Publications

2018

Production of hydrogen negative ions in an ECR volume source: balance between vibrational excitation and ionization
- Aleiferis S.
- Svarnas P.
- Béchu S.
- Tarvainen O.
- Bacal M.
Plasma Sources Science and Technology, IOP Publishing, 2018, 27 (7), pp.075015. The operation of an ECR-driven (2.45 GHz) hydrogen negative ion source is studied. Electron densities and temperatures are investigated with electrostatic probes and negative ion densities are measured with laser photodetachment. Vacuum ultraviolet irradiance measurements are focused on molecular transitions to the ground state while high-resolution visible emission spectroscopy is used to study the transitions between excited states for both molecules and atoms. The standalone operation of the source is found to be more efficient in higher pressures (12 mTorr) where negative ion densities are as high as 4×109 cm−3. Further investigation on the operation of the source reveals a rich vibrational spectrum. On the other hand, a limitation on the production of negative ions which is attributed to a lack of low-energy electrons becomes apparent. The underlying mechanisms that lead to this behavior are discussed along with possible solutions to this issue. Finally, the rates of different negative ion destruction processes are estimated and compared. (10.1088/1361-6595/aabf1b)
DOI : 10.1088/1361-6595/aabf1b
The Properties of Lion Roars and Electron Dynamics in Mirror Mode Waves Observed by the Magnetospheric MultiScale Mission
- Breuillard Hugo
- Le Contel Olivier
- Chust Thomas
- Berthomier Matthieu
- Retinò Alessandro
- Turner D. L.
- Nakamura R.
- Baumjohann W.
- Cozzani Giulia
- Catapano F.
- Alexandrova Alexandra
- Mirioni Laurent
- Graham D. B.
- Argall M. R.
- Fischer D.
- Wilder F. D.
- Gershman D. J.
- Varsani A.
- Lindqvist P.-A.
- Khotyaintsev Y. V.
- Marklund G.
- Ergun R. E.
- Goodrich K. A.
- Ahmadi N.
- Burch J. L.
- Torbert R. B.
- Needell G.
- Chutter M.
- Rau D.
- Dors I.
- Russell C. T.
- Magnes W.
- Strangeway R. J.
- Bromund K. R.
- Wei H.
- Plaschke F.
- Anderson B. J.
- Le G.
- Moore T. E.
- Giles B. L.
- Paterson W. R.
- Pollock C. J.
- Dorelli J. C.
- Avanov L. A.
- Saito Y.
- Lavraud B.
- Fuselier S. A.
- Mauk B. H.
- Cohen I. J.
- Fennell J. F.
Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2018, 123 (1), pp.93-103. Mirror mode waves are ubiquitous in the Earth's magnetosheath, in particular behind the quasi-perpendicular shock. Embedded in these nonlinear structures, intense lion roars are often observed. Lion roars are characterized by whistler wave packets at a frequency 100 Hz, which are thought to be generated in the magnetic field minima. In this study, we make use of the high time resolution instruments on board the Magnetospheric MultiScale mission to investigate these waves and the associated electron dynamics in the quasi-perpendicular magnetosheath on 22 January 2016. We show that despite a core electron parallel anisotropy, lion roars can be generated locally in the range 0.05-0.2fce by the perpendicular anisotropy of electrons in a particular energy range. We also show that intense lion roars can be observed up to higher frequencies due to the sharp nonlinear peaks of the signal, which appear as sharp spikes in the dynamic spectra. As a result, a high sampling rate is needed to estimate correctly their amplitude, and the latter might have been underestimated in previous studies using lower time resolution instruments. We also present for the first-time 3-D high time resolution electron velocity distribution functions in mirror modes. We demonstrate that the dynamics of electrons trapped in the mirror mode structures are consistent with the Kivelson and Southwood (1996) model. However, these electrons can also interact with the embedded lion roars: first signatures of electron quasi-linear pitch angle diffusion and possible signatures of nonlinear interaction with high-amplitude wave packets are presented. These processes can lead to electron untrapping from mirror modes. (10.1002/2017JA024551)
DOI : 10.1002/2017JA024551
Localized Oscillatory Energy Conversion in Magnetopause Reconnection
- Burch J. L.
