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
• 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.
• Electron transport parameters in NF<SUB>3</SUB>
  
  • Lisovskiy V. A.
  • Yegorenkov V. D.
  • Ogloblina P.
  • Booth Jean-Paul
  • Martins S.
  • Landry K.
  • Douai D.
  • Cassagne V.
  Journal of Physics D: Applied Physics, IOP Publishing, 2014, 47 (11), pp.115203. We present electron transport parameters (the first Townsend coefficient, the dissociative attachment coefficient, the fraction of electron energy lost by collisions with NF 3 molecules, the average and characteristic electron energy, the electron mobility and the drift velocity) in NF 3 gas calculated from published elastic and inelastic electron?NF 3 collision cross-sections using the BOLSIG code. Calculations were performed for the combined RB (Rescigno 1995 Phys. Rev. E 52 [http://dx.doi.org/10.1103/PhysRevA.52.329] 329 , Boesten et al 1996 J. Phys. B: At. Mol. Opt. Phys. 29 [http://dx.doi.org/10.1088/0953-4075/29/22/022] 5475 ) momentum-transfer cross-section, as well as for the JB (Joucoski and Bettega 2002 J. Phys. B: At. Mol. Opt. Phys. 35 [http://dx.doi.org/10.1088/0953-4075/35/4/303] 783 ) momentum-transfer cross-section. In addition, we have measured the radio frequency (rf) breakdown curves for various inter-electrode gaps and rfs, and from these we have determined the electron drift velocity in NF 3 from the location of the turning point in these curves. These drift velocity values are in satisfactory agreement with those calculated by the BOLSIG code employing the JB momentum-transfer cross-section. (10.1088/0022-3727/47/11/115203)
  DOI : 10.1088/0022-3727/47/11/115203
• 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
• 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
• BV technique for investigating 1-D interfaces
  
  • Dorville Nicolas
  • Belmont Gérard
  • Rezeau Laurence
  • Aunai Nicolas
  • Retinò Alessandro
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2014, 119, pp.1709-1720. To investigate the internal structure of the magnetopause with spacecraft data, it is crucial to be able to determine its normal direction and to convert the measured time series into spatial profiles. We propose here a new single-spacecraft method, called the BV method, to reach these two objectives. Its name indicates that the method uses a combination of the magnetic field (B) and velocity (V) data. The method is tested on simulation and on Cluster data, and a short overview of the possible products is given. We discuss its assumptions and show that it can bring a valuable improvement with respect to previous methods. (10.1002/2013JA018926)
  DOI : 10.1002/2013JA018926
• Langmuir probe analysis in electronegative plasmas
  
  • Bredin Jérôme
  • Chabert Pascal
  • Aanesland Ane
  Physics of Plasmas, American Institute of Physics, 2014, 21 (12), pp.123502. This paper compares two methods to analyze Langmuir probe data obtained in electronegative plasmas. The techniques are developed to allow investigations in plasmas, where the electronegativity &#945;0&#8201;=&#8201;n/ne (the ratio between the negative ion and electron densities) varies strongly. The first technique uses an analytical model to express the Langmuir probe current-voltage (I-V) characteristic and its second derivative as a function of the electron and ion densities (ne, n , n), temperatures (Te, T , T), and masses (me, m , m). The analytical curves are fitted to the experimental data by adjusting these variables and parameters. To reduce the number of fitted parameters, the ion masses are assumed constant within the source volume, and quasi-neutrality is assumed everywhere. In this theory, Maxwellian distributions are assumed for all charged species. We show that this data analysis can predict the various plasma parameters within 510%, including the ion temperatures when &#945;0&#8201;>&#8201;100. However, the method is tedious, time consuming, and requires a precise measurement of the energy distribution function. A second technique is therefore developed for easier access to the electron and ion densities, but does not give access to the ion temperatures. Here, only the measured I-V characteristic is needed. The electron density, temperature, and ion saturation current for positive ions are determined by classical probe techniques. The electronegativity &#945;0 and the ion densities are deduced via an iterative method since these variables are coupled via the modified Bohm velocity. For both techniques, a Child-Law sheath model for cylindrical probes has been developed and is presented to emphasize the importance of this model for small cylindrical Langmuir probes. (10.1063/1.4903328)
  DOI : 10.1063/1.4903328
• 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
• 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
• A model of the magnetosheath magnetic field during magnetic clouds
  
