Publications

2011

• Polar cap ion beams during periods of northward IMF: Cluster statistical results
  
  • Maggiolo R.
  • Echim M.
  • de Keyser J.
  • Fontaine Dominique
  • Jacquey C.
  • Dandouras I.
  Annales Geophysicae, European Geosciences Union, 2011, 29, pp.771-787. Above the polar caps and during prolonged periods of northward IMF, the Cluster satellites detect upward accelerated ion beams with energies up to a few keV. They are associated with converging electric field structures indicating that the acceleration is caused by a quasi-static field-aligned electric field that can extend to altitudes higher than 7 R<SUB>E</SUB> (Maggiolo et al., 2006; Teste et al., 2007). Using the AMDA science analysis service provided by the Centre de Données de la Physique des Plasmas, we have been able to extract about 200 events of accelerated upgoing ion beams above the polar caps from the Cluster database. Most of these observations are taken at altitudes lower than 7 R<SUB>E</SUB> and in the Northern Hemisphere. We investigate the statistical properties of these ion beams. We analyze their geometry, the properties of the plasma populations and of the electric field inside and around the beams, as well as their dependence on solar wind and IMF conditions. We show that ~40 % of the ion beams are collocated with a relatively hot and isotropic plasma population. The density and temperature of the isotropic population are highly variable but suggest that this plasma originates from the plasma sheet. The ion beam properties do not change significantly when the isotropic, hot background population is present. Furthermore, during one single polar cap crossing by Cluster it is possible to detect upgoing ion beams both with and without an accompanying isotropic component. The analysis of the variation of the IMF B<SUB>Z</SUB> component prior to the detection of the beams indicates that the delay between a northward/southward turning of IMF and the appearance/disappearance of the beams is respectively ~2 h and 20 min. The observed electrodynamic characteristics of high altitude polar cap ion beams suggest that they are closely connected to polar cap auroral arcs. We discuss the implications of these Cluster observations above the polar cap on the magnetospheric dynamics and configuration during prolonged periods of northward IMF. (10.5194/angeo-29-771-2011)
  DOI : 10.5194/angeo-29-771-2011
• Role of charge photodesorption in self-synchronized breakdown of surface streamers in air at atmospheric pressure
  
  • Guaitella Olivier
  • Marinov Ilya
  • Rousseau Antoine
  Applied Physics Letters, American Institute of Physics, 2011, 98, pp.071502. A surface dielectric barrier discharge configuration with two identical high voltage electrodes is investigated in air at atmospheric pressure. Synchronized breakdown of streamers on both electrodes is evidenced by statistical study. The light emitted by plasma filament on one electrode can trigger the breakdown of streamers on the other electrode. The role of photodesorption of negative charges deposited on the Pyrex dielectric barrier is responsible for these self-synchronized breakdowns. The binding energy of negative charges photodesorbed is estimated to be lower than 3.5 eV. (10.1063/1.3552965)
  DOI : 10.1063/1.3552965
• NO kinetics in pulsed low-pressure plasmas studied by time-resolved quantum cascade laser absorption spectroscopy
  
  • Welzel S.
  • Guaitella Olivier
  • Lazzaroni Claudia
  • Pintassilgo C.D.
  • Rousseau Antoine
  • Röpcke J.
  Plasma Sources Science and Technology, IOP Publishing, 2011, 20, pp.015020. Time-resolved quantum cascade laser absorption spectroscopy at 1897&#8201;cm&#8722;1 (5.27&#8201;µm) has been applied to study the NO(X) kinetics on the micro- and millisecond time scale in pulsed low-pressure N2/NO dc discharges. Experiments have been performed under flowing and static gas conditions to infer the gas temperature increase and the consequences for the NO line strength. A relatively small increase of ~20&#8201;K is observed during the early plasma phase of a few milliseconds. After some 10&#8201;ms gas temperatures up to 500&#8201;K can be deduced. The experimental data for the NO mixing ratio were compared with the results from a recently developed time-dependent model for pulsed N2O2 plasmas which are well in accord. The early plasma pulse is determined by vibrational heating of N2 while the excitation of NO(X) by N2 metastables is almost completely balanced. Efficient NO depletion occurs after several milliseconds by N atom impact. (10.1088/0963-0252/20/1/015020)
  DOI : 10.1088/0963-0252/20/1/015020
• Impact of collisionality on fluctuation characteristics of micro-turbulence
  
