Publications

2017

• 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
• Statistical study of the alteration of the magnetic structure of magnetic clouds in the Earth's magnetosheath
  
  • Turc Lucile
  • Fontaine Dominique
  • Escoubet C. Philippe
  • Kilpua E. K. J.
  • Dimmock A. P.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2017, 122 (3), pp.2956-2972. The magnetosheath plays a central role in the solar wind-magnetospheric coupling. Yet the effects of its crossing on solar wind structures such as magnetic clouds (MCs) are generally overlooked when assessing their geoeffectivity. Using 82 MCs observed simultaneously in the solar wind and the magnetosheath, we carry out the first statistical study of the alteration of their magnetic structure in the magnetosheath. For each event, the bow shock properties are obtained from a magnetosheath model. The comparison between the model results and observations shows that in 80% of cases, the MHD-based model captures well the magnetosheath transition; the other events are discussed separately. We find that just downstream of the bow shock the variation of the magnetic field direction shows a very good anticorrelation (r =- 0.91) with the angle between the upstream magnetic field and the shock normal. We then focus on the magnetic field north-south component B<SUB>z</SUB> because of its importance for geoeffectivity. Although the sign of B<SUB>z</SUB> is generally preserved in the magnetosheath, we also find evidence of long-lasting intervals of opposite B<SUB>z</SUB> signs in the solar wind and the magnetosheath during some events, with a |B<SUB>z</SUB>| reversal >10 nT at the magnetopause. We find that these reversals are due to the draping of the field lines and are associated with predominant upstream B<SUB>y</SUB>. In those cases, the estimated position of the regions of antiparallel fields along the magnetopause is independent of the sign of the upstream B<SUB>z</SUB>. This may have strong implications in terms of reconnection. (10.1002/2016JA023654)
  DOI : 10.1002/2016JA023654
• 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
• Acceleration of energetic electrons by waves in inhomogeneous solar wind plasmas
  
  • Krafft C.
  • Volokitin A.
  Journal of Plasma Physics, Cambridge University Press (CUP), 2017, 83 (2), pp.705830201. The paper studies the influence of the background plasma density fluctuations on the dynamics of the Langmuir turbulence generated by electron beams, for parameters typical for solar type III beams and plasmas near 1 AU. A self-consistent Hamiltonian model based on the Zakharov and the Newton equations is used, which presents several advantages compared to the Vlasov approach. Beams generating Langmuir turbulence can be accelerated as a result of wave transformation effects or/and decay cascade processes; in both cases, the beam-driven Langmuir waves transfer part of their energy to waves of smaller wavenumbers, which can be reabsorbed later on by beam particles of higher velocities. As a consequence, beams can conserve a large part of their initial kinetic energy while propagating and radiating wave turbulence over long distances in inhomogeneous plasmas. Beam particles can also be accelerated in quasi-homogeneous plasmas due to the second cascade of wave decay, the wave transformation processes being very weak in this case. The net gains and losses of energy of a beam and the wave turbulence it radiates are calculated as a function of the average level of plasma density fluctuations and the beam parameters. The results obtained provide relevant information on the mechanism of energy reabsorption by beams radiating Langmuir turbulence in solar wind plasmas. (10.1017/S0022377817000174)
  DOI : 10.1017/S0022377817000174
• Electron Scattering by High-frequency Whistler Waves at Earth's Bow Shock
  
