Publications

2018

• Self-organized patterns by a DC pin liquid anode discharge in ambient air: Effect of liquid types on formation
  
  • Zhang Shiqiang
  • Dufour Thierry
  Physics of Plasmas, American Institute of Physics, 2018, 25 (7), pp.073502. A pin liquid anode DC discharge is generated in open air without any additional gas feeding to form self-organized patterns (SOPs) on various liquid interfaces. Axially resolved emission spectra of the whole discharge reveal that the self-organized patterns are formed below a dark region and are visible mainly due to the N2 (C 3 -B 3 ) transitions. The high energy N2 (C) level is mainly excited by the impact of electrons heated by the local increased electric field at the interface. For the first time, the effect of the liquid type on the SOP formation is presented. With almost the same other discharge conditions, the formed SOPs are significantly different from HCl and H2SO4 liquid anodes. The SOP difference is repeated when the discharge current and gap distance change for both liquid anodes. The variations of SOP size and discretization as a function of discharge current and gap distance are discussed and confirm that different SOPs are formed by the HCl liquid anode from tap water or the H2SO4 liquid anode. A possible explanation is brought up to explain the dependence of SOPs on the liquid type. (10.1063/1.5030099)
  DOI : 10.1063/1.5030099
• Investigation of a plasma--target interaction through electric field characterization examining surface and volume charge contributions: modeling and experiment
  
  • Viegas Pedro
  • Slikboer Elmar
  • Obrusník Adam
  • Bonaventura Zdenek
  • Sobota Ana
  • Garcia-Caurel Enric
  • Guaitella Olivier
  • Bourdon Anne
  Plasma Sources Science and Technology, IOP Publishing, 2018, 27. Numerical simulations and experiments are performed to better understand the interaction between a pulsed helium plasma jet and a dielectric target. The focus of this work lies on the volume and surface charge influence on the electric field distribution. Experimentally, the electric field due to surface charges is measured inside an electro-optic target under exposure of a plasma jet, using the optical technique called Mueller polarimetry. For the first time, the time-resolved spatial distributions of both the axial and radial components of electric field inside the target are obtained simultaneously. A 2D fluid model is used in a complementary way to the experiments in order to study separately the contribution of volume charges and surface charges to the spatio-temporal evolutions of the electric field during the plasma--surface interaction. The experimental investigation shows that the average axial and radial components of electric field inside the dielectric target, only due to surface charges, are lower than generally reported for electric field values in the plasma plume. Thanks to the phenomenological comparison with experiments, simulations show that during the plasma--surface interaction two effects sequentially determine the electric field inside the target: firstly, a relatively high electric field is observed due to the proximity of the ionization front; afterwards, in longer timescales, lower electric fields are induced due to the contribution of both leftover volume charges close to the target and surface charges deposited on its surface. The experimental technique provides a unique way to examine this second phase of the plasma--surface interaction. (10.1088/1361-6595/aadcc0)
  DOI : 10.1088/1361-6595/aadcc0
• Study of Ionospheric Variability Using GNSS Observations
  
  • Taoufiq Jouan
  • Mourad Bouziani
  • Rachid Azzouzi
  • Amory-Mazaudier Christine
  Positioning, SCIRP, 2018, 09 (04), pp.79-96. <div><p>With the increasing number of applications of Global navigation satellite system, the modeling of the ionosphere is a crucial element for precise positioning. Indeed, the ionosphere delays the electromagnetic waves which pass through it and induces a delay of propagation related to the electronic density (TEC) Total Electronic Content and to the frequency of the wave. The impact of this ionospheric error often results in a poor determination of the station's position, particularly in strong solar activity. The first part of this paper focuses on a bibliographic study oriented first of all on the study of the ionosphere in relation to solar activity and secondly on the determination of the total electron content using GNSS measurements from the IGS network reference stations. Measurements were made on two permanent stations "RABT", "TETN". We selected years of GNSS measurements to evaluate the geomagnetic impact on the ionosphere, 2001, 2009 and 2013. A description of the ionospheric disturbances and geomagnetic storms was analyzed by determination of TEC, especially in high solar activity. The results show a strong dependence of the ionospheric activity with the geomagnetic activity.</p></div> (10.4236/pos.2018.94006)
  DOI : 10.4236/pos.2018.94006
• Kinetics of highly vibrationally excited O<SUB>2</SUB> (X) molecules in inductively-coupled oxygen plasmas
  
