Publications

2017

• On the historical origins of the CEJ, DP2 and Ddyn current systems and their roles in the predictions of ionospheric responses to geomagnetic storms at equatorial latitudes
  
  • Amory-Mazaudier Christine
  • Bolaji O. S.
  • Doumbia V.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2017. In this short letter, we recall the differences between the Counter electrojet (CEJ), which is a phenomenon observed on the magnetically quiet days and the disturbance dynamo (Ddyn), which can be observed during and after a geomagnetic storm. The CEJ is well-known to occur near the geomagnetic dip equator. It can be identified by a reversal in the horizontal component (H) of the geomagnetic field daily regular variations. In contrasts to equatorial electrojet (EEJ) that flows eastward in the daytime the CEJ in considered to flow westward. The magnetic signatures of the reversed solar quiet (Sq) current at the low latitude during magnetic storms are due to the Ddyn. This disturbance (Ddyn) is produced by current systems that are driven by thermospheric storm winds originating from the Joule heating of enhanced high latitude currents. The DP2 is the magnetic effect of current systems at high latitudes. These currents are associated with the coupling of magnetosphere and ionosphere through geomagnetic field lines. They are associated to the magnetospheric convection. During intense magnetic storms these high latitude currents are enhanced and their magnetic effects can extend toward the low latitudes This work shows that the study of magnetic perturbations makes it possible to understand the disturbances of the ionospheric electric currents. The use of an efficient treatment of the magnetic signals makes it possible to separate the magnetic effects of the different perturbations PPEF and DDEF. This was performed in the paper Nava et al. (2016). (10.1002/2017JA024132)
  DOI : 10.1002/2017JA024132
• Electron Scattering by High-frequency Whistler Waves at Earth's Bow Shock
  
  • Oka M.
  • Wilson Iii L. B.
  • Phan T. D.
  • Hull A. J.
  • Amano T.
  • Hoshino M.
  • Argall M. R.
  • Le Contel Olivier
  • Agapitov O.
  • Gershman D. J.
  • Khotyaintsev Y. V.
  • Burch J. L.
  • Torbert R. B.
  • Pollock C.
  • Dorelli J. C.
  • Giles B. L.
  • Moore T. E.
  • Saito Y.
  • Avanov L. A.
  • Paterson W. R.
  • Ergun R. E.
  • Strangeway R. J.
  • Russell C. T.
  • Lindqvist P. A.
  The Astrophysical Journal Letters, Bristol : IOP Publishing, 2017, 842 (2), pp.L11. Electrons are accelerated to non-thermal energies at shocks in space and astrophysical environments. While different mechanisms of electron acceleration have been proposed, it remains unclear how non-thermal electrons are produced out of the thermal plasma pool. Here, we report in situ evidence of pitch-angle scattering of non-thermal electrons by whistler waves at Earth's bow shock. On 2015 November 4, the Magnetospheric Multiscale (MMS) mission crossed the bow shock with an Alfvén Mach number ~11 and a shock angle ~84°. In the ramp and overshoot regions, MMS revealed bursty enhancements of non-thermal (0.5−2 keV) electron flux, correlated with high-frequency (0.2−0.4 Omega <SUB>ce</SUB>, where Omega <SUB>ce</SUB> is the cyclotron frequency) parallel-propagating whistler waves. The electron velocity distribution (measured at 30 ms cadence) showed an enhanced gradient of phase-space density at and around the region where the electron velocity component parallel to the magnetic field matched the resonant energy inferred from the wave frequency range. The flux of 0.5 keV electrons (measured at 1 ms cadence) showed fluctuations with the same frequency. These features indicate that non-thermal electrons were pitch-angle scattered by cyclotron resonance with the high-frequency whistler waves. However, the precise role of the pitch-angle scattering by the higher-frequency whistler waves and possible nonlinear effects in the electron acceleration process remains unclear. (10.3847/2041-8213/aa7759)
  DOI : 10.3847/2041-8213/aa7759
• Acceleration of energetic electrons by waves in inhomogeneous solar wind plasmas
  
  • Krafft C.
  • Volokitin A.
  Journal of Plasma Physics, Cambridge University Press (CUP), 2017, 83 (2), pp.705830201. The paper studies the influence of the background plasma density fluctuations on the dynamics of the Langmuir turbulence generated by electron beams, for parameters typical for solar type III beams and plasmas near 1 AU. A self-consistent Hamiltonian model based on the Zakharov and the Newton equations is used, which presents several advantages compared to the Vlasov approach. Beams generating Langmuir turbulence can be accelerated as a result of wave transformation effects or/and decay cascade processes; in both cases, the beam-driven Langmuir waves transfer part of their energy to waves of smaller wavenumbers, which can be reabsorbed later on by beam particles of higher velocities. As a consequence, beams can conserve a large part of their initial kinetic energy while propagating and radiating wave turbulence over long distances in inhomogeneous plasmas. Beam particles can also be accelerated in quasi-homogeneous plasmas due to the second cascade of wave decay, the wave transformation processes being very weak in this case. The net gains and losses of energy of a beam and the wave turbulence it radiates are calculated as a function of the average level of plasma density fluctuations and the beam parameters. The results obtained provide relevant information on the mechanism of energy reabsorption by beams radiating Langmuir turbulence in solar wind plasmas. (10.1017/S0022377817000174)
  DOI : 10.1017/S0022377817000174
• The nonlinear behavior of whistler waves at the reconnecting dayside magnetopause as observed by the Magnetospheric Multiscale mission: A case study
  
