Publications

2014

• Study of gas heating mechanisms in millisecond pulsed discharges and afterglows in air at low pressures
  
  • Pintassilgo C.D.
  • Guerra V.
  • Guaitella Olivier
  • Rousseau Antoine
  Plasma Sources Science and Technology, IOP Publishing, 2014, 23, pp.025006. A self-consistent model is developed to study the temporal variation of the gas temperature in millisecond single dc pulsed discharges and their afterglows in air-like mixtures (N220%O2) at low pressures. The model is based on the solutions to the time-dependent gas thermal balance equation, under the assumption of a parabolic gas temperature profile across the discharge tube, coupled to the electron, vibrational and chemical kinetics. Modelling results provide a satisfactory explanation for recently published time-resolved experimental data for the gas temperature in a 5 ms pulsed air plasma with a current of 150mA and the corresponding afterglow at a pressure of 133 Pa (1 Torr). It is shown that the main heating mechanisms during the first millisecond of the pulse come predominantly from O2 dissociation by electron impact through the pre-dissociative excited state O2(B 3− u ) and the quenching of nitrogen electronically excited states N2(A 3 u , B 3 g, a 1− u , a 1 g, w 1u) by O2, agreeing with other studies on fast gas heating in air plasmas. As the pulse duration increases, other gas heating sources become important, namely VT N2O energy exchanges, recombination of oxygen atoms at the wall, N2(A) quenching by O(3P) and reaction N(4S) NO(X) → N2(X, v ∼3) O, contributing altogether to an additional smooth increase in the gas temperature until the end of the pulse. In the first instants of the early afterglow, the gas temperature decreases very rapidly as a consequence of the minor role played by electronic collisions and due to a fast decay of N2 electronic states. For afterglow times up to 10 ms, the gas temperature continues to decrease, following the time-dependent kinetics of [N2(X,v)], [N(4S)], [O(3P)] and [NO(X)]. Sensitivity of the model to different input parameters such as thermal accommodation coefficient and probabilities for atomic recombination at the wall are reported. (10.1088/0963-0252/23/2/025006)
  DOI : 10.1088/0963-0252/23/2/025006
• A nanosecond surface dieletric barrier discharge in air at high pressure and different polarities of applied pulses. Transition to filamentary mode
  
  • Stepanyan S.A.
  • Starikovskiy a Yu
  • Popov N.A.
  • Starikovskaia Svetlana
  Plasma Sources Science and Technology, IOP Publishing, 2014, 23 (4), pp.045003. The development of a nanosecond surface dielectric barrier discharge in air at pressures 16 bar is studied. At atmospheric pressure, the discharge develops as a set of streamers starting synchronously from the high-voltage electrode and propagating along the dielectric layer. Streamers cover the dielectric surface creating a 'quasi-uniform' plasma layer. At high pressures and high voltage amplitudes on the cathode, filamentation of the discharge is observed a few nanoseconds after the discharge starts. Parameters of the observed 'streamers-to-filaments' transition are measured; physics of transition is discussed on the basis of theoretical estimates and numerical modeling. Ionization-heating instability on the boundary of the cathode layer is suggested as a mechanism of filamentation. (10.1088/0963-0252/23/4/045003)
  DOI : 10.1088/0963-0252/23/4/045003
• A radio-frequency sheath model for complex waveforms
  
  • Turner M.M.
  • Chabert Pascal
  Applied Physics Letters, American Institute of Physics, 2014, 104 (16), pp.164102. Plasma sheaths driven by radio-frequency voltages occur in contexts ranging from plasma processing to magnetically confined fusion experiments. An analytical understanding of such sheaths is therefore important, both intrinsically and as an element in more elaborate theoretical structures. Radio-frequency sheaths are commonly excited by highly anharmonic waveforms, but no analytical model exists for this general case. We present a mathematically simple sheath model that is in good agreement with earlier models for single frequency excitation, yet can be solved for arbitrary excitation waveforms. As examples, we discuss dual-frequency and pulse-like waveforms. The model employs the ansatz that the time-averaged electron density is a constant fraction of the ion density. In the cases we discuss, the error introduced by this approximation is small, and in general it can be quantified through an internal consistency condition of the model. This simple and accurate model is likely to have wide application. (10.1063/1.4872172)
  DOI : 10.1063/1.4872172
• Oxidation of isopropanol and acetone adsorbed on TiO<SUB>2</SUB> under plasma generated ozone flow: Gas phase and adsorbed species monitoring
  