  • Annusova Adriana
  • Marinov Daniil
  • Booth Jean-Paul
  • Sirse Nishant
  • Silva Mrio Lino Da
  • Lopez B.
  • Guerra V.
  Plasma Sources Science and Technology, IOP Publishing, 2018, 27 (4), pp.045006. The high degree of vibrational excitation of O 2 ground state molecules recently observed in inductively coupled plasma discharges is investigated experimentally in more detail and interpreted using a detailed self-consistent 0D global kinetic model for oxygen plasmas. Additional experimental results are presented and used to validate the model. The vibrational kinetics considers vibrational levels up to v = 41 and accounts for electron impact excitation and de-excitation (e-V), vibration-to-translation relaxation (V-T) in collisions with O 2 molecules and O atoms, vibration-to-vibration energy exchanges (V-V), excitation of electronically excited states, dissociative electron attachment, and electron impact dissociation. Measurements were performed at pressures of 10?80 mTorr (1.33 and 10.67 Pa) and radio frequency (13.56 MHz) powers up to 500 W. The simulation results are compared with the absolute densities in each O 2 vibrational level obtained by high sensitivity absorption spectroscopy measurements of the Schumann?Runge bands for O 2 ( X , v = 4?18), O( 3 P ) atom density measurements by two-photon absorption laser induced fluorescence (TALIF) calibrated against Xe, and laser photodetachment measurements of the O ? negative ions. The highly excited O 2 ( X , v ) distribution exhibits a shape similar to a Treanor-Gordiets distribution, but its origin lies in electron impact e-V collisions and not in V-V up-pumping, in contrast to what happens in all other molecular gases known to date. The relaxation of vibrational quanta is mainly due to V-T energy-transfer collisions with O atoms and to electron impact dissociation of vibrationally excited molecules, e O 2 ( X , v )?O( 3 P) O( 3 P). (10.1088/1361-6595/aab47d)
  DOI : 10.1088/1361-6595/aab47d
• Recent advances in the modeling and computer simulations of non-equilibrium plasma discharges
  
  • Raja Laxminarayan L
  • Bourdon Anne
  • Ventzek Peter L G
  Journal of Physics D: Applied Physics, IOP Publishing, 2018, 51 (15), pp.150202. The mathematical modeling and computer simulation of low-temperature plasmas is gradually such a level of maturity that these simulation tools can be used not just for improving scientific understanding but also as computer-aided engineering design tools in an industrial setting. These models necessarily involve the description of multiple physical phenomena occurring over a range of times and lengths, thereby complicating their numerical implementation and solution. This special issue presents 12 invited contributions that present recent developments in the field of modeling and simulation of low-temperature plasma discharges. This editorial introduces these papers by providing an overview of the context in which these papers are presented. (10.1088/1361-6463/aab1b9)
  DOI : 10.1088/1361-6463/aab1b9
• Experimental benchmark of kinetic simulations of capacitively coupled plasmas in molecular gases
  
  • Donkó Z.
  • Derzsi A.
  • Korolov Ihor
  • Hartmann P.
  • Brandt S.
  • Schulze J.
  • Berger B.
  • Koepke M.
  • Bruneau Bastien
  • Johnson Erik
  • Lafleur Trevor
  • Booth Jean-Paul
  • Gibson Andrew
  • O'Connell D.
  • Gans T.
  Plasma Physics and Controlled Fusion, IOP Publishing, 2018, 60 (1), pp.014010. We discuss the origin of uncertainties in the results of numerical simulations of low-temperature plasma sources, focusing on capacitively coupled plasmas. These sources can be operated in various gases/gas mixtures, over a wide domain of excitation frequency, voltage, and gas pressure. At low pressures, the non-equilibrium character of the charged particle transport prevails and particle-based simulations become the primary tools for their numerical description. The particle-in-cell method, complemented with Monte Carlo type description of collision processes, is a well-established approach for this purpose. Codes based on this technique have been developed by several authors/groups, and have been benchmarked with each other in some cases. Such benchmarking demonstrates the correctness of the codes, but the underlying physical model remains unvalidated. This is a key point, as this model should ideally account for all important plasma chemical reactions as well as for the plasma-surface interaction via including specific surface reaction coefficients (electron yields, sticking coefficients, etc). In order to test the models rigorously, comparison with experimental ?benchmark data? is necessary. Examples will be given regarding the studies of electron power absorption modes in O 2 , and CF 4 ?Ar discharges, as well as on the effect of modifications of the parameters of certain elementary processes on the computed discharge characteristics in O 2 capacitively coupled plasmas. (10.1088/1361-6587/aa8378)
  DOI : 10.1088/1361-6587/aa8378
• The effects of secondary electron emission on plasma sheath characteristics and electron transport in an ExB discharge via kinetic simulations
  
