Publications

2015

• Scaling of compressible magnetohydrodynamic turbulence in the fast solar wind
  
  • Sahraoui Fouad
  • Banerjee Supratik
  • Galtier Sébastien
  • Hadid L. Z.
  , 2015, 33, pp.SH33A-2456. The role of compressible uctuations in the energy cascade of fast solar wind turbulence is studiedusing an exact law derived recently for compressible isothermal magnetohydrodynamics and in-situobservations of the THEMIS spacecraft. For the first time, a direct turbulent energy cascade isevidenced over three decades of scales which is signicantly broader than the previous estimatesmade from an exact incompressible law or from a compressible heuristic model. Unlike previousworks, our evaluation gives an energy ux which keeps a constant sign over the inertial range. Aterm-by-term analysis reveals that the dominant contribution to the energy ux comes from purecompressible uctuations. Furthermore, the compressible turbulent cascade rate is shown to providethe adequate energy dissipation required to account for the local heating of the non-adiabatic solarwind.
• MMS Observations of Kinetic Features in the Earth's Bursty Bulk Flow Braking Region
  
  • Goodrich K. A.
  • Ergun R.
  • Wilder F. D.
  • Sturner A. P.
  • Holmes J.
  • Stawarz J. E.
  • Malaspina D.
  • Usanova M.
  • Torbert R. B.
  • Lindqvist P. A.
  • Khotyaintsev Y. V.
  • Burch J. L.
  • Russell C. T.
  • Strangeway R. J.
  • Pollock C. J.
  • Magnes W.
  • Le Contel Olivier
  • Giles B. L.
  • Chutter M.
  • Needell J.
  • Rau D.
  • Gershman D. J.
  , 2015, 44, pp.SM44A-08. We present MMS observations of particle and wave activity in the Earth's Bursty Bulk Flow (BBF) Braking region (6 - 12 Earth radii tailward). This region, previously examined by the THEMIS spacecraft, has shown evidence of bursty, high velocity, Earthward particle flows, turbulent magnetic fields, and large amplitude electric field signatures (amplitudes can, at times, exceed 100 mV/m). Kinetic features such as double layers, electron phase-space holes, and magnetic holes have been observed frequently throughout this region. The Magnetospheric Multi-scale (MMS) spacecraft, launched March 2015, are currently orbiting the Earth with the objective of observing the microphysics of magnetic reconnection. During its commissioning phase (March 2015 - August 2015), all four spacecraft apogees were primarily in the BBF Braking region. The presence of MMS in this region can offer higher spatial and temporal resolution of the BBF Braking region than ever before. We examine MMS observations kinetic structures (double layers, electron phase-space and magnetic holes) to further characterize the BBF braking region and its overall effects on the Earth space environment.
• Climatology of mid-latitude MSTID events observed by the DEMETER satellite in the period 2005-2010
  
  • Berthelier Jean-Jacques
  • Nguyen Cien-Thang
  • Amory-Mazaudier Christine
  • Petitdidier Monique
  , 2015, pp.SA23C-2357. Using plasma measurements from the CNES DEMETER micro-satellite, we have performed a global survey of ionospheric disturbances observed at middle and low latitudes on the nightime part of the DEMETER orbit in the local time sector 21.30-22.30 LT. This study encompasses the 6 years of the satellite operations, from 2005 to 2010, including years of moderate magnetic activity of solar cycles 23 and 24 and the deep solar minimum in 2009-2010. We report in this poster a statistical analysis of MSTID events characterized by quasi-periodic variations of the O+ density observed below ~ 40° geomagnetic latitudes with wavelengths ranging from 350 to 700 km. Although detected in both hemispheres they occur predominantly at southern latitudes with a rather strong peak over the Pacific ocean. A detailed analysis has shown that these events may be sorted in 4 categories according to their latitudinal extent. Most of them are restricted to a latitude band between ~ 15° and 40° geomagnetic in North or South but some of them extend from mid latitudes in one hemisphere to low latitude in the other hemisphere, thus spanning equatorial regions up to 5-10°. The apparent negative correlation with magnetic activity seems to indicate that most of these events are driven by AGW originating from low altitude atmospheric levels and not triggered by auroral phenomena. We shall present the seasonal and inter-annual variations showing significant changes associated with solar activity. Our results will be compared to other ground-based or satellite observations and our investigation pointed out a strong effect of these MSTID and their parent AGW on the electrodynamics of the low latitude ionosphere.
• Asymmetric kinetic equilibria: demonstration of the independence of magnetic reconnection signatures to the initial current sheet structure.
  
