New insight into short wavelength solar wind fluctuations from Vlasov theory

The nature of solar wind (SW) turbulence below the proton gyroscale is a topic that is being investigated extensively nowadays. Although recent observations gave evidence of the dominance of Kinetic Alfv\'en Waves (KAW) at sub-ion scales with $\omega<{\omega_{ci}}$, other studies suggest that the KAW mode cannot carry the turbulence cascade down to electron scales and that the whistler mode (i.e., $\omega>\omega_{ci}$) is more relevant. Here, we propose to study key properties of the short wavelength plasma modes under realistic SW conditions, typically $\beta_i\gtrsim \beta_e\sim 1$ and for high oblique angles of propagation $80^\circ\leq \Theta_{\bf kB}<90^\circ$ as observed from the Cluster data. The linear properties of the plasma modes under these conditions are poorly known, which contrasts with the well-documented cold plasma limit and/or moderate oblique angles of propagation ($\Theta_{\bf kB} <80^\circ$). Based on linear solutions of the Vlasov kinetic theory, we discuss the relevance of each plasma mode (fast, Bernstein, KAW, whistler) in carrying the energy cascade down to electron scales. We show, in particular, that the shear Alfv\'en mode extends at scales $k\rho_i\gtrsim1$ following either a whistler mode ($\omega>\omega_{ci}$) or a KAW mode (with $\omega<\omega_{ci}$) depending on the anisotropy $k_\parallel/ k_\perp$. This contrasts with the well-accepted idea that the whistler branch develops as a continuation at high frequencies of the fast magnetosonic mode. We show, furthermore, that the whistler branch is more damped than the KAW one, which makes the latter a more relevant candidate to carry the energy cascade down to electron scales. We discuss how these new findings may facilitate resolution of the controversy concerning the nature of the small scale turbulence, and we discuss the implications for present and future spacecraft wave measurements in the SW.Comment: 11 pages, 12 figures, submitted to Astrophysical Journa

Observations of How Magnetofluid Turbulence Dissipates at Small Scales

The solar wind is a turbulent magneto fluid that can be studied intensively at multiple scales. Investigations using single spacecraft have revealed much about the properties of the solar wind throughout the heliosphere (from 0.3 AU to 100 AU). More recently, data from multiple spacecraft have provided further details of both the statistical properties of the turbulence and its small-scale structure. In particular, high time resolution magnetic field measurements from the four Cluster spacecrafl have led to the conclusion that at spatial scales of order the proton inertial length and smaller, the turbulence becomes strongly anisotropic and the power in fluctuations that are perpendicular to the (local) magnetic field is measured to be much larger than that in fluctuations that are parallel to the magnetic field. As the spatial scales approach the electron inertial length, the power is almost completely dissipated. Various analysis techniques and theoretical ideas have been put forward to account for the properties of those measurements. The talk will describe the current state of observations, theory and simulations

Subion Scale Turbulence Driven by Magnetic Reconnection

The interplay between plasma turbulence and magnetic reconnection remains an unsettled question in astrophysical and laboratory plasmas. Here we report the first observational evidence that magnetic reconnection drives subion scale turbulence in magnetospheric plasmas by transferring energy to small scales. We employ a spatial coarse-grained model of Hall magnetohydrodynamics, enabling us to measure the nonlinear energy transfer rate across scale $\ell$ at position $x$. Its application to Magnetospheric Multiscale mission data shows that magnetic reconnection drives intense energy transfer to subion scales. This observational evidence is remarkably supported by the results from Hybrid Vlasov-Maxwell simulations of turbulence to which the coarse-grained model is also applied. These results can potentially answer some open questions on plasma turbulence in planetary environments

Local cascade and dissipation in incompressible Hall magnetohydrodynamic turbulence: the Coarse-Graining approach

We derive the coarse-graining (CG) equations of incompressible Hall Magnetohydrodynamics (HMHD) turbulence to investigate the {\it local (in space)} energy cascade rate as a function of the filtering scale $\ell$. First, the CG equations are space averaged to obtain the analytical expression of the mean cascade rate. Its application to 3 dimensional (3D) simulations of (weakly compressible) HMHD shows a cascade rate consistent with the value of the mean dissipation rate in the simulations and with the classical estimates based on the "third-order" law. Furthermore, we developed an anisotropic version of CG that allows us to study the magnitude of the cascade rate along different directions with respect to the mean magnetic field. Its implementation on the numerical data with moderate background magnetic field shows a weaker cascade along the magnetic field than in the perpendicular plane, while an isotropic cascade is recovered in the absence of a background field. The strength of the CG approach is further revealed when considering the {\it local-in-space} energy transfer, which is shown theoretically and numerically to match at a given position $\bm{x}$, when locally averaged over a neighboring region, the (quasi-)local dissipation. Prospects of exploiting this new model to investigate local dissipation in spacecraft data are discussed.Comment: 14 pages, 8 figures, submitted to Physical Review

