Publications

2016

• Evolution of nanosecond surface dielectric barrier discharge for negative polarity of voltage pulse
  
  • Soloviev V.R.
  • Krivtsov V.M.
  • Shcherbanev S.A.
  • Starikovskaia Svetlana
  Plasma Sources Science and Technology, IOP Publishing, 2016, 26 (1), pp.014001 (12pp). Surface dielectric barrier discharge, initiated by a high-voltage pulse of negative polarity in atmospheric pressure air, is studied numerically and experimentally. At a pulse duration of a few tens of nanoseconds, two waves of optical emission propagate from the high-voltage electrode corresponding to the leading and trailing edges of the high-voltage pulse. It is shown by means of numerical modeling that a glow-like discharge slides along the surface of the dielectric at the leading edge of the pulse, slowing down on the plateau of the pulse. When the trailing edge of the pulse arrives to the high-voltage electrode, a second discharge starts and propagates in the same direction. The difference is that the discharge corresponding to the trailing edge is not diffuse and demonstrates a well-pronounced streamer-like shape. The 2D (in numerical modeling) streamer propagates above the dielectric surface, leaving a gap of about 0.05 mm between the streamer and the surface. The calculated and experimentally measured emission picture, waveform of the electrical current, and deposited energy, qualitatively coincide. The sensitivity of the numerical solution to unknown physical parameters of the model is discussed. (10.1088/0963-0252/26/1/014001)
  DOI : 10.1088/0963-0252/26/1/014001
• Day-to-day variability of VTEC and ROTI in October 2012 with impact of high-speed solar wind stream on 13 October 2012
  
  • Azzouzi Ilyasse
  • Migoya-Orué Yenca
  • Coïsson Pierdavide
  • Amory-Mazaudier Christine
  • Fleury Rolland
  • Radicella Sandro
  Sun and Geosphere, BBC SWS Regional Network, 2016, 11 (1), pp.7-22. This paper presents the day-today variability of the Vertical Total Electron Content (VTEC) and the Rate of change of TEC Index (ROTI) in October 2012. We focused our attention to the impact of a high-speed solar wind stream (HSSWS) on the ionosphere in middle and low latitudes on 13 October 2012. This event was preceded by two other disturbances caused by a Coronal Mass Ejection (CME) at 05:26UT on 8 October and a HSSWS around 19:00UT on 9 October. The changes in the VTEC observed during the period between 8 and 12 October preceding the 13 October case showed a comparable response of the ionosphere in both hemispheres, varying mainly with latitude and presenting a stronger impact in the Northern hemisphere. The VTEC increased at the arrival of the CME on 8 October, then decreased, and increased again on 13 October. The solar wind speed associated with the second HSSWS reached its peak, 580 km/s around 17:00UT during the recovery phase of a geomagnetic storm started around 00:00UT on 13 October. Its impact was observed in Africa and in Eastern South America on the ROTI, an indicator of ionospheric scintillation. On 13 October, the ROTI was small over whole Africa and in Eastern South America at the moment the impact of the second HSSWS. These observations are interpreted as due to the ionospheric disturbance dynamo electric field associated with the Joule heating produced in the auroral zone by the HSSWS.
• Linear electromagnetic excitation of an asymmetric low pressure capacitive discharge with unequal sheath widths
  
  • Lieberman M.A.
  • Lichtenberg A.J.
  • Kawamura E.
  • Chabert Pascal
  Physics of Plasmas, American Institute of Physics, 2016, 23 (1), pp.013501. It is well-known that standing waves having radially center-high radio frequency (rf) voltage profiles exist in high frequency capacitive discharges. In this work, we determine the symmetric and antisymmetric radially propagating waves in a cylindrical capacitive discharge that is asymmetrically driven at the lower electrode by an rf voltage source. The discharge is modeled as a uniform bulk plasma which at lower frequencies has a thicker sheath at the smaller area powered electrode and a thinner sheath at the larger area grounded electrode. These are self-consistently determined at a specified density using the Child law to calculate sheath widths and the electron power balance to calculate the rf voltage. The fields and the system resonant frequencies are determined. The center-to-edge voltage ratio on the powered electrode is calculated versus frequency, and central highs are found near the resonances. The results are compared with simulations in a similar geometry using a two-dimensional hybrid fluid-analytical code, giving mainly a reasonable agreement. The analytic model may be useful for finding good operating frequencies for a given discharge geometry and power. (10.1063/1.4938204)
  DOI : 10.1063/1.4938204
• The Mass Spectrum Analyzer (MSA) on board the BepiColombo MMO
  
