Publications

2011

• Core turbulence in Tokamak plasmas : observations by EM wave scattering, reflectometry and others
  
  • Hennequin Pascale
  , 2011.
• Impact of collisionality on fluctuation characteristics of micro-turbulence
  
  • Vermare Laure
  • Hennequin Pascale
  • Gürcan Özgür D.
  • Honoré Cyrille
  • Berionni Vincent
  , 2011 (oral).
• RF waveform tailoring to control film morphology during nanocrystalline silicon PECVD
  
  • Booth Jean-Paul
  • Johnson E.V.
  • Delattre Pierre-Alexandre
  • Verbeke T.
  • Vanel J-C
  , 2011.
• Simulation numérique de la reconnexion magnétique : mécanismes cinétiques sous-jacents à la description fluide des ions
  
  • Aunai Nicolas
  , 2011. La capacité à libérer l’énergie stockée dans le champ magnétique et à briser le théorème du gel font de la reconnexion magnétique un des phénomènes les plus importants de la physique des plasmas. Lorsqu’elle se produit dans un environnement non-collisionel comme la magnétosphère terrestre, une modélisation cinétique est à priori nécessaire. Cependant la plupart de notre compréhension du phénomène se base sur un interprétation fluide, plus intuitive. Dans quelle mesure ces deux interprétations d’un même phénomène sont-elles reliées ? C’est la problématique à laquelle cette thèse s’intéresse, dans le cas de la reconnexion antiparallèle et pour la population ionique du plasma. La première partie de ce travail s’intéresse à l’accélération fluide et cinétique des protons au sein de la région de reconnexion. Il est montré comment le mouvement individuel des particules joue un rôle du point de vue fluide via la force de pression, jusqu’alors négligée dans les modèles. Ces résultats ont également mené dans une seconde partie à des prédictions et vérifications observationnelles basées sur les données des satellites Cluster. Dans un troisième temps, nous montrons le rôle important joué par le flux d’énergie thermique dans le transfert d’énergie au cours du processus de reconnexion, dans le cas symétrique et asymétrique. Enfin la dernière partie de ce manuscrit propose une solution au problème fondamental consistant décrire une couche de courant tangentielle asymétrique dans un état d’équilibre cinétique
• Seeing Inside Plasma Etch Reactors: from diagnostics to sensors for control
  
  • Booth Jean-Paul
  • Chabert Pascal
  • Sarot Rodolphe
  • Zaka-Ul-Islam Mujahid
  , 2011.
• Space Weather : An introduction
  
  • Amory-Mazaudier Christine
  , 2011.
• Space Weather : An Introduction
  
  • Amory-Mazaudier Christine
  , 2011.
• Time variations of the ionosphere at the northern tropical crest of ionization at Phu Thuy, Vietnam
  
  • Pham Thi Thu Hong
  • Amory-Mazaudier Christine
  • Le Huy M.
  Annales Geophysicae, European Geosciences Union, 2011, pp.197-207. This study is the first which gives the climatology of the ionosphere at the northern tropical crest of ionization in the Asian sector. We use the data from Phu Thuy station, in Vietnam, through three solar cycles (20, 21 and 22), showing the complete morphology of ionosphere parameters by analyzing long term variation, solar cycle variation and geomagnetic activity effects, seasonal evolution and diurnal development. Ionospheric critical frequencies, foF2, foF1 and foE, evolve according to the 11-year sunspot cycle. Seasonal variations show that foF2 exhibits a semiannual pattern with maxima at equinox, and winter and equinoctial anomalies depending on the phases of the sunspot solar cycle. 1foF2 exhibits a semiannual variation during the minimum phase of the sunspot solar cycle 20 and the increasing and decreasing phases of solar cycle 20, 21 and 22. 1foF1 exhibits an annual variation during the maximum phase of solar cycles 20, 21 and 22. 1h0F2 shows a regular seasonal variation for the different solar cycles while 1h0F1 exhibits a large magnitude dispersion from one sunspot cycle to another. The long term variations consist in an increase of 1.0MHz for foF2 and of 0.36MHz for foF1. foE increases 0.53MHz from solar cycle 20 to solar cycle 21 and then decreases −0.23MHz during the decreasing phase of cycle 21. The diurnal variation of the critical frequency foF2 shows minima at 05:00 LT and maxima around 14:00 LT. foF1 and foE have a maximum around noon. The diurnal variation of h0F2 exhibits a maximum around noon. The main features of h0F1 are a minimum near noon and the maximum near midnight. Other minima and maxima occur in the morning, at about 04:00 or 05:00 LT and in the afternoon, at about 18:00 or 19:00 LT but they are markedly smaller. Only during the maximum phase of all sunspot solar cycles the maximum near 19:00 LT is more pronounced. (10.5194/angeo-29-197-2011)
  DOI : 10.5194/angeo-29-197-2011
• Modeling Some Calibrated Cracks for E-NDE by a Difference Method
  
