Publications

2016

Combined use of LIDAR and hyperspectral measurements for remote sensing of fluorescence and vertical profile of canopies
- Ounis A.
- Bach J.
- Mahjoub A.
- Daumard Fabrice
- Moya I
- Goulas Y.
Revista de Teledetección, 2016 (45), pp.87-94. We report the development of a new LIDAR system (LASVEG) for airborne remote sensing of chlorophyll fluorescence (ChlF) and vertical profile of canopies. By combining laser-induced fluorescence (LIF), sun-induced fluorescence (SIF) and canopy height distribution, the new instrument will allow the simultaneous assessment of gross primary production (GPP), photosynthesis efficiency and above ground carbon stocks. Technical issues of the fluorescence LIDAR development are discussed and expected performances are presented. (10.4995/raet.2015.3982)
DOI : 10.4995/raet.2015.3982
Langmuir turbulence driven by beams in solar wind plasmas with long wavelength density fluctuations
- Krafft C.
- Volokitin A.
AIP Conference Proceedings, American Institute of Physics, 2016, 1720 (1), pp.040008. The self-consistent evolution of Langmuir turbulence generated by electron beams in solar wind plasmas with density inhomogeneities is calculated by numerical simulations based on a 1D Hamiltonian model. It is shown, owing to numerical simulations performed with parameters relevant to type III solar bursts' conditions at 1 AU, that the presence of long-wavelength random density fluctuations of sufficiently large average level crucially modifies the well-known process of beam interaction with Langmuir waves in homogeneous plasmas. (10.1063/1.4943819)
DOI : 10.1063/1.4943819
Poynting vector behaviour during the resonance scattering of a plane electromagnetic wave by a gyrotropic cylinder
- Es'Kin V. A.
- Ivoninsky A. V.
- Kudrin A. V.
- Krafft C.
Physica Scripta, IOP Publishing, 2016, 91 (1), pp.015502. The energy-flow structure during the resonance scattering of a normally incident plane electromagnetic H wave by a gyrotropic cylinder is studied. The main attention is focused on the bifurcations of the time-averaged Poynting vector field at the surface and volume plasmon resonances in the case where the cylinder is aligned with a gyrotropy axis. The behaviour of the Poynting vector field in this case is compared with that observed during the scattering by an isotropic cylinder, and significant differences in the energy-flow structures in the two cases are revealed. Conditions are found under which the maximum magnitude of the Poynting vector at the boundary of a gyrotropic cylinder turns out to be much greater than that at the boundary of an isotropic scatterer of the same shape and size. (10.1088/0031-8949/91/1/015502)
DOI : 10.1088/0031-8949/91/1/015502
Cold ion heating at the dayside magnetopause during magnetic reconnection
- Toledo-Redondo Sergio
- André M.
- Vaivads A.
- Khotyaintsev Y. V.
- Lavraud B.
- Graham D. B.
- Divin A. V.
- Aunai Nicolas
Geophysical Research Letters, American Geophysical Union, 2016, 43 (1), pp.58-66. Cold ions of ionospheric origin are known to be present in the magnetospheric side of the Earth's magnetopause. They can be very abundant, with densities up to 100 cm-3. These cold ions can mass load the magnetosphere, changing global parameters of magnetic reconnection, like the Alfvén speed or the reconnection rate. In addition they introduce a new length scale related to their gyroradius and kinetic effects which must be accounted for. We report in situ observations of cold ion heating in the separatrix owing to time and space fluctuations of the electric field. When this occurs, the cold ions are preheated before crossing the Hall electric field barrier. However, when this mechanism is not present cold ions can be observed well inside the reconnection exhaust. Our observations suggest that the perpendicular cold ion heating is stronger close to the X line owing to waves and electric field gradients linked to the reconnection process. (10.1002/2015GL067187)
DOI : 10.1002/2015GL067187
Cluster observations of reflected EMIC-triggered emission
- Grison B.
- Darrouzet F.
- Santolík O.
- Cornilleau-Wehrlin Nicole
- Masson A.