  • Dargent Jérémy
  • Aunai N.
  • Belmont Gérard
  • Dorville Nicolas
  • Lavraud B.
  • Hesse Michael
  , 2015, 51, pp.SM51A-2515. Current sheets are ubiquitous in space plasmas and yet hard to describe with a kinetic equilibrium. The BAS model is a semi-analytical model which provides a steady distribution function for asymmetric current sheet ions. In this paper, we prove that an ion kinetic equilibria produced by this model remain steady in a fully kinetic Particle-In-Cell simulation even if the electron distribution function is not an equilibrium. We then apply this equilibrium to look at the dependence of magnetic reconnection simulations upon their initial condition. We demonstrate that regardless of macroscopic or microscopic differences between initial current sheets, signatures of magnetic reconnection only depends on the upstream plasma. This demonstration is the first to confirm this widely use assumption and comforts the relevance of comparisons between simulations and observations in the electron decoupling region, such as in the context of the upcoming Magnetospheric Multiscale mission.
• Radiative Shock Experiments on Orion
  
  • Suzuki-Vidal Francisco
  • Swadling G.
  • Lebedev S.
  • Burdiak G.
  • Patankar S.
  • Smith R.
  • Foster J.
  • Skidmore J.
  • Gumbrell E.
  • Graham P.
  • Charles R.
  • Treadwell P.
  • Hopps N.
  • Danson C.
  • Stehlé Chantal
  • Chaulagain Uddhab
  • Spindloe C.
  • Kozlová Michaela
  • Larour Jean
  • Clayson Thomas
  , 2015. Counter-propagating are created and studied on Orion laser facility.
• Effect of electron ambient plasmas in reconnection jets and dipolarization fronts : MMS initial results
  
  • Nakamura R.
  • Torkar K.
  • Andriopoulou M.
  • Jeszenszky H.
  • Plaschke F.
  • Baumjohann W.
  • Magnes W.
  • Fischer D.
  • Schmid D.
  • Steller M.
  • Nakamura T.
  • Scharlemann C.
  • Torbert R. B.
  • Burch J. L.
  • Ergun R. E.
  • Lindqvist P. A.
  • Marklund G. T.
  • Khotyaintsev Y. V.
  • Russell C. T.
  • Strangeway R. J.
  • Leinweber H. K.
  • Anderson B. J.
  • Le G.
  • Bromund K. R.
  • Fuselier S. A.
  • Chutter M.
  • Slavin J. A.
  • Kepko L.
  • Le Contel Olivier
  • Pollock C. J.
  • Dorelli J. C.
  • Gershman D. J.
  • Mauk B.
  • Vaith H.
  • Kletzing C.
  • Bounds S. R.
  • Sigsbee K. M.
  , 2015, 43, pp.SM43A-02. With the successful launch of Magnetospheric Multiscale Misssion (MMS), it becomes possible to observe the dynamic signatures of magnetospheric transients with high-time resolution measurements of electromagnetic fields and plasma. The Active Spacecraft Potential Control (ASPOC) neutralizes the spacecraft potential by releasing positive charge produced by indium and thereby controlling the spacecraft potential in order to enable accurate measurements also in sparse plasma environments essential to study properties of reconnection. Since the current balance around the spacecraft is maintained by contribution also from the ambient plasma, predominantly electrons, ASPOC beam current values combined with spacecraft potential data from FIELDS instruments enable to deduce the ambient electron plasma parameters . Particularly, using data from multi-spacecraft measurements with different ASPOC current levels and FIELDS data, parameters on ambient electron temperature and density can be deduced. Monitoring the environmental plasma parameters are essential to determine the accurate scales of the structure or wave length relative to plasma scales and hence to understand the physical processes. In this study we investigate the changes of the electron parameters in the transient structures such as the magnetic field disturbance forming at the front of BBF/flow bursts, called dipolarization front (DF), and reconnection jets in thin current sheets obtained by MMS mainly during the commissioning phase when the spacecraft traversed the near-Earth tail.
• Observations and Simulations of the Interaction of Magnetic Clouds with the Bow Shock and Implications for their Couplings to the Magnetosphere
  