  • Vermare Laure
  • Hennequin Pascale
  • Gürcan Özgür D.
  • Bourdelle C.
  • Clairet F.
  • Garbet X.
  • Sabot R.
  • Tore Supra Team
  Physics of Plasmas, American Institute of Physics, 2011, 18, pp.012306. The influence of changing collisionality on density fluctuation characteristics is studied during dedicated &#957;&#8727; scaling experiments, using Doppler backscattering system. First, the repartition of fluctuation energy over different spatial scales, as represented by the wavenumber spectrum, is investigated and a modification of the shape of the perpendicular wavenumber spectrum in the low wavenumber part of the spectrum is observed when changing collisionality. In addition, a new procedure to evaluate the dispersion relation of micro-turbulence is presented. From the behavior of the perpendicular mean velocity of density fluctuations with the perpendicular wavenumber, different dispersion relations are obtained between low and high collisionality cases. (10.1063/1.3536648)
  DOI : 10.1063/1.3536648
• AC magnetic field measurements onboard Cross-Scale: scientific objectives and instrument design
  
  • Dudok de Wit Thierry
  • Coillot Christophe
  • Jannet Guillaume
  • Krasnoselskikh V.
  • Kretzschmar Matthieu
  • Pinçon Jean-Louis
  • Sahraoui Fouad
  Planetary and Space Science, Elsevier, 2011, 59 (7), pp.580-584. The ACB search-coil magnetometer for Cross-Scale will measure three components of the AC magnetic field up to 4 kHz, and one component up to 100 kHz. Turbulent and coherent magnetic field fluctuations in that frequency range play an important role in the acceleration, scattering, and thermalisation of particles. ACB will, together with the other instruments of the Cross-Scale wave consortium, allow to address the key science objectives associated with plasma waves. Here, we list some of the important issues, based on the experience drawn from Cluster, and describe the instrument. (10.1016/j.pss.2010.04.022)
  DOI : 10.1016/j.pss.2010.04.022
• Different regimes of MHD turbulence with mean magnetic field
  
  • Grappin Roland
  , 2011.
• Observations and modeling of forward and reflected chorus waves captured by THEMIS
  
  • Agapitov O
  • Krasnoselskikh V
  • Zaliznyak Yu
  • Angelopoulos V
  • Le Contel Olivier
  • Rolland G
  Annales Geophysicae, European Geosciences Union, 2011, 29, pp.541-550. Discrete ELF/VLF chorus emissions are the most intense electromagnetic plasma waves observed in the radiation belts of the Earth's magnetosphere. Chorus emissions, whistler-mode wave packets propagating roughly along magnetic field lines from a well-localized source in the vicinity of the magnetic equator to polar regions, can be reflected at low altitudes. After reflection, wave packets can return to the equatorial plane region. Understanding of whistler wave propagation and reflection is critical to a correct description of wave-particle interaction in the radiation belts. We focus on properties of reflected chorus emissions observed by the THEMIS (Time History of Events and Macroscale Interactions During Substorms) spacecraft Search Coil Magnetome-ter (SCM) and Electric Field Instrument (EFI) at ELF/VLF frequencies up to 4 kHz at L ≥ 8. We determine the direction of the Poynting flux and wave vector distribution for forward and reflected chorus waves. Although both types of chorus waves were detected near the magnetic equator and have similar , discrete structure and rising tones, reflected waves are attenuated by a factor of 10–30 and have 10% higher frequency than concurrently-observed forward waves. Model-ing of wave propagation and reflection using geometrical optics ray-tracing allowed us to determine the chorus source region location and explain observed propagation characteristics. We find that reflected wave attenuation at a certain spatial region is caused by divergence of the ray paths of these non-ducted emissions, and that the frequency shift is caused by generation of the reflected waves at lower L-shells where the local equatorial gyrofrequency is larger. (10.5194/angeo-29-541-2011)
  DOI : 10.5194/angeo-29-541-2011