Publications

2017

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
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
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
Multipoint Observations of Energetic Particle Injections and Substorm Activity During a Conjunction Between Magnetospheric Multiscale (MMS) and Van Allen Probes
- Turner D. L.
- Fennell J. F.
- Blake J. B.
- Claudepierre S. G.
- Clemmons J. H.
- Jaynes A. N.
- Leonard T.
- Baker D. N.
- Cohen I. J.
- Gkioulidou M.
- Ukhorskiy A. Y.
- Mauk B. H.
- Gabrielse C.
- Angelopoulos V.
- Strangeway R. J.
- Kletzing C. A.
- Le Contel Olivier
- Spence H. E.
- Torbert R. B.
- Burch J. L.
- Reeves G. D.
Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2017, 122 (11), pp.481-504. This study examines multipoint observations during a conjunction between Magnetospheric Multiscale (MMS) and Van Allen Probes on 7 April 2016 in which a series of energetic particle injections occurred. With complementary data from Time History of Events and Macroscale Interactions during Substorms, Geotail, and Los Alamos National Laboratory spacecraft in geosynchronous orbit (16 spacecraft in total), we develop new insights on the nature of energetic particle injections associated with substorm activity. Despite this case involving only weak substorm activity (maximum AE <300 nT) during quiet geomagnetic conditions in steady, below-average solar wind, a complex series of at least six different electron injections was observed throughout the system. Intriguingly, only one corresponding ion injection was clearly observed. All ion and electron injections were observed at <600 keV only. MMS reveals detailed substructure within the largest electron injection. A relationship between injected electrons with energy <60 keV and enhanced whistler mode chorus wave activity is also established from Van Allen Probes and MMS. Drift mapping using a simplified magnetic field model provides estimates of the dispersionless injection boundary locations as a function of universal time, magnetic local time, and L shell. The analysis reveals that at least five electron injections, which were localized in magnetic local time, preceded a larger injection of both electrons and ions across nearly the entire nightside of the magnetosphere near geosynchronous orbit. The larger ion and electron injection did not penetrate to L < 6.6, but several of the smaller electron injections penetrated to L < 6.6. Due to the discrepancy between the number, penetration depth, and complexity of electron versus ion injections, this event presents challenges to the current conceptual models of energetic particle injections. (10.1002/2017JA024554)
DOI : 10.1002/2017JA024554
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 B0. 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∥ symmetry breaking for their survival which can be supplied by various means like mean E × 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
Space Weather, from the Sun to the Earth, the key role of GNSS. Part II: Training on daily Global Positioning System (GPS) data
- Amory-Mazaudier Christine
- Fleury Rolland
- Gadimova Sharafat
- Touzani Abderrahmane
Coordinates, 2017, 13 (3), pp.31-36. The goal of this paper is to give a clear view of the Sun Earth relationships that are complex. The phenomena acting at large scales and essentially related to dynamic and electromagnetic physical processes have been addressed. Besides physics, the work done to develop the training in Space Weather by focusing on Global Navigation Satellite Systems has also been presented. Readers may recall that we published the first part of this article which focused on physics of the relationships Sun, Earth and Meteorology of Space. In this issue, aspects of GNSS training and capacity building are discussed.
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
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 ce, where Omega ce 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 Bz because of its importance for geoeffectivity. Although the sign of Bz is generally preserved in the magnetosheath, we also find evidence of long-lasting intervals of opposite Bz signs in the solar wind and the magnetosheath during some events, with a |Bz| 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 By. In those cases, the estimated position of the regions of antiparallel fields along the magnetopause is independent of the sign of the upstream Bz. 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
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||). 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|| 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 E were present in the night-side magnetosphere. This global dipolarization consisted of multiple short-timescale (a couple of minutes) B z 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 H2: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 i (~30 rho e) in the quasi-circular cross-section perpendicular to its axis, where rho i and rho e 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 em and V en 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
Global structure and sodium ion dynamics in Mercury's magnetosphere with the offset dipole
- Yagi Manabu
- Seki Kanako
- Matsumoto Y.
- Delcourt Dominique C.
- Leblanc François
Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2017, 122 (11), pp.10,990–11,002. We conducted global magnetohydrodynamics (MHD) simulation of Mercury's magnetosphere with the dipole offset, which was revealed by MESSENGER observations, in order to investigate its global structure under northward interplanetary magnetic field (IMF) conditions. Sodium ion dynamics originating from the Mercury's exosphere is also investigated based on statistical trajectory tracing in the electric and magnetic fields obtained from the MHD simulations. The results reveal a north-south asymmetry characterized by open field lines around southern polar region, and northward deflection of the plasma sheet in the far tail. The asymmetry of magnetic field structure near the planet drastically affects trajectories of sodium ion, and thus, their pressure distributions and precipitation pattern onto the planet. Weaker magnetic field strength in the southern hemisphere than in the north increases ion loss by precipitation onto the planetary surface in the southern hemisphere. The ‘sodium ring', which is formed by high-energy sodium ions drifting around the planet, is also found in the vicinity of the planet. The 'sodium ring' is almost circular under nominal solar wind conditions. The ring becomes partial under high solar wind density, because dayside magnetosphere is so compressed that there is no space for the sodium ions to drift around. In both cases, the 'sodium ring' is formed by sodium ions that are picked up and accelerated in the magnetosheath just outside the magnetopause and reentered into the magnetosphere due to combined effects of finite Larmor radius and convection electric field in the dawn-side magnetosphere. (10.1002/2017JA024082)
DOI : 10.1002/2017JA024082

Retour aux années