Publications

2016

• Multi-point ignition of Hydrogen/Air mixtures with single pulsed nanosecond surface dielectric barrier discharge. Morphology of the discharge at elevated pressures
  
  • Shcherbanev S.A.
  • Popov N A
  • Starikovskaia Svetlana
  , 2016, pp.AIAA-2016-1692.
• Kinetics of excited species at high specific energy deposition: quenching by electrons in the afterglow of a nanosecond capillary discharge
  
  • Lepikhin N D
  • Klochko A.V.
  • Popov N A
  • Starikovskaia Svetlana
  , 2016, pp.AIAA-2016-1213.
• Etude in-situ de la magnétopause Terrestre, de Cluster à MMS
  
  • Rezeau Laurence
  • Manuzzo Roberto
  • Belmont Gérard
  • Califano F.
  , 2016.
• Distinct responses of the low-latitude ionosphere to CME and HSSWS: The role of the IMF B^z oscillation frequency
  
  • Rodríguez-Zuluaga J.
  • Radicella S. M.
  • Nava B.
  • Amory-Mazaudier Christine
  • Mora-Páez H.
  • Alazo-Cuartas K.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2016. In this work an attempt to identify the role of the interplanetary magnetic field (IMF) in the response of the ionosphere to different solar phenomena is presented. For this purpose, the day-today variability of the equatorial ionospheric anomaly (EIA) and the main ionospheric disturbances are analyzed during one coronal mass ejection (CME) and two high-speed solar wind streams (HSSWSs). The EIA parameters considered are the zonal electric field and both the strength and position of its northern crest. The disturbances being the prompt penetration of magnetospheric electric field (PPMEF) and disturbance dynamo electric field (DDEF) are studied using the magnetic response of their equivalent current systems. In accordance, ground-based Global Navigation Satellite Systems receivers and magnetometers at geomagnetic low latitudes in the American sector are used. During both phenomena, patterns of PPMEF related to fluctuations of the IMF are observed. Diurnal and semidiurnal magnetic oscillations are found to be likely related to DDEF. Comparisons among the EIA parameters and the DDEF magnetic response exhibit poor relation during the CME in contrast to good relation during the HSSWSs. It is concluded that the response of the low-latitude ionosphere to solar phenomena is largely determined through the oscillation frequency of the IMF B z by affecting the generation of the PPMEF and DDEF differently. This is seen as an effect of how the energy from the solar wind is transferred into the magnetosphere-ionosphere system. (10.1002/2016JA022539)
  DOI : 10.1002/2016JA022539
• Solar wind test of the de Broglie-Proca massive photon with Cluster multi-spacecraft data
  
  • Retinò Alessandro
  • Spallicci Alessandro D. A. M.
  • Vaivads Andris
  Astroparticle Physics, Elsevier, 2016, 82, pp.49–55. Our understanding of the universe at large and small scales relies largely on electromagnetic observations. As photons are the messengers, fundamental physics has a concern in testing their properties, including the absence of mass. We use Cluster four spacecraft data in the solar wind at 1 AU to estimate the mass upper limit for the photon. We look for deviations from Ampère’s law, through the curlometer technique for the computation of the magnetic field, and through the measurements of ion and electron velocities for the computation of the current. We show that the upper bound for mγ lies between 1.4×10−491.4×10−49 and 3.4×10−513.4×10−51 kg, and thereby discuss the currently accepted lower limits in the solar wind. (10.1016/j.astropartphys.2016.05.006)
  DOI : 10.1016/j.astropartphys.2016.05.006
• A computational analysis of the vibrational levels of molecular oxygen in low-pressure stationary and transient radio-frequency oxygen plasma
  
  • Kemaneci Efe
  • Booth Jean-Paul
  • Chabert Pascal
  • van Dijk Jan
  • Mussenbrock Thomas
  • Brinkmann Ralf Peter
  Plasma Sources Science and Technology, IOP Publishing, 2016, 25 (2), pp.025025. Vibrational levels of molecular oxygen, O 2 ( v &#8201;&#8201;<&#8201;&#8201;42), are investigated in continuous and pulse-modulated low-pressure radio-frequency oxygen plasma with a global modelling approach. The model is benchmarked against a variety of pressure-, power- and time-resolved measurements of several inductive and asymmetric capacitive discharges available in the literature, and a good agreement is obtained. The sensitivity of the model with respect to the vibrational kinetics, the wall reactions and the spatial inhomogeneity of the charged particles are presented. The simulations without the vibrational levels are also shown for the sake of comparison. (10.1088/0963-0252/25/2/025025)
  DOI : 10.1088/0963-0252/25/2/025025
• Impact of the Eulerian chaos of magnetic field lines in magnetic reconnection
  