  • Wilder F. D.
  • Ergun R. E.
  • Newman D. L.
  • Goodrich K. A.
  • Trattner K. J.
  • Goldman M. V.
  • Eriksson S.
  • Jaynes A. N.
  • Leonard T.
  • Malaspina D. M.
  • Ahmadi N.
  • Schwartz S. J.
  • Burch J. L.
  • Torbert R. B.
  • Argall M. R.
  • Giles B. L.
  • Phan T. D.
  • Le Contel Olivier
  • Graham D. B.
  • Khotyaintsev Yu V.
  • Strangeway R. J.
  • Russell C. T.
  • Magnes W.
  • Plaschke F.
  • Lindqvist P.-A.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2017, 122 (5), pp.5487-5501. We show observations of whistler mode waves in both the low-latitude boundary layer (LLBL) and on closed magnetospheric field lines during a crossing of the dayside reconnecting magnetopause by the Magnetospheric Multiscale (MMS) mission on 11 October 2015. The whistlers in the LLBL were on the electron edge of the magnetospheric separatrix and exhibited high propagation angles with respect to the background field, approaching 40°, with bursty and nonlinear parallel electric field signatures. The whistlers in the closed magnetosphere had Poynting flux that was more field aligned. Comparing the reduced electron distributions for each event, the magnetospheric whistlers appear to be consistent with anisotropy-driven waves, while the distribution in the LLBL case includes anisotropic backward resonant electrons and a forward resonant beam at near half the electron-Alfvén speed. Results are compared with the previously published observations by MMS on 19 September 2015 of LLBL whistler waves. The observations suggest that whistlers in the LLBL can be both beam and anisotropy driven, and the relative contribution of each might depend on the distance from the X line. (10.1002/2017JA024062)
  DOI : 10.1002/2017JA024062
• Statistical study of the alteration of the magnetic structure of magnetic clouds in the Earth's magnetosheath
  
  • Turc Lucile
  • Fontaine Dominique
  • Escoubet C. Philippe
  • Kilpua E. K. J.
  • Dimmock A. P.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2017, 122 (3), pp.2956-2972. The magnetosheath plays a central role in the solar wind-magnetospheric coupling. Yet the effects of its crossing on solar wind structures such as magnetic clouds (MCs) are generally overlooked when assessing their geoeffectivity. Using 82 MCs observed simultaneously in the solar wind and the magnetosheath, we carry out the first statistical study of the alteration of their magnetic structure in the magnetosheath. For each event, the bow shock properties are obtained from a magnetosheath model. The comparison between the model results and observations shows that in 80% of cases, the MHD-based model captures well the magnetosheath transition; the other events are discussed separately. We find that just downstream of the bow shock the variation of the magnetic field direction shows a very good anticorrelation (r =- 0.91) with the angle between the upstream magnetic field and the shock normal. We then focus on the magnetic field north-south component B<SUB>z</SUB> because of its importance for geoeffectivity. Although the sign of B<SUB>z</SUB> is generally preserved in the magnetosheath, we also find evidence of long-lasting intervals of opposite B<SUB>z</SUB> signs in the solar wind and the magnetosheath during some events, with a |B<SUB>z</SUB>| reversal >10 nT at the magnetopause. We find that these reversals are due to the draping of the field lines and are associated with predominant upstream B<SUB>y</SUB>. In those cases, the estimated position of the regions of antiparallel fields along the magnetopause is independent of the sign of the upstream B<SUB>z</SUB>. This may have strong implications in terms of reconnection. (10.1002/2016JA023654)
  DOI : 10.1002/2016JA023654
• Optical emission spectrum of filamentary nanosecond surface dielectric barrier discharge
  
  • Shcherbanev S.A.
  • Khomenko A.Yu.
  • Stepanyan S.A.
  • Popov N.A.
  • Starikovskaia Svetlana
  Plasma Sources Science and Technology, IOP Publishing, 2017, 26 (2), pp.02LT01 (7pp). Streamer-to-filament transition is a general feature of high pressure high voltage (HV) nanosecond surface dielectric barrier discharges. The transition was studied experimentally using time- and space-resolved optical emission in UV and visible parts of spectra. The discharge was initiated by HV pulses 20 ns in duration and 2 ns rise time, positive or negative polarity, 2060 kV in amplitude on the HV electrode. The experiments were carried out in a single-shot regime at initial pressures P > 3 bar and ambient initial temperature in air, N2, H2:N2 and O2:Ar mixtures. It was shown that the transition to filamentary mode is accompanied by the appearance of intense continuous radiation and broad atomic lines. Electron density calculated from line broadening is characterized by high absolute values and long decay in the afterglow. The possible reasons for the continuous spectra were analyzed. (10.1088/1361-6595/26/2/02LT01)
  DOI : 10.1088/1361-6595/26/2/02LT01
• The role of thermal energy accommodation and atomic recombination probabilities in low pressure oxygen plasmas
  