  • Delcourt Dominique C.
  • Saito Y.
  • Leblanc Frédéric
  • Verdeil Christophe
  • Yokota S.
  • Fraenz M.
  • Fischer H.
  • Fiethe B.
  • Katra Bruno
  • Fontaine Dominique
  • Illiano Jean-Marie
  • Berthelier Jean-Jacques
  • Krupp N.
  • Buhrke U.
  • Bubenhagen F.
  • Michalik H.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2016, 121 (7), pp.6749-6761. Observations from the MESSENGER spacecraft have considerably enhanced our understanding of the plasma environment at Mercury. In particular, measurements from the Fast Imaging Plasma Spectrometer (FIPS) provide evidences of a variety of ion species of planetary origin (He+, O+, Na+) in the northern dayside cusp and in the nightside plasma sheet. A more comprehensive view of Mercury's plasma environment will be provided by the Bepi Colombo mission that will be launched in 2018. Onboard the Bepi Colombo MMO spacecraft, the MPPE (Mercury Plasma/Particle Experiment) consortium gathers different sensors dedicated to particle measurements. Among these sensors, the Mass Spectrum Analyzer (MSA) is the instrument dedicated to plasma composition analysis. It consists of a top-hat for energy analysis followed by a Time-Of-Flight (TOF) chamber to derive the ion mass. Taking advantage of the spacecraft rotation, MSA will measure three-dimensional distribution functions in one spin (4 s), from energies characteristic of exospheric populations (in the eV range) up to plasma sheet energies (up to ~38 keV/q). A notable feature of the MSA instrument is that the TOF chamber is polarized with a linear electric field that leads to isochronous TOFs and enhanced mass resolution (typically, m/∆m ≈ 40 for ions with energies up to 13 keV/q). At Mercury, this capability is of paramount importance to thoroughly characterize the wide variety of ion species originating from the planet surface. It is thus anticipated that MSA will provide unprecedented information on ion populations in the Hermean environment and hence improve our understanding of the coupling processes at work. (10.1002/2016JA022380)
  DOI : 10.1002/2016JA022380
• Hybrid global model of water cluster ions in atmospheric pressure Ar/H<SUB>2</SUB>O RF capacitive discharges
  
  • Tavant Antoine
  • Lieberman M.A.
  Journal of Physics D: Applied Physics, IOP Publishing, 2016, 49 (46), pp.465201. Water is a trace gas of strong interest for plasma-based medical applications. We use a hybrid global model to simulate a chemically complex Ar/ atmospheric pressure, radio frequency capacitive discharge, including 47 species with positive ion clusters up to . For a discharge gap of 1.5&#8201;mm driven at 27.12 MHz, we determine the discharge properties over a range of rf currents (150500 A m&#8722;2) and initial concentrations (0.252%). An isothermal plug-flow model is used with a gas residence time of 0.2&#8201;s for most calculations, with the gas temperature calculated self-consistently from the input power. The cluster density distributions are determined, and we find that the higher mass cluster densities decrease rapidly with increasing gas temperature. A simplified cluster dynamics analytic model is developed and solved to determine the cluster density distributions, which is in good agreement with the hybrid simulation results. (10.1088/0022-3727/49/46/465201)
  DOI : 10.1088/0022-3727/49/46/465201
• Charge transfer to a dielectric target by guided ionization waves using electric field measurements
  
  • Slikboer Elmar
  • Garcia-Caurel Enric
  • Guaitella Olivier
  • Sobota Ana
  Plasma Sources Science and Technology, IOP Publishing, 2016. A kHz-operated atmospheric pressure plasma jet is investigated by measuring charge transferred to a dielectric electro-optic surface (BSO crystal) allowing for the measurement of electric field by exploiting the Pockels effect. The electric field values, distribution of the surface discharge and amount of deposited charge are obtained for various parameters, including gas flow, applied voltage, target distance and the length of the capillary from ground to the end. A newly formed surface discharge emerges at the target when enough charge is deposited at the impact point and electric fields are high enough, i.e. 200 pC and 9 ± 2 kV cm&#8722;1. The maximum amount of charge transferred by a single ionization wave ('plasma bullet') is 350 ± 40 pC. Due to the emerging new surface discharge behind the impact point, the total charge deposited on the surface of the dielectric target can increase up to 950 pC. The shape of the secondary discharge on the target is found to be mainly driven by gas flow, while the applied voltage allows us to utilize longer distances within the boundaries set by this gas mixing. Finally the ionization wave is found to lose charge along its propagation on the inner walls of the capillary. The loss is estimated to be approximately 7.5 pC mm&#8722;1 of travel distance inside the capillary. (10.1088/1361-6595/aa53fe)
  DOI : 10.1088/1361-6595/aa53fe
• Two types of whistler waves in the hall reconnection region
  
