Publications

2017

• Measurements of density fluctuations in magnetic confined plasmas using Doppler backscattering technique
  
  • Vermare Laure
  • Hennequin Pascale
  • Honoré Cyrille
  • Pisarev V.
  • Giacalone J-C.
  , 2017.
• Induction effects of geomagnetic disturbances in the geo-electric field variations at low latitudes
  
  • Doumbia Vafi
  • Boka Kouadio
  • Kouassi Nguessan
  • Grodji Oswald Didier Franck
  • Amory-Mazaudier Christine
  • Menvielle Michel
  Annales Geophysicae, European Geosciences Union, 2017, 35 (1), pp.39 - 51. In this study we examined the influences of geomagnetic activity on the Earth surface electric field variations at low latitudes. During the International Equatorial Electrojet Year (IEEY) various experiments were performed along 5° W in West Africa from 1992 to 1995. Among other instruments, 10 stations equipped with magnetometers and telluric electric field lines operated along a meridian chain across the geomagnetic dip equator from November 1992 to December 1994. In the present work, the induced effects of space-weather-related geomagnetic disturbances in the equatorial electrojet (EEJ) influence area in West Africa were examined. For that purpose, variations in the north–south (E_x) and east–west (E_y) components of telluric electric field were analyzed, along with that of the three components (H, D and Z) of the geomagnetic field during the geomagnetic storm of 17 February 1993 and the solar flare observed on 4 April 1993. The most important induction effects during these events are associated with brisk impulses like storm sudden commencement (ssc) and solar flare effect (sfe) in the geomagnetic field variations. For the moderate geomagnetic storm that occurred on 17 February 1993, with a minimum Dst index of −110 nT, the geo-electric field responses to the impulse around 11:00 LT at LAM are E_x= 520 mV km⁻¹ and E_y = 400 mV km⁻¹. The geo-electric field responses to the sfe that occurred around 14:30 LT on 4 April 1993 are clearly observed at different stations as well. At LAM the crest-to-crest amplitude of the geo-electric field components associated with the sfe are E_x = 550 mV km⁻¹ and E_y = 340 mV km⁻¹. Note that the sfe impact on the geo-electric field variations decreases with the increasing distance of the stations from the subsolar point, which is located at about 5.13° N on 4 April. This trend does not reflect the sfe increasing amplitude near the dip equator due the high Cowling conductivity in the EEJ belt. (10.5194/angeo-35-39-2017)
  DOI : 10.5194/angeo-35-39-2017
• Nested polyhedra model of turbulence
  
  • Gürcan Özgür D.
  Physical Review E, American Physical Society (APS), 2017, 95 (6), pp.063102. A discretization of the wave-number space is proposed, using nested polyhedra, in the form of alternating dodecahedra and icosahedra that are self-similarly scaled. This particular choice allows the possibility of forming triangles using only discretized wave vectors when the scaling between two consecutive dodecahedra is equal to the golden ratio and the icosahedron between the two dodecahedra is the dual of the inner dodecahedron. Alternatively, the same discretization can be described as a logarithmically spaced (with a scaling equal to the golden ratio), nested dodecahedron-icosahedron compounds. A wave vector which points from the origin to a vertex of such a mesh, can always find two other discretized wave vectors that are also on the vertices of the mesh (which is not true for an arbitrary mesh). Thus, the nested polyhedra grid can be thought of as a reduction (or decimation) of the Fourier space using a particular set of self-similar triads arranged approximately in a spherical form. For each vertex (i.e., discretized wave vector) in this space, there are either 9 or 15 pairs of vertices (i.e., wave vectors) with which the initial vertex can interact to form a triangle. This allows the reduction of the convolution integral in the Navier-Stokes equation to a sum over 9 or 15 interaction pairs, transforming the equation in Fourier space to a network of " interacting " nodes that can be constructed as a numerical model, which evolves each component of the velocity vector on each node of the network. This model gives the usual Kolmogorov spectrum of k −5/3. Since the scaling is logarithmic, and the number of nodes for each scale is constant, a very large inertial range (i.e., a very high Reynolds number) with a much lower number of degrees of freedom can be considered. Incidentally, by assuming isotropy and a certain relation between the phases, the model can be used to systematically derive shell models. (10.1103/PhysRevE.95.063102)
  DOI : 10.1103/PhysRevE.95.063102
• Hemispheric asymmetries in the ionosphere response observed during the high-speed solar wind streams of the 24-28 August 2010
  