- Ergun R. E.
- Cassak P. A.
- Webster J. M.
- Torbert R. B.
- Giles B. L.
- Dorelli J. C.
- Rager A. C.
- Hwang K.-J.
- Phan T. D.
- Genestreti K. J.
- Allen R. C.
- Chen L.-J.
- Wang S.
- Gershman D. J.
- Le Contel Olivier
- Russell C. T.
- Strangeway R. J.
- Wilder F. D.
- Graham D. B.
- Hesse Michael
- Drake J. F.
- Swisdak M.
- Price L. M.
- Shay M. A.
- Lindqvist P.-A.
- Pollock C. J.
- Denton R. E.
- Newman D. L.
Geophysical Research Letters, American Geophysical Union, 2018, 45 (3), pp.1237-1245. Data from the NASA Magnetospheric Multiscale mission are used to investigate asymmetric magnetic reconnection at the dayside boundary between the Earth's magnetosphere and the solar wind. High-resolution measurements of plasmas and fields are used to identify highly localized ( 15 electron Debye lengths) standing wave structures with large electric field amplitudes (up to 100 mV/m). These wave structures are associated with spatially oscillatory energy conversion, which appears as alternatingly positive and negative values of J · E. For small guide magnetic fields the wave structures occur in the electron stagnation region at the magnetosphere edge of the electron diffusion region. For larger guide fields the structures also occur near the reconnection X-line. This difference is explained in terms of channels for the out-of-plane current (agyrotropic electrons at the stagnation point and guide field-aligned electrons at the X-line). (10.1002/2017GL076809)
DOI : 10.1002/2017GL076809
Ionospheric climatology at Africa EIA trough stations during descending phase of sunspot cycle 22
- Abedesin B.O.
- Rabiu A. B.
- Bolaji O. S.
- Amory-Mazaudier Christine
Journal of Atmospheric and Solar-Terrestrial Physics, Elsevier, 2018, 172, pp.83-99. The African equatorial ionospheric climatology during the descending phase of sunspot-cycle 22 (spanning 19921996) was investigated using 3 ionosondes located at Dakar (14.70 N, 342.60 E), Ouagadougou (12.420 N, 358.60 E), and Korhogo (9.510 N, 354.40 E). The variations in the virtual height of the F-layer (hF), maximum electron density (NmF2), vertical plasma drift (Vp) and zonal electric field (Ey) were presented. Significant decrease in the NmF2 amplitude compared to hF in all of the stations during the descending period is obvious. While NmF2 magnitude maximizes/minimizes during the E-seasons/J-season, hF attained highest/lowest altitude in J-season/D-season for all stations. D-season anomaly was evident in NmF2 at all stations. For any season, the intensity (Ibt) of NmF2 noon-bite-out is highest at Dakar owning to fountain effect and maximizes in March-E season. Stations across the EIA trough show nearly coherence ionospheric climatology characteristics whose difference is of latitudinal origin. Hemispheric dependence in NmF2 is obvious, with difference more significant during high-solar activity and closes with decreasing solar activity. The variability in the plasma drift during the entire phase is suggested to emanate from solar flux variations, and additionally from enhanced leakage of electric fields from high-to low-latitudes. Existing African regional model of evening/nightttime pre-reversal plasma drift/ sunspot number (PRE peak/R) relationship compares well with experimental observations at all stations with slight over-estimation. The correlation/root-mean-square-deviation (RMS dev) pair between the model and observed Vp during the descending phase recorded 94.9%/0.756, 92.4%/1.526, and 79.1%/3.612 at Korhogo, Ouagadougou and Dakar respectively. The Ey/hF and Ey/NmF2 relationships suggest that zonal electric field is more active in the lifting of hF and suppression of NmF2 during high- and moderate-solar activities when compared with low solar activity. This is the first work to show higher bite-out at the equatorial northern-station (Dakar) than southern-station (Korhogo) using ionosonde data. (10.1016/j.jastp.2018.03.009)
DOI : 10.1016/j.jastp.2018.03.009
Magnetic Reconnection, Turbulence, and Particle Acceleration: Observations in the Earth's Magnetotail
- Ergun R. E.
