Publications

2012

• Study of a fast gas heating in a capillary nanosecond discharge. Discharge parameters and temperature increase in the afterglow
  
  • Klochko A.V.
  • Popov N.A.
  • Starikovskaia Svetlana
  , 2012.
• Shadowgraphic and optical emission spectroscopy investigation of nanosecond discharge in water
  
  • Marinov Ilya
  • Guaitella Olivier
  • Rousseau Antoine
  • Starikovskaia Svetlana
  , 2012.
• Time-resolved electric field measurements in 1-5 atm nanosecond surface dielectric discharge. Ignition of combustible mixtures by surface discharge
  
  • Kosarev I.N.
  • Sagulenko P.N.
  • Khorunzhenko V.I.
  • Popov N.A.
  • Starikovskaia Svetlana
  , 2012.
• Absolute Cl and Cl<SUB>2</SUB> densities in a Cl<SUB>2</SUB> ICP determined by TALIF with a new calibration method
  
  • Booth Jean-Paul
  • Sirse Nishant
  • Azamoum Yasmina
  • Chabert Pascal
  , 2012.
• Effect of sheared flow on the growth rate and turbulence decorrelation
  
  • Gürcan Özgür D.
  Physical Review Letters, American Physical Society, 2012, 109, pp.155006. The effect of a large scale flow shear on a linearly unstable turbulent system is considered. A cubic equation describing the effective growth rate is obtained, which is shown to reduce to well-known forms in weak and strong shear limits. A shear suppression rule is derived which corresponds to the point where the effective growth rate becomes negative. The effect of flow shear on nonlinear mode coupling of drift or Rossby waves is also considered, and it is shown that the resonance manifold shrinks and weakens as the vortices are sheared. This leads to a reduction of the efficiency of three-wave interactions. Tilted eddies can then only couple to the large scale sheared flows, because the resonance condition for that interaction is trivially satisfied. It is argued that this leads to absorbtion of the sheared vortices by large scale flow structures. Studying the form of the effective growth rate for weak shear, it was shown that in addition to reducing the overall growth rate, a weak flow shear also reduces the wave number where the fluctuations are most unstable. (10.1103/PhysRevLett.109.155006)
  DOI : 10.1103/PhysRevLett.109.155006
• A global hybrid model for Mercury's interaction with the solar wind: Case study of the dipole representation
  
  • Richer Emilie
  • Modolo Ronan
  • Chanteur Gérard
  • Hess Sebastien
  • Leblanc François
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2012, 117 (A10), pp.A10228. The interaction of the solar wind (SW) with the magnetic field of Mercury is investigated by means of a three dimensional parallelized multispecies hybrid model. A comparison between two mathematical representations of Mercury's intrinsic magnetic field is studied. The first model is an Offset Dipole (OD) having the offset and dipolar moment reported by Anderson et al. (2011). The second model is a combination of a Dipole and a Quadrupole (DQ), the total field is fitted to the offset dipolar field, for northern latitudes greater than 50°. Simulations reproduce the features which characterize Mercury's interaction with the SW, encompassing the Bow Shock (BS), the magnetosheath, the magnetotail, the "cusps" region and the neutral current sheet. Global hybrid simulations of the Hermean magnetosphere run for the OD and DQ models demonstrate that the southern parts of the magnetospheres produced by the OD and DQ models differ greatly in topology and volume meanwhile their northern parts-are quite similar. In particular the DQ model exhibits a dome of closed field lines around the south pole in contrast to the OD. Without further information on the intrinsic magnetic field of the planet in the southern region which should be provided by BepiColombo after year 2020, we can only speculate on the influence of the different magnetic topologies on the magnetospheric dynamics. (10.1029/2012JA017898)
  DOI : 10.1029/2012JA017898
• Source location of falling tone chorus
  
