Publications

2009

• Polar cap boundary and the reconnection electric field
  
  • Aikio A.
  • Pitkänen T.
  • Kozlovsky A.
  • Amm Olaf
  • Fontaine Dominique
  • Hubert B.
  • Fazakerley A.
  • Tscherning C. C.
  , 2009, 11, pp.9311. Magnetic reconnection on the dayside magnetopause and in the nightside magnetotail are the main factors controlling the solar wind energy transfer into the magnetosphere and the ionosphere. Reconnection on the dayside magnetopause creates open magnetic flux and moves the polar cap boundary in the equatorward direction. Reconnection in the magnetotail, either at the distant neutral line or at the near-Earth neutral line during substorm conditions, closes magnetic field lines and moves the polar cap boundary into the poleward direction. The combined effect of dayside and nightside reconnection determines finally the dynamics of the polar cap boundary. A quantity that is related to changes in the amount of open magnetic flux is the reconnection electric field. In this talk, we will review some of the results obtained by using the EISCAT radar facility and supporting instruments (e.g. the MIRACLE magnetometers, the Cluster satellite, and global UVI imagers on Polar and IMAGE satellites) in estimating the motions of the polar cap boundary and the associated reconnection electric field. We have e.g. shown that the nightside reconnection close to substorm onset consists of a series of short-lived reconnection bursts and that isolated reconnection events may occur during the substorm recovery phase. We will also show, quantitatively for the first time to our knowledge, that intensifications in the local reconnection electric field have one-to-one correlation with the appearance of auroral poleward boundary intensifications (PBIs) within the same MLT location. These PBIs are observed by the Polar UVI instrument.
• Europlanet Integrated and Distributed Information Service
  
  • Schmidt Walter
  • Capria Maria Teresa
  • Chanteur Gérard
  • Tscherning C. C.
  , 2009, 11, pp.9366. During the past decades the various disciplines in planetary sciences have developed to a very high international standard. But the collaboration between the different fields should be improved. To overcome the current fragmentation of the EU Planetary Science community and thereby to increase the scientific return of the related investment, the EU commission is funding via its Framework Program 7 the development of the "Europlanet Research Infrastructure -Europlanet RI". The Europlanet RI will consolidate the integration of the European Planetary Science community which started with Europlanet's FP6 project and will integrate major parts of the related distributed European infrastructure to be shared, fed and expanded by all planetary scientists. This infrastructure encompasses as diverse components as space exploration, ground-based observations, laboratory experiments and numerical modeling teams. Europlanet RI aims at bringing scientists from Europe and beyond together who are working in these fields, support the exchange of experts and ideas and make as many resources and data as possible available to the research community. A central part of Europlanet RI is the "Integrated and Distributed Information Service" or Europlanet-IDIS. The task of IDIS as central part of Europlanet is to provide an easy-to-use Web-based platform to locate teams and laboratories with special knowledge needed to support the own research activities, give access to the wealth of already available data, initiate new research activities needed to interpret accumulated data or to solve open questions, and to exploit synergies between space-based missions and capabilities of ground based observatories. It also offers to a wide range of teams and laboratories the possibility to share their data, advertise their capabilities and increase the scientific return by cooperation. IDIS is organized as an EU FP7 Support Activity, consisting of different access nodes which are connected by integrated search facilities, compatible structures and a common management. Each of these nodes concentrates on a special field of planetary sciences, has its own team of related international experts and is responsible for the access to information and data centres related to its area of competence. Integrated keyword-based search-possibilities direct inquiries to those node(s), most likely to return the wanted information. These nodes are hosted by the following organizations: - The Finnish Meteorological Institute (FMI) in Helsinki, Finland, hosts the Technical Node for a wide range of support activities and provides the network management. - The Institute of Planetary Research (IPR) of DLR in Berlin, Germany, hosts the Planetary Surfaces and Interiors Node, concentrating on internal structure, formation and evolution of the planets, their moons, asteroids and comets. - The Institut für Weltraumforschung, IWF (Space Research Institute) of the Austrian Academy of Sciences (OeAW) in Graz hosts the Planetary Plasma Node in close cooperation with the French space plasma data center CDPP in Toulouse. - The Institut Pierre-Simon Laplace in Paris hosts the Planetary Atmospheres Node. - The Paris Observatory hosts the Virtual Observatory Paris Data Center providing among others access to a wide range of atomic and molecular spectral databases. - The Istituto di Fisica dello Spazio Interplanetario (IFSI) in Rome hosts the Small Bodies and Dust Node, in cooperation with the ESA/ESTECs Virtual Meteor Observatory in Noordwijk, The Netherlands, concentrating on research and observations related to solar system asteroids, comets, meteors and interplanetary dust. During the next four years a set of tools for describing, accessing and combining information and data from different sources will be developed, offering finally a Virtual Observatory like access to many data essential for planetary research from European and None-European sources. Web access via any of the mentioned nodes, e.g. the Technical Node at http://www.europlanet-idis.fi
• MHD wave turbulence, numerical results
  