  • Barakat Christelle
  • Gravejat Paul
  • Guaitella Olivier
  • Thévenet Frédéric
  • Rousseau Antoine
  Applied Catalysis B: Environmental, Elsevier, 2014, 147, pp.302-313. The regeneration of isopropanol (IPA) and/or acetone saturated TiO2 surface by ozone is investigated. TiO2 catalyst is placed downstream a dielectric barrier discharge and is subsequently exposed to ozone considered as the main oxidative species generated by non-thermal plasma and able to interact with the material surface at room temperature. The oxidation of isopropanol and/or acetone is monitored using two parallel and complementary infrared diagnostics: (1) Fourier Transform Infrared Spectroscopy for the analysis of the gas phase composition; and (2) Diffuse Reflectance Infrared Fourier Transform Spectroscopy for the in situ analysis of the adsorbent/catalyst surface. In this study, the pollutant is first adsorbed on the TiO2 surface, the plasma being switched off. The irreversibly adsorbed amounts of isopropanol and acetone have been respectively quantified as 5.3 &#956;mol/m2 and 1.9 &#956;mol/m2. In a second step, the plasma is switched on to regenerate the surface by mineralization of the adsorbed organic species. A 70-min plasma phase, with approximately 20 ppm of ozone constantly flowing through the adsorbent bed yields 8.5 nmol and 8.9 nmol of CO2 per injected joule of energy for isopropanol and acetone saturated surfaces, respectively. Acetone has been evidenced as the main oxidation intermediate of isopropanol on TiO2 surface. It has been proven that the complete oxidation of isopropanol and acetone is mainly limited by the acetone oxidation rate. Competitive adsorption on the surface of the catalyst between both compounds has been studied. Results obtained are compared with those observed in the photocatalytic oxidation of the same species. (10.1016/j.apcatb.2013.09.008)
  DOI : 10.1016/j.apcatb.2013.09.008
• Electron heating in capacitively coupled plasmas revisited
  
  • Lafleur Trevor
  • Chabert Pascal
  • Booth Jean-Paul
  Plasma Sources Science and Technology, IOP Publishing, 2014, 23 (3), pp.035010. We revisit the problem of electron heating in capacitively coupled plasmas (CCPs), and propose a method for quantifying the level of collisionless and collisional heating in plasma simulations. The proposed procedure, based on the electron mechanical energy conservation equation, is demonstrated with particle-in-cell simulations of a number of single and multi-frequency CCPs operated in regimes of research and industrial interest. In almost all cases tested, the total electron heating is comprised of collisional (ohmic) and pressure heating parts. This latter collisionless component is in qualitative agreement with the mechanism of electron heating predicted from the recent re-evaluation of theoretical models. Finally, in very electrically asymmetric plasmas produced in multi-frequency discharges, we observe an additional collisionless heating mechanism associated with electron inertia. (10.1088/0963-0252/23/3/035010)
  DOI : 10.1088/0963-0252/23/3/035010
• Ambipolar and non-ambipolar diffusion in an rf plasma source containing a magnetic filter
  
  • Lafleur Trevor
  • Aanesland Ane
  Physics of Plasmas, American Institute of Physics, 2014, 21, pp.063510. By placing a magnetic filter across a rectangular plasma source (closed at one end with a ceramic plate and an rf antenna, and terminated at the opposite end by a grounded grid), we experimentally investigate the effect of conducting and insulating source walls on the nature of the plasma diffusion phenomena. The use of a magnetic filter creates a unique plasma, characterized by a high upstream electron temperature (Teu&#8764;5 eV) near the rf antenna and a low downstream electron temperature (Ted&#8764;1 eV) near the grid, which more clearly demonstrates the role of the source wall materials. For conducting walls a net ion current to ground is measured on the grid, and the plasma potential is determined by a mean electron temperature within the source. For insulating walls the plasma potential is determined by the downstream electron temperature (i.e., Vp&#8764;5.2Ted in argon), and the net current to the grid is exactly zero. Furthermore, by inserting a small additional upstream conductor (that can be made floating or grounded through an external circuit switch), we demonstrate that the plasma potential can be controlled and set to a low (Vp&#8764;5.2Ted), or high (Vp&#8764;5.2Teu) value. (10.1063/1.4885109)
  DOI : 10.1063/1.4885109
• Surface deactivation of vibrationally excited N<SUB>2</SUB> studied using infrared titration combined with quantum cascade laser absorption spectroscopy
  
