Publications

2017

• MMS Observations of Reconnection at Dayside Magnetopause Crossings During Transitions of the Solar Wind to Sub-Alfvenic Flow
  
  • Marklund G. T.
  • Paulson K.
  • Petrinec S.
  • Phan T.
  • Pollock C.
  • Farrugia C. J.
  • Lugaz N.
  • Alm L.
  • Vasquez B. J.
  • Argall M. R.
  • Kucharek H.
  • Matsui H.
  • Torbert R. B.
  • Lavraud B.
  • Le Contel Olivier
  • Shuster J. R.
  • Burch J. L.
  • Khotyaintsev Y. V.
  • Giles B. L.
  • Fuselier S. A.
  • Gershman D. J.
  • Ergun R.
  • Eastwood Jonathan P.
  • Cohen I. J.
  • Dorelli J. C.
  • Lindqvist P. A.
  • Strangeway R. J.
  • Russell C. T.
  , 2017, 13. We present MMS) observations during two dayside magnetopause crossingsunder hitherto unexamined conditions: (i) when the bow shock is weakening and the solar wind transitioning to sub-Alfvenic flow, and (ii) when it is reforming. Interplanetary conditions consist of a magnetic cloud with (i) a strong B ( 20 nT) pointing south, and (ii) a density profile with episodic decreases to values of 0.3 /cc followed by moderate recovery. During the crossings he magnetosheath magnetic field is stronger than the magnetosphere field by a factor of 2.2. As a result, during the outbound crossing through the ion diffusion region, MMS observed an inversion of relative positions of the X and stagnation (S) lines from that typically the case: the S line was closer to the magnetosheath side. The S-line appears in the form of a slow expansion fan near which most of the energy dissipation is taking place. While in the magnetosphere between the crossings, MMS observed strong field and flow perturbations, which we argue to be due kinetic Alfvén waves.During the reconnection interval, whistler mode waves generated by an electron temperature anisotropy (Tperp>Tpar) were observed. Another aim of the paper isto distinguish bow shock-induced field and flow perturbations from reconnection-related signatures.The high resolution MMS data together with 2D hybrid simulations of bow shock dynamics helped us to distinguish between the two sources. We show examples of bow shock-related effects (such as heating) and reconnection effects such as accelerated flows satisfying the Walen relation.
• Multi-scale multi-point observation of dipolarization in the near-Earth's magnetotail
  
  • Nakamura R.
  • Varsani A.
  • Genestreti K.
  • Nakamura T.
  • Baumjohann W.
  • Birn Joachim
  • Le Contel Olivier
  • Nagai T.
  , 2017, 43. We report on evolution of the dipolarization in the near-Earth plasma sheet during two intense substorms based on observations when the four spacecraft of the Magnetospheric Multiscale (MMS) together with GOES and Geotail were located in the near Earth magnetotail. These multiple spacecraft together with the ground-based magnetogram enabled to obtain the location of the large- scale substorm current wedge (SCW) and overall changes in the plasma sheet configuration. MMS was located in the southern hemisphere at the outer plasma sheet and observed fast flow disturbances associated with dipolarizations. The high time-resolution measurements from MMS enable us to detect the rapid motion of the field structures and the flow disturbances separately and to resolve signatures below the ion-scales. We found small-scale transient field-aligned current sheets associated with upward streaming cold plasmas and Hall-current layers in the fast flow shear region. Observations of these current structures are compared with simulations of reconnection jets.
• Thin current sheets observation by MMS during a near-Earth's magnetotail reconnection event
  