  • Oka M.
  • Wilson Iii L. B.
  • Phan T. D.
  • Hull A. J.
  • Amano T.
  • Hoshino M.
  • Argall M. R.
  • Le Contel Olivier
  • Agapitov O.
  • Gershman D. J.
  • Khotyaintsev Y. V.
  • Burch J. L.
  • Torbert R. B.
  • Pollock C.
  • Dorelli J. C.
  • Giles B. L.
  • Moore T. E.
  • Saito Y.
  • Avanov L. A.
  • Paterson W. R.
  • Ergun R. E.
  • Strangeway R. J.
  • Russell C. T.
  • Lindqvist P. A.
  The Astrophysical Journal Letters, Bristol : IOP Publishing, 2017, 842 (2), pp.L11. Electrons are accelerated to non-thermal energies at shocks in space and astrophysical environments. While different mechanisms of electron acceleration have been proposed, it remains unclear how non-thermal electrons are produced out of the thermal plasma pool. Here, we report in situ evidence of pitch-angle scattering of non-thermal electrons by whistler waves at Earth's bow shock. On 2015 November 4, the Magnetospheric Multiscale (MMS) mission crossed the bow shock with an Alfvén Mach number ~11 and a shock angle ~84°. In the ramp and overshoot regions, MMS revealed bursty enhancements of non-thermal (0.5−2 keV) electron flux, correlated with high-frequency (0.2−0.4 Omega <SUB>ce</SUB>, where Omega <SUB>ce</SUB> is the cyclotron frequency) parallel-propagating whistler waves. The electron velocity distribution (measured at 30 ms cadence) showed an enhanced gradient of phase-space density at and around the region where the electron velocity component parallel to the magnetic field matched the resonant energy inferred from the wave frequency range. The flux of 0.5 keV electrons (measured at 1 ms cadence) showed fluctuations with the same frequency. These features indicate that non-thermal electrons were pitch-angle scattered by cyclotron resonance with the high-frequency whistler waves. However, the precise role of the pitch-angle scattering by the higher-frequency whistler waves and possible nonlinear effects in the electron acceleration process remains unclear. (10.3847/2041-8213/aa7759)
  DOI : 10.3847/2041-8213/aa7759
• On the historical origins of the CEJ, DP2 and Ddyn current systems and their roles in the predictions of ionospheric responses to geomagnetic storms at equatorial latitudes
  
  • Amory-Mazaudier Christine
  • Bolaji O. S.
  • Doumbia V.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2017. In this short letter, we recall the differences between the Counter electrojet (CEJ), which is a phenomenon observed on the magnetically quiet days and the disturbance dynamo (Ddyn), which can be observed during and after a geomagnetic storm. The CEJ is well-known to occur near the geomagnetic dip equator. It can be identified by a reversal in the horizontal component (H) of the geomagnetic field daily regular variations. In contrasts to equatorial electrojet (EEJ) that flows eastward in the daytime the CEJ in considered to flow westward. The magnetic signatures of the reversed solar quiet (Sq) current at the low latitude during magnetic storms are due to the Ddyn. This disturbance (Ddyn) is produced by current systems that are driven by thermospheric storm winds originating from the Joule heating of enhanced high latitude currents. The DP2 is the magnetic effect of current systems at high latitudes. These currents are associated with the coupling of magnetosphere and ionosphere through geomagnetic field lines. They are associated to the magnetospheric convection. During intense magnetic storms these high latitude currents are enhanced and their magnetic effects can extend toward the low latitudes This work shows that the study of magnetic perturbations makes it possible to understand the disturbances of the ionospheric electric currents. The use of an efficient treatment of the magnetic signals makes it possible to separate the magnetic effects of the different perturbations PPEF and DDEF. This was performed in the paper Nava et al. (2016). (10.1002/2017JA024132)
  DOI : 10.1002/2017JA024132
• Transfer of microwave energy along a filament plasma column in air
  
  • Prade Bernard
  • Houard Aurélien
  • Larour Jean
  • Pellet Michel
  • Mysyrowicz André
  Applied Physics B - Laser and Optics, Springer Verlag, 2017, 123, pp.40. We demonstrate the coupling of microwave radiation into a plasma channel formed by laser filamentation in air, leading to the amplification by two orders of magnitude of longitudinal oscillations of the plasma. Transfer of this longitudinal excitation towards unexcited region of the plasma column occurs over more than 10 cm, in good agreement with a theoretical model describing the propagation of a TM wave guided along the surface between air and plasma. We foresee that high power low frequency electromagnetic waves injected into a multi-filament plasma could initiate and sustain a long-lived plasma over several meters distance. (10.1007/s00340-016-6616-4)
  DOI : 10.1007/s00340-016-6616-4
• Erratum: "On the Existence of the Kolmogorov Inertial Range in the Terrestrial Magnetosheath Turbulence" (2017, ApJL, 836, L10)
  