  • Fontaine Dominique
  • Turc Lucile
  • Savoini Philippe
  • Modolo Ronan
  , 2015, pp.SM21C-09. Magnetic clouds are among the most geoeffective solar events capable to trigger strong magnetic storms in the terrestrial magnetosphere. However, the storm occurrence and strength are not yet fully explained. The magnetic clouds’ orientation, the presence of events/structures on their leading or trailing edges are presently discussed in the literature. In complement to these effects, we investigate here the interaction of magnetic clouds with the bow shock, the structure and propagation of the modified clouds downstream of it in the magnetosheath and the consequences for their interaction with the magnetosphere. This question is first tackled from observations. Correlated observations upstream (ACE) and downstream (CLUSTER) of the bow shock show that the interaction of magnetic clouds with the bow shock can strongly modify their downstream structure and lead to inexpected interactions with the magnetosphere. We also discuss this question from hybrid simulations of the interaction of magnetic clouds with the bow shock. We show that this interaction may produce in the magnetosheath very asymmetric distributions of magnetic field, density, temperature, velocity and that they depend on the shock configuration (quasi-perpendicular, quasi-parallel). We investigate the effects this asymmetric magnetosheath on key parameters for the interaction with the magnetopause, responsible for the development of geomagnetic activity in the magnetosphere.
• Observations of 3-D Electric Fields and Waves Associated With Reconnection at the Dayside Magnetopause
  
  • Wilder F. D.
  • Ergun R.
  • Goodrich K. A.
  • Malaspina D.
  • Eriksson S.
  • Stawarz J. E.
  • Sturner A. P.
  • Holmes J.
  • Burch J. L.
  • Torbert R. B.
  • Phan T.
  • Le Contel Olivier
  • Goldman M. V.
  • Newman D. L.
  • Lindqvist P. A.
  • Khotyaintsev Y. V.
  • Strangeway R. J.
  • Russell C. T.
  • Giles B. L.
  • Pollock C. J.
  , 2015, 41, pp.SM41I-08. The phenomenon of magnetic reconnection, especially at electron scales, is still poorly understood. One process that warrants further investigation is the role of wave phenomenon in mediating magnetic reconnection. Previous observations have shown the presence of electrostatic solitary waves (ESWs) as well as whistler mode waves near the dayside reconnection site. Additionally, recent simulations have suggested that whistler waves might be generated by electron phase space holes associated with ESWs as they propagate along the magnetic separatrix towards the diffusion region. Other observations have shown ESWs with distinct speeds and time scales, suggesting that different instabilities generate the ESWs. NASA's recently launched Magnetospheric Multiscale (MMS) mission presents a unique opportunity to investigate the roles of wave phenomena, such as ESWs and whistlers, in asymmetric reconnection at the dayside magnetopause. We will present 3-D electric and magnetic field data from magnetopause crossings by MMS during its first dayside science phase. Burst mode wave data and electron distributions from all four spacecraft will be analyzed to investigate the origin of these wave phenomena, as well as their impact on the reconnection electric field.
• Origin of the Ion Foreshock in a Quasi-perpendicular Curved Collisionless Shock: Particles Trajectory Analysis in 2D PIC Simulations
  
  • Savoini Philippe
  • Lembège Bertrand
  , 2015, 21, pp.SM21C-07. The ion foreshock located upstream of the Earth's shock wave is populated with ions having interacted with the shock, and then, reflected back with an high energy gain. Spacecrafts have clearly established the existence of two distinct populations in the quasi-perpendicular shock region (i.e. for 45° <= ThetaBn <= 90°, where ThetaBn is the angle between the shock normal and the upstream magnetic 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. One of the important unresolved problem is the exact origin of the particles contributing to these two populations. To our knowledge, it was the first time that full-particle simulations have been performed including self-consistently the shock front curvature and nonstationarity, and the time-of-flight effects. Our analysis evidences that these two backstreaming populations may be reflected by the front itself and can be differentiated both in terms of interaction time and trajectory within the shock front. In particular, simulations evidence that "GPB" population is characterized by a short interaction time (DeltaTinter = 1 to 2 tauci) while the "FAB" population corresponds to a much larger time range (from 1 tauci to 10 tauci), where tci is the upstream ion gyroperiod. Present individual ion trajectories evidence that "FAB" population shows a strong perpendicular drift at the shock front (i.e. strong dependence of the pitch angle to the perpendicular velocity) whereas the "GPB" population shows no perpendicular drift (i.e. its pitch angle is mainly driven by the parallel velocity). Such differences explain why the "FAB" population loses their gyro-phase coherency and become gyrotropic which is not the case for the "GPB". This important result was not expected and greatly simplifies the question of their origin.
• Swarm Observations of Field Aligned Currents during Geomagnetic Storms
  