  • Zaourar N.
  • Amory-Mazaudier Christine
  • Fleury Rolland
  Advances in Space Research, Elsevier, 2017. This paper presents the geomagnetic and ionospheric responses to a high speed solar wind stream (HSS) impacting the magnetosphere on 24 August 2010. We focus our study on the interhemispheric conjugated behavior. The solar wind speed remained very high during 5 days from 24 to 28 August 2010. By using magnetometer and ground-based GPS data from various approximately conjugated magnetic observatories and GPS stations, we studied the hemispheric asymmetries in the magnetic signature, Vertical Total Electron Content (VTEC) and scintillation activity during this HSS event. Geomagnetic activity reveals larger disturbances in amplitude in the Northern Hemisphere (NH) than in the southern Hemisphere (SH), and stronger asymmetries at higher latitudes, than at lower latitudes, between the conjugate observatories. VTEC variations reveal large increases in amplitude in the NH; while these effects are less pronounced in the SH. We investigate also the GPS scintillation activities occurring in the conjugated polar regions under HSSs conditions. At auroral latitudes, our results show a good correlation between the rate of VTEC index (ROTI) and auroral Al index, with more intense phase fluctuations in the NH. (10.1016/j.asr.2017.01.048)
  DOI : 10.1016/j.asr.2017.01.048
• Saturation of energetic-particle-driven geodesic acoustic modes due to wave–particle nonlinearity
  
  • Biancalani A.
  • Chavdarovski I.
  • Qiu Z.
  • Bottino A.
  • Sarto D. Del
  • Ghizzo A.
  • Gürcan Özgür D.
  • Morel Pierre
  • Novikau I.
  Journal of Plasma Physics, Cambridge University Press (CUP), 2017, 83 (6), pp.725830602. The nonlinear dynamics of energetic-particle (EP) driven geodesic acoustic modes (EGAM) is investigated here. A numerical analysis with the global gyrokinetic particle-in-cell code ORB5 is performed, and the results are interpreted with the analytical theory, in close comparison with the theory of the beam-plasma instability. Only axisymmetric modes are considered, with a nonlinear dynamics determined by wave-particle interaction. Quadratic scalings of the saturated electric field with respect to the linear growth rate are found for the case of interest. As a main result, the formula for the saturation level is provided. Near the saturation, we observe a transition from adiabatic to non-adiabatic dynamics, i.e., the frequency chirping rate becomes comparable to the resonant EP bounce frequency. The numerical analysis is performed here with electrostatic simulations with circular flux surfaces, and kinetic effects of the electrons are neglected. (10.1017/S0022377817000976)
  DOI : 10.1017/S0022377817000976
• 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
• 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
• 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
• 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
• 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
• Advanced Ion Mass Spectrometer for Giant Planet Ionosphere, Magnetospheres and Moons
  
  • Sittler E.C.
  • Cooper J.F.
  • Paschalidis N.
  • Jones S.
  • Brinkerhoff William
  • Paterson W. R.
  • Ali Ashraf
  • Coplan M.A.
  • Chornay D.
  • Sturners S.J.
  • Benna Mehdi
  • Bateman F.B.
  • Fontaine Dominique
  • Verdeil Christophe
  • Andre N.
  • Blanc Michel
  • Wurz Peter
  , 2017, pp.T1.023. We present our Advanced Ion Mass Spectrometer (AIMS) for outer planet missions which has been under development from various NASA sources (NASA Living with a Star Instrument Development (LWSID), NASA Astrobiology Instrument Development (ASTID), NASA Goddard Internal Research and Development (IRAD)s) to measure elemental, isotopic, and simple molecular composition abundances of 1 V to 25 kV hot ions with wide field-of-view (FOV) in the 1 - 60 amu mass range at mass resolution M/ DeltaM <= 60 over a wide dynamic range of particle intensities and penetrating radiation background from the inner magnetospheres of Jupiter and Saturn to the outer magnetospheric boundary regions and the upstream solar wind. This instrument will work for both spinning spacecraft and 3-axis stabilized spacecraft. AIMS will measure the ion velocity distribution functions (VDF) for the individual ion species from which velocity moments will give their ion density, flow velocity and temperature.
• 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
• 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
• 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
• Dynamic probing of plasma-catalytic surface processes: Oxidation of toluene on CeO₂
  
