Publications

2014

• Mars-Solar Wind Interaction: Coupling Between Hybrid, Ionospheric, Thermospheric and Exospheric Models
  
  • Leblanc François
  • Chaufray Jean-Yves
  • Modolo Ronan
  • Hess Sebastien
  • Yagi M.
  • Mancini M.
  • Forget François
  • Gonzalez-Galindo Francisco
  • Lorenzato L.
  • Mazelle Christian
  • Chanteur Gérard
  , 2014. The solar wind interaction with the Martian neutral envi- ronment is investigated by means of three dimensional hybrid magnetospheric simulations. In such formal- ism, ions have a kinetic description while electrons are treated as an inertialess fluid, ensuring the neutrality of the plasma and contributing to currents and pressure terms. This model has been successfully used to de- scribe the near ionized environment of Mars
• Experimental and numerical study of fast gas heating and O atom production in a capillary nanosecond discharge
  
  • Klochko A.V.
  • Salmon A.
  • Lemainque J.
  • Popov N.A.
  • Booth Jean-Paul
  • Xiong Z.
  • Kushner M.J.
  • Starikovskaia Svetlana
  , 2014, pp.2014-1030.
• Ignition of CH4:O2:Ar and n-C4H10:O2:Ar(N2) mixtures with initial temperatures between 650-950 K by a surface pulsed discharge
  
  • Stepanyan S.A.
  • Boumehdi M.A.
  • Vanhove G.
  • Desgroux Pascale
  • Starikovskaia Svetlana
  • Popov N.A.
  , 2014. (10.2514/6.2014-0665)
  DOI : 10.2514/6.2014-0665
• Adsorption, desorption and reactivity of O and N atoms on SiO2 surface
  
  • Rousseau Antoine
  , 2014.
• New ferromagnetic core shapes for induction sensors
  
  • Coillot Christophe
  • Moutoussamy Joël
  • Boda Mathieu
  • Leroy Paul
  Journal of Sensors and Sensor Systems, Copernicus Publ, 2014, pp.1-8. Induction sensors are used in a wide range of scientific and industrial applications. One way to improve these is rigorous modelling of the sensor combined with a low voltage and current input noise preamplifier aiming to optimize the whole induction magnetometer. In this paper, we explore another way, which consists in the use of original ferromagnetic core shapes of induction sensors, which bring substantial improvements. These new configurations are the cubic, orthogonal and coiled-core induction sensors. For each of them we give modelling elements and discuss their benefits and drawbacks with respect to a given noise-equivalent magnetic induction goal. Our discussion is supported by experimental results for the cubic and orthogonal configurations, while the coiled-core configuration remains open to experimental validation. The transposition of these induction sensor configurations to other magnetic sensors (fluxgate and giant magneto-impedance) is an exciting prospect of this work. (10.5194/jsss-3-1-2014)
  DOI : 10.5194/jsss-3-1-2014
• Multi Water Bag modelling of drift kinetic electrons and ions plasmas
  
  • Morel Pierre
  • Dreydemy Ghiro Florent
  • Berionni Vincent
  • Gürcan Özgür D.
  , 2014.
• Spatial Propagation of Turbulence and Formation of Mesoscopic Structures in Plasma Turbulence
  
  • Dif-Pradalier Guilhem
  • Ghendrih Ph.
  • Diamond P.H.
  • Garbet X.
  • Grandgirard V.
  • Norscini C.
  • Palermo F.
  • Sarazin Y.
  • Abiteboul J.
  • Dong Yue
  • Gürcan Özgür D.
  • Hennequin Pascale
  • Morel Pierre
  • Vermare Laure
  • Kosuga Y.
  , 2014.
• Radiation sources with planar wire arrays and planar foils for inertial confinement fusion and high energy density physics research
  