  • Huang S. Y.
  • Hadid Lina
  • Sahraoui Fouad
  • Yuan Z. G.
  • Deng X. H.
  The Astrophysical Journal Letters, Bristol : IOP Publishing, 2017, 837 (2), pp.L31. Not Available (10.3847/2041-8213/aa633c)
  DOI : 10.3847/2041-8213/aa633c
• MMS observations of whistler waves in electron diffusion region
  
  • Cao D.
  • Fu H.S.
  • Cao J.B.
  • Wang T. Y.
  • Graham D. B.
  • Chen Z. Z.
  • Peng F. Z.
  • Huang S. Y.
  • Khotyaintsev Y. V.
  • André M.
  • Russell C. T.
  • Giles B. L.
  • Lindqvist P.-A.
  • Torbert R. B.
  • Ergun R. E.
  • Le Contel Olivier
  • Burch J. L.
  Geophysical Research Letters, American Geophysical Union, 2017, 44 (9), pp.3954-3962. Whistler waves that can produce anomalous resistivity by affecting electrons' motion have been suggested as one of the mechanisms responsible for magnetic reconnection in the electron diffusion region (EDR). Such type of waves, however, has rarely been observed inside the EDR so far. In this study, we report such an observation by Magnetospheric Multiscale (MMS) mission. We find large-amplitude whistler waves propagating away from the X line with a very small wave-normal angle. These waves are probably generated by the perpendicular temperature anisotropy of the 300 eV electrons inside the EDR, according to our analysis of dispersion relation and cyclotron resonance condition; they significantly affect the electron-scale dynamics of magnetic reconnection and thus support previous simulations. (10.1002/2017GL072703)
  DOI : 10.1002/2017GL072703
• Long-lived laser-induced arc discharges for energy channeling applications
  
  • Point Guillaume
  • Arantchouk Léonid
  • Thouin Emmanuelle
  • Carbonnel Jérôme
  • Mysyrowicz André
  • Houard Aurélien
  Scientific Reports, Nature Publishing Group, 2017, 7 (1), pp.13801. Laser filamentation offers a promising way for the remote handling of large electrical power in the form of guided arc discharges. We here report that it is possible to increase by several orders of magnitude the lifetime of straight plasma channels from filamentation-guided sparks in atmospheric air. A 30 ms lifetime can be reached using a low-intensity, 100 mA current pulse. Stability of the plasma shape is maintained over such a timescale through a continuous Joule heating from the current. This paves the way for applications based on the generation of straight, long duration plasma channels, like virtual plasma antennas or contactless transfer of electric energy. (10.1038/s41598-017-14054-z)
  DOI : 10.1038/s41598-017-14054-z
• Evidence and relevance of spatially chaotic magnetic field lines in MCF devices
  