Geophysical Research Letters, American Geophysical Union, 2016, 43, pp.4164-4171. On 19 March 2001, the Cluster fleet recorded an electromagnetic rising tone on the nightside of the plasmasphere. The emission was found to propagate toward the Earth and toward the magnetic equator at a group velocity of about 200 km/s. The Poynting vector is mainly oblique to the background magnetic field and directed toward the Earth. The propagation angle thetak,B0 becomes more oblique with increasing magnetic latitude. Inside each rising tone thetak,B0 is more field aligned for higher frequencies. Comparing our results to previous ray tracing analysis we conclude that this emission is a triggered electromagnetic ion cyclotron (EMIC) wave generated at the nightside plasmapause. We detect the wave just after its reflection in the plasmasphere. The reflection makes the tone slope shallower. This process can contribute to the formation of pearl pulsations. (10.1002/2016GL069096)
DOI : 10.1002/2016GL069096
Ionospheric and magnetic signatures of a high speed solar wind in low latitudes on 13 October 2012
- Migoya-Orué Yenca
- Azzouzi Ilyasse
- Coisson Pierdavide
- Amory-Mazaudier Christine
- Fleury Rolland
- Radicella Sandro M.
Sun and Geosphere, BBC SWS Regional Network, 2016, 11 (1), pp.23-35. This paper presents the impact of a fast solar wind on the ionosphere, in low latitudes, on 13 October 2012. On that day, the high speed solar wind reached the Earth around 16:00UT, during the recovery phase of a geomagnetic storm which started around 00:00UT. The solar wind speed was determined to be 580km/s, on the same day, around 17:00UT. Its impact was observed in low and equatorial latitudes, in Africa and in Eastern South America, on the F layer and on the geomagnetic field variations. Through the analysis of magnetic indices, ionosonde characteristics and the horizontal component of the geomagnetic field, we found that the 13 October 2012 event exhibited a local impact, affecting the observatories situated in a longitude sector between 315°E and 45°E. Particularly, the F layer in Africa (observed by the ionosonde at Ascension Island) did not present any lift, and there was a delay for approximately two hours of the ascent of the F layer in America (the ionosonde at Fortaleza). In this case, there was an evident inhibition on the development of spread F at the time of the Pre Reversal Enhancement (PRE) in Africa and Eastern America, while the ionograms of the days before and after presented clear spread F traces. The disturbances of the ionospheric equivalent electric current (Diono) deduced from the variations of the geomagnetic field at M'Bour near Dakar (Africa) and at Kourou (Eastern America) exhibited on the dayside, an anti Sq current which is signature of the influence of the Disturbance Dynamo Electric Field (DDEF).
Global model of an iodine gridded plasma thruster
- Grondein Pascaline
- Lafleur Trevor
- Chabert Pascal
- Aanesland Ane
Physics of Plasmas, American Institute of Physics, 2016, 23 (3), pp.033514. Most state-of-the-art electric space propulsion systems such as gridded and Hall effect thrusters use xenon as the propellant gas. However, xenon is very rare, expensive to produce, and used in a number of competing industrial applications. Alternatives to xenon are currently being investigated, and iodine has emerged as a potential candidate. Its lower cost and larger availability, its solid state at standard temperature and pressure, its low vapour pressure and its low ionization potential make it an attractive option. In this work, we compare the performances of a gridded ion thruster operating separately with iodine and xenon, under otherwise identical conditions using a global model. The thruster discharge properties such as neutral, ion, and electron densities and electron temperature are calculated, as well as the thruster performance parameters such as thrust, specific impulse, and system efficiencies. For similar operating conditions, representative of realistic thrusters, the model predicts similar thrust levels and performances for both iodine and xenon. The thruster efficiency is however slightly higher for iodine compared with xenon, due to its lower ionization potential. This demonstrates that iodine could be a viable alternative propellant for gridded plasma thrusters. (10.1063/1.4944882)
DOI : 10.1063/1.4944882
Signatures of complex magnetic topologies from multiple reconnection sites induced by Kelvin-Helmholtz instability
- Vernisse Y.
- Lavraud B.