  • Gibson Andrew
  • Foucher Mickaël
  • Marinov Daniil
  • Chabert Pascal
  • Gans T.
  • Kushner M.J.
  • Booth Jean-Paul
  Plasma Physics and Controlled Fusion, IOP Publishing, 2017, 59 (2), pp.024004. Surface interaction probabilities are critical parameters that determine the behaviour of low pressure plasmas and so are crucial input parameters for plasma simulations that play a key role in determining their accuracy. However, these parameters are difficult to estimate without in situ measurements. In this work, the role of two prominent surface interaction probabilities, the atomic oxygen recombination coefficient ? O and the thermal energy accommodation coefficient ? E in determining the plasma properties of low pressure inductively coupled oxygen plasmas are investigated using two-dimensional fluid-kinetic simulations. These plasmas are the type used for semiconductor processing. It was found that ? E plays a crucial role in determining the neutral gas temperature and neutral gas density. Through this dependency, the value of ? E also determines a range of other plasma properties such as the atomic oxygen density, the plasma potential, the electron temperature, and ion bombardment energy and neutral-to-ion flux ratio at the wafer holder. The main role of ? O is in determining the atomic oxygen density and flux to the wafer holder along with the neutral-to-ion flux ratio. It was found that the plasma properties are most sensitive to each coefficient when the value of the coefficient is small causing the losses of atomic oxygen and thermal energy to be surface interaction limited rather than transport limited. (10.1088/1361-6587/59/2/024004)
  DOI : 10.1088/1361-6587/59/2/024004
• Localized reversal of the perpendicular velocity in Tore Supra ohmic, L-mode, limited plasmas
  
  • Trier Elisée
  • Hennequin Pascale
  • Gürcan Özgür D.
  • Sabot R.
  • Bucalossi J.
  • Guimarães-Filho Z.O.
  • Bourdelle C.
  • Clairet F.
  • Falchetto G.
  • Fenzi C.
  • Garbet X.
  • Maget P.
  • Vermare Laure
  • The Tore Supra Team
  Nuclear Fusion, IOP Publishing, 2017, 57 (4), pp.046021. In Tore Supra plasmas, the perpendicular velocity measured by Doppler reflectometry was observed to reverse in a localized zone close to a normalized radius???0.5?0.6, changing from a negative value (corresponding to a negative radial electric field E r ) to a positive value ( ##IMG## [http://ej.iop.org/images/0029-5515/57/4/046021/nfaa59bbieqn001.gif] E_\textr>0 ). This occurs in L-mode, ohmic plasmas with a negligible external momentum input, a non-circular limited cross-section, and an edge safety factor close to 3. This reversal is favoured by a decrease in the magnetic field, or an increase in density. It is accompanied by a characteristic behaviour of the MHD activity signal, whose amplitude decrease during a ramp-down of the edge safety factor as it approaches ##IMG## [http://ej.iop.org/images/0029-5515/57/4/046021/nfaa59bbieqn002.gif] q_a∼ 3.1 ?3.2. A m / n ??=??2/1 mode is involved in the mechanism causing these observations. (10.1088/1741-4326/aa59bb)
  DOI : 10.1088/1741-4326/aa59bb
• Transfer of microwave energy along a filament plasma column in air
  
  • Prade Bernard
  • Houard Aurélien
  • Larour Jean
  • Pellet Michel
  • Mysyrowicz André
  Applied Physics B - Laser and Optics, Springer Verlag, 2017, 123, pp.40. We demonstrate the coupling of microwave radiation into a plasma channel formed by laser filamentation in air, leading to the amplification by two orders of magnitude of longitudinal oscillations of the plasma. Transfer of this longitudinal excitation towards unexcited region of the plasma column occurs over more than 10 cm, in good agreement with a theoretical model describing the propagation of a TM wave guided along the surface between air and plasma. We foresee that high power low frequency electromagnetic waves injected into a multi-filament plasma could initiate and sustain a long-lived plasma over several meters distance. (10.1007/s00340-016-6616-4)
  DOI : 10.1007/s00340-016-6616-4
• Enhanced control of the ionization rate in radio-frequency plasmas with structured electrodes via tailored voltage waveforms
  