- Goodrich K. A.
- Wilder F. D.
- Ahmadi N.
- Holmes J. C.
- Eriksson S.
- Stawarz J. E.
- Nakamura R.
- Genestreti K. J.
- Hesse Michael
- Burch J. L.
- Torbert R. B.
- Phan T. D.
- Schwartz S. J.
- Eastwood Jonathan P.
- Strangeway R. J.
- Le Contel Olivier
- Russell C. T.
- Argall M. R.
- Lindqvist P.-A.
- Chen L. J.
- Cassak P. A.
- Giles B. L.
- Dorelli J. C.
- Gershman D. J.
- Leonard T. W.
- Lavraud B.
- Retinò Alessandro
- Matthaeus W. H.
- Vaivads A.
Geophysical Research Letters, American Geophysical Union, 2018, 45, pp.3338-3347. We report observations of turbulent dissipation and particle acceleration from large-amplitude electric fields (E) associated with strong magnetic field (B) fluctuations in the Earth's plasma sheet. The turbulence occurs in a region of depleted density with anti-earthward flows followed by earthward flows suggesting ongoing magnetic reconnection. In the turbulent region, ions and electrons have a significant increase in energy, occasionally >100 keV, and strong variation. There are numerous occurrences of |E| >100 mV/m including occurrences of large potentials (>1 kV) parallel to B and occurrences with extraordinarily large J · E (J is current density). In this event, we find that the perpendicular contribution of J · E with frequencies near or below the ion cyclotron frequency (fci) provide the majority net positive J · E. Large-amplitude parallel E events with frequencies above fci to several times the lower hybrid frequency provide significant dissipation and can result in energetic electron acceleration. (10.1002/2018GL076993)
DOI : 10.1002/2018GL076993
Du plasma dans l'espace ?
- Rezeau Laurence
Le Bulletin de l'Union des Professeurs de Physique et de Chimie, Union des professeurs de physique et de chimie, 2018 (1000), pp.153-162. Le mot plasma n'évoque pas d'abord l'espace, mais plutôt la médecine ou les écrans de télévision. Pourtant, le quatrième état de la matière constitue l'essentiel de la matière connue de l'Univers. Le milieu interplanétaire est un plasma, de même que l'environnement de la Terre au-dessus de quelques centaines de kilomètres. On a découvert ces plasmas au début du XXème siècle et on les explore depuis les débuts de l'ère spatiale. Les découvertes en physique des plasmas spatiaux sont donc fortement liées à l'exploration du Système solaire par les missions spatiales. Le Soleil interagit avec la Terre en l'éclairant, mais pas seulement ! Il éjecte aussi un vent de plasma qui nous bombarderait si nous n'avions pas un bouclier protecteur plutôt efficace, le champ magnétique terrestre. On sait maintenant faire le lien entre les éjections de plasma observées sur le Soleil et les magnifiques aurores boréales observées au sol.
