Publications

2016

• Characterization of Bismuth Silicon Oxide Crystals Using Imaging Mueller Ellipsometry
  
  • Slikboer Elmar
  • Yoo Sang Hyuk
  • Guaitella Olivier
  • Sobota Ana
  • Garcia-Caurel Enric
  , 2016.
• High sensitivity ultra-broad-band absorption spectroscopy of inductively coupled chlorine plasma
  
  • Marinov Daniil
  • Foucher Mickaël
  • Campbell Ewen
  • Brouard Mark
  • Chabert Pascal
  • Booth Jean-Paul
  Plasma Sources Science and Technology, IOP Publishing, 2016, 25 (3), pp.035019. We propose a method to measure the densities of vibrationally excited Cl 2 (v) molecules in levels up to v = 3 in pure chlorine inductively coupled plasmas. The absorption continuum of Cl 2 in the 250 – 450 nm spectral range is deconvoluted into the individual components originating from the different vibrational levels of the ground state, using a set of ab-initio absorption cross sections. It is shown that gas heating at constant pressure is the major depletion mechanism of the Cl 2 feedstock in the plasma. In these line-integrated absorption measurements, the absorption by the hot (and therefore rarefied) Cl 2 gas in the reactor centre is masked by the cooler (and therefore denser) Cl 2 near the walls. These radial gradients in temperature and density make it difficult to assess the degree of vibrational excitation in the centre of the reactor. The observed line-averaged vibrational distributions, when analyzed taking into account the radial temperature gradient, suggest that vibrational and translational degrees of freedom in the plasma are close to local equilibrium. This can be explained by efficient VT relaxation between Cl 2 and Cl atoms. Besides the Cl 2 (v) absorption band, a weak continuum absorption is observed at shorter wavelengths, and is attributed to photodetachment of Cl ‒ negative ions. Thus, line-integrated densities of negative ions in chlorine plasmas can be directly measured using broad-band absorption spectroscopy. (10.1088/0963-0252/25/3/035019)
  DOI : 10.1088/0963-0252/25/3/035019
• GNSS, Space Weather and Capacity building
  
  • Amory-Mazaudier Christine
  , 2016. During the last decade, the deployment of GPS over Africa and the Southern hemisphere allowed a great advance in Research in the countries where GPS receivers were installed. These research advances concern the Geodesy, ionospheric and atmospheric physics especially at low and equatorial latitudes, and Space weather effects on GPS system. The GNSS tools are cheap compared to satellite tools, and as a consequence permit the participation of all the countries to the research in various fields. The GNSS data are complementary of the satellite data. The GNSS tools became very useful for capacity building in research, especially in Space Weather. Another important point is that GNSS data are used for many applications useful for the development of a country (aviation, cadastre, agriculture, infrastructures of the country etc). It is important that all the users of GNSS data be aware of the progress in research on GNSS data, in order to take into account the scientific results in the development of their applications. Now with GNSS (GPS GLONASS GALLILEO ....), we can multiply the number of GNSS receivers and develop more research and application studies. This presentation will be devoted to the success story of the use of GNSS for capacity building in Space Weather, in Africa and Southern hemisphere.
• Predator Prey Dynamics in Magnetized Fusion Plasmas
  
  • Morel Pierre
  • Kobayashi Sumire
  • Donnel Peter
  • Berionni Vincent
  • Honoré Cyrille
  • Pisarev V.
  • Hennequin Pascale
  • Gürcan Özgür D.
  , 2016.
• Exploring turbulent energy dissipation and particle energization in space plasmas: the science of THOR mission
  
  • Retinò Alessandro
  , 2016.
• Synthetic diagnostic of Doppler Back-Scattering measurements on the Tore Supra Plasma #TS45511 with a dedicated GYSELA non-linear gyrokinetic simulation
  
  • Morel Pierre
  • Gassama Banda
  • Leybros Robin
  • Dif-Pradalier Guilhem
  • Hennequin Pascale
  • Vermare Laure
  • Gürcan Özgür D.
  • Grandgirard V.
  • Latu G.
  • Sarazin Y.
  • Ghendrih Ph.
  • Garbet X.
  , 2016.
• Unveiling coherent structures through entropy-complexity analysis
  
