Publications

2018

• Logarithmically discretized model of bounce averaged gyrokinetics and its implications on tokamak turbulence
  
  • Xu S.
  • Morel Pierre
  • Gürcan Özgür D.
  Physics of Plasmas, American Institute of Physics, 2018, 25 (10), pp.102306. A logarithmically discretized model, which consists of writing the system in log polar coordinates in wave-number domain and reducing the nonlinear interactions to a sum over neighboring scales that satisfy the triad conditions, is proposed for bounce averaged gyrokinetics, where the energy dependence is kept over a semi-regular grid that allows quadrature calculations in order to guarantee quasi-neutrality. The resulting model is a cheaper implementation of nonlinear multi-scale physics involving trapped electron modes, trapped ion modes, and zonal flows, which can handle anisotropy. The resulting wave-number spectrum is anisotropic at large scales, where the energy injection is clearly anisotropic, but is isotropised rapidly, leading generally towards an isotropic k−4 spectrum for spectral potential energy density for fully kinetic system and a k−5 spectrum for the system with one adiabatic species. Zonal flow damping, which is necessary for reaching a steady state in this model, plays an important role along with electron adiabaticity. Interesting dynamics akin to predator-prey evolution is observed among zonal flows and similarly large scale but radially elongated structures. (10.1063/1.5049681)
  DOI : 10.1063/1.5049681
• Living on mars: how to produce oxygen and fuel to get home
  
  • Guerra V.
  • Silva Tiago
  • Guaitella Olivier
  Europhysics News, EDP Sciences, 2018, 49 (3), pp.15-18. Sending a manned mission to Mars is one of the next major steps in space exploration. Creating a breathable environment, however, is a substantial challenge. A sustainable oxygen supply on the red planet can be achieved by converting carbon dioxide directly from the Martian atmosphere. A new solution to do so is on the way: plasma technology. (10.1051/epn/2018302)
  DOI : 10.1051/epn/2018302
• Higher-Order Turbulence Statistics in the Earth's Magnetosheath and the Solar Wind Using Magnetospheric Multiscale Observations
  
  • Chhiber R.
  • Chasapis A.
  • Bandyopadhyay R.
  • Parashar T. N.
  • Matthaeus W. H.
  • Maruca B. A.
  • Moore T. E.
  • Burch J. L.
  • Torbert R. B.
  • Russell C. T.
  • Le Contel Olivier
  • Argall M. R.
  • Fischer D.
  • Mirioni Laurent
  • Strangeway R. J.
  • Pollock C. J.
  • Giles B. L.
  • Gershman D. J.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2018, 123 (12), pp.9941-9954. High-resolution multispacecraft magnetic field measurements from the Magnetospheric Multiscale mission's flux-gate magnetometer are employed to examine statistical properties of plasma turbulence in the terrestrial magnetosheath and in the solar wind. Quantities examined include wave number spectra; structure functions of order two, four, and six; probability density functions of increments; and scale-dependent kurtoses of the magnetic field. We evaluate the Taylor frozen-in approximation by comparing single-spacecraft time series analysis with direct multispacecraft measurements, including evidence based on comparison of probability distribution functions. The statistics studied span spatial scales from the inertial range down to proton and electron scales. We find agreement of spectral estimates using three different methods, and evidence of intermittent turbulence in both magnetosheath and solar wind; however, evidence for subproton-scale coherent structures, seen in the magnetosheath, is not found in the solar wind. (10.1029/2018JA025768)
  DOI : 10.1029/2018JA025768
• Optical actinometry of O-atoms in pulsed nanosecond capillary discharge: peculiarities of kinetics at high specific deposited energy
  