  • Turc Lucile
  • Fontaine Dominique
  • Savoini Philippe
  • Kilpua E.K.J.
  Annales Geophysicae, European Geosciences Union, 2014, 32 (2), pp.157-173. Magnetic clouds (MCs) are huge interplanetary structures which originate from the Sun and have a paramount importance in driving magnetospheric storms. Before reaching the magnetosphere, MCs interact with the Earth's bow shock. This may alter their structure and therefore modify their expected geoeffectivity. We develop a simple 3-D model of the magnetosheath adapted to MCs conditions. This model is the first to describe the interaction of MCs with the bow shock and their propagation inside the magnetosheath. We find that when the MC encounters the Earth centrally and with its axis perpendicular to the Sun–Earth line, the MC's magnetic structure remains mostly unchanged from the solar wind to the magnetosheath. In this case, the entire dayside magnetosheath is located downstream of a quasi-perpendicular bow shock. When the MC is encountered far from its centre, or when its axis has a large tilt towards the ecliptic plane, the MC's structure downstream of the bow shock differs significantly from that upstream. Moreover, the MC's structure also differs from one region of the magnetosheath to another and these differences vary with time and space as the MC passes by. In these cases, the bow shock configuration is mainly quasi-parallel. Strong magnetic field asymmetries arise in the mag-netosheath; the sign of the magnetic field north–south component may change from the solar wind to some parts of the magnetosheath. We stress the importance of the B x component. We estimate the regions where the magnetosheath and magnetospheric magnetic fields are anti-parallel at the mag-netopause (i.e. favourable to reconnection). We find that the location of anti-parallel fields varies with time as the MCs move past Earth's environment, and that they may be situated near the subsolar region even for an initially northward magnetic field upstream of the bow shock. Our results point out the major role played by the bow shock configuration in modifying or keeping the structure of the MCs unchanged. Note that this model is not restricted to MCs, it can be used to describe the magnetosheath magnetic field under an arbitrary slowly varying interplanetary magnetic field. (10.5194/angeo-32-157-2014)
  DOI : 10.5194/angeo-32-157-2014
• 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
• Characterization of predator-prey dynamics, using the evolution of free energy in plasma turbulence
  
  • Morel Pierre
  • Gürcan Özgür D.
  • Berionni Vincent
  Plasma Physics and Controlled Fusion, IOP Publishing, 2014, 56 (1), pp.015002. A simple dynamical cascade model for the evolution of free energy is considered in the context of gyrokinetic formalism. It is noted that the dynamics of free energy, that characterize plasma micro-turbulence in magnetic fusion devices, exhibit a predatorprey character. Various key features of predatorprey dynamics such as the time delay between turbulence and large-scale flow structures, or the intermittency of the dynamics are identified in the quasi-steady-state phase of the nonlinear gyrokinetic simulations. A novel prediction on the ratio of turbulence amplitudes in different parts of the wavenumber domain that follows from this simple predatorprey model is compared to a set of nonlinear simulation results and is observed to hold quite well in a large range of physical parameters. Detailed validation of the predatorprey hypothesis using nonlinear gyrokinetics provides a very important input for the effort to apprehend plasma micro-turbulence, since the predatorprey idea can be used as a very effective intuitive tool for understanding and designing efficient transport models. (10.1088/0741-3335/56/1/015002)
  DOI : 10.1088/0741-3335/56/1/015002
• Acetylene photocatalytic oxidation using continuous flow reactor: Gas phase and adsorbed phase investigation, assessment of the photocatalyst deactivation
  