  • Chrisment Antoine M.
  • Firpo Marie-Christine
  , 2016.
• EMC ASPECTS OF TURBULENCE HEATING OBSERVER (THOR) SPACECRAFT
  
  • Soucek Jan
  • Ahlen L.
  • Bale Stuart
  • Bonnell J W
  • Boudin N.
  • Brienza D.
  • Carr C.
  • Cipriani Fabrice
  • Escoubet C. P.
  • Fazakerley Andrew F
  • Gehler M.
  • Génot Vincent
  • Hilgers A.
  • Hanock B.
  • Jannet G.
  • Junge A.
  • Khotyaintsev Yuri
  • de Keyser Johan
  • Kucharek H.
  • Lavraud B
  • Lau R.
  • Leblanc François
  • Magnes W.
  • Mansour M.
  • Marcucci M.F.
  • Nakamura Rumi
  • Němeček Z.
  • Owen C.
  • Phal Y.
  • Retinò Alessandro
  • Rodgers David
  • Šafránková J.
  • Sahraoui Fouad
  • Vainio R.
  • Wimmer-Schweingruber R.
  • Steinhagen J.
  • Vaivads A.
  • Wielders A.
  • Zaslavsky A.
  , 2016, 738, pp.1-4. Turbulence Heating ObserveR (THOR) is a spacecraft mission dedicated to the study of plasma turbulence in near-Earth space. The mission is currently under study for implementation as a part of ESA Cosmic Vision program. THOR will involve a single spinning spacecraft equipped with state of the art instruments capable of sensitive measurements of electromagnetic fields and plasma particles. The sensitive electric and magnetic field measurements require that the spacecraft-generated emissions are restricted and strictly controlled; therefore a comprehensive EMC program has been put in place already during the study phase. The THOR study team and a dedicated EMC working group are formulating the mission EMC requirements already in the earliest phase of the project to avoid later delays and cost increases related to EMC. This article introduces the THOR mission and reviews the current state of its EMC requirements.
• Experimental study of the collision of two laser-driven radiative shocks at the PALS laser
  
  • Singh Raj Laxmi
  • Stehlé Chantal
  • Suzuki-Vidal Francisco
  • Larour Jean
  • Chaulagain Uddhab
  • Clayson Thomas
  • Nejdl Jaroslav
  • Krus Miroslav
  • Kozlová Michaela
  • Dostál Jan
  • Acef Ouali
  • Barroso Patrice
  • Cotelo M.
  • Velarde P.
  • Rodriguez Perez R.
  • Gil J. M.
  , 2016. Radiative shocks are present in various astrophysical contexts and can be proxy of fundamental accretion processes, for instance X-ray signatures from accretion shocks can be related to the rate of mass accretion onto forming stars. Thus the study of hypersonic shocks (Mach number >> 1) in the laboratory Under controlled conditions is of primary interest in order to study the influence of radiation, and to compare with numerical simulations. In the past decade, several experiments on radiative shocks have been performed on various large-scale laser facilities, demonstrating the formation of shocks in Xenon with velocities ~50 - 150 km/s in background gas pressures ~0.1 - 1 bar (Bouquet et al. 2004, Gonzalez et. al. 2006, Reighard et. al. 2007, Stehlé et al. 2010, Doss et al. 2011, Drake et al. 2011, Dizière et al. 2012, Stehlé et al. 2012, Chaulagain et al. 2015). Many advances have been achieved in understanding the effect of radiation on the different shock components (radiative precursor, shock collapse, wall heating etc.), however, these studies were focused solely on the case of a single radiative shock. We have recently conducted experiments at the PALS laser facility, looking at the collision between two counter streaming radiative shocks. Besides providing a new experimental platform, these experiments aimed at studying how one radiative precursor is influenced by the presence of another. The experiments launched shocks with different shock speeds (~30-55 km/s and 10-25 km/s), at a range of different pressures (~0.1-0.3 bar), and with different gases (Ar, Xe). Optical interferometry allowed us to estimate several physical parameters such as shock speed and electron density in the precursor, whereas the use of time and spatially resolved optical spectroscopy led to a number of spectral signatures. We will present preliminary results together with numerical simulations.
• Counter-Propagating Laser Produced Radiative Shocks at the Orion Laser Facility
  