  • Bettaieb Laroussi
  • Kokabi Hamid
  • Poloujadoff Michel
  • Coillot Christophe
  Journal of Nondestructive Evaluation, Springer Verlag, 2011, 30 (3), pp.117 - 121. Electromagnetic Non Destructive Evaluation (E-NDE) is often conducted by inducing eddy currents in the structure to be examined, if this is conducting. Existence of flaws is detected by difference between the response of defect-free structures and damaged ones. In the present paper, we model such processes in order to predict the feasibility of this evaluation and to facilitate the interpretation of the observation. An original method is to represent a crack by a current source producing a magnetic signal. We have applied it to the case of a defect with a standard shape. The experimental evidences for the validity of this method are given. (10.1007/s10921-011-0097-5)
  DOI : 10.1007/s10921-011-0097-5
• Emission and propagation of Saturn kilometric radiation: Magnetoionic modes, beaming pattern, and polarization state
  
  • Lamy L.
  • Cecconi B.
  • Zarka P.
  • Canu Patrick
  • Schippers P.
  • Kurth W. S.
  • Mutel R. L.
  • Gurnett D. A.
  • Menietti D.
  • Louarn P.
  , 2011. The Cassini mission crossed the source region of the Saturn kilometric radiation (SKR) on 17 October 2008. On this occasion, the Radio and Plasma Wave Science (RPWS) experiment detected both local and distant radio sources, while plasma parameters were measured in situ by the magnetometer and the Cassini Plasma Spectrometer. A goniopolarimetric inversion was applied to RPWS three-antenna electric measurements to determine the wave vector k and the complete state of polarization of detected waves. We identify broadband extraordinary (X) mode as well as narrowband ordinary (O) mode SKR at low frequencies. Within the source region, SKR is emitted just above the X mode cutoff frequency in a hot plasma, with a typical electron-to-wave energy conversion efficiency of ˜1% (2% peak). The knowledge of the k vector is then used to derive the locus of SKR sources in the kronian magnetosphere, which shows X and O components emanating from the same regions. We also compute the associated beaming angle at the source θ‧ = (k, -B) either from (1) in situ measurements or a model of the magnetic field vector (for local to distant sources) or (2) polarization measurements (for local sources). Obtained results, similar for both modes, suggest quasi-perpendicular emission for local sources, whereas the beaming pattern of distant sources appears as a hollow cone with a frequency-dependent constant aperture angle: θ‧ = 75° ± 15° below 300 kHz, decreasing at higher frequencies to reach θ‧ (1000 kHz) = 50° ± 25°. Finally, we investigate quantitatively the SKR polarization state, observed to be strongly elliptical at the source, and quasi-purely circular for sources located beyond approximately two kronian radii. We show that conditions of weak mode coupling are achieved along the raypath, under which the magnetoionic theory satisfactorily describes the evolution of the observed polarization. These results are analyzed comparatively with the auroral kilometric radiation at Earth.
• Sq field characteristics at Phu Thuy, Vietnam, during solar cycle 23: comparisons with Sq field in other longitude sectors
  
