Publications

2017

• Vibrational kinetics of non-equilibrium CO<SUB>2</SUB> plasma discharge in low-excitation regime
  
  • Grofulovic Marija
  • Silva Tiago
  • Guerra V.
  • Pintassilgo C.D.
  • Klarenaar Bart
  • Engeln Richard
  • Morillo-Candas Ana-Sofia
  • Guaitella Olivier
  , 2017, 62.
• QDB: a new database of plasma chemistries and reactions
  
  • Tennyson Jonathan
  • Rahimi Sara
  • Hill Christian
  • Tse Lisa
  • Vibhakar Anuradha
  • Akello-Egwel Dolica
  • Brown Daniel B
  • Dzarasova Anna
  • Hamilton James R
  • Jaksch Dagmar
  • Mohr Sebastian
  • Wren-Little Keir
  • Bruckmeier Johannes
  • Agarwal Ankur
  • Bartschat Klaus
  • Annemie Bogaerts Annemie
  • Booth Jean-Paul
  • Goeckner Matthew J
  • Hassouni Khaled
  • Itikawa Yukikazu
  • Braams Bastiaan J
  • Krishnakumar E.
  • Laricchiuta Annarita
  • Mason Nigel J
  • Pandey Sumeet
  • Petrovic Zoran Lj
  • Pu Yi-Kang
  • Ranjan Alok
  • Rauf S.
  • Schulze J.
  • Turner M.M.
  • Ventzek Peter
  • Whitehead J.C.
  • Yoon Jung-Sik
  Plasma Sources Science and Technology, IOP Publishing, 2017, 26 (5), pp.055014. One of the most challenging and recurring problems when modeling plasmas is the lack of data on the key atomic and molecular reactions that drive plasma processes. Even when there are data for some reactions, complete and validated datasets of chemistries are rarely available. This hinders research on plasma processes and curbs development of industrial applications. The QDB project aims to address this problem by providing a platform for provision, exchange, and validation of chemistry datasets. A new data model developed for QDB is presented. QDB collates published data on both electron scattering and heavy-particle reactions. These data are formed into reaction sets, which are then validated against experimental data where possible. This process produces both complete chemistry sets and identifies key reactions that are currently unreported in the literature. Gaps in the datasets can be filled using established theoretical methods. Initial validated chemistry sets for SF 6 /CF 4 /O 2 and SF 6 /CF 4 /N 2 /H 2 are presented as examples. (10.1088/1361-6595/aa6669)
  DOI : 10.1088/1361-6595/aa6669
• Promoting lentil germination and stem growth by plasma activated tap water, demineralized water and liquid fertilizer
  
  • Zhang Shiqiang
  • Rousseau Antoine
  • Dufour Thierry
  RSC Advances, Royal Society of Chemistry, 2017, 7 (50), pp.31244–31251. Tap water, demineralized water and liquid fertilizer have been activated using an atmospheric pressure plasma jet (APPJ) to investigate their benefits for the germination rate and stem elongation rate of lentils from Puy-en-Velay (France). By plasma-activating tap water, we have obtained germination rates as high as 80% (instead of 30% with tap water). Also, higher stem elongation rates and final stem lengths were obtained using activated tap water compared with commercial fertilizer. We show that these rates of germination and stem growth strongly depend on the combination of two radicals generated in the liquids by the plasma: hydrogen peroxide and nitrate. This synergy appears to be a condition for releasing seed dormancy through the endogenous production of NO radicals. (10.1039/C7RA04663D)
  DOI : 10.1039/C7RA04663D
• Stable and unstable roots of ion temperature gradient driven mode using curvature modified plasma dispersion functions
  
  • Gultekin Ozgur
  • Gürcan Özgür D.
  Plasma Physics and Controlled Fusion, IOP Publishing, 2017, 60 (2), pp.025021. Basic, local kinetic theory of ion temperature gradient driven (ITG) mode, with adiabatic electrons is reconsidered. Standard unstable, purely oscillating as well as damped solutions of the local dispersion relation are obtained using a bracketing technique that uses the argument principle. This method requires computing the plasma dielectric function and its derivatives, which are implemented here using modified plasma dispersion functions with curvature and their derivatives, and allows bracketing/following the zeros of the plasma dielectric function which corresponds to different roots of the ITG dispersion relation. We provide an open source implementation of the derivatives of modified plasma dispersion functions with curvature, which are used in this formulation. Studying the local ITG dispersion, we find that near the threshold of instability the unstable branch is rather asymmetric with oscillating solutions towards lower wave numbers (i.e. drift waves), and damped solutions toward higher wave numbers. This suggests a process akin to inverse cascade by coupling to the oscillating branch towards lower wave numbers may play a role in the nonlinear evolution of the ITG, near the instability threshold. Also, using the algorithm, the linear wave diffusion is estimated for the marginally stable ITG mode. (10.1088/1361-6587/aa9e27)
  DOI : 10.1088/1361-6587/aa9e27
• Capacitively coupled hydrogen plasmas sustained by tailored voltage waveforms: vibrational kinetics and negative ions control
  