  • Kurita S.
  • Misawa H.
  • Cully C. M.
  • Le Contel Olivier
  • Angelopoulos V.
  Geophysical Research Letters, American Geophysical Union, 2012, 39, pp.22102. Chorus is characterized by its fine structures consisting of rising or falling tones believed to result from nonlinear wave-particle interactions. However, previous studies have showed that the intensity and propagation characteristics of rising and falling tone chorus are quite different, suggesting that their generation processes might be different. In this paper, the propagation direction of falling tone chorus is statistically investigated to identify its source region based on the Poynting vector measurement with THEMIS. The result shows that the falling tone chorus propagates from the magnetic equator to higher latitude both in the northern and southern hemispheres, in the same way as rising tone chorus. Our result shows that the magnetic equator is the common source location for both rising and falling tone chorus. The result emphasizes that the different properties between rising and falling tone chorus originate from their generation mechanism rather than source region. (10.1029/2012GL053929)
  DOI : 10.1029/2012GL053929
• Detection of Small-Scale Structures in the Dissipation Regime of Solar-Wind Turbulence
  
  • Perri S.
  • Goldstein M. L.
  • Dorelli J. C.
  • Sahraoui Fouad
  Physical Review Letters, American Physical Society, 2012, 109 (19), pp.191101. Recent observations of the solar wind have pointed out the existence of a cascade of magnetic energy from the scale of the proton Larmor radius &#961;p down to the electron Larmor radius &#961;e scale. In this Letter we study the spatial properties of magnetic field fluctuations in the solar wind and find that at small scales the magnetic field does not resemble a sea of homogeneous fluctuations, but rather a two-dimensional plane containing thin current sheets and discontinuities with spatial sizes ranging from l&#8819;&#961;p down to &#961;e and below. These isolated structures may be manifestations of intermittency that localize sites of turbulent dissipation. Studying the relationship between turbulent dissipation, reconnection, and intermittency is crucial for understanding the dynamics of laboratory and astrophysical plasmas. (10.1103/PhysRevLett.109.191101)
  DOI : 10.1103/PhysRevLett.109.191101
• Coronal heating in coupled photosphere-chromosphere-coronal systems: turbulence and leakage
  
  • Verdini Andrea
  • Grappin Roland
  • Velli Marco
  Astronomy & Astrophysics - A&A, EDP Sciences, 2012, 538, pp.70. Context. Coronal loops act as resonant cavities for low-frequency fluctuations that are transmitted from the deeper layers of the solar atmosphere. These fluctuations are amplified in the corona and lead to the development of turbulence that in turn is able to dissipate the accumulated energy, thus heating the corona. However, trapping is not perfect, because some energy leaks down to the chromosphere on a long timescale, limiting the turbulent heating. Aims. We consider the combined effects of turbulence and energy leakage from the corona to the photosphere in determining the turbulent energy level and associated heating rate in models of coronal loops, which include the chromosphere and transition region. Methods. We use a piece-wise constant model for the Alfvén speed in loops and a reduced MHD-shell model to describe the interplay between turbulent dynamics in the direction perpendicular to the mean field and propagation along the field. Turbulence is sustained by incoming fluctuations that are equivalent, in the line-tied case, to forcing by the photospheric shear flows. While varying the turbulence strength, we systematically compare the average coronal energy level and dissipation in three models with increasing complexity: the classical closed model, the open corona, and the open corona including chromosphere (or three-layer model), with the last two models allowing energy leakage. Results. We find that (i) leakage always plays a role. Even for strong turbulence, the dissipation time never becomes much lower than the leakage time, at least in the three-layer model; therefore, both the energy and the dissipation levels are systematically lower than in the line-tied model; (ii) in all models, the energy level is close to the resonant prediction, i.e., assuming an effective turbulent correlation time longer than the Alfvén coronal crossing time; (iii) the heating rate is close to the value given by the ratio of photospheric energy divided by the Alfvén crossing time; (iv) the coronal spectral range is divided in two: an inertial range with 5/3 spectral slope, and a large-scale peak where nonlinear couplings are inhibited by trapped resonant modes; (v) in the realistic three-layer model, the two-component spectrum leads to a global decrease in damping equal to Kolmogorov damping reduced by a factor urms/Vac where Vac is the coronal Alfvén speed. (10.1051/0004-6361/201118046)
  DOI : 10.1051/0004-6361/201118046
• Analysis of symmetry breaking mechanisms and the role of turbulence self-regulation in intrinsic rotation
  