  • Grappin Roland
  , 2009.
• Titan s plasma wake geometry from RPWS and MAG observations
  
  • Modolo Ronan
  • Canu P.
  • Bertucci C.
  • Rosenqvist L.
  • Kurth W. S.
  • Gurnett D.
  • Dougherty M. K.
  , 2009, 11, pp.EGU2009-5912. Up to now, several tens of Titan flybys have been successfully completed by Cassini and have revealed a highly dynamic structure of the near space environment of Titan. The upstream condition of the plasma flow is expected to affect Titan's induced magnetosphere. The Titan's plasma wake has been investigated using observations from the Radio and Plasma Wave Science (RPWS) instruments (Gurnett et al, 2004) and the dual Magnetometer Technique MAG instruments (Dougherty et al, 2004). Electric field emissions were detected by the RPWS antennas during Cassini passes through Titan's wake. These narrow band emissions are identified as upper hybrid resonance emissions and therefore can provide a density estimate of the Titan's cold plasma. Some of Titan's wake flybys show a very strong asymmetry between the inbound and the outbound pass. Good examples are Ta and Tb flybys (Wahlund et al, 2005). Both flybys have a similar trajectory in Titan Interaction coordinate System (TIIS) and have the same illumination condition but the density profiles present major differences. Some of the Cassini flybys have been set back in the DRAP coordinate system (Neubauer et al, 2006) such that the upstream direction of the magnetic field is fixed, in order to determine the geometry of the plasma wake and study asymmetries. Maps of cold plasma in Titan's environment are presented. Information concerning the geometry of the wake is crucial to estimate accurately the plasma escape.
• Nonstationarity of perpendicular shocks
  
  • Hellinger P.
  • Travnicek P.
  • Lembège Bertrand
  • Savoini Philippe
  , 2009.
• Heavy species kinetics in low-pressure dc pulsed discharges in air
  
  • Pintassilgo C.D.
  • Guaitella Olivier
  • Rousseau Antoine
  Plasma Sources Science and Technology, IOP Publishing, 2009, 18, pp.025005. A time-dependent kinetic model is presented to study low-pressure (133 and 210 Pa) pulsed discharges in air for dc currents ranging from 20 to 80mA with a pulse duration from 0.1 up to 1000 ms. The model provides the temporal evolution of the heavy species along the pulse within this range time, where the coupling between vibrational and chemical kinetics is taken into account. This work shows that the predicted values for NO(X) molecules and O(3P) atoms reproduce well previous measured data for these two species. A systematic analysis is carried out on the interpretation of experimental results. It is observed that the N2(X, v 13) + O → NO(X) + N(4S) and the reverse process NO(X) + N(4S) → N2(X, v ∼ 3) + O have practically the same rates for a pulse duration longer than 10 ms, each of them playing a dominant role in the populations of NO(X), N(4S) and, to a lesser extent, in O(3P) kinetics. Our simulations show that for shorter pulse durations, from 0.1 to 10 ms, NO(X) is produced mainly via the processes N2(A) + O → NO(X) + N(2D) and N(2D) + O2 → NO(X) + O, while the oxygen atoms are created mostly from electron impact dissociation of O2 molecules and by dissociative collisions with N2(A) and N2(B) molecules. (10.1088/0963-0252/18/2/025005)
  DOI : 10.1088/0963-0252/18/2/025005
• Etch process control with a deposition-tolerant planar electrostatic probe
  