  • Tavant Antoine
  • Croes Vivien
  • Lucken Romain
  • Lafleur Trevor
  • Bourdon Anne
  • Chabert Pascal
  Plasma Sources Science and Technology, IOP Publishing, 2018, 27 (12), pp.124001. Hall-effect thrusters, which are electrostatic devices based on an E B ´ plasma discharge, have successfully been used as satellite propulsion systems for the last few decades. However, the presence of anomalous electron cross-field transport is still poorly understood, and involves complex and strongly coupled mechanisms such as azimuthal electron drift instabilities and intense secondary electron emission (SEE) from the thruster walls. The present work focuses on the relative importance of these two phenomena. We use a 2D particle-in-cell/Monte Carlo collision model configured to simulate the radial-azimuthal directions near the thruster exit plane. A constant radial magnetic field and axial electric field are imposed, and electron drift instabilities are observed in the azimuthal (E B ´) direction. A simplified SEE model is implemented and an extensive parametric study is performed to directly determine the effect on electron transport. It is found that, for the operating conditions used in our simulations, SEE enhances the near-wall electron mobility by a factor 2, while reducing the bulk plasma mobility by about 20% (due to electron cooling). However, the dominant contribution to anomalous electron transport is still observed to be caused by electron drift instabilities driven by the E B ´ discharge configuration. SEE modifies the electron mobility profile, but the spatially-averaged value remains relatively constant. Three different operating regimes are identified depending on the SEE rate value: two that are stable, and a third which shows an oscillatory behaviour. In addition to electron transport, the kinetic simulations give new insight into the plasma sheath formation at the radial walls, and comparison with typical analytical sheath models demonstrate important differences. (10.1088/1361-6595/aaeccd)
  DOI : 10.1088/1361-6595/aaeccd
• Multi-variable comprehensive analysis of two great geomagnetic storms of 2015
  
  • Kashcheyey Anton
  • Migoya-Orué Yenca
  • Amory-Mazaudier Christine
  • Fleury Rolland
  • Nava B.
  • Alazo-Cuartas K.
  • Radicella S.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2018. During the year 2015 two great geomagnetic storms (Dst<-200nT) occurred on 17 March and 22 June. These two geomagnetic storms have similarities. They occurred during the same decreasing phase of the sunspot cycle 24. The interplanetary and magnetospheric environments were calm before the beginning of the storms. Both events were due to Coronal Mass Ejections (CME)and High Speed Solar Wind (HSSW). Variations of the solar wind velocity and the Bz component of the interplanetary magnetic field (IMF) were also similar. Two key features that are different for these storms are UT time of the beginning(04:45UT for 17March and 18:33UT for 22June) and season (equinox and solstice). The comparison of the impact of the storms on the Earth ionosphere and magnetosphere have been performed using diverse parameters including global ionospheric maps (GIMs) of vertical total electron content (VTEC), data from individual GNSS receivers, ionosondes, magnetometers and instruments from different space missions. Visualizing GIM data as the difference of VTEC between consecutive days allowed understanding better the effect of the storms as a function of time of the beginning of the storm and of the season. It is shown that the presence or absence of scintillations in GNSS signals during these 2 storms in African longitude sector is clearly related to the local time at a given station at the beginning of the storm. (10.1029/2017JA024900)
  DOI : 10.1029/2017JA024900
• 3D Anisotropy of Solar Wind Turbulence, Tubes, or Ribbons?
  
  • Verdini Andrea
  • Grappin Roland
  • Alexandrova Olga
  • Lion Sonny
  The Astrophysical Journal, American Astronomical Society, 2018, 853 (1), pp.85. We study the anisotropy with respect to the local magnetic field of turbulent magnetic fluctuations at magnetofluid scales in the solar wind. Previous measurements in the fast solar wind obtained axisymmetric anisotropy, despite that the analysis method allows nonaxisymmetric structures. These results are probably contaminated by the wind expansion that introduces another symmetry axis, namely, the radial direction, as indicated by recent numerical simulations. These simulations also show that while the expansion is strong, the principal fluctuations are in the plane perpendicular to the radial direction. Using this property, we separate 11 yr of Wind spacecraft data into two subsets characterized by strong and weak expansion and determine the corresponding turbulence anisotropy. Under strong expansion, the small-scale anisotropy is consistent with the Goldreich & Sridhar critical balance. As in previous works, when the radial symmetry axis is not eliminated, the turbulent structures are field-aligned tubes. Under weak expansion, we find 3D anisotropy predicted by the Boldyrev model, that is, turbulent structures are ribbons and not tubes. However, the very basis of the Boldyrev phenomenology, namely, a cross-helicity increasing at small scales, is not observed in the solar wind: the origin of the ribbon formation is unknown. (10.3847/1538-4357/aaa433)
  DOI : 10.3847/1538-4357/aaa433
• Cometary plasma response to interplanetary corotating interaction regions during 2016 June–September: a quantitative study by the Rosetta Plasma Consortium
  
