Publications

2011

• 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 cm−1 (5.27 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 K is observed during the early plasma phase of a few milliseconds. After some 10 ms gas temperatures up to 500 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
• 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
• 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 ν∗ 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
• 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
• Two-Temperature Models for Polar Plumes: Cooling by Means of Strong Base Heating
  
  • Grappin Roland
  • Wang Y-M
  • Pantellini F.
  The Astrophysical Journal, American Astronomical Society, 2011, 727 (1), pp.30. In earlier one-fluid hydrodynamical calculations incorporating heat conduction and radiative losses, it was shown that the high densities in polar plumes could be reproduced by including a concentrated heat source near the plume base, in addition to the global heating required in both the plume and interplume regions of the coronal hole. The extra heating (attributed to interchange reconnection between the open flux and an underlying magnetic bipole) results in lower flow speeds and temperatures relative to the interplume gas, predictions that have since been confirmed by spectroscopic measurements. Here, the model is extended to the two-fluid case, in which ions and electrons are allowed to have different temperatures, coupling is via Coulomb collisions, and heat transport is mainly by electrons. Again, we find that depositing energy very close to the coronal base, in either the protons or electrons (or both), raises the densities and decreases the flow speeds everywhere along the flux tube. The higher densities in turn act to lower the ion temperatures by coupling the protons more closely to the energy-losing electrons. In addition, we find that energy must be deposited globally in both the electrons and the ions; without this direct heating, the electrons would end up cooler in the interplume region than in the plume, contrary to observations. Increasing the rate of flux-tube expansion has the effect of lowering the electron and ion temperatures and reducing the asymptotic flow speed, both in the plume and the interplume region; the observed densities and temperatures can be matched by taking the magnetic field to fall off with radius roughly as r 4. (10.1088/0004-637X/727/1/30)
  DOI : 10.1088/0004-637X/727/1/30