  • Booth Jean-Paul
  • Keil D.
  • Thorgrimsson C.
  • Nagai M.
  • Albarede L.
  , 2009.
• Physics of multiple-frequency capacitive discharges
  
  • Chabert Pascal
  • Levif P.
  • Raimbault Jean-Luc
  • Turner M.M.
  • Lieberman M.A.
  , 2009.
• Analysis of energetic efficiency and kinetics of intermediates in the problem of plasma assisted ignition (AIAA-2009-692)
  
  • Aleksandrov N.L.
  • Kindusheva S.V.
  • Kosarev I.N.
  • Starikovskaia Svetlana
  • Starikovskii A.Yu.
  , 2009.
• Capture of solar wind alpha-particles by the Martian atmosphere
  
  • Chanteur Gérard
  • Dubinin E.
  • Modolo Ronan
  • Fraenz M.
  Geophysical Research Letters, American Geophysical Union, 2009, 36 (23), pp.L23105. Integration along He++ test-particle trajectories in the self-consistent electromagnetic fields generated by three-dimensional hybrid simulations of the solar wind/Mars interaction is used to evaluate the removal of solar wind α-particles due to charge-exchange processes with neutral species of the Martian exosphere. The total removal rate of solar wind He++ ions, transformed into either singly ionised or neutral helium, is equal to 6.7 × 1023 s−1, which corresponds approximately to 30% of the flux of solar α-particles through the planetary cross-section. The deposition rate of helium neutral atoms, created by double electronic capture on exospheric oxygen, impacting the exobase, and penetrating below where it can be trapped, is about 1.5 × 1023 s−1. That means an important contribution of the solar wind source to the helium balance of the Martian atmosphere. The implantation of the solar helium into the Martian atmosphere shows an asymmetry related to the orientation of the motional electric field of the solar wind, −VSW × BIMF. (10.1029/2009GL040235)
  DOI : 10.1029/2009GL040235
• What can we learn from HF signal scattered from a discrete arc?
  
  • Seran Elena
  • Godefroy Michel
  • Kauristie K.
  • Cerisier Jean-Claude
  • Berthelier Jean-Jacques
  • Lester M.
  • Sarri L.-E.
  Annales Geophysicae, European Geosciences Union, 2009, 27 (5), pp.1887-1896. We present observations of a discrete southward propagating arc which appeared in the mid-night sector at latitudes equatorward of main substorm activity. The arc observations were made simultaneously by the ALFA (Auroral Light Fine Analysis) optical camera, the SuperDARN-CUTLASS HF radar and the Demeter satellite during a coordinated multi-instrumental campaign conducted at the KEOPS/ESRANGE site in December 2006. The SuperDARN HF signal which is often lost in the regions of strong electron precipitation yields in our case clear backscatter from an isolated arc of weak intensity. Consequently we are able to study arc dynamics, the formation of meso-scale irregularities of the electron density along the arc, compare the arc motion with the convection of surrounding plasma and discuss the contribution of ionospheric ions in the arc erosion and its propagation. (10.5194/angeo-27-1887-2009)
  DOI : 10.5194/angeo-27-1887-2009
• Time resolved quantum cascade laser absorption spectroscopy on NO containing pulsed DC discharges
  
  • Welzel S.
  • Guaitella Olivier
  • Pintassilgo C.D.
  • Rousseau Antoine
  • Roepcke J.
  , 2009.
• A review of new wire arrays with open and closed magnetic configurations at the 1.6 MA Zebra generator for radiative properties and opacity effects
  
