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International audience; Parker Solar Probe data below 0.3 AU have revealed a near-Sun magnetic field dominated by Alfvénic structures that display back and forth reversals of the radial magnetic field. They are called magnetic switchbacks, they display no electron strahl variation consistent with magnetic field foldings within the same magnetic sector, and are associated with velocity spikes during an otherwise calmer background. They are thought to originate either at the photosphere through magnetic reconnection processes, or higher up in the corona and solar wind through turbulent processes.In this work, we analyze the spatial and temporal characteristic scales of these magnetic switchbacks. We define switchbacks as a deviation from the parker spiral direction and detect them automatically through perihelia encounters 1 to 6. We analyze the solid angle between the magnetic field and the parker spiral both over time and space. We perform a fast Fourier transformation to the obtained angle and find a periodical spatial variation with scales consistent with solar granulation. This suggests that switchbacks form near the photosphere and may be caused, or at least modulated, by solar convection.

International audience; It is known from laboratory plasma experiments that double layers (DLs) radiate in the electromagnetic spectrum; but this is only known qualitatively. In these experiments, it was shown that the electron beam created on the high-potential side of a DL generates nonlinear structures which couple to electromagnetic waves and act as a sender antenna. In the Earth auroral region, observations performed by auroral spacecraft have shown that DLs occur naturally in the source region of intense radio emissions called auroral kilometric radiation (AKR). Very high time-, spatial-, and temporal-resolution measurements are needed in order to characterize waves and particle distributions in the vicinity of DLs, which are moving transient structures. We report observations from the FAST satellite of a localized large-amplitude parallel electric field (˜ 300 mV m-1) recorded at the edges of the auroral density cavity. In agreement with laboratory experiments, on the high-potential side of the DL, elementary radiation events are detected. They occur substantially above the local electron gyrofrequency and are associated with the presence of electron holes. The velocity of these nonlinear structures can be derived from the measurement of the Doppler-shifted AKR frequency spectrum above the electron gyrofrequency. The generated electron holes appear as the nonlinear evolution of electrostatic waves generated by the electron-electron two-stream instability because they propagate at about half the beam velocity. It is pointed out that, in the vicinity of a DL, the shape of the electron distribution gives rise to a significant power recorded in the left-hand polarized ordinary (LO) mode.

International audience; The Electron Solar Probe Analyzer (SPAN-E) instruments are a matching pair of opposing electrostatic analyzer instruments that are a part of the Solar Wind Electrons Alphas and Protons (SWEAP) instrument suite on Parker Solar Probe (PSP). The SPAN-E instruments can measure electrons with energy between 5 eV and 30,000 eV in over 90% of the full sky. The SPAN-E instruments were launched from Florida in August of 2018 and a modicum of data from commissioning has just been returned. This presentation will show the details of the instrument operation and planned observation modes that are possible during the first Parker Solar Probe near-sun encounter, as well as show some of the initial electron data returned from spacecraft commissioning.

International audience; The Solar Wind Electrons Alphas and Protons (SWEAP) Investigation on Parker Solar Probe is the four sensor instrument suite responsible for determining the properties of ions and electrons in the coronal and solar wind thermal plasma. The Solar Probe Cup looks directly at the Sun around the Sun to make rapid measurements of ions and electrons flowing directly away from the Sun. The Solar Probe Analyzers look ahead (SPAN-A) and behind (SPAN-B) the spacecraft and make detailed maps of ions and electrons from all other directions in the sky. This talk reviews the SWEAP instrument suite, its commissioning status, and preliminary observations.

International audience

International audience; The Alfvén mission objective is to elucidate the particle acceleration processes and their consequences for electromagnetic radiation and energy transport in strongly magnetised plasmas. The Earth's Auroral Acceleration Region is a unique laboratory for investigating these processes. The only way to distinguish between the models describing acceleration processes at the heart of Magnetosphere-Ionosphere Coupling is to combine high-time resolution in situ measurements (as pioneered by FAST), multi-point measurements (as pioneered by CLUSTER), and auroral arc imaging in one mission. Charged particle acceleration in strongly magnetized plasmas requires the conversion of electromagnetic energy into magnetic-field-aligned particle kinetic energy. Alfvén will measure for the first time the occurrence and distribution of small scale parallel electric fields in space and time. In order to determine the relative efficiency of the different conversion mechanisms, Alfvén will also measure the corresponding particle energy fluxes locally and into the aurora. Alfvén will discover how electromagnetic radiation is generated in the acceleration region and how it escapes. Alfvén will make key measurements of Auroral Kilometric Radiation needed to test competing models of wave generation, mode conversion and escape from their source region. These will reveal the mode conversion processes and which information is ultimately carried by the polarization of radio waves reaching free space. Alfvén will discover the global impact of particle acceleration on the dynamic coupling between a magnetized object and its plasma environment. Dual spacecraft measurements offer the unique opportunity to unambiguously determine which part of the energy flowing into the ionosphere is eventually dissipated in this collisional plasma and which part is transmitted to outflowing ions of ionospheric origin. The Alfvén mission design involves use of two simple identical spacecraft, a comprehensive suite of inter-calibrated particles and fields instruments, cutting edge auroral imaging, easily accessible orbits that frequently visit the region of scientific interest and straightforward operations.