  • Firpo Marie-Christine
  • Lifschitz Agustin
  • Ettoumi Wahb
  • Farengo Ricardo
  • Ferrari Hugo
  • Garcia-Martinez Pablo Luis
  Plasma Physics and Controlled Fusion, IOP Publishing, 2017, 59 (3). Numerical evidence for the existence of spatially chaotic magnetic field lines about the collapse phase of tokamak sawteeth with incomplete reconnection is presented. This uses the results of extensive test particle simulations in different sets of electromagnetic perturbations tested against experimental JET measurements. In tokamak sawteeth, that form a laboratory prototype of magnetic reconnection, the relative magnetic perturbation δB/B may reach a few percents. This does not apply to tokamak operating regimes dominated by turbulence where δB/B is usually not larger than 10 −4. However, this small magnetic perturbation being sustained by a large spectrum of modes is shown to be sufficient to ensure the existence of stochastic magnetic field lines. This has important consequences for magnetic confinement fusion (MCF) where electrons are dominantly governed by the magnetic force. Indeed some overlap between magnetic resonances can locally induce chaotic magnetic field lines enabling the spatial redistribution of the electron population and of its thermal content. As they are the swiftest plasma particles, electrons feed back the most rapid perturbations of the magnetic field (10.1088/1361-6587/aa570d)
  DOI : 10.1088/1361-6587/aa570d
• Counterpropagating radiative shock experiments on the Orion laser
  
  • Suzuki-Vidal Francisco
  • Clayson Thomas
  • Stehlé Chantal
  • Swadling G. F.
  • Foster J.
  • Skidmore J.
  • Graham P.
  • Burdiak G.
  • Lebedev S. V.
  • Chaulagain Uddhab
  • Singh Raj Laxmi
  • Gumbrell E.
  • Patankar S.
  • Spindloe C.
  • Larour Jean
  • Kozlová Michaela
  • Rodriguez Perez R.
  • Gil J. M.
  • Espinosa G.
  • Velarde P.
  • Danson C.
  Physical Review Letters, American Physical Society, 2017, 119 (05), pp.055001. We present new experiments to study the formation of radiative shocks and the interaction between two counterpropagating radiative shocks. The experiments are performed at the Orion laser facility, which is used to drive shocks in xenon inside large aspect ratio gas cells. The collision between the two shocks and their respective radiative precursors, combined with the formation of inherently three-dimensional shocks, provides a novel platform particularly suited for the benchmarking of numerical codes. The dynamics of the shocks before and after the collision are investigated using point-projection x-ray backlighting while, simultaneously, the electron density in the radiative precursor was measured via optical laser interferometry. Modeling of the experiments using the 2D radiation hydrodynamic codes NYM and PETRA shows very good agreement with the experimental results. (10.1103/PhysRevLett.119.055001)
  DOI : 10.1103/PhysRevLett.119.055001
• Differential kinetic physics of solar-wind minor ions
  
  • Perrone Denise
  • Valentini F.
  • Servidio S.
  • Stabile S.
  • Pezzi O.
  • Sorriso-Valvo L.
  • de Marco R.
  • Marcucci M. F.
  • Brienza D.
  • Bruno Roberto
  • Lavraud Benoit
  • Retinò Alessandro
  • Vaivads A.
  • Consolini G.
  • de Keyser J.
  • Salatti M.
  • Veltri P.
  , 2017, 19, pp.13382. The solar wind, although predominantly constituted of protons, is also made up of a finite amount of alpha particles, together with a few percent of heavier ions. The kinetic properties of heavy ions in the solar wind are known to behave in a well organized way under most solar-wind flow conditions: their speeds are faster than that of hydrogen by about the local Alfvén speed, and their kinetic temperatures are more than proportional to their mass. Preferential heating and acceleration of heavy ions in the solar wind and corona represent a long-standing theoretical problem in space physics, and are distinct experimental signatures of kinetic processes occurring in collisionless plasmas. However, due to very scarce measurements of heavy ions at time resolutions comparable with their kinetic scales, energy partition between species in turbulent plasma dissipation is basically unexplored. For the moment, most of the information comes from numerical simulations and a crucial support is given by self-consistent, fully nonlinear Vlasov models. Here, hybrid Vlasov-Maxwell simulations are used to investigate the role of kinetic effects in a two-dimensional turbulent multi-ion plasma, composed of kinetic protons and alpha particles, and fluid electrons. The response of different ion species to the fluctuating electromagnetic fields appears to be different. In particular, a significant differential heating of alpha particles with respect to protons is observed, localized nearby the peaks of ion vorticity and where strong deviations from thermodynamic equilibrium are recovered. Then, the understanding of the complex process of particle heating results strongly related to the study of the non-Maxwellian features on the three-dimensional ion velocity distributions. These numerical results highlight the importance for the future space missions to provide detailed ion measurements to make a significant step forward in the problem of heating in turbulent space plasmas.
• Enhanced control of the ionization rate in radio-frequency plasmas with structured electrodes via tailored voltage waveforms
  
