Publications

2014

• The distinct character of anisotropy and intermittency in inertial and kinetic range solar wind plasma turbulence
  
  • Kiyani K. H.
  • Chapman S. C.
  • Osman Kareem
  • Sahraoui Fouad
  • Hnat B.
  , 2014, 16, pp.3690. The anisotropic nature of the scaling properties of solar wind magnetic turbulence fluctuations is investigated scale by scale using high cadence in situ magnetic field measurements from the Cluster, ACE and STEREO spacecraft missions in both fast and slow quiet solar wind conditions. The data span five decades in scales from the inertial range to the electron Larmor radius. We find a clear transition in scaling behaviour between the inertial and kinetic range of scales, which provides a direct, quantitative constraint on the physical processes that mediate the cascade of energy through these scales. In the inertial (magnetohydrodynamic) range the statistical nature of turbulent fluctuations are known to be anisotropic, both in the vector components of the magnetic field fluctuations (variance anisotropy) and in the spatial scales of these fluctuations (wavevector or k-anisotropy). We show for the first time that, when measuring parallel to the local magnetic field direction, the full statistical signature of the magnetic and Elsasser field fluctuations is that of a non-Gaussian globally scale-invariant process. This is distinct from the classic multi-exponent statistics observed when the local magnetic field is perpendicular to the flow direction. These observations suggest the weakness, or absence, of a parallel magnetofluid turbulence energy cascade. In contrast to the inertial range, there is a successive increase toward isotropy between parallel and transverse power at scales below the ion Larmor radius, with isotropy being achieved at the electron Larmor radius. Computing higher-order statistics, we show that the full statistical signature of both parallel, and perpendicular fluctuations at scales below the ion Larmor radius are that of an isotropic globally scale-invariant non-Gaussian process. Lastly, we perform a survey of multiple intervals of quiet solar wind sampled under different plasma conditions (fast, slow wind; plasma beta etc.) and find that the above results on the scaling transition between inertial and kinetic range scales are qualitatively robust, and that quantitatively, there is a spread in the values of the scaling exponents.
• Magnetic rotations and compressions at the magnetopause: "C" and "non-C" hodograms
  
  • Belmont Gérard
  • Dorville Nicolas
  • Rezeau Laurence
  , 2014, pp.6164. The magnetopause layer separates two media with different magnetic fields and plasmas: the magnetosheath and the magnetosphere. This current sheet therefore generally involves a net rotation of the tangential magnetic field and/ or a net change in the modulus of this vector between the two sides. Furthermore, for the same global jump, the variation of the magnetic field inside the current layer can be more or less complex. From ISEE measurements, Berchem and Russell (1982) have sorted the crossing observations into two classes: "C sheets" and "S sheets", in which the tangential magnetic hodograms resemble the shapes of these two letters. This classification has been used again recently by Panov (2011), using Cluster data. In the first class, the main variation concerns the direction, which rotates in a single sense; if this rotation is accompanied by a modulus change, this one occurs approximately at the same place and at the same scale. In the second class, the two kinds of variations can be more separated, in position and scale and rotations can occur in opposite senses. Dorville et al. (2014a) have shown that the first class can allow for the determination of an accurate normal direction and of a coordinate along this normal, enabling one to draw profiles of all quantities in the magnetopause. Dorville et al. (2014b) have analyzed in detail an example where the separation between the compressional and rotational features could be interpreted as the interaction between a slow shock and a rotational discontinuity. We extend here this analysis and show that the "non-C" cases are generally not "S-shaped" and that they can often be interpreted as a succession of relatively separated rotational and compressional features. Berchem and Russell, Magnetic Field Rotation Through the Magnetopause: ISEE 1 and 2 Observations, J. Geophys. Res., 87, 8139-8148, 1982 Panov et al., Two types of tangential magnetopause current sheets: Cluster observations and theory, J. Geophys. Res., 116, A12, 2156-2202, 2011 Dorville et al., BV technique for investigating 1-D interfaces, submitted to J. Geophys. Res., 2014a Dorville et al., Rotational/ Compressional nature of the Magnetopause: application of the BV technique on a magnetopause case study, submitted to J. Geophys. Res, 2014b
• Nonlinear Interaction of the Solar Wind with Earth's Bow Shock
  
