Publications

2016

• Compressible MHD Turbulence in the Slow Solar Wind: Energy Transfer Rate
  
  • Sahraoui Fouad
  • Andrés Nahuel
  • Hadid L. Z.
  • Galtier Sébastien
  • Dmitruk P.
  • Mininni P. D.
  , 2016, 21, pp.SH21C-2538. The role of compressible fluctuations in the MHD turbulence is investigated using direct numerical simulations and in-situ spacecraft in the solar wind. A focus is put on verifying the exact third-order law derived for compressible isothermal turbulence by Banerjee and Galtier, 2013. The numerical simulations use a 3D compressible MHD code in the isothermal limit (&#61543; =1) with low sonic Mach numbers (Ms<1). The main goal is to evaluate the relative importance of the new flux and source terms involved in the derived law. Direct comparison with spacecraft observations from the Themis spacecraft in the fast and slow solar wind will be made.
• On Statistics of Electric Field Amplitudes in the Langmuir Turbulence
  
  • Krasnoselskikh V.
  • Voshchepynets A.
  • Volokitin A.
  • Krafft C.
  , 2016, 41, pp.SH41A-2513. We present a systematic study of the properties of the Langmuir wave turbulence generated by bump-on-tail instability in strongly non-homogeneous plasma. This type of turbulence occurs in numerous processes involving electrons beams in space plasmas. We analyse the synthetic data obtained in the numerical simulation based on two different approaches: the Hamiltonian model, and so-called probabilistic model. The Hamiltonian model describes in the self-consistent manner the wave-particle and wave-wave interactions in inhomogeneous magnetized plasmas. The model enables us to study the general properties of the distributions of the amplitudes of the Langmuir waves driven by the high-velocity electron beams in the fluctuating plasma. We pay special attention to the study of statistics of Languir waves under conditions when the decay instability, involving ion-sound waves, is developed. The probabilistic model, being modified version of the standard quasi-linear theory requires much less computational resources. Due to this it enables us to performed a detailed analysis of the statistics of the amplitudes of the Langmuir waves in the plasma with density fluctuations. To analyze data obtained in both numerical models, a Pearson technique was used to classify the probability distribution functions (PDF) of the logarithm of wave intensity. It was shown that core parts the PDF's belong to Pearson types I,IV and VI, depending on the spatial profiles of the density fluctuations, rather than to the normal distribution. The study also showed that the high-amplitude parts of the distributions follow power-low or exponential decay, depending on the type of core distribution.
• Currents and associated electron scattering and bouncing near the diffusion region at Earth's magnetopause
  
  • Lavraud B.
  • Zhang Y.
  • Vernisse Y.
  • Gershman D. J.
  • Dorelli J. C.
  • Cassak P.
  • Dargent Jérémy
  • Pollock C.
  • Giles B. L.
  • Aunai N.
  • Argall M. R.
  • Avanov L. A.
  • Barrie A.
  • Burch J. L.
  • Chandler Michael O.
  • Chen L. J.
  • Clark G. B.
  • Cohen I. J.
  • Coffey V. N.
  • Eastwood Jonathan P.
  • Egedal J.
  • Eriksson S.
  • Ergun R.
  • Farrugia C. J.
  • Fuselier S. A.
  • Genot V. N.
  • Graham D. B.
  • Grigorenko E. E.
  • Hasegawa H.
  • Jacquey C.
  • Kacem I.
  • Khotyaintsev Y. V.
  • Macdonald E.
  • Magnes W.
  • Marchaudon A.
  • Mauk B.
  • Moore T. E.
  • Mukai Toshifumi
  • Nakamura R.
  • Paterson W. R.
  • Penou E.
  • Phan T.
  • Rager A. C.
  • Retinò Alessandro
  • Rong Z. J.
  • Russell C. T.
  • Saito Y.
  • Sauvaud J.-A.
  • Schwartz S. J.
  • Shen C.
  • Smith S. E.
  • Strangeway R. J.
  • Toledo-Redondo Sergio
  • Torbert R. B.
  • Turner D. L.
  • Wang S.
  • Yokota S.
  , 2016, 21, pp.SM21A-2404. Based on high-resolution measurements from NASA's Magnetospheric Multiscale mission, we present the dynamics of electrons associated with current systems observed near the diffusion region of magnetic reconnection at Earth's magnetopause. Using pitch angle distributions (PAD) and magnetic curvature analysis we demonstrate the occurrence of electron scattering in the curved magnetic field of the diffusion region down to energies of 20 eV. We show that scattering occurs closer to the current sheet as the electron energy decreases. The scattering of inflowing electrons, associated with field-aligned electrostatic potentials and Hall currents, produces a new population of scattered electrons with broader PAD which bounce back and forth in the exhaust. Except at the center of the diffusion region the two populations are collocated and behave adiabatically: the PAD of inflowing electrons focuses inward (towards lower magnetic field), while the bouncing population gradually peaks at 90° away from the center (where it mirrors owing to higher magnetic field and probable field-aligned potentials).
• Quasiperiodic modulation of equatorial noise emissions
  
