Publications

2017

• Intrinsic non-inductive current driven by ETG turbulence in tokamaks
  
  • Kaw P. K.
  • Singh R.
  • Gürcan Özgür D.
  Physics of Plasmas, American Institute of Physics, 2017, 24, pp.102303. Motivated by observations and physics understanding of the phenomenon of intrinsic rotation, it is suggested that similar considerations for electron dynamics may result in intrinsic current in tokamaks. We have investigated the possibility of intrinsic non-inductive current in the turbulent plasma of tokamaks. Ohm's law is generalized to include the effect of turbulent fluctuations in the mean field approach. This clearly leads to the identification of sources and the mechanisms of non-inductive current drive by electron temperature gradient turbulence. It is found that a mean parallel electro-motive force and hence a mean parallel current can be generated by (1) the divergence of residual current flux density and (2) a non-flux like turbulent source from the density and parallel electric field correlations. Both residual flux and the non-flux source require parallel wave-number k∥ symmetry breaking for their survival which can be supplied by various means like mean E × B shear, turbulence intensity gradient, etc. Estimates of turbulence driven current are compared with the background bootstrap current in the pedestal region. It is found that turbulence driven current is nearly 10% of the bootstrap current and hence can have a significant influence on the equilibrium current density profiles and current shear driven modes. (10.1063/1.4990746)
  DOI : 10.1063/1.4990746
• Absolute ozone densities in a radio-frequency driven atmospheric pressure plasma using two-beam UV-LED absorption spectroscopy and numerical simulations
  
  • Wijaikhum A.
  • Schröder D.
  • Schröter S.
  • Gibson A. R.
  • Niemi K.
  • Friderich J.
  • Greb A.
  • Schulz-von der Gathen V.
  • O'Connell D.
  • Gans T.
  Plasma Sources Science and Technology, IOP Publishing, 2017, 26. The efficient generation of reactive oxygen species (ROS) in cold atmospheric pressure plasma jets (APPJs) is an increasingly important topic, e.g. for the treatment of temperature sensitive biological samples in the field of plasma medicine. A 13.56 MHz radio-frequency (rf) driven APPJ device operated with helium feed gas and small admixtures of oxygen (up to 1%), generating a homogeneous glow-mode plasma at low gas temperatures, was investigated. Absolute densities of ozone, one of the most prominent ROS, were measured across the 11 mm wide discharge channel by means of broadband absorption spectroscopy using the Hartley band centred at lambda = 255 nm. A two-beam setup with a reference beam in Mach--Zehnder configuration is employed for improved signal-to-noise ratio allowing high-sensitivity measurements in the investigated single-pass weak-absorbance regime. The results are correlated to gas temperature measurements, deduced from the rotational temperature of the N<SUB>2</SUB> (C <SUP>3</SUP> {{{\Pi }}}<SUB>u</SUB><SUP> </SUP> \to B <SUP>3</SUP> {{{\Pi }}}<SUB>g</SUB><SUP> </SUP>, upsilo = 0 \to 2) optical emission from introduced air impurities. The observed opposing trends of both quantities as a function of rf power input and oxygen admixture are analysed and explained in terms of a zero-dimensional plasma-chemical kinetics simulation. It is found that the gas temperature as well as the densities of O and O<SUB>2</SUB>(b{}<SUP>1</SUP>{{{Sigma }}}<SUB>g</SUB><SUP> </SUP>) influence the absolute O<SUB>3</SUB> densities when the rf power is varied. (10.1088/1361-6595/aa8ebb)
  DOI : 10.1088/1361-6595/aa8ebb
• Space Weather, from the Sun to the Earth, the key role of GNSS. Part II: Training on daily Global Positioning System (GPS) data
  
  • Amory-Mazaudier Christine
  • Fleury Rolland
  • Gadimova Sharafat
  • Touzani Abderrahmane
  Coordinates, 2017, 13 (3), pp.31-36. The goal of this paper is to give a clear view of the Sun Earth relationships that are complex. The phenomena acting at large scales and essentially related to dynamic and electromagnetic physical processes have been addressed. Besides physics, the work done to develop the training in Space Weather by focusing on Global Navigation Satellite Systems has also been presented. Readers may recall that we published the first part of this article which focused on physics of the relationships Sun, Earth and Meteorology of Space. In this issue, aspects of GNSS training and capacity building are discussed.
• Experimental study of the interaction of two laser-driven radiative shocks at the PALS laser
  