  • Parks G. K.
  • Yang Z. W.
  • Liu Y.
  • Lee E.
  • Lin N.
  • Fu Suiyan
  • Cao J.B.
  • Canu Patrick
  • Dandouras Iannis
  • Rème H.
  • Goldstein M. L.
  , 2014, 16, pp.4424. The bow shock is the best-known collisionless shocks in nature. We have known from early on that the solar wind (SW) interaction with the bow shock produces gyrating and reflected particles. Some of these particles travel back into the upstream region, perturb the oncoming SW, and excite a host of nonlinear structures including hot flow anomalies, foreshock cavities and density holes. We have examined these nonlinear structures using data from 2003 when the four Cluster satellites were in a string-of-pearl configuration. We find that the nonlinear structures are evolving as they are convected with the solar wind toward Earth producing many shock-like features similar to those at the bow shock. Full 1D PIC simulation has reproduced many of the features, but the simulation requirements are different from observations. For example, the simulation shows that directly transmitted SW occurs only when the Mach number is small (sub-critical shocks). However, observations show that SW particles can penetrate the bow shock even in super-critical perpendicular shocks. This talk will discuss the new observations and simulation results with emphasis on understanding the SW dissipation mechanisms across the bow shock.
• Multi-instrument observations of multiple auroral arcs in the duskside polar cap region
  
  • Hosokawa Keisuke
  • Maggiolo Romain
  • Zhang Yongliang
  • Fear Rob
  • Fontaine Dominique
  • Cumnock Judy
  • Kullen Anita
  • Milan Steve
  • Kozlovsky Alexander
  • Echim Marius
  , 2014, 16, pp.10039. Polar cap auroral arcs (PCAs) are one of the outstanding phenomena in the polar cap region during periods of northward interplanetary magnetic field (IMF). Smaller scale PCAs tend to occur either in the duskside or dawnside of the polar cap and are known to drift in the dawn-dusk direction depending on the sign of the IMF By. Studies of PCAs are of particular importance because they represent dynamical characteristics of their source plasma in the magnetosphere, for example in the interaction region between the solar wind and magnetosphere or in the boundary between the plasma sheet and tail lobe. To date, however, very little has been known about the spatial structure and/or temporal evolution of the magnetospheric counterpart of PCAs. In order to gain more comprehensive understanding of the origin of PCAs, we have investigated an event of PCAs on November 10, 2005, during which multiple PCAs were detected by a ground-based all-sky camera at Resolute Bay, Canada. During this interval, several PCAs were detached from the duskside oval and moved poleward. The large-scale structure of these arcs was visualized by space-based imagers of TIMED/GUVI and DMSP/SSUSI. The images from these instruments indicate that the arcs were pointing towards the dayside cusp. In addition to these optical observations, we employ the Cluster satellites to reveal the particle signature corresponding to the small-scale PCAs. The ionospheric footprints of the 4 Cluster satellites encountered the PCAs sequentially and observed well correlated enhancements of electron fluxes at weak energies (< 1 keV). The Cluster satellites also detected signatures of upflowing ion beams exactly at the times of the satellite crossing of the PCAs. This implies that the ions were accelerated upward by a quasi-stationary electric field existing above the PCAs. Ionospheric convection measurement from one of the SuperDARN radars shows an existence of velocity shear across one of the PCAs. This signature is consistent with converging electric field structure in the vicinity of the arc. In the presentation, we will show the results of detailed comparison between the ground-based radio and optical signatures of the PCAs and those obtained by the Cluster spacecraft at magnetospheric altitudes.
• Low power hard-rad electronics for particle detection in space plasmas
  