  • Doyle Scott J.
  • Lafleur Trevor
  • Gibson Andrew R.
  • Tian Peng
  • Kushner Mark J.
  • Dedrick James
  Plasma Sources Science and Technology, IOP Publishing, 2017, 26. Radio-frequency capacitively coupled plasmas that incorporate structured electrodes enable increases in the electron density within spatially localized regions through the hollow cathode effect (HCE). This enables enhanced control over the spatial profile of the plasma density, which is useful for several applications including materials processing, lighting and spacecraft propulsion. However, asymmetries in the powered and grounded electrode areas inherent to the hollow cathode geometry lead to the formation of a time averaged dc self-bias voltage at the powered electrode. This bias alters the energy and flux of secondary electrons leaving the surface of the cathode and consequentially can moderate the increased localized ionization afforded by the hollow cathode discharge. In this work, two-dimensional fluid-kinetic simulations are used to demonstrate control of the dc self-bias voltage in a dual-frequency driven (13.56, 27.12 MHz), hollow cathode enhanced, capacitively coupled argon plasma over the 66.6--200 Pa (0.5--1.5 Torr) pressure range. By varying the phase offset of the 27.12 MHz voltage waveform, the dc self-bias voltage varies by 10%--15% over an applied peak-to-peak voltage range of 600--1000 V, with lower voltages showing higher modulation. Resulting ionization rates due to secondary electrons within the hollow cathode cavity vary by a factor of 3 at constant voltage amplitude, demonstrating the ability to control plasma properties relevant for maintaining and enhancing the HCE. (10.1088/1361-6595/aa96e5)
  DOI : 10.1088/1361-6595/aa96e5
• Long-lived laser-induced arc discharges for energy channeling applications
  
  • Point Guillaume
  • Arantchouk Léonid
  • Thouin Emmanuelle
  • Carbonnel Jérôme
  • Mysyrowicz André
  • Houard Aurélien
  Scientific Reports, Nature Publishing Group, 2017, 7 (1), pp.13801. Laser filamentation offers a promising way for the remote handling of large electrical power in the form of guided arc discharges. We here report that it is possible to increase by several orders of magnitude the lifetime of straight plasma channels from filamentation-guided sparks in atmospheric air. A 30 ms lifetime can be reached using a low-intensity, 100 mA current pulse. Stability of the plasma shape is maintained over such a timescale through a continuous Joule heating from the current. This paves the way for applications based on the generation of straight, long duration plasma channels, like virtual plasma antennas or contactless transfer of electric energy. (10.1038/s41598-017-14054-z)
  DOI : 10.1038/s41598-017-14054-z
• Controlling plasma properties under differing degrees of electronegativity using odd harmonic dual frequency excitation
  
  • Gibson Andrew R.
  • Gans Timo
  Plasma Sources Science and Technology, IOP Publishing, 2017, 26. The charged particle dynamics in low-pressure oxygen plasmas excited by odd harmonic dual frequency waveforms (low frequency of 13.56 MHz and high frequency of 40.68 MHz) are investigated using a one-dimensional numerical simulation in regimes of both low and high electronegativity. In the low electronegativity regime, the time and space averaged electron and negative ion densities are approximately equal and plasma sustainment is dominated by ionisation at the sheath expansion for all combinations of low and high frequency and the phase shift between them. In the high electronegativity regime, the negative ion density is a factor of 15--20 greater than the low electronegativity cases. In these cases, plasma sustainment is dominated by ionisation inside the bulk plasma and at the collapsing sheath edge when the contribution of the high frequency to the overall voltage waveform is low. As the high frequency component contribution to the waveform increases, sheath expansion ionisation begins to dominate. It is found that the control of the average voltage drop across the plasma sheath and the average ion flux to the powered electrode are similar in both regimes of electronegativity, despite the differing electron dynamics using the considered dual frequency approach. This offers potential for similar control of ion dynamics under a range of process conditions, independent of the electronegativity. This is in contrast to ion control offered by electrically asymmetric waveforms where the relationship between the ion flux and ion bombardment energy is dependent upon the electronegativity. (10.1088/1361-6595/aa8dcd)
  DOI : 10.1088/1361-6595/aa8dcd
• Evidence and relevance of spatially chaotic magnetic field lines in MCF devices
  
  • Firpo Marie-Christine
  • Lifschitz Agustin
  • Ettoumi Wahb
  • Farengo Ricardo
  • Ferrari Hugo
  • Garcia-Martinez Pablo Luis
  Plasma Physics and Controlled Fusion, IOP Publishing, 2017, 59 (3). Numerical evidence for the existence of spatially chaotic magnetic field lines about the collapse phase of tokamak sawteeth with incomplete reconnection is presented. This uses the results of extensive test particle simulations in different sets of electromagnetic perturbations tested against experimental JET measurements. In tokamak sawteeth, that form a laboratory prototype of magnetic reconnection, the relative magnetic perturbation δB/B may reach a few percents. This does not apply to tokamak operating regimes dominated by turbulence where δB/B is usually not larger than 10 −4. However, this small magnetic perturbation being sustained by a large spectrum of modes is shown to be sufficient to ensure the existence of stochastic magnetic field lines. This has important consequences for magnetic confinement fusion (MCF) where electrons are dominantly governed by the magnetic force. Indeed some overlap between magnetic resonances can locally induce chaotic magnetic field lines enabling the spatial redistribution of the electron population and of its thermal content. As they are the swiftest plasma particles, electrons feed back the most rapid perturbations of the magnetic field (10.1088/1361-6587/aa570d)
  DOI : 10.1088/1361-6587/aa570d
• Influence of neutral pressure on instability enhanced friction and ion velocities at the sheath edge of two-ion-species plasmas
  