  • Pham Thi Thu Hong
  • Amory-Mazaudier Christine
  • Le Huy M.
  Annales Geophysicae, European Geosciences Union, 2011, pp.1-17. Quiet days variations in the Earth's magnetic field (the Sq current system) are compared and contrasted for the Asian, African and American sectors using a new dataset from Vietnam. This is the first presentation of the variation of the Earth's magnetic field (Sq), during the solar cycle 23, at Phu Thuy, Vietnam (geographic latitudes 21.03 N and longitude: 105.95 E). Phu Thuy observatory is located below the crest of the equatorial fountain in the Asian longitude sector of the Northern Hemisphere. The morphology of the Sq daily variation is presented as a function of solar cycle and seasons. The diurnal variation of Phu Thuy is compared to those obtained in different magnetic observatories over the world to highlight the characteristics of the Phu Thuy observations. In other longitude sectors we find different patterns. At Phu Thuy the solar cycle variation of the amplitude of the daily variation of the X component is correlated to the F.10.7 cm solar radiation ( 0.74). This correlation factor is greater than the correlation factor obtained in two observatories located at the same magnetic latitudes in other longitude sectors: at Tamanrasset in the African sector ( 0.42, geographic latitude 22.79) and San Juan in the American sector ( 0.03, geographic latitude 18.38). At Phu Thuy, the Sq field exhibits an equinoctial and a diurnal asymmetry: - The seasonal variation of the monthly mean of X component exhibits the well known semiannual pattern with 2 equinox maxima, but the X component is larger in spring than in autumn. Depending of the phase of the sunspot cycle, the maximum amplitude of the X component varies in spring from 30 nT to 75 nT and in autumn from 20 nT to 60 nT. The maximum amplitude of the X component exhibits roughly the same variation in both solstices, varying from about 20 nT to 50 nT, depending on the position into the solar cycle. - In all seasons, the mean equinoctial diurnal Y component has a morning maximum Larger than the afternoon minimum i.e. the equivalent current flow over a day is more southward than northward. During winter, the asymmetry is maximum, it erases the afternoon minimum. At the Gnangara observatory, in Asian Southern Hemisphere, the diurnal Y pattern is opposite and the current flow is more northward. It seems that in the Asian sector, the northern and southern Sq current cells both contribute strongly to the equatorial electrojet. The pattern is different in the African and American sectors where the northern Sq current cell contribution to the equatorial electrojet is smaller than the southern one. These observations can explain the unexpected maximum of amplitude of the equatorial electrojet observed in the Asian sector where the internal field is very large. During winter the Y component flow presents an anomaly, it is always southward during the whole day and there is no afternoon northward circulation. (10.5194/angeo-29-1-2011)
  DOI : 10.5194/angeo-29-1-2011
• Estimation of the Gas Temperature of NO during a DC Plasma Pulse using Quantum Cascade Laser (QCL) Absorption Spectroscopy
  
  • Hübner M.
  • Marinov Daniil
  • Guaitella Olivier
  • Rousseau Antoine
  • Roepcke J.
  , 2011.
• Experimental and modeling analysis of fast ionization wave discharge propagation in a rectangular geometry
  
  • Takashima K.
  • Adamovich I.V.
  • Xiong Z.
  • Kushner M.J.
  • Starikovskaia Svetlana
  • Czarnetzki U.
  • Luggenhölscher D.
  Physics of Plasmas, American Institute of Physics, 2011, 18, pp.083505. Fast ionization wave (FIW), nanosecond pulse discharge propagation in nitrogen and helium in a rectangular geometry channel/waveguide is studied experimentally using calibrated capacitive probe measurements. The repetitive nanosecond pulse discharge in the channel was generated using a custom designed pulsed plasma generator (peak voltage 1040 kV, pulse duration 30100 ns, and voltage rise time ∼1 kV/ns), generating a sequence of alternating polarity high-voltage pulses at a pulse repetition rate of 20 Hz. Both negative polarity and positive polarity ionization waves have been studied. Ionization wave speed, as well as time-resolved potential distributions and axial electric field distributions in the propagating discharge are inferred from the capacitive probe data. ICCD images show that at the present conditions the FIW discharge in helium is diffuse and volume-filling, while in nitrogen the discharge propagates along the walls of the channel. FIW discharge propagation has been analyzed numerically using quasi-one-dimensional and two-dimensional kinetic models in a hydrodynamic (drift-diffusion), local ionization approximation. The wave speed and the electric field distribution in the wave front predicted by the model are in good agreement with the experimental results. A self-similar analytic solution of the fast ionization wave propagation equations has also been obtained. The analytic model of the FIW discharge predicts key ionization wave parameters, such as wave speed, peak electric field in the front, potential difference across the wave, and electron density as functions of the waveform on the high voltage electrode, in good agreement with the numerical calculations and the experimental results. (10.1063/1.3619810)
  DOI : 10.1063/1.3619810
• Alfvén : Magnetosphere -Ionosphere Connection Explorers
  