- Eriksson S.
- Gershman D. J.
- Dorelli J. C.
- Pollock C.
- Giles B. L.
- Aunai Nicolas
- Avanov L.
- Burch J. L.
- Chandler Michael O.
- Coffey Victoria
- Dargent Jérémy
- Ergun R. E.
- Farrugia C. J.
- Génot V.
- Graham D. B.
- Hasegawa H.
- Jacquey C.
- Kacem I.
- Khotyaintsev Y. V.
- Li W.
- Magnes W.
- Marchaudon A.
- Moore T. E.
- Paterson W. R.
- Penou E.
- Phan T. D.
- Retinò Alessandro
- Russell C. T.
- Saito Y.
- Sauvaud J.-A.
- Torbert R.
- Wilder F. D.
- Yokota S.
Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2016, 121 (10), pp.9926-9939. The Magnetospheric Multiscale mission has demonstrated the frequent presence of reconnection exhausts at thin current sheets within Kelvin-Helmholtz (KH) waves at the flank magnetopause. Motivated by these recent observations, we performed a statistical analysis of the boundary layers on the magnetosheath side of all KH current sheets on 8 September 2015. We show 86% consistency between the exhaust flows and particle leakage in the magnetosheath boundary layers but further highlight the very frequent presence of additional boundary layer signatures that do not come from the locally observed reconnection exhausts. These additional electron and ion boundary layers, of various durations and at various positions with respect to the leading and trailing boundaries of the KH waves, signal connections to reconnection sites at other locations. Based on the directionality and extent of these layers, we provide an interpretation whereby complex magnetic topologies can arise within KH waves from the combination of reconnection in the equatorial plane and at midlatitudes in the Southern and Northern Hemispheres, where additional reconnection sites are expected to be triggered by the three-dimensional field lines interweaving induced by the KH waves at the flanks (owing to differential flow and magnetic field shear with latitude). The present event demonstrates that the three-dimensional development of KH waves can induce plasma entry (through reconnection at both midlatitude and equatorial regions) already sunward of the terminator where the instability remains in its linear stage. (10.1002/2016JA023051)
DOI : 10.1002/2016JA023051
First results of the magnetospheric multiscale mission (MMS)
- Le Contel Olivier
- Lavraud B.
- Retinò Alessandro
- Jacquey C.
- Breuillard Hugo
- Vernisse Y.
- Chasapis A.
- Aunai N.
- Dargent Jérémy
- Chust Thomas
- Rezeau Laurence
- Mirioni Laurent
- Kacem I.
- Génot V.
- Penou E.
- Sauvaud J.-A.
- Leroy Paul
- Alison Dominique
- Coillot Christophe
- Aoustin C.
- Le Comte E.
- Rouzaud J.
French report to COSPAR, 2016.
Logarithmic discretization and systematic derivation of shell models in two-dimensional turbulence
- Gürcan Özgür D.
- Morel Pierre
- Kobayashi Sumire
- Singh Rameswar
- Xu S.
- Diamond P.H.
Physical Review E, American Physical Society (APS), 2016, 94, pp.033106. A detailed systematic derivation of a logarithmically discretized model for two-dimensional turbulence is given, starting from the basic fluid equations and proceeding with a particular form of discretization of the wave-number space. We show that it is possible to keep all or a subset of the interactions, either local or disparate scale, and recover various limiting forms of shell models used in plasma and geophysical turbulence studies. The method makes no use of the conservation laws even though it respects the underlying conservation properties of the fluid equations. It gives a family of models ranging from shell models with nonlocal interactions to anisotropic shell models depending on the way the shells are constructed. Numerical integration of the model shows that energy and enstrophy equipartition seem to dominate over the dual cascade, which is a common problem of two-dimensional shell models. (10.1103/PhysRevE.94.033106)
DOI : 10.1103/PhysRevE.94.033106
A comparative experimental kinetic study of spontaneous and plasma-assisted cool flames in a rapid compression machine
- Vanhove G.
- Boumehdi M.-A.
- Shcherbanev S.A.
- Fenard Y.
