Publications

2017

• 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
• 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
• 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.
• 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
• 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
• 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.
• Turbulence of Weak Gravitational Waves in the Early Universe
  
  • Galtier Sébastien
  • Nazarenko Sergey V.
  Physical Review Letters, American Physical Society, 2017, 119 (22), pp.221101. We study the statistical properties of an ensemble of weak gravitational waves interacting nonlinearly in a flat space-time. We show that the resonant three-wave interactions are absent and develop a theory for four-wave interactions in the reduced case of a 2.5+1 diagonal metric tensor. In this limit, where only plus-polarized gravitational waves are present, we derive the interaction Hamiltonian and consider the asymptotic regime of weak gravitational wave turbulence. Both direct and inverse cascades are found for the energy and the wave action, respectively, and the corresponding wave spectra are derived. The inverse cascade is characterized by a finite-time propagation of the metric excitations—a process similar to an explosive nonequilibrium Bose–Einstein condensation, which provides an efficient mechanism to ironing out small-scale inhomogeneities. The direct cascade leads to an accumulation of the radiation energy in the system. These processes might be important for understanding the early Universe where a background of weak nonlinear gravitational waves is expected. (10.1103/PhysRevLett.119.221101)
  DOI : 10.1103/PhysRevLett.119.221101
• 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.
• Promoting lentil germination and stem growth by plasma activated tap water, demineralized water and liquid fertilizer
  
  • Zhang Shiqiang
  • Rousseau Antoine
  • Dufour Thierry
  RSC Advances, Royal Society of Chemistry, 2017, 7 (50), pp.31244–31251. Tap water, demineralized water and liquid fertilizer have been activated using an atmospheric pressure plasma jet (APPJ) to investigate their benefits for the germination rate and stem elongation rate of lentils from Puy-en-Velay (France). By plasma-activating tap water, we have obtained germination rates as high as 80% (instead of 30% with tap water). Also, higher stem elongation rates and final stem lengths were obtained using activated tap water compared with commercial fertilizer. We show that these rates of germination and stem growth strongly depend on the combination of two radicals generated in the liquids by the plasma: hydrogen peroxide and nitrate. This synergy appears to be a condition for releasing seed dormancy through the endogenous production of NO radicals. (10.1039/C7RA04663D)
  DOI : 10.1039/C7RA04663D
• QDB: a new database of plasma chemistries and reactions
  
  • Tennyson Jonathan
  • Rahimi Sara
  • Hill Christian
  • Tse Lisa
  • Vibhakar Anuradha
  • Akello-Egwel Dolica
  • Brown Daniel B
  • Dzarasova Anna
  • Hamilton James R
  • Jaksch Dagmar
  • Mohr Sebastian
  • Wren-Little Keir
  • Bruckmeier Johannes
  • Agarwal Ankur
  • Bartschat Klaus
  • Annemie Bogaerts Annemie
  • Booth Jean-Paul
  • Goeckner Matthew J
  • Hassouni Khaled
  • Itikawa Yukikazu
  • Braams Bastiaan J
  • Krishnakumar E.
  • Laricchiuta Annarita
  • Mason Nigel J
  • Pandey Sumeet
  • Petrovic Zoran Lj
  • Pu Yi-Kang
  • Ranjan Alok
  • Rauf S.
  • Schulze J.
  • Turner M.M.
  • Ventzek Peter
  • Whitehead J.C.
  • Yoon Jung-Sik
  Plasma Sources Science and Technology, IOP Publishing, 2017, 26 (5), pp.055014. One of the most challenging and recurring problems when modeling plasmas is the lack of data on the key atomic and molecular reactions that drive plasma processes. Even when there are data for some reactions, complete and validated datasets of chemistries are rarely available. This hinders research on plasma processes and curbs development of industrial applications. The QDB project aims to address this problem by providing a platform for provision, exchange, and validation of chemistry datasets. A new data model developed for QDB is presented. QDB collates published data on both electron scattering and heavy-particle reactions. These data are formed into reaction sets, which are then validated against experimental data where possible. This process produces both complete chemistry sets and identifies key reactions that are currently unreported in the literature. Gaps in the datasets can be filled using established theoretical methods. Initial validated chemistry sets for SF 6 /CF 4 /O 2 and SF 6 /CF 4 /N 2 /H 2 are presented as examples. (10.1088/1361-6595/aa6669)
  DOI : 10.1088/1361-6595/aa6669
• Interplay between Alfvén and magnetosonic waves in compressible magnetohydrodynamics turbulence
  
