Publications

2017

Optical emission spectrum of filamentary nanosecond surface dielectric barrier discharge
- Shcherbanev S.A.
- Khomenko A.Yu.
- Stepanyan S.A.
- Popov N.A.
- Starikovskaia Svetlana
Plasma Sources Science and Technology, IOP Publishing, 2017, 26 (2), pp.02LT01 (7pp). Streamer-to-filament transition is a general feature of high pressure high voltage (HV) nanosecond surface dielectric barrier discharges. The transition was studied experimentally using time- and space-resolved optical emission in UV and visible parts of spectra. The discharge was initiated by HV pulses 20 ns in duration and 2 ns rise time, positive or negative polarity, 2060 kV in amplitude on the HV electrode. The experiments were carried out in a single-shot regime at initial pressures P > 3 bar and ambient initial temperature in air, N2, H2:N2 and O2:Ar mixtures. It was shown that the transition to filamentary mode is accompanied by the appearance of intense continuous radiation and broad atomic lines. Electron density calculated from line broadening is characterized by high absolute values and long decay in the afterglow. The possible reasons for the continuous spectra were analyzed. (10.1088/1361-6595/26/2/02LT01)
DOI : 10.1088/1361-6595/26/2/02LT01
Advanced Ion Mass Spectrometer for Giant Planet Ionosphere, Magnetospheres and Moons
- Sittler E.C.
- Cooper J.F.
- Paschalidis N.
- Jones S.
- Brinkerhoff William
- Paterson W. R.
- Ali Ashraf
- Coplan M.A.
- Chornay D.
- Sturners S.J.
- Benna Mehdi
- Bateman F.B.
- Fontaine Dominique
- Verdeil Christophe
- Andre N.
- Blanc Michel
- Wurz Peter
, 2017, pp.T1.023. We present our Advanced Ion Mass Spectrometer (AIMS) for outer planet missions which has been under development from various NASA sources (NASA Living with a Star Instrument Development (LWSID), NASA Astrobiology Instrument Development (ASTID), NASA Goddard Internal Research and Development (IRAD)s) to measure elemental, isotopic, and simple molecular composition abundances of 1 V to 25 kV hot ions with wide field-of-view (FOV) in the 1 - 60 amu mass range at mass resolution M/ DeltaM <= 60 over a wide dynamic range of particle intensities and penetrating radiation background from the inner magnetospheres of Jupiter and Saturn to the outer magnetospheric boundary regions and the upstream solar wind. This instrument will work for both spinning spacecraft and 3-axis stabilized spacecraft. AIMS will measure the ion velocity distribution functions (VDF) for the individual ion species from which velocity moments will give their ion density, flow velocity and temperature.
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 N2 (C 3 {{{\Pi }}}u \to B 3 {{{\Pi }}}g , 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 O2(b{}1{{{Sigma }}}g ) influence the absolute O3 densities when the rf power is varied. (10.1088/1361-6595/aa8ebb)
DOI : 10.1088/1361-6595/aa8ebb
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
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.
Vibrational kinetics of non-equilibrium CO2 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.
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.
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
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
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
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
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∥ symmetry breaking for their survival which can be supplied by various means like mean E × B shear, turbulence intensity gradient, etc. Estimates of turbulence driven current are compared with the background bootstrap current in the pedestal region. It is found that turbulence driven current is nearly 10% of the bootstrap current and hence can have a significant influence on the equilibrium current density profiles and current shear driven modes. (10.1063/1.4990746)
DOI : 10.1063/1.4990746
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
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 B0. 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
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
An alternative formulation for exact scaling relations in hydrodynamic and magnetohydrodynamic turbulence
- Banerjee Supratik
- Galtier Sébastien
Journal of Physics A: Mathematical and General (1975 - 2006), IOP Publishing, 2017, 50, pp.015501. We propose an alternative formulation for the exact relations in three-dimensional homogeneous turbulence using two-point statistics. Our finding is illustrated with incompressible hydrodynamic, standard and Hall magnetohydrodynamic turbulence. In this formulation, the cascade rate of an inviscid invariant of turbulence can be expressed simply in terms of mixed second-order structure functions. Besides the usual variables like the velocity \mathbfu , vorticity \boldsymbolomega , magnetic field \mathbfb and the current \mathbfj , the vectors \mathbfu× \boldsymbolomega , \mathbfu× \mathbfb and \mathbfj× \mathbfb are also found to play a key role in the turbulent cascades. The current methodology offers a simple algebraic form which is specially interesting to study anisotropic space plasmas like the solar wind, with, a faster statistical convergence than the classical laws written in terms of third-order correlators. (10.1088/1751-8113/50/1/015501)
DOI : 10.1088/1751-8113/50/1/015501
Nested Polyhedra Models for turbulence
- Gürcan Özgür D.