  • Berthomier Matthieu
  • Fazakerlay, N. A.
  • Forsyth C.
  • Pottelette Raymond
  • Alexandrova Olga
  • Anastasiadis A.
  • Aruliah A.
  • Blelly Pierre-Louis
  • Briand Carine
  • Bruno R.
  • Canu Patrick
  • Cecconi Baptiste
  • Chust Thomas
  • Daglis I.
  • Davie J.
  • Dunlop M.
  • Fontaine Dominique
  • Génot Vincent
  • Gustavsson B.
  • Haerendel G.
  • Hamrin M.
  • Hapgood M.
  • Hess S.
  • Kataria D.
  • Kauristie K.
  • Kemble S.
  • Khotyaintsev Y.
  • Koskinen H.
  • Lamy Laurent
  • Lanchester B.
  • Louarn P.
  • Lucek E.
  • Lundin R.
  • Maksimovic M.
  • Manninen J.
  • Marchaudon Aurélie
  • Marghitu O.
  • Marklund G.
  • Milan S.
  • Moen J.
  • Mottez Fabrice
  • Nilsson Hans
  • Parrot Michel
  • Ostgaard N.
  • J. Owen C.
  • Pedersen A.
  • Perry C.
  • Pinçon Jean-Louis
  • Pitout Frederic
  • Pulkkinen T.
  • J. Rae I.
  • Rezeau Laurence
  • Roux A.
  • Sandahl I.
  • Sandberg I.
  • Turunen E.
  • Vogt J.
  • Walsh A.
  • E. J. Watt C.
  • A. Wild J.
  • Yamauchi M.
  • Zarka Philippe
  • Zouganelis I.
  Experimental Astronomy, Springer Link, 2011, pp.1. The Alfvén concept is designed specifically to take the next step in studying the aurora, by making the crucial high-time resolution, multi-scale measurements in the AAR, needed to address the key science questions of auroral plasma physics. The new knowledge that the mission will produce will find application in studies of the Sun, the processes that accelerate the solar wind and that produce aurora on other planets. (10.1007/s10686-011-9273-y)
  DOI : 10.1007/s10686-011-9273-y
• Emission and propagation of Saturn kilometric radiation: Magnetoionic modes, beaming pattern, and polarization state
  
  • Lamy L.
  • Cecconi B.
  • Zarka P.
  • Canu Patrick
  • Schippers P.
  • Kurth W. S.
  • Mutel R. L.
  • Gurnett D. A.
  • Menietti D.
  • Louarn P.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2011, 116, pp.4212. The Cassini mission crossed the source region of the Saturn kilometric radiation (SKR) on 17 October 2008. On this occasion, the Radio and Plasma Wave Science (RPWS) experiment detected both local and distant radio sources, while plasma parameters were measured in situ by the magnetometer and the Cassini Plasma Spectrometer. A goniopolarimetric inversion was applied to RPWS three-antenna electric measurements to determine the wave vector k and the complete state of polarization of detected waves. We identify broadband extraordinary (X) mode as well as narrowband ordinary (O) mode SKR at low frequencies. Within the source region, SKR is emitted just above the X mode cutoff frequency in a hot plasma, with a typical electron-to-wave energy conversion efficiency of 1% (2% peak). The knowledge of the k vector is then used to derive the locus of SKR sources in the kronian magnetosphere, which shows X and O components emanating from the same regions. We also compute the associated beaming angle at the source theta' = (k, -B) either from (1) in situ measurements or a model of the magnetic field vector (for local to distant sources) or (2) polarization measurements (for local sources). Obtained results, similar for both modes, suggest quasi-perpendicular emission for local sources, whereas the beaming pattern of distant sources appears as a hollow cone with a frequency-dependent constant aperture angle: theta' = 75° ± 15° below 300 kHz, decreasing at higher frequencies to reach theta' (1000 kHz) = 50° ± 25°. Finally, we investigate quantitatively the SKR polarization state, observed to be strongly elliptical at the source, and quasi-purely circular for sources located beyond approximately two kronian radii. We show that conditions of weak mode coupling are achieved along the raypath, under which the magnetoionic theory satisfactorily describes the evolution of the observed polarization. These results are analyzed comparatively with the auroral kilometric radiation at Earth. (10.1029/2010JA016195)
  DOI : 10.1029/2010JA016195
• Oxidation of NO into NO<SUB>2</SUB> by surface adsorbed O atoms
  