  • Firpo Marie-Christine
  • Ettoumi Wahb
  • Lifschitz A. F.
  • Retinò Alessandro
  • Farengo R F
  • Ferrari H E
  • García-Martínez P L
  Physics of Plasmas, American Institute of Physics, 2016, 23 (12). Stochasticity is an ingredient that may allow the breaking of the frozen-in law in the reconnec-tion process. It will first be argued that non-ideal effects may be considered as an implicit way to introduce stochasticity. Yet there also exists an explicit stochasticity that does not require the invocation of non-ideal effects. This comes from the spatial (or Eulerian) chaos of magnetic field lines that can show up only in a truly three-dimensional description of magnetic reconnection since two-dimensional models impose the integrability of the magnetic field lines. Some implications of this magnetic braiding, such as the increased particle finite-time Lyapunov exponents and increased acceleration of charged particles, are discussed in the frame of tokamak sawteeth that form a laboratory prototype of spontaneous magnetic reconnection. A justification for an increased reconnection rate with chaotic vs integrable magnetic field lines is proposed. Moreover, in 3D, the Eulerian chaos of magnetic field lines may coexist with the Eulerian chaos of velocity field lines, that is more commonly named turbulence. (10.1063/1.4972544)
  DOI : 10.1063/1.4972544
• Double and Single Planar Wire Arrays on University-Scale Low-Impedance LTD Generator
  
  • Safronova Alla S.
  • Kantsyrev Viktor L.
  • Weller Michael E.
  • Shlyaptseva V. V.
  • Shrestha I. K.
  • Lorance M. Y.
  • Schmidt-Petersen M. T.
  • Stafford A.
  • Cooper M. C.
  • Steiner A. M.
  • Yager-Elorriaga D. A.
  • Patel S. G.
  • Jordan N. M.
  • Gilgenbach R. M.
  • Chuvatin Alexandre S.
  IEEE Transactions on Plasma Science, Institute of Electrical and Electronics Engineers, 2016, 44 (4), pp.432-440. Planar wire array (PWA) experiments were performed on Michigan Accelerator for Inductive Z-pinch Experiments, the University of Michigan's low-impedance linear transformer driver (LTD)-driven generator (0.1 &#937;, 0.5-1 MA, and 100-200 ns), for the first time. It was demonstrated that Al wire arrays [both double PWA (DPWA) and single PWA (SPWA)] can be successfully imploded at LTD generator even at the relatively low current of 0.3-0.5 MA. In particular, implosion characteristics and radiative properties of PWAs of different load configurations [for DPWA from Al and stainless steel wires with different wire diameters, interwire gaps, and interplanar gaps (IPGs) and for Al SPWA of different array widths and number of wires] were studied. The major difference from the DPWA experiments on high-impedance Zebra accelerator was in the current rise time that was influenced by the load inductance and was increased up to about 150 ns during the first campaign (and was even longer in the second campaign). The implosion dynamics of DPWAs strongly depends on the critical load parameter, the aspect ratio (the ratio of the array width to IPG) as for Al DPWAs on high-impedance Zebra, but some differences were observed, for low-aspect ratio loads in particular. Analysis of X-ray images and spectroscopy indicates that K-shell Al plasmas from Al PWAs reached the electron temperatures up to more than 450 eV and densities up to 2 x 10²&#8304; cm&#8315;³. Despite the low mass of the loads, opacity effects were observed in the most prominent K-shell Al lines almost in every shot. (10.1109/TPS.2016.2538291)
  DOI : 10.1109/TPS.2016.2538291
• Larger sized planar wire arrays of complex configuration on 1.51.8 MA Z-pinch generator
  