  • Huang S. Y.
  • Fu H.S.
  • Yuan Z. G.
  • Vaivads A.
  • Khotyaintsev Y. V.
  • Retinò Alessandro
  • Zhou M.
  • Graham D. B.
  • Fujimoto K.
  • Sahraoui Fouad
  • Deng X. H.
  • Ni B.
  • Pang Y.
  • Fu S. Y.
  • Wang D. D.
  • Zhou X. M.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2016, 121 (7), pp.6639-6646. Whistler waves are believed to play an important role during magnetic reconnection. Here we report the near-simultaneous occurrence of two types of the whistler-mode waves in the magnetotail Hall reconnection region. The first type is observed in the magnetic pileup region of downstream and propagates away to downstream along the field lines and is possibly generated by the electron temperature anisotropy at the magnetic equator. The second type, propagating toward the X line, is found around the separatrix region and probably is generated by the electron beam-driven whistler instability or Cerenkov emission from electron phase-space holes. These observations of two different types of whistler waves are consistent with recent kinetic simulations and suggest that the observed whistler waves are a consequence of magnetic reconnection. (10.1002/2016JA022650)
  DOI : 10.1002/2016JA022650
• Experimental and simulation study of a capacitively coupled oxygen discharge driven by tailored voltage waveforms
  
  • Derzsi A.
  • Lafleur Trevor
  • Booth Jean-Paul
  • Korolov Ihor
  • Donko Zoltan
  Plasma Sources Science and Technology, IOP Publishing, 2016, 25 (1), pp.015004. We report experimental and particle-based kinetic simulation studies of low-pressure capacitively coupled oxygen plasmas driven by tailored voltage waveforms that consist of up to four harmonics of base frequency 13.56 MHz. Experimentally determined values of DC self-bias and electrical power deposition, as well as flux density and flux-energy distribution of the positive ions at the grounded electrode are compared with simulation data for a wide range of operating conditions. Very good agreement is found for self-bias and flux-energy distribution of the positive ions at the electrodes, while a fair agreement is reached for discharge power and ion flux data. The simulated spatial and temporal behaviour of the electric field, electron density, electron power absorption, ionization rate and mean electron energy shows a transition between sheath expansion heating and drift-ambipolar discharge modes, induced by changing either the number of harmonics comprising the excitation waveform or the gas pressure. The simulations indicate that under our experimental conditions the plasma operates at high electronegativity, and also reveal the crucial role of singlet metastable molecules in establishing discharge behavior via the fast destruction of negative ions within the bulk plasma. (10.1088/0963-0252/25/1/015004)
  DOI : 10.1088/0963-0252/25/1/015004
• Electron power absorption dynamics in capacitive radio frequency discharges driven by tailored voltage waveforms in CF<SUB>4</SUB>
  
  • Brandt S.
  • Berger B.
  • Schüngel E.
  • Korolov Ihor
  • Derzsi A.
  • Bruneau Bastien
  • Johnson E.V.
  • Lafleur Trevor
  • O'Connell D.
  • Koepke M.
  • Gans T.
  • Booth Jean-Paul
  • Donkó Z.
  • Schulze J.
  Plasma Sources Science and Technology, IOP Publishing, 2016, 25 (4), pp.045015. The power absorption dynamics of electrons and the electrical asymmetry effect in capacitive radio-frequency plasmas operated in CF4 and driven by tailored voltage waveforms are investigated experimentally in combination with kinetic simulations. The driving voltage waveforms are generated as a superposition of multiple consecutive harmonics of the fundamental frequency of 13.56 MHz. Peaks/valleys and sawtooth waveforms are used to study the effects of amplitude and slope asymmetries of the driving voltage waveform on the electron dynamics and the generation of a DC self-bias in an electronegative plasma at different pressures. Compared to electropositive discharges, we observe strongly different effects and unique power absorption dynamics. At high pressures and high electronegativities, the discharge is found to operate in the drift-ambipolar (DA) heating mode. A dominant excitation/ionization maximum is observed during sheath collapse at the edge of the sheath which collapses fastest. High negative-ion densities are observed inside this sheath region, while electrons are confined for part of the RF period in a potential well formed by the ambipolar electric field at this sheath edge and the collapsed (floating potential) sheath at the electrode. For specific driving voltage waveforms, the plasma becomes divided spatially into two different halves of strongly different electronegativity. This asymmetry can be reversed electrically by inverting the driving waveform. For sawtooth waveforms, the discharge asymmetry and the sign of the DC self-bias are found to reverse as the pressure is increased, due to a transition of the electron heating mode from the &#945;-mode to the DA-mode. These effects are interpreted with the aid of the simulation results. (10.1088/0963-0252/25/4/045015)
  DOI : 10.1088/0963-0252/25/4/045015
• Numerical and experimental study of the dynamics of a $\mu$s helium plasma gun discharge with various amounts of N$_2$ admixture
  
