Publications

2016

The Baseline Th17 Lymphocytes Level Is a Predictive Marker of Good Response to Biologics in Rheumatoid Arthritis
- Salomon Sarah
- Guignant Caroline
- Morel Pierre
- Gubler Brigitte
- Fardellone Patrice
- Marolleau Jean-Pierre
- Goeb Vincent
Arthritis & rheumatology, Wiley, 2016, 68 (10).
Chiral exact relations for helicities in Hall magnetohydrodynamic turbulence
- Banerjee Supratik
- Galtier Sébastien
Physical Review E, American Physical Society (APS), 2016, 93, pp.033120. Besides total energy, three-dimensional incompressible Hall magnetohydrodynamics (MHD) possesses two inviscid invariants, which are the magnetic helicity and the generalized helicity. Exact relations are derived for homogeneous (nonisotropic) stationary Hall MHD turbulence (and also for its inertialess electron MHD limit) with nonzero helicities and in the asymptotic limit of large Reynolds numbers. The universal laws are written only in terms of mixed second-order structure functions, i.e., the scalar product of two different increments. It provides, therefore, a direct measurement of the dissipation rates for the corresponding invariant flux. This study shows that the generalized helicity cascade is strongly linked to the left polarized fluctuations, while the magnetic helicity cascade is linked to the right polarized fluctuations. (10.1103/PhysRevE.93.033120)
DOI : 10.1103/PhysRevE.93.033120
A Review of General Physical and Chemical Processes Related to Plasma Sources and Losses for Solar System Magnetospheres
- Seki K.
- Nagy A.
- Jackman C. M.
- Crary F.
- Fontaine Dominique
- Zarka P.
- Wurz Peter
- Milillo A.
- Slavin J. A.
- Delcourt Dominique
- Wiltberger M.
- Ilie R.
- Jia X.
- Ledvina S. A.
- Liemohn M. W.
- Schunk R. W.
- Blanc Michel
- Chappell Charles R.
- Krupp N.
, 2016, pp.27-89. The aim of this paper is to provide a review of general processes related to plasma sources, their transport, energization, and losses in the planetary magnetospheres. We provide background information as well as the most up-to-date knowledge of the comparative studies of planetary magnetospheres, with a focus on the plasma supply to each region of the magnetospheres. This review also includes the basic equations and modeling methods commonly used to simulate the plasma sources of the planetary magnetospheres. In this paper, we will describe basic and common processes related to plasma supply to each region of the planetary magnetospheres in our solar system. First, we will describe source processes in Sect. 1. Then the transport and energization processes to supply those source plasmas to various regions of the magnetosphere are described in Sect. 2. Loss processes are also important to understand the plasma population in the magnetosphere and Sect. 3 is dedicated to the explanation of the loss processes. In Sect. 4, we also briefly summarize the basic equations and modeling methods with a focus on plasma supply processes for planetary magnetospheres.
A comparative experimental kinetic study of spontaneous and plasma-assisted cool flames in a rapid compression machine
- Vanhove G.
- Boumehdi M.-A.
- Shcherbanev S.A.
- Fenard Y.
- Desgroux Pascale
- Starikovskaia Svetlana
Proceedings of the Combustion Institute, Elsevier, 2016. Plasma-assisted cool flames of n- heptane were generated in the combustion chamber of a rapid compression machine coupled with a nanosecond dielectric barrier discharge, at a pressure of 1.5 bar and temperature T = 650 K. Increasing of the voltage pulse amplitude at the electrode resulted in a transition from no reactivity to induced cool flame and then to fast ignition. Sampling of the reacting mixture was performed at selected times during the experiments to draw mole fraction profiles of the fuel and major low temperature stable intermediates, showing a gradual increase in the mole fraction of these species after the discharge. Comparison with a spontaneous cool flame case at a slightly higher pressure shows that no new species are formed in the plasma-assisted case, and that after the initiation of reactivity by the discharge at the nanosecond timescale, the distribution and relative importance of the main reaction pathways is conserved at the millisecond timescale. Differences in the shape of the mole fraction and light emission profiles however suggest that the plasma-assisted cool flame is propagative. (10.1016/j.proci.2016.09.007)
DOI : 10.1016/j.proci.2016.09.007
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
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
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
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
Hybrid global model of water cluster ions in atmospheric pressure Ar/H2O 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 mm driven at 27.12 MHz, we determine the discharge properties over a range of rf currents (150500 A m−2) and initial concentrations (0.252%). An isothermal plug-flow model is used with a gas residence time of 0.2 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
