Publications

2016

• The 2π charged particles analyzer: All-sky camera concept and development for space missions
  
  • Vaisberg Oleg
  • Berthelier Jean-Jacques
  • Moore T.
  • Avanov L.
  • Leblanc François
  • Leblanc Frédéric
  • Moiseev Pavel P.
  • Moiseenko D.
  • Becker Joël
  • Collier Michael R.
  • Laky G.
  • Keller J.
  • Koynash G.
  • Lichtenneger H.
  • Leibov A. W.
  • Zhuravlev R.
  • Shestakov A.
  • Burch J.
  • Mccomas D.
  • Shuvalov S.
  • Chornay D.
  • Torkar K.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2016, 121 (12), pp.11,750–11,765. Increasing the temporal resolution and instant coverage of velocity space of space plasma measurements is one of the key issues for experimentalists. Today the top-hat plasma analyzer appears to be the favorite solution due to its relative simplicity and the possibility to extend its application by adding a mass-analysis section and an electrostatic angular scanner. Similarly, great success has been achieved in MMS mission using such multiple top-hat analyzers to achieve unprecedented temporal resolution. An instantaneous angular coverage of charged particles measurements is an alternative approach to pursuing the goal of high time resolution. This was done with FONEMA 4-D and, to a lesser extent, by DYMIO instruments for Mars-96 and with the FIPS instrument for MESSENGER mission. In this paper we describe, along with precursors, a plasma analyzer with a 2π electrostatic mirror that was developed originally for the Phobos-Soil mission with a follow-up in the frame of the BepiColombo mission, and is under development for future Russian missions. Different versions of instrument are discussed along with their advantages and drawbacks. (10.1002/2016JA022568)
  DOI : 10.1002/2016JA022568
• Pressure broadening of atomic oxygen two-photon absorption laser induced fluorescence
  
  • Marinov Daniil
  • Drag Cyril
  • Blondel Christophe
  • Guaitella Olivier
  • Golda Judith
  • Klarenaar Bart
  • Engeln Richard
  • Gathen Volker Schulz-von Der
  • Booth Jean-Paul
  Plasma Sources Science and Technology, IOP Publishing, 2016, 25 (6), pp.06LT03. Atomic oxygen, considered to be a determining reactant in plasma applications at ambient pressure, is routinely detected by two-photon absorption laser induced fluorescence (TALIF). Here, pressure broadening of the (2 p 4 3 P 2 ?????3 p 3 P J =0,1,2 ) two-photon transition in oxygen atoms was investigated using a high-resolution TALIF technique in normal and Doppler-free configurations. The pressure broadening coefficients determined were ##IMG## [http://ej.iop.org/images/0963-0252/25/6/06LT03/psstaa4481ieqn001.gif] γ_\textO_2 ??=??0.40??±??0.08? cm ?1 /bar for oxygen molecules and ##IMG## [http://ej.iop.org/images/0963-0252/25/6/06LT03/psstaa4481ieqn002.gif] γ_\textHe ??=??0.46??±??0.03?cm ?1 /bar for helium atoms. These correspond to pressure broadening rate constants ##IMG## [http://ej.iop.org/images/0963-0252/25/6/06LT03/psstaa4481ieqn003.gif] k_\textPB^\textO_2 ??=??9 · 10 ?9 cm 3 s ?1 and ##IMG## [http://ej.iop.org/images/0963-0252/25/6/06LT03/psstaa4481ieqn004.gif] k_\textPB^\textHe ??=??4 · 10 ?9 cm 3 s ?1 , respectively. The well-known quenching rate constants of O(3 p 3 P J ) by O 2 and He are at least one order of magnitude smaller, which signifies that non-quenching collisions constitute the main line-broadening mechanism. In addition to providing new insights into collisional processes of oxygen atoms in electronically excited 3 p 3 P J state, reported pressure broadening parameters are important for quantification of oxygen TALIF line profiles when both collisional and Doppler broadening mechanisms are important. Thus, the Doppler component (and hence the temperature of oxygen atoms) can be accurately determined from high resolution TALIF measurements in a broad range of conditions. (10.1088/0963-0252/25/6/06LT03)
  DOI : 10.1088/0963-0252/25/6/06LT03
• Controlling the shape of the ion energy distribution at constant ion flux and constant mean ion energy with tailored voltage waveforms
  
  • Bruneau Bastien
  • Lafleur Trevor
  • Booth Jean-Paul
  • Johnson Erik
  Plasma Sources Science and Technology, IOP Publishing, 2016, 25 (2), pp.025006. In this paper, we investigate the excitation of a capacitively coupled plasma using a non-sinusoidal voltage waveform whose amplitude- and slope-asymmetry varies continuously with a period which is a multiple of the fundamental RF period. We call this period the ?beating? period. Through particle-in-cell (PIC) simulations, we show that such waveforms cause oscillation of the self-bias at this beating frequency, corresponding to the charging and discharging of the external capacitor. The amplitude of this self-bias oscillation depends on the beating period, the value of the external capacitor, and the ion flux to the electrodes. This self-bias oscillation causes temporal modulation of the ion flux distribution function (IFDF), albeit at a constant ion flux and constant mean ion energy, and allows the energy width of the IFDF (averaged over the beating period) to be varied in a controlled fashion. (10.1088/0963-0252/25/2/025006)
  DOI : 10.1088/0963-0252/25/2/025006
• Effect of gas properties on the dynamics of the electrical slope asymmetry effect in capacitive plasmas: comparison of Ar, H<SUB>2</SUB> and CF<SUB>4</SUB>
  