  • Kantsyrev Viktor L.
  • Chuvatin Alexandre S.
  • Safronova Alla S.
  • Rudakov Leonid I.
  • Esaulov A. A.
  • Velikovich A. L.
  • Shrestha Ishor
  • Astanovitsky A.
  • Osborne Glenn C.
  • Shlyaptseva V. V.
  • Weller Michael E.
  • Keim S.
  • Stafford A.
  • Cooper M. C.
  Physics of Plasmas, American Institute of Physics, 2014, 21 (03), pp.031204. This article reports on the joint success of two independent lines of research, each of them being a multi-year international effort. One of these is the development of innovative sources, such as planar wire arrays (PWAs). PWAs turned out to be a prolific radiator, which act mainly as a resistor, even though the physical mechanism of efficient magnetic energy conversion into radiation still remains unclear. We review the results of our extensive studies of PWAs. We also report the new results of the experimental comparison PWAs with planar foil liners (another promising alternative to wire array loads at multi-mega-ampere generators). Pioneered at UNR, the PWA Z-pinch loads have later been tested at the Sandia National Laboratories (SNL) on the Saturn generator, on GIT-12 machine in Russia, and on the QiangGuang-1 generator in China, always successfully. Another of these is the drastic improvement in energy efficiency of pulsed-power systems, which started in early 1980s with Zucker's experiments at Naval Research Laboratory (NRL). Successful continuation of this approach was the Load Current Multiplier (LCM) proposed by Chuvatin in collaboration with Rudakov and Weber from NRL. The 100 ns LCM was integrated into the Zebra generator, which almost doubled the plasma load current, from 0.9 to 1.7 MA. The two above-mentioned innovative approaches were used in combination to produce a new compact hohlraum radiation source for ICF, as jointly proposed by SNL and UNR [Jones et al., Phys. Rev. Lett. 104, 125001 (2010)]. The first successful proof-of-the-principle experimental implementation of new hohlraum concept at university-scale generator Zebra/LCM is demonstrated. A numerical simulation capability with VisRaD code (from PRISM Co.) established at UNR allowed for the study of hohlraum coupling physics and provides the possibility of optimization of a new hohlraum. Future studies are discussed. (10.1063/1.4865367)
  DOI : 10.1063/1.4865367
• Turbulence elasticity-A new mechanism for transport barrier dynamics
  
  • Guo Z. B.
  • Diamond P.H.
  • Kosuga Y.
  • Gürcan Özgür D.
  Physics of Plasmas, American Institute of Physics, 2014, 21 (9). We present a new, unified model of transport barrier formation in ``elastic'' drift wave-zonal flow (DW-ZF) turbulence. A new physical quantity-the delay time (i.e., the mixing time for the DW turbulence)-is demonstrated to parameterize each stage of the transport barrier formation. Quantitative predictions for the onset of limit-cycle-oscillation (LCO) among DW and ZF intensities (also denoted as I-mode) and I-mode to high-confinement mode (H-mode) transition are also given. The LCO occurs when the ZF shearing rate (vertical bar < u >(ZF)'vertical bar) enters the regime Delta omega(k) < vertical bar < V >(ZF)'vertical bar < tau(-1)(cr), where Delta omega(k) is the local turbulence decorrelation rate and tau(cr) is the threshold delay time. In the basic predator-prey feedback system, tau(cr) is also derived. The I-H transition occurs when vertical bar < V >(ExB)'vertical bar > tau(-1)(cr), where the mean E x B shear flow driven by ion pressure ``locks'' the DW-ZF system to the H-mode by reducing the delay time below the threshold value. (C) 2014 AIP Publishing LLC. (10.1063/1.4894695)
  DOI : 10.1063/1.4894695
• Complete multi-field characterization of the geodesic acoustic mode in the TCV tokamak
  
  • de Meijere C. A.
  • Coda S.
  • Huang Z.
  • Vermare Laure
  • Vernay T.
  • Vuille V.
  • Brunner Stephan
  • Dominski J.
  • Hennequin Pascale
  • Kraemer-Flecken A.
  • Merlo G.
  • Porte L.
  • Villard Laurent
  Plasma Physics and Controlled Fusion, IOP Publishing, 2014, 56 (7), pp.072001. The geodesic acoustic mode (GAM) is a coherently oscillating zonal flow that may regulate turbulence in toroidal plasmas. Uniquely, the complete poloidal and toroidal structure of the magnetic component of the turbulence-driven GAM has been mapped in the TCV tokamak. Radially localized measurements of the fluctuating density, ECE radiative temperature and poloidal flow show that the GAM is a fully coherent, radially propagating wave. These observations are consistent with electrostatic, gyrokinetic simulations. (10.1088/0741-3335/56/7/072001)
  DOI : 10.1088/0741-3335/56/7/072001
• The FIELDS Instrument Suite on MMS: Scientific Objectives, Measurements, and Data Products
  