  • Zhu Yifei
  • Lepikhin N D
  • Orel Inna
  • Salmon A.
  • Klochko A.V.
  • Starikovskaia Svetlana
  Plasma Sources Science and Technology, IOP Publishing, 2018. Density of O-atoms was studied in capillary nanosecond discharge in air with 5.3% additions of Ar at 28.5 mbar. Time-resolved electrical current, longitudinal electric fifield, optical emission of O(3p3P), Ar(2p1) and their ratio, and emission of N2(C)were measured. A kinetic scheme describing consistent behavior of the set of the experimental data was developed. The main processes responsible for population and decay of the species of interest were selected on the basis of sensitivity and rate analysis. The electric fifield was taken as input data; all other experimentally obtained signals were modeled; experimental data and results of calculations are in good agreement. The role of the reactions between excited, charged species and electrons in early afterglow for pulsed discharges at high reduced electric fifields and high specifific deposited energy was discussed. Density of O atoms in the ground state was calculated. It was concluded that Ar-based traditional actinometry demands an advanced kinetic modeling in the case of the nanosecond discharge with a high specifific energy deposition. (10.1088/1361-6595/aac95f)
  DOI : 10.1088/1361-6595/aac95f
• Imaging axial and radial electric field components in dielectric targets under plasma exposure
  
  • Slikboer Elmar
  • Sobota Ana
  • Guaitella Olivier
  • Garcia-Caurel Enric
  Journal of Physics D: Applied Physics, IOP Publishing, 2018, 51 (11), pp.115203. Mueller polarimetry is used to investigate the behavior of an electro optic target (BSO crystal) under exposure of guided ionization waves produced by an atmospheric pressure plasma jet. For the first time, this optical technique is time resolved to obtain the complete Mueller matrix of the sample right before and after the impact of the discharges. By analyzing the induced birefringence, the spatial profiles and local values are obtained of both the electric field and temperature in the sample. Electric fields are generated due to deposited surface charges and a temperature profile is present, due to the heat transferred by the plasma jet. The study of electric field dynamics and local temperature increase at the target, due to the plasma jet is important for biomedical applications, as well as surface functionalization. This work shows how Mueller polarimetry can be used as a novel diagnostic to simultaneously acquire the spatial distribution and local values of both the electric field and temperature, by coupling the external source of anisotropy to the measured induced birefringence via the symmetry point group of the examined material. (10.1088/1361-6463/aaad99)
  DOI : 10.1088/1361-6463/aaad99
• 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
• A rotational Raman study under non-thermal conditions in a pulsed CO<SUB>2</SUB> glow discharge
  
  • Klarenaar Bart
  • Grovulović Marija
  • Morillo-Candas Ana-Sofia
  • Bekerom D C M van Den
  • Damen Mark
  • Sanden Richard van De
  • Guaitella Olivier
  • Engeln Richard
  Plasma Sources Science and Technology, IOP Publishing, 2018, 27 (4), pp.045009. The implementation of in situ rotational Raman spectroscopy is realized for a pulsed glow discharge in CO2 in the mbar range and is used to study the rotational temperature and molecular number densities of CO2, CO, and O2. The polarizability anisotropy of these molecules is required for extracting number densities from the recorded spectra and is determined for incident photons of 532 nm. The spatiotemporally-resolved measurements are performed in the same reactor and at equal discharge conditions (510 ms onoff cycle, 50 mA plasma current, 6.7 mbar pressure) as in recently published work employing in situ Fourier transform infrared (FTIR) spectroscopy. The rotational temperature ranges from 394 to 809 K from start to end of the discharge pulse and is constant over the length of the reactor. The discharge is demonstrated to be spatially uniform in gas composition, with a CO2 conversion factor of 0.15 ± 0.02. Rotational temperatures and molecular composition agree well with the FTIR results, while the spatial uniformity confirms the assumption made for the FTIR analysis of a homogeneous medium over the line-of-sight of absorption. Furthermore, the rotational Raman spectra of CO2 are related to vibrational temperatures through the vibrationally averaged nuclear spin degeneracy, which is expressed in the intensity ratio between even and odd numbered Raman peaks. The elevation of the odd averaged degeneracy above thermal conditions agrees well with the elevation of vibrational temperatures of CO2, acquired in the FTIR study. (10.1088/1361-6595/aabab6)
  DOI : 10.1088/1361-6595/aabab6
• Observations of core ion cyclotron emission on ASDEX Upgrade tokamak
  