  • Clayson Thomas
  • Suzuki-Vidal Francisco
  • Lebedev S.
  • Swadling G.
  • 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
  • Awe Team The
  , 2016. The Orion high-power laser facility at AWE Aldermaston, UK, was used to produce hyper-sonic (M>>1) radiative shocks in a variety of noble gases. These experiments aimed to study the radiative precursor, a heat and ionization wave preceding the shock front and, for the first time, the dynamics of colliding, counter propagating radiative shocks. Laser ablation of a piston, at intensities of ~6x1014 W/cm2, drove counterpropagating shocks, with velocities between 60 km/s and 120 km/s, into a gas cell, filled to pressures between 0.1 bar and 1.0 bar. Targets were 4mm long octagonal gas cells, produced by SciTech Precision, with a diameter of 8mm to remove the effect of wall shocks. X-ray backlighting and optical self-emission streak Imaging were used to image the shock front and collision dynamics. Multi-frame and streaked interferometry were used to image the radiative precursor and determine its electron density. These experiments compared the shock and collision dynamics in different gases (e.g. Ne, Ar, Kr, Xe), maintaining a constant mass density in order to keep the hydrodynamics in the shock consistent while varying the strength of the radiative precursor losses. In some cases the shocks exhibited features suggesting the formation of hydrodynamic or radiative instabilities. The experimental data is in good agreement with 2-D numerical radiative-hydrodynamic simulations and provides a new benchmark for codes to be tested against. Project supported by Orions Academic Access Programme (through AWE and CLF), and in part by the Royal Society, and by EPSRC through a DTA Scholarship and by Labex PLAS@PAR (ANR-11-IDEX-0004-02). The authors would like to acknowledge the help and support from the staff at AWE Aldermaston.
• The importance of surface interaction probabilities in low pressure plasma simulations for process design
  
  • Gibson Andrew
  • Foucher Mickaël
  • Marinov Daniil
  • Chabert Pascal
  • Gans T.
  • Guerra V.
  • Kushner M.J.
  • Booth Jean-Paul
  , 2016.
• Studying the plume neutralization process of the PEGASES thruster
  
  • Cichocki F.
  • Rafalskyi D.V.
  • Aanesland Ane
  , 2016.
• Turbulent reconnection and associated particle heating and acceleration in the Earth's magnetosheath
  
  • Chasapis A.
  • Retinò Alessandro
  • Le Contel Olivier
  • Matthaeus W. H.
  • Breuillard Hugo
  • Sahraoui Fouad
  • Vaivads A.
  • Khotyaintsev Y. V.
  • Burch Jim
  • Moore Tom
  • Fuselier Stephen
  • Torbert Roy
  • Mauk Barry
  • Pollock Craig
  • Torkar Klaus
  • Ergun Robert
  , 2016, 18, pp.16046. Magnetic reconnection is a fundamental mechanism of energy dissipation and particle energization in space plasma. Spacecraft observations and numerical studies have established that it occurs in small-scale intermittent structures such as thin current sheets that form spontaneously in turbulent plasma. This kind of turbulent reconnection leads to significant particle heating and acceleration as well as to the dissipation of turbulent energy at kinetic scales. However, the extent of its contribution to turbulent dissipation has yet to be determined. Here we present results from in situ observations made by MMS and CLUSTER in the Earth's magnetosheath. A statistical study of a large number of thin current sheets allows us to establilsh their importance for dissipation while the in-depth study of reconnecting current sheets yields valuable insight into the exact mechanisms of particle heating and acceleration.
• The physics of magnetic reconnection onset at the subsolar magnetopause: MMS observations
  