  • Nakamura R.
  • Varsani A.
  • Nakamura T.
  • Genestreti K.
  • Plaschke F.
  • Baumjohann W.
  • Nagai T.
  • Burch J. L.
  • Cohen I. J.
  • Ergun R.
  • Fuselier S. A.
  • Giles B. L.
  • Le Contel Olivier
  • Lindqvist P. A.
  • Magnes W.
  • Schwartz S. J.
  • Strangeway R. J.
  • Torbert R. B.
  , 2017, 22. During summer 2017, the four spacecraft of the Magnetospheric Multiscale (MMS) mission traversed the nightside magnetotail current sheet at an apogee of 25 RE. They detected a number of flow reversal events suggestive of the passage of the reconnection current sheet. Due to the mission's unprecedented high-time resolution and spatial separation well below the ion scales, structure of thin current sheets is well resolved both with plasma and field measurements. In this study we examine the detailed structure of thin current sheets during a flow reversal event from tailward flow to Earthward flow, when MMS crossed the center of the current sheet . We investigate the changes in the structure of the thin current sheet relative to the X-point based on multi-point analysis. We determine the motion and strength of the current sheet from curlometer calculations comparing these with currents obtained from the particle data. The observed structures of these current sheets are also compared with simulations.
• Generation of Electron Whistler Waves at the Mirror Mode Magnetic Holes: MMS Observations and PIC Simulation
  
  • Ahmadi N.
  • Wilder F. D.
  • Usanova M.
  • Ergun R.
  • Argall M. R.
  • Goodrich K. A.
  • Eriksson S.
  • Germaschewski K.
  • Torbert R. B.
  • Lindqvist P. A.
  • Le Contel Olivier
  • Khotyaintsev Y. V.
  • Strangeway R. J.
  • Schwartz S. J.
  • Giles B. L.
  • Burch J. L.
  , 2017, 24. The Magnetospheric Multiscale (MMS) mission observed electron whistler waves at the center and at the gradients of magnetic holes on the dayside magnetosheath. The magnetic holes are nonlinear mirror structures which are anti-correlated with particle density. We used expanding box Particle-in-cell simulations and produced the mirror instability magnetic holes. We show that the electron whistler waves can be generated at the gradients and the center of magnetic holes in our simulations which is in agreement with MMS observations. At the nonlinear regime of mirror instability, the proton and electron temperature anisotropy are anti-correlated with the magnetic hole. The plasma is unstable to electron whistler waves at the minimum of the magnetic field structures. In the saturation regime of mirror instability, when magnetic holes are dominant, electron temperature anisotropy develops at the edges of the magnetic holes and electrons become isotropic at the magnetic field minimum. We investigate the possible mechanism for enhancing the electron temperature anisotropy and analyze the electron pitch angle distributions and electron distribution functions in our simulations and compare it with MMS observations.
• Quasiperiodic modulation of equatorial noise emissions: Cluster and Van Allen Probes observations
  
  • Nemec F.
  • Santolik O.
  • Boardsen S. A.
  • Hospodarsky G. B.
  • Pickett J. S.
  • Cornilleau-Wehrlin Nicole
  • Kurth W. S.
  • Darrouzet F.
  • Kletzing C.
  , 2017, 51. Equatorial noise emissions (fast magnetosonic waves) are routinely observed in the equatorial region of the inner magnetosphere, propagating nearly perpendicular to the ambient magnetic field. Although most events are continuous in time, some are formed by nearly periodically repeating wave elements. We present a survey of these events with the quasiperiodic time modulation observed by the Cluster and Van Allen Probes spacecraft. Local plasma density measurements are used to evaluate the event locations with respect to the plasmapause. It is shown that although the events may occur both inside and outside the plasmasphere, the occurrence of some events is clearly limited to just outside the plasmasphere, with a sudden disappearance at the plasmapause. The fine frequency structure of the events, which is related to the proton gyrofrequency in the source region, is used to determine the source radial distances. Finally, the analysis of multi-spacecraft measurements allows us to estimate the spatiotemporal variability of the events.
• Observations of electron vortex magnetic holes and related wave-particle interactions in the turbulent magnetosheath
  