International audience; The Alfvén mission will explore particle acceleration processes and their consequences for electromagnetic radiation and energy transport in strongly magnetised plasmas. In particular it will address the following three key questions. Alfvén will discover where and how particle acceleration occurs in strongly magnetized plasmas. Charged particle acceleration in strongly magnetized plasmas requires the conversion of electromagnetic energy into magnetic-field-aligned particle kinetic energy. Several pathways of energy conversion have been proposed; to understand which are important, Alfvén will measure for the first time in a strongly magnetized plasma the occurrence and distribution of small scale parallel electric fields in space and time. In order to determine the relative efficiency of the different conversion mechanisms, Alfvén will also measure the corresponding particle energy fluxes locally and into the aurora. Alfvén discoveries will inform efforts to understand similar processes in other strongly magnetized plasmas, such as recent work to resolve paradoxes in models of solar flares. Alfvén will discover how electromagnetic radiation is generated in the acceleration region and how it escapes. One of the most important consequences of particle acceleration in strong magnetic fields is the generation of non-thermal electromagnetic radiation. Some of the brightest astrophysical radio signals are from coherent generation in plasmas, which also occurs on every magnetized planet. Alfvén will make key measurements of Earth's powerful Auroral Kilometric Radiation (AKR) needed to test competing models of wave generation, mode conversion and escape from their source region. These will reveal the mode conversion processes and which information is ultimately carried by the polarization of radio waves reaching free space. The resulting discoveries will make a strong contribution to a better understanding of astrophysical radio sources. Alfvén will discover the global impact of particle acceleration on the dynamic coupling between a magnetized object and its plasma environment. Energy can be transported over vast distances in several forms regulated by the magnetic field, including Poynting flux of plasma waves, accelerated particle fluxes, and bulk plasma flows. A key to understanding the coupling between a magnetized object and the surrounding plasma is how the energy converts from one type to another. Dual spacecraft measurements offer the unique opportunity to unambiguously determine which part of the energy flowing into the ionosphere is eventually dissipated in this collisional plasma and which part is transmitted to outflowing ions of ionospheric origin. Alfvén will discover what combination of plasma and magnetic conditions controls the conversion of Poynting flux into particle energy at Earth. These conditions will be compared to those at the outer planets, illuminating the theoretical descriptions of energy deposition in these remote environments. The Alfvén mission design involves use of two simple identical spacecraft, a comprehensive suite of inter-calibrated particles and fields instruments, cutting edge auroral imaging, easily accessible orbits that frequently visit the region of scientific interest and straightforward operations. This has not previously been possible, but is now compelling and timely. It is a low risk mission that is compatible with the M5 cost cap.

International audience; On January 22nd 2016, MMS was located in Earth's magnetosheath and detected intense lion roars showing a secondary bandwidth. Detailed polarization analysis, using burst data from SCM and EDP instruments, and numerical simulation, using WHAMP, are performed in this study. They show that these mainly perpendicular fluctuations are highly nonlinear whistler wave packets, and that a high sampling rate is needed to pick up the peaks of the signal. As a result, their amplitude might have been underestimated in previous missions such as Cluster, which can have a significant impact on electron dynamics. Using FPI burst data, we show that electron velocity distribution functions exhibit a gyrophase-bunched signature in the presence of these lion roars. The analysis of magnetic and density fluctuations, inferred from spacecraft potential, also show the highly-compressible nature of turbulence up to electron scales.

International audience; Acceleration processes in space plasmas are complex because they involve the interaction of particles with electromagnetic fields that may be distributed both in space and time. Understanding these processes in the solar wind requires high-time resolution observations at electron-scale. In this weakly magnetized medium, measuring both the energy spectrum and the 3D pitch-angle electron distribution at high-time resolution remains one of the main challenges of space plasma instrumentation. We both present the scientific challenges of these electron-scale measurements in the solar wind and recent advances in the development of high-time resolution electron spectrometers.