  • Kwon J.M.
  • Yi Sukyoung
  • Rhee T.
  • Diamond P.H.
  • Miki K.
  • Hahm T.S.
  • Kim J.Y.
  • Gürcan Özgür D.
  • Mcdevitt C.J.
  Nuclear Fusion, IOP Publishing, 2012, 52, pp.013004. We present analyses of mechanisms which convert radial inhomogeneity to broken k||-symmetry and thus produce turbulence driven intrinsic rotation in tokamak plasmas. By performing gyrokinetic simulations of ITG turbulence, we explore the many origins of broken k||-symmetry in the fluctuation spectrum and identify both E × B shear and the radial gradient of turbulence intensitya ubiquitous radial inhomogeneity in tokamak plasmasas important k||-symmetry breaking mechanisms. By studying and comparing the correlations between residual stress, E × B shearing, fluctuation intensity and its radial gradient, we investigate the dynamics of residual stress generation by various symmetry breaking mechanisms and explore the implication of the self-regulating dynamics of fluctuation intensity and E × B shearing for intrinsic rotation generation. Several scalings for intrinsic rotation are reported and are linked to investigations of underlying local dynamics. It is found that stronger intrinsic rotation is generated for higher values of ion temperature gradient, safety factor and weaker magnetic shear. These trends are broadly consistent with the intrinsic rotation scaling found from experimentthe so-called Rice scaling. (10.1088/0029-5515/52/1/013004)
  DOI : 10.1088/0029-5515/52/1/013004
• A dc-pulsed capacitively coupled planar Langmuir probe for plasma process diagnostics and monitoring
  
  • Samara V.
  • Booth Jean-Paul
  • de Marneffe J.-F.
  • Milenin A.P.
  • Brouri M.
  • Boullart W.
  Plasma Sources Science and Technology, IOP Publishing, 2012, 21, pp.065004. An improvement to the RF-biased planar Langmuir probe technique proposed by Braithwaite et al (1996 Plasma Sources Sci. Technol. 5 67) is demonstrated, and applied to the case of an industrial CCP reactor. Compared with the RF-biased probe, the new technique uses dc pulses instead of RF bursts, which provides similar results but with simpler electronics. The ion fluxes determined by both techniques are compared under the same O2/Ar plasma conditions using available literature data for the RF-biased case. The data show not only the same trends but very close absolute values of ion fluxes for all studied plasma conditions after correcting for the chamber-area difference. Furthermore, the new technique has the additional benefit of providing information on the 'electron transition region' of the IV curve, as well as allowing the resistance and capacitance of films deposited on the probe to be determined. Finally, both experimental data and numerical simulations of the IV characteristics and the film parameters are presented for different oxidizing plasmas. (10.1088/0963-0252/21/6/065004)
  DOI : 10.1088/0963-0252/21/6/065004
• Enhanced sheath heating in capacitively coupled discharges due to non-sinusoidal voltage waveforms
  
  • Lafleur Trevor
  • Boswell R.W.
  • Booth Jean-Paul
  Applied Physics Letters, American Institute of Physics, 2012, 100, pp.194101. Through the use of particle-in-cell simulations, we demonstrate that the power deposition in capacitively coupled discharges (in argon) can be increased by replacing sinusoidal waveforms with Gaussian-shaped voltage pulses (with a repetition frequency of 13.56 MHz). By changing the Gaussian pulse width, electron heating can be directly controlled, allowing for an increased plasma density and ion flux for the same gas pressure and geometrical operating conditions. Analysis of the power deposition profiles and electron distribution functions shows that enhanced electron-sheath heating is responsible for the increased power absorption. (10.1063/1.4712128)
  DOI : 10.1063/1.4712128
• Separate control of the ion flux and ion energy in capacitively coupled rf discharges using voltage waveform tailoring
  