  • Hajra Rajkumar
  • Henri Pierre
  • Myllys Minna
  • Héritier Kevin
  • Galand Marina
  • Simon wedlund Cyril
  • Breuillard Hugo
  • Behar Etienne
  • Edberg Niklas
  • Goetz Charlotte
  • Nilsson Hans
  • Eriksson Anders I.
  • Goldstein Raymond
  • Tsurutani Bruce T
  • Moré Jérome
  • Vallières Xavier
  • Wattieaux Gaëtan
  Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP): Policy P - Oxford Open Option A, 2018, 480 (4), pp.4544-4556. Four interplanetary corotating interaction regions (CIRs) were identified during 2016 June–September by the Rosetta Plasma Consortium (RPC) monitoring in situ the plasma environment of the comet 67P/Churyumov–Gerasimenko (67P) at heliocentric distances of ∼3–3.8 au. The CIRs, formed in the interface region between low- and high-speed solar wind streams with speeds of ∼320–400 km s−1 and ∼580–640 km s−1, respectively, are characterized by relative increases in solar wind proton density by factors of ∼13–29, in proton temperature by ∼7–29, and in magnetic field by ∼1–4 with respect to the pre-CIR values. The CIR boundaries are well defined with interplanetary discontinuities. Out of 10 discontinuities, four are determined to be forward waves and five are reverse waves, propagating at ∼5–92 per cent of the magnetosonic speed at angles of ∼20°–87° relative to ambient magnetic field. Only one is identified to be a quasi-parallel forward shock with magnetosonic Mach number of ∼1.48 and shock normal angle of ∼41°. The cometary ionosphere response was monitored by Rosetta from cometocentric distances of ∼4–30 km. A quiet time plasma density map was developed by considering dependences on cometary latitude, longitude, and cometocentric distance of Rosetta observations before and after each of the CIR intervals. The CIRs lead to plasma density enhancements of ∼500–1000 per cent with respect to the quiet time reference level. Ionospheric modelling shows that increased ionization rate due to enhanced ionizing (>12–200 eV) electron impact is the prime cause of the large cometary plasma density enhancements during the CIRs. Plausible origin mechanisms of the cometary ionizing electron enhancements are discussed. (10.1093/mnras/sty2166)
  DOI : 10.1093/mnras/sty2166
• SMILEI : A collaborative, open-source, multi-purpose particle-in-cell code for plasma simulation
  
  • Derouillat J.
  • Beck A.
  • Pérez F.
  • Vinci T.
  • Chiaramello M.
  • Grassi A.
  • Flé M.
  • Bouchard G.
  • Plotnikov I.
  • Aunai Nicolas
  • Dargent Jérémy
  • Riconda C.
  • Grech M.
  Computer Physics Communications, Elsevier, 2018, 222, pp.351-373. SMILEI is a collaborative, open-source, object-oriented (C ) particle-in-cell code. To benefit from the latest advances in high-performance computing (HPC), SMILEI is co-developed by both physicists and HPC experts. The code's structures, capabilities, parallelization strategy and performances are discussed. Additional modules (e.g. to treat ionization or collisions), benchmarks and physics highlights are also presented. Multi-purpose and evolutive, SMILEI is applied today to a wide range of physics studies, from relativistic laser-plasma interaction to astrophysical plasmas. (10.1016/j.cpc.2017.09.024)
  DOI : 10.1016/j.cpc.2017.09.024
• Kinetic study of CO<SUB>2</SUB> plasmas under non-equilibrium conditions. II. Input of vibrational energy
  
  • Grofulovic Marija
  • Silva Tiago
  • Klarenaar Bart
  • Morillo-Candas Ana-Sofia
  • Guaitella Olivier
  • Engeln Richard
  • Pintassilgo C.D.
  • Guerra V.
  Plasma Sources Science and Technology, IOP Publishing, 2018. This is the second of two papers presenting the study of vibrational energy exchanges in non-equilibrium CO₂ plasmas in low-excitation conditions. The companion paper addresses a theoretical and experimental investigation of the time relaxation of ~70 individual vibrational levels of ground-state CO₂(X¹&#931;) molecules during the afterglow of a pulsed DC glow discharge, operating at pressures of a few Torr and discharge currents around 50 mA, where the rate coefficients for vibration-translation (V-T) and vibration-vibration (V-V) energy transfers among these levels are validated. Herein the investigation focus the active discharge, by extending the model with the inclusion of electron impact processes for vibrational excitation and de-excitation (e-V). The time-dependent calculated densities of the different vibrational levels are compared with experimental data obtained from time-resolved in situ Fourier Transform Infrared spectroscopy. It is shown that the vibrational temperature of the asymmetric stretching mode is always larger than the vibrational temperatures of the bending and symmetric stretching modes along the discharge pulse, the latter two remaining very nearly the same and close to the gas temperature. The general good agreement between the model predictions and the experimental results validates the e-V rate coefficients used and gives confidence that the proposed kinetic scheme provides a solid basis to understand the vibrational energy exchanges occurring in CO₂ plasmas. (10.1088/1361-6595/aadb60)
  DOI : 10.1088/1361-6595/aadb60
• Fast gas heating and radial distribution of active species in nanosecond capillary discharge in pure nitrogen and N<SUB>2</SUB>:O<SUB>2</SUB> mixtures
  