  • Jia Zixian
  • Wang Xianjie
  • Thevenet Frederic
  • Rousseau Antoine
  Plasma Processes and Polymers, Wiley-VCH Verlag, 2017. This article reports the use of innovative diagnostics to monitor toluene adsorption and oxidation on CeO2 surface under non-thermal plasma (NTP) exposure. Two plasma-catalytic configurations are explored, namely: post-plasma catalysis (PPC) and in-plasma catalysis (IPC). Since heterogeneous processes are pointed out as key steps of the plasma-catalyst coupling, the catalyst surface has been monitored by two complementary in situ diagnostics: (i) diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) and (ii) transmission fourier transform infrared spectroscopy using Sorbent track (ST) device. Dielectric barrier discharges (DBD) are used in both PPC and IPC configurations to induce adsorbed toluene oxidation. Toluene in dry air is first adsorbed on the selected catalytic surface: ceria (CeO2). Subsequently, the plasma is switched on. During the experiment, the ceria surface is monitored by infrared to study toluene adsorption and oxidation mechanisms. The adsorption capacity of toluene on ceria is, respectively, measured in the configurations of PPC and IPC by DRIFTS and ST. The oxidation of toluene by plasma follows a first-order reaction regardless of plasma configuration and injected power and IPC is more effective for the toluene removal than PPC. Intermediates of toluene (benzyl alcohol, benzaldehyde and benzoic acid) are also identified on the surface and their respective temporal evolutions as a function of the plasma exposure are studied.ppap201600114-gra-0001 (10.1002/ppap.201600114)
  DOI : 10.1002/ppap.201600114
• Kinetic simulation of asymmetric magnetic reconnection with cold ions
  
  • Dargent Jérémy
  • Aunai Nicolas
  • Lavraud B.
  • Toledo-Redondo Sergio
  • Shay M. A.
  • Cassak P. A.
  • Malakit K.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2017, 122 (5), pp.5290-5306. At the dayside magnetopause, the magnetosphere often contains a cold ion population of ionospheric origin. This population is not always detectable by particle instruments due to its low energy, despite having an important contribution to the total ion density and therefore an impact on key plasma processes such as magnetic reconnection. The exact role and implications of this low-temperature population are still not well known and has not been addressed with numerical simulation before. We present 2-D fully kinetic simulations of asymmetric magnetic reconnection with and without a cold ion population on the magnetospheric side of the magnetopause, but sharing the same total density, temperature, and magnetic field profiles. The comparison of the simulations suggests that cold ions directly impact signatures recently suggested as a good marker of the X line region: the Larmor electric field. Our simulations reveal that this electric field, initially present all along the magnetospheric separatrix, is related to the bounce of magnetosheath ions at the magnetopause magnetic field reversal through Speiser-like orbits. Once reconnection widens the current sheet away from the X line, the bouncing stops and the electric field signature remains solely confined near the X line. When cold ions are present, however, their very low temperature enables them to E × B drift in the electric field structure. If their density is large enough compared to other ions, their contribution to the momentum equation is capable of maintaining the signature away from the X line. This effect must be taken into account when analyzing in situ spacecraft measurements. (10.1002/2016JA023831)
  DOI : 10.1002/2016JA023831
• Nested Polyhedra Models for turbulence
  