  • Ochoukov R.
  • Bobkov V.
  • Chapman B.
  • Dendy R.
  • Dunne M.
  • Faugel H.
  • García Muñoz M.
  • Geiger B.
  • Hennequin Pascale
  • Mcclements K. G.
  • Moseev D.
  • Nielsen S.
  • Rasmussen J.
  • Schneider P.
  • Weiland M.
  • Noterdaeme J.-M.
  Review of Scientific Instruments, American Institute of Physics, 2018, 89 (10), pp.10J101. The B-dot probe diagnostic suite on the ASDEX Upgrade tokamak has recently been upgraded with a new 125 MHz, 14 bit resolution digitizer to study ion cyclotron emission (ICE). While classic edge emission from the low field side plasma is often observed, we also measure waves originating from the core with fast fusion protons or beam injected deuterons being a possible emission driver. Comparing the measured frequency values with ion cyclotron harmonics present in the plasma places the origin of this emission on the magnetic axis, with the fundamental hydrogen/second deuterium cyclotron harmonic matching the observed values. The actual values range from ∼27 MHz at the on-axis toroidal field BT = -1.79 T to ∼40 MHz at BT = -2.62 T. When the magnetic axis position evolves during this emission, the measured frequency values track the changes in the estimated on-axis cyclotron frequency values. Core ICE is usually a transient event lasting ∼100 ms during the neutral beam startup phase. However, in some cases, core emission occurs in steady-state plasmas and lasts for longer than 1 s. These observations suggest an attractive possibility of using a non-perturbing ICE-based diagnostic to passively monitor fusion alpha particles at the location of their birth in the plasma core, in deuterium-tritium burning devices such as ITER and DEMO. (10.1063/1.5035180)
  DOI : 10.1063/1.5035180
• Generation of Electron Whistler Waves at the Mirror Mode Magnetic Holes: MMS Observations and PIC Simulation
  
  • Ahmadi N.
  • Wilder F. D.
  • Ergun R. E.
  • Argall M.
  • Usanova M. E.
  • Breuillard Hugo
  • Malaspina D.
  • Paulson K.
  • Germaschewski K.
  • Eriksson S.
  • Goodrich K. A.
  • Torbert R.
  • Le Contel Olivier
  • Strangeway R. J.
  • Russell C. T.
  • Burch J. L.
  • Giles B. L.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2018, 123, pp.6383-6393. The Magnetospheric Multiscale mission has observed electron whistler waves at the center and at the edges of magnetic holes in the dayside magnetosheath. The magnetic holes are nonlinear mirror structures since their magnitude is anticorrelated with particle density. In this article, we examine the growth mechanisms of these whistler waves and their interaction with the host magnetic hole. In the observations, as magnetic holes develop and get deeper, an electron population gets trapped and develops a temperature anisotropy favorable for whistler waves to be generated. In addition, the decrease in magnetic field magnitude and the increase in density reduce the electron resonance energy, which promotes the electron cyclotron resonance. To investigate this process, we used expanding box particle-in-cell simulations to produce the mirror instability, which then evolve into magnetic holes. The simulation shows that whistler waves can be generated at the center and edges of magnetic holes, which reproduces the primary features of the MMS observations. The simulation shows that the electron temperature anisotropy develops in the center of the magnetic hole once the mirror instability reaches its nonlinear stage of evolution. The plasma is then unstable to whistler waves at the minimum of the magnetic field structures. In the saturation regime of mirror instability, when magnetic holes are developed, the electron temperature anisotropy appears at the edges of the holes and electron distributions become more isotropic at the magnetic field minimum. At the edges, the expansion of magnetic holes decelerates the electrons, which leads to temperature anisotropies. (10.1029/2018JA025452)
  DOI : 10.1029/2018JA025452
• Excitation and relaxation of the asymmetric stretch mode of CO<SUB>2</SUB> in a pulsed glow discharge
  