  • Safronova Alla S.
  • Kantsyrev Viktor L.
  • Weller Michael E.
  • Shlyaptseva V. V.
  • Shrestha I. K.
  • Stafford A.
  • Schmidt-Petersen M. T.
  • Lorance M. Y.
  • Schultz K. A.
  • Chuvatin Alexandre S.
  Physics of Plasmas, American Institute of Physics, 2016, 23, pp.101210. Two new approaches of (i) simultaneous study of implosion and radiative characteristics of different materials in wire array Z-pinch plasmas in one shot and (ii) investigation of larger sized wire arrays (to enhance energy coupling to plasmas and provide better diagnostic access) were developed in experiments with 1.51.8 MA Zebra with a Load Current Multiplier. In particular, the larger sized multi-plane Planar Wire Arrays with two outer planes placed at 9 and 15&#8201;mm from each other and then as far as at 19&#8201;mm (compared with 6&#8201;mm studied before at standard 1 MA current) and with a modified central plane with 8 to 12 empty slots were investigated. Though K-shell Al and L-shell Ni, Cu plasmas have similar electron temperatures and densities, the ablation dynamics and radiation of Al and Ni, Cu planes are somewhat different, which was investigated in detail using the full set of diagnostics and modeling. Advantages of using such wire arrays at higher currents to study plasma flow and radiation from different materials and jets are highlighted. (10.1063/1.4965239)
  DOI : 10.1063/1.4965239
• Orientation of the X-line in asymmetric magnetic reconnection
  
  • Aunai Nicolas
  • Hesse Michael
  • Lavraud B.
  • Dargent Jérémy
  • Smets Roch
  Journal of Plasma Physics, Cambridge University Press (CUP), 2016, 82 (4), pp.535820401. Magnetic reconnection can occur in current sheets separating magnetic fields sheared by any angle and of arbitrarily different amplitudes. In such asymmetric and non-coplanar systems, it is not yet understood what the orientation of the X-line will be. Studying how this orientation is determined locally by the reconnection process is important to understand systems such as the Earth magnetopause, where reconnection occurs in regions with large differences in upstream plasma and field properties. This study aims at determining what the local X-line orientation is for different upstream magnetic shear angles in an asymmetric set-up relevant to the Earth's magnetopause. We use two-dimensional hybrid simulations and vary the simulation plane orientation with regard to the fixed magnetic field profile and search for the plane maximizing the reconnection rate. We find that the plane defined by the bisector of upstream fields maximizes the reconnection rate and this appears not to depend on the magnetic shear angle, domain size or upstream plasma and asymmetries. (10.1017/S0022377816000647)
  DOI : 10.1017/S0022377816000647
• Cone angle control of the interaction of magnetic clouds with the Earth's bow shock
  
  • Turc Lucile
  • Escoubet C. Philippe
  • Fontaine Dominique
  • Kilpua E. K. J.
  • Enestam S.
  Geophysical Research Letters, American Geophysical Union, 2016, 43, pp.4781-4789. Not Available (10.1002/2016GL068818)
  DOI : 10.1002/2016GL068818
• Electron scale structures and magnetic reconnection signatures in the turbulent magnetosheath
  
  • Yordanova E.
  • Vörös Z.
  • Varsani A.
  • Graham D. B.
  • Norgren C.
  • Khotyaintsev Y. V.
  • Vaivads A.
  • Eriksson E.
  • Nakamura R.
  • Lindqvist P.-A.
  • Marklund G.
  • Ergun R. E.
  • Magnes W.
  • Baumjohann W.
  • Fischer D.
  • Plaschke F.
  • Narita Y.
  • Russell C. T.
  • Strangeway R. J.
  • Le Contel Olivier
  • Pollock C.
  • Torbert R. B.
  • Giles B. J.
  • Burch J. L.
  • Avanov L. A.
  • Dorelli J. C.
  • Gershman D. J.
  • Paterson W. R.
  • Lavraud B.
  • Saito Y.
  Geophysical Research Letters, American Geophysical Union, 2016, 43 (12), pp.5969-5978. Collisionless space plasma turbulence can generate reconnecting thin current sheets as suggested by recent results of numerical magnetohydrodynamic simulations. The Magnetospheric Multiscale (MMS) mission provides the first serious opportunity to verify whether small ion-electron-scale reconnection, generated by turbulence, resembles the reconnection events frequently observed in the magnetotail or at the magnetopause. Here we investigate field and particle observations obtained by the MMS fleet in the turbulent terrestrial magnetosheath behind quasi-parallel bow shock geometry. We observe multiple small-scale current sheets during the event and present a detailed look of one of the detected structures. The emergence of thin current sheets can lead to electron scale structures. Within these structures, we see signatures of ion demagnetization, electron jets, electron heating, and agyrotropy suggesting that MMS spacecraft observe reconnection at these scales. (10.1002/2016GL069191)
  DOI : 10.1002/2016GL069191
• Emission spectroscopy of partial discharges in air-filled voids in Unfilled epoxy
  