  • Bourdon Anne
  • Darny Thibault
  • Pechereau François
  • Pouvesle Jean-Michel
  • Viegas Pedro
  • Iséni Sylvain
  • Robert Eric
  Plasma Sources Science and Technology, IOP Publishing, 2016, 25 (3), pp.035002. This paper presents a combined 2D numerical and experimental study of the influence of N$_2$ admixture on the dynamics of a He–N$_2$ discharge in the 10 cm long dielectric tube of a plasma gun setup. First, the comparison between experiments and simulations is carried out on the ionization front propagation velocity in the tube. The importance of taking into account a detailed kinetic scheme for the He–N$_2$ mixture in the simulations to obtain a good agreement with the experiments is put forward. For the μs driven plasma gun, the two-and three-body Penning reactions occurring in the plasma column behind the ionization front, are shown to play a key role on the discharge dynamics. In the experiments and simulations, the significant influence of the amplitude of the applied voltage on the ionization front propagation velocity is observed. As the amount of N$_2$ varies, simulation results show that the ionization front velocity, depends on a complex coupling between the kinetics of the discharge, the photoionization and the 2D structure of the discharge in the tube. Finally, the time evolution of axial and radial components of the electric field measured by an electro-optic probe set outside the tube are compared with simulation results. A good agreement is obtained on both components of the electric field. In the tube, simulations show that the magnitude of the axial electric field on the discharge axis depends weakly on the amount of N 2 conversely to the magnitude of the off-axis peak electric field. Both, simulations and first measurements in the tube or within the plasma plume show peak electric fields of the order of 45 kV·cm$^{−1}$ . (10.1088/0963-0252/25/3/035002)
  DOI : 10.1088/0963-0252/25/3/035002
• Full particle-in-cell simulations of kinetic equilibria and the role of the initial current sheet on steady asymmetric magnetic reconnection
  
  • Dargent Jérémy
  • Aunai Nicolas
  • Belmont Gérard
  • Dorville Nicolas
  • Lavraud B.
  • Hesse M.
  Journal of Plasma Physics, Cambridge University Press (CUP), 2016, 82 (03), pp.905820305. Tangential current sheets are ubiquitous in space plasmas and yet hard to describe with a kinetic equilibrium. In this paper, we use a semi-analytical model, the BAS model, which provides a steady ion distribution function for tangential asymmetric current sheet and we prove that an ion kinetic equilibrium produced by this model remains steady in a fully kinetic Particle-In-Cell simulation even if the electron distribution function does not satisfy the time independent Vlasov equation. We then apply this equilibrium to look at the dependence of magnetic reconnection simulations upon their initial condition. We show that, as the current sheet evolves from symmetric to asymmetric upstream plasmas, the reconnection rate is impacted, the X line and the electron flow stagnation point separate from one another and start to drift. For the simulated systems, we investigate the overall evolution of the reconnection process via the classical signatures discussed in the literature and searched in the Magnetospheric MultiScale data. We show that they seem robust and do not depend on the specific details of the internal structure of the initial current sheet. (10.1017/S002237781600057X)
  DOI : 10.1017/S002237781600057X
• The Earth: Plasma Sources, Losses, and Transport Processes
  
  • Welling D. T.
  • André M.
  • Dandouras Iannis
  • Delcourt Dominique
  • Fazakerley A.
  • Fontaine Dominique
  • Foster John
  • Ilie R.
  • Kistler L. M.
  • Lee J. H.
  • Liemohn M. W.
  • Slavin J. A.
  • Wang Chih-Ping
  • Wiltberger M.
  • Yau Andrew
  • Blanc Michel
  • Chappell Charles R.
  • Krupp N.
  , 2016, pp.145. Not Available
• Velocity diffusion of energetic electrons in the solar wind
  
  • Volokitin A.
  • Krafft C.
  AIP Conference Proceedings, American Institute of Physics, 2016, 1720 (1), pp.070007. Particle diffusion in velocity space is studied on the basis of 1D simulations of Langmuir turbulence generated by electron beams in solar wind plasmas. Using a large amount of particle trajectories calculated with a great accuracy and over long times and analyzing them with statistical algorithms, the diffusion coefficients of particles in wave packets are estimated, as well as their relation to the waves' intensities and spectra and their dependence on the average level of background plasma density fluctuations. Results are compared with analytical solutions provided by the quasilinear theory of weak turbulence. (10.1063/1.4943844)
  DOI : 10.1063/1.4943844
• MMS observations of ion-scale magnetic island in the magnetosheath turbulent plasma
  