  • Huang S. Y.
  • Sahraoui Fouad
  • Yuan Z.
  • He J.
  • Zhao J.
  • Du J.
  • Le Contel Olivier
  • Wang X.
  • Deng X.
  • Fu H.
  • Zhou M.
  • Shi Q.
  • Breuillard Hugo
  • Pang Y.
  • Yu X.
  • Wang D.
  , 2017, 11. Magnetic hole is characterized by a magnetic depression, a density peak, a total electron temperature increase (with a parallel temperature decrease but a perpendicular temperature increase), and strong currents carried by the electrons. The current has a dip in the core region of the magnetic hole and a peak in the outer region of the magnetic hole. There is an enhancement in the perpendicular electron fluxes at 90° pitch angles inside the magnetic hole, implying that the electrons are trapped within it. The variations of the electron velocity components Vem and Ven suggest that an electron vortex is formed by trapping electrons inside the magnetic hole in the circular cross-section. These observations demonstrate the existence of a new type of coherent structures behaving as an electron vortex magnetic hole in turbulent space plasmas as predicted by recent kinetic simulations. We perform a statistically study using high time solution data from the MMS mission. The magnetic holes with short duration (i.e., < 0.5 s) have their cross section smaller than the ion gyro-radius. Superposed epoch analysis of all events reveals that an increase in the electron density and total temperature, significantly increase (resp. decrease) the electron perpendicular (resp. parallel) temperature, and an electron vortex inside the holes. Electron fluxes at 90° pitch angles with selective energies increase in the KSMHs, are trapped inside KSMHs and form the electron vortex due to their collective motion. All these features are consistent with the electron vortex magnetic holes obtained in 2D and 3D particle-in-cell simulations, indicating that the observed the magnetic holes seem to be best explained as electron vortex magnetic holes. It is furthermore shown that the magnetic holes are likely to heat and accelerate the electrons. We also investigate the coupling between whistler waves and electron vortex magnetic holes. These whistler waves can be locally generated inside electron vortex magnetic holes by electron temperature anisotropic instability.
• A study on the non Maxwellian nature of ion velocity distribution functions using Magnetospheric Multiscale (MMS) data
  
  • Valentini F.
  • Perri S.
  • Yordanova E.
  • Paterson W. R.
  • Gershman D. J.
  • Giles B. L.
  • Pollock C. J.
  • Dorelli J. C.
  • Avanov L. A.
  • Lavraud B.
  • Saito Y.
  • Nakamura R.
  • Fischer D.
  • Baumjohann W.
  • Plaschke F.
  • Narita Y.
  • Magnes W.
  • Russell C. T.
  • Strangeway R. J.
  • Le Contel Olivier
  , 2017, 11. The interplanetary space is permeated by a plasma where effects of collisions among particles can be considered negligible. In such a weekly collisional medium, in the range of scales where kinetic effects dominate the plasma dynamics, the particle velocity distribution functions (VDF) are observed to be far from the thermodynamic equilibrium. Moreover, recent numerical self-consistent and nonlinear models of plasma turbulence dynamics have shown the presence of significant non-Maxwellian features in the particle VDFs, caused by kinetic effects, which become dominant in the turbulent cascade at ion scales. In particular, a kinetic hybrid Vlasov-Maxwell (HVM) numerical code, which reproduces the turbulent energy cascade down to ion scales, has highlighted significant departures of the ion VDFs from Maxwellian and a local temperature anisotropy close to current sheets structures generated by the turbulent cascade and close to regions of high ion vorticity.In this work, we make use of the high resolution (150 ms) ion and electron VDFs from Fast Plasma Investigation (FPI) instrument on board MMS and the about 1kHz resolution magnetic field data to investigate the possible presence of non-Maxwellian features in the ion VDFs close to intermittent magnetic structures and regions of high current density and vorticity. The data are relevant to a period where the MMS spacecraft was immersed in the turbulent magnetosheath (see Yordanova et al., 2016). The aim is to compare the analysis made by Valentini et al., 2016 on proton and alpha particles in the HVM simulations with the analysis made on the MMS data, and to deeply characterize the ion dynamics in the near Earth plasma. It is worth mentioning that thanks to its very high resolution plasma data, MMS has given the opportunity to study in details kinetic effects in plasma turbulence, down to electron scales.
• Statistical Analysis of Solar Events Associated with SSC over Year of Solar Maximum during Cycle 23: 1. Identification of Related Sun-Earth Events
  