  • Marinov Daniil
  • Lopatik D.
  • Guaitella Olivier
  • Ionikh Y.
  • Röpcke J.
  • Rousseau Antoine
  Journal of Physics D: Applied Physics, IOP Publishing, 2014, 47 (1), pp.015203. The wall de-excitation probability of vibrationally excited nitrogen molecules was determined using infrared (IR) titration with CO, CO 2 and N 2 O. Gas mixtures of N 2 with 0.05?0.5% of CO (CO 2 or N 2 O) were excited by a pulsed dc discharge at p = 133 Pa in a cylindrical discharge tube. During the afterglow, the vibrational relaxation of titrating molecules was monitored in situ with quantum cascade laser absorption spectroscopy. The value of was deduced from measured vibrational relaxation times using a model of vibrational kinetics in N 2 . It was found that adsorption of IR tracers on the surface may increase the value of by a factor up to two, depending on the molecule and the surface material. It was demonstrated that N 2 O is the most inert and reliable tracer and it was used for the determination of on silica, Pyrex, TiO 2 , Al 2 O 3 and anodized aluminum. Pretreatment of the silica surface by low-pressure plasma was found to have a strong effect on the vibrational de-excitation. Values of measured after O 2 , Ar and N 2 plasma pretreatment of the same silica discharge tube were 5.7 × 10 ?4 , 8.2 × 10 ?4 and 11 × 10 ?4 , respectively. This study clearly demonstrates that the presence of adsorbed atoms and molecules on the surface may significantly alter the value of . (10.1088/0022-3727/47/1/015203)
  DOI : 10.1088/0022-3727/47/1/015203
• Plasma composition and ion acceleration in the PEGASES thruster
  
  • Renaud D.
  • Mazouffre S.
  • Aanesland Ane
  Space Propulsion, 2014 (2969109).
• Pulsed discharges in a wide density range: plasma development and media excitation
  
  • Starikovskaia Svetlana
  • Starikovskii A.Yu.
  , 2014. The Chapter demonstrates the peculiarities of pulsed nonequilibrium plasma generation in different media by nano- and picosecond high-voltage discharges. Fast ionization waves in long tubes at low pressures, streamers and dielectric barrier discharges at moderate and atmospheric pressures, surface dielectric barrier discharges at elevated pressures are considered. Special attention is given to start of picoseconds and nanosecond discharges in liquid media. The data used were consciously restricted to ICCD fast imaging of picoseconds and nanosecond discharges, to underline the dynamics of pulsed discharge development and the importance of spatial distribution of the discharge energy.
• Investigation of drift velocity effects on the EDGE and SOL transport.
  
  • Leybros Robin
  • Bufferand H.
  • Ciraolo G.
  • Fedorczak N.
  • Ghendrih Ph.
  • Hennequin Pascale
  • Marandet Y.
  • Serre E.
  • Schwander F.
  • Tamain P.
  , 2014.
• The double well mass filter
  
  • Gueroult R
  • Fisch Nathaniel J.
  • Rax Jean-Marcel
  Physics of Plasmas, American Institute of Physics, 2014, 21 (2), pp.020701. Various mass filter concepts based on rotating plasmas have been suggested with the specific purpose of nuclear waste remediation. We report on a new rotating mass filter combining radial separation with axial extraction. The radial separation of the masses is the result of a “double-well” in effective radial potential in rotating plasma with a sheared rotation profile. (10.1063/1.4864325)
  DOI : 10.1063/1.4864325
• Time-resolved imaging of nanosecond-pulsed micro-discharges in heptane
  