  • Singh R. L.
  • Stehlé C.
  • Suzuki-Vidal F.
  • Kozlova M.
  • Larour Jean
  • Chaulagain U.
  • Clayson T.
  • Rodriguez R.
  • Gil M.
  • Nejdl J.
  • Krus M.
  • Dostal J.
  • Dudzak R.
  • Barroso P.
  • Acef O.
  • Cotelo M.
  • Velarde P.
  High Energy Density Physics, Elsevier, 2017, 23, pp.20 - 30. Radiative shocks (RS) are complex phenomena which are ubiquitous in astrophysical environments. The study of such hypersonic shocks in the laboratory, under controlled conditions, is of primary interest to understand the physics at play and also to check the ability of numerical simulations to reproduce the experimental results. In this context, we conducted, at the Prague Asterix Laser System facility (PALS), the first experiments dedicated to the study of two counter-propagating radiative shocks propagating at non-equal speeds up to 25–50 km/s in noble gases at pressures ranging between 0.1 and 0.6 bar. These experiments highlighted the interaction between the two radiative precursors. This interaction is qualitatively but not quantitatively described by 1D simulations. Preliminary results obtained with XUV spectroscopy leading to the estimation of shock temperature and ion charge of the plasma are also presented. (10.1016/j.hedp.2017.03.001)
  DOI : 10.1016/j.hedp.2017.03.001
• Multipoint Observations of Energetic Particle Injections and Substorm Activity During a Conjunction Between Magnetospheric Multiscale (MMS) and Van Allen Probes
  
  • Turner D. L.
  • Fennell J. F.
  • Blake J. B.
  • Claudepierre S. G.
  • Clemmons J. H.
  • Jaynes A. N.
  • Leonard T.
  • Baker D. N.
  • Cohen I. J.
  • Gkioulidou M.
  • Ukhorskiy A. Y.
  • Mauk B. H.
  • Gabrielse C.
  • Angelopoulos V.
  • Strangeway R. J.
  • Kletzing C. A.
  • Le Contel Olivier
  • Spence H. E.
  • Torbert R. B.
  • Burch J. L.
  • Reeves G. D.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2017, 122 (11), pp.481-504. This study examines multipoint observations during a conjunction between Magnetospheric Multiscale (MMS) and Van Allen Probes on 7 April 2016 in which a series of energetic particle injections occurred. With complementary data from Time History of Events and Macroscale Interactions during Substorms, Geotail, and Los Alamos National Laboratory spacecraft in geosynchronous orbit (16 spacecraft in total), we develop new insights on the nature of energetic particle injections associated with substorm activity. Despite this case involving only weak substorm activity (maximum AE <300 nT) during quiet geomagnetic conditions in steady, below-average solar wind, a complex series of at least six different electron injections was observed throughout the system. Intriguingly, only one corresponding ion injection was clearly observed. All ion and electron injections were observed at <600 keV only. MMS reveals detailed substructure within the largest electron injection. A relationship between injected electrons with energy <60 keV and enhanced whistler mode chorus wave activity is also established from Van Allen Probes and MMS. Drift mapping using a simplified magnetic field model provides estimates of the dispersionless injection boundary locations as a function of universal time, magnetic local time, and L shell. The analysis reveals that at least five electron injections, which were localized in magnetic local time, preceded a larger injection of both electrons and ions across nearly the entire nightside of the magnetosphere near geosynchronous orbit. The larger ion and electron injection did not penetrate to L < 6.6, but several of the smaller electron injections penetrated to L < 6.6. Due to the discrepancy between the number, penetration depth, and complexity of electron versus ion injections, this event presents challenges to the current conceptual models of energetic particle injections. (10.1002/2017JA024554)
  DOI : 10.1002/2017JA024554
• Study of Plasma Waves Observed onboard Rosetta in the 67P/ChuryumovGerasimenko Comet Environment Using High Time Resolution Density Data Inferred from RPC-MIP and RPC-LAP Cross-calibration
  
  • Breuillard H.
  • Henri P.
  • Vallières Xavier
  • Eriksson A. I.
  • Odelstad E.
  • Johansson F. L.
  • Richter I.
  • Goetz C.
  • Wattieaux G.
  • Tsurutani B.
  • Hajra R.
  • Le Contel O.
  , 2017, 2017. During two years, the groundbreaking ESA/Rosetta mission was able to escort comet 67P where previous cometary missions were only limited to flybys. This enabled for the first time to make in-situ measurements of the evolution of a comet's plasma environment. The density and temperature measured by Rosetta are derived from RPC-Mutual Impedance Probe (MIP) and RPC-Langmuir Probe (LAP). On one hand, low time resolution electron density are calculated using the plasma frequency extracted from the MIP mutual impedance spectra. On the other hand, high time resolution density fluctuations are estimated from the spacecraft potential measured by LAP. In this study, using a simple spacecraft charging model, we perform a cross-calibration of MIP plasma density and LAP spacecraft potential variations to obtain high time resolution measurements of the electron density. These results are also used to constrain the electron temperature. Then we make use of these new dataset, together with RPC-MAG magnetic field measurements, to investigate for the first time the compressibility and the correlations between plasma and magnetic field variations, for both singing comet waves and steepened waves observed, respectively during low and high cometary outgassing activity, in the plasma environment of comet 67P.
• Vibrational kinetics of non-equilibrium CO<SUB>2</SUB> plasma discharge in low-excitation regime
  