  • Gürcan Özgür D.
  , 2017.
• An alternative formulation for exact scaling relations in hydrodynamic and magnetohydrodynamic turbulence
  
  • Banerjee Supratik
  • Galtier Sébastien
  Journal of Physics A: Mathematical and General (1975 - 2006), IOP Publishing, 2017, 50, pp.015501. We propose an alternative formulation for the exact relations in three-dimensional homogeneous turbulence using two-point statistics. Our finding is illustrated with incompressible hydrodynamic, standard and Hall magnetohydrodynamic turbulence. In this formulation, the cascade rate of an inviscid invariant of turbulence can be expressed simply in terms of mixed second-order structure functions. Besides the usual variables like the velocity \mathbfu , vorticity \boldsymbolomega , magnetic field \mathbfb and the current \mathbfj , the vectors \mathbfu× \boldsymbolomega , \mathbfu× \mathbfb and \mathbfj× \mathbfb are also found to play a key role in the turbulent cascades. The current methodology offers a simple algebraic form which is specially interesting to study anisotropic space plasmas like the solar wind, with, a faster statistical convergence than the classical laws written in terms of third-order correlators. (10.1088/1751-8113/50/1/015501)
  DOI : 10.1088/1751-8113/50/1/015501
• Nonlinear radiation generation processes in the auroral acceleration region
  
  • Pottelette Raymond
  • Berthomier Matthieu
  Annales Geophysicae, European Geosciences Union, 2017, 35 (6), pp.1241-1248. It is known from laboratory plasma experiments that double layers (DLs) radiate in the electromagnetic spectrum; but this is only known qualitatively. In these experiments, it was shown that the electron beam created on the high-potential side of a DL generates nonlinear structures which couple to electromagnetic waves and act as a sender antenna. In the Earth auroral region, observations performed by auroral spacecraft have shown that DLs occur naturally in the source region of intense radio emissions called auroral kilometric radiation (AKR). Very high time-, spatial-, and temporal-resolution measurements are needed in order to characterize waves and particle distributions in the vicinity of DLs, which are moving transient structures. We report observations from the FAST satellite of a localized large-amplitude parallel electric field ( 300 mV m<SUP>-1</SUP>) recorded at the edges of the auroral density cavity. In agreement with laboratory experiments, on the high-potential side of the DL, elementary radiation events are detected. They occur substantially above the local electron gyrofrequency and are associated with the presence of electron holes. The velocity of these nonlinear structures can be derived from the measurement of the Doppler-shifted AKR frequency spectrum above the electron gyrofrequency. The generated electron holes appear as the nonlinear evolution of electrostatic waves generated by the electron-electron two-stream instability because they propagate at about half the beam velocity. It is pointed out that, in the vicinity of a DL, the shape of the electron distribution gives rise to a significant power recorded in the left-hand polarized ordinary (LO) mode. (10.5194/angeo-35-1241-2017)
  DOI : 10.5194/angeo-35-1241-2017
• Zipper-like periodic magnetosonic waves: Van Allen Probes, THEMIS, and magnetospheric multiscale observations
  
  • Li J.
  • Bortnik J.
  • Li W.
  • Ma Q.
  • Thorne R. M.
  • Kletzing C. A.
  • Kurth W. S.
  • Hospodarsky G. B.
  • Wygant J.
  • Breneman A.
  • Thaller S.
  • Funsten H. O.
  • Mitchell D. G.
  • Manweiler J. W.
  • Torbert R. B.
  • Le Contel Olivier
  • Ergun R. E.
  • Lindqvist P.-A.
  • Torkar Klaus
  • Nakamura R.
  • Andriopoulou M.
  • Russell C. T.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2017, 122 (2), pp.1600-1610. An interesting form of "zipper-like" magnetosonic waves consisting of two bands of interleaved periodic rising-tone spectra was newly observed by the Van Allen Probes, the Time History of Events and Macroscale Interactions during Substorms (THEMIS), and the Magnetospheric Multiscale (MMS) missions. The two discrete bands are distinct in frequency and intensity; however, they maintain the same periodicity which varies in space and time, suggesting that they possibly originate from one single source intrinsically. In one event, the zipper-like magnetosonic waves exhibit the same periodicity as a constant-frequency magnetosonic wave and an electrostatic emission, but the modulation comes from neither density fluctuations nor ULF waves. A statistical survey based on 3.5 years of multisatellite observations shows that zipper-like magnetosonic waves mainly occur on the dawnside to noonside, in a frequency range between 10 f<SUB>cp</SUB> and f<SUB>LHR</SUB>. The zipper-like magnetosonic waves may provide a new clue to nonlinear excitation or modulation process, while its cause still remains to be fully understood. (10.1002/2016JA023536)
  DOI : 10.1002/2016JA023536
• Power coupling mode transitions induced by tailored voltage waveforms in capacitive oxygen discharges
  