  • Le G.
  • Lühr H.
  • Anderson B. J.
  • Strangeway R. J.
  • Russell C. T.
  • Slavin J. A.
  • Bromund K. R.
  • Plaschke F.
  • Magnes W.
  • Fischer D.
  • Nakamura R.
  • Leinweber H. K.
  • Torbert R. B.
  • Le Contel Olivier
  • Oliveira D. M.
  • Raeder J.
  • Kepko L.
  , 2015, 11, pp.SM11A-06. Field-aligned currents connect the Earth's magnetosphere to the high latitude ionosphere, and provide a main channel for energy transfer from the magnetosphere to the ionosphere. They are driven by solar wind-magnetosphere interactions and respond dynamically to changes in the solar wind and interplanetary magnetic field. Enhanced interaction during geomagnetic storms significantly intensifies their strength and variability. In this paper, we review our recent observations of field-aligned currents (FACs) during geomagnetic storms using observations from polar orbiting Swarm constellation as well as the Active Magnetosphere and Polar Electrodynamics Response Experiment (AMPERE). Both temporal resolutions and spatial coverage of these observations provide new insights in understanding the FACs and the magnetosphere-ionosphere coupling. We will discuss their spatial and temporal evolutions, ionospheric closure currents, and hemispheric asymmetry during storms.
• Search Coil and Fluxgate Data Merging on MMS: Examples on Dipolarization Event Cases
  
  • Plaschke F.
  • Fischer D.
  • Magnes W.
  • Valavanoglou A.
  • Le Contel Olivier
  • Nakamura R.
  • Andriopoulou M.
  • Schmid D.
  • Baumjohann W.
  • Torbert R. B.
  • Russell C.
  • Strangeway R. J.
  • Leinweber H. K.
  • Bromund K. R.
  • Anderson B. J.
  • Le G.
  • Chutter M.
  • Needell J.
  • Dors I.
  • Slavin J. A.
  • Kepko L.
  • Mirioni Laurent
  , 2015, 51. The instrument suite of MMS mission includes one search coil and two fluxgate magnetometers on each observatory and can therefore provide the possibility to study events that cross the sensitive frequency range of both instrument types. It is therefore desirable to have a common merged data product that combines the best parts of both instruments. Extensive ground based test measurements have been performed to identify the properties of the instruments. New models for compensating time and frequency properties were created and the difference to existing calibrations is analyzed. Considerations for application as well as signal processing constraints are discussed and the resulting method is applied on data from the mission. Dipolarization events can serve as suitable example, since they contain a variety of disturbances with different characteristic scales: transient filamentary properties, sharp fronts, reconfiguration of the current sheet, wave signatures on kinetic as well as fluid scales, thus requiring highest sensitivity data in a wide frequency range. We show these different signatures relevant to the dipolarization events based on the analysis of these newly produced data.
• Magnetospheric Multiscale Observations of Ultra Low Frequency Waves in the Inner Magnetosphere
  