  • Doyle Scott J.
  • Lafleur Trevor
  • Gibson Andrew R.
  • Tian Peng
  • Kushner Mark J.
  • Dedrick James
  Plasma Sources Science and Technology, IOP Publishing, 2017, 26. Radio-frequency capacitively coupled plasmas that incorporate structured electrodes enable increases in the electron density within spatially localized regions through the hollow cathode effect (HCE). This enables enhanced control over the spatial profile of the plasma density, which is useful for several applications including materials processing, lighting and spacecraft propulsion. However, asymmetries in the powered and grounded electrode areas inherent to the hollow cathode geometry lead to the formation of a time averaged dc self-bias voltage at the powered electrode. This bias alters the energy and flux of secondary electrons leaving the surface of the cathode and consequentially can moderate the increased localized ionization afforded by the hollow cathode discharge. In this work, two-dimensional fluid-kinetic simulations are used to demonstrate control of the dc self-bias voltage in a dual-frequency driven (13.56, 27.12 MHz), hollow cathode enhanced, capacitively coupled argon plasma over the 66.6--200 Pa (0.5--1.5 Torr) pressure range. By varying the phase offset of the 27.12 MHz voltage waveform, the dc self-bias voltage varies by 10%--15% over an applied peak-to-peak voltage range of 600--1000 V, with lower voltages showing higher modulation. Resulting ionization rates due to secondary electrons within the hollow cathode cavity vary by a factor of 3 at constant voltage amplitude, demonstrating the ability to control plasma properties relevant for maintaining and enhancing the HCE. (10.1088/1361-6595/aa96e5)
  DOI : 10.1088/1361-6595/aa96e5
• Controlling plasma properties under differing degrees of electronegativity using odd harmonic dual frequency excitation
  
  • Gibson Andrew R.
  • Gans Timo
  Plasma Sources Science and Technology, IOP Publishing, 2017, 26. The charged particle dynamics in low-pressure oxygen plasmas excited by odd harmonic dual frequency waveforms (low frequency of 13.56 MHz and high frequency of 40.68 MHz) are investigated using a one-dimensional numerical simulation in regimes of both low and high electronegativity. In the low electronegativity regime, the time and space averaged electron and negative ion densities are approximately equal and plasma sustainment is dominated by ionisation at the sheath expansion for all combinations of low and high frequency and the phase shift between them. In the high electronegativity regime, the negative ion density is a factor of 15--20 greater than the low electronegativity cases. In these cases, plasma sustainment is dominated by ionisation inside the bulk plasma and at the collapsing sheath edge when the contribution of the high frequency to the overall voltage waveform is low. As the high frequency component contribution to the waveform increases, sheath expansion ionisation begins to dominate. It is found that the control of the average voltage drop across the plasma sheath and the average ion flux to the powered electrode are similar in both regimes of electronegativity, despite the differing electron dynamics using the considered dual frequency approach. This offers potential for similar control of ion dynamics under a range of process conditions, independent of the electronegativity. This is in contrast to ion control offered by electrically asymmetric waveforms where the relationship between the ion flux and ion bombardment energy is dependent upon the electronegativity. (10.1088/1361-6595/aa8dcd)
  DOI : 10.1088/1361-6595/aa8dcd
• Influence of neutral pressure on instability enhanced friction and ion velocities at the sheath edge of two-ion-species plasmas
  