  • Retinò Alessandro
  , 2016, 18, pp.EPSC2016-15763. Magnetic reconnection is a fundamental process occurring in thin current sheets where a change in the magnetic field topology leads to fast magnetic energy conversion into charged particles energy. A key yet poorly understood aspect is how reconnection is initiated in the diffusion region by microphysical processes occurring at electron scales, the so-called onset problem. Reconnection onset leads to the energization of particles around reconnection sites, yet the exact energization mechanisms are also not yet fully understood. Simulations have provided some suggestions on the mechanisms responsible for onset and particle energization, however direct observations have been scarce so far. The four-spacecraft Magnetospheric Multiscale Mission (NASA/MMS) has been launched in March 2015 and allows, for the first time, in-situ observations of reconnection diffusion regions with adequate resolution to study electron scales. Here we present MMS observations in diffusion regions at the subsolar magnetopause and we investigate the conditions for reconnection onset. We select a few events with multiple crossings of the magnetopause current sheet for which signatures of absence of reconnection are rapidly followed by signatures of reconnection, and compare the measured electric field with the electric field due to both kinetic effects (electron pressure tensor, electron inertia terms) and to anomalous resistivity associated to different wave modes (e.g. lower hybrid waves, whistler waves, etc.). We also analyze electron distribution functions to study the mechanisms of electron energization in the diffusion region.
• New observations of flux ropes in the magnetotail reconnection region
  
  • Huang S. Y.
  • Retinò Alessandro
  • Phan T. D.
  • Daughton W. Bill
  • Vaivads A.
  • Karimabadi H.
  • Pang Y.
  • Zhou M.
  • Sahraoui Fouad
  • Li G. L.
  • Yuan Z. G.
  • Deng X. H.
  • Fu H.S.
  • Fu S. Y.
  • Wang D. D.
  , 2016, 18, pp.EPSC2016-7122. Magnetic reconnection is a fundamental physical process that enables the rapid transfer of magnetic energy into plasma kinetic and thermal energy in the laboratory, astrophysical and space plasma. Flux ropes have been suggested to play important role in controlling the micro-scale physics of magnetic reconnection and electron acceleration. In this presentation, we report new observations of flux ropes in the magnetotail reconnection region based on the Cluster multi-spacecraft data. Firstly, two consecutive magnetic flux ropes, separated by less than 30 s (Deltat < 30 s), are observed within one magnetic reconnection diffusion region without strong guide field. In spite of the small but non-trivial global scale negative guide field (-By), there exists a directional change of the core fields of two flux ropes, i.e. -By for the first one, and By for the second one. This is inconsistent with any theory and simulations. Therefore, we suggest that the core field of flux ropes is formed by compression of the local preexisting By, and that the directional change of core field is due to the change of local preexisting By. Such a change in ambientBy might be caused by some microscale physics. Secondary, we will present in-situ observations of a small scale flux rope locally formed at the separatrix region of magnetic reconnection without large guide field. Bidirectional electron beams (cold and hot beams) and density cavity accompanied by intense wave activities substantiate the crossing of the separatrix region. Density compression and one parallel electron beam are detected inside the flux rope. We suggest that this flux rope is locally generated at the separatrix region due to the tearing instability within the separatrix current layer. This observation sheds new light on the 3D picture of magnetic reconnection in space plasma.
• Does the plasma radiate near a Double Layer?
  
  • Pottelette Raymond
  • Berthomier Matthieu
  • Pickett J. S.
  , 2016, 18, pp.EPSC2016-3017. 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.
• Coexistence of weak and strong wave turbulence in incompressible Hall MHD
  