  • Strangeway R. J.
  • Russell C. T.
  • Burch J. L.
  • Torbert R. B.
  • Magnes W.
  • Plaschke F.
  • Leinweber H. K.
  • Bromund K. R.
  • Fischer D.
  • Anderson B. J.
  • Le G.
  • Chutter M.
  • Slavin J. A.
  • Kepko L.
  • Le Contel Olivier
  • Nakamura R.
  • Baumjohann W.
  • Argall M. R.
  • Chi P. J.
  , 2015, 41, pp.SM41H-2571. The apogee of the Magnetospheric Multiscale (MMS) spacecraft was in the predawn local time sector early in the MMS commissioning phase. On several orbits in this phase MMS observed large amplitude (10s of nT) Pc5 pulsations, typically around 5 to 7 Earth radii, near dawn. Because MMS was in a string-of-pearls configuration we could determine the phase velocity of the waves along the spacecraft separation vector. Preliminary analysis indicates that this was of the order 30-50 km/s, much larger than the spacecraft velocity. Furthermore, the waves are propagating tailwards. Given a nominal wave period of the order 5 minutes, the wavelength of the waves is around 2 Earth radii, assuming azimuthal propagation. This corresponds to an m-number of about 20. The waves used for this initial study were observed on several successive orbits during the recovery phase of the March 17, 2015 geomagnetic storm. We will present additional analysis of the properties of these ULF waves as observed during the MMS commissioning phase, during which time the spacecraft apogee migrated from dawn to dusk through the nightside.
• Etude des vitesses de dérive fluides dans le plasma de bord des tokamaks : modélisation numérique et comparaison simulation/expérience
  
  • Leybros Robin
  , 2015. Le transport des particules et de la chaleur dans la zone de bord des tokamaks joue un rôle déterminant à la fois sur les performances du plasma confiné et sur l’extraction de la puissance et ainsi la durée de vie des composants face au plasma. C’est dans ce contexte que s’inscrit ce travail de thèse, qui porte sur le rôle joué par les écoulements transverses au champ magnétique dans l’équilibre entre dynamique parallèle et dynamique perpendiculaire qui régit la région périphérique d’un tokamak. Ces écoulements peuvent produire des asymétries poloïdales du dépôt de chaleur et de particules sur les composants face au plasma, et plus généralement des asymétries des diverses quantités dans le plasma. Les vitesses de dérive radiale sont d’origine électrique (liées à la présence d’un champ électrique radial résultant de l’équilibre des charges) ou liées aux effets de la géométrie toroïdale induisant une inhomogénéité du champ magnétique (vitesse de gradient-courbure). Pour progresser dans la compréhension de ces phénomènes, la modélisation numérique du transport et de la turbulence en géométrie complexe est indispensable. En complément, des outils de diagnostic synthétique permettant de modéliser les processus de mesure dans les plasmas numériques sont développés pour permettre une comparaison réaliste entre modèles et expériences. La modélisation des vitesses de dérive perpendiculaire a été introduite dans le code SOLEDGE2D décrivant le transport de la densité, quantité de mouvement et énergie d’un plasma de tokamak. Nous avons d’abord étudié l’impact d’un champ électrique prescrit sur les équilibres plasma, pour comprendre les mécanismes à l’origine des asymétries du plasma et étudier l’établissement d’écoulement parallèle et d’asymétrie du dépôt de chaleur sur les composants face au plasma. Nous avons ensuite implémenté un modèle auto-consistant de résolution du potentiel électrique dans les équations fluides de SOLEDGE2D afin de comprendre l’équilibre du champ électrique et d’étudier l’effet de la configuration magnétique du tokamak et de la vitesse de gradient-courbure sur ce dernier. Dans la deuxième partie de cette thèse, un diagnostic synthétique permettant de modéliser les mesures expérimentales de rétro-diffusion Doppler a été développé et testé en vue d’être appliqué aux simulations du code fluide 3D turbulent, TOKAM3X. Ce diagnostic permet de mesurer la vitesse perpendiculaire du plasma à partir du mouvement des fluctuations de densité. Il a été utilisé ici pour comparer les asymétries de vitesse observées expérimentalement aux asymétries mesurées dans les simulations numériques.
• Quantitative Diagnostics of Inductive Plasmas in Chlorine, Oxygen and Chlorine-Oxygen Mixtures
  