  • Shcherbanev S.A.
  • Nadinov I.U.
  • Auvray Philippe
  • Starikovskaia Svetlana
  • Pancheshnyi Sergey V.
  • Herrmann L.G.
  IEEE Transactions on Plasma Science, Institute of Electrical and Electronics Engineers, 2016, 44 (7), pp.1219-1227. Emission optical spectroscopy is used as a technique to study partial discharges (PDs) in four unfilled epoxy samples encompassing an artificial air-filled cavity. It is shown that emission spectroscopy can be used to estimate the density and the chemical composition of a gas from the spectrally resolved emission and time-resolved pulse shape of the PDs at any time during the aging process. Two scenarios are observed: either PD continues until the sample breaks down (observed in 1 out of 4 samples) or PD stops at a certain point without sample breakdown (3 out of 4 samples). For both the scenarios, a stable initial phase with a gradual decrease of emission intensity from the discharge is typical for a few hundreds of hours of continuous discharge operation. At this stage, the spectrum of the second positive system of molecular nitrogen dominates in the entire spectral range of 350500 nm studied in this work. Furthermore, time-resolved measurements indicate two types of discharges of very different frequencies and magnitudes as well as a decrease of the pressure in the voids as a function of aging time. Then, a sharp 500% increase of the N2 emission is observed 2 days before the breakdown; during the last day a spectrum of CO and some other C-N-O-H containing molecules is observed instead of the spectrum of molecular nitrogen. This allows predicting a breakdown at least a few hours before it happens by analyzing the broad emission spectra behavior. Additionally, the possible role of surface conductivity increase during aging on PD inhibition is discussed. (10.1109/TPS.2016.2576560)
  DOI : 10.1109/TPS.2016.2576560
• Influence of the angular scattering of electrons on the runaway threshold in air
  
  • Chanrion Olivier
  • Bonaventura Z.
  • Bourdon Anne
  • Neubert Torsten
  Plasma Physics and Controlled Fusion, IOP Publishing, 2016, 58, pp.044001. The runaway electron mechanism is of great importance for the understanding of the generation of x- and gamma rays in atmospheric discharges. In 1991, terrestrial gamma-ray flashes (TGFs) were discovered by the Compton Gamma-Ray Observatory. Those emissions are bremsstrahlung from high energy electrons that run away in electric fields associated with thunderstorms. In this paper, we discuss the runaway threshold definition with a particular interest in the influence of the angular scattering for electron energy close to the threshold. In order to understand the mechanism of runaway, we compare the outcome of different FokkerPlanck and Monte Carlo models with increasing complexity in the description of the scattering. The results show that the inclusion of the stochastic nature of collisions smooths the probability to run away around the threshold. Furthermore, we observe that a significant number of electrons diffuse out of the runaway regime when we take into account the diffusion in angle due to the scattering. Those results suggest using a runaway threshold energy based on the FokkerPlanck model assuming the angular equilibrium that is 1.6 to 1.8 times higher than the one proposed by [1, 2], depending on the magnitude of the ambient electric field. The threshold also is found to be 5 to 26 times higher than the one assuming forward scattering. We give a fitted formula for the threshold field valid over a large range of electric fields. Furthermore, we have shown that the assumption of forward scattering is not valid below 1 MeV where the runaway threshold usually is defined. These results are important for the thermal runaway and the runaway electron avalanche discharge mechanisms suggested to participate in the TGF generation. (10.1088/0741-3335/58/4/044001)
  DOI : 10.1088/0741-3335/58/4/044001
• Equatorial noise emissions with a quasi-periodic modulation observed by DEMETER at harmonics of the O⁺ ion gyrofrequency
  