  • Berthomier Matthieu
  • Techer Jean-Denis
  , 2014, 16, pp.14178. Particle detection in highly-radiative environment is one of the experimental challenges of planetary exploration. We present the design and performances of a compact electron detector that takes advantage of the development of a hard-rad and ultra low-power front-end electronics. The Applied Specific Integrated Circuit (ASIC) consists of charge sensitive amplifiers and discriminators allowing a 4.5MHz periodic counting rate. The 16-channels ASIC only takes 30mW of power which is the power budget of single channel hybrid components with similar performances. Each channel can be independently configured in order to adjust the detection threshold of the discriminator. An internal test circuitry is used to monitor the behavior of the electronics. This component, that has been tested at high ionizing doses, is immune to Single Event Latchups up to at least 80 MeV.cm²/mg and it will fly on the Solar Orbiter ESA mission.
• 3D hybrid simulation of the interaction of a magnetic cloud with a bow shock
  
  • Turc Lucile
  • Fontaine Dominique
  • Savoini Philippe
  • Modolo Ronan
  , 2014, 16, pp.EGU2014-6176. Magnetic clouds (MCs) are a subset of coronal mass ejections which are known for their importance in driving geomagnetic storms. Studies based on both observations and modelling have shown that the structure of an MC downstream of Earth's bow shock strongly depends on the encountered shock configuration. In order to complement these initial works, we use 3D hybrid simulations (i.e. ions dynamics are fully described and electrons are a massless fluid) to model the interaction of an MC with a planetary bow shock. These global simulations allow to generate a bow shock where full curvature effects are self-consistently included in a supercritical regime (MA >= 5) as observed in front of a magnetic obstacle. Then, an MC modelled by a flux rope (Burlaga et al., 1988) is injected upstream and propagates towards this shock. We investigate the interaction of the MC with the bow shock, and in particular the impact on the MC's structure of the different domains of the shock wave from the quasi-perpendicular to the quasi-parallel (and its associated ion foreshock region). We use virtual spacecraft to probe the magnetosheath and compare their outputs to real spacecraft data.
• Solar wind turbulent cascade between ion and electron scales and quasi-parallel whistler waves
  
  • Alexandrova O.
  • Lacombe C.
  • Mangeney André
  • Grappin Roland
  • Maksimovic M.
  , 2014, 16, pp.8192. The solar wind is probably the best laboratory to study turbulence in astrophysical plasmas. In addition to the presence of a magnetic field, the differences with neutral fluid isotropic turbulence are: (i) weakness of collisional dissipation and (ii) presence of several characteristic space and time scales. Here we focus on the observational properties of the solar wind magnetic field turbulence around ion and electron characteristic scales. Around ion scales, magnetic spectra are variable and ion instabilities occur as a function of the local plasma parameters. Between ion and electron scales, a small scale turbulent cascade seems to be established, with wave vectors k&#8869; mainly perpendicular to the average B field. It is characterised by a well defined power-law spectrum in magnetic and density fluctuations with a spectral index close to -2.8. Approaching electron scales, the fluctuations are no more self-similar: an exponential cut-off is usually observed indicating an onset of dissipation. The small scale inertial range between ion and electron scales and the electron dissipation range can be together described by ~ k&#8869;-alpha exp(-k&#8869;ld), with alpha ~= 8/3 and the dissipation scale ld close to the electron Larmor radius ld ~= rhoe. The nature of this small scale cascade and a possible dissipation mechanism are still under debate. Different spectra are however observed in some regions of the solar wind, with quasi-parallel whistlers between the lower hybrid frequency and about half the electron cyclotron frequency. Such whistler waves may have variable intensity with respect to the background turbulence. Consequently, the total magnetic spectra may present a break, a knee or a more or less intense bump around frequencies at which whistlers propagate. We discuss a possible generation mechanism of quasi-parallel whistler waves in the solar wind.
• The effect of solar illumination on ionospheric outflow composition in the polar cap region
  