  • Adrian P. J.
  • Baalrud S. D.
  • Lafleur T.
  Physics of Plasmas, American Institute of Physics, 2017, 24. The Instability Enhanced Friction theory [Baalrud et al., Phys. Rev. Lett. 103, 205002 (2009)] is extended to account for the influence of neutral pressure in predicting the flow speed of each ion species at the sheath edge of plasmas containing two ion species. Particle-in-cell simulations show that the theory accurately predicts both the neutral pressure cutoff of ion-ion two-stream instabilities and the ion flow speeds at the sheath edge as pressure is varied over several orders of magnitude. The simulations are used to directly calculate the instability-enhanced ion-ion friction force. At sufficiently high neutral pressure, the simulations also provide evidence for collisional modifications to the Bohm criterion. (10.1063/1.4986239)
  DOI : 10.1063/1.4986239
• Erratum: "On the Existence of the Kolmogorov Inertial Range in the Terrestrial Magnetosheath Turbulence" (2017, ApJL, 836, L10)
  
  • Huang S. Y.
  • Hadid Lina
  • Sahraoui Fouad
  • Yuan Z. G.
  • Deng X. H.
  The Astrophysical Journal Letters, Bristol : IOP Publishing, 2017, 837 (2), pp.L31. Not Available (10.3847/2041-8213/aa633c)
  DOI : 10.3847/2041-8213/aa633c
• Counterpropagating radiative shock experiments on the Orion laser
  
  • Suzuki-Vidal Francisco
  • Clayson Thomas
  • Stehlé Chantal
  • Swadling G. F.
  • Foster J.
  • Skidmore J.
  • Graham P.
  • Burdiak G.
  • Lebedev S. V.
  • Chaulagain Uddhab
  • Singh Raj Laxmi
  • Gumbrell E.
  • Patankar S.
  • Spindloe C.
  • Larour Jean
  • Kozlová Michaela
  • Rodriguez Perez R.
  • Gil J. M.
  • Espinosa G.
  • Velarde P.
  • Danson C.
  Physical Review Letters, American Physical Society, 2017, 119 (05), pp.055001. We present new experiments to study the formation of radiative shocks and the interaction between two counterpropagating radiative shocks. The experiments are performed at the Orion laser facility, which is used to drive shocks in xenon inside large aspect ratio gas cells. The collision between the two shocks and their respective radiative precursors, combined with the formation of inherently three-dimensional shocks, provides a novel platform particularly suited for the benchmarking of numerical codes. The dynamics of the shocks before and after the collision are investigated using point-projection x-ray backlighting while, simultaneously, the electron density in the radiative precursor was measured via optical laser interferometry. Modeling of the experiments using the 2D radiation hydrodynamic codes NYM and PETRA shows very good agreement with the experimental results. (10.1103/PhysRevLett.119.055001)
  DOI : 10.1103/PhysRevLett.119.055001
• MMS observations of whistler waves in electron diffusion region
  
  • Cao D.
  • Fu H.S.
  • Cao J.B.
  • Wang T. Y.
  • Graham D. B.
  • Chen Z. Z.
  • Peng F. Z.
  • Huang S. Y.
  • Khotyaintsev Y. V.
  • André M.
  • Russell C. T.
  • Giles B. L.
  • Lindqvist P.-A.
  • Torbert R. B.
  • Ergun R. E.
  • Le Contel Olivier
  • Burch J. L.
  Geophysical Research Letters, American Geophysical Union, 2017, 44 (9), pp.3954-3962. Whistler waves that can produce anomalous resistivity by affecting electrons' motion have been suggested as one of the mechanisms responsible for magnetic reconnection in the electron diffusion region (EDR). Such type of waves, however, has rarely been observed inside the EDR so far. In this study, we report such an observation by Magnetospheric Multiscale (MMS) mission. We find large-amplitude whistler waves propagating away from the X line with a very small wave-normal angle. These waves are probably generated by the perpendicular temperature anisotropy of the 300 eV electrons inside the EDR, according to our analysis of dispersion relation and cyclotron resonance condition; they significantly affect the electron-scale dynamics of magnetic reconnection and thus support previous simulations. (10.1002/2017GL072703)
  DOI : 10.1002/2017GL072703
• Differential kinetic physics of solar-wind minor ions
  