  • Klarenaar Bart
  • Morillo-Candas Ana-Sofia
  • Grofulovic Marija
  • Sanden Richard van De
  • Engeln Richard
  • Guaitella Olivier
  Plasma Sources Science and Technology, IOP Publishing, 2018, 28, pp.035011. The excitation and relaxation of the vibrations of CO₂ as well as the reduction of CO₂ to CO are studied in a pulsed glow discharge. Two diagnostics are employed, being (1) time-resolved <i>in situ</i> Fourier transform infrared (FTIR) spectroscopy and (2) spatiotemporally resolved <i>in situ</i> rotational Raman spectroscopy. Experiments are conducted within a pressure range of 1.3-6.7 mbar and a current range of 10-50 mA. In the afterglow, the rate of exponential decay from the asymmetric stretch temperature (<i>T</i>₃) to the rotational temperature (<i>T</i>_rot) is found to be only dependent on <i>T</i>_rot, in the conditions under study. The decay rate <i>&#961;</i>_{<i>T</i>₃-<i>T</i>_rot} follows the relation <i>&#961;</i>_{<i>T</i>₃-<i>T</i>_rot} = 388 s^-1 exp((<i>T</i>_rot - 273 K)/(154 K)). Pressure and varying concentrations of CO and (presumably) atomic oxygen did not show to be of significant influence. In the active part of the discharge the excitation of <i>T</i>₃ showed to be positively related to current and negatively to pressure. However, the contribution of current to vibrational excitation is ambiguous: the conversion of CO₂ and therefore the fraction of CO in the discharge, is found to be strongly dependent on the current, with a conversion factor of 0.05 to 0.18 for 10 mA to 50 mA, while CO can contribute to the excitation through near-resonant collisions. A clear relation between the elevation of <i>T</i>₃ and the dissociation of CO₂ could not be confirmed, though conversion peaks are observed in the near afterglow, which motivate future experiments on vibrational ladder-climbing directly after termination of the discharge. (10.1088/1361-6595/aada5e)
  DOI : 10.1088/1361-6595/aada5e
• Turbulence and microprocesses in inhomogeneous solar wind plasmas
  
  • Krafft C.
  • Volokitin A.
  • Gauthier Gaétan
  , 2018. The random density fluctuations observed in the solar wind plasma crucially influence on the Langmuir wave turbulence generated by energetic electron beams ejected during solar bursts. Those are powerful phenomena consisting of a chain of successive processes leading ultimately to strong electromagnetic emissions. The small-scale processes governing the interactions between the waves, the beams and the inhomogeneous plasmas need to be studied to explain such macroscopic phenomena. Moreover, the complexity induced by the plasma irregularities requires to find new approaches and modelling. Therefore theoretical and numerical tools were built to describe the Langmuir wave turbulence and the beams dynamics in inhomogeneous plasmas, in the form of a self-consistent Hamiltonian model including a fluid description for the plasma and a kinetic approach for the beam. On this basis, numerical simulations were performed in order to shed light on the impact of the density fluctuations on the beam dynamics, the electromagnetic wave radiation, the generation of Langmuir wave turbulence, the waves coupling and decay phenomena involving Langmuir and low frequency waves, the acceleration of beam electrons, their diffusion mechanisms, the modulation of the Langmuir waveforms and the statistical properties of the radiated fields distributions.
• Kinetic study of low-temperature CO<SUB>2</SUB> plasmas under non-equilibrium conditions. I. Relaxation of vibrational energy
  
  • Silva Tiago
  • Grofulovic Marija
  • Klarenaar Bart
  • Morillo-Candas Ana-Sofia
  • Guaitella Olivier
  • Engeln Richard
  • Pintassilgo C.D.
  • Guerra V.
  Plasma Sources Science and Technology, IOP Publishing, 2018, 27 (1), pp.015019. A kinetic model to describe the time evolution of ~ 70 individual CO2(X-1 Sigma( )) vibrational levels during the afterglow of a pulsed DC glow discharge is developed in order to contribute towards the understanding of vibrational energy transfer in CO2 plasmas. The results of the simulations are compared against in situ Fourier Transform Infrared spectroscopy data obtained in a pulsed dc glow discharge and its afterglow at pressures of a few Torr and discharge currents around 50 mA. The very good agreement between the model predictions and the experimental results shows a validation of the kinetic scheme considered and the corresponding V-T and V-V rate coefficients. In this sense, it establishes a reaction mechanism for the vibrational kinetics of these CO2 energy levels and delivers a firm basis to understand the vibrational relaxation in CO2 plasmas. It is shown that first-order perturbation theories, namely Schwartz-Slawsky-Herzfeld (SSH) and Sharma-Brau (SB) methods, provide a good description of CO2 vibrations under low excitation regimes. (10.1088/1361-6595/aaa56a)
  DOI : 10.1088/1361-6595/aaa56a
• New Insights into the Nature of Turbulence in the Earth's Magnetosheath Using Magnetospheric MultiScale Mission Data
  