  • Guaitella Olivier
  • Hübner M.
  • Marinov Daniil
  • Guerra V.
  • Pintassilgo C.D.
  • Welzel S.
  • Röpcke J.
  • Rousseau Antoine
  Contributions to Plasma Physics, Wiley-VCH Verlag, 2011, 51 (2-3), pp.176-181. Plasma-surface interactions are increasingly recognised as a key factor in explaining molecule production and conversion processes. In order to scrutinise such effects well-defined surface and gas phase conditions are required. Hence, the inner surface of a Pyrex tube was treated by a capacitively coupled RF plasma at low pressure. The post-plasma oxidation of gas mixtures containing 1 % NO into NO<SUB>2</SUB> has been studied by means of quantum cascade laser absorption spectroscopy in the mid-infrared spectral range. The plasma pre-treatment experiments with oxygen containing precursors suggest O atom adsorption on the Pyrex tube with a surface density of 2.7 x 1014 cm2. A simple kinetic model was developed and shows good agreement with the measured NO and NO<SUB>2</SUB> gas phase concentrations. In the model a fraction of the surface is considered to be covered with chemisorption sites where atoms and molecules can be adsorbed, whereas they can be removed only by recombination (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) (10.1002/ctpp.201000068)
  DOI : 10.1002/ctpp.201000068
• Evolution of micro-turbulence characteristics with collisionality at the tokamak core-edge interface
  
  • Vermare Laure
  • Hennequin Pascale
  • Gürcan Özgür D.
  • Honoré Cyrille
  • Berionni Vincent
  • Bourdelle C.
  • Casati A.
  • Clairet F.
  • Garbet X.
  • Giacalone J-C.
  • Sabot R.
  • Tore Supra Team
  , 2011, oral.
• Compressible Kelvin-Helmholtz instability in supermagnetosonic regimes
  
  • Palermo F.
  • Faganello M.
  • Califano F.
  • Pegoraro F.
  • Le Contel Olivier
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2011, 116, pp.4223. We investigate the transition from submagnetosonic to supermagnetosonic regimes in the presence of a sheared flow and density variations typically observed between the solar wind and the Earth's magnetosphere. In particular, we show the possibility of generating quasi-perpendicular magnetosonic shock structures under typical conditions that can be realized at the magnetosphere flanks. Here the Kelvin-Helmholtz instability generates rolled-up, large- scale vortices that propagate along the flanks of the magnetosphere. The shocks are generated by those vortices for which the magnetosonic Mach number turns out to be of the order of unity or larger. (10.1029/2010JA016400)
  DOI : 10.1029/2010JA016400
• A mechanism for heating electrons in the magnetopause current layer and adjacent regions
  