  • Lafleur Trevor
  • Delattre Pierre-Alexandre
  • Johnson E.V.
  • Booth Jean-Paul
  Applied Physics Letters, American Institute of Physics, 2012, 101, pp.124104. We experimentally characterize an argon plasma in a geometrically symmetric, capacitively coupled rf discharge, excited by pulse-type tailored waveforms (generated using multiple voltage harmonics). The results confirm a number of predictions made by recent particle-in-cell simulations of a similar system and demonstrate a unique form of control over the ion flux and ion energy in capacitively coupled plasmas; by increasing the number of applied harmonics (equivalent to decreasing the pulse width), it is possible to increase the plasma density and ion flux (together with the power deposition) while keeping the average ion energy on one of the electrodes low and constant. (10.1063/1.4754692)
  DOI : 10.1063/1.4754692
• Absolute atomic chlorine densities in a Cl<SUB>2</SUB> ICP determined by Two-Photon Laser Induced Fluorescence with a new calibration method
  
  • Booth Jean-Paul
  • Azamoum Yasmina
  • Sirse Nishant
  • Chabert Pascal
  Journal of Physics D: Applied Physics, IOP Publishing, 2012, 45, pp.195201. Absolute densities of chlorine atoms were determined in an inductively coupled plasma in pure chlorine gas as a function of gas pressure and RF power by two-photon laser-induced fluorescence. A new technique is proposed to put the relative two-photon laser-induced fluorescence (TALIF) measurements on an absolute scale, based on photolysis of Cl2 gas (without plasma) with a tripled Nd&#8201;:&#8201;YAG laser at 355 nm. Because the dissociation cross-section and photo-dissociation laser beam energy density are well known, the absolute densities can be determined with high accuracy. We find that the ratio of the Cl atom density normalized to the Cl2 gas density without plasma at the reactor centre increases with RF power and decreases with gas pressure, reaching 20% at 2 mTorr 500 WRF. (10.1088/0022-3727/45/19/195201)
  DOI : 10.1088/0022-3727/45/19/195201
• Analysis of radiation from silver HED plasma sources with the potential for lasing
  
  • Weller Michael E.
  • Safronova Alla S.
  • Kantsyrev Viktor L.
  • Esaulov A. A.
  • Stafford A.
  • Shrestha Ishor
  • Osborne Glenn C.
  • Shlyaptseva V. V.
  • Keim S. F.
  • Zunino H. A.
  • Chuvatin Alexandre S.
  • Apruzese J. P.
  • Golovkin I. E.
  • Macfarlane J. J.
  , 2012, pp.2P78. Silver (Ag) high energy density plasmas were produced using uniform and combined single planar wire array (SPWA) z-pinches. Ag SPWAs were recently introduced as an efficient x-ray radiator and have shown to create L-shell plasmas that have the highest electron temperature (>;1.8 keV) observed on Zebra so far and upwards of 30 kJ of energy output, which is of interest for future applications of inertial confinement fusion1. A set of diagnostics included fast, filtered x-ray diodes; a Ni bolometer; laser shadowgraphy and optical streak cameras; time-gated and time-integrated x-ray pinhole cameras; and time-integrated spatially resolved (TISR) and time-gated spatially-integrated (TGSI) x-ray spectrometers. In particular, a new time-gated hard x-ray spectrometer was fielded to attain first results to understand how Ag plasmas evolve in time. In addition, an important question about such Ag plasmas is whether lasing occurs in the Na-like and Ne-like soft x-ray range, and if so, at what gains? Our suite of theoretical diagnostics was expanded with HELIOS-CR code, that was utilized to study implosion characterisitcs and radiative characteristics of Ag wire arrays as well as to calculate possible lasing gains. Lastly, the results of new experiments on Zebra with the load current multiplier (LCM) at enhanced current of 1.5 - 1.7 MA were analyzed and compared to those of standard configurations. (10.1109/PLASMA.2012.6383634)
  DOI : 10.1109/PLASMA.2012.6383634
• Velocity diffusion in plasma waves excited by electron beams
  