International audience; We analyze two ion scale dipolarization fronts associated with field-aligned currents detected by the Magnetospheric Multiscale mission during a large substorm on 10 August 2016. The first event corresponds to a fast dawnward flow with an antiparallel current and could be generated by the wake of a previous fast earthward flow. It is associated with intense lower hybrid drift waves detected at the front and propagating dawnward with a perpendicular phase speed close to the electric drift and the ion thermal velocity. The second event corresponds to a flow reversal: from southwward/dawnward to northward/duskward associated with a parallel current consistent with a brief expansion of the plasma sheet before the front crossing and with a smaller lower hybrid drift wave activity. Electromagnetic electron phase-space holes are detected near these low-frequency drift waves during both events. The drift waves could accelerate electrons parallel to the magnetic field and produce the parallel electron drift needed to generate the electron holes. Yet we cannot rule out the possibility that the drift waves are produced by the antiparallel current associated with the fast flows, leaving the source for the electron holes unexplained.

International audience; Particle acceleration mechanisms in solar system plasmas usually imply the conversion of electromagnetic energy into particle kinetic energy. These processes may take different forms depending on plasma magnetization but in most cases they involve multi-scale phenomena that cannot be described by ideal MHD. Little evidence has been gathered on how particle acceleration works in strongly magnetized plasmas. We will show how Earth's auroral regions provide the unique opportunity to address the open questions on particle acceleration in low beta plasmas. Single point observations in the auroral regions have suggested that acceleration by Alfvén waves would be responsible for filamentary acceleration along magnetic field lines. In the auroral regions, this mechanism would be associated with the generation of the sub-km scale auroral arcs. However single spacecraft measurements cannot evaluate the energy exchanged over a large volume of space between waves and particles. They cannot assess the efficiency of this mechanism, nor can they tell us where and when it is effective and how it relates to the evolving boundary conditions of the system. Numerical simulations alone cannot fully describe this multi-scale and non-local process in the inhomogeneous auroral plasma. Alternatively, it has been proposed from high-time resolution particle measurements in the auroral regions that localized parallel electric fields would explain the larger scale arcs that can be observed by onboard imagers. Single spacecraft measurements cannot follow the formation and evolution of these transient structures or the complex transport phenomena associated with the strong plasma turbulence that develop along magnetic field lines around these structures. Multi-point CLUSTER observations have shown how these potential acceleration structures were distributed in space and time. However we still miss the dynamic picture of how these structures are created on how they can be maintained in space and time. We will show that the only way to distinguish between these models describing acceleration processes in strongly magnetized plasmas is to combine advanced numerical simulations with high-time resolution in situ measurements, multi-point measurements, and auroral arc imaging. We will describe how the Alfvén mission concept, that will be proposed to the ESA M5 AO, will allow a major breakthrough in our understanding of particle acceleration mechanisms in solar system plasmas.

International audience; Earth is an intense radio source in the kilometer wavelength range. Being a direct consequence of the parallel acceleration processes taking place in the Earth's auroral region, the radiation contains fundamental information on the characteristic spatial and temporal scales of the turbulent accelerating layer. It is now widely assumed that the cyclotron maser instability leads to Auroral Kilometric Radiation (AKR) generation. It has been suggested from the FAST measurements that the AKR results from a so-called horseshoe electron distribution. This distribution is generated when a localized parallel electric field - called Double Layer (DL) - accelerates earthward the electrons that propagate into an increasing magnetic field. The magnetic moment of the electrons is conserved so that their pitch angle is increased. This results in the creation of a horseshoe-like shape for the electron distribution exhibiting large positive velocity gradients in the direction perpendicular to B, thereby providing free energy for the AKR generation which takes place at the local electron gyrofrequency. In these circumstances, the radiation is generated far away (several thousand kilometers) from a DL, because the parallel accelerated electrons need to travel a long distance before forming a horseshoe distribution. From an experimental point of view, it is not an easy task to highlight the presence of DLs, because they are moving transient structures so that high time resolution measurements are needed. A detailed analysis suggests that these large-amplitude parallel electric fields are located inside sharp density gradients at the interface separating the cold, dense ionospheric plasma from the hot, tenuous magnetospheric plasma. We present some FAST observations which illustrate the generation of elementary radiation events in the neighborhood of a DL. The events occur 10 to 20% above the local electron gyrofrequency in association with the presence of nonlinear coherent structures (such as electron holes) located on the high potential side of the DL. These observational results might encourage investigation of such radiating processes because they could be relevant to other astrophysical radio sources, such as the recently discovered aurora around a brown dwarf.