Perpendicular Current Reduction Caused by Cold Ions of Ionospheric Origin in Magnetic Reconnection at the Magnetopause: Particle‐in‐Cell Simulations and Spacecraft Observations
- Toledo‐redondo Sergio
- Dargent Jérémy
- Aunai Nicolas
- Lavraud Benoit
- André Mats
- Li Wenya
- Giles Barbara
- Lindqvist Per‐arne
- Ergun Robert
- Russell Christopher
- Burch James
Geophysical Research Letters, American Geophysical Union, 2018, 45 (19), pp.10,033-10,042. Cold ions of ionospheric origin are present throughout the Earth's magnetosphere, including the dayside magnetopause, where they modify the properties of magnetic reconnection, a major coupling mechanism at work between the magnetosheath and the magnetosphere. We present Magnetospheric MultiScale (MMS) spacecraft observations of the reconnecting magnetopause with different amounts of cold ions and show that their presence reduces the Hall term in the Ohm's law. Then, we compare two particle-in-cell simulations, with and without cold ions on the magnetospheric side. The cold ions remain magnetized inside the magnetospheric separatrix region, leading to the reduction of the perpendicular currents associated with the Hall effect. Moreover, this reduction is proportional to the relative number density of cold ions. And finally, the Hall electric field peak is reduced along the magnetospheric separatrix owing to cold ions. This should have an effect on energy conversion by reconnection from electromagnetic fields to kinetic energy of the particles (10.1029/2018GL079051)
DOI : 10.1029/2018GL079051
Plasma acceleration on multiscale temporal variations of electric and magnetic fields during substorm dipolarization in the Earth’s magnetotail
- Parkhomenko Elena
- Vitalevna-Malova Helmi
- Evgenevna-Grigorenko Elena
- Yurevich-Popov Victor
- Alekseevich-Petrukovich Anatolii
- Delcourt Dominique C.
- Aleksandrovna-Kronberg Elena
- Daly Patrick W.
- Matveevich-Zelenyi Lev
Annals of Geophysics, Istituto Nazionale di Geofisica e Vulcanologia (INGV), 2018, 61 (3), pp.GM334. Magnetic field dipolarizations are often observed in the magnetotail during substorms. These generally include three temporal scales: (1) actual dipolarization when the normal magnetic field changes during several minutes from minimum to maximum level; (2) sharp Bz bursts (pulses) interpreted as the passage of multiple dipolarization fronts with characteristic time scales < 1 min, and (3) bursts of electric and magnetic fluctuations with frequencies up to electron gyrofrequency occurring at the smallest time scales (≤ 1 s). We present a numerical model where the contributions of the above processes (1)-(3) in particle acceleration are analyzed. It is shown that these processes have a resonant character at different temporal scales. While O+ ions are more likely accelerated due to the mechanism (1), H+ ions (and to some extent electrons) are effectively accelerated due to the second mechanism. High-frequency electric and magnetic fluctuations accompanying magnetic dipolarization as in (3) are also found to efficiently accelerate electrons. (10.4401/ag-7582)
DOI : 10.4401/ag-7582
Magnetic Reconnection at a Thin Current Sheet Separating Two Interlaced Flux Tubes at the Earth's Magnetopause
- Kacem I.
- Jacquey C.
- Génot V.
- Lavraud B.
- Vernisse Y.
- Marchaudon A.
- Le Contel Olivier
- Breuillard Hugo
- Phan T. D.
- Hasegawa H.
- Oka M.
- Trattner K. J.
- Farrugia C. J.
- Paulson K.
- Eastwood Jonathan P.
- Fuselier S. A.
- Turner D. L.
- Eriksson S.
- Wilder F. D.
- Russell C. T.
- Oieroset M.
- Burch J. L.
- Graham D. B.
- Sauvaud J.-A.
- Avanov L.
- Chandler Michael O.
- Coffey Victoria
- Dorelli J. C.
- Gershman D. J.
- Giles B. L.
- Moore T. E.
- Saito Y.
- Chen L. J.
- Penou E.
Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2018, 123 (3), pp.1779-1793. The occurrence of spatially and temporally variable reconnection at the Earth's magnetopause leads to the complex interaction of magnetic fields from the magnetosphere and magnetosheath. Flux transfer events (FTEs) constitute one such type of interaction. Their main characteristics are (1) an enhanced core magnetic field magnitude and (2) a bipolar magnetic field signature in the component normal to the magnetopause, reminiscent of a large-scale helicoidal flux tube magnetic configuration. However, other geometrical configurations which do not fit this classical picture have also been observed. Using high-resolution measurements from the Magnetospheric Multiscale mission, we investigate an event in the vicinity of the Earth's magnetopause on 7 November 2015. Despite signatures that, at first glance, appear consistent with a classic FTE, based on detailed geometrical and dynamical analyses as well as on topological signatures revealed by suprathermal electron properties, we demonstrate that this event is not consistent with a single, homogenous helicoidal structure. Our analysis rather suggests that it consists of the interaction of two separate sets of magnetic field lines with different connectivities. This complex three-dimensional interaction constructively conspires to produce signatures partially consistent with that of an FTE. We also show that, at the interface between the two sets of field lines, where the observed magnetic pileup occurs, a thin and strong current sheet forms with a large ion jet, which may be consistent with magnetic flux dissipation through magnetic reconnection in the interaction region. (10.1002/2017JA024537)
DOI : 10.1002/2017JA024537
Large-Amplitude High-Frequency Waves at Earth's Magnetopause
- Graham D. B.