  • Maes Lukas
  • Maggiolo Romain
  • Haaland Stein
  • Dandouras Iannis
  • de Keyser J.
  • Fear Rob
  • Fontaine Dominique
  , 2014, 16, pp.15163. We use measurements by the CODIF ion spectrometer aboard the Cluster spacecraft, to investigate the composition of upflowing ion beams detected in the magnetospheric lobes during periods of northward IMF. These ion beams consist of ionospheric ions originating from the local polar ionosphere and are accelerated upward by a quasi-static electric field. This field-aligned electric field effectively acts as an extension of the experiment, probing the plasma at the altitude just below the bottom of the acceleration region and accelerating the ions into the energy range accessible by the CODIF detector. In this way it becomes possible to analyze the composition of upflowing ionospheric ions just above the polar ionosphere where ions are usually too cold to be measured by ion detectors due to the spacecraft charging We make a statistical analysis of the change in the composition of upflowing ions as a function of the solar zenith angle at the local ionosphere for a set of ~70 events. We show that the composition undergoes a very distinct regime change around 100° solar zenith angle, which corresponds to the solar terminator at ionospheric altitude. While the H density only shows weak variations with the solar zenith angle, the amount of O ions sharply decreases around 100° solar zenith angle. This illustrates how the alteration of ionospheric properties by solar illumination can affect the ionospheric upflow composition, and particularly the amount of O upflowing from the polar ionosphere. With a very simple model we investigate the implications of these observations on the seasonal variation of the average composition of ionospheric plasma upflowing from the polar ionosphere. Considering both the northern and southern polar regions, we show that the proportion of the polar ionosphere which is sunlit (i.e. below 100° solar zenith angle) varies through the year. Therefore the O dependency on solar illumination evidenced by Cluster suggests that ionospheric outflow will exhibit seasonal variations. Due to this seasonal effect, we may expect a higher amount of O ions escaping the polar ionosphere during spring/autumn than during winter/summer.
• Cluster crossings of the magnetopause to be used in two fluid simulations to investigate Kelvin-Helmholtz instability.
  
  • Rossi C.
  • Califano F.
  • Retinò Alessandro
  • Rezeau Laurence
  , 2014, 16, pp.11677. Kelvin-Helmholtz (KH) instability plays a fundamental role in the entry of solar wind plasma into the magnetosphere during northward interplanetary magnetic field. This instability may drive the formation of a mixing layer due to the development of small-scale secondary instabilities after the formation of large-scale rolled-up vortices. A number of spacecraft observations have shown that physical quantities measured at the flank low-latitude magnetopause/boundary layer are compatible with Kelvin-Helmholtz vortex structures. These observations are in agreement with different types of numerical simulations (MHD, two-fluid, particle-in-cell). Nevertheless simulations are usually performed by assuming idealized initial conditions for the magnetopause boundary e.g. very thin magnetopause, constant density and/or temperature across the boundary etc. Here we perform Cluster spacecraft data analysis of the low latitude boundary layer in order to obtain more realistic initial conditions to be used in two-fluid simulations of KH instability. The goal is to study and understand how such more realistic large-scale conditions affect the onset and evolution of small-scale secondary instabilities such as Rayleigh-Taylor and reconnection. We made a list of magnetopause/boundary layer crossings possibly close to the onset of KH instability and provide large-scale profiles of several quantities across the boundary (velocity, density, magnetic field, etc.) close to equilibrium. For a few cases, we use such profiles as initial conditions for two-fluid simulations of KH instability and discuss the occurrence and evolution of secondary instabilities within KH vortexes. The research leading to these results has received funding from the European Commission's Seventh Framework Programme (FP7/20072013) under the grant agreement SWIFF (Project No. 263340, www.swi.eu).
• Characterization through global hybrid simulations of solar wind ions impacting the dayside of Mercury
  