  • Thevenet F.
  • Guillard C.
  • Rousseau A.
  Chemical Engineering Journal, Elsevier, 2014, 244, pp.50-58. Acetylene, used as a model volatile organic compound (VOC), is submitted to photocatalytic oxidation. This study is based on the simultaneous characterisation of: (i) the gas phase at the reactor outlet; (ii) the adsorbed phase on the photocatalytic media. Experiments are performed in a continuous flow reactor, and analytical procedures have been developed to identify and quantify the gaseous and adsorbed side-products. The photocatalytic media consists in P25 Degussa TiO2 nanoparticles deposited on glass fibres. First, the process efficiency is investigated through C2H2 conversion rate and mineralisation. The treatment performances tend to decrease with time regarding conversion and mineralisation. Then, the oxidation process is investigated through gaseous and adsorbed by-products. Three carboxylic acids have been quantified in the adsorbed phase during oxidative treatment; their temporal evolutions are determined. Their contribution to the carbon balance is discussed. It is evidenced that their adsorption on the photocatalytic media leads to a saturation of the surface. Formaldehyde, glyoxal and formic acid are quantified in the gas phase. Their cumulative temporal profiles and their contribution to the carbon balance confirm the hypothesis of a surface deactivation. The decrease of the process performances with time and the increase of gaseous by-products are correlated with the photocatalyst coverage by adsorbed acids. Carbon balances calculated for various treatment times, give an overview of the process evolution. The regeneration of the photocatalyst surface is possible under synthetic air; 80% of the adsorbed compounds are mineralised. The performances of a cyclic procedure (treatment/regeneration) are evaluated. This approach preserves the photocatalyst performances and ensures a mineralisation of 85% of the converted acetylene. (C) 2014 Elsevier B.V. All rights reserved. (10.1016/j.cej.2014.01.038)
  DOI : 10.1016/j.cej.2014.01.038
• Waveforms of Langmuir turbulence in inhomogeneous solar wind plasmas
  
  • Krafft C
  • Volokitin A.
  • Krasnoselskikh V.V.
  • Dudok de Wit Thierry
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2014, 119, pp.9369–9382. Modulated Langmuir waveforms have been observed by several spacecraft in various regions of the heliosphere, such as the solar wind, the electron foreshock, the magnetotail, or the auroral ionosphere. Many observations revealed the bursty nature of these waves, which appear to be highly modulated, localized, and clumped into spikes with peak amplitudes typically 3 orders of magnitude above the mean. The paper presents Langmuir waveforms calculated using a Hamiltonian model describing self-consistently the resonant interaction of an electron beam with Langmuir wave packets in a plasma with random density fluctuations. These waveforms, obtained for different profiles of density fluctuations and ranges of parameters relevant to solar type III electron beams and plasmas measured at 1 AU, are presented in the form they would appear if recorded by a satellite moving in the solar wind. Comparison with recent measurements by the STEREO and WIND satellites shows that their characteristic features are very similar to the observations. (10.1002/2014JA020329)
  DOI : 10.1002/2014JA020329
• Radiation in the neighbourhood of a double layer
  
  • Pottelette Raymond
  • Berthomier Matthieu
  • Pickett J. S.
  Annales Geophysicae, European Geosciences Union, 2014, 32, pp.677-687. In the auroral kilometric radiation (AKR) source region, acceleration layers narrow in altitude and associated with parallel field-aligned potential drops of several kV can be identified by using both particles and wave-field high time-resolution measurements from the Fast Auroral SnapshoT explorer spacecraft (FAST). These so-called double layers (DLs) are recorded around density enhancements in the auroral cavity, where the enhancement can be at the edge of the cavity or even within the cavity at a small scale. Once immersed in the plasma, DLs necessarily accelerate particles along the magnetic field lines, thereby generating locally strong turbulent processes leading to the formation of nonlinear phase space holes. The FAST data reveal the asymmetric character of the turbulence: the regions located on the high-potential side of the DLs are characterized by the presence of electron holes, while on the low-potential side, ion holes are recorded. The existence of these nonlinear phase space holes may affect the AKR radiation pattern in the neighbourhood of a DL where the electron distribution function is drastically different from a horseshoe shape. We present some observations which illustrate the systematic generation of elementary radiation events occurring significantly above the local electron gyrofrequency in the presence of electron holes. These fine-scale AKR radiators are associated with a local electron distribution which presents a pronounced beam-like shape. (10.5194/angeo-32-677-2014)
  DOI : 10.5194/angeo-32-677-2014
• Whistler mode waves at magnetotail dipolarization fronts
  