  • Perrone Denise
  • Valentini F.
  • Servidio S.
  • Stabile S.
  • Pezzi O.
  • Sorriso-Valvo L.
  • de Marco R.
  • Marcucci M. F.
  • Brienza D.
  • Bruno Roberto
  • Lavraud Benoit
  • Retinò Alessandro
  • Vaivads A.
  • Consolini G.
  • de Keyser J.
  • Salatti M.
  • Veltri P.
  , 2017, 19, pp.13382. The solar wind, although predominantly constituted of protons, is also made up of a finite amount of alpha particles, together with a few percent of heavier ions. The kinetic properties of heavy ions in the solar wind are known to behave in a well organized way under most solar-wind flow conditions: their speeds are faster than that of hydrogen by about the local Alfvén speed, and their kinetic temperatures are more than proportional to their mass. Preferential heating and acceleration of heavy ions in the solar wind and corona represent a long-standing theoretical problem in space physics, and are distinct experimental signatures of kinetic processes occurring in collisionless plasmas. However, due to very scarce measurements of heavy ions at time resolutions comparable with their kinetic scales, energy partition between species in turbulent plasma dissipation is basically unexplored. For the moment, most of the information comes from numerical simulations and a crucial support is given by self-consistent, fully nonlinear Vlasov models. Here, hybrid Vlasov-Maxwell simulations are used to investigate the role of kinetic effects in a two-dimensional turbulent multi-ion plasma, composed of kinetic protons and alpha particles, and fluid electrons. The response of different ion species to the fluctuating electromagnetic fields appears to be different. In particular, a significant differential heating of alpha particles with respect to protons is observed, localized nearby the peaks of ion vorticity and where strong deviations from thermodynamic equilibrium are recovered. Then, the understanding of the complex process of particle heating results strongly related to the study of the non-Maxwellian features on the three-dimensional ion velocity distributions. These numerical results highlight the importance for the future space missions to provide detailed ion measurements to make a significant step forward in the problem of heating in turbulent space plasmas.
• Drift waves, intense parallel electric fields, and turbulence associated with asymmetric magnetic reconnection at the magnetopause
  
  • Ergun R. E.
  • Chen L.-J.
  • Wilder F. D.
  • Ahmadi N.
  • Eriksson S.
  • Usanova M. E.
  • Goodrich K. A.
  • Holmes J. C.
  • Sturner A. P.
  • Malaspina D. M.
  • Newman D. L.
  • Torbert R. B.
  • Argall M. R.
  • Lindqvist P.-A.
  • Burch J. L.
  • Webster J. M.
  • Drake J. F.
  • Price L.
  • Cassak P. A.
  • Swisdak M.
  • Shay M. A.
  • Graham D. B.
  • Strangeway R. J.
  • Russell C. T.
  • Giles B. L.
  • Dorelli J. C.
  • Gershman D. J.
  • Avanov L.
  • Hesse Michael
  • Lavraud B.
  • Le Contel Olivier
  • Retinò Alessandro
  • Phan T. D.
  • Goldman M. V.
  • Stawarz J. E.
  • Schwartz S. J.
  • Eastwood Jonathan P.
  • Hwang K.-J.
  • Nakamura R.
  • Wang S.
  Geophysical Research Letters, American Geophysical Union, 2017, 44 (7), pp.2978-2986. Observations of magnetic reconnection at Earth's magnetopause often display asymmetric structures that are accompanied by strong magnetic field (B) fluctuations and large-amplitude parallel electric fields (E<SUB>||</SUB>). The B turbulence is most intense at frequencies above the ion cyclotron frequency and below the lower hybrid frequency. The B fluctuations are consistent with a thin, oscillating current sheet that is corrugated along the electron flow direction (along the X line), which is a type of electromagnetic drift wave. Near the X line, electron flow is primarily due to a Hall electric field, which diverts ion flow in asymmetric reconnection and accompanies the instability. Importantly, the drift waves appear to drive strong parallel currents which, in turn, generate large-amplitude ( 100 mV/m) E<SUB>||</SUB> in the form of nonlinear waves and structures. These observations suggest that turbulence may be common in asymmetric reconnection, penetrate into the electron diffusion region, and possibly influence the magnetic reconnection process. (10.1002/2016GL072493)
  DOI : 10.1002/2016GL072493
• Near-Earth plasma sheet boundary dynamics during substorm dipolarization
  