- Vaivads A.
- Khotyaintsev Y. V.
- André M.
- Le Contel Olivier
- Malaspina D. M.
- Lindqvist P.-A.
- Wilder F. D.
- Ergun R. E.
- Gershman D. J.
- Giles B. L.
- Magnes W.
- Russell C. T.
- Burch J. L.
- Torbert R. B.
Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2018, 123 (4), pp.2630-2657. Large-amplitude waves near the electron plasma frequency are found by the Magnetospheric Multiscale (MMS) mission near Earth's magnetopause. The waves are identified as Langmuir and upper hybrid (UH) waves, with wave vectors either close to parallel or close to perpendicular to the background magnetic field. The waves are found all along the magnetopause equatorial plane, including both flanks and close to the subsolar point. The waves reach very large amplitudes, up to 1 V m-1, and are thus among the most intense electric fields observed at Earth's magnetopause. In the magnetosphere and on the magnetospheric side of the magnetopause the waves are predominantly UH waves although Langmuir waves are also found. When the plasma is very weakly magnetized only Langmuir waves are likely to be found. Both Langmuir and UH waves are shown to have electromagnetic components, which are consistent with predictions from kinetic wave theory. These results show that the magnetopause and magnetosphere are often unstable to intense wave activity near the electron plasma frequency. These waves provide a possible source of radio emission at the magnetopause. (10.1002/2017JA025034)
DOI : 10.1002/2017JA025034
Non-adiabatic energization and transport of planetary ions in the magnetospheric flanks of Mercury
- Aizawa S.
- Delcourt Dominique
- Terada N.
- Kasaba Y.
- Katoh Y.
, 2018, 2018, pp.pp. 10. We investigate the acceleration and transport of planetary ions within Kelvin-Helmholtz (KH) vortices that develop in the magnetospheric flanks of Mercury, using single-particle trajectory calculations in a field model obtained from MHD simulations. Due to the presence of heavy ions of planetary origin (e.g., O+, Na+, and K+) following ionization of exospheric neutrals and the complicated field structure during the KH vortex development, the scale of electric field variation may be comparable with ion gyration motion. Therefore ions may experience non-adiabatic energization as they drift across the magnetopause. In this study, we consider realistic configurations for both dawn and dusk magnetospheric flanks, and we focus on the effect of the spatial and temporal variations of the electric field magnitude and orientation along the ion path on the ion dynamics. We show that the intensification rather than the change of orientation is responsible for large non-adiabatic energization of heavy ions of planetary origin. This energization systematically occurs for ions with low initial energies in the direction perpendicular to the magnetic field, the energy gain being of the order of the energy corresponding to the maximum ExB drift speed, ɛmax, in a like manner to a pickup ion process. It is also found that ions that have initial energies comparable to ɛmax may be decelerated depending upon gyration phase. We find that ions with initial perpendicular energies much larger than ɛmax are little affected along the ion path through KH vortices. By comparing dynamical regimesin the dawn versus dusk regions, and also by considering different IMF directions, we show that the ion transport across the magnetopause is controlled by the orientation of the magnetosheath electric field and that the rate of energization depends upon the scale of KH vortices versus Larmor radii.