- Desgroux Pascale
- Starikovskaia Svetlana
Proceedings of the Combustion Institute, Elsevier, 2016. Plasma-assisted cool flames of n- heptane were generated in the combustion chamber of a rapid compression machine coupled with a nanosecond dielectric barrier discharge, at a pressure of 1.5 bar and temperature T = 650 K. Increasing of the voltage pulse amplitude at the electrode resulted in a transition from no reactivity to induced cool flame and then to fast ignition. Sampling of the reacting mixture was performed at selected times during the experiments to draw mole fraction profiles of the fuel and major low temperature stable intermediates, showing a gradual increase in the mole fraction of these species after the discharge. Comparison with a spontaneous cool flame case at a slightly higher pressure shows that no new species are formed in the plasma-assisted case, and that after the initiation of reactivity by the discharge at the nanosecond timescale, the distribution and relative importance of the main reaction pathways is conserved at the millisecond timescale. Differences in the shape of the mole fraction and light emission profiles however suggest that the plasma-assisted cool flame is propagative. (10.1016/j.proci.2016.09.007)
DOI : 10.1016/j.proci.2016.09.007
Magnetospheric Multiscale observations of large-amplitude, parallel, electrostatic waves associated with magnetic reconnection at the magnetopause
- Ergun R. E.
- Holmes J. C.
- Goodrich K. A.
- Wilder F. D.
- Stawarz J. E.
- Eriksson S.
- Newman D. L.
- Schwartz S. J.
- Goldman M. V.
- Sturner A. P.
- Malaspina D. M.
- Usanova M. E.
- Torbert R. B.
- Argall M.
- Lindqvist P.-A.
- Khotyaintsev Y. V.
- Burch J. L.
- Strangeway R. J.
- Russell C. T.
- Pollock C. J.
- Giles B. L.
- Dorelli J. J. C.
- Avanov L.
- Hesse Michael
- Chen L. J.
- Lavraud B.
- Le Contel Olivier
- Retinò Alessandro
- Phan T. D.
- Eastwood Jonathan P.
- Oieroset M.
- Drake J. F.
- Shay M. A.
- Cassak P. A.
- Nakamura R.
- Zhou M.
- Ashour-Abdalla M.
- André M.
Geophysical Research Letters, American Geophysical Union, 2016, 43 (11), pp.5626-5634. We report observations from the Magnetospheric Multiscale satellites of large-amplitude, parallel, electrostatic waves associated with magnetic reconnection at the Earth's magnetopause. The observed waves have parallel electric fields (E||) with amplitudes on the order of 100 mV/m and display nonlinear characteristics that suggest a possible net E||. These waves are observed within the ion diffusion region and adjacent to (within several electron skin depths) the electron diffusion region. They are in or near the magnetosphere side current layer. Simulation results support that the strong electrostatic linear and nonlinear wave activities appear to be driven by a two stream instability, which is a consequence of mixing cold (<10 eV) plasma in the magnetosphere with warm (~100 eV) plasma from the magnetosheath on a freshly reconnected magnetic field line. The frequent observation of these waves suggests that cold plasma is often present near the magnetopause. (10.1002/2016GL068992)
DOI : 10.1002/2016GL068992
Exact scaling laws for helical three-dimensional two-fluid turbulent plasmas
- Andrés Nahuel
- Galtier Sébastien
- Sahraoui Fouad
Physical Review E, American Physical Society (APS), 2016, 94 (6), pp.063206. We derive exact scaling laws for a three-dimensional incompressible helical two-fluid plasma, without the assumption of isotropy. For each ideal invariant of the two-fluid model, i.e., the total energy, the electron helicity, and the proton helicity, we derive simple scaling laws in terms of two-point increment correlation functions expressed in terms of the velocity field of each species and the magnetic field. These variables are appropriate for comparison with direct numerical simulation data and with in situ measurements in the near-Earth space over a broad range of spatial scales. Finally, using the exact scaling laws and dimensional analysis we predict the magnetic energy and electron helicity spectra for different ranges of scales. (10.1103/PhysRevE.94.063206)
DOI : 10.1103/PhysRevE.94.063206
In situ observations of flux rope at the separatrix region of magnetic reconnection
- Pang Y.