  • Volokitin A.
  • Krafft C.
  Plasma Physics and Controlled Fusion, IOP Publishing, 2012, 54, pp.085002. New results provided by numerical simulations of the weak instability of a warm electron beam in a collisionless plasma are presented. The theoretical model considers the self-consistent resonant interactions of beam particles with wave packets of broad spectra; it is derived using some of the initial approximations of the standard derivation of the quasilinear diffusion equation in the weak turbulence approach, without, however, the assumption of randomly phased waves. A huge number of particle trajectories calculated over long times by a symplectic code are analyzed using various statistical algorithms. The dynamics of the beam relaxation and the saturation of the wave spectrum are studied and compared with the analytical solutions provided by the quasilinear theory of weak turbulence. The most interesting results concern the presence of strong and persistent irregularities in the wave energy spectrum at saturation, which are linked to large velocity variations observed in the particles' dynamics and to non-Gaussian local diffusion. Quantitative estimates of the diffusion coefficients are given and compared with predictions of the weak turbulence theory. (10.1088/0741-3335/54/8/085002)
  DOI : 10.1088/0741-3335/54/8/085002
• THEMIS observation of chorus elements without a gap at half the gyrofrequency
  
  • Kurita S.
  • Katoh Y.
  • Omura Y.
  • Angelopoulos V.
  • Cully C. M.
  • Le Contel Olivier
  • Misawa H.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2012, 117, pp.11223. Using waveform data obtained by one of the THEMIS satellites, we report properties of rising tone chorus elements without a gap at half the gyrofrequency in a region close to the magnetic equator. The wave normal angle of the chorus elements is typically field-aligned in the entire frequency range of both upper-band and lower-band chorus emissions. We find that the observed frequency sweep rates are consistent with the estimation based on the nonlinear wave growth theory of Omura et al. (2008). In addition, we compare the frequency profiles of the chorus wave amplitudes with those of the optimum and threshold wave amplitudes derived from the nonlinear wave growth theory for triggering rising tone chorus emissions. The results of the comparison show a reasonable agreement, indicating that rising tone chorus elements are continually generated through a triggering process which generates elements with the optimum amplitudes for nonlinear growth. (10.1029/2012JA018076)
  DOI : 10.1029/2012JA018076
• Centrifugally stimulated exospheric ion escape at Mercury
  
  • Delcourt Dominique C.
  • Seki K.
  • Terada N.
  • Moore T. E.
  Geophysical Research Letters, American Geophysical Union, 2012, 39, pp.22105. We investigate the transport of ions in the low-altitude magnetosphere of Mercury. We show that, because of small spatial scales, the centrifugal effect due to curvature of the E × B drift paths can lead to significant particle energization in the parallel direction. We demonstrate that because of this effect, ions with initial speed smaller than the escape speed such as those produced via thermal desorption can overcome gravity and escape into the magnetosphere. The escape route of this low-energy exosphere originating material is largely controlled by the magnetospheric convection rate. This escape route spreads over a narrower range of altitudes when the convection rate increases. Bulk transport of low-energy planetary material thus occurs within a limited region of space once moderate magnetospheric convection is established. These results suggest that, via release of material otherwise gravitationally trapped, the E × B related centrifugal acceleration is an important mechanism for the net supply of plasma to the magnetosphere of Mercury. (10.1029/2012GL054085)
  DOI : 10.1029/2012GL054085
• Dynamics of neutral gas depletion investigated by time- and space-resolved measurement of xenon atom ground state density
  