  • Lepikhin N D
  • Popov N.A.
  • Starikovskaia Svetlana
  Plasma Sources Science and Technology, IOP Publishing, 2018, 27, pp.055005. Fast gas heating is studied experimentally and numerically using pulsed nanosecond capillary discharge in pure nitrogen and N2:O2 mixtures under the conditions of high specific deposited energy (up to 1 eV/molecule) and high reduced electric fields (100300 Td). Deposited energy, electric field and gas temperature are measured as functions of time. The radial distribution of active species is analyzed experimentally. The roles of processes involving excited N2 molecules and ions and N(2D) excited nitrogen species leading to heat release are analyzed using numerical modeling in the framework of 1D axial approximation. (10.1088/1361-6595/aab74e)
  DOI : 10.1088/1361-6595/aab74e
• Poloidal asymmetries of flows in the Tore Supra tokamak
  
  • Vermare Laure
  • Hennequin Pascale
  • Gürcan Özgür D.
  • Garbet X.
  • Honoré Cyrille
  • Clairet F.
  • Giacalone J-C.
  • Morel Pierre
  • Storelli A.
  • Team Tore Supra
  Physics of Plasmas, American Institute of Physics, 2018, 25 (2), pp.020704. Simultaneous measurements of binormal velocity of density fluctuations using two separate Doppler backscattering systems at the low field side and at the top of the plasma show significant poloidal asymmetry. The measurements are performed in the core region between the radii 0.7&#8201;<&#8201;&#961;&#8201; < &#8201;0.95, over a limited number of L-mode discharges covering a wide range of plasma conditions in the Tore Supra tokamak. A possible generation mechanism by the ballooned structure of the underlying turbulence, in the form of convective cells, is proposed for explaining the observation of these poloidally asymmetric mean flows. (10.1063/1.5022122)
  DOI : 10.1063/1.5022122
• Electron Power-Law Spectra in Solar and Space Plasmas
  
  • Oka Mitsuo
  • Birn J.
  • Battaglia Marina
  • Chaston C. C.
  • Hatch S. M.
  • Livadiotis G.
  • Imada S.
  • Miyoshi Y.
  • Kuhar M.
  • Effenberger F.
  • Eriksson E.
  • Khotyaintsev Yu. V.
  • Retinò Alessandro
  Space Science Reviews, Springer Verlag, 2018, 214. Particles are accelerated to very high, non-thermal energies in solar and space plasma environments. While energy spectra of accelerated electrons often exhibit a power law, it remains unclear how electrons are accelerated to high energies and what processes determine the power-law index delta . Here, we review previous observations of the power-law index delta in a variety of different plasma environments with a particular focus on sub-relativistic electrons. It appears that in regions more closely related to magnetic reconnection (such as the `above-the-looptop' solar hard X-ray source and the plasma sheet in Earth's magnetotail), the spectra are typically soft (delta &gsim;4). This is in contrast to the typically hard spectra (delta &lsim;4) that are observed in coincidence with shocks. The difference implies that shocks are more efficient in producing a larger non-thermal fraction of electron energies when compared to magnetic reconnection. A caveat is that during active times in Earth's magnetotail, delta values seem spatially uniform in the plasma sheet, while power-law distributions still exist even in quiet times. The role of magnetotail reconnection in the electron power-law formation could therefore be confounded with these background conditions. Because different regions have been studied with different instrumentations and methodologies, we point out a need for more systematic and coordinated studies of power-law distributions for a better understanding of possible scaling laws in particle acceleration as well as their universality. (10.1007/s11214-018-0515-4)
  DOI : 10.1007/s11214-018-0515-4
• Electron bulk acceleration and thermalization at Earth's quasi-perpendicular bow shock
  