THEORY OF A STRIP ANTENNA LOCATED AT THE INTERFACE OF AN ISOTROPIC MEDIUM AND A MAGNETOPLASMA
- Kudrin Alexander
- Zaitseva Anna
- Zaboronkova Tatyana
- Krafft Catherine
Progress In Electromagnetics Research C, EMW Publishing, 2018, 84, pp.255-267. (10.2528/PIERC18042401)
DOI : 10.2528/PIERC18042401
Méthodes mathématiques pour la physique
- Dotsenko Vladimir
- Courtat Axel
- Gauthier Gaétan
, 2018, pp.704 pages. EAN − 9782100777051 Cet ouvrage regroupe en un seul volume toutes les méthodes mathématiques de base indispensables pour la physique. Chaque méthode ou définition introduite est présentée de manière formelle puis systématiquement replacée dans le contexte...
Plasma non-uniformity in a symmetric radiofrequency capacitively-coupled reactor with dielectric side-wall: a two dimensional particle-in-cell/Monte Carlo collision simulation
- Liu Yue
- Booth Jean-Paul
- Chabert Pascal
Plasma Sources Science and Technology, IOP Publishing, 2018, 27 (2), pp.025006. A Cartesian-coordinate two-dimensional electrostatic particle-in-cell/Monte Carlo collision (PIC/MCC) plasma simulation code is presented, including a new treatment of charge balance at dielectric boundaries. It is used to simulate an Ar plasma in a symmetric radiofrequency capacitively-coupled parallel-plate reactor with a thick (3.5 cm) dielectric side-wall. The reactor size (12 cm electrode width, 2.5 cm electrode spacing) and frequency (15 MHz) are such that electromagnetic effects can be ignored. The dielectric side-wall effectively shields the plasma from the enhanced electric field at the powered-grounded electrode junction, which has previously been shown to produce locally enhanced plasma density (Dalvie et al 1993 Appl. Phys. Lett. 62 3207?9; Overzet and Hopkins 1993 Appl. Phys. Lett. 63 2484?6; Boeuf and Pitchford 1995 Phys. Rev. E 51 1376?90). Nevertheless, enhanced electron heating is observed in a region adjacent to the dielectric boundary, leading to maxima in ionization rate, plasma density and ion flux to the electrodes in this region, and not at the reactor centre as would otherwise be expected. The axially-integrated electron power deposition peaks closer to the dielectric edge than the electron density. The electron heating components are derived from the PIC/MCC simulations and show that this enhanced electron heating results from increased Ohmic heating in the axial direction as the electron density decreases towards the side-wall. We investigated the validity of different analytical formulas to estimate the Ohmic heating by comparing them to the PIC results. The widespread assumption that a time-averaged momentum transfer frequency, v m , can be used to estimate the momentum change can cause large errors, since it neglects both phase and amplitude information. Furthermore, the classical relationship between the total electron current and the electric field must be used with caution, particularly close to the dielectric edge where the (neglected) pressure gradient term becomes significant. (10.1088/1361-6595/aaa86e)
DOI : 10.1088/1361-6595/aaa86e
Whistler envelope solitons. II. Interaction with non-relativistic electron beams in plasmas with density inhomogeneities
- Krafft C.
- Volokitin A. S.
Physics of Plasmas, American Institute of Physics, 2018, 25 (10), pp.102302. This paper studies the self-consistent interactions between whistler envelope solitons and electron beams in inhomogeneous plasmas, using a Hamiltonian model of wave-particle interaction where nonlinear equations describing the dynamics of whistler and ion acoustic waves and including a beam current term are coupled with Newton equations. It allows describing the parallel propagation of narrowband whistlers interacting with arbitrary particle distributions in irregular plasmas. It is shown that the whistler envelope soliton does not exchange energy with all the resonant electrons as in the case of whistler turbulence but mostly with those moving in its close vicinity (locality condition), even if the downstream particle distribution is perturbed. During these interactions, the soliton can either damp and accelerate particles, or absorb beam energy and cause electron deceleration. If the energy exchanges are significant, the envelope is deformed; its upstream front can steepen, whereas oscillations can appear on its downstream side. Weak density inhomogeneities as the random fluctuations of the solar wind plasma have no strong impact on the interactions of the whistler soliton with the resonant particles. (10.1063/1.5041075)
DOI : 10.1063/1.5041075

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