  • Booth Jean-Paul
  • Foucher Mickaël
  • Marinov Daniil
  • Chabert Pascal
  , 2015. Inductively-coupled plasmas in molecular, electronegative gases are widely used for plasma processing of surfaces, for instance in CMOS manufacture. The complexity of these systems is such that they can only be described by multi-physics models which describe both the plasma physics and the molecular collisional processes. However, rigorous validation of these models by comparison to quantitative measurements of particle densities over a wide range of parameter space has not been performed. We have chosen to study the Cl2/O2 system because of the industrial process relevance but also because methods exist to measure the density of many of the particles present. Electron densities were measured by microwave hairpin resonator. Absolute Cl and O atom densities were determined by Two-photon Absorption Laser-Induced Fluorescence [1, 2]. A new ultra-low noise broadband UV-visible absorption bench [3] allows measurement of the densities of ground state Cl2 molecules, ClxOy reaction products and vibrationally excited states of Cl2 and O2. Whereas plasmas in O2 show high vibrational excitation (up to 10,000K) with gas translational temperatures reaching up to 900K, in Cl2 the vibrational temperature is in equilibrium with the gas translational temperature (about 1000K). These results will be compared to the current state of the art in 2-D hybrid fluid models as well as simpler global models, allowing the chemical and energy transfer mechanisms to be understood. 1) Booth, J.P., Y. Azamoum, N. Sirse, and P. Chabert, Journal of Physics D: Applied Physics, 45, 195201. (2012) 2) Niemi, K., V. Schulz-von der Gathen, and H.F. Dobele, Plasma Sources Science & Technology, 14, (2005) 3) Foucher, M., D. Marinov, E. Carbone, P. Chabert, and J.-P. Booth, Plasma Sources Science and Technology, 24, (2015)
• Two-fluid numerical simulations of turbulence inside Kelvin-Helmholtz vortices: Intermittency and reconnecting current sheets
  
  • Rossi C.
  • Califano F.
  • Retinò Alessandro
  • Sorriso-Valvo L.
  • Henri Pierre
  • Servidio S.
  • Valentini F.
  • Chasapis A.
  • Rezeau Laurence
  Physics of Plasmas, American Institute of Physics, 2015, 22 (12), pp.122303. The turbulence developing inside Kelvin-Helmholtz vortices has been studied using a two-fluid numerical simulation. From an initial large-scale velocity shear, the nonlinear evolution of the instability leads to the formation of a region inside the initial vortex characterized by small-scale fluctuations and structures. The magnetic energy spectrum is compatible with a Kolmogorov-like power-law decay, followed by a steeper power-law below proton scales, in agreement with other studies. The magnetic field increments show non-Gaussian distributions with increasing tails going towards smaller scales, consistent with presence of intermittency. The strong magnetic fieldfluctuations populating the tails of the distributions have been identified as current sheets by using the Partial Variance of the Increments (PVI) method. The strongest current sheets (largest PVI) appear around proton scales and below. By selecting several of such current sheets, it has been found that most of them are consistent with ongoing magnetic reconnection. The detailed study of one reconnecting current sheet as crossed by a virtual spacecraft is also presented. Inflow and outflow regions have been identified and the reconnection rate has been estimated. The observation of reconnection rates higher than typical fast rate suggests that reconnection in turbulentplasma can be faster than laminar reconnection. This study indicates that intermittency and reconnecting current sheets are important ingredients of turbulence within Kelvin-Helmholtz vortices and that reconnection can play an important role for energy dissipation therein. ∼0.1 (10.1063/1.4936795)
  DOI : 10.1063/1.4936795
• Optimization of an electromagnetic generator for strong shocks in low pressure gas
  
  • Larour Jean
  • Singh Raj Laxmi
  • Stehlé Chantal
  • Ciardi Andrea
  • Chaulagain Uddhab
  • Suzuki-Vidal Francisco
  High Energy Density Physics, Elsevier, 2015, 17, pp.129-134. (10.1016/j.hedp.2015.05.004)
  DOI : 10.1016/j.hedp.2015.05.004
• Caractérisation et modélisation d'un propulseur plasma à résonance cyclotronique des électrons
  
  • Cannat Félix
  , 2015. L'objet de ce travail consiste à la caractérisation et à la modélisation d'un propulseur électrique à résonance cyclotronique des électrons. L’objectif est d’étudier la physique du propulseur (transfert d’énergie par résonance, processus d’ionisation, couplage micro-onde/plasma, processus d’accélération) afin d’améliorer ses performances, son efficacité ainsi que le développement d’outils de dimensionnement. Un prototype expérimental du propulseur a été caractérisé autour des degrés de libertés de fonctionnement tels que la fréquence, le champ magnétique, la puissance, la géométrie et le débit de gaz. Les résultats obtenus permettent de définir les conditions pour un fonctionnement nominal du propulseur en termes de performances et d’efficacité. Il a été montré que la position de la zone résonance ainsi que la pression de fonctionnement sont les deux paramètres clés pour l’optimisation du propulseur. Ces travaux de recherche ont permis d’augmenter les performances et le rendement total du propulseur. Pour une puissance de 30 Watts et un débit de 0.1 mg/s, le propulseur fourni une poussée de 1 mN avec une impulsion spécifique de 1000 s pour 16 % d’efficacité totale. En parallèle, un modèle de décharge est adapté au propulseur. Il estime les performances du propulseur, permet d’identifier les points importants et apporte des perspectives de dimensionnement pour une nouvelle version du propulseur. Pour compléter ce modèle, des simulations préliminaires de propagation d’ondes électromagnétiques et de couplage micro-onde plasma magnétisé sont réalisées. Les résultats obtenues permettent de mieux comprendre la déposition de puissance micro-onde dans le propulseur.
• GIRGEA : A scientific network without borders
  