- Wang D. D.
- Huang S. Y.
- Retinò Alessandro
- Phan T. D.
- Daughton W.
- Vaivads A.
- Karimabadi H.
- Zhou M.
- Sahraoui Fouad
- Li G. L.
- Yuan Z. G.
- Deng X. H.
- Fu H.S.
- Fu S. Y.
Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2016, 121 (1), pp.205-213. We present the first 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 activity 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 3-D picture of magnetic reconnection in space plasma. (10.1002/2015JA021468)
DOI : 10.1002/2015JA021468
Mars-solar wind interaction: LatHyS, an improved parallel 3-D multispecies hybrid model
- Modolo Ronan
- Hess Sebastien
- Mancini Marco
- Leblanc François
- Chaufray Jean-Yves
- Brain David
- Leclercq Ludivine
- Esteban Hernandez Rosa
- Chanteur Gérard
- Weill Philippe
- González-Galindo Francisco
- Forget François
- Yagi Manabu
- Mazelle Christian
Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2016, 121 (7), pp.6378–6399. In order to better represent Mars-Solar wind interaction, we present an unprecedented model achieving spatial resolution down to 50 km, a so far unexplored resolution for global kinetic models of the Martian ionized environment. Such resolution approaches the ionospheric plasma scale height. In practice, the model is derived from a first version described in Modolo et al. [2005]. An important effort of parallelization has been conducted and is presented here. A better description of the ionosphere was also implemented including ionospheric chemistry, electrical conductivities and a drag force modelling the ion-neutral collisions in the ionosphere. This new version of the code, named LatHyS (Latmos Hybrid Simulation), is here used to characterize the impact of various spatial resolutions on simulation results. In addition, and following a global model challenge effort [Brain et al., 2010], we present the results of simulation run for three cases which allows addressing the effect of the supra-thermal corona and of the solar EUV activity on the magnetospheric plasma boundaries and on the global escape. Simulation results showed that global patterns are relatively similar for the different spatial resolution runs but finest grid runs provide a better representation of the ionosphere and display more details of the planetary plasma dynamic. Simulation results suggest that a significant fraction of escaping O+ ions is originated from below 1200 km altitude. (10.1002/2015JA022324)
DOI : 10.1002/2015JA022324
Electron density measurements in highly electronegative plasmas
- Rafalskyi D.V.
- Lafleur Trevor
- Aanesland Ane
Plasma Sources Science and Technology, IOP Publishing, 2016, 25 (4), pp.047001. In this paper we present experimental measurements of the electron density in very electronegative ionion ArSF 6 plasmas where previous investigations using Langmuir probes have observed electronegativities of up to 5000. The electron density is measured using a short matched dipole probe technique that provides a tolerance better than  ±2 · 10 13 m −3 . The results demonstrate that the electron density in the low pressure plasma source (which contains a magnetic filter) can be reduced to around 2.7 · 10 13 m −3 with a corresponding plasma electronegativity of about 4000; close to that from fluid simulation predictions. The highest electronegativity, and lowest electron density, is achieved with a pure SF 6 plasma, while adding only 6% SF 6 to Ar allows the electronegativity to be increased from 0 to a few hundred with a corresponding decrease in the electron density by more than a thousand. The impedance probe based on a short matched dipole appears to be a practical diagnostic that can be used for independent measurements of the electron density in very electronegative plasmas, and opens up the possibility to further investigate and optimize electronegative plasma sources. (10.1088/0963-0252/25/4/047001)
DOI : 10.1088/0963-0252/25/4/047001
The Baseline Th17 Lymphocytes Level Is a Predictive Marker of Good Response to Biologics in Rheumatoid Arthritis
- Salomon Sarah
- Guignant Caroline
- Morel Pierre
- Gubler Brigitte
- Fardellone Patrice
- Marolleau Jean-Pierre
- Goeb Vincent
Arthritis & rheumatology, Wiley, 2016, 68 (10).