  • Derzsi A.
  • Bruneau Bastien
  • Gibson Andrew
  • Johnson Erik
  • O'Connell D.
  • Gans T.
  • Booth Jean-Paul
  • Donko Zoltan
  Plasma Sources Science and Technology, IOP Publishing, 2017, 26 (3), pp.034002. Low-pressure capacitively coupled radio frequency discharges operated in O 2 and driven by tailored voltage waveforms are investigated experimentally and by means of kinetic simulations. Pulse-type (peaks/valleys) and sawtooth-type voltage waveforms that consist of up to four consecutive harmonics of the fundamental frequency are used to study the amplitude asymmetry effect as well as the slope asymmetry effect at different fundamental frequencies (5, 10, and 15 MHz) and at different pressures (50?700 mTorr). Values of the DC self-bias determined experimentally and spatio-temporal excitation rates derived from phase resolved optical emission spectroscopy measurements are compared with particle-in-cell/Monte Carlo collisions simulations. The spatio-temporal distributions of the excitation rate obtained from experiments are well reproduced by the simulations. Transitions of the discharge electron heating mode from the drift-ambipolar mode to the ? -mode are induced by changing the number of consecutive harmonics included in the driving voltage waveform or by changing the gas pressure. Changing the number of harmonics in the waveform has a strong effect on the electronegativity of the discharge, on the generation of the DC self-bias and on the control of ion properties at the electrodes, both for pulse-type, as well as sawtooth-type driving voltage waveforms The effect of the surface quenching rate of oxygen singlet delta metastable molecules on the spatio-temporal excitation patterns is also investigated. (10.1088/1361-6595/aa56d6)
  DOI : 10.1088/1361-6595/aa56d6
• Electron Heating at Kinetic Scales in Magnetosheath Turbulence
  
  • Chasapis A.
  • Matthaeus W. H.
  • Parashar T. N.
  • Le Contel Olivier
  • Retinò Alessandro
  • Breuillard Hugo
  • Khotyaintsev Y. V.
  • Vaivads A.
  • Lavraud B.
  • Eriksson E.
  • Moore T. E.
  • Burch J. L.
  • Torbert R. B.
  • Lindqvist P.-A.
  • Ergun R. E.
  • Marklund G.
  • Goodrich K. A.
  • Wilder F. D.
  • Chutter M.
  • Needell J.
  • Rau D.
  • Dors I.
  • Russell C. T.
  • Le G.
  • Magnes W.
  • Strangeway R. J.
  • Bromund K. R.
  • Leinweber H. K.
  • Plaschke F.
  • Fischer D.
  • Anderson B. J.
  • Pollock C. J.
  • Giles B. L.
  • Paterson W. R.
  • Dorelli J. C.
  • Gershman D. J.
  • Avanov L.
  • Saito Y.
  The Astrophysical Journal, American Astronomical Society, 2017, 836, pp.247. We present a statistical study of coherent structures at kinetic scales, using data from the Magnetospheric Multiscale mission in the Earth's magnetosheath. We implemented the multi-spacecraft partial variance of increments (PVI) technique to detect these structures, which are associated with intermittency at kinetic scales. We examine the properties of the electron heating occurring within such structures. We find that, statistically, structures with a high PVI index are regions of significant electron heating. We also focus on one such structure, a current sheet, which shows some signatures consistent with magnetic reconnection. Strong parallel electron heating coincides with whistler emissions at the edges of the current sheet. (10.3847/1538-4357/836/2/247)
  DOI : 10.3847/1538-4357/836/2/247
• Counter-propagating radiative shock experiments on the Orion laser and the formation of radiative precursors
  