  • Huang S. Y.
  • Sahraoui Fouad
  • Retinò Alessandro
  • Le Contel Olivier
  • Yuan Z. G.
  • Chasapis A.
  • Aunai Nicolas
  • Breuillard Hugo
  • Deng X. H.
  • Zhou M.
  • Fu H.S.
  • Pang Y.
  • Wang D. D.
  • Torbert R. B.
  • Goodrich K. A.
  • Ergun R. E.
  • Khotyaintsev Y. V.
  • Lindqvist P.-A.
  • Russell C. T.
  • Strangeway R. J.
  • Magnes W.
  • Bromund K.
  • Leinweber H.
  • Plaschke F.
  • Anderson B. J.
  • Pollock C. J.
  • Giles B. L.
  • Moore T. E.
  • Burch J. L.
  Geophysical Research Letters, American Geophysical Union, 2016, 43 (15), pp.7850-7858. In this letter, first observations of ion-scale magnetic island from the Magnetospheric Multiscale mission in the magnetosheath turbulent plasma are presented. The magnetic island is characterized by bipolar variation of magnetic fields with magnetic field compression, strong core field, density depletion, and strong currents dominated by the parallel component to the local magnetic field. The estimated size of magnetic island is about 8 d<SUB>i</SUB>, where d<SUB>i</SUB> is the ion inertial length. Distinct particle behaviors and wave activities inside and at the edges of the magnetic island are observed: parallel electron beam accompanied with electrostatic solitary waves and strong electromagnetic lower hybrid drift waves inside the magnetic island and bidirectional electron beams, whistler waves, weak electromagnetic lower hybrid drift waves, and strong broadband electrostatic noise at the edges of the magnetic island. Our observations demonstrate that highly dynamical, strong wave activities and electron-scale physics occur within ion-scale magnetic islands in the magnetosheath turbulent plasma. (10.1002/2016GL070033)
  DOI : 10.1002/2016GL070033
• Experimental investigation of electron transport across a magnetic field barrier in electropositive and electronegative plasmas
  
  • Thomas M B
  • Rafalskyi D.V.
  • Lafleur Trevor
  • Aanesland Ane
  Plasma Sources Science and Technology, IOP Publishing, 2016, 25 (4), pp.045018. In this paper we experimentally investigate the drift of electrons in low temperature plasmas containing a magnetic field barrier; a plasma configuration commonly used in gridded negative ion sources. A planar Langmuir probe array is developed to quantify the drift of electrons over the cross-section of the ion-extraction region of an ionion plasma source. The drift is studied as a function of pressure using both electropositive plasmas (Ar), as well electronegative plasmas (Ar and SF 6 mixtures), and is demonstrated to result from an interaction of the applied magnetic field and the electric fields in the sheath and pre-sheath near the transverse boundaries. The drift enhances electron transport across the magnetic field by more than two orders of magnitude compared with simple collisional transport, and is found to be strongly dependant on pressure. The lowest pressure resulted in the highest influence of the drift across the extraction area and is found to be 30%. (10.1088/0963-0252/25/4/045018)
  DOI : 10.1088/0963-0252/25/4/045018
• Differential kinetic dynamics and heating of ions in the turbulent solar wind
  
  • Valentini F.
  • Perrone D.
  • Stabile S.
  • Pezzi O.
  • Servidio S.
  • de Marco R.
  • Marcucci M. F.
  • Bruno Roberto
  • Lavraud B.
  • de Keyser J.
  • Consolini G.
  • Brienza D.
  • Sorriso-Valvo L.
  • Retinò Alessandro
  • Vaivads A.
  • Salatti M.
  • Veltri P.
  New Journal of Physics, Institute of Physics: Open Access Journals, 2016, 18, pp.125001. The solar wind plasma is a fully ionized and turbulent gas ejected by the outer layers of the solar corona at very high speed, mainly composed by protons and electrons, with a small percentage of helium nuclei and a significantly lower abundance of heavier ions. Since particle collisions are practically negligible, the solar wind is typically not in a state of thermodynamic equilibrium. Such a complex system must be described through self-consistent and fully nonlinear models, taking into account its multi-species composition and turbulence. We use a kinetic hybrid Vlasov-Maxwell numerical code to reproduce the turbulent energy cascade down to ion kinetic scales, in typical conditions of the uncontaminated solar wind plasma, with the aim of exploring the differential kinetic dynamics of the dominant ion species, namely protons and alpha particles. We show that the response of different species to the fluctuating electromagnetic fields is different. In particular, a significant differential heating of alphas with respect to protons is observed. Interestingly, the preferential heating process occurs in spatial regions nearby the peaks of ion vorticity and where strong deviations from thermodynamic equilibrium are recovered. Moreover, by feeding a simulator of a top-hat ion spectrometer with the output of the kinetic simulations, we show that measurements by such spectrometer planned on board the Turbulence Heating ObserveR (THOR mission), a candidate for the next M4 space mission of the European Space Agency, can provide detailed three-dimensional ion velocity distributions, highlighting important non-Maxwellian features. These results support the idea that future space missions will allow a deeper understanding of the physics of the interplanetary medium. (10.1088/1367-2630/18/12/125001)
  DOI : 10.1088/1367-2630/18/12/125001
• The Search-Coil Magnetometer for MMS
  