  • Roux A.
  • Robert Patrick
  • Le Contel Olivier
  • Angelopoulos V.
  • Auster U.
  • Bonnell J. W.
  • Cully C. M.
  • Ergun R. E.
  • Mcfadden J. P.
  Annales Geophysicae, European Geosciences Union, 2011, 29, pp.2305-2316. Taking advantage of the string-of-pearls configuration of the five THEMIS spacecraft during the early phase of their mission, we analyze observations taken simultaneously in the magnetosheath, the magnetopause current layer and the magnetosphere. We find that electron heating coincides with ultra low frequency waves. It seems unlikely that electrons are heated by these waves because the electron thermal velocity is much larger than the Alfvén velocity (V<SUB>a</SUB>). In the short transverse scale (k<SUB>\bot</SUB>rho<SUB>i</SUB> >> 1) regime, however, short scale Alfvén waves (SSAWs) have parallel phase velocities much larger than V<SUB>a</SUB> and are shown to interact, via Landau damping, with electrons thereby heating them. The origin of these waves is also addressed. THEMIS data give evidence for sharp spatial gradients in the magnetopause current layer where the highest amplitude waves have a large component deltaB perpendicular to the magnetopause and k azimuthal. We suggest that SSAWs are drift waves generated by temperature gradients in a high beta, large T<SUB>i</SUB>/T<SUB>e</SUB> magnetopause current layer. Therefore these waves are called SSDAWs, where D stands for drift. SSDAWs have large k<SUB>\bot</SUB> and therefore a large Doppler shift that can exceed their frequencies in the plasma frame. Because they have a small but finite parallel electric field and a magnetic component perpendicular to the magnetopause, they could play a key role at reconnecting magnetic field lines. The growth rate depends strongly on the scale of the gradients; it becomes very large when the scale of the electron temperature gradient gets below 400 km. Therefore SSDAW's are expected to limit the sharpness of the gradients, which might explain why Berchem and Russell (1982) found that the average magnetopause current sheet thickness to be ~400-1000 km (~500 km in the near equatorial region). (10.5194/angeo-29-2305-2011)
  DOI : 10.5194/angeo-29-2305-2011
• Ion acceleration in antiparallel collisionless magnetic reconnection: Kinetic and fluid aspects
  
  • Aunai Nicolas
  • Belmont Gérard
  • Smets Roch
  Comptes Rendus. Physique, Académie des sciences (Paris), 2011, 12, pp.141-150. Not Available (10.1016/j.crhy.2010.11.004)
  DOI : 10.1016/j.crhy.2010.11.004
• A generalization of the rocket formula and its application to advanced space propulsion systems
  
  • Nasi L.
  • Raimbault Jean-Luc
  Acta Astronautica, Elsevier, 2011, 68 (1-2), pp.34-38. A generalized rocket formula is derived from a first principles approach. The resulting expression of the thrust is applied to advanced space propulsion systems and a possible link between the asymptotic propellant velocity and the velocity at thruster exit is given. An estimation of the thrust modification due to spacecraftplume interactions is also considered. (10.1016/j.actaastro.2010.07.015)
  DOI : 10.1016/j.actaastro.2010.07.015
• Multi-spacecraft investigation of space turbulence: lessons from Cluster and input to the Cross- Scale mission
  
  • Sahraoui Fouad
  • Goldstein M.L.
  • Belmont Gérard
  • Roux A.
  • Rezeau Laurence
  • Canu Patrick
  • Robert Patrick
  • Cornilleau-Wehrlin Nicole
  • Le Contel Olivier
  • Dudok de Wit Thierry
  • Pinçon Jean-Louis
  • Kiyani K.
  Planetary and Space Science, Elsevier, 2011, 59 (7), pp.Pages 585-591. Investigating space plasma turbulence from single-point measurements is known to be characterized by unavoidable ambiguities in disentangling temporal and spatial variations. Solving this problem has been one of the major goals of the Cluster mission. For that purpose multipoint measurements techniques, such as the $k$-filtering, have been developed. Such techniques combine several time series recorded simultaneously at different points in space to estimate the corresponding energy density in the wavenumber space. Here we apply the technique to both simulated and Cluster magnetometer data in the solar wind (SW) and investigate the errors and limitations that arise due to the separation of the spacecraft and the quality of the tetrahedral configuration. Specifically, we provide an estimation of the minimum and maximum scales that can be accurately measured given a specific distance between the satellites and show the importance of the geometry of the tetrahedron and the relationship of that geometry to spatial aliasing. We also present recent results on characterizing small scale SW turbulence and provide scientific arguments supporting the need of new magnetometers having better sensitivity than the existing ones. Throughout the paper we emphasize technical challenges and their solutions that can be considered for a better preparation of the Cross- Scale mission. (10.1016/j.pss.2010.06.001)
  DOI : 10.1016/j.pss.2010.06.001
• Discharge resistance and power dissipation in the self-pulsing regime of micro-hollow cathode discharges
  