  • Adrian P. J.
  • Baalrud S. D.
  • Lafleur T.
  Physics of Plasmas, American Institute of Physics, 2017, 24. The Instability Enhanced Friction theory [Baalrud et al., Phys. Rev. Lett. 103, 205002 (2009)] is extended to account for the influence of neutral pressure in predicting the flow speed of each ion species at the sheath edge of plasmas containing two ion species. Particle-in-cell simulations show that the theory accurately predicts both the neutral pressure cutoff of ion-ion two-stream instabilities and the ion flow speeds at the sheath edge as pressure is varied over several orders of magnitude. The simulations are used to directly calculate the instability-enhanced ion-ion friction force. At sufficiently high neutral pressure, the simulations also provide evidence for collisional modifications to the Bohm criterion. (10.1063/1.4986239)
  DOI : 10.1063/1.4986239
• Zipper-like periodic magnetosonic waves: Van Allen Probes, THEMIS, and magnetospheric multiscale observations
  
  • Li J.
  • Bortnik J.
  • Li W.
  • Ma Q.
  • Thorne R. M.
  • Kletzing C. A.
  • Kurth W. S.
  • Hospodarsky G. B.
  • Wygant J.
  • Breneman A.
  • Thaller S.
  • Funsten H. O.
  • Mitchell D. G.
  • Manweiler J. W.
  • Torbert R. B.
  • Le Contel Olivier
  • Ergun R. E.
  • Lindqvist P.-A.
  • Torkar Klaus
  • Nakamura R.
  • Andriopoulou M.
  • Russell C. T.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2017, 122 (2), pp.1600-1610. An interesting form of "zipper-like" magnetosonic waves consisting of two bands of interleaved periodic rising-tone spectra was newly observed by the Van Allen Probes, the Time History of Events and Macroscale Interactions during Substorms (THEMIS), and the Magnetospheric Multiscale (MMS) missions. The two discrete bands are distinct in frequency and intensity; however, they maintain the same periodicity which varies in space and time, suggesting that they possibly originate from one single source intrinsically. In one event, the zipper-like magnetosonic waves exhibit the same periodicity as a constant-frequency magnetosonic wave and an electrostatic emission, but the modulation comes from neither density fluctuations nor ULF waves. A statistical survey based on 3.5 years of multisatellite observations shows that zipper-like magnetosonic waves mainly occur on the dawnside to noonside, in a frequency range between 10 f<SUB>cp</SUB> and f<SUB>LHR</SUB>. The zipper-like magnetosonic waves may provide a new clue to nonlinear excitation or modulation process, while its cause still remains to be fully understood. (10.1002/2016JA023536)
  DOI : 10.1002/2016JA023536
• Electron Heating at Kinetic Scales in Magnetosheath Turbulence
  
  • Chasapis A.
  • Matthaeus W. H.
  • Parashar T. N.
  • Le Contel Olivier
  • Retinò Alessandro
  • Breuillard Hugo
  • Khotyaintsev Y. V.
  • Vaivads A.
  • Lavraud B.
  • Eriksson E.
  • Moore T. E.
  • Burch J. L.
  • Torbert R. B.
  • Lindqvist P.-A.
  • Ergun R. E.
  • Marklund G.
  • Goodrich K. A.
  • Wilder F. D.
  • Chutter M.
  • Needell J.
  • Rau D.
  • Dors I.
  • Russell C. T.
  • Le G.
  • Magnes W.
  • Strangeway R. J.
  • Bromund K. R.
  • Leinweber H. K.
  • Plaschke F.
  • Fischer D.
  • Anderson B. J.
  • Pollock C. J.
  • Giles B. L.
  • Paterson W. R.
  • Dorelli J. C.
  • Gershman D. J.
  • Avanov L.
  • Saito Y.
  The Astrophysical Journal, American Astronomical Society, 2017, 836, pp.247. We present a statistical study of coherent structures at kinetic scales, using data from the Magnetospheric Multiscale mission in the Earth's magnetosheath. We implemented the multi-spacecraft partial variance of increments (PVI) technique to detect these structures, which are associated with intermittency at kinetic scales. We examine the properties of the electron heating occurring within such structures. We find that, statistically, structures with a high PVI index are regions of significant electron heating. We also focus on one such structure, a current sheet, which shows some signatures consistent with magnetic reconnection. Strong parallel electron heating coincides with whistler emissions at the edges of the current sheet. (10.3847/1538-4357/836/2/247)
  DOI : 10.3847/1538-4357/836/2/247
• Nonlinear radiation generation processes in the auroral acceleration region
  