International audience; Turbulence Heating ObserveR (THOR) is the first mission ever flown in space dedicated to plasma turbulence. Specifically, THOR will study how turbulent fluctuations at kinetic scales heat and accelerate particles in different turbulent environments within the near-Earth space. To achieve this goal, THOR payload is being designed to measure electromagnetic fields and particle distribution functions with unprecedented resolution and accuracy. Here we present the Ion Mass Spectrometer (IMS) instrument that will measure the full three-dimensional distribution functions of near-Earth main ion species (H , He , He and O ) at high time resolution (~ 150 ms for H , ~ 300 ms for He ) with energy resolution down to ~ 10% in the range 10 eV/q to 30 keV/q and angular resolution ~ 10°. Such high time resolution is achieved by mounting multiple sensors around the spacecraft body, in similar fashion to the MMS/FPI instrument. Each sensor combines a top-hat electrostatic analyzer with deflectors at the entrance together with a time-of-flight section to perform mass selection. IMS electronics includes a fast sweeping high voltage board that is required to make measurements at high cadence. Ion detection includes Micro Channel Plates (MCP) combined with Application-Specific Integrated Circuits (ASICs) for charge amplification, discrimination and time-to-digital conversion (TDC). IMS is being designed to address many of THOR science requirements, in particular ion heating and acceleration by turbulent fluctuations in foreshock, shock and magnetosheath regions. The IMS instrument is being designed and will be built by an international consortium of scientific institutes with main hardware contributions from France, USA, Japan and Germany.

International audience; This poster will present the proposed Alfvén mission concept and is complemented by a presentation of the mission scientific goals planned for the ST1.5 session. The Alfvén mission has the scientific objective of studying particle acceleration and other forms of electromagnetic energy conversion in a collisionless low beta plasma. The mission is proposed to operate in the Earth's Auroral Acceleration Region (AAR), the most accessible laboratory for investigating plasmas at an interface where ideal magneto-hydrodynamics does not apply. Alfvén is designed to answer questions about where and how the particles that create the aurorae are accelerated, how and why they emit auroral kilometric radiation, what creates and maintains large scale electric fields aligned with the magnetic field, and to elucidate the ion outflow processes which are slowly removing the Earth's atmosphere. The mission will provide the required coordinated two-spacecraft observations within the AAR several times a day. From well designed separations along or across the magnetic field lines, using a comprehensive suite of inter-calibrated particles and field instruments, it will measure the parallel electric fields, variations in particle flux, and wave energy that will answer open questions on energy conversion. It will use onboard auroral imagers to determine how this energy conversion occurs in the regional context and, together with its orbit design, this makes the mission ideally suited to resolving spatio-temporal ambiguities that have plagued previous auroral satellite studies. The spacecraft observations will be complemented by coordinated observations with the existing dense network of ground based observatories, for more detailed ionospheric and auroral information when Alfvén overflights occur.

International audience; The Alfvén mission is a candidate to the 2014 ESA Call for M-class science missions. Its main scientific objective is to elucidate the universal physical processes at work in the Auroral Acceleration Region (AAR). The AAR is a unique laboratory for investigating strongly magnetized plasmas at an interface where ideal magneto-hydrodynamics does not apply. The Alfvén mission will investigate fundamental and multi-scale physical processes that govern what Nobel Prize laureate Hannes Alfvén named the Plasma Universe. The mission concept is designed to teach us where and how the particles that create the aurorae are accelerated, how they emit radiation, and to elucidate the ion heating and outflow processes which are slowly removing the Earth's atmosphere. The only way to distinguish between the models describing acceleration processes at the heart of Magnetosphere-Ionosphere (MI) coupling is to combine high-time resolution in situ measurements (as pioneered by the FAST mission), multi-point measurements (as pioneered by CLUSTER), and auroral arc imaging in one mission. Taking advantage of the existing dense network of ground based observatories the Alfvén mission will also allow a major breakthrough in our understanding of solar terrestrial relationships by providing key experimental measurements to large scale models of MI electrodynamics.

International audience; Innovative particle detectors are needed for future heliophysics missions in order to access to high-time resolution phenomena within limited resources. One of the main challenges is to accurately monitor solar wind plasmas from non-spinning platforms. Such an innovative particle detector which is based on a new optical concept allows the coverage of 4pi str solid angle with only two sensor heads. It fits the need of all-sky thermal plasma measurements on three axis stabilized spacecraft which are the most commonly used platforms for heliophysics missions with imaging capabilities. This 3D field-of-view plasma analyzer also takes advantage of the new possibilities offered by the development of an ultra low-power multichannel charge sensitive amplifier used for the imaging detector of the instrument. We present the design and measured performances of a prototype model that will fly on a test rocket in 2014. One of the possible applications of this innovative particle detector is the investigation of electron time scale phenomena in the turbulent solar wind of the inner heliosphere with unprecedented time resolution below 10 msec.