  • Diomede P.
  • Bruneau Bastien
  • Longo S.
  • Johnson E.V.
  • Booth Jean-Paul
  Plasma Sources Science and Technology, IOP Publishing, 2017, 26 (7), pp.075007. A comprehensive hybrid model of a hydrogen capacitively coupled plasma, including a detailed description of the molecular vibrational kinetics, has been applied to the study of the effect of tailored voltage waveforms (TVWs) on the production kinetics and transport of negative ions in these discharges. Two kinds of TVWs are considered, valleys-to-peaks and saw-tooth, with amplitude and slope asymmetry respectively. By tailoring the voltage waveform only, it is possible to exert substantial control over the peak density and position of negative ions inside the discharge volume. This control is particularly effective for saw-tooth waveforms. Insight into the mechanisms allowing this control is provided by an analysis of the model results. This reveals the roles of the vibrational distribution function and of the electron energy distribution and their correlations, as well as changes in the negative ion transport in the electric field when using different TVWs. Considering the chemical reactivity of H ? ions, the possibility of a purely electrical control of the negative ion cloud in a reactor operating with a feedstock gas diluted by hydrogen may find interesting applications. This is the first study of vibrational kinetics in the context of TVWs in molecular gases. (10.1088/1361-6595/aa752c)
  DOI : 10.1088/1361-6595/aa752c
• Turbulence of Weak Gravitational Waves in the Early Universe
  
  • Galtier Sébastien
  • Nazarenko Sergey V.
  Physical Review Letters, American Physical Society, 2017, 119 (22), pp.221101. We study the statistical properties of an ensemble of weak gravitational waves interacting nonlinearly in a flat space-time. We show that the resonant three-wave interactions are absent and develop a theory for four-wave interactions in the reduced case of a 2.5+1 diagonal metric tensor. In this limit, where only plus-polarized gravitational waves are present, we derive the interaction Hamiltonian and consider the asymptotic regime of weak gravitational wave turbulence. Both direct and inverse cascades are found for the energy and the wave action, respectively, and the corresponding wave spectra are derived. The inverse cascade is characterized by a finite-time propagation of the metric excitations—a process similar to an explosive nonequilibrium Bose–Einstein condensation, which provides an efficient mechanism to ironing out small-scale inhomogeneities. The direct cascade leads to an accumulation of the radiation energy in the system. These processes might be important for understanding the early Universe where a background of weak nonlinear gravitational waves is expected. (10.1103/PhysRevLett.119.221101)
  DOI : 10.1103/PhysRevLett.119.221101
• Interplay between Alfvén and magnetosonic waves in compressible magnetohydrodynamics turbulence
  
  • Andrés Nahuel
  • Leoni P. Clark Di
  • Mininni P. D.
  • Dmitruk P.
  • Sahraoui Fouad
  • Matthaeus W. H.
  Physics of Plasmas, American Institute of Physics, 2017, 24, pp.102314. Using spatio-temporal spectra, we show direct evidence of excitation of magnetosonic and Alfvén waves in three-dimensional compressible magnetohydrodynamic turbulence at small Mach numbers. For the plasma pressure dominated regime, or the high beta regime (with beta the ratio between fluid and magnetic pressure), and for the magnetic pressure dominated regime, or the low beta regime, we study magnetic field fluctuations parallel and perpendicular to a guide magnetic field B<SUB>0</SUB>. In the low beta case, we find excitation of compressible and incompressible fluctuations, with a transfer of energy towards Alfvénic modes and to a lesser extent towards magnetosonic modes. In particular, we find signatures of the presence of fast magnetosonic waves in a scenario compatible with that of weak turbulence. In the high beta case, fast and slow magnetosonic waves are present, with no clear trace of Alfvén waves, and a significant part of the energy is carried by two-dimensional turbulent eddies. (10.1063/1.4997990)
  DOI : 10.1063/1.4997990
• Intrinsic non-inductive current driven by ETG turbulence in tokamaks
  
  • Kaw P. K.
  • Singh R.
  • Gürcan Özgür D.
  Physics of Plasmas, American Institute of Physics, 2017, 24, pp.102303. Motivated by observations and physics understanding of the phenomenon of intrinsic rotation, it is suggested that similar considerations for electron dynamics may result in intrinsic current in tokamaks. We have investigated the possibility of intrinsic non-inductive current in the turbulent plasma of tokamaks. Ohm's law is generalized to include the effect of turbulent fluctuations in the mean field approach. This clearly leads to the identification of sources and the mechanisms of non-inductive current drive by electron temperature gradient turbulence. It is found that a mean parallel electro-motive force and hence a mean parallel current can be generated by (1) the divergence of residual current flux density and (2) a non-flux like turbulent source from the density and parallel electric field correlations. Both residual flux and the non-flux source require parallel wave-number k&#8741; symmetry breaking for their survival which can be supplied by various means like mean E&#8201;×&#8201;B shear, turbulence intensity gradient, etc. Estimates of turbulence driven current are compared with the background bootstrap current in the pedestal region. It is found that turbulence driven current is nearly 10% of the bootstrap current and hence can have a significant influence on the equilibrium current density profiles and current shear driven modes. (10.1063/1.4990746)
  DOI : 10.1063/1.4990746
• 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
• 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.
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• 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