  • Amory-Mazaudier Christine
  , 2015. Présentation du réseau scientifique pour lequel j'ai reçu la médaille Marcel Nicolet
• A short-pulse mode for the SPHINX LTD Z-pinch driver
  
  • d'Almeida Thierry
  • Lassalle Francis
  • Zucchini Frédéric
  • Loyen Arnaud
  • Morell Alain
  • Chuvatin Alexandre S.
  , 2015, 60 (19), pp.UP12.00012. The SPHINX machine is a 6MA, 1 &#956;s, LTD Z-pinch driver at CEA Gramat (France) and primarily used for studying radiation effects. Different power amplification concepts were examined in order to reduce the current rise time without modifying the generator discharge scheme, including the Dynamic Load Current Multiplier (DLCM) proposed by Chuvatin [1]. A DLCM device, capable of shaping the current pulse without reducing the rise time, was developed at CEA. This device proved valuable for isentropic compression experiments in cylindrical geometry [2]. Recently, we achieved a short pulse operation mode by inserting a vacuum closing switch between the DLCM and the load. The current rise time was reduced to &#8764; 300 ns. We explored the use of a reduced-height wire array for the Dynamic Flux Extruder in order to improve the wire array compression rate and increase the efficiency of the current transfer to the load. These developments are presented. Potential benefits of these developments for future Z pinch experiments are discussed. [1] A.S. Chuvatin, Dynamic Current Multiplier; 14th Symposium on High Current Electronics, Tomsk, Russia, pp 232-235 (2006). [2] T. d'Almeida et al, Phys. Plasmas, 20, 092512-1 092512-16 (2013).
• The Largest Multi-Planar Wire Arrays on Zebra with LCM and their Applications
  
  • Safronova Alla S.
  • Kantsyrev Viktor L.
  • Weller Michael E.
  • Shlyaptseva V. V.
  • Shrestha I. K.
  • Lorance M. Y.
  • Stafford A.
  • Schultz K. A.
  • Coverdale C. A.
  • Chuvatin Alexandre S.
  , 2015, 60 (19), pp.YO4.00001. Two new approaches of i) simultaneous study of implosion and radiative characteristics of different materials in wire array Z-pinch plasma in one shot [Safronova et al, PoP 21, 031205 (2014)] and ii) investigation of larger sized wire arrays (to enhance energy coupling to plasmas and provide better diagnostic access) were further developed in experiments with 1.7 MA Zebra with a Load Current Multiplier. In particular, the largest multi-Planar Wire Arrays with two outer planes from alloyed Al wires placed as far from each other as at 19 mm (compare with 6 and 9 mm studied before) and with a modified central plane from Ni-60 (mostly Cu), were investigated. Though K-shell Al and L-shell Cu plasmas have similar temperatures and densities, the ablation dynamics and radiation of Al and Cu planes is somewhat different, which was investigated in detail using the full set of diagnostics and modeling. Advantages of using such wire arrays at higher currents to study plasma flow and radiation from different materials and jets are highlighted. This work was supported by NNSA under DOE Cooperative Agreement DE-NA0001984 and in part by DE-NA0002075. SNL is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U.S. DOE under Contract DE-AC04-94AL85000.
• How to optimize VOC abatement using plasma-catalyst technology?
  