  • Nemec F.
  • Santolik O.
  • Pickett J. S.
  • Cornilleau-Wehrlin Nicole
  • Parrot M.
  , 2016, 43. Equatorial noise (EN) emissions are electromagnetic waves routinely observed in the inner magnetosphere within a few degrees from the geomagnetic equator. They propagate in the extraordinary mode nearly perpendicular to the ambient magnetic field, i.e., their frequencies are approximately limited by the lower hybrid frequency. Although they are usually continuous in time, about 5 percent of the events exhibit a clear quasiperiodic modulation of the wave intensity. We analyze in total 118 such EN events measured by the Cluster spacecraft. It is shown that more intense events typically have lower modulation periods. The fine harmonic structure identifiable when high resolution data are available allows us to estimate the radial distance of their source. We analyze in situ measured particle distribution functions and magnetic field pulsations in an attempt to determine the origin of the observed intensity variations. Finally, we use the data from the low altitude satellite DEMETER to demonstrate that these emissions can be observed at altitudes as low as 700 km, in particular during geomagnetically disturbed periods.
• Observations of EMIC Triggered Emissions off the Magnetic Equatorial Plane
  
  • Grison B.
  • Breuillard Hugo
  • Santolik O.
  • Cornilleau-Wehrlin Nicole
  , 2016, 11. On 19/08/2005 Cluster spacecraft had their perigee close to the dayside of the Earth magnetic equatorial plane, at about 14 hours Magnetic Local Time. The spacecraft crossed the equator from the southern hemisphere toward the northern hemisphere. In the Southern hemisphere, at about -23° magnetic latitude (MLAT) and at distance of 5.25 Earth Radii from Earth, Cluster 3 observes an EMIC triggered emission between the He and the proton local gyrofrequencies. The magnetic waveform (STAFF instrument data) is transformed into the Fourier space for a study based on single value decomposition (SVD) analysis. The emission lasts about 30s. The emission frequency rises from 1Hz up to 1.9Hz. The emission polarization is left-hand, its coherence value is high and the propagation angle is field aligned (lower than 30º). The Poynting flux orientation could not be established. Based on previous study results, these properties are indicative of an observation in vicinity of the source region of the triggered emission. From our knowledge this is the first time that EMIC triggered emission are observed off the magnetic equator. In order to identify the source region we study two possibilities: a source region at higher latitudes than the observations (and particles orbiting in "Shabansky" orbits) and a source region close to the magnetic equatorial plane, as reported in previous studies. We propose to identify the source region from ray tracing analysis and to compare the observed propagation angle in several frequency ranges to the ray tracing results.
• Beyond the Maltese Cross: Geometry of Turbulence between 0.2 and 1 AU
  
  • Montagud-Camps Victor
  • Verdini Andrea
  • Grappin Roland
  , 2016, 44, pp.SH44A-03. The spectral anisotropy of turbulent structures has been measured in the solar wind since 1990, relying on the assumption of axisymmetry around the mean magnetic field. However, early and recent works indicate that this hypothesis might be partially wrong, thus raising two questions: (i) is it correct to interpret measurements at 1 AU (the so-called maltese cross) in term of a sum of slab and 2D turbulence? (ii) what information is really contained in the maltese cross? We solve direct numerical simulations of the MHD equations including the transverse stretching exerted by the mean solar wind flow and study the genuine 3D anisotropy of turbulence as well as that one resulting from the assumption of axisymmetry around the mean field, B0. We show that the a slab component results from the axisymmetry assumption when the real anisotropy is ruled by the radial axis. This strongly depends on the initial state of fluctuations (at 0.2 AU in our simulations): a spectrum axisymmetric around B0 roughly conserves its symmetry, thus resisting the stretching in directions perpendicular to the radial; an isotropic spectrum instead becomes essentially axisymmetric with respect to the radial direction, even at inertial-range scales. We suggest that close to the Sun, slow-wind turbulence has a spectrum that is axisymmetric around B0 and the measured 2D component at 1 AU describes the real shape of turbulent structures. On the contrary, fast-wind turbulence has a more isotropic spectrum at the source and becomes radially symmetric at 1 AU. Such structure is hidden by the symmetrization applied to the data that instead returns a slab geometry. We conlcude by discussing the cascade rates associated to fast and slow wind.
• Turbulence Heating Observer - Thor
  