  • Pottelette Raymond
  • Berthomier Matthieu
  Annales Geophysicae, European Geosciences Union, 2017, 35 (6), pp.1241-1248. It is known from laboratory plasma experiments that double layers (DLs) radiate in the electromagnetic spectrum; but this is only known qualitatively. In these experiments, it was shown that the electron beam created on the high-potential side of a DL generates nonlinear structures which couple to electromagnetic waves and act as a sender antenna. In the Earth auroral region, observations performed by auroral spacecraft have shown that DLs occur naturally in the source region of intense radio emissions called auroral kilometric radiation (AKR). Very high time-, spatial-, and temporal-resolution measurements are needed in order to characterize waves and particle distributions in the vicinity of DLs, which are moving transient structures. We report observations from the FAST satellite of a localized large-amplitude parallel electric field ( 300 mV m<SUP>-1</SUP>) recorded at the edges of the auroral density cavity. In agreement with laboratory experiments, on the high-potential side of the DL, elementary radiation events are detected. They occur substantially above the local electron gyrofrequency and are associated with the presence of electron holes. The velocity of these nonlinear structures can be derived from the measurement of the Doppler-shifted AKR frequency spectrum above the electron gyrofrequency. The generated electron holes appear as the nonlinear evolution of electrostatic waves generated by the electron-electron two-stream instability because they propagate at about half the beam velocity. It is pointed out that, in the vicinity of a DL, the shape of the electron distribution gives rise to a significant power recorded in the left-hand polarized ordinary (LO) mode. (10.5194/angeo-35-1241-2017)
  DOI : 10.5194/angeo-35-1241-2017
• 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
• 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
• Power coupling mode transitions induced by tailored voltage waveforms in capacitive oxygen discharges
  
  • Derzsi A.
  • Bruneau Bastien
  • Gibson Andrew
  • Johnson Erik
  • O'Connell D.
  • Gans T.
  • Booth Jean-Paul
  • Donko Zoltan
  Plasma Sources Science and Technology, IOP Publishing, 2017, 26 (3), pp.034002. Low-pressure capacitively coupled radio frequency discharges operated in O 2 and driven by tailored voltage waveforms are investigated experimentally and by means of kinetic simulations. Pulse-type (peaks/valleys) and sawtooth-type voltage waveforms that consist of up to four consecutive harmonics of the fundamental frequency are used to study the amplitude asymmetry effect as well as the slope asymmetry effect at different fundamental frequencies (5, 10, and 15 MHz) and at different pressures (50?700 mTorr). Values of the DC self-bias determined experimentally and spatio-temporal excitation rates derived from phase resolved optical emission spectroscopy measurements are compared with particle-in-cell/Monte Carlo collisions simulations. The spatio-temporal distributions of the excitation rate obtained from experiments are well reproduced by the simulations. Transitions of the discharge electron heating mode from the drift-ambipolar mode to the ? -mode are induced by changing the number of consecutive harmonics included in the driving voltage waveform or by changing the gas pressure. Changing the number of harmonics in the waveform has a strong effect on the electronegativity of the discharge, on the generation of the DC self-bias and on the control of ion properties at the electrodes, both for pulse-type, as well as sawtooth-type driving voltage waveforms The effect of the surface quenching rate of oxygen singlet delta metastable molecules on the spatio-temporal excitation patterns is also investigated. (10.1088/1361-6595/aa56d6)
  DOI : 10.1088/1361-6595/aa56d6
• Nested Polyhedra Models for turbulence
  