  • Chanteur Gérard
  • Modolo Ronan
  • Hess Sebastien
  • Leblanc François
  • Richer Emilie
  , 2014, 16, pp.EGU2014-12542. It has long been suspected since Mariner-10 observations that solar wind ions could reach the surface of Mercury: Kallio & Janhunen (2003) and Travnicek et al (2010) have presented simulated maps of precipitating proton fluxes. Attempts to refine estimations of precipitating fluxes of solar wind ions are important as these precipitations create additional sources of exospheric and possibly magnetospheric populations, and as their space-weathering effects modify the properties of the regolith. We run the global hybrid model used by Richer et al. (2012) which takes self-consistently into account the alpha particles of the solar wind to estimate fluxes of solar wind protons and alphas impacting the surface of Mercury under different IMF conditions. The internal source of the Hermean magnetic field is axisymmetric and is the superposition of a dipole and a quadrupole consistent with MESSENGER observations (Anderson et al., 2011) as in Richer et al. (2012). Results are briefly compared to predictions made with the offset dipole model of the planetary field. New simulations, made with an improved spatial resolution of 40km, reveal important differences between proton and alpha fluxes and show large variations with interplanetary conditions. In a first step we investigate the properties of solar wind ions impacting the dayside of the planet, precipitations on the night side will be examined later in a second step. References Anderson et al., Science, 333 , 1859, (2011) Kallio, E., and P. Janhunen, Solar wind and magnetospheric ion impact on Mercury's surface, Geophys. Res. Lett., 30(17), 1877, doi:10.1029/2003GL017842, 2003. Travnicek, P.M., D. Schriver, P. Hellinger, D. Hercik, B.J. Anderson, M. Sarantos, and J.A.Slavin, Mercury's magnetosphere-solar wind interaction for northward and southward interplanetary magnetic field: Hybrid simulation results, Icarus, doi:10.1016/j.icarus.2010.01.008, 2010 Richer, E., R. Modolo, G. M. Chanteur, S. Hess, and F. Leblanc (2012), A global hybrid model for Mercury's interaction with the solar wind: Case study of the dipole representation, J. Geophys. Res., 117, A10228, doi:10.1029/2012JA017898.
• A simple model of the structure of magnetic clouds downstream of Earth's bow shock
  
  • Turc Lucile
  • Fontaine Dominique
  • Savoini Philippe
  • Kilpua E. K. J.
  , 2014, 16, pp.6119. Magnetic clouds (MCs) are a subset of coronal mass ejections which are known for their importance in driving geomagnetic storms. Yet little is known about their interaction with Earth's bow shock and their propagation into the magnetosheath, and spacecraft observations only provide us with a limited coverage of the magnetosheath. In order to have a more global view of the interaction of an MC with Earth's bow shock, we develop a simple model of the magnetosheath magnetic field, adapted to MC conditions. We show several example MCs, corresponding to different orientations of the MC's axis and leading to different shock configurations. We find that the MC's structure is roughly unchanged inside the magnetosheath when the shock is quasi-perpendicular, while it is strongly altered in the quasi-parallel regime, in agreement with the observations. We show that in some cases the magnetic field North-South component can reverse in some parts of the magnetosheath. Finally, we discuss the impact of the alteration of the MC's structure through the bow shock and in the magnetosheath on the reconnection regions and on the MC's geoeffectivity.
• In situ observations of ion scale current sheet and associated electron heating in Earth's magnetosheath turbulence
  