  • Andrés Nahuel
  • Leoni P. Clark Di
  • Mininni P. D.
  • Dmitruk P.
  • Sahraoui Fouad
  • Matthaeus W. H.
  Physics of Plasmas, American Institute of Physics, 2017, 24, pp.102314. Using spatio-temporal spectra, we show direct evidence of excitation of magnetosonic and Alfvén waves in three-dimensional compressible magnetohydrodynamic turbulence at small Mach numbers. For the plasma pressure dominated regime, or the high beta regime (with beta the ratio between fluid and magnetic pressure), and for the magnetic pressure dominated regime, or the low beta regime, we study magnetic field fluctuations parallel and perpendicular to a guide magnetic field B<SUB>0</SUB>. In the low beta case, we find excitation of compressible and incompressible fluctuations, with a transfer of energy towards Alfvénic modes and to a lesser extent towards magnetosonic modes. In particular, we find signatures of the presence of fast magnetosonic waves in a scenario compatible with that of weak turbulence. In the high beta case, fast and slow magnetosonic waves are present, with no clear trace of Alfvén waves, and a significant part of the energy is carried by two-dimensional turbulent eddies. (10.1063/1.4997990)
  DOI : 10.1063/1.4997990
• 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
• Stable and unstable roots of ion temperature gradient driven mode using curvature modified plasma dispersion functions
  
  • Gultekin Ozgur
  • Gürcan Özgür D.
  Plasma Physics and Controlled Fusion, IOP Publishing, 2017, 60 (2), pp.025021. Basic, local kinetic theory of ion temperature gradient driven (ITG) mode, with adiabatic electrons is reconsidered. Standard unstable, purely oscillating as well as damped solutions of the local dispersion relation are obtained using a bracketing technique that uses the argument principle. This method requires computing the plasma dielectric function and its derivatives, which are implemented here using modified plasma dispersion functions with curvature and their derivatives, and allows bracketing/following the zeros of the plasma dielectric function which corresponds to different roots of the ITG dispersion relation. We provide an open source implementation of the derivatives of modified plasma dispersion functions with curvature, which are used in this formulation. Studying the local ITG dispersion, we find that near the threshold of instability the unstable branch is rather asymmetric with oscillating solutions towards lower wave numbers (i.e. drift waves), and damped solutions toward higher wave numbers. This suggests a process akin to inverse cascade by coupling to the oscillating branch towards lower wave numbers may play a role in the nonlinear evolution of the ITG, near the instability threshold. Also, using the algorithm, the linear wave diffusion is estimated for the marginally stable ITG mode. (10.1088/1361-6587/aa9e27)
  DOI : 10.1088/1361-6587/aa9e27
• 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&#8741; symmetry breaking for their survival which can be supplied by various means like mean E&#8201;×&#8201;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
• Capacitively coupled hydrogen plasmas sustained by tailored voltage waveforms: vibrational kinetics and negative ions control
  
  • Diomede P.
  • Bruneau Bastien
  • Longo S.
  • Johnson E.V.
  • Booth Jean-Paul
  Plasma Sources Science and Technology, IOP Publishing, 2017, 26 (7), pp.075007. A comprehensive hybrid model of a hydrogen capacitively coupled plasma, including a detailed description of the molecular vibrational kinetics, has been applied to the study of the effect of tailored voltage waveforms (TVWs) on the production kinetics and transport of negative ions in these discharges. Two kinds of TVWs are considered, valleys-to-peaks and saw-tooth, with amplitude and slope asymmetry respectively. By tailoring the voltage waveform only, it is possible to exert substantial control over the peak density and position of negative ions inside the discharge volume. This control is particularly effective for saw-tooth waveforms. Insight into the mechanisms allowing this control is provided by an analysis of the model results. This reveals the roles of the vibrational distribution function and of the electron energy distribution and their correlations, as well as changes in the negative ion transport in the electric field when using different TVWs. Considering the chemical reactivity of H ? ions, the possibility of a purely electrical control of the negative ion cloud in a reactor operating with a feedstock gas diluted by hydrogen may find interesting applications. This is the first study of vibrational kinetics in the context of TVWs in molecular gases. (10.1088/1361-6595/aa752c)
  DOI : 10.1088/1361-6595/aa752c
• 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
• 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.
• Measurements of density fluctuations in magnetic confined plasmas using Doppler backscattering technique
  
  • Vermare Laure
  • Hennequin Pascale
  • Honoré Cyrille
  • Pisarev V.
  • Giacalone J-C.
  , 2017.
• Saturation of energetic-particle-driven geodesic acoustic modes due to wave–particle nonlinearity
  