  • Hamdan A.
  • Marinov Ilya
  • Belmonte Thierry
  • Rousseau A.
  Journal of Physics D: Applied Physics, IOP Publishing, 2014, 47 (5). Nanosecond-pulsed micro-discharges in heptane are studied by time-resolved imaging in pin-to-plate configuration. When a voltage of +5 kV is applied to the pin electrode, the discharge exhibits one maximum in light intensity. At +15 kV, filtered images show that up to three maxima can be identified. These maxima are associated with local electron-ion recombination and bremsstrahlung emission and attributed to the development of a complex space-charge field. In the post-discharge, the dynamics of the gas bubble can be simulated by the Gilmore model, and the pressure evolution in this bubble is predicted. From our results, it seems reasonable to think that the gas bubble develops from the post-discharge of the spark. Results obtained by using the double-pulse technique show that light emission during the post-discharge of the second discharge lasts 10 times longer than the post-discharge of the first spark. The pressure drop in the gas bubble, predicted by the Gilmore model, is used to explain this result and it provides a control method by optical diagnostics in liquids. (10.1088/0022-3727/47/5/055203)
  DOI : 10.1088/0022-3727/47/5/055203
• Fourier spectrum and phases for a signal in a finite interval
  
  • Dorville Nicolas
  • Belmont Gérard
  • Sahraoui Fouad
  • Rezeau Laurence
  , 2014, 13, pp.SH13B-4086. When investigating the physics of turbulent media, as the solar wind or the magnetosheath plasmas, obtaining accurate Fourier spectra and phases is a crucial issue. For the different fields, the spectra allow in particular verifying whether one or several power laws can be determined in different frequency ranges. Accurate phases are necessary as well for all the "higher order statistics" studies in Fourier space, the coherence ones and for the polarization studies. Unfortunately, the Fourier analysis is not unique for a finite time interval of duration T: the frequencies lower than 1/T have a large influence on the result, which can hardly be controlled. This unknown "trend" has in particular the effect of superposing jumps at the edges of the interval, for the function under study itself, as well as for all its derivatives. The Fourier transform obtained directly by FFT (Fast Fourier Transform) is generally much influenced by these effects and cannot be used without care for wide band signals. The interferences between the jumps and the signal itself also provide "hairs" on the spectrum, which are clearly visible fluctuations with df&#8776;1/T. These fluctuations are usually eliminated by smoothing the spectrum, or by averaging several successive spectra. Nevertheless, such smoothing introduces uncertainties on the spectral laws and it makes the phases lost. Windowing is also a method currently used to suppress the jumps, but it modifies the signal (the windowed trend has a spectrum, which is convolved with the searched one) and the phases are also lost to a large extent. Here, we present a new data processing technique to circumvent these difficulties. It takes advantage of the fact that the signal is generally not unknown out of the interval under study: the complete signal is tapered to this interval of interest thanks to a new kind of window, sharp but not square. This kind of window is such that the spectrum obtained can then be deconvolved almost exactly, through a minimization procedure based on the weak- hypothesis that it is smooth at the scale of a few successive spectral points. Then, a later step allows reconstructing the phases. Tests with synthetic data are presented, that demonstrate the efficiency of the method, and first results from Cluster data are also shown.
• Kelvin-Helmholtz Vortices and Double Mid-Latitude Reconnection at the Earth's Magnetopause: comparison between observations and simulations
  
  • Faganello Matteo
  • Califano F.
  • Pegoraro F.
  • Retinò Alessandro
  EPL - Europhysics Letters, European Physical Society / EDP Sciences / Società Italiana di Fisica / IOP Publishing, 2014. Observational signatures of Kelvin-Helmholtz (K-H) vortices and of double mid-latitude reconnection are highlighted in satellite data of the THEMIS mission. It is shown that the plasma fluid quantities at the low-latitude flank of the Earth's magnetosphere are compatible with K-H vortices, as described by three-dimensional simulations. At the same time it is shown that the particle fluxes are compatible with the presence of magnetic field lines, embedded in the K-H vortices, that close on Earth but are connected to the solar wind at low-latitude. These field lines are generated during the K-H evolution by magnetic reconnection proceeding spontaneously in both hemispheres at mid-latitudes, allowing the solar wind plasma to enter the Earth's magnetosphere directly.
• Dynamics of plasma evolution in a nanosecond underwater discharge
  