  • Chasapis A.
  • Retinò Alessandro
  • Sahraoui Fouad
  • Greco A.
  • Vaivads A.
  • Sundkvist D.
  • Canu Patrick
  , 2014, 16, pp.15462. Magnetic reconnection occurs in thin current sheets that form in turbulent plasmas. Numerical simulations indicate that turbulent reconnection contributes to the dissipation of magnetic field energy and results in particle heating and non-thermal acceleration. Yet in situ measurements are required to determine its importance as a dissipation mechanism at those scales. The Earth's magnetosheath downstream of the quasi-parallel shock is a turbulent near-Earth environment that offers a privileged environment for such a study. Here we present a study of the properties of thin current sheets by using Cluster data. We studied the distribution of the current sheets as a function of their magnetic shear angle, the PVI index and the electron heating. The properties of the observed current sheets were different for high shear (theta > 90 degrees) and low shear current sheets (theta < 90 degrees). These high-shear current sheets account for about 20% of the total and have an average thickness comparable to the ion inertial length. Enhancement of electron temperature within these current sheets suggest that they are important for local electron heating and energy dissipation.
• BV technique accuracy: comparison with other single spacecraft techniques
  
  • Belmont Gérard
  • Dorville Nicolas
  • Rezeau Laurence
  , 2014.
• Origin and acceleration mechanisms of backstreaming ion populations in the Earth's quasi-perpendicular Ion Foreshock: Full-particle 2D simulation results
  
  • Savoini Philippe
  • Lembège Bertrand
  , 2014, 16, pp.2793. The ion foreshock located upstream of the Earth's bow shock is populated with ions reflected back by the shock front with an high energy gain. In-situ spacecraft measurements have clearly established the existence of two distinct populations in the foreshock upstream of the quasi-perpendicular shock region (i.e. for 45° <= ThetaBn <= 90° , where ThetaBnis the angle between the shock normal and the upstream magnetostatic field): (i) field-aligned ion beams (or ' FAB ') characterized by a gyrotropic distribution, and (ii) gyro-phase bunched ions (or ' GPB ') characterized by a NON gyrotropic distribution, which exhibits a non-vanishing perpendicular bulk velocity. The use of 2D PIC simulations of a curved shock, where full curvature effects, time of flight effects and both electrons and ions dynamics are fully described, has evidenced that the shock front itself can be the possible source of the different backstreaming ions. Our analysis evidences the importance of the interaction time (Deltainter) with the shock front, in particular ' GPB ' and ' FAB ' populations are characterized by a short (Deltainter= 1 to 2 tauci) and much larger (Deltainter= 1 to 10 tauci) interaction time respectively, where tauci is the ion upstream gyroperiod. This discrimination allows a deeper statistical analysis: (i) backstreaming ions are splitted into both ' FAB ' and ' GPB ' populations depending on their injection angle when hitting the shock front (i.e. defined between the local normal to the shock front and the gyration velocity vector at the time ions hit the front). (ii) As a consequence, ion trajectories strongly differ between the ' FAB ' and ' GPB ' populations at the shock front. In particular, ' FAB ' ions suffer multi-bounces along the curved front whereas ' GPB ' ions make only one bounce. Such differences can explain why the ' FAB ' population loses their gyro-phase coherency and become gyrotropic which is not the case for the ' GPB '. As also evidenced by these simulations, the origin of both populations can be associated directly to their interaction with the shock front itself and do not require any upstream instability which can be another source for such backstreaming ions.
• Oxydation of Volatile Organic Compounds adsorbed onto catalytic surfaces using Non Thermal Plasma
  
  • Rousseau Antoine
  , 2014.
• Etude de l’impact des flux zonaux sur la turbulence dans les plasmas, sur la transition L-H et la production d’entropie.
  