  • Chen L.-J.
  • Wang S.
  • Wilson Iii L. B.
  • Schwartz S. J.
  • Bessho N.
  • Moore T. E.
  • Gershman D. J.
  • Giles B. L.
  • Malaspina D. M.
  • Wilder F. D.
  • Ergun R. E.
  • Hesse Michael
  • Lai H.
  • Russell C. T.
  • Strangeway R. J.
  • Torbert R. B.
  • Viñas A.-F.
  • Burch J. L.
  • Lee S.
  • Pollock C.
  • Dorelli J. C.
  • Paterson W. R.
  • Ahmadi N.
  • Goodrich K. A.
  • Lavraud B.
  • Le Contel Olivier
  • Khotyaintsev Y. V.
  • Lindqvist P.-A.
  • Boardsen S.
  • Wei H.
  • Le A.
  • Avanov L. A.
  Physical Review Letters, American Physical Society, 2018, 120, pp.225101. Electron heating at Earth's quasiperpendicular bow shock has been surmised to be due to the combined effects of a quasistatic electric potential and scattering through wave-particle interaction. Here we report the observation of electron distribution functions indicating a new electron heating process occurring at the leading edge of the shock front. Incident solar wind electrons are accelerated parallel to the magnetic field toward downstream, reaching an electron-ion relative drift speed exceeding the electron thermal speed. The bulk acceleration is associated with an electric field pulse embedded in a whistler-mode wave. The high electron-ion relative drift is relaxed primarily through a nonlinear current-driven instability. The relaxed distributions contain a beam traveling toward the shock as a remnant of the accelerated electrons. Similar distribution functions prevail throughout the shock transition layer, suggesting that the observed acceleration and thermalization is essential to the cross-shock electron heating. (10.1103/PhysRevLett.120.225101)
  DOI : 10.1103/PhysRevLett.120.225101
• Solar Wind Turbulence Studies Using MMS Fast Plasma Investigation Data
  
  • Bandyopadhyay Riddhi
  • Chasapis A.
  • Chhiber R.
  • Parashar T. N.
  • Maruca B. A.
  • Matthaeus W. H.
  • Schwartz S. J.
  • Eriksson S.
  • Le Contel Olivier
  • Breuillard Hugo
  • Burch J. L.
  • Moore T. E.
  • Pollock C. J.
  • Giles B. L.
  • Paterson W. R.
  • Dorelli J. C.
  • Gershman D. J.
  • Torbert R. B.
  • Russell C. T.
  • Strangeway R. J.
  The Astrophysical Journal, American Astronomical Society, 2018, 866 (2), pp.81. Studies of solar wind turbulence traditionally employ high-resolution magnetic field data, but high-resolution measurements of ion and electron moments have been possible only recently. We report the first turbulence studies of ion and electron velocity moments accumulated in pristine solar wind by the Fast Plasma Investigation (FPI) instrument on board the Magnetospheric Multiscale Mission. Use of these data is made possible by a novel implementation of a frequency domain Hampel filter, described herein. After presenting procedures for processing of the data, we discuss statistical properties of solar wind turbulence extending into the kinetic range. Magnetic field fluctuations dominate electron and ion-velocity fluctuation spectra throughout the energy-containing and inertial ranges. However, a multispacecraft analysis indicates that at scales shorter than the ion inertial length, electron velocity fluctuations become larger than ion-velocity and magnetic field fluctuations. The kurtosis of ion-velocity peaks around a few ion inertial lengths and returns to a near Gaussian value at sub-ion scales. (10.3847/1538-4357/aade93)
  DOI : 10.3847/1538-4357/aade93
• Wave Phenomena and Beam-Plasma Interactions at the Magnetopause Reconnection Region
  
  • Burch J. L.
  • Webster J. M.
  • Genestreti K. J.
  • Torbert R. B.
  • Giles B. L.
  • Fuselier S. A.
  • Dorelli J. C.
  • Rager A. C.
  • Phan T. D.
  • Allen R. C.
  • Chen L.-J.
  • Wang S.
  • Le Contel Olivier
  • Russell C. T.
  • Strangeway R. J.
  • Ergun R. E.
  • Jaynes A. N.
  • Lindqvist P.-A.
  • Graham D. B.
  • Wilder F. D.
  • Hwang K.-J.
  • Goldstein J.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2018, 123 (2), pp.1118-1133. This paper reports on Magnetospheric Multiscale observations of whistler mode chorus and higher-frequency electrostatic waves near and within a reconnection diffusion region on 23 November 2016. The diffusion region is bounded by crescent-shaped electron distributions and associated dissipation just upstream of the X-line and by magnetic field-aligned currents and electric fields leading to dissipation near the electron stagnation point. Measurements were made southward of the X-line as determined by southward directed ion and electron jets. We show that electrostatic wave generation is due to magnetosheath electron beams formed by the electron jets as they interact with a cold background plasma and more energetic population of magnetospheric electrons. On the magnetosphere side of the X-line the electron beams are accompanied by a strong perpendicular electron temperature anisotropy, which is shown to be the source of an observed rising-tone whistler mode chorus event. We show that the apex of the chorus event and the onset of electrostatic waves coincide with the opening of magnetic field lines at the electron stagnation point. (10.1002/2017JA024789)
  DOI : 10.1002/2017JA024789
• How dielectric, metallic and liquid targets influence the evolution of electron properties in a pulsed He jet measured by Thomson and Raman scattering
  