  • Meyrand Romain
  • Kiyani K. H.
  • Galtier Sébastien
  , 2016, 18, pp.EPSC2016-18282. We report a numerical investigation of 3D Hall Magnetohydrodynamic turbulence with a strong mean magnetic field. By using a helicity decomposition and a cross-bicoherence analysis, we observe that the nonlinear 3-wave coupling is substantial among ion cyclotron and whistler waves. By studying in detail the degree of nonlinearity of these two populations we show that ion cyclotron and whistler turbulent fluctuations belong respectively to strong and weak wave turbulence. The non trivial blending of these two regime give rise to anomalous anisotropy and scaling properties. The separation of the weak random wave and strong coherent turbulence component can however be effectively done using simultaneous space and time Fourier transforms. Using this techniques we show that it is possible to recover some statistical prediction of weak turbulent theory.
• Electromagnetic wave activity detected by MMS at the vicinity of the magnetopause and its relation to heating and acceleration of particles
  
  • Le Contel Olivier
  • Retinò Alessandro
  • Breuillard Hugo
  • Berthomier Matthieu
  • Mirioni Laurent
  • Sahraoui Fouad
  • Chust Thomas
  • Chasapis A.
  • Aunai N.
  • Lavraud Benoit
  • Lindqvist Per-Arne
  • Khotyaintsev Y. V.
  • Vaivads A.
  • Marklund Goran
  • Ergun Robert E.
  • Goodrich Katherine
  • Wilder Frederick D.
  • Argall Matthew
  • Burch Jim L.
  • Torbert Roy B.
  , 2016, 18, pp.12674. In the present study, we analyze different dayside magnetopause crossings detected by the MMS mission in order to investigate the relation between the electromagnetic wave activity and particle heating/acceleration. In particular, our study is focused on two different frequency ranges: (1) 1-10 Hz range which corresponds to the frequency domain of kinetic Alfvén and lower-hybrid waves, (2) 10 Hz-1kHz which corresponds mainly to the whistler mode wave frequency domain. After characterizing the different types of waves, we estimate their respective energy content as well as their possible role for heating and accelerating the plasma.
• New Observations of Solar Wind Interaction with Earth's Bow Shock
  
  • Parks G. K.
  • Lee E.
  • Yang Z. W.
  • Liu Y.
  • Fu Suiyan
  • Dandouras Iannis
  • Rème H.
  • Canu Patrick
  • Goldstein M. L.
  , 2016, 18, pp.2380. The mass, charge and energy dependence of the SW interaction with the bow shock was studied from early days of HEOS-1 and ISEE (Formisano et al, 1970; Peterson et al., 1979). These observations have shown that while thermalization of H occurs across the boundary, sometimes the SW He ions are found with unchanged energy spectra downstream of the shock inside the magnetosheath and that both SW H and He beams could be found in the downstream magnetosheath with the same bulk velocities. These studies however used He data accumulated over 30 minutes and since the SW dynamics include much faster time variations the results are likely affected by spatial and temporal variations. Moreover, it was not known at that time that the plasma in the neighborhood of the bow shock often include the reflected, gyrating and particles leaking out of the magnetosheath (Skopke et al., 1982; Thomsen et al., 1985) and since these particles occupy different parts of the velocity space, they can significantly affect the SW velocity and temperature computed from first and second velocity moments. To alleviate these problems, a microprocessor-controlled SW plasma experiment was designed and flown on Cluster that selects only particles near the peak energy of the SW distribution, thereby minimizing contamination from the other particles (Rème et al., 2001). We have studied ~110 shock crossings upstream and downstream of the quasi-perpendicular and quasi-parallel bow shock regions and find that in 44 cases the SW beams crossed the shock retaining much of their upstream features. On average the temperature of upstream SW H ions was ~4 eV and in the magnetosheath ~4.2 eV, indicating there was little or no heating of the SW going across the bow. The He ions have temperatures typically 4 times that of H ions in the SW a value consistent with equipartition of energy. Unlike H ions, He ions very often do not slow down going across the shock. These observations indicate that the SW interaction with the bow shock is much more complicated than existing models predict and they are important constraints for developing new models.
• THOR Ion Mass Spectrometer instrument - IMS
  