  • Clayson Thomas
  • Suzuki-Vidal Francisco
  • Lebedev S. V.
  • Swadling G. F.
  • Stehlé Chantal
  • Burdiak G. C.
  • Foster J. M.
  • Skidmore J.
  • Graham P.
  • Gumbrell E.
  • Patankar S.
  • Spindloe C.
  • Chaulagain Uddhab
  • Kozlová Michaela
  • Larour Jean
  • Singh Raj Laxmi
  • Rodriguez Perez R.
  • Gil J. M.
  • Espinosa G.
  • Velarde P.
  • Danson C.
  High Energy Density Physics, Elsevier, 2017, 23, pp.60-72. We present results from new experiments to study the dynamics of radiative shocks, reverse shocks and radiative precursors. Laser ablation of a solid piston by the Orion high-power laser at AWE Aldermaston UK was used to drive radiative shocks into a gas cell initially pressurised between 0.1 and 1.0 bar with different noble gases. Shocks propagated at 80 ± 10 km/s and experienced strong radiative cooling resulting in post-shock compressions of × 25 ± 2. A combination of X-ray backlighting, optical self-emission streak imaging and interferometry (multi-frame and streak imaging) were used to simultaneously study both the shock front and the radiative precursor. These experiments present a new configuration to produce counter-propagating radiative shocks, allowing for the study of reverse shocks and providing a unique platform for numerical validation. In addition, the radiative shocks were able to expand freely into a large gas volume without being confined by the walls of the gas cell. This allows for 3-D effects of the shocks to be studied which, in principle, could lead to a more direct comparison to astrophysical phenomena. By maintaining a constant mass density between different gas fills the shocks evolved with similar hydrodynamics but the radiative precursor was found to extend significantly further in higher atomic number gases (∼ 4 times further in xenon than neon). Finally, 1-D and 2-D radiative-hydrodynamic simulations are presented showing good agreement with the experimental data. (10.1016/j.hedp.2017.03.002)
  DOI : 10.1016/j.hedp.2017.03.002
• Electrostatic analyzer with a 3-D instantaneous field of view for fast measurements of plasma distribution functions in space
  
  • Morel Xavier
  • Berthomier Matthieu
  • Berthelier Jean-Jacques
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2017, 122 (3), pp.3397-3410. We describe the concept and properties of a new electrostatic optic which aims to provide a 2π sr instantaneous field-of-view to characterize space plasmas. It consists of a set of concentric toroidal electrodes that form a number of independent energy selective channels. Charged particles are deflected towards a common imaging planar detector. The full 3D distribution function of charged particles is obtained through a single energy sweep. Angle and energy resolution of the optics depends on the number of toroidal electrodes, on their radii of curvature, on their spacing, and on the angular aperture of the channels. We present the performances, as derived from numerical simulations, of an initial implementation of this concept that would fit the need of many space plasma physics applications. The proposed instrument has 192 entrance windows corresponding to 8 polar channels each with 24 azimuthal sectors. The initial version of this 3D plasma analyzer may cover energies from a few eV up to 30 keV, typically with a channel dependent energy resolution varying from 10% to 7%. The angular acceptance varies with the direction of the incident particle from 3° to 12°. With a total geometric factor of two sensor heads reaching ~ 0.23 cm² · sr · eV/eV, this “donut” shape analyzer has enough sensitivity to allow very fast measurements of plasma distribution functions in most terrestrial and planetary environments on three-axis stabilized as well as on spinning satellites. (10.1002/2016JA023596)
  DOI : 10.1002/2016JA023596