  • Klarenaar Bart
  • Guaitella Olivier
  • Engeln Richard
  • Sobota Ana
  Plasma Sources Science and Technology, IOP Publishing, 2018, 27 (8), pp.085004. Thomson scattering using a Bragg grating notch filter is used to determine the electron properties of a pulsed, kHz-driven, non-thermal atmospheric pressure plasma jet in helium expanding in air. The plasma jet is allowed to freely expand or interact with targets with different electrical properties, i.e. glass, copper and water. With the same setup, Raman scattering is used to determine spatially- and time-resolved the densities and rotational temperatures of oxygen and nitrogen molecules entrained into the jet. Fast imaging is used to determine the development of the discharge in the plasma jet as well as its behavior in the plasma-target interaction zone. As the discharge approaches the target, the rise of electron density was followed by the fall of electron temperature. The discharge is influenced only over a few millimeters before it hits the target. The electron density and temperature during the spreading of the discharge on the low-permittivity target are measured to be resp. 2 × 1019 m&#8722;3 and &#8776;1 eV. During the return stroke on the high-permittivity and the metallic target the densities rise with a factor 1.5 resp. 2.2, and the temperature with a factor 2.5 for both cases. The discharges on the high- and low-permittivity targets extinguished soon after the initial impact of the ionization front, while the diffuse discharge on the metallic target extinguished only after the end of the voltage pulse (with a duration of 1 &#956;s). In the diffuse discharge the electron temperature reaches 3.4 eV, the gas temperature increases by approximately 100 K and the electron density increases by approximately a factor three with respect to before its formation. (10.1088/1361-6595/aad4d7)
  DOI : 10.1088/1361-6595/aad4d7
• Geocatalytic uptake of ozone onto natural mineral dust
  
  • Wang Xianjie
  • Romanias Manolis
  • Thevenet Frederic
  • Rousseau Antoine
  Catalysts, MDPI, 2018, 8 (7), pp.263. Beyond tailored and synthetic catalysts sought out for ozone decomposition, mineral dusts provide naturally mixed metal oxide materials. The steady-state uptake of O3 evidenced across a wide concentration range signifies the catalytic decomposition of O3. The geocatalytic properties of such natural mineral dust open up new perspectives in atmospheric chemistry and catalytic processes. (10.3390/catal8070263)
  DOI : 10.3390/catal8070263
• Compressible Magnetohydrodynamic Turbulence in the Earth’s Magnetosheath: Estimation of the Energy Cascade Rate Using in situ Spacecraft Data
  
  • Hadid Lina
  • Sahraoui Fouad
  • Galtier Sébastien
  • Huang S.Y.
  Physical Review Letters, American Physical Society, 2018, 120 (5), pp.055102. The first estimation of the energy cascade rate |εC| of magnetosheath turbulence is obtained using the CLUSTER and THEMIS spacecraft data and an exact law of compressible isothermal magnetohydrodynamics turbulence. |εC | is found to be of the order of 10−13J.m−3.s−1, at least two orders of magnitude larger than its value in the solar wind (order of 10−16 J.m−3.s−1 in the fast wind). Two types of turbulence are evidenced and shown to be dominated either by incompressible Alfénic or compressible magnetosonic-like fluctuations. Density fluctuations are shown to amplify the cascade rate and its spatial anisotropy in comparison with incompressible Alfv´enic turbulence. Furthermore, for compressible magnetosonic fluctuations, large cascade rates are found to lie mostly near the linear kinetic instability of the mirror mode. New empirical power-laws relating |C | to the turbulent Mach number and to the internal energy are evidenced. These new finding have potential applications in distant astrophysical plasmas that are not accessible to in situ measurements. (10.1103/PhysRevLett.120.055102)
  DOI : 10.1103/PhysRevLett.120.055102
• Local energy transfer rate and kinetic signatures in solar wind turbulence
  