, 2017.
Kinetic simulation of asymmetric magnetic reconnection with cold ions
- Dargent Jérémy
- Aunai Nicolas
- Lavraud B.
- Toledo-Redondo Sergio
- Shay M. A.
- Cassak P. A.
- Malakit K.
Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2017, 122 (5), pp.5290-5306. At the dayside magnetopause, the magnetosphere often contains a cold ion population of ionospheric origin. This population is not always detectable by particle instruments due to its low energy, despite having an important contribution to the total ion density and therefore an impact on key plasma processes such as magnetic reconnection. The exact role and implications of this low-temperature population are still not well known and has not been addressed with numerical simulation before. We present 2-D fully kinetic simulations of asymmetric magnetic reconnection with and without a cold ion population on the magnetospheric side of the magnetopause, but sharing the same total density, temperature, and magnetic field profiles. The comparison of the simulations suggests that cold ions directly impact signatures recently suggested as a good marker of the X line region: the Larmor electric field. Our simulations reveal that this electric field, initially present all along the magnetospheric separatrix, is related to the bounce of magnetosheath ions at the magnetopause magnetic field reversal through Speiser-like orbits. Once reconnection widens the current sheet away from the X line, the bouncing stops and the electric field signature remains solely confined near the X line. When cold ions are present, however, their very low temperature enables them to E × B drift in the electric field structure. If their density is large enough compared to other ions, their contribution to the momentum equation is capable of maintaining the signature away from the X line. This effect must be taken into account when analyzing in situ spacecraft measurements. (10.1002/2016JA023831)
DOI : 10.1002/2016JA023831
Dynamic probing of plasma-catalytic surface processes: Oxidation of toluene on CeO2
- Jia Zixian
- Wang Xianjie
- Thevenet Frederic
- Rousseau Antoine
Plasma Processes and Polymers, Wiley-VCH Verlag, 2017. This article reports the use of innovative diagnostics to monitor toluene adsorption and oxidation on CeO2 surface under non-thermal plasma (NTP) exposure. Two plasma-catalytic configurations are explored, namely: post-plasma catalysis (PPC) and in-plasma catalysis (IPC). Since heterogeneous processes are pointed out as key steps of the plasma-catalyst coupling, the catalyst surface has been monitored by two complementary in situ diagnostics: (i) diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) and (ii) transmission fourier transform infrared spectroscopy using Sorbent track (ST) device. Dielectric barrier discharges (DBD) are used in both PPC and IPC configurations to induce adsorbed toluene oxidation. Toluene in dry air is first adsorbed on the selected catalytic surface: ceria (CeO2). Subsequently, the plasma is switched on. During the experiment, the ceria surface is monitored by infrared to study toluene adsorption and oxidation mechanisms. The adsorption capacity of toluene on ceria is, respectively, measured in the configurations of PPC and IPC by DRIFTS and ST. The oxidation of toluene by plasma follows a first-order reaction regardless of plasma configuration and injected power and IPC is more effective for the toluene removal than PPC. Intermediates of toluene (benzyl alcohol, benzaldehyde and benzoic acid) are also identified on the surface and their respective temporal evolutions as a function of the plasma exposure are studied.ppap201600114-gra-0001 (10.1002/ppap.201600114)
DOI : 10.1002/ppap.201600114
Power coupling mode transitions induced by tailored voltage waveforms in capacitive oxygen discharges
- Derzsi A.
- Bruneau Bastien
- Gibson Andrew
- Johnson Erik
- O'Connell D.
- Gans T.