  • Breuillard Hugo
  • Matteini L.
  • Argall M. R.
  • Sahraoui Fouad
  • Andriopoulou M.
  • Le Contel Olivier
  • Retinò Alessandro
  • Mirioni Laurent
  • Huang S. Y.
  • Gershman D. J.
  • Ergun R. E.
  • Wilder F. D.
  • Goodrich K. A.
  • Ahmadi N.
  • Yordanova E.
  • Vaivads A.
  • Turner D. L.
  • Khotyaintsev Y. V.
  • Graham D. B.
  • Lindqvist P.-A.
  • Chasapis A.
  • Burch J. L.
  • Torbert R. B.
  • Russell C. T.
  • Magnes W.
  • Strangeway R. J.
  • Plaschke F.
  • Moore T. E.
  • Giles B. L.
  • Paterson W. R.
  • Pollock C. J.
  • Lavraud B.
  • Fuselier S. A.
  • Cohen I. J.
  The Astrophysical Journal, American Astronomical Society, 2018, 859, pp.127. The Earth's magnetosheath, which is characterized by highly turbulent fluctuations, is usually divided into two regions of different properties as a function of the angle between the interplanetary magnetic field and the shock normal. In this study, we make use of high-time resolution instruments on board the Magnetospheric MultiScale spacecraft to determine and compare the properties of subsolar magnetosheath turbulence in both regions, i.e., downstream of the quasi-parallel and quasi-perpendicular bow shocks. In particular, we take advantage of the unprecedented temporal resolution of the Fast Plasma Investigation instrument to show the density fluctuations down to sub-ion scales for the first time. We show that the nature of turbulence is highly compressible down to electron scales, particularly in the quasi-parallel magnetosheath. In this region, the magnetic turbulence also shows an inertial (Kolmogorov-like) range, indicating that the fluctuations are not formed locally, in contrast with the quasi-perpendicular magnetosheath. We also show that the electromagnetic turbulence is dominated by electric fluctuations at sub-ion scales (f &gt; 1 Hz) and that magnetic and electric spectra steepen at the largest-electron scale. The latter indicates a change in the nature of turbulence at electron scales. Finally, we show that the electric fluctuations around the electron gyrofrequency are mostly parallel in the quasi-perpendicular magnetosheath, where intense whistlers are observed. This result suggests that energy dissipation, plasma heating, and acceleration might be driven by intense electrostatic parallel structures/waves, which can be linked to whistler waves. (10.3847/1538-4357/aabae8)
  DOI : 10.3847/1538-4357/aabae8
• Plasmaspheric Plumes and EMIC Rising Tone Emissions
  
  • Grison B.
  • Hanzelka M.
  • Breuillard Hugo
  • Darrouzet F.
  • Santolík O.
  • Cornilleau-Wehrlin Nicole
  • Dandouras I.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2018, 123 (11), pp.9443-9452. Due to its polar orbit Cluster spacecraft crossed plasmaspheric plumes out of the magnetic equatorial plane. We study the occurrence of broadband, narrowband, and rising tone emissions in the plume vicinity, below the local proton gyrofrequency. Based on a database of 935 Cluster plumes crossings, reduced to 189 unique plumes, we find that broadband activity is the most common case. We confirm result from a previous study showing that plume vicinity is not a preferred place for observing narrowband emissions. Rising tones are the less frequently observed of these three kinds of emissions. Nevertheless, ElectroMagnetic Ion Cyclotron (EMIC) rising tone occurrence rate is high compared to the narrowband one: Tones are seen in six of 30 plume events (20%) when narrowband emissions are observed. Rising tones are observed at absolute magnetic latitudes larger than 17° and up to 35° . We detail the 16 August 2005 plume crossing when a rising tone is observed. Results of a ray tracing analysis agree with a tone triggering process taking place above 15° of magnetic latitude. (10.1029/2018JA025796)
  DOI : 10.1029/2018JA025796
• A new multi-fluid model for space plasma simulations
  