  • Torbert R. B.
  • Russell C. T.
  • Magnes W.
  • Ergun R. E.
  • Lindqvist P.-A.
  • Le Contel Olivier
  • Vaith H.
  • Macri J.
  • Myers S.
  • Rau D.
  • Needell J.
  • King B.
  • Granoff M.
  • Chutter M.
  • Dors I.
  • Olsson G.
  • Khotyaintsev Y. V.
  • Eriksson A.
  • Kletzing C. A.
  • Bounds S.
  • Anderson B.
  • Baumjohann W.
  • Steller M.
  • Bromund K.
  • Le G.
  • Nakamura R.
  • Strangeway R. J.
  • Leinweber H. K.
  • Tucker S.
  • Westfall J.
  • Fischer D.
  • Plaschke F.
  • Porter J.
  • Lappalainen K.
  Space Science Reviews, Springer Verlag, 2014, pp.1-31. Not Available (10.1007/s11214-014-0109-8)
  DOI : 10.1007/s11214-014-0109-8
• Circulation of Heavy Ions and Their Dynamical Effects in the Magnetosphere: Recent Observations and Models
  
  • Kronberg E. A.
  • Ashour-Abdalla M.
  • Dandouras I.
  • Delcourt Dominique C.
  • Grigorenko E. E.
  • Kistler L. M.
  • Kuzichev I. V.
  • Liao J.
  • Maggiolo R.
  • Malova H. V.
  • Orlova K. G.
  • Peroomian V.
  • Shklyar D. R.
  • Shprits Y. Y.
  • Welling D. T.
  • Zelenyi L. M.
  Space Science Reviews, Springer Verlag, 2014, 184 (1-4), pp.173-235. Knowledge of the ion composition in the near-Earths magnetosphere and plasma sheet is essential for the understanding of magnetospheric processes and instabilities. The presence of heavy ions of ionospheric origin in the magnetosphere, in particular oxygen (O ), influences the plasma sheet bulk properties, current sheet (CS) thickness and its structure. It affects reconnection rates and the formation of Kelvin-Helmholtz instabilities. This has profound consequences for the global magnetospheric dynamics, including geomagnetic storms and substorm-like events. The formation and demise of the ring current and the radiation belts are also dependent on the presence of heavy ions. In this review we cover recent advances in observations and models of the circulation of heavy ions in the magnetosphere, considering sources, transport, acceleration, bulk properties, and the influence on the magnetospheric dynamics. We identify important open questions and promising avenues for future research. (10.1007/s11214-014-0104-0)
  DOI : 10.1007/s11214-014-0104-0
• On the origin of falling-tone chorus elements in Earth's inner magnetosphere
  
  • Breuillard H
  • Agapitov O
  • Artemyev A
  • Krasnoselskikh V
  • Le Contel Olivier
  • Cully C. M.
  • Angelopoulos V
  • Zaliznyak Y
  • Rolland G
  Annales Geophysicae, European Geosciences Union, 2014, 32, pp.1477-1485. Generation of extremely/very low frequency (ELF/VLF) chorus waves in Earth's inner magnetosphere has received increased attention recently because of their significance for radiation belt dynamics. Though past theoretical and numerical models have demonstrated how rising-tone chorus elements are produced, falling-tone chorus element generation has yet to be explained. Our new model proposes that weak-amplitude falling-tone chorus elements can be generated by magnetospheric reflection of rising-tone elements. Using ray tracing in a realistic plasma model of the inner magnetosphere, we demonstrate that rising-tone elements originating at the magnetic equator propagate to higher latitudes. Upon reflection there, they propagate to lower L-shells and turn into oblique falling tones of reduced power, frequency, and bandwidth relative to their progenitor rising tones. Our results are in good agreement with comprehensive statistical studies of such waves, notably using magnetic field measurements from THEMIS (Time History of Events and Macroscale Interactions during Substorms) spacecraft. Thus, we conclude that the proposed mechanism can be responsible for the generation of weak-amplitude falling-tone chorus emissions. (10.5194/angeo-32-1477-2014)
  DOI : 10.5194/angeo-32-1477-2014
• Ion flux asymmetry in radiofrequency capacitively-coupled plasmas excited by sawtooth-like waveforms
  