  • Rousseau Antoine
  , 2015.
• Magnetic Reconnection in laser-driven HEDP : recent experiments & hybrid simulations
  
  • Smets Roch
  • Fuchs J. C.
  • Grisollet A.
  • Riquier R.
  , 2015.
• Turbulent Heating ObserveR THOR
  
  • Retinò Alessandro
  , 2015.
• Signatures of solar event at middle and low latitudes in the Europe-African sector, during geomagnetic storms, October 2013
  
  • Azzouzi Ilyasse
  • Migoya-Orué Y.
  • Amory-Mazaudier Christine
  • Fleury Rolland
  • Radicella S.M.
  • Touzani A.
  Advances in Space Research, Elsevier, 2015, 56 (9), pp.2040–2055. This paper presents the variability of the total electron content, VTEC, the ROTI index (proxy of the scintillation index) and the transient variations of the Earth's magnetic field associated to the impacts of solar events during October 2013. The observations are from middle and low latitudes in European African longitude sector. During October 2013, there are four solar events reaching the Earth. The two first events, on October 2 and October 8 are CME, the third event on October 14, is a jet of fast solar wind flowing from a solar coronal hole, and the last event on October 30 is a slow solar wind with southward excursions of the Bz component of the Interplanetary magnetic field, associated to CME passing near the Earth. For the four events, the variation of VTEC at middle latitudes is the same and presents an increase of VTEC at the time of the impact followed by a decrease of VTEC, lasting one or several days. At low latitudes, no clear common pattern for all the events appears. For the four events the variation of the ROTI index over Africa is different showing the asymmetry between West and East Africa. For the first event, on October 2, the scintillations are not inhibited, for the second and the fourth events on October 8 and 30, the scintillations are inhibited on East Africa and for the third event (high speed solar wind stream), on October 14, the scintillations are inhibited over the whole Africa. The available data allow the full explanation of the observations of October 14, indeed, on this day, there is no post sunset increase of the virtual height h'F2 at Ascension Island. There is no Pre Reversal Enhancement (PRE) of the eastward electric field; it is this electric field which moves up the F layer, the necessary condition for the existence of scintillation. The analysis of the variations of the Earth's magnetic field at low latitudes highlights the presence of the ionospheric disturbance dynamo on October 14, which produces a decrease of the Equatorial Electrojet, several hours after the impact of the high speed solar wind. The disturbance dynamo electric field (DDEF) is westward during the day and till after sunset and turns eastward around 22.30LT. So, on October 14, the westward DDEF inhibits the eastward regular electric field. (10.1016/j.asr.2015.06.010)
  DOI : 10.1016/j.asr.2015.06.010
• Nighttime morphology of vertical plasma drifts at Ouagadougou during different seasons and phases of sunspot cycles 20-22
  
  • Adebesin B. O.
  • Rabiu A. B.
  • Adeniyi J. O.
  • Amory-Mazaudier Christine
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2015, 120 (11), pp.10020–10038. The nighttime morphology of vertical plasma drift (V d) inferred from ground-based measurements of the F layer height at Ouagadougou (12.4°N, 358.6°E) in the African Equatorial Ionization Anomaly trough was investigated. The observation covers four seasons, four sunspot cycle phases, annual, and 11 year sunspot cycle (SC) variations of the SCs 20–22 spanning 1966–1998 and a first attempt of such study. The annual mean peak magnitudes of V d during the prereversal enhancement (PRE) and minimum reversal periods exhibit the 11 year sunspot cycle evolution with the sunspot number (Rz). The PRE peak/Rz and reversal peak/Rz relationships are 98.7% and 84.8%, respectively. PRE peak in June solstice appears 1 h later than for other seasons and is attributed to a decrease in the equatorial zonal wind/conductivity gradient. The highest PRE magnitude and downward perturbation drifts near dusk appear during the equinoxes and lowest in June solstice for all cycles. There is semiannual asymmetry in the variation of V d during all cycles of the PRE event with peaks in March and September/October. A remarkable feature is the consistent local presunrise drift enhancement for two SCs 20 and 21, which is not a regular feature of the equatorial ionosphere. The rate of inhibition of scintillation effect increases with decreasing phase of sunspot activity and maximizes during the solstices. Both the PRE and minimum reversal peak magnitudes are influenced by the phase of sunspot cycle. Ouagadougou data in this study had shown reliable drift characteristics and can be integrated into the African regional empirical drift model. (10.1002/2015JA021737)
  DOI : 10.1002/2015JA021737