Observations and Interpretation of Magnetofluid Turbulence at Small Scales

High time resolution magnetic field measurements from the four Cluster spacecraft have revealed new features of the properties of magnetofluid turbulence at small spatial scales; perhaps even revealing the approach to the dissipation regime at scales close to the electron inertial length. Various analysis techniques and theoretical ideas have been put forward to account for the properties of those measurements. The talk will describe the current state of observations and theory, and will point out on-going and planned research that will further our understanding of how magnetofluid turbulence dissipates. The observations and theories are directly germane to studies being planned as part of NASA's forthcoming Magnetospheric Multiscale Mission

A New Technique for the Calculation and 3D Visualisation of Magnetic Complexities on Solar Satellite Images

YesIn this paper, we introduce two novel models for processing real-life satellite images to quantify and then visualise their magnetic structures in 3D. We believe this multidisciplinary work is a real convergence between image processing, 3D visualization and solar physics. The first model aims to calculate the value of the magnetic complexity in active regions and the solar disk. A series of experiments are carried out using this model and a relationship has been indentified between the calculated magnetic complexity values and solar flare events. The second model aims to visualise the calculated magnetic complexities in 3D colour maps in order to identify the locations of eruptive regions on the Sun. Both models demonstrate promising results and they can be potentially used in the fields of solar imaging, space weather and solar flare prediction and forecasting

Toward new Real-time operating system providing reliability for dynamically reconfigurable systems

Les systèmes électroniques sont de plus en plus présents dans les sociétés modernes, on peut les retrouver sous des formes très variées, très simple comme le réveil au chevet du lit ou très complexe comme un satellite de télécommunication en orbite. De nos jours, la majorité de ces inventions reposent en partie sur des "systèmes sur puces" afin de parvenir à accomplir leurs fonction principale, à savoir nous simplifier notre quotidien.Toutefois, à cause de leur nature physique, ces systèmes peuvent subir des dysfonctionnements dûs aux environnements dans lesquels ils évoluent. Des phénomènes naturels peuvent provoquer des aléas susceptibles d'avoir des conséquences graves sur la sûreté de fonctionnement du système.Cette thèse étudie la fiabilité d'une classe spécifique de systèmes sur puce capables de se reconfigurer partiellement de manière dynamique. Nous explorons la possibilité d'utiliser leur capacité de reconfiguration dynamique partielle (RDP) pour durcir les applications sur FPGAs. Nous avons proposé l'utilisation des approches de sauvegarde et de restauration de contexte pour la tolérance contre les fautes transitoire. La RDP est utilisée pour la gestion de contexte des tâches matérielles de l'application reconfigurable, le recours à la RDP permet de réduire les modifications à apporter au système initial et la complexité du système résultant. Après identification des limitations de l'approche "Backward Error Recovery" sur les plateformes FPGAs à base de mémoire SRAM, nous proposons un nouveau algorithme de placement des ressources sur FPGA afin de minimiser les temps d'accès des opérations de sauvegarde et de restauration d'une tâche matérielle. L'évaluation de la fiabilité de notre approche est réalisée à travers une campagne d'injection de faute sur une plateforme de démonstration basée sur un FPGA Virtex-5 qui intègre le contrôleur de fiabilité et une application de chiffrement de données.Electronic systems are a growing need in modern societies, they can be found in a variety of forms, simple as an Alarm Clock at the bedside or very complex as a telecommunications satellite into orbit. Today, the majority of these inventions are based mainly on "systems on chips", in order to achieve their primary function: simplify our daily lives.However, because of their physical nature, these systems can suffer from malfunctions due to the environments in which they operate. Natural phenomena can cause hazards which may have serious consequences on system dependability.This thesis focuses on a specific class of systems on chip which are able to reconfigure dynamically and partially and their reliability. We explore the possibility of using their partial dynamic reconfiguration capability (PDR) for hardening applications on FPGAs. We have proposed the use of checkpoint approaches and context restoration for tolerance against transient faults. PDR is used for managing the context of hardware tasks present on the application. the use of RDP reduces changes to the original system and therefore the complexity of the resulting system. After identifying the limitations of the "Backward Error Recovery" approach into SRAM-based FPGAs platforms, we propose a new resource placement algorithm on FPGA to minimize the access time needed by check-pointing and rolling back operations of hardware tasks. The evaluation of the overall reliability of our approach is achieved through fault injection campaign on demonstration platform running on a Virtex-5 that integrates our reliability controller and hosts a data encryption application

Review of kinetic turbulence in collisionless space plasmas

International audienc