  • Manuzzo Roberto
  • Califano F.
  • Belmont Gérard
  • Rezeau Laurence
  • Aunai N.
  , 2018, pp.SM11C-2792. We propose a new numerical code based on a new multi-species theoretical model to study the mass, momentum and energy exchanges (MMEE) that happen across the magnetospheric boundaries. We use two distinct populations for ions, one cold and one hot (plus one neutralising electron population), to take into account the differences between the properties of the plasmas coming from the magnetosphere and from the solar wind. This approach represents a step forward in the context of the study of coupled large-scale plasma systems being a new and efficient compromise between fluid and kinetic codes in tracing the different plasma contributions during MMEE. Due to the very important role that magnetic reconnection plays in connecting the shocked Solar Wind to the Earth's magnetosphere, we show and discuss the results we obtained about the simulations of the tearing mode instability occurring across an Earth's magnetopause that we modelled thanks to our most recents MMS observations [Rezeau 2018]. &
• 8th International Workshop on Plasma Spectroscopy (IPS)
  
  • Guaitella Olivier
  • Morillo-Candas Ana-Sofia
  • Klarenaar Bart
  • Engeln Richard
  • Silva Tiago
  • Guerra V.
  , 2018.
• Turbulent Heating between 0.2 and 1 au: A Numerical Study
  
  • Montagud-Camps Victor
  • Grappin Roland
  • Verdini Andrea
  The Astrophysical Journal, American Astronomical Society, 2018, 853 (2), pp.153. The heating of the solar wind is key to understanding its dynamics and acceleration process. The observed radial decrease of the proton temperature in the solar wind is slow compared to the adiabatic prediction, and it is thought to be caused by turbulent dissipation. To generate the observed 1/ R decrease, the dissipation rate has to reach a specific level that varies in turn with temperature, wind speed, and heliocentric distance. We want to prove that MHD turbulent simulations can lead to the 1/ R profile. We consider here the slow solar wind, characterized by a quasi-2D spectral anisotropy. We use the expanding box model equations, which incorporate into 3D MHD equations the expansion due to the mean radial wind, allowing us to follow the plasma evolution between 0.2 and 1 au. We vary the initial parameters: Mach number, expansion parameter, plasma ? , and properties of the energy spectrum as the spectral range and slope. Assuming turbulence starts at 0.2 au with a Mach number equal to unity, with a 3D spectrum mainly perpendicular to the mean field, we find radial temperature profiles close to 1/ R on average. This is done at the price of limiting the initial spectral extent, corresponding to the small number of modes in the inertial range available, due to the modest Reynolds number reachable with high Mach numbers. (10.3847/1538-4357/aaa1ea)
  DOI : 10.3847/1538-4357/aaa1ea
• Multiscale Currents Observed by MMS in the Flow Braking Region
  