  • Berionni Vincent
  , 2014. Un des obstacles principaux au succès de la fusion thermonucléaire par confinement magnétique réside dans la présence de turbulence qui engendre un transport radial du plasma vers les parois des tokamaks. Pour étudier le mécanisme de réduction de la turbulence par les flux zonaux, qui permet d'atteindre un mode de confinement élevé, un modèle en couches dans l'espace de Fourier est utilisé. Basé sur les équations d'Hasegawa-Mima généralisées, il a permis d'étudier finement la dynamique des interactions de type prédateurs-proies entre les flux zonaux et la turbulence d'onde de dérive, soulignant l'importance du rôle du phénomène de friction des flux zonaux dans le comportement du système considéré. Une fois étendu à un plus grand nombre de couches, le comportement du système est en accord avec la règle de suppression de la turbulence par le cisaillement ExB . Le modèle révèle le transfert d'enstrophie potentielle turbulente qui se produit depuis les échelles d'injection vers les échelles de dissipation, résultant directement de l'action du cisaillement. Parallèlement, un modèle simple de transport radial en une dimension est proposé. En incluant l'évolution de la pression, de la densité, et de l'intensité de la turbulence, il permet de reproduire un mécanisme basique de transition L-H. L'influence de plusieurs paramètres du modèle sur la nature de la transition L-H est mise en évidence. Un troisième modèle couplant les deux précédents est alors construit pour reproduire la phénoménologie de la transition L-H en incluant les aspects spatial et spectral. Un comportement similaire aux observations expérimentales est constaté, et le rôle prépondérant des flux zonaux dans le déclenchement de la transition est mis en évidence. A l'aide de son aspect spectral, le modèle couplé prédit un aplatissement auto-cohérent du spectre turbulent lors de l'accès au mode H. L'impact de la diffusion radiale de la turbulence sur la dynamique de la transition est aussi discuté. Dans la dernière partie, une interprétation de la transition L-H à partir de la production d'entropie est proposée.
• Compact 180-kV Marx generator triggered in atmospheric air by femtosecond laser filaments
  
  • Arantchouk Léonid
  • Point G
  • Brelet Yohann
  • Larour Jean
  • Carbonnel Jérôme
  • André Yves-Bernard
  • Mysyrowicz A
  • Houard Aurélien
  Applied Physics Letters, American Institute of Physics, 2014, 104, pp.103506. We developed a compact Marx generator triggered in atmospheric air by a single femtosecond laser beam undergoing filamentation. Voltage pulses of 180 kV could be generated with a subnanosecond jitter. The same laser beam was also used to initiate simultaneously guided discharges up to 21 cm long at the output of the generator. (10.1063/1.4868227)
  DOI : 10.1063/1.4868227
• The JET real-time plasma-wall load monitoring system
  
  • Valcarcel D. F.
  • Alves D.
  • Card P.
  • Carvalho B. B.
  • Devaux Stéphane
  • Felton R.
  • Goodyear A.
  • Lomas P. J.
  • Maviglia F.
  • Mccullen P.
  • Reux C.
  • Rimini F.
  • Stephen A.
  • Zabeo L.
  • Zastrow K-D.
  • Contributors Jet Efda
  Fusion Engineering and Design, Elsevier, 2014, 89 (3), pp.243-258. In the past. the Joint European Torus (JET) has operated with a first-wall composed of Carbon Fibre Composite (CFC) tiles. The thermal properties of the wall were monitored in real-time during plasma operations by the WALLS system. This software routinely performed model-based thermal calculations of the divertor and Inner Wall Guard Limiter (IWGL) tiles calculating bulk temperatures and strike-point positions as well as raising alarms when these were beyond operational limits. Operation with the new ITER-like wall presents a whole new set of challenges regarding machine protection. One example relates to the new beryllium limiter tiles with a melting point of 1278 degrees C, which can be achieved during a plasma discharge well before the bulk temperature rises to this value. This requires new and accurate power deposition and thermal diffusion models. New systems were deployed for safe operation with the new wall: the Real-time Protection Sequencer (RTPS) and the Vessel Thermal Map (VTM). The former allows for a coordinated stop of the pulse and the latter uses the surface temperature map, measured by infrared (IR) cameras, to raise alarms in case of hot-spots. Integration of WALLS with these systems is required as RTPS responds to raised alarms and VTM, the primary protection system for the ITER-like wall, can use WALLS as a vessel temperature provider. This paper presents the engineering design, implementation and results of WALLS towards D-T operation, where it will act as a primary protection system when the IR cameras are blinded by the fusion reaction neutrons. The first operational results, with emphasis on its performance, are also presented. (10.1016/j.fusengdes.2013.10.010)
  DOI : 10.1016/j.fusengdes.2013.10.010
• A model for capacitive discharges with arbitrary RF waveform excitation including the electrical asymmetry effect and the associated self-bias
  