  • Viberg H.
  • Khotyaintsev Y. V.
  • Vaivads A.
  • André M.
  • Fu H.S.
  • Cornilleau-Wehrlin Nicole
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2014, 119, pp.2605-2611. We report the statistics of whistler mode waves observed in relation to dipolarization fronts (DFs) in Earth's magnetotail using data from the four Cluster spacecraft spanning a period of 9 years, 20012009. We show that whistler mode waves are common in a vicinity of DFs: between 30 and 60% of all DFs are associated with whistlers. Whistlers are about 7 times more likely to be observed near a DF than at any random location in the magnetotail. Therefore, whistlers are a characteristic signature of DFs. We find that whistlers are most often detected in the flux pileup region (FPR) following the DF, close to the center of the current sheet (Bx&#8201;&#8764;&#8201;0) and in association with anisotropic electron distributions (Tperp>T&#8741;). This suggests that we typically observe emissions in the source region where they are generated by the anisotropic electrons produced by the betatron process inside the FPR. (10.1002/2014JA019892)
  DOI : 10.1002/2014JA019892
• Radiation from Ag high energy density Z-pinch plasmas and applications to lasing
  
  • Weller Michael E.
  • Safronova Alla S.
  • Kantsyrev Viktor L.
  • Esaulov A. A.
  • Shrestha Ishor
  • Apruzese J. P.
  • Giuliani J. L.
  • Chuvatin Alexandre S.
  • Stafford A.
  • Keim S. F.
  • Shlyaptseva V. V.
  • Osborne Glenn C.
  • Petkov E. E.
  Physics of Plasmas, American Institute of Physics, 2014, 21 (03), pp.031206. Silver (Ag) wire arrays were recently introduced as efficient x-ray radiators and have been shown to create L-shell plasmas that have the highest electron temperature (>1.8&#8201;keV) observed on the Zebra generator so far and upwards of 30&#8201;kJ of energy output. In this paper, results of single planar wire arrays and double planar wire arrays of Ag and mixed Ag and Al that were tested on the UNR Zebra generator are presented and compared. To further understand how L-shell Ag plasma evolves in time, a time-gated x-ray spectrometer was designed and fielded, which has a spectral range of approximately 3.55.0&#8201;Å. With this, L-shell Ag as well as cold L&#945; and L&#946; Ag lines was captured and analyzed along with photoconducting diode (PCD) signals (>0.8&#8201;keV). Along with PCD signals, other signals, such as filtered XRD (>0.2&#8201;keV) and Si-diodes (SiD) (>9&#8201;keV), are analyzed covering a broad range of energies from a few eV to greater than 53&#8201;keV. The observation and analysis of cold L&#945; and L&#946; lines show possible correlations with electron beams and SiD signals. Recently, an interesting issue regarding these Ag plasmas is whether lasing occurs in the Ne-like soft x-ray range, and if so, at what gains? To help answer this question, a non-local thermodynamic equilibrium (LTE) kinetic model was utilized to calculate theoretical lasing gains. It is shown that the Ag L-shell plasma conditions produced on the Zebra generator at 1.7 maximum current may be adequate to produce gains as high as 6&#8201;cm&#8722;1 for various 3p&#8201;&#8594;&#8201;3s transitions. Other potential lasing transitions, including higher Rydberg states, are also included in detail. The overall importance of Ag wire arrays and plasmas is discussed. (10.1063/1.4865368)
  DOI : 10.1063/1.4865368
• Simulation of long term variation of the F2-layer critical frequency f0F2 at the northern tropical crest of ionization at Phu Thuy, Vietnam with the thermosphere-ionosphere-electrodynamics general circulation model (TIE-GCM)
  