  • Parrot Michel
  • Nĕmec František
  • Santolík Ondřej
  • Cornilleau-Wehrlin Nicole
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2016, 121 (10), pp.10,289–10,302. The analysis of ionospheric equatorial noise (EN) with a quasi-periodic (QP) modulation observed by the DEMETER spacecraft is presented. These EN emissions also called whistler mode or fast magnetosonic waves play an important role in acceleration of radiation belt electrons. A statistical analysis with 103 events shows that they occur just after intense magnetic storms. Usually, they are generated by unstable proton ring distribution close to the magnetic equator at harmonics of the proton gyrofrequency in the inner magnetosphere (2 < L < 8). But at lower L values down in the ionosphere three events have been analyzed and it appears that the EN waves are at harmonics of - or very close to - a O⁺ ion gyrofrequency which can be found close or slightly above the satellite. The wave propagation analysis indicates that these emissions are coming from an area above the satellite. Concerning one event, the EN emissions are observed on several consecutive orbits and there is a temporal coincidence with observations performed by the CLUSTER satellites at higher altitudes in the magnetosphere. EN emissions at lower frequencies have been also observed by the CLUSTER satellites in the same longitudinal sector as DEMETER but at ~5 R_E. The analysis of the STAFF data onboard C1 reveals that the magnetic field spectrogram has peaks close to harmonics of the local proton gyrofrequency as usually reported. It is shown that the DEMETER and CLUSTER EN waves have a similar QP modulation but with slightly different period and frequency. (10.1002/2016JA022989)
  DOI : 10.1002/2016JA022989
• Beyond the Maltese Cross: Geometry of Turbulence Between 0.2 and 1 au
  
  • Verdini Andrea
  • Grappin Roland
  The Astrophysical Journal, American Astronomical Society, 2016, 831. The spectral anisotropy of turbulent structures has been measured in the solar wind since 1990, relying on the assumption of axisymmetry about the mean magnetic field, B <SUB>0</SUB>. However, several works indicate that this hypothesis might be partially wrong, thus raising two questions: (i) is it correct to interpret measurements at 1 au (the so-called Maltese cross) in term of a sum of slab and two-dimensional (2D) turbulence; and (ii) what information is really contained in the Maltese cross? We solve direct numerical simulations of the magnetohydrodynamic equations including the transverse stretching exerted by the solar wind flow and study the genuine 3D anisotropy of turbulence as well as that one resulting from the assumption of axisymmetry about B <SUB>0</SUB>. We show that the evolution of the turbulent spectrum from 0.2 to 1 au depends strongly on its initial anisotropy. An axisymmetric spectrum with respect to B <SUB>0</SUB> keeps its axisymmetry, i.e., resists stretching perpendicular to radial, while an isotropic spectrum becomes essentially axisymmetric with respect to the radial direction. We conclude that close to the Sun, slow-wind turbulence has a spectrum that is axisymmetric around B <SUB>0</SUB> and the measured 2D component at 1 au describes the real shape of turbulent structures. In contrast, fast-wind turbulence has a more isotropic spectrum at the source and becomes radially symmetric at 1 au. Such structure is hidden by the symmetrization applied to the data that instead returns a slab geometry. (10.3847/0004-637X/831/2/179)
  DOI : 10.3847/0004-637X/831/2/179
• Ion injection at Quasi-parallel Shocks Seen by the Cluster Spacecraft
  
  • Johlander A.
  • Vaivads A.
  • Khotyaintsev Y. V.
  • Retinò Alessandro
  • Dandouras I.
  The Astrophysical Journal Letters, Bristol : IOP Publishing, 2016, 817 (1), pp.L4. Collisionless shocks in space plasma are known to be capable of accelerating ions to very high energies through diffusive shock acceleration (DSA). This process requires an injection of suprathermal ions, but the mechanisms producing such a suprathermal ion seed population are still not fully understood. We study acceleration of solar wind ions resulting from reflection off short large-amplitude magnetic structures (SLAMSs) in the quasi-parallel bow shock of Earth using in situ data from the four Cluster spacecraft. Nearly specularly reflected solar wind ions are observed just upstream of a SLAMS. The reflected ions are undergoing shock drift acceleration (SDA) and obtain energies higher than the solar wind energy upstream of the SLAMS. Our test particle simulations show that solar wind ions with lower energy are more likely to be reflected off the SLAMS, while high-energy ions pass through the SLAMS, which is consistent with the observations. The process of SDA at SLAMSs can provide an effective way of accelerating solar wind ions to suprathermal energies. Therefore, this could be a mechanism of ion injection into DSA in astrophysical plasmas. (10.3847/2041-8205/817/1/L4)
  DOI : 10.3847/2041-8205/817/1/L4
• Poynting vector and wave vector directions of equatorial chorus
  