  • Retinò Alessandro
  • Vaivads A.
  • Escoubet C. Philippe
  • Khotyaintsev Y. V.
  • Soucek J.
  • Valentini F.
  • Chen C. H. K.
  • Fazakerley A.
  • Lavraud B.
  • Marcucci M. F.
  • Narita Y.
  • Vainio Rami O.
  • Gehler M.
  • Voirin T.
  • Wielders A.
  • Boudin N.
  • Osuna P.
  , 2016, 12, pp.SH12A-01. Turbulent fluctuations are ubiquitous in astrophysical plasmas and reach up scales as large as stars, bubbles and clouds blown out by stellar winds as well as entire galaxies. However, most of the irreversible energy dissipation associated to turbulent fluctuations occurs at very small scales, the so-called kinetic scales, where the plasma no longer behaves as a fluid and the properties of individual plasma species (electrons, protons, and other ions) become important. The heating of different plasma species as well as the acceleration of particles to high energies are governed by kinetic processes which determine how the turbulent electromagnetic fluctuations dissipate. Thus, processes at kinetic scales directly affect the large-scale properties of astrophysical plasmas. Turbulence Heating ObserveR (THOR) is one of the three candidates for selection as the next ESA M-class mission (M4). THOR will be the first mission ever flown in space that is fully dedicated to study plasma turbulent fluctuations and associated energization mechanisms. It will explore the kinetic plasma processes that determine the fundamental behavior of the majority of baryonic matter in the universe, and will lead to an understanding of the basic plasma heating and particle acceleration mechanisms, of their effect on different plasma species and of their relative importance in different turbulent regimes. THOR will provide closure of these fundamental questions by making detailed in situ measurements of the closest available dilute and turbulent magnetized plasmas - the Near-Earth's space - at unprecedented temporal and spatial resolution. THOR focuses on particular regions in space: the pristine solar wind, the Earth's bow shock and interplanetary shocks, and the compressed solar wind regions downstream of shocks. These regions are selected because of their different turbulence properties and reflect the properties of a number of distant astrophysical environments. Here we present THOR's science as well as the results of the ongoing mission study, currently undertaken at ESA.
• Space Weather : From the Sun to the Earth, the key role of GNSS
  
  • Amory-Mazaudier Christine
  , 2016. Since two decades a new scientific discipline Space Weather based on the integration of the physical processes between the Sun and the Earth is developing. The interest of this global approach is to unify different disciplines of the past (Solar Physics, Physics of the magnetosphere, Ionospheric studies etc) and also to connect the fundamental research to the applications in GNSS. This paper is devoted to : - the main solar physical processes at the origin of GNSS technical disruptions - the main progress in the knowledge of Ionosphere made with GNSS - the training on GNSS and Space weather, to be develop
• Evaluation of the generalized Ohm's law at the subsolar magnetopause diffusion region with MMS data
  
  • Cozzani Giulia
  • Retinò Alessandro
  • Le Contel Olivier
  • Chasapis A.
  • Califano F.
  • Khotyaintsev Y. V.
  • Vaivads A.
  • Breuillard Hugo
  • Mirioni Laurent
  • Lavraud B.
  • Torbert R. B.
  • Lindqvist P. A.
  • Ergun R.
  • Giles B. L.
  • Russell C. T.
  • Nakamura R.
  • Moore T. E.
  • Burch J. L.
  , 2016, 21, pp.SM21A-2411. Magnetic reconnection is a fundamental process occurring in thin current sheets where a change in the magnetic field topology leads to fast magnetic energy conversion into energy of charged particles. A key yet poorly understood aspect is how the reconnection electric field is sustained in the diffusion region by the different terms in the generalized Ohm's law. In particular, the role of the pressure and inertia terms is not yet fully understood as well as the importance of the anomalous resistivity term and its source. Simulations have provided some estimations of the different terms; however direct observations have been scarce so far. The four-spacecraft Magnetospheric Multiscale Mission (NASA/MMS) allows, for the first time, the full evaluation of the generalized Ohm's law in the diffusion region. Here we present MMS observations at a few subsolar diffusion region crossings on October,3rd 2015 where MMS spacecraft were separated by 25 km. We compare the measured electric field with the electric field due to both kinetic effects (electron pressure tensor, electron inertia terms) and to anomalous resistivity associated to different wave modes. The electric field is balanced by the Hall term at ion scales as expected. At smaller scales, preliminary results indicate that the electric field is mainly balanced by the divergence of the electron pressure tensor, although the contribution of anomalous resistivity is not negligible.
• NO2 adsorption mechanism on TiO2: An in-situ transmission infrared spectroscopy study
  