  • Marinov Ilya
  • Starikovskaia Svetlana
  • Rousseau Antoine
  Journal of Physics D: Applied Physics, IOP Publishing, 2014, 47 (22), pp.224017. A positive discharge in water is generated by applying a 30 ns high-voltage (HV) pulse on a micrometre scale electrode. The applied voltage ranges from 6 to 15 kV and a fast plasma propagating mode is launched with a velocity of up to 60 km s&#8722;1 . Time-resolved shadowgraphy and spectroscopy are performed to monitor the time evolution of the discharge structure and of the plasma emission spectra. By analysing the dynamics of the shock front velocity and the lateral expansion of the plasma channel, it is possible to estimate the pressure at the ignition of the plasma by two independent methods: very good agreement is found at 6 kV giving initial pressures of 0.4 GPa and 0.3 GPa, respectively. At 15 kV, only the shock front velocity method is applicable under our experimental conditions, giving an estimate of the initial pressure of 5.8 GPa. Such high initial pressures show that, under a nanosecond HV pulse, the plasma is ignited directly in the dense phase. Emission spectra show a strong continuum emission as well as a broad Balmer &#945; line with a strong red shift, with an estimate of the initial plasma density of 1.3 × 1026 m&#8722;3. The relaxation of discharge pressure and plasma density is studied under a series of six successive pulses. (10.1088/0022-3727/47/22/224017)
  DOI : 10.1088/0022-3727/47/22/224017
• Equivalence of the hard-wall and kinetic-fluid models of collisionless electron heating in capacitively coupled discharges
  
  • Lafleur Trevor
  • Chabert Pascal
  • Turner Miles
  • Booth Jean-Paul
  Plasma Sources Science and Technology, IOP Publishing, 2014, 23 (1), pp.015016. By re-evaluating the hard-wall collisionless electron heating model from first principles, we show that despite previous criticisms (Gozadinos et al 2001 Phys. Rev. Lett. 87 [http://dx.doi.org/10.1103/PhysRevLett.87.135004] 135004 ), this model can in general be made consistent with the requirement of radio frequency (rf) current continuity at the sheath edge, while still producing a net heating effect. In addition, we demonstrate that the hard-wall and kinetic-fluid heating models stem from the same basic physical mechanism, and are in many ways the same theory; they differ only in the spatial region where electron heating is assumed to occur, and the way in which the effective electron distribution function is determined. Fundamentally, both models predict that collisionless heating occurs because of a non-isothermal compression and expansion of the plasma electrons by an oscillating rf sheath. (10.1088/0963-0252/23/1/015016)
  DOI : 10.1088/0963-0252/23/1/015016
• Ground state bromine atom density measurements by two-photon absorption laser-induced fluorescence
  
  • Sirse Nishant
  • Foucher Mickaël
  • Chabert Pascal
  • Booth Jean-Paul
  Plasma Sources Science and Technology, IOP Publishing, 2014, 23 (6), pp.062003. Ground state bromine atom detection by two-photon absorption laser-induced fluorescence (TALIF) is demonstrated. The bromine atoms are excited by two-photon absorption at 252.594 nm to the state and detected by 635.25 nm fluorescence to the (5s) 4 P 5/2 state. The atoms are generated in a radio-frequency inductively-coupled plasma in pure HBr. The excitation laser also causes some photodissociation of HBr molecules, but this can be minimized by not focussing the laser beam, still giving adequate signal levels. We determined the natural lifetime of the emitting state, and the rate constant for quenching of this state by collision with HBr molecules, ... (10.1088/0963-0252/23/6/062003)
  DOI : 10.1088/0963-0252/23/6/062003
• Weak turbulence theory for rotating magnetohydrodynamics and planetary flows
  