A Review of General Physical and Chemical Processes Related to Plasma Sources and Losses for Solar System Magnetospheres
- Seki K.
- Nagy A.
- Jackman C. M.
- Crary F.
- Fontaine Dominique
- Zarka P.
- Wurz Peter
- Milillo A.
- Slavin J. A.
- Delcourt Dominique
- Wiltberger M.
- Ilie R.
- Jia X.
- Ledvina S. A.
- Liemohn M. W.
- Schunk R. W.
- Blanc Michel
- Chappell Charles R.
- Krupp N.
, 2016, pp.27-89. The aim of this paper is to provide a review of general processes related to plasma sources, their transport, energization, and losses in the planetary magnetospheres. We provide background information as well as the most up-to-date knowledge of the comparative studies of planetary magnetospheres, with a focus on the plasma supply to each region of the magnetospheres. This review also includes the basic equations and modeling methods commonly used to simulate the plasma sources of the planetary magnetospheres. In this paper, we will describe basic and common processes related to plasma supply to each region of the planetary magnetospheres in our solar system. First, we will describe source processes in Sect. 1. Then the transport and energization processes to supply those source plasmas to various regions of the magnetosphere are described in Sect. 2. Loss processes are also important to understand the plasma population in the magnetosphere and Sect. 3 is dedicated to the explanation of the loss processes. In Sect. 4, we also briefly summarize the basic equations and modeling methods with a focus on plasma supply processes for planetary magnetospheres.
Tailored voltage waveform capacitively coupled plasmas in electronegative gases: frequency dependence of asymmetry effects
- Schüngel E.
- Korolov Ihor
- Bruneau Bastien
- Derzsi A.
- Johnson E.V.
- O'Connell D.
- Gans T.
- Booth Jean-Paul
- Donkó Z.
- Schulze J.
Journal of Physics D: Applied Physics, IOP Publishing, 2016, 49 (26), pp.265203. Capacitively coupled radio frequency plasmas operated in an electronegative gas (CF 4 ) and driven by voltage waveforms composed of four consecutive harmonics are investigated for different fundamental driving frequencies using PIC/MCC simulations and an analytical model. As has been observed previously for electropositive gases, the application of peak-shaped waveforms (that are characterized by a strong amplitude asymmetry) results in the development of a DC self-bias due to the electrical asymmetry effect (EAE), which increases the energy of ions arriving at the powered electrode. In contrast to the electropositive case (Korolov et al 2012 J. Phys. D: Appl. Phys . 45 465202) the absolute value of the DC self-bias is found to increase as the fundamental frequency is reduced in this electronegative discharge, providing an increased range over which the DC self-bias can be controlled. The analytical model reveals that this increased DC self-bias is caused by changes in the spatial profile and the mean value of the net charge density in the grounded electrode sheath. The spatio-temporally resolved simulation data show that as the frequency is reduced the grounded electrode sheath region becomes electronegative. The presence of negative ions in this sheath leads to very different dynamics of the power absorption of electrons, which in turn enhances the local electronegativity and plasma density via ionization and attachment processes. The ion flux to the grounded electrode (where the ion energy is lowest) can be up to twice that to the powered electrode. At the same time, while the mean ion energies at both electrodes are quite different, their ratio remains approximately constant for all base frequencies studied here. (10.1088/0022-3727/49/26/265203)
DOI : 10.1088/0022-3727/49/26/265203
Chiral exact relations for helicities in Hall magnetohydrodynamic turbulence
- Banerjee Supratik
- Galtier Sébastien
Physical Review E, American Physical Society (APS), 2016, 93, pp.033120. Besides total energy, three-dimensional incompressible Hall magnetohydrodynamics (MHD) possesses two inviscid invariants, which are the magnetic helicity and the generalized helicity. Exact relations are derived for homogeneous (nonisotropic) stationary Hall MHD turbulence (and also for its inertialess electron MHD limit) with nonzero helicities and 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. It provides, therefore, a direct measurement of the dissipation rates for the corresponding invariant flux. 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. (10.1103/PhysRevE.93.033120)
DOI : 10.1103/PhysRevE.93.033120
Direct Evidence of the Transition from Weak to Strong Magnetohydrodynamic Turbulence
- Meyrand Romain
- Galtier Sébastien
- Kiyani K. H.
