas and at surfaces, (iii) to describe the current status of industrial process monitoring in the mid-infrared and (iv) to discuss the potential of advanced instrumentation based on EC-QCLs for plasma diagnostics. (10.1088/0022-3727/45/42/423001)
  DOI : 10.1088/0022-3727/45/42/423001
• Thin current sheets in the presence of a guiding magnetic field in Earth's magnetosphere
  
  • Malova H. V.
  • Popov V. Y.
  • Mingalev O. V.
  • Mingalev I. V.
  • Melnik M. N.
  • Artemyev A. V.
  • Petrukovich A. A.
  • Delcourt Dominique C.
  • Shen C.
  • Zelenyi L. M.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2012, 117, pp.4212. A self-consistent theory of relatively thin anisotropic current sheets (TCS) in collisionless plasma is developed, taking into account the presence of a guiding field B<SUB>y</SUB> (all notations are used in the GSM coordinate system). TCS configurations with a finite value of guiding field B<SUB>y</SUB> are often observed in Earth's magnetotail and are typical for Earth's magnetopause. A characteristic signature of such configurations is the existence of a magnetic field component along the direction of TCS current. A general case is considered in this paper with global sheared magnetic field B<SUB>y</SUB> = const. Analytical and numerical (particle-in-cell) models for such plasma equilibria are analyzed and compared with each other as well as with Cluster observations. It is shown that, in contrast to the case with B<SUB>y</SUB> = 0, the character of ``particle-current sheet'' interaction is drastically changed in the case of a global magnetic shear. Specifically, serpentine-like parts of ion trajectories in the neutral plane become more tortuous, leading to a thicker current sheet. The reflection coefficient of particles coming from northern and southern sources also becomes asymmetric and depends upon the value of the B<SUB>y</SUB> component. As a result, the degree of asymmetry of magnetic field, plasma, and current density profiles appears characteristic of current sheets with a constant B<SUB>y</SUB>. In addition, in the presence of nonzero guiding field, the curvature current of electrons in the center of the current sheet decreases, yielding an effective thickening of the sheet. Implications of these results for current sheets in Earth's magnetosphere are discussed. (10.1029/2011JA017359)
  DOI : 10.1029/2011JA017359
• Model of a low-pressure radio-frequency inductive discharge in Ar/O<SUB>2</SUB> used for plasma spray deposition
  
  • Lazzaroni Claudia
  • Baba K.
  • Nikravech M.
  • Chabert Pascal
  Journal of Physics D: Applied Physics, IOP Publishing, 2012, 45, pp.485207. A global (volume-averaged) model of a low-pressure radio-frequency (RF) inductive discharge used for nanostructured zinc oxide thin film deposition, the so-called spray-plasma device, is proposed. The plasma reactor is fed with an admixture of argon and oxygen and the pressure is typically several tens of mTorr. In the first step of the modelling, the injector and the substrate holder are not taken into account, and therefore zinc-containing species are not considered. The global model is based on the numerical integration of the particle balance equations and the electronic power balance equation. The model is first run until the steady state is reached to determine the equilibrium discharge parameters that are the species densities and the electron temperature. A parametric study is carried out varying the gas pressure, the RF power and the O2 fraction in the reactor. A parameter of great importance for the deposition process is the flux of the reactive species on the substrate holder and the model allows a fast exploration of this parameter. For continuous plasmas, the ratio of the reactive species flux to the total positive ion flux can be controlled varying the three basic parameters cited before (pressure, power and dilution). In the last part of the paper, we also investigate pulsed plasmas and the effect of the duty cycle variations on the neutral/ion flux ratio. (10.1088/0022-3727/45/48/485207)
  DOI : 10.1088/0022-3727/45/48/485207
• ON THE NATURE OF THE SOLAR WIND FROM CORONAL PSEUDOSTREAMERS
  
  • Wang Y-M
  • Grappin Roland
  • Robbrecht E.
  • Sheeley N R
  The Astrophysical Journal, American Astronomical Society, 2012, 749 (2), pp.182. Coronal pseudostreamers, which separate like-polarity coronal holes, do not have current sheet extensions, unlike the familiar helmet streamers that separate opposite-polarity holes. Both types of streamers taper into narrow plasma sheets that are maintained by continual interchange reconnection with the adjacent open magnetic field lines. White-light observations show that pseudostreamers do not emit plasma blobs; this important difference from helmet streamers is due to the convergence of like-polarity field lines above the X-point, which prevents the underlying loops from expanding outward and pinching off. The main component of the pseudostreamer wind has the form of steady outflow along the open field lines rooted just inside the boundaries of the adjacent coronal holes. These flux tubes are characterized by very rapid expansion below the X-point, followed by reconvergence at greater heights. Analysis of an idealized pseudostreamer configuration shows that, as the separation between the underlying holes increases, the X-point rises and the expansion factor f ss at the source surface increases. In situ observations of pseudostreamer crossings indicate wind speeds v ranging from ~350 to ~550 km s1, with O7 /O6 ratios that are enhanced compared with those in high-speed streams but substantially lower than in the slow solar wind. Hydrodynamic energy-balance models show that the empirical v-f ss relation overestimates the wind speeds from nonmonotonically expanding flux tubes, particularly when the X-point is located at low heights and f ss is small. We conclude that pseudostreamers produce a "hybrid" type of outflow that is intermediate between classical slow and fast solar wind. (10.1088/0004-637X/749/2/182)
  DOI : 10.1088/0004-637X/749/2/182
• Variation of F2 layer critical frequency with solar cycle at Dakar station
  
  • Thiam N. M.
  • Ouattara Frédéric Martial
  • Gnabahou Doua Allain
  • Amory-Mazaudier Christine
  • Fleury Rolland
  • Lassurdie-Duchesne P.
  Journal des sciences, Université Cheikh Anta Diop, 2012, 11 (2), pp.16-20. ...
• The International Research Group in geophysics, Europa Africa : a laboratory without borders in the Earth Science and Environment
  
  • Amory-Mazaudier Christine
  Journal of Life Sciences, 2012, 6, pp.336-342. ...
• Determination of TEC by using pseudo range at Koudougou station in Burkina Faso
  
  • Ouattara Frédéric Martial
  • Zoundi C.
  • Amory-Mazaudier Christine
  • Fleury Rolland
  • Lassudrie Duchesne P.
  Journal des sciences, Université Cheikh Anta Diop, 2012, 11 (1), pp.12-19. ...