  • Bruneau Bastien
  • Lafleur Trevor
  • Gans T.
  • O'Connell D.
  • Greb Arthur
  • Korolov Ihor
  • Derzsi A.
  • Donkó Z.
  • Brandt S.
  • Schüngel E.
  • Schulze J.
  • Diomede P.
  • Economou D. J.
  • Longo S.
  • Johnson E.V.
  • Booth Jean-Paul
  Plasma Sources Science and Technology, IOP Publishing, 2016, 25 (1), pp.01LT02. Tailored voltage excitation waveforms provide an efficient control of the ion energy (through the electrical asymmetry effect) in capacitive plasmas by varying the ?amplitude? asymmetry of the waveform. In this work, the effect of a ?slope? asymmetry of the waveform is investigated by using sawtooth-like waveforms, through which the sheath dynamic can be manipulated. A remarkably different discharge dynamic is found for Ar, H 2 , and CF 4 gases, which is explained by the different dominant electron heating mechanisms and plasma chemistries. In comparison to Argon we find that the electrical asymmetry can even be reversed by using an electronegative gas such as CF 4 . Phase resolved optical emission spectroscopy measurements, probing the spatiotemporal distribution of the excitation rate show excellent agreement with the results of particle-in-cell simulations, confirming the high degree of correlation between the excitation rates with the dominant heating mechanisms in the various gases. It is shown that, depending on the gas used, sawtooth-like voltage waveforms may cause a strong asymmetry. (10.1088/0963-0252/25/1/01LT02)
  DOI : 10.1088/0963-0252/25/1/01LT02
• Electron Acceleration by Langmuir Waves Produced by a Decay Cascade
  
  • Krafft C.
  • Volokitin A. S.
  The Astrophysical Journal, American Astronomical Society, 2016, 821 (2), pp.99. It was recently reported that a significant part of the Langmuir waveforms observed by the STEREO satellite during type III solar radio bursts are likely consistent with the occurrence of electrostatic decay instabilities, when a Langmuir wave L resonantly interacts with another Langmuir wave L <SUP>\prime</SUP> and an ion sound wave S <SUP>\prime</SUP> through the decay channel L \to L <SUP>\prime</SUP> S <SUP>\prime</SUP> . Usually such wave-wave interactions occur in regions of the solar wind where the presence of electron beams can drive Langmuir turbulence to levels allowing waves L to decay. Moreover, such solar wind plasmas can present long-wavelength, randomly fluctuating density inhomogeneities or monotonic density gradients which can significantly modify the development of such resonant instabilities. If some conditions are met, the waves can encounter a second decay cascade (SDC) according to L <SUP>\prime</SUP> \to L <SUP>\prime\prime</SUP> S <SUP>\prime\prime</SUP> . Analytical estimates and observations based on numerical simulations show that the Langmuir waves L <SUP>\prime\prime</SUP> produced by this SDC can accelerate beam particles up to velocities and kinetic energies exceeding two times the beam drift velocity v<SUB>b</SUB> and half the initial beam energy, respectively. Moreover, this process can be particularly efficient if the scattering effects of waves on the background plasma inhomogeneities have already accelerated a sufficient amount of beam electrons up to the velocity range where the phase velocities of the L <SUP>\prime\prime</SUP> waves are lying. The paper shows that the conditions necessary for such process to occur can be easily met in solar wind plasmas if the beam velocities do not exceed around 35 times the plasma thermal velocity. (10.3847/0004-637X/821/2/99)
  DOI : 10.3847/0004-637X/821/2/99
• Diffusion of Energetic Electrons in Turbulent Plasmas of the Solar Wind
  
  • Volokitin A. S.
  • Krafft C.
  The Astrophysical Journal, American Astronomical Society, 2016, 833 (2), pp.166. A method of calculation of the diffusion coefficients D (v) of particles in velocity space, based on the statistical analysis of the motion of a great number of test electrons, is proposed. In the case of Langmuir turbulence developing in plasmas with fluctuating density inhomogeneities such as the solar wind, simulations provide coefficients D (v) which mainly depend on the Langmuir wave spectra and agree well with the analytical predictions D <SUB>th</SUB>(v) of the quasilinear theory of weak turbulence. Nevertheless, some noticeable differences exist with this theory: in the range of phase velocity of the short waves where the main part of the wave energy is concentrated, D (v) is noticeably smaller than D <SUB>th</SUB>(v), due to the scattering, the reflection, and the focusing effects encountered by the Langmuir waves when they interact with the plasma density inhomogeneities. Moreover, the probability of large velocity jumps in the particles' trajectories essentially exceeds the probability of a Gaussian distribution. These large jumps, which are connected with the waves' transformation processes, modify the nature of the particle diffusion, which is no more classical. These higher order effects cause the discrepancies observed with the quasilinear theory, which does not take them into account in its perturbative approach. The solar wind plasmas, which present fluctuating density inhomogeneities of noticeable average levels, are a very good laboratory to study such diffusion processes, which can eventually influence significantly on the development of essential physical phenomena, as electromagnetic radio emissions by type III solar radio bursts, for example. (10.3847/1538-4357/833/2/166)
  DOI : 10.3847/1538-4357/833/2/166