  • Retinò Alessandro
  • Kucharek H.
  • Saito Y.
  • Fraenz Markus
  • Verdeil Christophe
  • Leblanc F.
  • Techer Jean-Denis
  • Jeandet A.
  • Macri J.
  • Gaidos John
  • Granoff M.
  • Yokota S.
  • Fontaine Dominique
  • Berthomier Matthieu
  • Delcourt Dominique
  • Kistler L. M.
  • Galvin A. B.
  • Kasahara S.
  • Kronberg E. A.
  , 2016, 18, pp.EPSC2016-15367. 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.
• New Exact Relations for Helicities in Hall Magnetohydrodynamic Turbulence
  
  • Banerjee Supratik
  • Galtier Sébastien
  , 2016, 18, pp.EPSC2016-7291. Hall magnetohydrodynamics is a mono-fluid plasma model appropriate for probing Finalsome of the physical processes (other than pure kinetic effects) at length scales smaller than the scales of standard MHD. In sub-ionic space plasma turbulence (e.g. the solar wind) this fluid model has been proved to be useful. Three-dimensional incompressible Hall magnetohydrodynamics (MHD) possesses three inviscid invariants which are the total energy, the magnetic helicity and the generalized helicity. In this presentation, we would like to discuss new exact relations for helicities (magnetic helicities and generalized helicities) which are derived for homogeneous stationary (not necessarily isotropic) Hall MHD turbulence (and also for its inertialess electron MHD limit) in the asymptotic limit of large Reynolds numbers. The universal laws are written only in terms of mixed second-order structure functions, i.e. the scalar product of two different increments and are written simply as eta<SUB>M</SUB> = d<SUB>i</SUB> < delta ( b × j) · delta b >, with eta<SUB>M</SUB> the average magnetic helicity flux rate, b the magnetic field, j the current and ± eta<SUB>G</SUB> = < delta ( v × Omega ) · delta Omega > , with eta<SUB>M</SUB> the average generalized helicity flux rate, v the fluid velocity and Omega = b d<SUB>I</SUB> omega being the generalized helicity where omega is simply the fluid vorticity ( = nabla × v). It provides, therefore, a direct measurement of the dissipation rates for the corresponding helicities even in case of an anisotropic plasma turbulence. This study shows that the generalized helicity cascade is strongly linked to the left polarized fluctuations while the magnetic helicity cascade is linked to the right polarized fluctuations. The newly derived relations also show that like energy, a non-zero helicity flux can only be associated to a departure of Beltrami flow state. Reference S. Banerjee & S. Galtier, Chiral Exact Relations for Helicities in Hall Magnetohydrodynamic Turbulence (submitted).
• The role of waves and DC electric fields for electron heating and acceleration in the diffusion region
  
  • Graham Daniel
  • Khotyaintsev Y. V.
  • Vaivads A.
  • Norgren Cecilia
  • Andre M.
  • Lindqvist Per-Arne
  • Le Contel Olivier
  • Ergun Robert
  • Goodrich Katherine
  • Torbert Roy
  • Burch J. L.
  • Russell C. T.
  • Magnes Werner
  • Giles B. L.
  • Pollock Craig
  • Mauk Barry
  • Fuselier Stephen
  , 2016, 18, pp.EPSC2016-10458. Magnetic reconnection is a fundamental process in solar and astrophysical plasmas. The processes operating at electron spatial-scales, which enable magnetic field lines to reconnect, are generally difficult to resolve and identify. However, the recently launched Magnetospheric Multiscale (MMS) mission is specifically designed to resolve electron spatial scales. We use the MMS spacecraft to investigate the process operating within the diffusion region to determine the causes of electron heating and acceleration. In particular, we investigate the type of electrostatic and electromagnetic waves that develop and how they affect the electron distributions. We also compare the roles of wave-particle interactions with DC electric fields to determine which is responsible for the electron heating observed in diffusion regions.
• A new technique for the investigation of the energy cascade associated with coherent structures in Kelvin-Helmholtz turbulence
  