  • Grofulovic Marija
  • Silva Tiago
  • Guerra V.
  • Pintassilgo C.D.
  • Klarenaar Bart
  • Engeln Richard
  • Morillo-Candas Ana-Sofia
  • Guaitella Olivier
  , 2017, 62.
• Three-dimensional Simulations and Spacecraft Observations of Sub-ion Scale Turbulence in the Solar Wind: Influence of Landau Damping
  
  • Kobayashi Sumire
  • Sahraoui Fouad
  • Passot T.
  • Laveder D.
  • Sulem P.
  • Huang S. Y.
  • Henri Pierre
  • Smets R.
  The Astrophysical Journal, American Astronomical Society, 2017, 839 (2), pp.122. Three-dimensional nonlinear finite Larmor radius (FLR)–Landau fluid simulations, which include some small-scale $({k}_{\perp }{\rho }_{i}\gtrsim 1)$ kinetic effects, are performed to explore the nature of the sub-ion scale turbulence in the solar wind and to investigate the role of Landau damping and FLR corrections. The resulting steady-state magnetic power spectrum in the dispersive range display exponents that vary within a range of values compatible with statistical results reported from in situ spacecraft measurements of solar wind turbulence as well as from gyrokinetic simulations. The spectral slopes are shown to depend on the strength of the nonlinear effects and on the scale at which turbulent fluctuations are driven in the simulations. The influence of Landau damping is addressed by comparison with simulations where the double-adiabatic closure is imposed. The role of FLR corrections is also analyzed. Comparison with in situ observations in the solar wind are performed to enlighten the influence of the fluctuations power at different scales on the spectral slopes in the sub-ion range. Using diagnosis of both magnetic compressibility and frequency-wavenumber spectra, it is shown that in spite of the evidence of the presence of fast-magnetosonic modes, the magnetic energy is mostly distributed around the kinetic Alfvén waves and the slow modes, in agreement with solar wind measurements. The observed large broadening about the linear dispersion relations may reflect the presence of coherent structures. (10.3847/1538-4357/aa67f2)
  DOI : 10.3847/1538-4357/aa67f2
• 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
• 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
• 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
• 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
• 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
• 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.
• 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
• 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
• Measurements of density fluctuations in magnetic confined plasmas using Doppler backscattering technique
  
  • Vermare Laure
  • Hennequin Pascale
  • Honoré Cyrille
  • Pisarev V.
  • Giacalone J-C.
  , 2017.
• 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
• 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 <SUB>E</SUB> were present in the night-side magnetosphere. This global dipolarization consisted of multiple short-timescale (a couple of minutes) B <SUB> z </SUB> 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
• 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 <SUB>i</SUB> (~30 rho <SUB>e</SUB>) in the quasi-circular cross-section perpendicular to its axis, where rho <SUB>i</SUB> and rho <SUB>e</SUB> 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 <SUB>em</SUB> and V <SUB>en</SUB> 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
• 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
• 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
• Ignition of high pressure lean H<SUB>2</SUB>:air mixture along the multiple channels of nanosecond surface discharge
  
  • Shcherbanev S.A.
  • Popov N.A.
  • Starikovskaia Svetlana
  Combustion and Flame, Elsevier, 2017, 176, pp.272284. The initiation of combustion of lean H2 :air mixtures, ER = 0.50.6 , by nanosecond surface dielectric bar- rier discharge (nSDBD) was studied experimentally at high initial pressures, P=36 bar. The discharge was studied in different gas mixtures for the pressure range 112 bar. The ignition was initiated by two different discharge modes: streamer or filamentary nSDBD. The influence of the discharge structure and energy deposition on the ignition was demonstrated. Three regimes of multi-point ignition were observed: ignition with a few kernels, quasi-uniform ignition along the edge of the high voltage electrode and ignition along the plasma channels. The velocities of flame propagation were analyzed. The minimum ignition energy of the discharge and ignition delay time of combustion have been measured and analyzed with the help of kinetic numerical modeling. (10.1016/j.combustflame.2016.07.035)
  DOI : 10.1016/j.combustflame.2016.07.035