  • Le Contel Olivier
  • Leroy Paul
  • Roux A.
  • Coillot Christophe
  • Alison Dominique
  • Bouabdellah Abdel
  • Mirioni Laurent
  • Meslier L.
  • Galic A.
  • Vassal M. C.
  • Torbert R. B.
  • Needell J.
  • Rau D.
  • Dors I.
  • Ergun R. E.
  • Westfall J.
  • Summers D.
  • Wallace J.
  • Magnes W.
  • Valavanoglou A.
  • Olsson G.
  • Chutter M.
  • Macri J.
  • Myers S.
  • Turco S.
  • Nolin J.
  • Bodet D.
  • Rowe K.
  • Tanguy M.
  • de La Porte B.
  Space Science Reviews, Springer Verlag, 2016, 199 (1-4), pp.257-282. The tri-axial search-coil magnetometer (SCM) belongs to the FIELDS instrumentation suite on the Magnetospheric Multiscale (MMS) mission (Torbert et al. in Space Sci. Rev. (2014), this issue). It provides the three magnetic components of the waves from 1 Hz to 6 kHz in particular in the key regions of the Earth’s magnetosphere namely the subsolar region and the magnetotail. Magnetospheric plasmas being collisionless, such a measurement is crucial as the electromagnetic waves are thought to provide a way to ensure the conversion from magnetic to thermal and kinetic energies allowing local or global reconfigurations of the Earth’s magnetic field. The analog waveforms provided by the SCM are digitized and processed inside the digital signal processor (DSP), within the Central Electronics Box (CEB), together with the electric field data provided by the spin-plane double probe (SDP) and the axial double probe (ADP). On-board calibration signal provided by DSP allows the verification of the SCM transfer function once per orbit. Magnetic waveforms and on-board spectra computed by DSP are available at different time resolution depending on the selected mode. The SCM design is described in details as well as the different steps of the ground and in-flight calibrations. (10.1007/s11214-014-0096-9)
  DOI : 10.1007/s11214-014-0096-9
• Observations of whistler mode waves with nonlinear parallel electric fields near the dayside magnetic reconnection separatrix by the Magnetospheric Multiscale mission
  
  • Wilder F. D.
  • Ergun R. E.
  • Goodrich K. A.
  • Goldman M. V.
  • Newman D. L.
  • Malaspina D. M.
  • Jaynes A. N.
  • Schwartz S. J.
  • Trattner K. J.
  • Burch J. L.
  • Argall M. R.
  • Torbert R. B.
  • Lindqvist P.-A.
  • Marklund G.
  • Le Contel Olivier
  • Mirioni Laurent
  • Khotyaintsev Y. V.
  • Strangeway R. J.
  • Russell C. T.
  • Pollock C. J.
  • Giles B. L.
  • Plaschke F.
  • Magnes W.
  • Eriksson S.
  • Stawarz J. E.
  • Sturner A. P.
  • Holmes J. C.
  Geophysical Research Letters, American Geophysical Union, 2016, 43 (12), pp.5909-5917. We show observations from the Magnetospheric Multiscale (MMS) mission of whistler mode waves in the Earth's low-latitude boundary layer (LLBL) during a magnetic reconnection event. The waves propagated obliquely to the magnetic field toward the X line and were confined to the edge of a southward jet in the LLBL. Bipolar parallel electric fields interpreted as electrostatic solitary waves (ESW) are observed intermittently and appear to be in phase with the parallel component of the whistler oscillations. The polarity of the ESWs suggests that if they propagate with the waves, they are electron enhancements as opposed to electron holes. The reduced electron distribution shows a shoulder in the distribution for parallel velocities between 17,000 and 22,000 km/s, which persisted during the interval when ESWs were observed, and is near the phase velocity of the whistlers. This shoulder can drive Langmuir waves, which were observed in the high-frequency parallel electric field data. (10.1002/2016GL069473)
  DOI : 10.1002/2016GL069473
• Two interacting X lines in magnetotail: Evolution of collision between the counterstreaming jets
  
  • Alexandrova Alexandra
  • Nakamura R.
  • Panov Evgeny V.
  • Sasunov Yury L.
  • Nakamura T. K. M.
  • Vörös Z.
  • Retinò Alessandro
  • Semenov Vladimir S.
  Geophysical Research Letters, American Geophysical Union, 2016, 43 (15), pp.7795-7803. We study the process of collision between the counterstreaming jets flowing out from two reconnection sites in the Earth's magnetotail. The X lines, bracketing the region of jets collision, were passing by two Cluster probes successively in tailward direction. Two probes observed two different stages of the collision process. At the jets collision site, a probe first observed an ion-scale current sheet-like structure, while the other probe observed more compressed one later. The strong wave activities on both ion and electron scales were seen within the compressed layer. Such evolution of the jets collision resulting in the formation of the compressed boundary between the active X lines shows an example of interaction between the X lines during multiple reconnection. (10.1002/2016GL069823)
  DOI : 10.1002/2016GL069823
• Multispacecraft analysis of dipolarization fronts and associated whistler wave emissions using MMS data
  