  • Chabert Pascal
  • Lafleur Trevor
  • Booth Jean-Paul
  • Turner Miles
  , 2014.
• Characteristics of Jupiter's magnetospheric turbulence observed by Galileo
  
  • Tao Chihiro
  • Sahraoui Fouad
  • Fontaine Dominique
  • de Patoul Judith
  • Khurana Khristian
  • Retinò Alessandro
  , 2014.
• BV TECHNIQUE FOR INVESTIGATING 1D INTERFACES
  
  • Dorville Nicolas
  • Belmont Gérard
  • Rezeau Laurence
  • Aunai N.
  • Retinò Alessandro
  , 2014.
• STUDY OF KELVIN-HELMHOLTZ INSTABILITY AT THE MAGNETOPAUSE BY COMBINING TWO-FLUID SIMULATIONS WITH CLUSTER IN SITU DATA
  
  • Rossi C.
  • Califano F.
  • Retinò Alessandro
  • Rezeau Laurence
  , 2014.
• Case study of an atypical magnetopause crossing
  
  • Dorville Nicolas
  • Belmont Gérard
  • Rezeau Laurence
  • Grappin Roland
  • Retinò Alessandro
  , 2014.
• Rôle de l'onde de choc terrestre dans l'interaction vent-solaire / magnétosphère
  
  • Fontaine Dominique
  • Turc Lucile
  • Savoini Philippe
  , 2014.
• Développement d'un imageur à rayons X durci pour l'environnement radiatif du Laser Mégajoule
  
  • Rousseau Adrien
  , 2014. La fusion thermonucléaire peut être obtenue sur les installations laser de classe mégajoule (NIF, LMJ) par l'implosion d'un mélange de Deutérium-Tritium confiné dans un microballon. Afin d'apporter les corrections adéquates sur les conditions expérimentales en vue de la réussite de ces expériences de fusion, il est nécessaire, entre autre, de qualifier la symétrie d'implosion. C'est le rôle dévolu à des chaînes de mesure spécifiques appelées diagnostics d'imagerie X. Aucun imageur X conçu à ce jour ne permet de réaliser cette mesure sans être perturbé par l'ambiance radiative engendrée par les produits des réactions nucléaires. L'imageur X développé dans cette thèse devra donc réaliser une image à haute résolution et à haute énergie tout en considérant les contraintes liées à cette ambiance nucléaire. La démarche a consisté tout d'abord à concevoir un système d'imagerie X permettant de réaliser l'image du microballon avec une résolution de 5 µm dans la bande 10-95 keV et à garantir sa survie face à l'agression nucléaire. Cette image X a été convertie en lumière visible par un scintillateur afin de permettre son transport vers une zone radio protégée où le système d'enregistrement est localisé. Cet analyseur optique constitué d'un amplificateur de luminance et d'un détecteur pixélisé a également été étudié et une nouvelle méthode permettant de réduire les perturbations transitoires induites par les rayonnements ionisants a été mise au point. La fonction de transport d'image est assurée au moyen d'un relai optique, conçu spécialement pour supporter les perturbations induites par les rayonnements ionisants. Ce dimensionnement par parties associé à des simulations Monte-Carlo (GEANT4) et des campagnes expérimentales (sur l'installation OMEGA du LLE) ont permis d'aboutir à une architecture cohérente de diagnostic permettant de supporter des niveaux de perturbations encore jamais atteints.