  • Grison B.
  • Bocchialini Karine
  • Menvielle M.
  • Chambodut Aude
  • Cornilleau-Wehrlin Nicole
  • Fontaine Dominique
  • Marchaudon A.
  • Pick Monique
  • Pitout F.
  • Schmieder Brigitte
  • Régnier Stéphane
  • Zouganelis Yannis
  , 2017, 31. Taking the 32 sudden storm commencements (SSC) listed by the observatory de l'Ebre / ISGI over the year 2002 (maximal solar activity) as a starting point, we performed a statistical analysis of the related solar sources, solar wind signatures, and terrestrial responses. For each event, we characterized and identified, as far as possible, (i) the sources on the Sun (Coronal Mass Ejections -CME-), with the help of a series of herafter detailed criteria (velocities, drag coefficient, radio waves, polarity), as well as (ii) the structure and properties in the interplanetary medium, at L1, of the event associated to the SSC: magnetic clouds -MC-, non-MC interplanetary coronal mass ejections -ICME-, co-rotating/stream interaction regions -SIR/CIR-, shocks only and unclear events that we call "miscellaneous" events. The categorization of the events at L1 is made on published catalogues. For each potential CME/L1 event association we compare the velocity observed at L1 with the one observed at the Sun and the estimated balistic velocity. Observations of radio emissions (Type II, Type IV detected from the ground and /or by WIND) associated to the CMEs make the solar source more probable. We also compare the polarity of the magnetic clouds with the hemisphere of the solar source. The drag coefficient (estimated with the drag-based model) is calculated for each potential association and it is compared to the expected range values. We identified a solar source for 26 SSC related events. 12 of these 26 associations match all criteria. We finally discuss the difficulty to perform such associations.
• Small Scales Structure of MHD Turbulence, Tubes or Ribbons?
  
  • Verdini Andrea
  • Grappin Roland
  • Alexandrova O.
  • Lion S.
  , 2017, 41, pp.SH41D-02. Observations in the solar wind indicate that turbulent eddies change their anisotropy with scales [1]. At large scales eddies are elongated in direction perpendicular to the mean-field axis. This is the result of solar wind expansion that affects both the anisotropy and single-spacecraft measurments [2,3]. At small scales one recovers the anisotropy expected in strong MHD turbulence and constrained by the so-called critical balance: eddies are elongated along the mean-field axis. However, the actual eddy shape is intermediate between tubes and ribbons, preventing us to discriminate between two concurrent theories that predict 2D axysimmetric anisotropy [4] or full 3D anisotropy [5]. We analyse 10 years of WIND data and apply a numerically-derived criterion to select intervals in which solar wind expansion is expected to be negligible. By computing the anisotropy of structure functions with respect to the local mean field we obtain for the first time scaling relations that are in agreement with full 3D anisotropy, i.e. ribbons-like structures. However, we cannot obtain the expected scaling relations for the alignment angle which, according to the theory, is physically responsible for the departure from axisymmetry. In addition, a further change of anisotropy occurs well above the proton scales. We discuss the implication of our findings and how numerical simulations can help interpreting the observed spectral anisotropy. [1] Chen et al., ApJ, 768:120, 2012 [2] Verdini & Grappin, ApJL, 808:L34, 2015 [3] Vech & Chen, ApJL, 832:L16, 2016 [4] Goldreich & Shridar, ApJ, 438:763, 1995 [5] Boldyrev, ApJL, 626:L37, 2005
• Diffusion Region's Structure at the Subsolar Magnetopause with MMS Data
  
