Publications

2011

• Predator prey oscillations in a simple cascade model of drift wave turbulence
  
  • Berionni Vincent
  • Gürcan Özgür D.
  , 2011.
• 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
• 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
• 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.
• 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
• 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
• 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
• Vibrational relaxation of N<SUB>2</SUB> studied by IR titration with time-resolved Qantum Cascade Laser diagnostics
  
  • Marinov Daniil
  • Lopatik D.
  • Guaitella Olivier
  • Roepcke J.
  • Rousseau Antoine
  , 2011.
• Modeling the superstorm in November 2003
  
  • Fok M.-C. H.
  • Moore T. E.
  • Slinker Steve P.
  • Fedder Joel A.
  • Delcourt Dominique C.
  • Nosé Masahito
  • Chen Sheng-Hsien
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2011, 116. The superstorm on 20-21 November 2003 was the largest geomagnetic storm in solar cycle 23 as measured by Dst, which attained a minimum value of -422 nT. We have simulated this storm to understand how particles originating from the solar wind and ionosphere get access to the magnetosphere and how the subsequent transport and energization processes contribute to the buildup of the ring current. The global electromagnetic configuration and the solar wind H<SUP> </SUP> distribution are specified by the Lyon-Fedder-Mobarry (LFM) magnetohydrodynamics model. The outflow of H<SUP> </SUP> and O<SUP> </SUP> ions from the ionosphere are also considered. Their trajectories in the magnetosphere are followed by a test-particle code. The particle distributions at the inner plasma sheet established by the LFM model and test-particle calculations are then used as boundary conditions for a ring current model. Our simulations reproduce the rapid decrease of Dst during the storm main phase and the fast initial phase of recovery. Shielding in the inner magnetosphere is established at early main phase. This shielding field lasts several hours and then breaks down at late main phase. At the peak of the storm, strong penetration of ions earthward to L shell of 1.5 is revealed in the simulation. It is surprising that O<SUP> </SUP> is significant but not the dominant species in the ring current in our calculation for this major storm. It is very likely that substorm effects are not well represented in the models and O<SUP> </SUP> energization is underestimated. Ring current simulation with O<SUP> </SUP> energy density at the boundary set comparable to Geotail observations produces excellent agreement with the observed symH. As expected in superstorms, ring current O<SUP> </SUP> is the dominant species over H<SUP> </SUP> during the main to midrecovery phase of the storm. (10.1029/2010JA015720)
  DOI : 10.1029/2010JA015720
• Whistler eigenmodes of magnetic flux tubes in a magnetoplasma
  
  • Kudrin A. V.
  • Bakharev P. V.
  • Zaboronkova T. M.
  • Krafft C.
  Plasma Physics and Controlled Fusion, IOP Publishing, 2011, 53, pp.065005. Guided propagation of whistler waves along cylindrical non-uniformities of a dc magnetic field is studied within the framework of a full-wave approach. Conditions are revealed under which such guiding structures, commonly known as magnetic flux tubes, can support volume and surface eigenmodes in the whistler range. The dispersion properties and field structures of whistler eigenmodes guided by flux tubes with an enhanced magnetic field are calculated and analysed for plasma parameters typical of laboratory experiments. The results obtained are useful in understanding the basic features of whistler wave guidance by magnetic flux tubes and can be applied to interpreting the data of the relevant experiments. (10.1088/0741-3335/53/6/065005)
  DOI : 10.1088/0741-3335/53/6/065005
• Proton acceleration in antiparallel collisionless magnetic reconnection: Kinetic mechanisms behind the fluid dynamics
  
  • Aunai Nicolas
  • Belmont Gérard
  • Smets Roch
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2011, 116, pp.9232. This paper investigates the proton kinetic mechanisms leading to the formation of plasma jets in antiparallel magnetic reconnection. In particular, the interaction of the protons with the Hall electric field in the proton non-ideal region is discussed. The study, based on a two-dimensional hybrid simulation, details the important role of the proton pressure force in the acceleration process and its role in maintaining open and steady the proton outflow channel. When no fluid closure is assumed, it is found that this force arises from a strong anisotropy in velocity space which comes from kinetic effect. By analyzing the distribution functions and the individual particle dynamics, it is shown that the mixing of protons bouncing in a divergent electrostatic potential well associated to the Hall effect statistically couples the two in-plane velocity components of the particles. This coupling results, from the macroscopic point of view, in off-diagonal components of the pressure tensor. (10.1029/2011JA016688)
  DOI : 10.1029/2011JA016688
• The proton pressure tensor as a new proxy of the proton decoupling region in collisionless magnetic reconnection
  
  • Aunai Nicolas
  • Retinò Alessandro
  • Belmont Gérard
  • Smets Roch
  • Lavraud B.
  • Vaivads A.
  Annales Geophysicae, European Geosciences Union, 2011, 29, pp.1571-1579. Cluster data is analyzed to test the proton pressure tensor variations as a proxy of the proton decoupling region in collisionless magnetic reconnection. The Hall electric potential well created in the proton decoupling region results in bounce trajectories of the protons which appears as a characteristic variation of one of the in-plane off-diagonal components of the proton pressure tensor in this region. The event studied in this paper is found to be consistent with classical Hall field signatures with a possible 20% guide field. Moreover, correlations between this pressure tensor component, magnetic field and bulk flow are proposed and validated, together with the expected counterstreaming proton distribution functions. (10.5194/angeo-29-1571-2011)
  DOI : 10.5194/angeo-29-1571-2011
• Stochastic treatment of finite-N effects in mean-field systems and its application to the lifetimes of coherent structures
  