  • Bruneau Bastien
  • Novikova T.
  • Lafleur Trevor
  • Booth Jean-Paul
  • Johnson E.V.
  Plasma Sources Science and Technology, IOP Publishing, 2014, 23 (6), pp.065010. Using particle-in-cell simulations, we predict that it is possible to obtain a significant difference between the ion flux to the powered electrode and that to the grounded electrode?with about 50% higher ion flux on one electrode?in a geometrically symmetric, radiofrequency capacitively-coupled plasma reactor by applying a non-sinusoidal, ?Tailored? voltage waveform. This sawtooth-like waveform presents different rising and falling slopes over one cycle. We show that this effect is due to differing plasma sheath motion in front of each electrode, which induces a higher ionization rate in front of the electrode which has the fastest positive rising voltage. Together with the higher ion flux comes a lower voltage drop across the sheath, and therefore a reduced maximum ion bombardment energy; a result in contrast to typical process control mechanisms. (10.1088/0963-0252/23/6/065010)
  DOI : 10.1088/0963-0252/23/6/065010
• Plasma-assisted ignition and combustion: nanosecond discharges and development of kinetic mechanisms
  
  • Starikovskaia Svetlana
  Journal of Physics D: Applied Physics, IOP Publishing, 2014, 47 (35), pp.353001 (34pp). This review covers the results obtained in the period 20062014 in the field of plasma-assisted combustion, and in particular the results on ignition and combustion triggered or sustained by pulsed nanosecond discharges in different geometries. Some benefits of pulsed high voltage discharges for kinetic study and for applications are demonstrated. The necessity of and the possibility of building a particular kinetic mechanism of plasma-assisted ignition and combustion are discussed. The most sensitive regions of parameters for plasmacombustion kinetic mechanisms are selected. A map of the pressure and temperature parameters (PT diagram) is suggested, to unify the available data on ignition delay times, ignition lengths and densities of intermediate species reported by different authors. (10.1088/0022-3727/47/35/353001)
  DOI : 10.1088/0022-3727/47/35/353001
• What is the size of a floating sheath?
  
  • Chabert Pascal
  Plasma Sources Science and Technology, IOP Publishing, 2014, 23 (6), pp.065042. The size of the positive space charge sheath that forms in front of an object immersed in a plasma and not dc-connected to ground with an external circuit (a floating sheath) is calculated numerically. If the sheath edge is defined as the position at which the ion fluid speed equals the Bohm speed, it is shown that the sheath size varies significantly with the discharge parameters, typically from s float &#8776; 7 &#955; Des to s float &#8776; 14 &#955; Des , where s float is the floating sheath size and &#955; Des is the Debye length at the sheath edge. However, if the sheath edge is defined as a significant departure from quasi-neutrality, then the floating sheath size is almost independent of the discharge parameters and may be approximated by s float &#8776; 5 &#955; Des . (10.1088/0963-0252/23/6/065042)
  DOI : 10.1088/0963-0252/23/6/065042
• Evolution of Turbulence in the Expanding Solar Wind, a Numerical Study
  
  • Dong Yue
  • Verdini Andrea
  • Grappin Roland
  The Astrophysical Journal, American Astronomical Society, 2014, 793, pp.118. We study the evolution of turbulence in the solar wind by solving numerically the full three-dimensional (3D) magnetohydrodynamic (MHD) equations embedded in a radial mean wind. The corresponding equations (expanding box model or EBM) have been considered earlier but never integrated in 3D simulations. Here, we follow the development of turbulence from 0.2 AU up to about 1.5 AU. Starting with isotropic spectra scaling as k <SUP>-1</SUP>, we observe a steepening toward a k <SUP>-5/3</SUP> scaling in the middle of the wave number range and formation of spectral anisotropies. The advection of a plasma volume by the expanding solar wind causes a non-trivial stretching of the volume in directions transverse to radial and the selective decay of the components of velocity and magnetic fluctuations. These two effects combine to yield the following results. (1) Spectral anisotropy: gyrotropy is broken, and the radial wave vectors have most of the power. (2) Coherent structures: radial streams emerge that resemble the observed microjets. (3) Energy spectra per component: they show an ordering in good agreement with the one observed in the solar wind at 1 AU. The latter point includes a global dominance of the magnetic energy over kinetic energy in the inertial and f <SUP>-1</SUP> range and a dominance of the perpendicular-to-the-radial components over the radial components in the inertial range. We conclude that many of the above properties are the result of evolution during transport in the heliosphere, and not just the remnant of the initial turbulence close to the Sun. (10.1088/0004-637X/793/2/118)
  DOI : 10.1088/0004-637X/793/2/118
• The influence of the geometry and electrical characteristics on the formation of the atmospheric pressure plasma jet
  
