Publications

2017

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
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
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
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
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
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
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
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.
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 (Ex) and east–west (Ey) 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 Ex = 520 mV km−1 and Ey = 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 Ex = 550 mV km−1 and Ey = 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
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
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
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
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
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
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
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
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
Measurements of density fluctuations in magnetic confined plasmas using Doppler backscattering technique
- Vermare Laure
- Hennequin Pascale
- Honoré Cyrille
- Pisarev V.
- Giacalone J-C.
, 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
Interplanetary coronal mass ejection observed at STEREO-A, Mars, comet 67P/Churyumov-Gerasimenko, Saturn, and New Horizons en-route to Pluto. Comparison of its Forbush decreases at 1.4, 3.1 and 9.9 AU
- Witasse O.
- Sánchez-Cano B.
- Mays M.
- Kajdič P.
- Opgenoorth H.
- Elliott H.
- Richardson G.
- Zouganelis I.
- Zender J.
- Wimmer-Schweingruber R.
- Turc Lucile
- Taylor M.
- Roussos E.
- Rouillard A.
- Richter I.
- Richardson J.
- Ramstad R.
- Provan G.
- Posner A.
- Plaut J.
- Odstrcil D.
- Nilsson H.
- Niemenen P.
- Milan S.
- Mandt K.
- Lohf H.
- Lester M.
- Lebreton Jean-Pierre
- Kuulkers E.
- Krupp N.
- Koenders C.
- James M.
- Intzekara D.
- Holmstrom M.
- Hassler M.
- Hall S.
- Guo J.
- Goldstein R.
- Goetz C.
- Glassmeier H.
- Génot V.
- Evans H.
- Espley J.
- Edberg N.
- Dougherty M.
- Cowley S.
- Burch J.
- Behar E.
- Barabash S.
- Andrews D. J.
- Altobelli N.
Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2017, Accepted Manuscript (8), pp.64 pages. We discuss observations of the journey throughout the Solar System of a large interplanetary coronal mass ejection (ICME) that was ejected at the Sun on 14 October 2014. The ICME hit Mars on 17 October, as observed by the Mars Express, MAVEN, Mars Odyssey and MSL missions, 44 hours before the encounter of the planet with the Siding-Spring comet, for which the space weather context is provided. It reached comet 67P/Churyumov-Gerasimenko, which was perfectly aligned with the Sun and Mars at 3.1 AU, as observed by Rosetta on 22 October. The ICME was also detected by STEREO-A on 16 October at 1 AU, and by Cassini in the solar wind around Saturn on the 12 November at 9.9 AU. Fortuitously, the New Horizons spacecraft was also aligned with the direction of the ICME at 31.6 AU. We investigate whether this ICME has a non-ambiguous signature at New Horizons. A potential detection of this ICME by Voyager-2 at 110-111 AU is also discussed. The multi-spacecraft observations allow the derivation of certain properties of the ICME, such as its large angular extension of at least 116°, its speed as a function of distance, and its magnetic field structure at four locations from 1 to 10 AU. Observations of the speed data allow two different solar wind propagation models to be validated. Finally, we compare the Forbush decreases (transient decreases followed by gradual recoveries in the galactic cosmic ray intensity) due to the passage of this ICME at Mars, comet 67P and Saturn. (10.1002/2017JA023884)
DOI : 10.1002/2017JA023884
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
Nested Polyhedra Models for turbulence
- Gürcan Özgür D.
, 2017.
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

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