  • Cozzani Giulia
  • Retinò Alessandro
  • Califano F.
  • Alexandrova Alexandra
  • Catapano F.
  • Fu H.
  • Le Contel Olivier
  • Khotyaintsev Y. V.
  • Vaivads A.
  • Ahmadi N.
  • Lindqvist P. A.
  • Breuillard Hugo
  • Mirioni Laurent
  • Ergun R.
  • Torbert R. B.
  • Giles B. L.
  • Russell C. T.
  • Nakamura R.
  • Moore T. E.
  • Fuselier S. A.
  • Mauk B.
  • Burch J. L.
  , 2017, pp.SM34A-02. Magnetic reconnection occurs in the magnetosphere in thin current sheets, where a change in the magneticfield topology leads to rapid conversion of magnetic energy into ion and electron energy. To allow for magneticfield reconfiguration, both ions and electrons have to become demagnetized in the ion and electron diffusionregions, respectively. MMS spacecraft observations at inter-spacecraft separation 10 km (correspondingto 5 dₑ at the magnetopause) allow, for the first time, to make multi-point studies of the structure of theelectron diffusion region (EDR). We present MMS observations on January,27th 2017 of one magnetopausecrossing close to the subsolar point showing several signatures consistent with an EDR encounter nearbya magnetic field minimum. The proximity to the reconnection site is further substantiated by the FirstOrder Taylor Expansion (FOTE) method applied to the magnetic field data. Observations suggest that allspacecraft passed through the EDR. Despite of the small inter-spacecraft separation (7 km), the observationsshow important differences among spacecraft. We focus on the comparison between MMS3 and MMS4 sincethey show the most striking differences. MMS3 measures a stronger parallel electron heating and highercurrent densities than MMS4. Both satellites observe crescent-shaped electron distribution functions on themagnetospheric side but MMS4 observes them over a longer time interval. These observations suggest thatMMS3 is passing closer to the reconnection site than MMS4. The differences between the observations by thetwo spacecraft indicate that the EDR is rather structured over scales of a few electron inertial lengths. Wealso evaluate the Generalized Ohm's law and find that the electric field is mainly balanced by the divergenceof the electron pressure tensor while the electron inertia term is negligible.
• Compressible turbulence in the near-Earth space: energy cascade rate from the MHD tothe sub-ion scales
  
  • Andrés Nahuel
  • Sahraoui Fouad
  • Hadid L. Z.
  • Huang S. Y.
  • Galtier Sébastien
  , 2017, 11, pp.SH11A-2432. The role of compressible fluctuations in Hall MHD (HMHD) turbulence is investigated using direct numerical simulations and in-situ spacecraft in the near-Earth space. A focus is put on verifying the new exact third-order law derived recently for compressible isothermal HMHD turbulence (Andrés, Galtier and Sahraoui, 2017). The numerical simulations use a 3D compressible HMHD code in the isothermal limit (gamma = 1) with low sonic Mach numbers (Ms < 1). The main goal is to estimate the energy cascade rate of turbulence over a broad range of scales that span both the inertial and sub-ion (dispersive) ranges. Preliminary comparison with observations from the recently launched multispacecraft NASA/MMS (Magnetospheric MultiScale) mission in the solar wind are made.
• Numerical investigation of thermal and chemical effects of nanosecond repetitively pulsed discharges on a laminar premixed counterflow flame
  
  • Heitz Sylvain
  • Moeck Jonas
  • Bourdon Anne
  • Lacoste Deanna
  , 2017.
• Fast energy relaxation in the afterglow of a nanosecond capillary discharge in nitrogen/oxygen mixtures
  