  • Gürcan Özgür D.
  , 2017.
• Dynamic probing of plasma-catalytic surface processes: Oxidation of toluene on CeO₂
  
  • Jia Zixian
  • Wang Xianjie
  • Thevenet Frederic
  • Rousseau Antoine
  Plasma Processes and Polymers, Wiley-VCH Verlag, 2017. This article reports the use of innovative diagnostics to monitor toluene adsorption and oxidation on CeO2 surface under non-thermal plasma (NTP) exposure. Two plasma-catalytic configurations are explored, namely: post-plasma catalysis (PPC) and in-plasma catalysis (IPC). Since heterogeneous processes are pointed out as key steps of the plasma-catalyst coupling, the catalyst surface has been monitored by two complementary in situ diagnostics: (i) diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) and (ii) transmission fourier transform infrared spectroscopy using Sorbent track (ST) device. Dielectric barrier discharges (DBD) are used in both PPC and IPC configurations to induce adsorbed toluene oxidation. Toluene in dry air is first adsorbed on the selected catalytic surface: ceria (CeO2). Subsequently, the plasma is switched on. During the experiment, the ceria surface is monitored by infrared to study toluene adsorption and oxidation mechanisms. The adsorption capacity of toluene on ceria is, respectively, measured in the configurations of PPC and IPC by DRIFTS and ST. The oxidation of toluene by plasma follows a first-order reaction regardless of plasma configuration and injected power and IPC is more effective for the toluene removal than PPC. Intermediates of toluene (benzyl alcohol, benzaldehyde and benzoic acid) are also identified on the surface and their respective temporal evolutions as a function of the plasma exposure are studied.ppap201600114-gra-0001 (10.1002/ppap.201600114)
  DOI : 10.1002/ppap.201600114
• Statistical analysis of solar events associated with SSC over year of solar maximum during cycle 23: 2. Characterisation on the Sun-Earth path - Geoeffectiveness
  
  • Cornilleau-Wehrlin Nicole
  • Bocchialini Karine
  • Menvielle M.
  • Fontaine Dominique
  • Grison B.
  • Marchaudon A.
  • Pick Monique
  • Pitout F.
  • Schmieder Brigitte
  • Régnier Stéphane
  • Zouganelis Yannis
  • Chambodut Aude
  , 2017, 31. Taking the 32 sudden storm commencements (SSC) listed by the observatory de l'Ebre / ISGI over the year 2002 (maximal solar activity) as a starting point, we performed a statistical analysis of the related solar sources, solar wind signatures, and terrestrial responses. For each event, we characterized and identified, as far as possible, (i) the sources on the Sun (Coronal Mass Ejections -CME-), with the help of a series of criteria (velocities, drag coefficient, radio waves, magnetic field polarity), as well as (ii) the structure and properties in the interplanetary medium, at L1, of the event associated to the SSC: magnetic clouds -MC-, non-MC interplanetary coronal mass ejections -ICME-, co-rotating/stream interaction regions -SIR/CIR-, shocks only and unclear events that we call "miscellaneous" events. The geoeffectiveness of the events, classified by category at L1, is analysed by their signatures in the Earth ionized (magnetosphere and ionosphere) and neutral (thermosphere) environments, using a broad set of in situ, remote and ground based instrumentation. The role of the presence of a unique or of a multiple source at the Sun, of its nature, halo or non halo CME, is also discussed. The set of observations is statistically analyzed so as to evaluate and compare the geoeffectiveness of the events. The results obtained for this set of geomagnetic storms started by SSCs is compared to the overall statistics of year 2002, relying on already published catalogues of events, allowing assessing the relevance of our approach ; for instance all the 12 well identified Magnetic Clouds of 2002 give rise to SSCs.