  • Liard Laurent
  • Aanesland Ane
  • Chabert Pascal
  Journal of Physics D: Applied Physics, IOP Publishing, 2012, 45, pp.235201. The dynamics of neutral gas depletion in high-density plasmas is investigated by time- and space-resolved measurements of the xenon ground state density. Two-photon absorbed laser induced fluorescence experiments were carried out in a helicon reactor operating at 10 mTorr in xenon gas. When the plasma is magnetized, a plasma column is formed from the bottom of the chamber up to the pumping region. In this situation it is found that two phenomena, with different time scales, are responsible for the neutral gas depletion. The magnetized plasma column is ignited in a short (millisecond) time scale leading to a neutral gas depletion at the discharge centre and to an increase of neutral gas density at the reactor walls. This is explained both by neutral gas heating and by the rise of the plasma pressure at the discharge centre. Then, on a much longer (second) time scale, the overall neutral gas density in the reactor decreases due to higher pumping efficiency when the magnetized plasma column is ignited. The pumping enhancement is not observed when the plasma is not magnetized, probably because in this case the dense plasma column vanishes and the plasma is more localized near the antenna. (10.1088/0022-3727/45/23/235201)
  DOI : 10.1088/0022-3727/45/23/235201
• Electron energy distribution function and plasma parameters across magnetic filters
  
  • Aanesland Ane
  • Bredin Jérôme
  • Chabert Pascal
  • Godyak V.
  Applied Physics Letters, American Institute of Physics, 2012, 100, pp.044102. The electron energy distribution function (EEDF) is measured across a magnetic filter in inductively coupled plasmas. The measured EEDFs are found to be Maxwellian in the elastic energy range with the corresponding electron temperature monotonously decreasing along the positive gradient of the magnetic field. At the maximum of the magnetic field, the electron temperature reaches its minimum and remains nearly constant in the area of the negative gradient of the field, where the plasma density distribution exhibits a local minimum. (10.1063/1.3680088)
  DOI : 10.1063/1.3680088
• An electromagnetic theory of turbulence driven poloidal rotation
  
  • Mcdevitt C.J.
  • Gürcan Özgür D.
  Physics of Plasmas, American Institute of Physics, 2012, 19, pp.102311. An electromagnetic theory of turbulence driven poloidal rotation is developed with particular emphasis on understanding poloidal rotation in finite-&#946; plasmas. A relation linking the flux of polarization charge to the divergence of the total turbulent stress is derived for electromagnetic gyrokinetic modes. This relation is subsequently utilized to derive a constraint on the net electromagnetic turbulent stress exerted on the poloidal flow. Various limiting cases of this constraint are considered, where it is found that electromagnetic contributions to the turbulent stress may either enhance or reduce the net turbulent stress depending upon the branch of turbulence excited. (10.1063/1.4764078)
  DOI : 10.1063/1.4764078
• Quasilinear transport modelling at low magnetic shear
  
  • Citrin Jonathan
  • Bourdelle C.
  • Cottier P.
  • Escande D.F.
  • Gürcan Özgür D.
  • Hatch D.R.
  • Hogeweij G.M.D.
  • Jenko F.
  • Pueschel M.J.
  Physics of Plasmas, American Institute of Physics, 2012, 19, pp.062305. Accurate and computationally inexpensive transport models are vital for routine and robust predictions of tokamak turbulent transport. To this end, the QuaLiKiz [Bourdelle et al., Phys. Plasmas 14, 112501 (2007)] quasilinear gyrokinetic transport model has been recently developed. QuaLiKiz flux predictions have been validated by non-linear simulations over a wide range in parameter space. However, a discrepancy is found at low magnetic shear, where the quasilinear fluxes are significantly larger than the non-linear predictions. This discrepancy is found to stem from two distinct sources: the turbulence correlation length in the mixing length rule and an increase in the ratio between the quasilinear and non-linear transport weights, correlated with increased non-linear frequency broadening. Significantly closer agreement between the quasilinear and non-linear predictions is achieved through the development of an improved mixing length rule, whose assumptions are validated by non-linear simulations. (10.1063/1.4719697)
  DOI : 10.1063/1.4719697
• Symmetry breaking effects of density gradient on parallel momentum transport: A new rau s * effect
  