  • Sivachandiran L.
  • Thevenet F.
  • Rousseau Antoine
  • Bianchi D.
  Applied Catalysis B: Environmental, Elsevier, 2016, 198, pp.411–419. The adsorption of NO2 on oxidized TiO2 surface, under dark condition at 296 K, has been investigated by in-situ transmission Fourier Transform Infrared Spectroscopy (trans-FTIR) as a function of time. It enabled the determination of detailed NO2 reactive adsorption mechanisms on TiO2. It was evidenced that, as soon as NO2 molecules adsorb on TiO2 surface it dimerize to adsorbed N2O4 species. The strongly adsorbed N2O4 undergoes intramolecular disproportionation reaction and produces: (i) weakly adsorbed monodentate nitrate (m-NO3−) species and, (ii) highly reactive NO+ and/or N2O3 species on Ti4+ sites and O2− sites, respectively. The NO+ species reacts with surface lattice oxygen (O2−) and produces more stable NO2− on Ti4+ sites. Then, the NO2− undergoes intermolecular disproportionation reaction with another strongly adsorbed N2O4 molecule and produces strongly adsorbed bidentate nitrate (b-NO3−) species on Ti4+ sites and releases NO in the gas phase. It was also noticed that, as adsorption time increases, the weakly adsorbed m-NO3− species are converted into strongly adsorbed b-NO3− species. The intramolecular disproportionation reaction rate depends on NO2 partial pressure, whereas the intermolecular disproportionation reaction rate depends on the coverage of NO2− species and the number of available Ti4+ sites. This mechanism is assessed for different NO2 partial pressures ranging from 25 to 100 Pa. This study reveals that the configuration and the amount of the N-containing species on activated TiO2 surface depend on the NO2 concentration and the contact time. (10.1016/j.apcatb.2016.05.065)
  DOI : 10.1016/j.apcatb.2016.05.065
• Solar Wind Electrons Alphas and Protons (SWEAP) Investigation: Design of the Solar Wind and Coronal Plasma Instrument Suite for Solar Probe Plus
  
  • Kasper Justin
  • Abiad Robert
  • Austin Gerry
  • Balat-Pichelin Marianne J.H.
  • Bale Stuart
  • Belcher John
  • Berg Peter
  • Bergner Henry
  • Berthomier Matthieu
  • Bookbinder Jay
  • Brodu Etienne
  • Caldwell David
  • Case Anthony
  • Chandran Benjamin
  • Cheimets Peter
  • Cirtain Jonathan
  • Cranmer Steven
  • Curtis David
  • Daigneau Peter
  • Dalton Greg
  • Dasgupta Brahmananda
  • Detomaso David
  • Diaz-Aguado Millan
  • Djordjevic Blagoje
  • Donaskowski Bill
  • Effinger Michael
  • Florinski Vladimir
  • Fox Nichola
  • Freeman Mark
  • Gallagher Dennis
  • Gary S. Peter
  • Gauron Tom
  • Gates Richard
  • Goldstein Melvin
  • Golub Leon
  • Gordon Dorothy
  • Gurnee Reid
  • Guth Giora
  • Halekas Jasper
  • Hatch Ken
  • Heerikuisen Jacob
  • Ho George
  • Hu Qiang
  • Johnson Greg
  • Jordan Steven
  • Korreck Kelly
  • Larson Davin
  • Lazarus Alan
  • Li Gang
  • Livi Roberto
  • Ludlam Michael
  • Maksimovic Milan
  • Mcfadden James
  • Marchant William
  • Maruca Bennet
  • Mccomas David
  • Messina Luciana
  • Mercer Tony
  • Park Sang
  • Peddie Andrew
  • Pogorelov Nikolai
  • Reinhart Matthew
  • Richardson John
  • Robinson Miles
  • Rosen Irene
  • Skoug Ruth
  • Slagle Amanda
  • Steinberg John
  • Stevens Michael
  • Szabo Adam
  • Taylor Ellen
  • Tiu Chris
  • Turin Paul
  • Velli Marco
  • Webb Gary
  • Whittlesey Phyllis
  • Wright Ken
  • Wu S.
  • Zank Gary
  Space Science Reviews, Springer Verlag, 2016, 204 (1-4), pp.131-186. The Solar Wind Electrons Alphas and Protons (SWEAP) Investigation on Solar Probe Plus is a four sensor instrument suite that provides complete measurements of the electrons and ionized helium and hydrogen that constitute the bulk of solar wind and coronal plasma. SWEAP consists of the Solar Probe Cup (SPC) and the Solar Probe Analyzers (SPAN). SPC is a Faraday Cup that looks directly at the Sun and measures ion and electron fluxes and flow angles as a function of energy. SPAN consists of an ion and electron electrostatic analyzer (ESA) on the ram side of SPP (SPAN-A) and an electron ESA on the anti-ram side (SPAN-B). The SPAN-A ion ESA has a time of flight section that enables it to sort particles by their mass/charge ratio, permitting differentiation of ion species. SPAN-A and -B are rotated relative to one another so their broad fields of view combine like the seams on a baseball to view the entire sky except for the region obscured by the heat shield and covered by SPC. Observations by SPC and SPAN produce the combined field of view and measurement capabilities required to fulfill the science objectives of SWEAP and Solar Probe Plus. SWEAP measurements, in concert with magnetic and electric fields, energetic particles, and white light contextual imaging will enable discovery and understanding of solar wind acceleration and formation, coronal and solar wind heating, and particle acceleration in the inner heliosphere of the solar system. SPC and SPAN are managed by the SWEAP Electronics Module (SWEM), which distributes power, formats onboard data products, and serves as a single electrical interface to the spacecraft. SWEAP data products include ion and electron velocity distribution functions with high energy and angular resolution. Full resolution data are stored within the SWEM, enabling high resolution observations of structures such as shocks, reconnection events, and other transient structures to be selected for download after the fact. This paper describes the implementation of the SWEAP Investigation, the driving requirements for the suite, expected performance of the instruments, and planned data products, as of mission preliminary design review. (10.1007/s11214-015-0206-3)
  DOI : 10.1007/s11214-015-0206-3
• Electrostatic PIC for Space propulsion: LPPic2D
  