  • Lazzaroni Claudia
  • Chabert Pascal
  Plasma Sources Science and Technology, IOP Publishing, 2011, 20, pp.055004. Micro-hollow cathode discharges (MHCDs), driven by a dc voltage source, may operate in a self-pulsing regime during which the voltage and the current across the discharge are pulsed with a frequency of several tens of kilohertz. A model for the self-pulsing regime of MHCDs is proposed based on an equivalent electrical circuit of the whole device. The discharge itself is modeled by a non-linear resistance in series with an inductance, and it is placed in parallel with the capacitance of the electrodedielectricelectrode sandwich hosting the discharge micro-hole. The capacitance of the coaxial cable used to feed the device is also included. It is shown that a detailed comparison between theory and experiments allows the discharge non-linear resistance to be accurately determined. When the discharge current is maximum, this resistance is about 2500&#8201;&#937; at 50&#8201;Torr and decreases to about 750&#8201;&#937; at 150&#8201;Torr. The absorbed power is calculated throughout the self-pulsing cycle and may be above 100&#8201;W at the current peak, while the time-averaged power remains a fraction of a Watt. (10.1088/0963-0252/20/5/055004)
  DOI : 10.1088/0963-0252/20/5/055004
• Three-dimensional spatial structures of solar wind turbulence from 10 000-km to 100-km scales
  
  • Narita Y.
  • Glassmeier K.-H.
  • Goldstein M. L.
  • Motschmann U.
  • Sahraoui Fouad
  Annales Geophysicae, European Geosciences Union, 2011, 29, pp.1731-1738. Using the four Cluster spacecraft, we have determined the three-dimensional wave-vector spectra of fluctuating magnetic fields in the solar wind. Three different solar wind intervals of Cluster data are investigated for this purpose, representing three different spatial scales: 10 000 km, 1000 km, and 100 km. The spectra are determined using the wave telescope technique (k-filtering technique) without assuming the validity of Taylor's frozen-in-flow hypothesis nor are any assumptions made as to the symmetry properties of the fluctuations. We find that the spectra are anisotropic on all the three scales and the power is extended primarily in the directions perpendicular to the mean magnetic field, as might be expected of two-dimensional turbulence, however, the analyzed fluctuations are not axisymmetric. The lack of axisymmetry invalidates some earlier techniques using single spacecraft observations that were used to estimate the percentage of magnetic energy residing in quasi-two-dimensional power. However, the dominance of two-dimensional turbulence is consistent with the relatively long mean free paths of cosmic rays in observed in the heliosphere. On the other hand, the spectra also exhibit secondary extended structures oblique from the mean magnetic field direction. We discuss possible origins of anisotropy and asymmetry of solar wind turbulence spectra. (10.5194/angeo-29-1731-2011)
  DOI : 10.5194/angeo-29-1731-2011
• On the dispersion features of whistler waves in almost pure ion plasmas
  
  • Lundin B. V.
  • Krafft C.
  Physics of Plasmas, American Institute of Physics, 2011, 18, pp.102114. It is shown that in a multi-ion plasma of moderate density enriched by a large amount of negatively charged ions and/or heavy particulates, the lower cutoff frequencies of the electron whistler and the Z-mode (extraordinary) waves tend to each other, approaching the ion plasma frequency omegapi. The evolution of the dispersion curves omega(k, theta) of both wave modes is studied as a function of the relative electron density, beginning from the case of a moderate density plasma with comparable values of electron gyro- and plasma frequencies and omegapi essentially exceeding the ions' gyrofrequencies. When the fraction of free electrons is very small the transparency frequency domain of the electron whistler mode becomes very narrow, being located in the vicinity of omegapi. If the negatively charged ions have the smallest specific charges among other ion species then, under similar conditions, the so-called crossover effect and the accompanying polarization sense reverse can occur at frequencies essentially greater than the ions' gyrofrequencies. The revealed effects are characteristic of plasmas with excess of electronegative gas molecules or dust particulates highly adhesive to electrons, i.e., almost pure ion plasmas and/or pair-ion plasmas with extra small fractions of free electrons. Moreover, it is found that the vanishingly small electron fraction providing the same value of the electron whistler ion cutoff frequency normalized to the ion plasma frequency is essentially less for pair fullerene C<SUB>60</SUB><SUP> /-</SUP> than for pair hydrogen H /- plasmas. The technique to determine omegapi using the evolution of the whistler wave magnetic field polarization ellipse is also described. (10.1063/1.3650075)
  DOI : 10.1063/1.3650075