Electron power absorption dynamics in capacitive radio frequency discharges driven by tailored voltage waveforms in CF4
- 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 α-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
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−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−1 of travel distance inside the capillary. (10.1088/1361-6595/aa53fe)
DOI : 10.1088/1361-6595/aa53fe
An expression for the hl 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
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
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
A comparison between micro hollow cathode discharges and atmospheric pressure plasma jets in Ar/O2 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 mm gap, at atmospheric pressure, while the MHCD is driven by a DC voltage source, at 100 Torr and in a 400 μ 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
Turbulence intermittency linked to the weakly coherent mode in ASDEX Upgrade I-mode plasmas
- Happel T.
- Manz P.
- Ryter F.
- Hennequin Pascale
- Hetzenecker A.
- Conway G. D.
- Guimarais L.
- Honoré Cyrille
- Stroth U.
- Viezzer E.
- The Asdex Upgrade Team
Nuclear Fusion, IOP Publishing, 2016, 56 (6), pp.064004. This letter shows for the first time a pronounced increase of extremely intermittent edge density turbulence behavior inside the confinement region related to the I-mode confinement regime in the ASDEX Upgrade tokamak. With improving confinement, the perpendicular propagation velocity of density fluctuations in the plasma edge increases together with the intermittency of the observed density bursts. Furthermore, it is shown that the weakly coherent mode, a fluctuation feature generally observed in I-mode plasmas, is connected to the observed bursts. It is suggested that the large amplitude density bursts could be generated by a non-linearity similar to that in the Korteweg?de-Vries equation which includes the radial temperature gradient. (10.1088/0029-5515/56/6/064004)
DOI : 10.1088/0029-5515/56/6/064004
Transport matrix for particles and momentum in collisional drift waves turbulence in linear plasma devices
- Ashourvan A.
- Diamond P.H.
- Gürcan Özgür D.
Physics of Plasmas, American Institute of Physics, 2016, 23, pp.022309. The relationship between the physics of turbulent transport of particles and azimuthal momentum in a linear plasma device is investigated using a simple model with a background density gradient and zonal flows driven by turbulent stresses. Pure shear flow driven Kelvin-Helmholtz instabilities (k∥=0) relax the flow and drive an outward (down gradient) flux of particles. However, instabilities at finite k∥ with flow enhanced pumping can locally drive an inward particle pinch. The turbulent vorticity flux consists of a turbulent viscosity term, which acts to reduce the global vorticity gradient and the residual vorticity flux term, accelerating the zonal flows from rest. Moreover, we use the positivity of the production of fluctuation potential enstrophy to obtain a constraint relation, which tightly links the vorticity transport to the particle transport. This relation can be useful in explaining the experimentally observed correlation between the presence of E×B flow shear and the measured inward particle flux in various magnetically confined plasma devices. (10.1063/1.4942420)
DOI : 10.1063/1.4942420
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
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
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
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
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
Capacitively coupled hydrogen plasmas sustained by tailored voltage waveforms: excitation dynamics and ion flux asymmetry
- Bruneau B.
- Diomede P.
- Economou D. J.
- Longo S.
- Gans T.
- O'Connell D.
- Greb A.
- Johnson E.
- Booth Jean-Paul
Plasma Sources Science and Technology, IOP Publishing, 2016, 25. Parallel plate capacitively coupled plasmas in hydrogen at relatively high pressure (~1 Torr) are excited with tailored voltage waveforms containing up to five frequencies. Predictions of a hybrid model combining a particle-in-cell simulation with Monte Carlo collisions and a fluid model are compared to phase resolved optical emission spectroscopy measurements, yielding information on the dynamics of the excitation rate in these discharges. When the discharge is excited with amplitude asymmetric waveforms, the discharge becomes electrically asymmetric, with different ion energies at each of the two electrodes. Unexpectedly, large differences in the \text{H}2 fluxes to each of the two electrodes are caused by the different \text{H}3 energies. When the discharge is excited with slope asymmetric waveforms, only weak electrical asymmetry of the discharge is observed. In this case, electron power absorption due to fast sheath expansion at one electrode is balanced by electron power absorption at the opposite electrode due to a strong electric field reversal. (10.1088/0963-0252/25/4/045019)
DOI : 10.1088/0963-0252/25/4/045019

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