  • Nakamura R.
  • Varsani Ali
  • Genestreti Kevin J.
  • Le Contel Olivier
  • Nakamura T. K. M.
  • Baumjohann W.
  • Nagai Tsugunobu
  • Artemyev A. V.
  • Birn Joachim
  • Sergeev Victor A.
  • Apatenkov Sergey
  • Ergun Robert E.
  • Fuselier Stephen A.
  • Gershman D. J.
  • Giles Barbara J.
  • Khotyaintsev Y. V.
  • Lindqvist Per-Arne
  • Magnes Werner
  • Mauk Barry
  • Petrukovich Anatoli
  • Russell Christopher T.
  • Stawarz J. E.
  • Strangeway Robert J.
  • Anderson Brian
  • Burch James L.
  • Bromund Ken R.
  • Cohen Ian
  • Fischer David
  • Jaynes Allison
  • Kepko Laurence
  • Le Guan
  • Plaschke Ferdinand
  • Reeves Geoff
  • Singer Howard J.
  • Slavin J. A.
  • Torbert Roy B.
  • Turner Drew L.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2018, 123 (2), pp.1260-1278. We present characteristics of current layers in the off-equatorial near-Earth plasma sheet boundary observed with high time-resolution measurements from the Magnetospheric Multiscale mission during an intense substorm associated with multiple dipolarizations. The four Magnetospheric Multiscale spacecraft, separated by distances of about 50 km, were located in the southern hemisphere in the dusk portion of a substorm current wedge. They observed fast flow disturbances (up to about 500 km/s), most intense in the dawn-dusk direction. Field-aligned currents were observed initially within the expanding plasma sheet, where the flow and field disturbances showed the distinct pattern expected in the braking region of localized flows. Subsequently, intense thin field-aligned current layers were detected at the inner boundary of equatorward moving flux tubes together with Earthward streaming hot ions. Intense Hall current layers were found adjacent to the field-aligned currents. In particular, we found a Hall current structure in the vicinity of the Earthward streaming ion jet that consisted of mixed ion components, that is, hot unmagnetized ions, cold E × B drifting ions, and magnetized electrons. Our observations show that both the near-Earth plasma jet diversion and the thin Hall current layers formed around the reconnection jet boundary are the sites where diversion of the perpendicular currents take place that contribute to the observed field-aligned current pattern as predicted by simulations of reconnection jets. Hence, multiscale structure of flow braking is preserved in the field-aligned currents in the off-equatorial plasma sheet and is also translated to ionosphere to become a part of the substorm field-aligned current system. (10.1002/2017JA024686)
  DOI : 10.1002/2017JA024686
• Numerical study on the time evolutions of the electric field in helium plasma jets with positive and negative polarities
  
  • Viegas Pedro
  • Pechereau François
  • Bourdon Anne
  Plasma Sources Science and Technology, IOP Publishing, 2018, 27, pp.025007. This paper presents 2D simulations of atmospheric pressure discharges in helium with N2 and O2 admixtures, propagating in a dielectric tube between a point electrode and a grounded metallic target. For both positive and negative polarities, the propagation of the first ionization front is shown to correspond to a peak of the absolute value of the axial electric field inside the tube, but also outside the tube. After the impact on the metallic target, a rebound front is shown to propagate from the target to the point electrode. This rebound front is 23 times faster than the first ionization front. Close to the high voltage point, this rebound front corresponds to a second peak of the absolute value of the axial electric field. Close to the target, as the first ionization and rebound fronts are close in time, only one peak is observed. The dynamics of the absolute value of the radial component of electric field outside the tube is shown to present an increase during the first ionization front propagation and a fast decrease corresponding to the propagation of the rebound front. These time evolutions of the electric field components are in agreement with experiments. Finally, we have shown that the density of metastable He * in 99% He1% N2 and 99% He1% O2 atmospheric pressure discharges are very close. Close to the grounded target, the peak density of reactive species is significantly increased due to the synergy between the first ionization and rebound fronts, as observed in experiments. Similar results are obtained for both voltage polarities, but the peak density of metastable He* close to the target is shown to be two times less in negative polarity than in positive polarity. (10.1088/1361-6595/aaa7d4)
  DOI : 10.1088/1361-6595/aaa7d4
• Turbulence in space plasmas and beyond
  
  • Galtier Sébastien
  Journal of Physics A: Mathematical and General (1975 - 2006), IOP Publishing, 2018, 51, pp.293001. Most of the visible matter in the Universe is in the form of highly turbulent plasmas. For a long time the turbulent character of astrophysical fluids has been neglected and not well understood. One reason for this is the extremely complicated physics involved in astrophysical processes ranging from the machinery of stars, solar and stellar winds, accretion disks to interstellar clouds and galaxies. The other reason is that turbulence constitutes in itself a difficult subject where most of the fundamental results belongs to the incompressible hydrodynamics. Nevertheless, significant theoretical progress has been made during the last years to incorporate some ingredients like compressibility or small-scale plasma physics which are fundamental in astrophysics. This paper reviews some of these results with a strong focus on space plasmas (solar wind, solar corona). Turbulence in interstellar clouds (supersonic flows) and cosmology (space-time fluctuations) are also briefly mentioned. (10.1088/1751-8121/aac4c7)
  DOI : 10.1088/1751-8121/aac4c7
• Electromagnetic Wave Emissions from a Turbulent Plasma with Density Fluctuations
  