  • Galtier Sébastien
  Journal of Fluid Mechanics, Cambridge University Press (CUP), 2014, 757, pp.114-154. A weak turbulence theory is derived for magnetohydrodynamics (MHD) under rapid rotation and in the presence of a uniform large-scale magnetic field which is associated with a constant Alfvén velocity . The angular velocity is assumed to be uniform and parallel to . Such a system exhibits left and right circularly polarized waves which can be obtained by introducing the magneto-inertial length . In the large-scale limit ( , with being the wavenumber) the left- and right-handed waves tend to the inertial and magnetostrophic waves, respectively, whereas in the small-scale limit ( ) pure Alfvén waves are recovered. By using a complex helicity decomposition, the asymptotic weak turbulence equations are derived which describe the long-time behaviour of weakly dispersive interacting waves via three-wave interaction processes. It is shown that the nonlinear dynamics is mainly anisotropic, with a stronger transfer perpendicular than parallel to the rotation axis. The general theory may converge to pure weak inertial/magnetostrophic or Alfvén wave turbulence when the large- or small-scale limits are taken, respectively. Inertial wave turbulence is asymptotically dominated by the kinetic energy/helicity, whereas the magnetostrophic wave turbulence is dominated by the magnetic energy/helicity. For both regimes, families of exact solutions are found for the spectra, which do not correspond necessarily to a maximal helicity state. It is shown that the hybrid helicity exhibits a cascade whose direction may vary according to the scale at which the helicity flux is injected, with an inverse cascade if and a direct cascade otherwise. The theory is relevant to the magnetostrophic dynamo, whose main applications are the Earth and the giant planets, such as Jupiter and Saturn, for which a small ( ) Rossby number is expected. (10.1017/jfm.2014.490)
  DOI : 10.1017/jfm.2014.490
• In situ spatiotemporal measurements of the detailed azimuthal substructure of the substorm current wedge
  
  • Forsyth C.
  • Fazakerley A.
  • Rae I. J.
  • Watt C. E. J.
  • Murphy K.
  • Wild James A.
  • Karlsson T.
  • Mutel R. L.
  • Owen C. J.
  • Ergun R.
  • Masson A.
  • Berthomier Matthieu
  • Donovan E.
  • Frey H.~u.
  • Matzka J.
  • Stolle C.
  • Zhang Y.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2014, 119 (2), pp.927-946. The substorm current wedge (SCW) is a fundamental component of geomagnetic substorms. Models tend to describe the SCW as a simple line current flowing into the ionosphere toward dawn and out of the ionosphere toward dusk, linked by a westward electrojet. We use multispacecraft observations from perigee passes of the Cluster 1 and 4 spacecraft during a substorm on 15 January 2010, in conjunction with ground-based observations, to examine the spatial structuring and temporal variability of the SCW. At this time, the spacecraft traveled east-west azimuthally above the auroral region. We show that the SCW has significant azimuthal substructure on scales of 100&#8201;km at altitudes of 40007000&#8201;km. We identify 26 individual current sheets in the Cluster 4 data and 34 individual current sheets in the Cluster 1 data, with Cluster 1 passing through the SCW 120240&#8201;s after Cluster 4 at 13002000&#8201;km higher altitude. Both spacecraft observed large-scale regions of net upward and downward field-aligned current, consistent with the large-scale characteristics of the SCW, although sheets of oppositely directed currents were observed within both regions. We show that the majority of these current sheets were closely aligned to a north-south direction, in contrast to the expected east-west orientation of the preonset aurora. Comparing our results with observations of the field-aligned current associated with bursty bulk flows (BBFs), we conclude that significant questions remain for the explanation of SCW structuring by BBF-driven wedgelets. Our results therefore represent constraints on future modeling and theoretical frameworks on the generation of the&#8201;SCW. (10.1002/2013JA019302)
  DOI : 10.1002/2013JA019302
• Wave normal angles of whistler-mode chorus rising and falling tones
  