International audience; The Alfvén mission was proposed to the ESA M3 call for missions in 2010. Its scientific objective was to study the Auroral Acceleration Region (AAR), the most accessible laboratory for investigating plasmas at an interface where ideal magneto-hydrodynamics does not apply. Alfvén was designed to teach us where and how the particles that create the aurorae are accelerated, how and why they emit auroral kilometric radiation, what creates and maintains large scale electric fields aligned with the magnetic field, and to elucidate the ion outflow processes which are slowly removing the Earth's atmosphere. The auroral regions are the interface connecting the solar wind-driven collisionless magnetosphere to the collisional ionosphere at the top of Earth's atmosphere. Solar wind energy, transmitted via the magnetosphere, is dissipated in this interface, often explosively during magnetic substorms. The plasma organizes itself on a hierarchy of spatial and temporal scales, manifesting as auroral structures ranging from huge long-lived arcs to tiny flickering filaments. The only way to make substantial further progress in auroral plasma science and to elucidate the fundamental physics of the acceleration processes at the heart of magnetosphere-ionosphere coupling is to combine the advantages of high-time resolution in situ measurements (as pioneered by the FAST mission), with the advantages of multi-point measurements (as pioneered by Cluster) in one mission. The mission concept also envisages continuous auroral imaging from the spacecraft, guaranteeing an understanding of the context (auroral morphology and motion) within which the in situ plasma measurements are made, and strong coordination with the existing dense network of ground based observatories, for more detailed ionospheric and auroral information when Alfvén overflights occur. We will review the ESA M3 Alfvén concept, consider recent scientific progress in this area, and discuss possible developments of the concept for a possible ESA M4 proposal.

International audience; A new 3D field-of-view toroidal space plasma analyzer based on an innovative optical concept allows the coverage of 4pi str solid angle with only two sensor heads. It fits the need of all-sky thermal plasma measurements on three-axis stabilized spacecraft which are the most commonly used platforms for planetary missions. The 3D plasma analyzer also takes advantage of the new possibilities offered by the development of an ultra low-power multi-channel charge sensitive amplifier used for the imaging detector of the instrument. We present the design and measured performances of a prototype model that will fly on a test rocket in 2014.

International audience; 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.

International audience; In spring 2013, the Cluster spacecraft have visited the Auroral Acceleration Region (AAR) for the second and final time. The spacecraft constellation was arranged to produce very small separation magnetic field aligned conjunctions (~10s km) between C3 and C4, with C1 relatively nearby. The goal was to allow study of electron and ion holes, including their propagation between C3 and C4, and their roles in generating waves that may be observed locally and also at C1. Detailed planning work has tried to maximize the opportunities to use the Cluster payload effectively during these conjunctions, but the presence of auroral activity during the relatively few AAR passes cannot be guaranteed in advance. The dataset may also be valuable for other aspects of auroral science, as data is collected throughout the AAR crossings, not only at the conjunctions. We intend to present first results from this campaign.

International audience; A VLF saucer is a natural radio-wave phenomenon observed in the auroral zone since the 1960's. It has a characteristic V-shaped signature on electric field spectrograms in the VLF range. Many properties of VLF saucers have been established in the 1970's based on Alouette and Isis spacecraft. Further investigations continued thanks to satellites flying over the auroral zone, such as Viking, Polar and FAST. Since 2006, the orbits of the ESA/NASA Cluster satellites are slowly evolving from a nominal polar orbit to an oblique one. Meanwhile, the perigee of their orbits, originally at 19,000 km, naturally decreased to a few hundred kilometres and since 2011 have been steadily increasing back to the original perigee. Since spring 2009, Cluster scientists can make use of this natural orbital drift to target a new key region of the magnetosphere: the Auroral Acceleration Region (AAR). The AAR continues to be targeted by the Cluster mission, with a recent data campaign achieved successfully in Spring 2013. On rare occasions, VLF saucers are observed by the Cluster spacecraft, as they need to fly close enough to their source to catch them. Unique observations of electrostatic VLF saucers by the four Cluster satellites will be presented. These data not only enable for the first time to triangulate their source region, but they also allow revisiting some of the hypotheses commonly used so far in the analysis of their source region. Finally, the multi-point observations of VLF saucers question fundamental aspects of their generation. Indeed, it is difficult to understand, based on previously published studies, how transient structures such as electron holes are able to support the continuous generation of these electrostatic waves during several minutes, as observed by Cluster.

International audience