Physical Review Letters, American Physical Society, 2016, 116, pp.105002. One of the most important predictions in magnetohydrodynamics is that in the presence of a uniform magnetic field b0e^|| a transition from weak to strong wave turbulence should occur when going from large to small perpendicular scales. This transition is believed to be a universal property of several anisotropic turbulent systems. We present, for the first time, direct evidence of such a transition using a decaying three-dimensional direct numerical simulation of incompressible balanced magnetohydrodynamic turbulence with a grid resolution of 30722×256 . From large to small scales, the change of regime is characterized by (i) a change of slope in the energy spectrum going from approximately -2 to -3 /2 , (ii) an increase of the ratio between the wave and nonlinear times, with a critical ratio of chic1 /3 , (iii) a modification of the isocontours of energy revealing a transition from a purely perpendicular cascade to a cascade compatible with the critical-balance-type phenomenology, and (iv) an absence followed by a dramatic increase of the communication between Alfvén modes. The changes happen at approximately the same transition scale and can be seen as manifest signatures of the transition from weak to strong wave turbulence. Furthermore, we observe a significant nonlocal three-wave coupling between strongly and weakly nonlinear modes resulting in an inverse transfer of energy from small to large scales. (10.1103/PhysRevLett.116.105002)
DOI : 10.1103/PhysRevLett.116.105002
Experimental investigation of electron transport across a magnetic field barrier in electropositive and electronegative plasmas
- Thomas M B
- Rafalskyi D.V.
- Lafleur Trevor
- Aanesland Ane
Plasma Sources Science and Technology, IOP Publishing, 2016, 25 (4), pp.045018. In this paper we experimentally investigate the drift of electrons in low temperature plasmas containing a magnetic field barrier; a plasma configuration commonly used in gridded negative ion sources. A planar Langmuir probe array is developed to quantify the drift of electrons over the cross-section of the ion-extraction region of an ionion plasma source. The drift is studied as a function of pressure using both electropositive plasmas (Ar), as well electronegative plasmas (Ar and SF 6 mixtures), and is demonstrated to result from an interaction of the applied magnetic field and the electric fields in the sheath and pre-sheath near the transverse boundaries. The drift enhances electron transport across the magnetic field by more than two orders of magnitude compared with simple collisional transport, and is found to be strongly dependant on pressure. The lowest pressure resulted in the highest influence of the drift across the extraction area and is found to be 30%. (10.1088/0963-0252/25/4/045018)
DOI : 10.1088/0963-0252/25/4/045018
Differential kinetic dynamics and heating of ions in the turbulent solar wind
- Valentini F.
- Perrone D.
- Stabile S.
- Pezzi O.
- Servidio S.
- de Marco R.
- Marcucci M. F.
- Bruno Roberto
- Lavraud B.
- de Keyser J.
- Consolini G.
- Brienza D.
- Sorriso-Valvo L.
- Retinò Alessandro
- Vaivads A.
- Salatti M.
- Veltri P.