  • Singh Rameswar
  • Singh R.
  • Kaw P.
  • Gürcan Özgür D.
  • Diamond P.H.
  • Nordman H.
  Physics of Plasmas, American Institute of Physics, 2012, 19, pp.012301. Symmetry breaking effects of density gradient on parallel momentum transport is studied via quasilinear theory. It is shown that finite &#961;*s(&#8801;&#961;s/Ln), where &#961;s is ion sound radius and Ln is density scale length, leads to symmetry breaking of the ion temperature gradient (ITG) eigenfunction. This broken symmetry persists even in the absence of mean poloidal (from radial electric field shear) and toroidal flows. This effect, as explained in the text, originates from the divergence of polarization particle current in the ion continuity equation. The form of the eigenfunction allows the microturbulence to generate parallel residual stress via &#12296;k&#8214;&#12297; symmetry breaking. Comparison with the &#8594;E×&#8594;B shear driven parallel residual stress, parallel polarization stress and turbulence intensity gradient driven parallel residual stress are discussed. It is shown that this &#961;*s driven parallel residual stress may become comparable to &#8594;E×&#8594;B shear driven parallel residual stress in small Ln region. In the regular drift wave ordering, where &#961;*s&#8810;1, this effect is found to be of the same order as the parallel polarization stress. This &#961;*s driven parallel residual stress can also overtake the turbulence intensity gradient driven parallel residual stress in strong density gradient region whereas the later one is dominant in the strong profile curvature region. The parallel momentum diffusivity is found to remain undisturbed by this &#961;*s effect as long as the turbulence intensity inhomogenity is not important. (10.1063/1.3672518)
  DOI : 10.1063/1.3672518
• Dynamic Martian magnetosphere: Transient twist induced by a rotation of the IMF
  
  • Modolo Ronan
  • Chanteur Gérard
  • Dubinin Eduard
  Geophysical Research Letters, American Geophysical Union, 2012, 39 (1), pp.L01106. Simulation studies of the Martian environment are usually restricted to stationary situations under various steady conditions of the solar wind and solar radiation. Dynamic transients and their implications have so far attracted little attention although global simulation models can provide valuable insights to understand disagreements between simulations and in situ observations. We make use of a three dimensional multispecies hybrid simulation model to investigate the response of the Martian plasma environment to a sudden rotation of the IMF. The simulation model couples charged and neutral species via three ionisation mechanisms: the absorption of solar extreme ultraviolet radiation, the impact of solar wind electrons, and the charge exchange between ions and neutral atoms. When a rotational discontinuity conveyed by the solar wind reaches the Martian environment the bow shock adapts quickly to the new solar wind conditions in contrast to the induced magnetosphere, especially the magnetic lobes in the wake. Timescales necessary to recover a stationary state can be estimated from such simulations and have some implications for space observations especially in the use of magnetic field proxies and for organizing particle measurements made by a spacecraft like Mars Express without an onboard magnetometer. (10.1029/2011GL049895)
  DOI : 10.1029/2011GL049895
• On time resolved gas temperature measurements in a pulsed dc plasma using quantum cascade laser absorption spectroscopy
  
  • Hübner M.
  • Marinov Daniil
  • Guaitella Olivier
  • Rousseau Antoine
  • Roepcke J.
  Measurement Science and Technology, IOP Publishing, 2012, 23, pp.115602. With a time resolution of 33 µs, the gas temperature in a pulsed dc air plasma admixed with 0.8% NO has been measured by quantum cascade laser absorption spectroscopy (QCLAS). For this purpose, the temperature dependent intensity ratios of two absorption structures of NO at 1900 cm&#8722;1 (5.26 µm) have been used. The QCLAS system worked in the Intra Pulse Mode with a pulse repetition frequency of 30 kHz leading to a spectrum recorded each 33 µs. In a low pressure discharge, the influence of nonlinear absorption phenomena causing strong distorted absorption structures of NO has been taken into account by a calibration routine based on tabulated line strengths. Different mean plasma currents have been applied to the discharge leading to gas temperature values ranging from about 300 K up to about 500 K. (10.1088/0957-0233/23/11/115602)
  DOI : 10.1088/0957-0233/23/11/115602