  • Rossi C.
  • Camporeale E.
  • Califano F.
  • Cerri Silvio Sergio
  • Retinò Alessandro
  • Sorriso-Valvo L.
  • Carbone V.
  , 2016, 18, pp.EPSC2016-13318. The dissipation of turbulent energy at small scales in space plasmas is an open and challenging problem. Coherent structures at the kinetic scales could play a fundamental role in redistributing the plasma energy thus replacing in some sense the role of collisions. Coherent structures in the form of current sheets (CS) are associated with localized particle heating, and are generally responsible for the observed intermittent nature of plasma turbulence. Still, the contribution of such structures to the local energy spectrum shaping is not well understood. Here, for the first time, we apply a 'space-filter' technique to two-fluid plasma simulations of Kelvin-Helmholtz turbulence to obtain a local measure of the inter-scale transfer and to characterize the contribution of coherent structures to the energy spectrum. This technique, used in hydrodynamics and in Large-Eddy-Simulation communities, is applied here for the first time to space plasma turbulence. Specifically, we study in detail the current sheets forming in turbulent Kelvin-Helmholtz vortices by the Partial Variance of Increments (PVI) technique, and we discuss the correlation between the inter-scale transfer and high values of the PVI index.
• Turbulence Heating ObserveR - THOR: Mission overview and payload summary
  
  • Wielders A.
  • Boudin N.
  • Vaivads A.
  • Khotyaintsev Y. V.
  • Lavraud Benoit
  • Sahraoui Fouad
  • Nakamura R.
  • Owen C.
  • Fazakerley A.
  • Nemecek Z.
  • Soucek J.
  • Marcucci M. F.
  • Wimmer-Schweingruber R. F.
  • Retinò Alessandro
  • Gehler M.
  • Escoubet P.
  , 2016, 18, pp.EPSC2016-15629. The Turbulence Heating ObserveR (THOR) mission was selected as one of the three candidates of the Call for Medium Class Missions M4 in the European Space Agency's Science Programme with a launch planned in 2026. THOR is the first mission ever flown in space dedicated to plasma turbulence. THOR will lead to an understanding of the basic plasma heating and particle energization processes, of their effect on different plasma species and of their relative importance in different turbulent regimes. The THOR mission features one single spinning spacecraft with 10 scientific instruments focusing on particular regions in three different elliptical orbits around the Earth; pristine solar wind, Earth's bow shock and interplanetary shocks, and compressed solar wind regions downstream of shocks. These regions are selected because of their differing turbulent fluctuation characteristics, and reflect similar astrophysical environments. The THOR mission, the conceptual design of the spacecraft and a summary of the payload will be presented. Furthermore, driving requirements and their implications for the spacecraft like Electromagnetic Compatibility and cleanliness will be discussed.
• Multi-Spacecraft Analysis of Plasma Jet Events and Associated Whistler-Wave Emissions using MMS Data
  
  • Breuillard Hugo
  • Le Contel Olivier
  • Retinò Alessandro
  • Chasapis A.
  • Chust Thomas
  • Cohen Ian
  • Wilder Frederick
  • Graham Daniel
  • Khotyaintsev Y. V.
  , 2016, 18, pp.13754. Plasma jets aka bursty bulk flows play a crucial role in Earth's plasmasheet dynamics, in particular during substorms where they can sometimes even penetrate down to the geosynchronous orbit. The energy input from the solar wind is partly dissipated in jet fronts(also called dipolarization fronts) in the form of strong whistler waves that can heat and accelerate energetic electrons. The ratio of the energy transported during jets to the substorm energy consumption is still under debate due to instrumental limitations. In May 2015 the Magnetospheric Multiscale (MMS) mission evolves in a string-of-pearls configuration with an average inter-satellite distance of 300 km which allows us to study in detail the microphysics of these phenomena. Thus in this study we employ MMS data to investigate the properties of jet fronts propagating earthward and their associated whistler-mode wave emissions. We show that the spatial dynamics of jet fronts are of the order of the ion gyroradius and whistler-wave dynamics have a temporal scale of a few seconds. We also investigate the energy dissipation associated with such waves and their interaction with energetic electrons in the vicinity of the flow/jet braking region. In addition, we make use of ray tracing simulations to evaluate their propagation properties, as well as their impact on particles in the off-equatorial magnetosphere.