  • Lepikhin Nikita
  , 2017. The main aim of the present work was to investigate, how the plasma kinetics changes at the conditions of high specific energy deposition at high reduced electric fields. The nanosecond capillary discharge was used as an experimental tool. The measurements are performed for pure nitrogen and nitrogen/oxygen mixtures. Electric parameters of the discharge are measured: the applied voltage, the energy deposition, the electric field, and the electric current. The spectra of the optical emission of the discharge are obtained. The electron density in the discharge pulses is measured. The plasma decay is studied by the measurements of the electron density in the afterglow of the discharge as well. The processes controlling the plasma decay are determined. Depopulation of excited molecules on the example of N2(C) state of molecular nitrogen is studied in nitrogen/oxygen mixtures. The processes responsible for depopulation of excited species in the afterglow of the nanosecond discharge at high specific deposited energy at high reduced electric field are discussed. The radial distributions of the excited species at different gas compositions are investigated and compared. The experimental and numerical studies of the processes responsible for fast gas heating in pure nitrogen and in nitrogen/oxygen mixtures in the afterglow of nanosecond capillary discharge are performed. The peculiarities of the fast gas heating at conditions of the nanosecond discharge at high specific deposited energy at high reduced electric field are discussed. The modification of the kinetic scheme currently in use is proposed.
• Kinetics of atoms and metastable molecules in oxygen plasmas revisited: an experimental study
  
  • Booth Jean-Paul
  • Chatterjee Abhyuday
  • Guaitella Olivier
  • Morillo-Candas Ana-Sofia
  • Drag Cyril
  • Lopaev Dmitry
  • Zyryanov Sergey
  • de Oliveira N.
  • Nahon Laurent
  , 2017.
• Recent advances in atmospheric, solar-terrestrial physics and space weather from a north-south network of scientist [2006-2016] Part B: results and capacity building
  
  • Amory-Mazaudier Christine
  • Fleury Rolland
  • Petitdidier Monique
  • Soula Serge
  • Masson Frédéric
  • Davila Jospeh
  • Doherty Patricia
  • Elias Ana Georgina
  • Gadimova Sharafat
  • Makela Jonathan
  • Nava Bruno
  • Radicella Sandro Maria
  • Richardson John
  • Touzani Abderrahmane
  Sun and Geosphere, BBC SWS Regional Network, 2017, 12 (Supplement), pp.21 - 69. This paper reviews scientific advances achieved by a North-South network between 2006 and 2016. These scientific advances concern solar terrestrial physics, atmospheric physics and space weather. This part B is devoted to the results and capacity building. Our network began in 1991, in solar terrestrial physics, by our participation in the two projects: International Equatorial Electrojet Year IEEY [1992-1993] and International Heliophysical Year IHY [2007-2009]. These two projects were mainly focused on the equatorial ionosphere in Africa. In Atmospheric physics our research focused on gravity waves in the framework of the African Multidisciplinary Monsoon Analysis project n°1 [2005-2009 ], on hydrology in the Congo river basin and on lightning in Central Africa, the most lightning part of the world. In Vietnam the study of a broad climate data base highlighted global warming. In space weather, our results essentially concern the impact of solar events on global navigation satellite system GNSS and on the effects of solar events on the circulation of electric currents in the earth (GIC). This research began in the framework of the international space weather initiative project ISWI [2010-2012]. Finally, all these scientific projects have enabled young scientists from the South to publish original results and to obtain positions in their countries. These projects have also crossed disciplinary boundaries and defined a more diversified education which led to the training of specialists in a specific field with knowledge of related scientific fields.
• Variability of the Magnetic Field Power Spectrum in the Solar Wind at Electron Scales
  
  • Roberts Owen Wyn
  • Alexandrova Olga
  • Kajdič P.
  • Turc Lucile
  • Perrone D.
  • Escoubet P.
  • Walsh A.
  The Astrophysical Journal, American Astronomical Society, 2017, 850 (2), pp.120. (10.3847/1538-4357/aa93e5)
  DOI : 10.3847/1538-4357/aa93e5
• Boosting germination of seeds using non thermal plasma treatment
  
  • Rousseau Antoine
  , 2017.
• Kinetics of metastable states and atoms in DC discharges in pure O<SUB>2</SUB>: an experimental study
  