  • Croes Vivien
  • Lafleur Trevor
  • Bourdon Anne
  • Chabert Pascal
  , 2016.
• Turbulence and dissipation in magnetized plasmas
  
  • Sahraoui Fouad
  , 2016.
• Multifrequency impedance matching solutions for plasma excitation by Tailored Voltage Waveforms
  
  • Johnson Erik
  • Dine Sebastien
  • Booth Jean-Paul
  , 2016. Tailored Voltage Waveforms (TVWs) and the Electrical Asymmetry Effect they induce in plasmas are useful tools to both optimize plasma processes and gain insight into the role of specific plasma parameters (ion bombardment energy, species flux) in processing outcomes. However, the multi-frequency nature of these waveforms, which are composed of a fundamental frequency in the MHz range and a number of its harmonics (eg 13.56MHz 27.12MHz 40.68MHz.), leads to a practical technical challenge, namely multi-harmonic impedance matching. Although impedance matching the 50 ohm output of an amplifier to a plasma processing chamber with a large reactive component is easily achieved for a single frequency using a passive component matchbox, doing the same at multiple harmonics is much more challenging due to the frequency response of every circuit element (including the chamber). One strategy that has been employed and deployed as a commercial product is the use of multiple amplifiers, matchboxes, and filter sets, one for each frequency used. Although technically effective, using individual amplifiers for each frequency may not be the most cost-effective solution. Alternatively, we have previously proposed a technique to simultaneously match at multiple frequencies using a passive multi-frequency matchbox (MFMB), but this solution is difficult to optimise due to variations in components affecting the response at pairs of frequencies. In this work, we present results from a new design of MFMB using only passive components. Critically, this new design allows (1) independent control of the frequency response at each harmonic, and (2) the use of a single high-power amplifier. Circuit simulation results as well as experimental resultsare shown for a small area, laboratory plasma processing chamber during an argon plasma for three-frequency operation, and for fundamental frequencies between 9 and 15 MHz. It is demonstrated that although adjusting the matching condition for the fundamental frequency (1f) changes the matching for the other two (2f, 3f), the converse is not true; adjusting the matching on the higher harmonics does not impact that of the fundamental. Furthermore, we show that this improved matching is indeed due to better power transfer and not parasitic losses in the matching network.
• Translational and Vibrational Energy in Cl<SUB>2</SUB> and O<SUB>2</SUB> Plasmas Probed by Innovative Optical Diagnostics
  