  • Taubenschuss U.
  • Khotyaintsev Y. V.
  • Santolík O.
  • Vaivads A.
  • Cully C. M.
  • Le Contel Olivier
  • Angelopoulos V.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2014. We present a study of wave normal angles (&#952;k) of whistler mode chorus emission as observed by Time History of Events and Macroscale Interactions during Substorms (THEMIS) during the year 2008. The three inner THEMIS satellites THA, THD, and THE usually orbit Earth close to the dipole magnetic equator (±20°), covering a large range of L shells from the plasmasphere out to the magnetopause. Waveform measurements of electric and magnetic fields enable a detailed polarization analysis of chorus below 4 kHz. When displayed in a frequency-&#952;k histogram, four characteristic regions of occurrence are evident. They are separated by gaps at f/fc,e&#8776;0.5 (f is the chorus frequency, fc,e is the local electron cyclotron frequency) and at &#952;k&#8764;40°. Below &#952;k&#8764;40°, the average value for &#952;k is predominantly field aligned, but slightly increasing with frequency toward half of fc,e (&#952;k up to 20°). Above half of fc,e, the average &#952;k is again decreasing with frequency. Above &#952;k&#8764;40°, wave normal angles are usually close to the resonance cone angle. Furthermore, we present a detailed comparison of electric and magnetic fields of chorus rising and falling tones. Falling tones exhibit peaks in occurrence solely for &#952;k>40° and are propagating close to the resonance cone angle. Nevertheless, when comparing rising tones to falling tones at &#952;k>40°, the ratio of magnetic to electric field shows no significant differences. Thus, we conclude that falling tones are generated under similar conditions as rising tones, with common source regions close to the magnetic equatorial plane. (10.1002/2014JA020575)
  DOI : 10.1002/2014JA020575
• Neutralizer-free gridded ion thruster
  
  • Rafalskyi D.V.
  • Aanesland Ane
  American Institute of Aeronautics and Astronautics paper, 2014, Propulsion and Energy Forum. (10.2514/6.2014-3423)
  DOI : 10.2514/6.2014-3423
• Planetary Science Virtual Observatory architecture
  
  • Erard S.
  • Cecconi B.
  • Le Sidaner P.
  • Berthier J.
  • Henry F.
  • Chauvin C.
  • André N.
  • Génot V.
  • Jacquey C.
  • Gangloff M.
  • Bourrel N.
  • Schmitt B.
  • Capria M.-Th.
  • Chanteur Gérard
  Astronomy and Computing, Elsevier, 2014, 7-8, pp.71-80. In the framework of the Europlanet-RI program, a prototype of Virtual Observatory dedicated to Planetary Science was defined. Most of the activity was dedicated to the elaboration of standards to retrieve and visualize data in this field, and to provide light procedures to teams who wish to contribute with on-line data services. The architecture of this VO system and selected solutions are presented here, together with existing demonstrators. (10.1016/j.ascom.2014.07.005)
  DOI : 10.1016/j.ascom.2014.07.005
• Rotational/compressional nature of the magnetopause: Application of the BV technique on a magnetopause case study
  
  • Dorville Nicolas
  • Belmont Gérard
  • Rezeau Laurence
  • Grappin Roland
  • Retinò Alessandro
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2014, 119, pp.1898-1908. The magnetopause boundary implies two main kinds of variations: a density/temperature gradient and a magnetic field rotation. Other variations are associated with these two, concerning in particular the flow velocity, the electric field, and the plasma composition. Compressional and rotational variations are always observed in a close vicinity of each other, if not inseparably mixed. We present a case study from the Cluster data where the two are clearly separated and investigate the natures of both layers, using the new BV method for discontinuity analysis. We evidence that the first one is a slow shock while the second is a rotational discontinuity. The interaction between these two kinds of discontinuities is then studied with the help of 1.5-D magnetohydrodynamics simulations. The comparison with the data is quite positive and, associated with general theoretical arguments, leads to think that most of the generic properties of the magnetopause may be interpreted in this sense. Our results suggest that a shaken magnetopause is made of the sum of several discontinuities: slow shocks and rotational discontinuities. A statistical study on a larger set of data will be necessary to check this conjecture. (10.1002/2013JA018927)
  DOI : 10.1002/2013JA018927
• Phase space structures in gyrokinetic simulations of plasma turbulence
  