  • Booth Jean-Paul
  • Chatterjee Abhyuday
  • Guaitella Olivier
  • de Oliveira N.
  • Nahon Laurent
  • Western Colin
  • Zyryanov Sergey
  • Lopaev Dmitry
  , 2017. A comprehensive study of DC discharges in pure O2 gas in a Pyrex tube is presented using a range of diagnostics. Fourier-transform vacuum ultraviolet absorption spectroscopy (FT-VUVAS) provided high-resolution (106) spectra in the region 120-170 nm of O2 (X), O2 (a), O2 (b) and ground state O atoms, allowing their absolute densities to be determined. Optical Emission Spectroscopy (OAS) was used to determine the gas temperature from the O2 (b&#61614;X) emission spectrum. Time-resolved OAS of partially-modulated discharges was used to probe the loss rates of O2 (b) and of O atoms. From these measurements the surface loss coefficients of these species can be determined, as well as the rate constants for electron impact dissociation of O2. A remarkable increase in the surface loss coefficient on Pyrex of O2 (b) and O atoms is observed at low pressures, corresponding to the onset of energetic ion bombardment.
• Two Dimensional PIC/MCC Simulations of RF CCPs with a Dielectric Side Wall
  
  • Liu Yue
  , 2017. A Cartesian-coordinate two-dimensional electrostatic Particle-in-cell/Monte-Carlo Collision (PIC/MCC) plasma simulation code is presented, including a new treatment of charge balance at dielectric boundaries. It is used to simulate an Ar plasma in a symmetric radiofrequency capacitively-coupled parallel-plate reactor with a thick dielectric side-wall. The dielectric side-wall effectively shields the plasma from the enhanced electric field at the powered-grounded electrode junction, which has previously been shown to produce locally enhanced plasma density. Nevertheless, enhanced electron heating is observed in a region adjacent to the dielectric boundary, leading to maxima in ionization rate, plasma density and ion flux to the electrodes in this region. The electron heating components are derived from the PIC/MCC simulations and show that this enhanced electron heating results from increased Ohmic heating in the axial direction as the electron density decreases towards the side-wall. We investigated the validity of different analytical formulas to estimate the Ohmic heating by comparing them to the PIC results. The x component electron heating near the corners was observed at higher driving frequency, which is caused by a significant RF oscillating field in the x direction.
• Bidimensional particle-in-cell simulations : Impact of dielectric walls on electron drift instability in Hall effect thrusters
  
  • Tavant Antoine
  • Croes Vivien
  • Lafleur Trevor
  • Bourdon Anne
  • Chabert Pascal
  , 2017. Hall effect thrusters (HET) are one of the main technology used and studied for spacecraft electrical propulsion. Grid-less, they present net advantages. However, their operation characteristics are not understood yet, resulting in an increasing need for predictive models, and a better understanding of the plasma discharge complex behavior. HETs consist of an \textbfE×B discharge in an annular ceramic channel. One of the main characteristic of the thruster is its lifetime, limited by the ceramic channel eroded by the plasma. A better understanding of wall erosion is necessary, however long experiments are costly, and erosion diagnostics and measurements are difficult to perform. A bidimensional r&#8722;&#952; particle-in-cell simulation is therefore developed to investigate the plasma interaction with the ceramic walls. The dielectric aspect is emphasized: studies are done with metallic walls as well as dielectrics with various geometries and characteristics. Moreover impact and use of parietal capacitive probes is studied. Then secondary electron emissions are implemented to better understand the material effects.
• Modeling wall ion fluxes in an RF discharge: insights from 2D PIC simulation
  