  • Nakamura R.
  • Nagai Tsugunobu
  • Birn Joachim
  • Sergeev Victor A.
  • Le Contel Olivier
  • Varsani Ali
  • Baumjohann W.
  • Nakamura T. K. M.
  • Apatenkov Sergey
  • Artemyev A. V.
  • Ergun Robert E.
  • Fuselier Stephen A.
  • Gershman D. J.
  • Giles Barbara J.
  • Khotyaintsev Y. V.
  • Lindqvist Per-Arne
  • Magnes Werner
  • Mauk Barry
  • Russell Christopher T.
  • Singer Howard J.
  • Stawarz J. E.
  • Strangeway Robert J.
  • Anderson Brian
  • Bromund Ken R.
  • Fischer David
  • Kepko Laurence
  • Le Guan
  • Plaschke Ferdinand
  • Slavin J. A.
  • Cohen Ian
  • Jaynes Allison
  • Turner Drew L.
  Earth Planets and Space, Springer / Terra Scientific Publishing Company, 2017, 69, pp.129. We report on the large-scale evolution of dipolarization in the near-Earth plasma sheet during an intense (AL -1000 nT) substorm on August 10, 2016, when multiple spacecraft at radial distances between 4 and 15 R <SUB>E</SUB> were present in the night-side magnetosphere. This global dipolarization consisted of multiple short-timescale (a couple of minutes) B <SUB> z </SUB> disturbances detected by spacecraft distributed over 9 MLT, consistent with the large-scale substorm current wedge observed by ground-based magnetometers. The four spacecraft of the Magnetospheric Multiscale were located in the southern hemisphere plasma sheet and observed fast flow disturbances associated with this dipolarization. The high-time-resolution measurements from MMS enable us to detect the rapid motion of the field structures and flow disturbances separately. A distinct pattern of the flow and field disturbance near the plasma boundaries was found. We suggest that a vortex motion created around the localized flows resulted in another field-aligned current system at the off-equatorial side of the BBF-associated R1/R2 systems, as was predicted by the MHD simulation of a localized reconnection jet. The observations by GOES and Geotail, which were located in the opposite hemisphere and local time, support this view. We demonstrate that the processes of both Earthward flow braking and of accumulated magnetic flux evolving tailward also control the dynamics in the boundary region of the near-Earth plasma sheet.[Figure not available: see fulltext.] (10.1186/s40623-017-0707-2)
  DOI : 10.1186/s40623-017-0707-2
• Intermittent energy dissipation by turbulent reconnection
  
  • Fu H.S.
  • Vaivads A.
  • Khotyaintsev Y. V.
  • André M.
  • Cao J.B.
  • Olshevsky V.
  • Eastwood Jonathan P.
  • Retinò Alessandro
  Geophysical Research Letters, American Geophysical Union, 2017, 44 (1), pp.37-43. Magnetic reconnection−-the process responsible for many explosive phenomena in both nature and laboratory−-is efficient at dissipating magnetic energy into particle energy. To date, exactly how this dissipation happens remains unclear, owing to the scarcity of multipoint measurements of the "diffusion region" at the sub-ion scale. Here we report such a measurement by Cluster−-four spacecraft with separation of 1/5 ion scale. We discover numerous current filaments and magnetic nulls inside the diffusion region of magnetic reconnection, with the strongest currents appearing at spiral nulls (O-lines) and the separatrices. Inside each current filament, kinetic-scale turbulence is significantly increased and the energy dissipation, E' s j, is 100 times larger than the typical value. At the jet reversal point, where radial nulls (X-lines) are detected, the current, turbulence, and energy dissipations are surprisingly small. All these features clearly demonstrate that energy dissipation in magnetic reconnection occurs at O-lines but not X-lines. (10.1002/2016GL071787)
  DOI : 10.1002/2016GL071787
• Ignition of high pressure lean H<SUB>2</SUB>:air mixture along the multiple channels of nanosecond surface discharge
  
  • Shcherbanev S.A.
  • Popov N.A.
  • Starikovskaia Svetlana
  Combustion and Flame, Elsevier, 2017, 176, pp.272284. The initiation of combustion of lean H2 :air mixtures, ER = 0.50.6 , by nanosecond surface dielectric bar- rier discharge (nSDBD) was studied experimentally at high initial pressures, P=36 bar. The discharge was studied in different gas mixtures for the pressure range 112 bar. The ignition was initiated by two different discharge modes: streamer or filamentary nSDBD. The influence of the discharge structure and energy deposition on the ignition was demonstrated. Three regimes of multi-point ignition were observed: ignition with a few kernels, quasi-uniform ignition along the edge of the high voltage electrode and ignition along the plasma channels. The velocities of flame propagation were analyzed. The minimum ignition energy of the discharge and ignition delay time of combustion have been measured and analyzed with the help of kinetic numerical modeling. (10.1016/j.combustflame.2016.07.035)
  DOI : 10.1016/j.combustflame.2016.07.035
• MMS Observation of Magnetic Reconnection in the Turbulent Magnetosheath
  