  • Taubenschuss U.
  • Santolík O.
  • Breuillard Hugo
  • Li W.
  • Le Contel Olivier
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2016, 121 (12), pp.11,912-11,928. We present new results on wave vectors and Poynting vectors of chorus rising and falling tones on the basis of 6 years of THEMIS (Time History of Events and Macroscale Interactions during Substorms) observations. The majority of wave vectors is closely aligned with the direction of the ambient magnetic field (B<SUB>0</SUB>). Oblique wave vectors are confined to the magnetic meridional plane, pointing away from Earth. Poynting vectors are found to be almost parallel to B<SUB>0</SUB>. We show, for the first time, that slightly oblique Poynting vectors are directed away from Earth for rising tones and toward Earth for falling tones. For the majority of lower band chorus elements, the mutual orientation between Poynting vectors and wave vectors can be explained by whistler mode dispersion in a homogeneous collisionless cold plasma. Upper band chorus seems to require inclusion of collisional processes or taking into account azimuthal anisotropies in the propagation medium. The latitudinal extension of the equatorial source region can be limited to ±6<SUP>o</SUP> around the B<SUB>0</SUB> minimum or approximately ±5000 km along magnetic field lines. We find increasing Poynting flux and focusing of Poynting vectors on the B<SUB>0</SUB> direction with increasing latitude. Also, wave vectors become most often more field aligned. A smaller group of chorus generated with very oblique wave normals tends to stay close to the whistler mode resonance cone. This suggests that close to the equatorial source region (within 20<SUP>o</SUP> latitude), a wave guidance mechanism is relevant, for example, in ducts of depleted or enhanced plasma density. (10.1002/2016JA023389)
  DOI : 10.1002/2016JA023389
• Evolution of nanosecond surface dielectric barrier discharge for negative polarity of voltage pulse
  
  • Soloviev V.R.
  • Krivtsov V.M.
  • Shcherbanev S.A.
  • Starikovskaia Svetlana
  Plasma Sources Science and Technology, IOP Publishing, 2016, 26 (1), pp.014001 (12pp). Surface dielectric barrier discharge, initiated by a high-voltage pulse of negative polarity in atmospheric pressure air, is studied numerically and experimentally. At a pulse duration of a few tens of nanoseconds, two waves of optical emission propagate from the high-voltage electrode corresponding to the leading and trailing edges of the high-voltage pulse. It is shown by means of numerical modeling that a glow-like discharge slides along the surface of the dielectric at the leading edge of the pulse, slowing down on the plateau of the pulse. When the trailing edge of the pulse arrives to the high-voltage electrode, a second discharge starts and propagates in the same direction. The difference is that the discharge corresponding to the trailing edge is not diffuse and demonstrates a well-pronounced streamer-like shape. The 2D (in numerical modeling) streamer propagates above the dielectric surface, leaving a gap of about 0.05 mm between the streamer and the surface. The calculated and experimentally measured emission picture, waveform of the electrical current, and deposited energy, qualitatively coincide. The sensitivity of the numerical solution to unknown physical parameters of the model is discussed. (10.1088/0963-0252/26/1/014001)
  DOI : 10.1088/0963-0252/26/1/014001
• Kinetic studies of NO formation in pulsed air-like low-pressure dc plasmas
  