  • Booth Jean-Paul
  • Marinov Daniil
  • Foucher Mickaël
  • Guaitella Olivier
  • Drag Cyril
  • Agarwal Ankur
  • Rauf S.
  , 2016. A common assumption for Low-temperature plasmas is that neutral molecules and atoms in the system are in thermal equilibrium with the surrounding ambient (room) temperature, and only charged particles, which can acquire energy from applied electric fields, have higher mean energies. In reality, energy can be transferred from electrons or ions to the neutral gas, increasing the gas translational temperature. Furthermore, non-equilibrium vibrational or rotational distributions can occur in molecular gas plasmas. This can have significant effects on the plasma dynamics. Firstly, since most plasma reactors operate in a pressure-controlled regime, high gas temperatures will cause a considerable decrease in gas density (and therefore in electron-neutral collision rates). Secondly, the rates of activated processes may be significantly increased by translational energy. Vibrational excitation can lead to large increases in the rates of electron dissociative attachment and neutral dissociation. We have developed a new, unambiguous technique to measure gas translational temperature of atoms, using Doppler-resolution Two-Photon Absorption Laser Induced Fluorescence (HR-TALIF) employing a specially-built narrow-bandwidth tuneable pulsed UV laser. Initial results have been obtained on oxygen atoms, where a measurement precision of ±10K is readily obtained. In a DC glow discharge in pure O2 the gas temperature up to 550K are observed. The technique will be extended to the study of lower-pressure inductively-coupled plasmas, where higher temperatures are expected, and to chlorine atoms. In order to investigate vibrational distributions, we have developed a high-sensitivity ultra-broadband ultraviolet absorption spectrometer. This employs a highly-stable laser-plasma light source and achromatic optics, allowing absorption spectra over a 250nm range to be measured with a baseline stability of the order 10-5. In pure O2 discharges (both DC glow and in a low-pressure ICP reactor) we were able to observe oxygen molecules in vibrationally-excited levels up to v=18 (more than half-way to dissociation), with a tail vibrational temperature of 7000K. Vibrational excitation was also detected in Cl2 molecules in a pure Cl2 ICP. However, Cl2 appears to be close to thermal equilibrium with the gas translational temperature, which nevertheless approaches 2000K in this case. This work was performed within the LABEX Plas@par project, and received financial state aid managed by the Agence Nationale de la Recherche, as part of the programme "Investissements d'avenir" under the reference ANR-11-IDEX-0004-02 and ANR project CleanGRAPH ((ANR-13-BS09-0019).It was also supported by the Applied Materials University Research Partnership Program
• Charged Particle Dynamics in Technological Radio Frequency Plasmas Operated in CF<SUB>4</SUB>
  
  • Schulze J.
  • Berger B.
  • Brandt S.
  • Bruneau Bastien
  • Liu Y.
  • Korolov Ihor
  • Derzsi A.
  • Schuengel E.
  • Koepke M.
  • Mussenbrock T.
  • Johnson E.V.
  • Lafleur Trevor
  • Booth Jean-Paul
  • O'Connell D.
  • Gans T.
  • Wang Yn
  • Donkó Z.
  , 2016. ion energy distribution functions (IEDF) are investigated in electronegative capacitive RF plasmas operated in CF4 based on a combination of experiments, PIC simulations, and models. In the experiment, Phase Resolved Optical Emission Spectroscopy is used to access the space and time resolved electron dynamics. The DC self bias and IEDFs are measured at the electrodes. For a single frequency discharge operated at 13.56 MHz and 80 Pa we demonstrate that the presence of an electronegative gas can change the electron power absorption dynamics completely compared to electropositive gases by inducing a heating mode transition. Reducing the driving frequency results in the formation of stable striations of the optical emission and electron impact excitation rate due to the collective response of positive and negative ions to the driving frequency. Based on this fundamental understanding, we show that tailoring the driving voltage waveform using a superposition of multiple consecutive harmonics of a fundamental frequency with individually adjustable harmonics amplitudes and phases allows for control of the DC self bias, the shape and mean energy of the IEDF, the electron power absorption dynamics, and the spatial division of the discharge into two halves of strongly different electronegativity.
• 3rd International Conference on Ignition Systems for Gasoline Engines
  
  • Starikovskaia Svetlana
  , 2016.
• Ignition and combustion sustained by low temperature plasmas and spark discharges: difference in physical properties of plasma and kinetic mechanisms
  
  • Shcherbanev S.A.
  • Starikovskaia Svetlana
  , 2016.
• Counter-streaming radiative shock experiments on the Orion laser
  