- Booth Jean-Paul
- Donko Zoltan
Plasma Sources Science and Technology, IOP Publishing, 2017, 26 (3), pp.034002. Low-pressure capacitively coupled radio frequency discharges operated in O 2 and driven by tailored voltage waveforms are investigated experimentally and by means of kinetic simulations. Pulse-type (peaks/valleys) and sawtooth-type voltage waveforms that consist of up to four consecutive harmonics of the fundamental frequency are used to study the amplitude asymmetry effect as well as the slope asymmetry effect at different fundamental frequencies (5, 10, and 15 MHz) and at different pressures (50?700 mTorr). Values of the DC self-bias determined experimentally and spatio-temporal excitation rates derived from phase resolved optical emission spectroscopy measurements are compared with particle-in-cell/Monte Carlo collisions simulations. The spatio-temporal distributions of the excitation rate obtained from experiments are well reproduced by the simulations. Transitions of the discharge electron heating mode from the drift-ambipolar mode to the ? -mode are induced by changing the number of consecutive harmonics included in the driving voltage waveform or by changing the gas pressure. Changing the number of harmonics in the waveform has a strong effect on the electronegativity of the discharge, on the generation of the DC self-bias and on the control of ion properties at the electrodes, both for pulse-type, as well as sawtooth-type driving voltage waveforms The effect of the surface quenching rate of oxygen singlet delta metastable molecules on the spatio-temporal excitation patterns is also investigated. (10.1088/1361-6595/aa56d6)
DOI : 10.1088/1361-6595/aa56d6
Nonlinear radiation generation processes in the auroral acceleration region
- Pottelette Raymond
- Berthomier Matthieu
Annales Geophysicae, European Geosciences Union, 2017, 35 (6), pp.1241-1248. It is known from laboratory plasma experiments that double layers (DLs) radiate in the electromagnetic spectrum; but this is only known qualitatively. In these experiments, it was shown that the electron beam created on the high-potential side of a DL generates nonlinear structures which couple to electromagnetic waves and act as a sender antenna. In the Earth auroral region, observations performed by auroral spacecraft have shown that DLs occur naturally in the source region of intense radio emissions called auroral kilometric radiation (AKR). Very high time-, spatial-, and temporal-resolution measurements are needed in order to characterize waves and particle distributions in the vicinity of DLs, which are moving transient structures. We report observations from the FAST satellite of a localized large-amplitude parallel electric field ( 300 mV m-1) recorded at the edges of the auroral density cavity. In agreement with laboratory experiments, on the high-potential side of the DL, elementary radiation events are detected. They occur substantially above the local electron gyrofrequency and are associated with the presence of electron holes. The velocity of these nonlinear structures can be derived from the measurement of the Doppler-shifted AKR frequency spectrum above the electron gyrofrequency. The generated electron holes appear as the nonlinear evolution of electrostatic waves generated by the electron-electron two-stream instability because they propagate at about half the beam velocity. It is pointed out that, in the vicinity of a DL, the shape of the electron distribution gives rise to a significant power recorded in the left-hand polarized ordinary (LO) mode. (10.5194/angeo-35-1241-2017)
DOI : 10.5194/angeo-35-1241-2017
Zipper-like periodic magnetosonic waves: Van Allen Probes, THEMIS, and magnetospheric multiscale observations
- Li J.
- Bortnik J.
- Li W.
- Ma Q.
- Thorne R. M.
- Kletzing C. A.
- Kurth W. S.
- Hospodarsky G. B.
- Wygant J.
- Breneman A.
- Thaller S.
- Funsten H. O.
- Mitchell D. G.
- Manweiler J. W.
- Torbert R. B.
- Le Contel Olivier
- Ergun R. E.
- Lindqvist P.-A.
- Torkar Klaus
- Nakamura R.
- Andriopoulou M.
- Russell C. T.
Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2017, 122 (2), pp.1600-1610. An interesting form of "zipper-like" magnetosonic waves consisting of two bands of interleaved periodic rising-tone spectra was newly observed by the Van Allen Probes, the Time History of Events and Macroscale Interactions during Substorms (THEMIS), and the Magnetospheric Multiscale (MMS) missions. The two discrete bands are distinct in frequency and intensity; however, they maintain the same periodicity which varies in space and time, suggesting that they possibly originate from one single source intrinsically. In one event, the zipper-like magnetosonic waves exhibit the same periodicity as a constant-frequency magnetosonic wave and an electrostatic emission, but the modulation comes from neither density fluctuations nor ULF waves. A statistical survey based on 3.5 years of multisatellite observations shows that zipper-like magnetosonic waves mainly occur on the dawnside to noonside, in a frequency range between 10 fcp and fLHR. The zipper-like magnetosonic waves may provide a new clue to nonlinear excitation or modulation process, while its cause still remains to be fully understood. (10.1002/2016JA023536)
DOI : 10.1002/2016JA023536
Electron Heating at Kinetic Scales in Magnetosheath Turbulence
- Chasapis A.
- Matthaeus W. H.
- Parashar T. N.
- Le Contel Olivier
- Retinò Alessandro
- Breuillard Hugo
- Khotyaintsev Y. V.
- Vaivads A.
- Lavraud B.
- Eriksson E.
- Moore T. E.
- Burch J. L.
- Torbert R. B.
- Lindqvist P.-A.
- Ergun R. E.
- Marklund G.
- Goodrich K. A.
- Wilder F. D.
- Chutter M.
- Needell J.
- Rau D.
- Dors I.
- Russell C. T.
- Le G.
- Magnes W.
- Strangeway R. J.
- Bromund K. R.
- Leinweber H. K.
- Plaschke F.
- Fischer D.
- Anderson B. J.
- Pollock C. J.
- Giles B. L.
- Paterson W. R.
- Dorelli J. C.
- Gershman D. J.
- Avanov L.
- Saito Y.
The Astrophysical Journal, American Astronomical Society, 2017, 836, pp.247. We present a statistical study of coherent structures at kinetic scales, using data from the Magnetospheric Multiscale mission in the Earth's magnetosheath. We implemented the multi-spacecraft partial variance of increments (PVI) technique to detect these structures, which are associated with intermittency at kinetic scales. We examine the properties of the electron heating occurring within such structures. We find that, statistically, structures with a high PVI index are regions of significant electron heating. We also focus on one such structure, a current sheet, which shows some signatures consistent with magnetic reconnection. Strong parallel electron heating coincides with whistler emissions at the edges of the current sheet. (10.3847/1538-4357/836/2/247)
DOI : 10.3847/1538-4357/836/2/247
Climatology of ionospheric scintillation over the Vietnam low-latitude region for the period 2006-2014
- Lan Tran Thi
- Minh Le Huy
- Amory-Mazaudier Christine
- Fleury Rolland
Advances in Space Research, Elsevier, 2017. This paper presents the characteristics of the occurrence of ionospheric scintillations at low-latitude, over Vietnam, by using continuous data of three GSV4004 receivers located at PHUT/Hanoï (105.9 o E, 21.0 o N; magnetic latitude 14.4 o N), HUES/Hue (107.6 o E, 16.5 o N; magnetic latitude 9.5 o N) and HOCM/ Ho Chi Minh city (106.6 o E, 10.8 o N; magnetic latitude 3.3 o N) for the period 2006-2014. The results show that the scintillation activity is maximum during equinox months for all the years and depends on solar activity as expected. The correlations between the monthly percentage scintillation occurrence and the F10.7 flux are of 0.40, 0.52 and 0.67 for PHUT, HUES and HOCM respectively. The distribution of scintillation occurrences is dominant in the pre-midnight sector and around the northern crest of the equatorial ionization anomaly (EIA), from the 15 o N to 20 o N geographic latitude with a maximum at 16 o N. The results obtained from the directional analysis show higher distributions of scintillations in the southern sky of PHUT and in the northern sky of HUES and HOCM, and in the elevation angles smaller than 40 o. The correlation between ROTI and S 4 is low and 2 rather good at PHUT (under EIA) than HOCM (near equator). We found better correlation in the post-midnight hours and less correlation in the pre-midnight hours for all stations. When all satellites are considered during the period of 2009-2011, the range of variation of the ration between ROTI and S 4 is from 1 to 7 for PHUT, from 0.3 to 6 for HUES and from 0.7 to 6 for HOCM. (10.1016/j.asr.2017.05.005)
DOI : 10.1016/j.asr.2017.05.005

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