  • Vörös Z.
  • Yordanova E.
  • Varsani A.
  • Genestreti K. J.
  • Khotyaintsev Y. V.
  • Li W.
  • Graham D. B.
  • Norgren C.
  • Nakamura R.
  • Narita Y.
  • Plaschke F.
  • Magnes W.
  • Baumjohann W.
  • Fischer D.
  • Vaivads A.
  • Eriksson E.
  • Lindqvist P.-A.
  • Marklund G.
  • Ergun R. E.
  • Leitner M.
  • Leubner M. P.
  • Strangeway R. J.
  • Le Contel Olivier
  • Pollock C.
  • Giles B. J.
  • Torbert R. B.
  • Burch J. L.
  • Avanov L. A.
  • Dorelli J. C.
  • Gershman D. J.
  • Paterson W. R.
  • Lavraud B.
  • Saito Y.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2017, 122 (11), pp.442-467. In this paper we use the full armament of the MMS (Magnetospheric Multiscale) spacecraft to study magnetic reconnection in the turbulent magnetosheath downstream of a quasi-parallel bow shock. Contrarily to the magnetopause and magnetotail cases, only a few observations of reconnection in the magnetosheath have been reported. The case study in this paper presents, for the first time, both fluid-scale and kinetic-scale signatures of an ongoing reconnection in the turbulent magnetosheath. The spacecraft are crossing the reconnection inflow and outflow regions and the ion diffusion region (IDR). Inside the reconnection outflows D shape ion distributions are observed. Inside the IDR mixing of ion populations, crescent-like velocity distributions and ion accelerations are observed. One of the spacecraft skims the outer region of the electron diffusion region, where parallel electric fields, energy dissipation/conversion, electron pressure tensor agyrotropy, electron temperature anisotropy, and electron accelerations are observed. Some of the difficulties of the observations of magnetic reconnection in turbulent plasma are also outlined. (10.1002/2017JA024535)
  DOI : 10.1002/2017JA024535
• Magnetospheric Multiscale Observations of Electron Vortex Magnetic Hole in the Turbulent Magnetosheath Plasma
  
  • Huang S. Y.
  • Sahraoui Fouad
  • Yuan Z. G.
  • He J. S.
  • Zhao J. S.
  • Le Contel Olivier
  • Deng X. H.
  • Zhou M.
  • Fu H.S.
  • Shi Q. Q.
  • Lavraud B.
  • Pang Y.
  • Yang J.
  • Wang D. D.
  • Li H. M.
  • Yu X. D.
  • Pollock C. J.
  • Giles B. L.
  • Torbert R. B.
  • Russell C. T.
  • Goodrich K. A.
  • Gershman D. J.
  • Moore T. E.
  • Ergun R. E.
  • Khotyaintsev Y. V.
  • Lindqvist P.-A.
  • Strangeway R. J.
  • Magnes W.
  • Bromund K.
  • Leinweber H.
  • Plaschke F.
  • Anderson B. J.
  • Burch J. L.
  The Astrophysical Journal Letters, Bristol : IOP Publishing, 2017, 836 (2), pp.L27. We report on the observations of an electron vortex magnetic hole corresponding to a new type of coherent structure in the turbulent magnetosheath plasma using the Magnetospheric Multiscale mission data. The magnetic hole is characterized by a magnetic depression, a density peak, a total electron temperature increase (with a parallel temperature decrease but a perpendicular temperature increase), and strong currents carried by the electrons. The current has a dip in the core region and a peak in the outer region of the magnetic hole. The estimated size of the magnetic hole is about 0.23 rho <SUB>i</SUB> (~30 rho <SUB>e</SUB>) in the quasi-circular cross-section perpendicular to its axis, where rho <SUB>i</SUB> and rho <SUB>e</SUB> are respectively the proton and electron gyroradius. There are no clear enhancements seen in high-energy electron fluxes. However, there is an enhancement in the perpendicular electron fluxes at 90° pitch angle inside the magnetic hole, implying that the electrons are trapped within it. The variations of the electron velocity components V <SUB>em</SUB> and V <SUB>en</SUB> suggest that an electron vortex is formed by trapping electrons inside the magnetic hole in the cross-section in the M−N plane. These observations demonstrate the existence of a new type of coherent structures behaving as an electron vortex magnetic hole in turbulent space plasmas as predicted by recent kinetic simulations. (10.3847/2041-8213/aa5f50)
  DOI : 10.3847/2041-8213/aa5f50
• E x B staircases and barrier permeability in magnetised plasmas
  
  • Hornung G.
  • Dif-Pradalier Guilhem
  • Clairet F.
  • Sarazin Y.
  • Sabot R.
  • Hennequin Pascale
  • Verdoolaege G.
  Nuclear Fusion, IOP Publishing, 2017, 57 (1), pp.014006. In-depth experimental characterisation of spontaneous shear flow patterning into a so-called ##IMG## [http://ej.iop.org/images/0029-5515/57/1/014006/nfaa42aaieqn003.gif] \mathbfE× \mathbfB staircase?named after its planetary analogue?is shown in magnetised plasma turbulence, using ultrafast-sweeping reflectometry in the Tore Supra tokamak. Staircase signatures are found in a large variety of L-mode plasma conditions. Sensitivity to the dominant source of free energy is highlighted for the first time. A connection between staircase shear layer permeability and deviation from gyro-Bohm confinement scaling is strongly suggested, opening new routes to understanding confinement in drift-wave turbulence. (10.1088/0029-5515/57/1/014006)
  DOI : 10.1088/0029-5515/57/1/014006