  • Suzuki-Vidal Francisco
  • Clayson Thomas
  • Swadling G. F.
  • Patankar S.
  • Burdiak G. C.
  • Lebedev S. V.
  • Smith R. A.
  • Stehlé Chantal
  • Chaulagain Uddhab
  • Singh Raj Laxmi
  • Larour Jean
  • Kozlová Michaela
  • Spindloe C.
  • Foster J.
  • Skidmore J.
  • Gumbrell E.
  • Graham P.
  • Danson C.
  , 2016, 61 (18). The formation of radiative shocks, shocks in which the structure of density and temperature is affected by radiation from the shock-heated matter, is ubiquitous in many astrophysical scenarios. Experiments were performed at the Orion laser using a new target configuration that allows studying the formation of single and counter-streaming radiative shocks in gas-filled targets (Ne, Ar, Kr, Xe), with initial pressures ~0.1-1 bar and a driver intensity of ~6x10**14 W/cm2. The shocks propagate at velocities ~60 km/s and were diagnosed with optical interferometry (streaked and time-resolved) and point-projection X-ray backlighting allowing to probe simultaneously the pre-shock radiative precursor and the shock front itself. Besides varying the extent of the radiative precursor the results show that different gases seem to have an effect on the shock front as evidenced by a number of spatial features. The results are compared with radiative hydrodynamics simulations in 1-D (HELIOS) and 2-D (NYM/PETRA). http://absimage.aps.org/image/DPP16/MWS_DPP16-2016-000529.pdf
• Counter-propagating radiative shock experiments on the Orion laser facility
  
  • Clayson Thomas
  • Suzuki-Vidal Francisco
  • Lebedev S. V.
  • Swadling G. F.
  • Burdiak G. C.
  • Patankar S.
  • Smith R. A.
  • Foster J.
  • Skidmore J.
  • Gumbrell E.
  • Graham P.
  • Danson C.
  • Stehlé Chantal
  • Singh Raj Laxmi
  • Chaulagain Uddhab
  • Larour Jean
  • Kozlová Michaela
  • Spindloe C.
  , 2016, 61 (18). The Orion high-power laser facility, at AWE Aldermaston UK, was used to produce hyper-sonic radiative shocks, travelling at ~60km/s, in noble gases, between 0.1 and 1.0 bar. These experiments aimed to study the radiative precursor, a heat and ionization wave preceding the shock front, and dynamics of colliding radiative shocks. X-ray backlighting and optical self-emission streak imaging were used to study the shock front and collision dynamics, while multi-frame and streaked interferometry were used to simultaneously study the radiative precursor. These experiments compared the shock and collision dynamics in different gases (e.g. Ne, Ar, Kr, Xe), while maintaining a constant mass density, to vary the strength of the radiative precursor. Some shocks exhibited features suggesting the formation of hydrodynamic or radiative instabilities. The experimental data is in good agreement with 2-D rad-hydro simulations and provides a new benchmark for codes to be tested against. http://absimage.aps.org/image/DPP16/MWS_DPP16-2016-000820.pdf
• Cathode-less gridded ion thrusters for small satellites
  
  • Aanesland Ane
  • Rafalskyi D.V.
  , 2016.
• SMILEI: A collaborative, open-source, multi-purpose PIC code for the next generation of super-computers
  
  • Grech M.
  • Derouillat J.
  • Beck A.
  • Chiaramello M.
  • Grassi A.
  • Niel F.
  • Pérez F.
  • Vinci T.
  • Flé M.
  • Aunai N.
  • Dargent Jérémy
  • Plotnikov I.
  • Bouchard G.
  • Savoini Philippe
  • Riconda C.
  , 2016, pp.GP10.006. Over the last decades, Particle-In-Cell (PIC) codes have been central tools for plasma simulations. Today, new trends in High-Performance Computing (HPC) are emerging, dramatically changing HPC-relevant software design and putting some - if not most - legacy codes far beyond the level of performance expected on the new and future massively-parallel super computers. SMILEI is a new open-source PIC code co-developed by both plasma physicists and HPC specialists, and applied to a wide range of physics-related studies: from laser-plasma interaction to astrophysical plasmas. It benefits from an innovative parallelization strategy that relies on a super-domain-decomposition allowing for enhanced cache-use and efficient dynamic load balancing. Beyond these HPC-related developments, SMILEI also benefits from additional physics modules allowing to deal with binary collisions, field and collisional ionization and radiation back-reaction. This poster presents the SMILEI project, its HPC capabilities and illustrates some of the physics problems tackled with SMILEI.
• Dynamique des plasmas radio-fréquence à couplage inductif en gaz halogénés simples
  
  • Foucher Mickaël
  , 2016. Les plasmas radio-fréquences à couplage inductif en gaz halogénés simples (cl2/hbr/o2) sont fortement utilisés dans l'industrie des semi-conducteurs. Cependant, notre connaissance des processus réactionnels de ces plasmas est encore très partielle. De nombreux travaux de simulations (fluides, particulaires...), visant à améliorer celle-ci, ont été produits ces dernières décennies. Toutefois, trop peu de résultats expérimentaux sont disponibles dans la littérature afin de valider ou améliorer ces simulations. L'objectif de cette thèse est alors de produire un ensemble complet de résultats experimentaux. Nous nous focalisons essentiellement sur le cas des plasmas de cl2 et de o2 purs. Dans cette thèse, nous étendons les résultats expérimentaux déjà présents dans la littérature : densités de charges et de neutres, températures translationnelles. En particulier, les tendances en fonction de la pression, essentielles pour la simulation, sont soigneusement étudiées. Les vibrations moléculaires sont également étudiées à l'aide d'un montage innovant de spectroscopie d'absorption. Nous montrons que les simulations sont encore loin de représenter fidèlement les processus réactionnels des plasmas étudiés. Nous tentons de fournir à cet effet quelques pistes d'améliorations. Ce travail est la base nécessaire à l'amélioration continue des plasmas industriels utilisés pour la gravure de semi-conducteurs.
• Advanced Ion Mass spectrometer for Giant Planet Ionospheres, Magnetospheres and Moons
  