  • Ghendrih Philippe
  • Norscini C.
  • Cartier-Michaud T.
  • Dif-Pradalier Guilhem
  • Abiteboul J.
  • Dong Yue
  • Garbet X.
  • Gürcan Özgür D.
  • Hennequin Pascale
  • Grandgirard Virginie
  • Latu G.
  • Morel Pierre
  • Sarazin Y.
  • Storelli A.
  • Vermare Laure
  The European Physical Journal D : Atomic, molecular, optical and plasma physics, EDP Sciences, 2014, 68 (10), pp.303. Gyrokinetic simulations of fusion plasmas give extensive information in 5D on turbulence and transport. This paper highlights a few of these challenging physics in global, flux driven simulations using experimental inputs from Tore Supra shot TS45511. The electrostatic gyrokinetic code GYSELA is used for these simulations. The 3D structure of avalanches indicates that these structures propagate radially at localised toroidal angles and then expand along the field line at sound speed to form the filaments. Analysing the poloidal mode structure of the potential fluctuations (at a given toroidal location), one finds that the low modes m = 0 and m = 1 exhibit a global structure; the magnitude of the m = 0 mode is much larger than that of the m = 1 mode. The shear layers of the corrugation structures are thus found to be dominated by the m = 0 contribution, that are comparable to that of the zonal flows. This global mode seems to localise the m = 2 mode but has little effect on the localisation of the higher mode numbers. However when analysing the pulsation of the latter modes one finds that all modes exhibit a similar phase velocity, comparable to the local zonal flow velocity. The consequent dispersion like relation between the modes pulsation and the mode numbers provides a means to measure the zonal flow. Temperature fluctuations and the turbulent heat flux are localised between the corrugation structures. Temperature fluctuations are found to exhibit two scales, small fluctuations that are localised by the corrugation shear layers, and appear to bounce back and forth radially, and large fluctuations, also readily observed on the flux, which are associated to the disruption of the corrugations. The radial ballistic velocity of both avalanche events if of the order of 0.5&#961;&#8727;c0 where &#961;&#8727; = &#961;0/a, a being the tokamak minor radius and &#961;0 being the characteristic Larmor radius, &#961;0 = c0/&#937;0. c0 is the reference ion thermal velocity and &#937;0 = qiB0/mi the reference ion Larmor frequency for the characteristic amplitude of the magnetic field B0, qi and mi being, respectively, the ion charge and mass. The electric drift velocity is also found to exhibit a poloidal pattern, with maximum amplitude of the fluctuations either in the top or in the bottom regions of the machine depending on the sign of the zonal flow shear. This effect is found to be correlated to the stopping capability of the corrugation structures. The neoclassical properties stemming from the trapped particle drifts lead to large distortion of the distribution function. As expected, these prevail at the outer part of the simulation region despite the large collisionality. The distribution function fluctuations appear to be aligned along the v&#8741; = const. lines at constant poloidal angle. A specific symmetry is observed regarding the interplay of turbulence with the trapped-passing region. (10.1140/epjd/e2014-50210-8)
  DOI : 10.1140/epjd/e2014-50210-8
• Kinetic Turbulence in the Terrestrial Magnetosheath: Cluster Observations
  
  • Huang S. Y.
  • Sahraoui Fouad
  • Deng X. H.
  • He J. S.
  • Yuan Z. G.
  • Zhou M.
  • Pang Y.
  • Fu H.S.
  The Astrophysical Journal Letters, Bristol : IOP Publishing, 2014, 789, pp.L28. We present a first statistical study of subproton- and electron-scale turbulence in the terrestrial magnetosheath using waveform data measured by the Cluster/STAFF search coil magnetometer in the frequency range [1, 180] Hz. It is found that clear spectral breaks exist near the electron scale, which separate two power-law-like frequency bands referred to as the dispersive and the electron dissipation ranges. The frequencies of the breaks f<SUB>b</SUB> are shown to be well correlated with the electron gyroscale rho <SUB>e</SUB> rather than with the electron inertial length d<SUB>e</SUB> . The distribution of the slopes below f<SUB>b</SUB> is found to be narrow and peaks near -2.9, while that of the slopes above f<SUB>b</SUB> is found to be broader, peaking near -5.2, with values as low as -7.5. This is the first time that such steep power-law spectra are reported in space plasma turbulence. These observations provide new constraints on theoretical modeling of kinetic turbulence and dissipation in collisionless magnetized plasmas. (10.1088/2041-8205/789/2/L28)
  DOI : 10.1088/2041-8205/789/2/L28