  • Volokitin A. S.
  • Krafft Catherine
  The Astrophysical Journal, American Astronomical Society, 2018, 868. In the solar wind, Langmuir turbulence can generate electromagnetic waves at the fundamental plasma frequency omega <SUB> p </SUB>. This process can likely result from either linear wave transformations on the ambient random density inhomogeneities or resonant three-wave interactions involving Langmuir waves and ion acoustic oscillations. In the presence of sufficiently intense plasma density fluctuations of scales much larger than the Langmuir wavelengths, the first mechanism may be more efficient than the second one. A new approach to calculate the electromagnetic wave emissions by Langmuir wave turbulence in plasmas with background density fluctuations is developed. The evolution of the Langmuir turbulence is studied by numerically solving the Zakharov equations in such a two-dimensional plasma. The dynamics of the spatial distributions of the electric currents with frequencies close to omega <SUB> p </SUB> is calculated, as well as their emission into electromagnetic waves. The efficiency of this radiation is determined as a function of the level of the Langmuir turbulence, the characteristics of the density fluctuations, the background plasma temperature, the position of the satellite receiver, and the durations of the source's emissions and spacecraft's observations. The results obtained by the theoretical modeling and numerical simulations are successfully compared with space observations of electromagnetic waves radiated during Type III solar radio bursts. (10.3847/1538-4357/aae7cc)
  DOI : 10.3847/1538-4357/aae7cc
• Plasma-catalytic mineralization of toluene adsorbed on CeO<SUB>2</SUB>
  
  • Jia Zixian
  • Wang Xianjie
  • Foucher Emeric
  • Thevenet Frederic
  • Rousseau Antoine
  Catalysts, MDPI, 2018, 8 (8), pp.303. In the context of coupling nonthermal plasmas with catalytic materials, CeO2 is used as adsorbent for toluene and combined with plasma for toluene oxidation. Two configurations are addressed for the regeneration of toluene saturated CeO2: (i) in plasma-catalysis (IPC); and (ii) post plasma-catalysis (PPC). As an advanced oxidation technique, the performances of toluene mineralization by the plasma-catalytic systems are evaluated and compared through the formation of CO2. First, the adsorption of 100 ppm of toluene onto CeO2 is characterized in detail. Total, reversible and irreversible adsorbed fractions are quantified. Specific attention is paid to the influence of relative humidity (RH): (i) on the adsorption of toluene on CeO2; and (ii) on the formation of ozone in IPC and PPC reactors. Then, the mineralization yield and the mineralization efficiency of adsorbed toluene are defined and investigated as a function of the specific input energy (SIE). Under these conditions, IPC and PPC reactors are compared. Interestingly, the highest mineralization yield and efficiency are achieved using the in-situ configuration operated with the lowest SIE, that is, lean conditions of ozone. Based on these results, the specific impact of RH on the IPC treatment of toluene adsorbed on CeO2 is addressed. Taking into account the impact of RH on toluene adsorption and ozone production, it is evidenced that the mineralization of toluene adsorbed on CeO2 is directly controlled by the amount of ozone produced by the discharge and decomposed on the surface of the coupling material. Results highlight the key role of ozone in the mineralization process and the possible detrimental effect of moisture. (10.3390/catal8080303)
  DOI : 10.3390/catal8080303
• Time of flight dispersed and repetitive ion structures in the diffuse auroral zone originating from 1-2 Re altitudes
  
  • Sauvaud Jean-André
  • Delcourt Dominique
  • Parrot Michel
  • Payan Denis
  • Penou Emmanuel
  , 2018, pp.2062. The AMBRE experiment onboard the ocean topography mapper JASON-3 aims at measuring auroral particle precipitation using two top-hat analyzers for electrons and ions in the 20 eV-28 keV energy range. The JASON-3 spacecraft that has a nearly circular orbit at an altitude of 1336 km with an inclination of 66°, at times probes the equatorward part of the auroral oval in a nearly tangentially 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 ion bands/micro-injections with energies in the 200 eV-28 keV range and which exhibit clear time of flight dispersions. 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. More radial orbits show that the ion bands are detected inside the diffuse auroral zone up to the encounter of auroral arcs. Such observations of dispersed downflowing ions are new and we argue that these structures are produced by localized wave-particle interactions.
• 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