  • Sobota Ana
  • Guaitella Olivier
  • Rousseau Antoine
  Plasma Sources Science and Technology, IOP Publishing, 2014, 23, pp.025016. An extensive electrical study was performed on a coaxial geometry atmospheric pressure plasma jet source in helium, driven by 30 kHz sine voltage. Two modes of operation were observed, a highly reproducible low-power mode that features the emission of one plasma bullet per voltage period and an erratic high-power mode in which micro-discharges appear around the grounded electrode. The minimum of power transfer efficiency corresponds to the transition between the two modes. Effective capacitance was identified as a varying property influenced by the discharge and the dissipated power. The charge carried by plasma bullets was found to be a small fraction of charge produced in the source irrespective of input power and configuration of the grounded electrode. The biggest part of the produced charge stays localized in the plasma source and below the grounded electrode, in the range 1.23.3 nC for ground length of 38 mm. (10.1088/0963-0252/23/2/025016)
  DOI : 10.1088/0963-0252/23/2/025016
• Evidence of magnetic reconnection from wave measurements at Saturn's magnetopause: Cassini RPWS observations
  
  • Retinò Alessandro
  • Masters A.
  • Vaivads A.
  • Khotyaintsev Y. V.
  • Fujimoto M.
  • Kasahara S.
  • Badman S. V.
  • Canu Patrick
  • Chust Thomas
  • Modolo Ronan
  • Gurnett D. A.
  • Dougherty M. K.
  , 2014, 9, pp.EPSC2014-802. Magnetic reconnection is a universal mechanism that is responsible for major energy conversion in planetary magnetospheres. Recent theoretical estimations suggest that reconnection is infrequent at Saturn's magnetopause and that it is not a major driver of the dynamics of the kronian magnetosphere. This scenario need however to be confirmed by in situ observations at the magnetopause current sheet. Evidence of reconnection in the form of accelerated plasma jets is difficult at Saturn's magnetopause due to limitations in the field of view of particle detectors. Here we show evidence of reconnection for one magnetopause event by using measurements of low frequency waves (lower-hybrid, whistlers, plasma/upper hybrid). We discuss how wave measurements can be used as evidence of reconnection in planetary magnetospheres.
• Outflow and plasma acceleration in Titan's induced magnetotail: Evidence of magnetic tension forces
  
  • Romanelli N.
  • Modolo Ronan
  • Dubinin E.
  • Berthelier Jean-Jacques
  • Bertucci C.
  • Wahlund J. E.
  • Leblanc François
  • Canu Patrick
  • Edberg Niklas Jt
  • Waite H.
  • Kurth W. S.
  • Gurnett D.
  • Coates A.
  • Dougherty M.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2014, 119 (12), pp.9992–10005. Cassini plasma wave and particle observations are combined with magnetometer measurements to study Titan's induced magnetic tail. In this study, we report and analyze the plasma acceleration in Titan's induced magnetotail observed in flybys T17, T19 and T40. Radio and Plasma Wave Science (RPWS) observations show regions of cold plasma with electron densities between 0.1 and a few tens of electrons per cubic centimeter. The Cassini Plasma Spectrometer-Ion Mass Spectrometer (CAPS-IMS) measurements suggest that ionospheric plasma in this region is composed of ions with masses ranging from 15 to 17 amu and from 28 to 31 amu. From these measurements, we determine the bulk velocity of the plasma and the Alfvén velocity in Titan's tail region. Finally, a Walén test of such measurements suggest that the progressive acceleration of the ionospheric plasma shown by CAPS can be interpreted in terms of magnetic tension forces. (10.1002/2014JA020391)
  DOI : 10.1002/2014JA020391
• Compact hohlraum configuration with parallel planar-wire-array x-ray sources at the 1.7-MA Zebra generator
  