  • Kantsyrev Viktor L.
  • Safronova Alla S.
  • Esaulov A. A.
  • Williamson Kenneth M.
  • Shrestha Ishor
  • Yilmaz M. F.
  • Osborne Glenn C.
  • Weller Michael E.
  • Ouart N. D.
  • Shlyaptseva V. V.
  • Rudakov Leonid I.
  • Chuvatin Alexandre S.
  • Velikovich A. L.
  High Energy Density Physics, Elsevier, 2009, 5 (3), pp.115-123. Review The studies emphasize investigation of plasma formation, implosion, and radiation features as a function of two load configurations: compact multi-planar and cylindrical wire arrays. Experiments with different Z-pinch loads were performed on 1.6 MA, 100 ns, Zebra generator at University of Nevada, Reno. The multi-planar wire arrays (PWAs) were studied in open and closed configurations with Al, Cu, brass, Mo and W wires. In the open magnetic configurations (single, double, triple PWAs) magnetic fields are present inside the arrays from the beginning of discharge, while in closed configurations (prism-like PWA) the global magnetic field is excluded inside before plasma flow occurs. The new prism-like PWA allows high flexibility in control of implosion dynamics and precursor formation. The spectral modeling, magneto-hydrodynamic (MHD) and wire ablation dynamic model (WADM) codes were used to describe the plasma evolution and plasma parameters. Experimentally observed electron temperature and density in multiple bright spots reached 1.4 keV and 5 × 10E21 cm−3, respectively. Two types of bright spots were observed. With peak currents up to 1.3 MA opacity effects became more pronounced and led to a limiting of the X-ray yields from compact cylindrical arrays. Despite different magnetic energy to plasma coupling mechanisms early in the implosion a comparison of compact double PWA and cylindrical WA results indicates that during the stagnation stage the same plasma heating mechanism may occur. The double PWA was found to be the best radiator tested at University scale 1 MA generator. It is characterized by a combination of larger yield and power, mm-scale size, and provides the possibility of radiation pulse shaping. Further, the newer configuration, the double PWA with skewed wires, was tested and showed the possibility of a more effective X-ray generation. (10.1016/j.hedp.2009.04.001)
  DOI : 10.1016/j.hedp.2009.04.001
• Turbulence in the TORE SUPRA Tokamak: Measurements and Validation of Nonlinear Simulations
  
  • Casati A.
  • Gerbaud T.
  • Hennequin P.
  • Heuraux Stéphane
  Physical Review Letters, American Physical Society, 2009, 102, pp.165005. Turbulence measurements in TORE SUPRA tokamak plasmas have been quantitatively compared to predictions by nonlinear gyrokinetic simulations. For the first time, numerical results simultaneously match within experimental uncertainty (a) the magnitude of effective heat diffusivity, (b) rms values of density fluctuations, and (c) wave-number spectra in both the directions perpendicular to the magnetic field. Moreover, the nonlinear simulations help to revise as an instrumental effect the apparent experimental evidence of strong turbulence anisotropy at spatial scales of the order of ion-sound Larmor radius.
• FLUCTUATION MEASUREMENTS AND THEIR LINK WITH TRANSPORT ON TORE SUPRA
  
  • Sabot R.
  • Hennequin Pascale
  • Colas L.
  Fusion Science and Technology, Taylor & Francis, 2009, 56 (3), pp.1253-1272. Measurement of turbulence properties provides key insight to understand anomalous transport in magnetic fusion devices. On Tore Supra, scattering diagnostics and reflectometers have been used to measure density fluctuations in the plasma core. A cross-polarization scattering diagnostic was also the first diagnostic to measure the turbulence magnetic fluctuations in a fusion plasma core. This paper presents the principle and the experimental setup of these diagnostics, with chosen results illustrating their capabilities to determine the spatial structure of the turbulence and to assess the link between energy transport and fluctuations. These flexible and complementary measurements made it possible to analyze the confinement and fluctuation scaling laws with non-dimensional parameters, which requires a wide variety of plasma conditions.
• Unveiling the nature of out-of-equilibrium phase transitions in a system with long-range interactions
  