  • Ettoumi Wahb
  • Firpo Marie-Christine
  Physical Review E, American Physical Society (APS), 2011, 84, pp.030103(R). A stochastic treatment yielding to the derivation of a general Fokker-Planck equation is presented to model the slow convergence toward equilibrium of mean-field systems due to finite-N effects. The thermalization process involves notably the disintegration of coherent structures that may sustain out-of-equilibrium quasistationary states. The time evolution of the fraction of particles remaining close to a mean-field potential trough is analytically computed. This indicator enables to estimate the lifetime of coherent structures and thermalization time scale in mean-field systems. (10.1103/PhysRevE.84.030103)
  DOI : 10.1103/PhysRevE.84.030103
• Predator prey oscillations in a simple cascade model of drift wave turbulence
  
  • Berionni Vincent
  • Gürcan Özgür D.
  Physics of Plasmas, American Institute of Physics, 2011, 18, pp.112301. A reduced three shell limit of a simple cascade model of drift wave turbulence, which emphasizes nonlocal interactions with a large scale mode, is considered. It is shown to describe both the well known predator prey dynamics between the drift waves and zonal flows and to reduce to the standard three wave interaction equations. Here, this model is considered as a dynamical system whose characteristics are investigated. The analytical solutions for the purely nonlinear limit are given in terms of the Jacobi elliptic functions. An approximate analytical solution involving Jacobi elliptic functions and exponential growth is computed using scale separation for the case of unstable solutions that are observed when the energy injection rate is high. The fixed points of the system are determined, and the behavior around these fixed points is studied. The system is shown to display periodic solutions corresponding to limit cycle oscillations, apparently chaotic phase space orbits, as well as unstable solutions that grow slowly while oscillating rapidly. The period doubling route to transition to chaos is examined. (10.1063/1.3656953)
  DOI : 10.1063/1.3656953
• Wavenumber spectrum of micro-turbulence in tokamak plasmas / Spectre en nombre d'onde de la micro-turbulence dans les plasmas de tokamak
  
  • Vermare Laure
  • Gürcan Özgür D.
  • Hennequin Pascale
  • Honoré Cyrille
  • Garbet X.
  • Giacalone J-C.
  • Sabot R.
  • Clairet F.
  • Tore Supra Team
  Comptes Rendus. Physique, Académie des sciences (Paris), 2011, 12 (2), pp.115 - 122. A better understanding of turbulent transport in a tokamak plasma requires precise comparisons between experimental observation and theoretical prediction of micro-turbulence characteristics. The repartition of fluctuation energy over different spatial scales, which contains detailed information about the character of underlying instabilities and the mechanisms involved in energy transfer between different scales, is one of the few quantities allowing a high detail comparison. The present article reports the investigation performed on the Tore Supra tokamak on the wavenumber spectrum of micro-turbulence using Doppler backscattering. The theoretical approach consists of the derivation of spectral models that include interactions between fluctuations and large scale flow structures. Une meilleure compréhension du transport turbulent dans les plasmas de tokamak exige des comparaisons précises entre les observations expérimentales et les prédictions théoriques des caractéristiques de la micro-turbulence. La répartition de l&#700;énergie des fluctuations sur les différentes échelles spatiales, qui contient des informations sur le type instabilités sous-jacentes et sur les mécanismes de transfert d&#700;énergie entre échelles spatiales, est l&#700;une des rares quantités permettant une comparaison de niveau élevé. Cet article présente le travail mené sur le tokamak Tore Supra sur l&#700;étude du spectre en nombre d&#700;onde de la micro-turbulence mesuré par rétro-diffusion Doppler. L&#700;approche théorique consiste en la dérivation de modéles spectraux qui inclut les interactions entre les fluctuations et les structures d&#700;écoulement de grandes échelles. (10.1016/j.crhy.2010.11.003)
  DOI : 10.1016/j.crhy.2010.11.003
• Collisionality scaling in Tore Supra: detailed energy confinement analysis, turbulence measurements and gyrokinetic modelling
  
  • Bourdelle C.
  • Gerbaud T.
  • Vermare Laure
  • Casati A.
  • Aniel Thierry
  • Artaud J.F.
  • Basiuk Vincent
  • Bucalossi J.
  • Clairet F.
  • Corre Y.
  • Devynck P.
  • Falchetto G.
  • Fenzi C.
  • Garbet X.
  • Guirlet R.
  • Gürcan Özgür D.
  • Heuraux S.
  • Hennequin Pascale
  • Hoang G.T.
  • Imbeaux Frédéric
  • Manenc L.
  • Monier-Garbet P.
  • Moreau P.
  • Sabot R.
  • Segui J.-L.
  • Sirinelli A.
  • Villegas D.
  • Tore Supra Team
  Nuclear Fusion, IOP Publishing, 2011, 51, pp.063037. This paper presents the first observation of geodesic acoustic modes (GAMs) on Tore Supra plasmas. Using the Doppler backscattering system, the oscillations of the plasma flow velocity, localized between r/a = 0.85 and r/a = 0.95, and with a frequency, typically around 10 kHz, have been observed at the plasma edge in numerous discharges. When the additional heating power is varied, the frequency is found to scale with Cs/R. The MUltiple SIgnal Classification (MUSIC) algorithm is employed to access the temporal evolution of the perpendicular velocity of density fluctuations. The method is presented in some detail, and is validated and compared against standard methods, such as the conventional fast Fourier transform method, using a synthetic signal. It stands out as a powerful data analysis method to follow the Doppler frequency with a high temporal resolution, which is important in order to extract the dynamics of GAMs. (10.1088/0029-5515/51/6/063037)
  DOI : 10.1088/0029-5515/51/6/063037
• 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