  • Biancalani A.
  • Chavdarovski I.
  • Qiu Z.
  • Bottino A.
  • Sarto D. Del
  • Ghizzo A.
  • Gürcan Özgür D.
  • Morel Pierre
  • Novikau I.
  Journal of Plasma Physics, Cambridge University Press (CUP), 2017, 83 (6), pp.725830602. The nonlinear dynamics of energetic-particle (EP) driven geodesic acoustic modes (EGAM) is investigated here. A numerical analysis with the global gyrokinetic particle-in-cell code ORB5 is performed, and the results are interpreted with the analytical theory, in close comparison with the theory of the beam-plasma instability. Only axisymmetric modes are considered, with a nonlinear dynamics determined by wave-particle interaction. Quadratic scalings of the saturated electric field with respect to the linear growth rate are found for the case of interest. As a main result, the formula for the saturation level is provided. Near the saturation, we observe a transition from adiabatic to non-adiabatic dynamics, i.e., the frequency chirping rate becomes comparable to the resonant EP bounce frequency. The numerical analysis is performed here with electrostatic simulations with circular flux surfaces, and kinetic effects of the electrons are neglected. (10.1017/S0022377817000976)
  DOI : 10.1017/S0022377817000976
• 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
• 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
• Drift waves, intense parallel electric fields, and turbulence associated with asymmetric magnetic reconnection at the magnetopause
  
  • Ergun R. E.
  • Chen L.-J.
  • Wilder F. D.
  • Ahmadi N.
  • Eriksson S.
  • Usanova M. E.
  • Goodrich K. A.
  • Holmes J. C.
  • Sturner A. P.
  • Malaspina D. M.
  • Newman D. L.
  • Torbert R. B.
  • Argall M. R.
  • Lindqvist P.-A.
  • Burch J. L.
  • Webster J. M.
  • Drake J. F.
  • Price L.
  • Cassak P. A.
  • Swisdak M.
  • Shay M. A.
  • Graham D. B.
  • Strangeway R. J.
  • Russell C. T.
  • Giles B. L.
  • Dorelli J. C.
  • Gershman D. J.
  • Avanov L.
  • Hesse Michael
  • Lavraud B.
  • Le Contel Olivier
  • Retinò Alessandro
  • Phan T. D.
  • Goldman M. V.
  • Stawarz J. E.
  • Schwartz S. J.
  • Eastwood Jonathan P.
  • Hwang K.-J.
  • Nakamura R.
  • Wang S.
  Geophysical Research Letters, American Geophysical Union, 2017, 44 (7), pp.2978-2986. Observations of magnetic reconnection at Earth's magnetopause often display asymmetric structures that are accompanied by strong magnetic field (B) fluctuations and large-amplitude parallel electric fields (E<SUB>||</SUB>). The B turbulence is most intense at frequencies above the ion cyclotron frequency and below the lower hybrid frequency. The B fluctuations are consistent with a thin, oscillating current sheet that is corrugated along the electron flow direction (along the X line), which is a type of electromagnetic drift wave. Near the X line, electron flow is primarily due to a Hall electric field, which diverts ion flow in asymmetric reconnection and accompanies the instability. Importantly, the drift waves appear to drive strong parallel currents which, in turn, generate large-amplitude ( 100 mV/m) E<SUB>||</SUB> in the form of nonlinear waves and structures. These observations suggest that turbulence may be common in asymmetric reconnection, penetrate into the electron diffusion region, and possibly influence the magnetic reconnection process. (10.1002/2016GL072493)
  DOI : 10.1002/2016GL072493
• 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
• E x B staircases and barrier permeability in magnetised plasmas
  
  • Hornung G.
  • Dif-Pradalier Guilhem
  • Clairet F.
  • Sarazin Y.
  • Sabot R.
  • Hennequin Pascale
  • Verdoolaege G.
  Nuclear Fusion, IOP Publishing, 2017, 57 (1), pp.014006. In-depth experimental characterisation of spontaneous shear flow patterning into a so-called ##IMG## [http://ej.iop.org/images/0029-5515/57/1/014006/nfaa42aaieqn003.gif] \mathbfE× \mathbfB staircase?named after its planetary analogue?is shown in magnetised plasma turbulence, using ultrafast-sweeping reflectometry in the Tore Supra tokamak. Staircase signatures are found in a large variety of L-mode plasma conditions. Sensitivity to the dominant source of free energy is highlighted for the first time. A connection between staircase shear layer permeability and deviation from gyro-Bohm confinement scaling is strongly suggested, opening new routes to understanding confinement in drift-wave turbulence. (10.1088/0029-5515/57/1/014006)
  DOI : 10.1088/0029-5515/57/1/014006