New Journal of Physics, Institute of Physics: Open Access Journals, 2016, 18, pp.125001. The solar wind plasma is a fully ionized and turbulent gas ejected by the outer layers of the solar corona at very high speed, mainly composed by protons and electrons, with a small percentage of helium nuclei and a significantly lower abundance of heavier ions. Since particle collisions are practically negligible, the solar wind is typically not in a state of thermodynamic equilibrium. Such a complex system must be described through self-consistent and fully nonlinear models, taking into account its multi-species composition and turbulence. We use a kinetic hybrid Vlasov-Maxwell numerical code to reproduce the turbulent energy cascade down to ion kinetic scales, in typical conditions of the uncontaminated solar wind plasma, with the aim of exploring the differential kinetic dynamics of the dominant ion species, namely protons and alpha particles. We show that the response of different species to the fluctuating electromagnetic fields is different. In particular, a significant differential heating of alphas with respect to protons is observed. Interestingly, the preferential heating process occurs in spatial regions nearby the peaks of ion vorticity and where strong deviations from thermodynamic equilibrium are recovered. Moreover, by feeding a simulator of a top-hat ion spectrometer with the output of the kinetic simulations, we show that measurements by such spectrometer planned on board the Turbulence Heating ObserveR (THOR mission), a candidate for the next M4 space mission of the European Space Agency, can provide detailed three-dimensional ion velocity distributions, highlighting important non-Maxwellian features. These results support the idea that future space missions will allow a deeper understanding of the physics of the interplanetary medium. (10.1088/1367-2630/18/12/125001)
DOI : 10.1088/1367-2630/18/12/125001
Two interacting X lines in magnetotail: Evolution of collision between the counterstreaming jets
- Alexandrova Alexandra
- Nakamura R.
- Panov Evgeny V.
- Sasunov Yury L.
- Nakamura T. K. M.
- Vörös Z.
- Retinò Alessandro
- Semenov Vladimir S.
Geophysical Research Letters, American Geophysical Union, 2016, 43 (15), pp.7795-7803. We study the process of collision between the counterstreaming jets flowing out from two reconnection sites in the Earth's magnetotail. The X lines, bracketing the region of jets collision, were passing by two Cluster probes successively in tailward direction. Two probes observed two different stages of the collision process. At the jets collision site, a probe first observed an ion-scale current sheet-like structure, while the other probe observed more compressed one later. The strong wave activities on both ion and electron scales were seen within the compressed layer. Such evolution of the jets collision resulting in the formation of the compressed boundary between the active X lines shows an example of interaction between the X lines during multiple reconnection. (10.1002/2016GL069823)
DOI : 10.1002/2016GL069823
Multispacecraft analysis of dipolarization fronts and associated whistler wave emissions using MMS data
- Breuillard Hugo
- Le Contel Olivier
- Retinò Alessandro
- Chasapis A.
- Chust Thomas
- Mirioni Laurent
- Graham D. B.
- Wilder F. D.
- Cohen I.
- Vaivads A.
- Khotyaintsev Y. V.
- Lindqvist P.-A.
- Marklund G. T.
- Burch J. L.
- Torbert R. B.
- Ergun R. E.
- Goodrich K. A.
- Macri J.
- Needell J.
- Chutter M.
- Rau D.
- Dors I.
- Russell C. T.
- Magnes W.
- Strangeway R. J.
- Bromund K. R.
- Plaschke F.
- Fischer D.
- Leinweber H. K.
- Anderson B. J.
- Le G.
- Slavin J. A.
- Kepko E. L.
- Baumjohann W.
- Mauk B.
- Fuselier S. A.
- Nakamura R.
Geophysical Research Letters, American Geophysical Union, 2016, 43 (14), pp.7279-7286. Dipolarization fronts (DFs), embedded in bursty bulk flows, play a crucial role in Earth's plasma sheet dynamics because the energy input from the solar wind is partly dissipated in their vicinity. This dissipation is in the form of strong low-frequency waves that can heat and accelerate energetic electrons up to the high-latitude plasma sheet. However, the dynamics of DF propagation and associated low-frequency waves in the magnetotail are still under debate due to instrumental limitations and spacecraft separation distances. In May 2015 the Magnetospheric Multiscale (MMS) mission was in a string-of-pearls configuration with an average intersatellite distance of 160 km, which allows us to study in detail the microphysics of DFs. Thus, in this letter we employ MMS data to investigate the properties of dipolarization fronts propagating earthward and associated whistler mode wave emissions. We show that the spatial dynamics of DFs are below the ion gyroradius scale in this region (500 km), which can modify the dynamics of ions in the vicinity of the DF (e.g., making their motion nonadiabatic). We also show that whistler wave dynamics have a temporal scale of the order of the ion gyroperiod (a few seconds), indicating that the perpendicular temperature anisotropy can vary on such time scales. (10.1002/2016GL069188)
DOI : 10.1002/2016GL069188

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