  • Firpo Marie-Christine
  EPL - Europhysics Letters, European Physical Society / EDP Sciences / Società Italiana di Fisica / IOP Publishing, 2009, 88, pp.30010. Recently, there has been some vigorous interest in the out-of-equilibrium quasistationary states (QSSs), with lifetimes diverging with the number N of degrees of freedom, emerging from numerical simulations of the ferromagnetic XY Hamiltonian Mean Field (HMF) starting from some special initial conditions. Phase transitions have been reported between low-energy magnetized QSSs and large-energy unexpected, antiferromagnetic-like, QSSs with low magnetization. This issue is addressed here in the Vlasov N→∞ limit. It is argued that the time-asymptotic states emerging in the Vlasov limit can be related to simple generic time-asymptotic forms for the force field. The proposed picture unveils the nature of the out-of-equilibrium phase transitions reported for the ferromagnetic HMF: this is a bifurcation point connecting an effective integrable Vlasov one-particle time-asymptotic dynamics to a partly ergodic one which means a brutal open-up of the Vlasov one-particle phase space. Illustration is given by investigating the time-asymptotic value of the magnetization at the phase transition, under the assumption of a sufficiently rapid time-asymptotic decay of the transient force field. (10.1209/0295-5075/88/30010)
  DOI : 10.1209/0295-5075/88/30010
• Kelvin-Helmholtz waves at the Earth's magnetopause: Multiscale development and associated reconnection
  
  • Hasegawa H.
  • Retinò Alessandro
  • Vaivads A.
  • Khotyaintsev Y. V.
  • André M.
  • Nakamura T. K. M.
  • Teh W.-L.
  • Sonnerup B. U. Ö.
  • Schwartz S. J.
  • Seki Y.
  • Fujimoto M.
  • Saito Y.
  • Rème H.
  • Canu Patrick
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2009, 114, pp.12207. We examine traversals on 20 November 2001 of the equatorial magnetopause boundary layer simultaneously at 1500 magnetic local time (MLT) by the Geotail spacecraft and at 1900 MLT by the Cluster spacecraft, which detected rolled-up MHD-scale vortices generated by the Kelvin-Helmholtz instability (KHI) under prolonged northward interplanetary magnetic field conditions. Our purpose is to address the excitation process of the KHI, MHD-scale and ion-scale structures of the vortices, and the formation mechanism of the low-latitude boundary layer (LLBL). The observed KH wavelength (>4 × 10<SUP>4</SUP> km) is considerably longer than predicted by the linear theory from the thickness (1000 km) of the dayside velocity shear layer. Our analyses suggest that the KHI excitation is facilitated by combined effects of the formation of the LLBL presumably through high-latitude magnetopause reconnection and compressional magnetosheath fluctuations on the dayside, and that breakup and/or coalescence of the vortices are beginning around 1900 MLT. Current layers of thickness a few times ion inertia length 100 km and of magnetic shear 60° existed at the trailing edges of the vortices. Identified in one such current sheet were signatures of local reconnection: Alfvénic outflow jet within a bifurcated current sheet, nonzero magnetic field component normal to the sheet, and field-aligned beam of accelerated electrons. Because of its incipient nature, however, this reconnection process is unlikely to lead to the observed dusk-flank LLBL. It is thus inferred that the flank LLBL resulted from other mechanisms, namely, diffusion and/or remote reconnection unidentified by Cluster. (10.1029/2009JA014042)
  DOI : 10.1029/2009JA014042
• Dust Detection by the Wave Instrument on STEREO: Nanoparticles Picked up by the Solar Wind?
  