  • Breuillard Hugo
  • Le Contel Olivier
  • Retinò Alessandro
  • Chasapis A.
  • Chust Thomas
  • Mirioni Laurent
  • Graham D. B.
  • Wilder F. D.
  • Cohen I.
  • Vaivads A.
  • Khotyaintsev Y. V.
  • Lindqvist P.-A.
  • Marklund G. T.
  • Burch J. L.
  • Torbert R. B.
  • Ergun R. E.
  • Goodrich K. A.
  • Macri J.
  • Needell J.
  • Chutter M.
  • Rau D.
  • Dors I.
  • Russell C. T.
  • Magnes W.
  • Strangeway R. J.
  • Bromund K. R.
  • Plaschke F.
  • Fischer D.
  • Leinweber H. K.
  • Anderson B. J.
  • Le G.
  • Slavin J. A.
  • Kepko E. L.
  • Baumjohann W.
  • Mauk B.
  • Fuselier S. A.
  • Nakamura R.
  Geophysical Research Letters, American Geophysical Union, 2016, 43 (14), pp.7279-7286. Dipolarization fronts (DFs), embedded in bursty bulk flows, play a crucial role in Earth's plasma sheet dynamics because the energy input from the solar wind is partly dissipated in their vicinity. This dissipation is in the form of strong low-frequency waves that can heat and accelerate energetic electrons up to the high-latitude plasma sheet. However, the dynamics of DF propagation and associated low-frequency waves in the magnetotail are still under debate due to instrumental limitations and spacecraft separation distances. In May 2015 the Magnetospheric Multiscale (MMS) mission was in a string-of-pearls configuration with an average intersatellite distance of 160 km, which allows us to study in detail the microphysics of DFs. Thus, in this letter we employ MMS data to investigate the properties of dipolarization fronts propagating earthward and associated whistler mode wave emissions. We show that the spatial dynamics of DFs are below the ion gyroradius scale in this region (500 km), which can modify the dynamics of ions in the vicinity of the DF (e.g., making their motion nonadiabatic). We also show that whistler wave dynamics have a temporal scale of the order of the ion gyroperiod (a few seconds), indicating that the perpendicular temperature anisotropy can vary on such time scales. (10.1002/2016GL069188)
  DOI : 10.1002/2016GL069188
• The Alfvén Mission for the ESA M5 Call: Mission Concept
  
  • Fazakerley A.
  • Berthomier Matthieu
  • Pottelette Raymond
  • Forsyth C.
  , 2016, 18, pp.EPSC2016-16890. This poster will present the proposed Alfvén mission concept and is complemented by a presentation of the mission scientific goals planned for the ST1.5 session. The Alfvén mission has the scientific objective of studying particle acceleration and other forms of electromagnetic energy conversion in a collisionless low beta plasma. The mission is proposed to operate in the Earth's Auroral Acceleration Region (AAR), the most accessible laboratory for investigating plasmas at an interface where ideal magneto-hydrodynamics does not apply. Alfvén is designed to answer questions about where and how the particles that create the aurorae are accelerated, how and why they emit auroral kilometric radiation, what creates and maintains large scale electric fields aligned with the magnetic field, and to elucidate the ion outflow processes which are slowly removing the Earth's atmosphere. The mission will provide the required coordinated two-spacecraft observations within the AAR several times a day. From well designed separations along or across the magnetic field lines, using a comprehensive suite of inter-calibrated particles and field instruments, it will measure the parallel electric fields, variations in particle flux, and wave energy that will answer open questions on energy conversion. It will use onboard auroral imagers to determine how this energy conversion occurs in the regional context and, together with its orbit design, this makes the mission ideally suited to resolving spatio-temporal ambiguities that have plagued previous auroral satellite studies. The spacecraft observations will be complemented by coordinated observations with the existing dense network of ground based observatories, for more detailed ionospheric and auroral information when Alfvén overflights occur.
• Near-field plume properties of an ion beam formed by alternating extraction and acceleration of oppositely charged ions
  
  • Oudini N.
  • Aanesland Ane
  • Chabert Pascal
  • Lounes-Mahloul S.
  • Bendib A.
  Plasma Sources Science and Technology, IOP Publishing, 2016, 25 (5), pp.055013. This paper is devoted to study the expansion of a beam composed of packets of positively and negatively charged ions generated by alternating extraction and acceleration. This beam is extracted from an ionion plasma, i.e. the electron density is negligible compared to the negative ion density. The alternating acceleration of ions is ensured by two grids placed in the ionion plasma region. The screen grid in contact with the plasma is biased with a square voltage waveform while the acceleration grid is grounded. A two-dimensional particle-in-cell (2D-PIC) code and an analytical model are used to study the properties of the near-field plume downstream of the acceleration grid. It is shown that the possible operating bias frequency is delimited by an upper limit and a lower one that are in the low MHz range. The simulations show that alternating acceleration with bias frequencies close to the upper frequency limit for the system can achieve high ion exhaust velocities, similar to traditional gridded ion thrusters, and with lower beam divergence than in classical systems. Indeed, ionion beam envelope might be reduced to 15° with 70% of ion flux contained within an angle of 3°. Thus, this alternating acceleration method is promising for electric space propulsion. (10.1088/0963-0252/25/5/055013)
  DOI : 10.1088/0963-0252/25/5/055013
• An expression for the h<SUB>l</SUB> factor in low-pressure electronegative plasma discharges
  