  • Hübner M.
  • Gortschakow S.
  • Guaitella Olivier
  • Marinov Daniil
  • Rousseau Antoine
  • Röpcke J.
  • Loffhagen D.
  Plasma Sources Science and Technology, IOP Publishing, 2016, 25 (3), pp.035005. The kinetics of the formation of NO in pulsed air-like dc plasmas at a pressure of 1.33 mbar and mean currents between 50 and 150 mA of discharge pulses with 5&#8201;ms duration has been investigated both experimentally and by self-consistent numerical modelling. Using time-resolved quantum cascade laser absorption spectroscopy, the densities of NO, NO2 and N2O have been measured in synthetic air as well as in air with 0.8% of NO2 and N2O, respectively. The temporal evolution of the NO density shows four distinct phases during the plasma pulse and the early afterglow in the three gas mixtures that were used. In particular, a steep density increase during the ignition phase and after termination of the discharge current pulse has been detected. The NO concentration has been found to reach a constant value of , , and for mean plasma currents of 50 mA, 100 mA and 150 mA, respectively, in the afterglow. The measured densities of NO2 and N2O in the respective mixture decrease exponentially during the plasma pulse and remain almost constant in the afterglow, especially where the admixture of NO2 has a remarkable impact on the NO production during the ignition. The numerical results of the coupled solution of a set of rate equations for the various heavy particles and the time-dependent Boltzmann equation of the electrons agree quite well with the experimental findings for the different air-like plasmas. The main reaction processes have been analysed on the basis of the model calculations and the remaining differences between the experiment and modelling especially during the afterglow are discussed. (10.1088/0963-0252/25/3/035005)
  DOI : 10.1088/0963-0252/25/3/035005
• Linear electromagnetic excitation of an asymmetric low pressure capacitive discharge with unequal sheath widths
  
  • Lieberman M.A.
  • Lichtenberg A.J.
  • Kawamura E.
  • Chabert Pascal
  Physics of Plasmas, American Institute of Physics, 2016, 23 (1), pp.013501. It is well-known that standing waves having radially center-high radio frequency (rf) voltage profiles exist in high frequency capacitive discharges. In this work, we determine the symmetric and antisymmetric radially propagating waves in a cylindrical capacitive discharge that is asymmetrically driven at the lower electrode by an rf voltage source. The discharge is modeled as a uniform bulk plasma which at lower frequencies has a thicker sheath at the smaller area powered electrode and a thinner sheath at the larger area grounded electrode. These are self-consistently determined at a specified density using the Child law to calculate sheath widths and the electron power balance to calculate the rf voltage. The fields and the system resonant frequencies are determined. The center-to-edge voltage ratio on the powered electrode is calculated versus frequency, and central highs are found near the resonances. The results are compared with simulations in a similar geometry using a two-dimensional hybrid fluid-analytical code, giving mainly a reasonable agreement. The analytic model may be useful for finding good operating frequencies for a given discharge geometry and power. (10.1063/1.4938204)
  DOI : 10.1063/1.4938204
• Long-lived plasma and fast quenching of N<SUB>2</SUB>(C<SUP>3</SUP>P<SUB>u</SUB>) by electrons in the afterglow of a nanosecond capillary discharge in nitrogen
  
  • Lepikhin N D
  • Klochko A.V.
  • Popov N A
  • Starikovskaia Svetlana
  Plasma Sources Science and Technology, IOP Publishing, 2016, 25 (4), pp.045003. Quenching of electronically excited nitrogen state, ##IMG## [http://ej.iop.org/images/0963-0252/25/4/045003/psstaa2269ieqn003.gif] \textN_2≤ft(\textC^3Π_u,v^\prime=0\right) , in the afterglow of nanosecond capillary discharge in pure nitrogen is studied. It is found experimentally that an additional collisional mechanism appears and dominates at high specific deposited energies leading to the anomalously fast quenching of the ##IMG## [http://ej.iop.org/images/0963-0252/25/4/045003/psstaa2269ieqn004.gif] \textN_2≤ft(\textC^3Π_u\right) in the afterglow. On the basis of obtained experimental data and of the analysis of possible quenching agents, it is concluded that the anomalously fast deactivation of the ##IMG## [http://ej.iop.org/images/0963-0252/25/4/045003/psstaa2269ieqn005.gif] \textN_2≤ft(\textC^3Π_u\right) can be explained by quenching by electrons. Long-lived plasma at time scale of hundreds nanoseconds after the end of the pulse is observed. High electron densities, about 10 14 cm &#1074;3 at 27 mbar, are sustained by reactions of associative ionization. Kinetic 1D numerical modeling and comparison of calculated results with experimentally measured electric fields in the second high-voltage pulse 250 ns after the initial pulse, and electron density measurements in the afterglow confirm the validity of the suggested mechanism. (10.1088/0963-0252/25/4/045003)
  DOI : 10.1088/0963-0252/25/4/045003
• Comment on "Insight into hydrogenation of graphene: Effect of hydrogen plasma chemistry" [Appl. Phys. Lett. 105, 183104 (2014)]
  