  • Sorriso-Valvo L.
  • Catapano F.
  • Retinò Alessandro
  • Greco A.
  • Perri S.
  • Marino R.
  • Pezzi O.
  • Perrone D.
  • Bruno Roberto
  • Valentini F.
  • Servidio S.
  • Panebianco V.
  , 2018, 20, pp.EGU2018-6552. The transfer of energy from large to small scales in space turbulence is an important ingredient of the longstanding question about the mechanism of the interplanetary plasma heating. Statistical analysis in the context of magnetohydrodynamic (MHD) turbulence provided evidence that the total transported energy is compatible with the observed heating of the solar wind as it expands in the heliosphere. However, in order to understand which processes contribute to the plasma heating, it is necessary to have a local description of the energy flux across scales. To this aim, we propose a proxy of the scale-dependent, local energy transfer that includes magnetic, velocity and cross-helicity terms, and is based on the third-order moment scaling law for MHD turbulence. Data from Helios2 are used to determine the statistical properties of such a proxy in comparison with the magnetic and velocity fields PVI, and the correlation with local solar wind heating is pointed out. MMS data are used to study the correlation with kinetic-scale features, as for example the temperature anisotropy, the heat flux, the agyrothropy of the pressure tensor, and the deviation form Maxwellian. A comparison with hybrid direct numerical simulations of the Vlasov-Maxwell system, including alpha particles, is also performed. The good correlation between the turbulent local energy flux and the indicators of kinetic processes found in the data and in the simulations suggests an important role played by this proxy in the study of plasma energy dissipation.
• The effect of liquid target on a nonthermal plasma jet−imaging, electric fields, visualization of gas flow and optical emission spectroscopy
  
  • Kovačević Vv
  • Sretenović Gb
  • Slikboer Elmar
  • Guaitella Olivier
  • Sobota Ana
  • Kuraica Mm
  Journal of Physics D: Applied Physics, IOP Publishing, 2018, 51 (6), pp.065202. The article describes the complex study of the interaction of a helium plasma jet with distilled water and saline. The discharge development, spatial distribution of the excited species, electric field measurement results and the results of the Schlieren imaging are presented. The results of the experiments showed that the plasmaliquid interaction could be prolonged with the proper choice of the gas composition between the jet nozzle and the target. This depends on the gas flow and the target distance. Increased conductivity of the liquid does not affect the discharge properties significantly. An increase of the gas flow enables an extension of the plasma duration on the liquid surface up to 10 µs, but with a moderate electric field strength in the ionization wave. In contrast, there is a significant enhancement of the electric field on the liquid surface, up to 30&#8201;kV cm&#8722;1 for low flows, but with a shorter time of the overall plasma liquid interaction. Ignition of the plasma jet induces a gas flow modification and may cause turbulences in the gas flow. A significant influence of the plasma jet causing a mixing in the liquid is also recorded and it is found that the plasma jet ignition changes the direction of the liquid circulation. (10.1088/1361-6463/aaa288)
  DOI : 10.1088/1361-6463/aaa288
• Low-Altitude Observations of Recurrent Short-Lived keV Ion Micro-Injections Inside the Diffuse Auroral Zone
  
  • Sauvaud J.-A.
  • Delcourt Dominique C.
  • Parrot Michel
  • Payan D.
  • Raita T.
  • Penou E.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2018, 123, pp.2054–2063. The AMBRE experiment onboard the ocean topography mapper JASON‐3 aims at measuring the spacecraft potential as well as auroral particle precipitation using two top‐hat analyzers for electrons and ions in the 20 eV‐28 keV energy range. The JASON‐3 spacecraft has a nearly circular orbit at an altitude of 1336 km with an inclination of 66°, at times probing the equatorward part of the auroral oval in a nearly tangential manner upon leaving the outer radiation belt. In this region of space, during periods of enhanced geomagnetic activity with small or moderate storms, AMBRE detected recurrent “micro‐injections” of ions with energies in the 200 eV‐28 keV range and which exhibit clear time of flight dispersion. Ray tracing using single trajectory computations suggests that these ions are launched from a source located in the 8000‐12000 km altitudinal range and subsequently propagate downward toward the ionosphere. Such observations of quasi‐periodic dispersed downflowing ions are new and we argue that these structures could be produced by ion‐wave interactions at mid‐altitudes. (10.1002/2017JA025075)
  DOI : 10.1002/2017JA025075
• Nested polyhedra model of isotropic magnetohydrodynamic turbulence
  
  • Gürcan Özgür D.
  Physical Review E, American Physical Society (APS), 2018, 97, pp.063111. A nested polyhedra model has been developed for magnetohydrodynamic turbulence. Driving only the velocity field at large scales with random, divergence-free forcing results in a clear, stationary k^-5/3 spectrum for both kinetic and magnetic energies. Since the model naturally effaces disparate scale interactions, does not have a guide field, and avoids injecting any sign of helicity by random forcing, the resulting three-dimensional k spectrum is statistically isotropic. The strengths and weaknesses of the model are demonstrated by considering large or small magnetic Prandtl numbers. It was also observed that the timescale for the equipartition offset with those of the smallest scales shows a k^-1/2 scaling. (10.1103/PhysRevE.97.063111)
  DOI : 10.1103/PhysRevE.97.063111