  • Chabert Pascal
  Plasma Sources Science and Technology, IOP Publishing, 2016, 25 (2), pp.025010. The positive ion flux exiting a low-pressure plasma discharge is a crucial quantity in global (volume-averaged) models. In discharges containing only electrons and positive ions (electropositive discharges), it is common to write this flux , where is the central positive ion density, is the positive ion fluid speed at the sheath edge (the Bohm speed), and is the positive ion edge-to-centre density ratio. There are well established formulae for in electropositive discharges, but for discharges containing negative ions (electronegative discharges), the analysis is more complicated. The purpose of this paper is to propose a formula for the factor in low-pressure electronegative discharges. We use the numerical solution of fluid equations with Boltzmann negative ions, including Poisson's equation, as a guide to derive an analytical expression that can easily be incorporated in global models. The parameter space in which the derived expression is valid is discussed at the end of the paper. (10.1088/0963-0252/25/2/025010)
  DOI : 10.1088/0963-0252/25/2/025010
• A comparison between micro hollow cathode discharges and atmospheric pressure plasma jets in Ar/O<SUB>2</SUB> gas mixtures
  
  • Lazzaroni Claudia
  • Chabert Pascal
  Plasma Sources Science and Technology, IOP Publishing, 2016, 25 (6), pp.065015. Using global models, micro hollow cathode discharges (MHCDs) are compared to radiofrequency atmospheric pressure plasma jets (APPJs) in terms of reactive oxygen species (ROS) production. Ar/O 2 gas mixtures are investigated, typically with a small percentage of oxygen in argon. The same chemical reaction set, involving 17 species and 128 chemical reactions in the gas phase, is used for both devices, operated in the typical geometries previously published; the APPJ is driven by a radiofrequency voltage across a 1&#8201;mm gap, at atmospheric pressure, while the MHCD is driven by a DC voltage source, at 100 Torr and in a 400 &#956; m hole. The MHCD may be operated either in the self-pulsing or in the normal (stationary) regime, depending on the driving voltage. The comparison shows that in both regimes, the MHCD produces larger amounts of ##IMG## [http://ej.iop.org/images/0963-0252/25/6/065015/psstaa4123ieqn001.gif] \textO_2^\ast , while the APPJ produces predominantly reactive oxygen ground state species, ##IMG## [http://ej.iop.org/images/0963-0252/25/6/065015/psstaa4123ieqn002.gif] \textO and ##IMG## [http://ej.iop.org/images/0963-0252/25/6/065015/psstaa4123ieqn003.gif] \textO_3 . These large differences in ROS composition are mostly due to the higher plasma density produced in the MHCD. The difference in operating pressure is a second order effect. (10.1088/0963-0252/25/6/065015)
  DOI : 10.1088/0963-0252/25/6/065015
• Estimating some parameters of the equatorial ionosphere electrodynamics from ionosonde data in West Africa
  
  • Grodji F.O.
  • Doumbia V.
  • Boka K.
  • Amory-Mazaudier Christine
  • Cohen Y.
  • Fleury Rolland
  Advances in Space Research, Elsevier, 2016. During the International Equatorial Electrojet Year (IEEY), an IPS-42 ionosonde located at Korhogo (9.33°N, 5.42°W, -1.88°dip-lat) and a meridian chain of 10 magnetic stations were setup in West Africa (5°West longitude). In this work, some characteristic parameters of the equatorial electrojet were estimated on the basis of the IPS-42 ionosonde data at Korhogo during the years 1993 and 1994. The study consisted of determining the zonal electric field through an estimate of the plasma vertical drift velocity. The daytime plasma vertical drift velocity was estimated from the time rates of change of the F-layer virtual height variations and a correction term that takes into account the ionization production and recombination effects. This method resulted in an improved vertical drift velocity, which was found to be comparable to the results of previous studies. The estimated vertical drift velocity was used in a semi-empirical approach which involved the IRI-2012 model for the Pedersen and Hall conductivities and the IGRF-10 model for the geomagnetic main field intensity. Thus the zonal and polarization electric fields on one hand, and the eastward Pedersen, Hall and the equatorial electrojet current densities on the other hand, were estimated. Furthermore the integrated peak current density at the EEJ center was estimated from ionosonde observations and compared with that inferred from magnetometer data. The integrated EEJ peak current densities obtained from both experiments were found to be in the same order and their seasonal variations exhibit the same trends as well. (10.1016/j.asr.2016.09.004)
  DOI : 10.1016/j.asr.2016.09.004