  • Meyer-Vernet N.
  • Maksimovic M.
  • Czechowski A.
  • Mann I. R.
  • Zouganelis I.
  • Goetz K.
  • Kaiser M. L.
  • St. Cyr O. C.
  • Bougeret J.-L.
  • Bale S. D.
  Solar Physics, Springer Verlag, 2009, 256 (1-2), pp.463-474. The STEREO wave instrument (S/WAVES) has detected a very large number of intense voltage pulses. We suggest that these events are produced by impact ionisation of nanoparticles striking the spacecraft at a velocity of the order of magnitude of the solar wind speed. Nanoparticles, which are half-way between micron-sized dust and atomic ions, have such a large charge-to-mass ratio that the electric field induced by the solar wind magnetic field accelerates them very efficiently. Since the voltage produced by dust impacts increases very fast with speed, such nanoparticles produce signals as high as do much larger grains of smaller speeds. The flux of 10-nm radius grains inferred in this way is compatible with the interplanetary dust flux model. The present results may represent the first detection of fast nanoparticles in interplanetary space near Earth orbit. (10.1007/s11207-009-9349-2)
  DOI : 10.1007/s11207-009-9349-2
• Regeneration of adsorbent/catalytic material by a Dielectric Barrier Discharge (DBD)
  
  • Youssef Joseph
  • Bouamra K.
  • Makarov M.
  • Guaitella Olivier
  • Rousseau Antoine
  , 2009.
• Influence of dielectric material on chemistry reactivity in Dielectric Barrier Discharge (DBD)
  
  • Youssef Joseph
  • Bouamra K.
  • Makarov M.
  • Guaitella Olivier
  • Rousseau Antoine
  , 2009.
• Global distribution of whistler-mode chorus waves observed on the THEMIS spacecraft
  
  • Li W.
  • Thorne R. M.
  • Angelopoulos V.
  • Bortnik J.
  • Cully C. M.
  • Ni B.
  • Le Contel Olivier
  • Roux A.
  • Auster U.
  • Magnes W.
  Geophysical Research Letters, American Geophysical Union, 2009, 36, pp.9104. Whistler mode chorus waves are receiving increased scientific attention due to their important roles in both acceleration and loss processes of radiation belt electrons. A new global survey of whistler-mode chorus waves is performed using magnetic field filter bank data from the THEMIS spacecraft with 5 probes in near-equatorial orbits. Our results confirm earlier analyses of the strong dependence of wave amplitudes on geomagnetic activity, confinement of nightside emissions to low magnetic latitudes, and extension of dayside emissions to high latitudes. An important new finding is the strong occurrence rate of chorus on the dayside at L > 7, where moderate dayside chorus is present >10% of the time and can persist even during periods of low geomagnetic activity. (10.1029/2009GL037595)
  DOI : 10.1029/2009GL037595
• Electrostatic solitary waves in current layers: from Cluster observations during a super-substorm to beam experiments at the LAPD
  