  • Vesey R. A.
  • Kantsyrev Viktor L.
  • Chuvatin Alexandre S.
  • Rudakov Leonid I.
  • Velikovich A. L.
  • Shreshta I. K.
  • Esaulov A. A.
  • Safronova Alla S.
  • Shlyaptseva V. V.
  • Osborne Glenn C.
  • Astanovitsky A. L.
  • Weller Michael E.
  • Stafford A.
  • Schultz K. A.
  • Cooper M. C.
  • Cuneo Michael E.
  • Jones B.
  Physical Review E, American Physical Society (APS), 2014, 90 (6), pp.063101. A compact Z-pinch x-ray hohlraum design with parallel-driven x-ray sources is experimentally demonstrated in a configuration with a central target and tailored shine shields at a 1.7-MA Zebra generator. Driving in parallel two magnetically decoupled compact double-planar-wire Z pinches has demonstrated the generation of synchronized x-ray bursts that correlated well in time with x-ray emission from a central reemission target. Good agreement between simulated and measured hohlraum radiation temperature of the central target is shown. The advantages of compact hohlraum design applications for multi-MA facilities are discussed. (10.1103/PhysRevE.90.063101)
  DOI : 10.1103/PhysRevE.90.063101
• Kinetic simulations of electric field structure within magnetic island during magnetic reconnection and their applications to the satellite observations
  
  • Huang S. Y.
  • Zhou M.
  • Yuan Z. G.
  • Deng X. H.
  • Sahraoui Fouad
  • Pang Y.
  • Fu S. Y.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2014, 119, pp.7402-7412. islands are considered to play a crucial role in collisionless magnetic reconnection. We use particle-in-cell simulations to investigate electric field E<SUB>z</SUB> structure in the magnetic islands (including primary and secondary islands) with and without a guide field during magnetic reconnection. It is found that the electric field has multilayers in the primary island and a large bipolar structure in the secondary island in the absence of guide field. The electric field is provided by the Hall term (J × B)<SUB>z</SUB> (mainly), the divergence of electron pressure tensor, and the convective term (V<SUB>i</SUB> × B)<SUB>z</SUB> in the outer and the inner region of primary island, while the electric field is much smaller (~0) in the middle and the core region of primary island due to the cancelation of the three terms. The single bipolar electric field is primarily provided by the Hall term in the secondary island. In the presence of a guide field, the electric field has multiple layers in the primary island (similar to zero guide field case) and the secondary island. However, there still exists one single large sharp bipolar structure of electric field in the central region of the secondary island. The differences of electric field in the primary and secondary islands are essentially due to the variations of the current J<SUB>y</SUB>. These features can be used as the observational criteria to identify different types of magnetic islands in the magnetosphere using the data of future mission, such as the Magnetospheric Multiscale mission. (10.1002/2014JA020054)
  DOI : 10.1002/2014JA020054
• Magnetic clouds' structure in the magnetosheath as observed by Cluster and Geotail: four case studies
  