  • Marinov Daniil
  Applied Physics Letters, American Institute of Physics, 2016, 108. Not Available (10.1063/1.4953260)
  DOI : 10.1063/1.4953260
• The Mass Spectrum Analyzer (MSA) on board the BepiColombo MMO
  
  • Delcourt Dominique C.
  • Saito Y.
  • Leblanc Frédéric
  • Verdeil Christophe
  • Yokota S.
  • Fraenz M.
  • Fischer H.
  • Fiethe B.
  • Katra Bruno
  • Fontaine Dominique
  • Illiano Jean-Marie
  • Berthelier Jean-Jacques
  • Krupp N.
  • Buhrke U.
  • Bubenhagen F.
  • Michalik H.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2016, 121 (7), pp.6749-6761. Observations from the MESSENGER spacecraft have considerably enhanced our understanding of the plasma environment at Mercury. In particular, measurements from the Fast Imaging Plasma Spectrometer (FIPS) provide evidences of a variety of ion species of planetary origin (He+, O+, Na+) in the northern dayside cusp and in the nightside plasma sheet. A more comprehensive view of Mercury's plasma environment will be provided by the Bepi Colombo mission that will be launched in 2018. Onboard the Bepi Colombo MMO spacecraft, the MPPE (Mercury Plasma/Particle Experiment) consortium gathers different sensors dedicated to particle measurements. Among these sensors, the Mass Spectrum Analyzer (MSA) is the instrument dedicated to plasma composition analysis. It consists of a top-hat for energy analysis followed by a Time-Of-Flight (TOF) chamber to derive the ion mass. Taking advantage of the spacecraft rotation, MSA will measure three-dimensional distribution functions in one spin (4 s), from energies characteristic of exospheric populations (in the eV range) up to plasma sheet energies (up to ~38 keV/q). A notable feature of the MSA instrument is that the TOF chamber is polarized with a linear electric field that leads to isochronous TOFs and enhanced mass resolution (typically, m/∆m ≈ 40 for ions with energies up to 13 keV/q). At Mercury, this capability is of paramount importance to thoroughly characterize the wide variety of ion species originating from the planet surface. It is thus anticipated that MSA will provide unprecedented information on ion populations in the Hermean environment and hence improve our understanding of the coupling processes at work. (10.1002/2016JA022380)
  DOI : 10.1002/2016JA022380
• Day-to-day variability of VTEC and ROTI in October 2012 with impact of high-speed solar wind stream on 13 October 2012
  
  • Azzouzi Ilyasse
  • Migoya-Orué Yenca
  • Coïsson Pierdavide
  • Amory-Mazaudier Christine
  • Fleury Rolland
  • Radicella Sandro
  Sun and Geosphere, BBC SWS Regional Network, 2016, 11 (1), pp.7-22. This paper presents the day-today variability of the Vertical Total Electron Content (VTEC) and the Rate of change of TEC Index (ROTI) in October 2012. We focused our attention to the impact of a high-speed solar wind stream (HSSWS) on the ionosphere in middle and low latitudes on 13 October 2012. This event was preceded by two other disturbances caused by a Coronal Mass Ejection (CME) at 05:26UT on 8 October and a HSSWS around 19:00UT on 9 October. The changes in the VTEC observed during the period between 8 and 12 October preceding the 13 October case showed a comparable response of the ionosphere in both hemispheres, varying mainly with latitude and presenting a stronger impact in the Northern hemisphere. The VTEC increased at the arrival of the CME on 8 October, then decreased, and increased again on 13 October. The solar wind speed associated with the second HSSWS reached its peak, 580 km/s around 17:00UT during the recovery phase of a geomagnetic storm started around 00:00UT on 13 October. Its impact was observed in Africa and in Eastern South America on the ROTI, an indicator of ionospheric scintillation. On 13 October, the ROTI was small over whole Africa and in Eastern South America at the moment the impact of the second HSSWS. These observations are interpreted as due to the ionospheric disturbance dynamo electric field associated with the Joule heating produced in the auroral zone by the HSSWS.