  • Pickett J. S.
  • Chen L.-J.
  • Santolík O.
  • Grimald S.
  • Lavraud B.
  • Verkhoglyadova O. P.
  • Tsurutani B. T.
  • Lefebvre B.
  • Fazakerley A.
  • Lakhina G. S.
  • Ghosh S. S.
  • Grison B.
  • Décréau Pierrette
  • Gurnett D. A.
  • Torbert R.
  • Cornilleau-Wehrlin Nicole
  • Dandouras I.
  • Lucek E.
  Nonlinear Processes in Geophysics, European Geosciences Union (EGU), 2009, 16 (3), pp.431-442. Electrostatic Solitary Waves (ESWs) have been observed by several spacecraft in the current layers of Earth's magnetosphere since 1982. ESWs are manifested as isolated pulses (one wave period) in the high time resolution waveform data obtained on these spacecraft. They are thus nonlinear structures generated out of nonlinear instabilities and processes. We report the first observations of ESWs associated with the onset of a super-substorm that occurred on 24 August 2005 while the Cluster spacecraft were located in the magnetotail at around 18-19 R<SUB>E</SUB> and moving northward from the plasma sheet to the lobes. These ESWs were detected in the waveform data of the WBD plasma wave receiver on three of the Cluster spacecraft. The majority of the ESWs were detected about 5 min after the super-substorm onset during which time 1) the PEACE electron instrument detected significant field-aligned electron fluxes from a few 100 eV to 3.5 keV, 2) the EDI instrument detected bursts of field-aligned electron currents, 3) the FGM instrument detected substantial magnetic fluctuations and the presence of Alfvén waves, 4) the STAFF experiment detected broadband electric and magnetic waves, ion cyclotron waves and whistler mode waves, and 5) CIS detected nearly comparable densities of H and O ions and a large tailward H velocity. We compare the characteristics of the ESWs observed during this event to those created in the laboratory at the University of California-Los Angeles Plasma Device (LAPD) with an electron beam. We find that the time durations of both space and LAPD ESWs are only slightly larger than the respective local electron plasma periods, indicating that electron, and not ion, dynamics are responsible for generation of the ESWs. We have discussed possible mechanisms for generating the ESWs in space, including the beam and kinetic Buneman type instabilities and the acoustic instabilities. Future studies will examine these mechanisms in more detail using the space measurements as inputs to models, and better relate the ESW space measurements to the laboratory through PIC code models. (10.5194/npg-16-431-2009)
  DOI : 10.5194/npg-16-431-2009
• Influence of dielectric material in Dielectric Barrier Discharge (DBD) for chemistry reactivity control
  
  • Youssef Joseph
  • Bouamra K.
  • Makarov M.
  • Guaitella Olivier
  • Rousseau Antoine
  , 2009.
• Oblique propagation of whistler mode waves in the chorus source region
  
  • Santolík O.
  • Gurnett D. A.
  • Pickett J. S.
  • Chum J.
  • Cornilleau-Wehrlin Nicole
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2009, 114. Whistler mode chorus has been shown to play a role in the process of local acceleration of electrons in the outer Van Allen radiation belt. Most of the quasi-linear and nonlinear theoretical studies assume that the waves propagate parallel to the terrestrial magnetic field. We show a case where this assumption is invalid. We use data from the Cluster spacecraft to characterize propagation and spectral properties of chorus. The recorded high-resolution waveforms show that chorus in the source region can be formed by a succession of discrete wave packets with decreasing frequency that sometimes change into shapeless hiss. These changes occur at the same time in the entire source region. Multicomponent measurements show that waves in both these regimes can be found at large angles to the terrestrial magnetic field. The hiss intervals contain waves propagating less than one tenth of a degree from the resonance cone. In the regime of discrete wave packets the peak of the wave energy density is found at a few degrees from the resonance cone in a broad interval of azimuth angles. The wave intensity increases with the distance from the magnetic field minimum along a given field line, indicating a gradual amplification of chorus in the source region. (10.1029/2009JA014586)
  DOI : 10.1029/2009JA014586
• Self synchronization of surface discharges in a two electrodes device
  
  • Allegraud Katia
  • Rousseau Antoine
  IEEE Transactions on Dielectrics and Electrical Insulation, Institute of Electrical and Electronics Engineers, 2009, 16 (2), pp.435-439. A twin electrode device coupled to the same high voltage power supply is used to study the propagation of surface streamers. These two identical electrodes are separated from the grounded one by a pyrex plate acting as a dielectric barrier. The gas is dry air, at atmospheric pressure. 1 ns time resolved imaging of the discharge propagation is performed to monitor the discharge ignition and propagation. The discharge consists in filaments which propagate on the dielectric as cathode directed streamers. Each filament transfers 1 nC. The propagation velocities vary from 3.4times107 cm/s at the beginning of the propagation to 7times106 cm/s at the end of the propagation. Ignition at one electrode triggers ignition at the other within 2 ns. (10.1109/TDEI.2009.4815175)
  DOI : 10.1109/TDEI.2009.4815175