  • Lucken Romain
  • Tavant Antoine
  • Croes Vivien
  • Lafleur Trevor
  • Raimbault Jean-Luc
  • Bourdon Anne
  • Chabert Pascal
  , 2017. Global models of plasma discharges have been widely used to simulate plasma reactors in the fields of plasma processing and space propulsion. These models rely on accurate description of the ion current leaving the plasma: after undergoing a pre-sheath drop, the ions enter the sheath at Bohm velocity. The pre-sheath drop is characterized by an edge-to-center plasma density ratio and heuristic models were formerly derived to understand how this parameter varies with plasma temperatures and ion mean free path, based on one-dimensional (1D) transport theory, and validated by 1D simulation. A model of ICP discharges was implemented into a 2D benchmarked PIC code, running with various gases (Ar, He, Xe). These simulations show that the ion flux has a strong spatial dependency in agreement with former results and that it is affected by the aspect ratio of the discharge reactor. The influence of dielectric walls is also investigated.
• Plasma jets and electric fields delivery on targets relevant for biomedical applications
  
  • Robert Eric
  • Darny Thibault
  • Pouvesle Jean-Michel
  • Puech Vincent
  • Douat Claire
  • Dozias Sébastien
  • Bourdon Anne
  , 2017. The study of plasma jets operating in free jet mode and on conductive targets relevant for biomedical applications is discussed. The simultaneous diagnostics of helium metastable through laser absorption, electric field (EF) with an electro-optic probe and current appears as a unique approach to get deep insights on the mechanisms triggered when primary ionization wave (IW), driving the plasma jet propagation, impacts the target. Secondary IWs, back and forth travelling from the plasma jet powered electrode and the grounded target, is measured and may result, depending on the operating parameters of the device, in the transition to a glow like discharge. In such situation, huge enhancement of reactive species production is triggered in connection with significant increase of current flowing through the target. This study allow for a better analysis of the plasma jet delivery on target relevant for biomedical applications and open up opportunities to control reactive species concentration and current amplitude in such experiments. These experimental results are in good agreement with modeling work recently published by group of M.J. Kushner (University of Michigan) on the plasma jet touching or not targets of various natures. The second aspect of the study deals with the characterization of both the amplitude and the topology of the transient EF generated in the vicinity of the plasma jets. Time resolved longitudinal and radial EF, with respect to the jet propagation axis, having amplitudes ranging from a few to a few tens of kV/cm have been measured. There also a good agreement is achieved with modeling data from the group of A. Bourdon (LPP laboratory) which allow extending this diagnostics to region where experimental analysis is hard or disturbing with our probe. It is probably worth considering such intense EF with respect to their potential impact on biological samples.
• Electric field rebound of He plasma jets with positive and negative polarities on metal and dielectric targets
  
  • Viegas Pedro
  • Obrusník A.
  • Bonaventura Z.
  • Bourdon Anne
  , 2017.
• Kinetics of nanosecond discharges at high specific energy release
  
  • Starikovskaia Svetlana
  , 2017.
• Kinetic, Unstructured Finite Element PIC-DSMC Simulation of Ultra-Fast Pin-to-Plane Discharge in Air
  
  • Moore Christopher
  • Fierro Andrew
  • Pouvesle Jean-Michel
  • Robert Eric
  • Bourdon Anne
  • Jorgenson Roy
  • Jindal Ashish
  • Hopkins Mattew
  , 2017, 62 (10), pp.21. Recently, highly reproducible breakdown experiments in air at atmospheric pressure, leading to large volume homogeneous plasmas, have been performed in a 1.5 cm gap, pin-to-plane geometry with ˜2 ns rise-time [1]. The present work compares temporally resolved experimental results for the electric field and electron density to kinetic simulations using an unstructured finite element Particle-In-Cell code that models the collisions via Direct Simulation Monte Carlo. The model includes electronneutral elastic, excitation, ionization, and attachment collisions; ion and photon induced electron emission from surfaces; ion-neutral collisions; and self-absorption, photoionization, and photodissociation. The model tracks excited state neutrals which can be quenched through collisions with the background gas and surfaces or spontaneously emit a photon (isotropically) and transition to a lower state. [1] J-M. Pouvesle, et al. “Experimental Study of an Ultra-Fast Atmospheric Pressure Discharge in a Pin-to-Plate Geometry”, ICOPS 2017. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.