  • Turc Lucile
  • Fontaine Dominique
  • Savoini Philippe
  • Kilpua E. K. J.
  Annales Geophysicae, European Geosciences Union, 2014, 32, pp.1247-1261. Magnetic clouds (MCs) are large-scale magnetic flux ropes ejected from the Sun into the interplanetary space. They play a central role in solar-terrestrial relations as they can efficiently drive magnetic activity in the near-Earth environment. Their impact on the Earth's magnetosphere is often attributed to the presence of southward magnetic fields inside the MC, as observed in the upstream solar wind. However, when they arrive in the vicinity of the Earth, MCs first encounter the bow shock, which is expected to modify their properties, including their magnetic field strength and direction. If these changes are significant, they can in turn affect the interaction of the MC with the magnetosphere. In this paper, we use data from the Cluster and Geotail spacecraft inside the magnetosheath and from the Advanced Composition Explorer (ACE) upstream of the Earth's environment to investigate the impact of the bow shock's crossing on the magnetic structure of MCs. Through four example MCs, we show that the evolution of the MC's structure from the solar wind to the magnetosheath differs largely from one event to another. The smooth rotation of the MC can either be preserved inside the magnetosheath, be modified, i.e. the magnetic field still rotates slowly but at different angles, or even disappear. The alteration of the magnetic field orientation across the bow shock can vary with time during the MC's passage and with the location inside the magnetosheath. We examine the conditions encountered at the bow shock from direct observations, when Cluster or Geotail cross it, or indirectly by applying a magnetosheath model. We obtain a good agreement between the observed and modelled magnetic field direction and shock configuration, which varies from quasi-perpendicular to quasi-parallel in our study. We find that the variations in the angle between the magnetic fields in the solar wind and in the magnetosheath are anti-correlated with the variations in the shock obliquity. When the shock is in a quasi-parallel regime, the magnetic field direction varies significantly from the solar wind to the magnetosheath. In such cases, the magnetic field reaching the magnetopause cannot be approximated by the upstream magnetic field. Therefore, it is important to take into account the conditions at the bow shock when estimating the impact of an MC with the Earth's environment because these conditions are crucial in determining the magnetosheath magnetic field, which then interacts with the magnetosphere. (10.5194/angeo-32-1247-2014)
  DOI : 10.5194/angeo-32-1247-2014
• NO oxidation on plasma pretreated Pyrex: the case for a distribution of reactivity of adsorbed O atoms
  
  • Guerra V.
  • Marinov Daniil
  • Guaitella Olivier
  • Rousseau Antoine
  Journal of Physics D: Applied Physics, IOP Publishing, 2014, 47 (22), pp.224012. The formation of NO 2 molecules on a Pyrex surface, as a result of NO oxidation by adsorbed O atoms on the wall, is experimentally demonstrated and quantified. The measurements reveal that the characteristic times of heterogeneous NO 2 production and NO gas phase decay change from ?60 to ?1500 s as the gas phase concentration of NO introduced in a tube pretreated with an oxygen radiofrequency discharge increases from 10 13 to 10 15 cm ?3 . Moreover, a clear variation of the characteristic loss frequency of NO molecules when small amounts of NO are successively injected in the tube is detected, between ?7 × 10 ?2 and ?5 × 10 ?3 s ?1 . The complex surface kinetics observed is studied and interpreted with the help of a mesoscopic surface model accounting for Eley?Rideal NO oxidation and slow NO 2 adsorption, confirming the existence of adsorption sites possessing a distribution of reactivity on the surface. (10.1088/0022-3727/47/22/224012)
  DOI : 10.1088/0022-3727/47/22/224012
• Radio-frequency capacitively coupled plasmas in hydrogen excited by tailored voltage waveforms: comparison of simulations with experiments
  
  • Diomede P.
  • Economou D. J.
  • Lafleur Trevor
  • Booth Jean-Paul
  • Longo S.
  Plasma Sources Science and Technology, IOP Publishing, 2014, 23 (6), pp.065049. A combined computational-experimental study was performed of a geometrically symmetric capacitively coupled plasma in hydrogen sustained by tailored voltage waveforms consisting of the sum of up to three harmonics. Predictions of a particle-in-cell with Monte Carlo collisions/fluid hybrid model were in reasonably good agreement compared to data from an array of experimental plasma diagnostics. The plasma was electrically asymmetric, with a dc self-bias developed, for all but a sinusoidal voltage waveform. Hydrogen ions (H<SUP> </SUP>,H <SUP> </SUP><SUB>2</SUB>,H <SUP> </SUP><SUB>3</SUB>) bombarding the electrodes exhibited different ion flux-distribution functions due to their different masses and collisionality in the sheath. Plasma density, ion flux and absolute value of the dc self-bias all increased with increasing the number of harmonics. The energy of ions bombarding the substrate electrode may be controlled by switching the applied voltage waveform from (positive) peaks to (negative) valleys. (10.1088/0963-0252/23/6/065049)
  DOI : 10.1088/0963-0252/23/6/065049