  • Sittler E.C.
  • Cooper J.F.
  • Paschalidis N.
  • Jones S. L.
  • Brinckerhoff W. L.
  • Paterson W. R.
  • Ali A.
  • Coplan M.A.
  • Chornay D.
  • Sturners S.J.
  • Benna Mehdi
  • Bateman F.B.
  • Fontaine Dominique
  • Verdeil Christophe
  • Andre N.
  • Blanc Michel
  • Wurz Peter
  , 2016, 1980, pp.4088. Advanced Ion Mass Spectrometer is being developed to measure both major and minor ion species from 1 V to 25 kV with wide field-of-view in the 1-60 amu mass range at M/DeltaM <= 60 over a wide range of ion intensities within high radiation environments.
• Champ électrique et onde d'ionisation dans un jet plasma atmosphérique pulsé : comparaison de diagnostics
  
  • Iséni Sylvain
  • Damany X
  • Sretenović G
  • Kovačević V
  • Krstić I
  • Pechereau François
  • Dozias S
  • Pouvesle J.-M
  • Bourdon Anne
  • Kuraica M
  • Robert E
  , 2016. Les jets de plasma froid dans les gaz rares à la pression atmosphérique résultent de la propagation d'ondes d'ionisation se propageant le plus souvent dans un capillaire diélectrique pour ensuite donner lieu à la formation d'une plume plasma s'étendant dans l'atmosphère ambiant [1]. De nombreuses applications tirent parti de ces décharges à température ambiante notamment le domaine du vivant. Avec l'avènement de l'utilisation du plasma en biologie et en médecine, il est déjà démontré que ces jets plasmas possèdent un grand potentiel pour le déclenchement et l'activation de mécanismes biologiques comme la prolifération de cellules ou l'inactivation de microorganismes. Bien que de nombreuses études présentent la formation d'espèces chimiques réactives produites par le plasma comme acteur principal, la contribution d'autres éléments composant le plasma reste encore mal identifiée. C'est notamment le cas des champs électriques transitoires générés par ces jets. Sur cette affiche seront présentés les résultats de mesures du champ électrique transitoire résultant généré par des jets d'hélium à la pression atmosphérique. En effet, la caractérisation expérimentale du champ électrique est nécessaire à la compréhension de mécanismes plasmas ainsi qu'à la validation de simulations numériques. Cependant, la mesure du champ électrique dans ou proche des conditions d'utilisation constitue un véritable défi expérimental. L'approche proposée est basée sur la comparaison de deux méthodes reposant sur des principes différents. La première consiste en une sonde électro-optique sensible à l'effet Pockels et permettant de mesurer simultanément deux composantes orthogonales du champ électrique [2]. Le vecteur champ électrique est alors caractérisé dans l'espace et dans le temps au voisinage du jet plasma. La seconde méthode fait appel à la spectroscopie d'émission afin d'observer la dépendance de polarisation de l'effet Stark de la raie d'hélium à 492.19 nm en fonction du champ électrique [3]. Bien que non-intrusive, cette technique ne se prête qu'à des mesures dans le volume plasma, là où l'hélium est excité. Ces travaux sont en cours de réalisation via le projet bilatéral PHC Pavle Savic 2016 (n°36216UA). XD remercie ses partenaires de financement INEL/Région Centre Val de Loire. References [1] Xiong Z, Robert E, Sarron V, Pouvesle J-M and Kushner M J 2013, J. Phys. D. Appl. Phys. 46 155203 [2] Gaborit G, Jarrige P, Lecoche F, Dahdah J, Duraz E, Volat C and Duvillaret L 2014, IEEE Trans. Plasma Sci. 42 1265–73 [3] Sretenović G B, Krstić I B, Kovačević V V, Obradović B M and Kuraica M M 2014, J. Phys. D. Appl. Phys. 47 102001 Mots clés : jet plasma atmosphérique, diagnostic plasma, spectroscopie, champ électrique, plasma médecine.