  • Pham Thi Thu Hong
  • Amory-Mazaudier Christine
  • Le Huy Minh
  Vietnam Journal of Earth Sciences, Vietnam Academy of Science and Technology (VAST), 2014 (36), pp.470-479. In this work, the long-term variations of the simulated f0F2 by the NCAR thermosphere ionosphere-electrodynamics general circulation model (TIE-GCM) at the northern tropical crest of ionization at Phu Thuy-Vietnam (geographic latitudes 21.030N and longitude: 105.950E) during the period from 1962 to 2002 are examined to evaluate the ability of this model to reproduce the major features of the f0F2 as observed. The TIE-GCM simulates the influences of migrating and non-migrating diurnal and semidiurnal tides at the lower thermosphere, and changes of geomagnetic activity on the long-term variation of the f0F2. It reproduces well the diurnal and seasonal variations. We analyze the diurnal and seasonal variations of the observed f0F2 at Phu Thuy in approximately the same solar activity condition as in 1964, 1996 for the March and September equinoxes and June and December solstices. The local time and seasonal structures of these simulated results correspond well to those that are observed in 1964. On the contrary, the TIE-GCM model does not reproduce the amplitude observed at Thuy Phu in 1996. The TIE-GCM model with the chosen inputs does not yet allow us to explain well the long-term variations observed at Phu Thuy. We also try the different numerical simulations to understand how the long-term variation of the f0F2 is formed, how it relates to the current global system and its relationship with the thermosphere wind. The simulations show that the calculated NmF2 values are lower than the observed values. We find that the modeled contributions of the migrating and non-migrating diurnal and semidiurnal tides may cause them to play a major role in reducing the amplitude of the NmF2. The contributions of the integrated hemispheric power of auroral electrons and the cross polar cap potential seem to play an important role in increasing the amplitude of the NmF2. Keywords: F2 layer; Long-term trends; Ionosphere equatorial ionization anomaly; Ionosphere (ionospheric conductivities, ionospheric currents and electric field), thermospheric tides, Electrodynamics of the ionosphere (ionospheric dynamo).
• On the relationship between quadrupolar magnetic field and collisionless reconnection
  
  • Smets Roch
  • Aunai Nicolas
  • Belmont Gérard
  • Boniface C.
  • Fuchs J. C.
  Physics of Plasmas, American Institute of Physics, 2014, 21 (6), pp.062111. Using hybrid simulations, we investigate the onset of fast reconnection between two cylindrical magnetic shells initially close to each other. This initial state mimics the plasma structure in High Energy Density Plasmas induced by a laser-target interaction and the associated self-generated magnetic field. We clearly observe that the classical quadrupolar structure of the out-of-plane magnetic field appears prior to the reconnection onset. Furthermore, a parametric study reveals that, with a non-coplanar initial magnetic topology, the reconnection onset is delayed and possibly suppressed. The relation between the out-of-plane magnetic field and the out-of-plane electric field is discussed. (10.1063/1.4885097)
  DOI : 10.1063/1.4885097
• Helicon plasma thruster discharge model
  
  • Lafleur Trevor
  Physics of Plasmas, American Institute of Physics, 2014, 21, pp.043507. By considering particle, momentum, and energy balance equations, we develop a semi-empirical quasi one-dimensional analytical discharge model of radio-frequency and helicon plasma thrusters. The model, which includes both the upstream plasma source region as well as the downstream diverging magnetic nozzle region, is compared with experimental measurements and confirms current performance levels. Analysis of the discharge model identifies plasma power losses on the radial and back wall of the thruster as the major performance reduction factors. These losses serve as sinks for the input power which do not contribute to the thrust, and which reduce the maximum plasma density and hence propellant utilization. With significant radial plasma losses eliminated, the discharge model (with argon) predicts specific impulses in excess of 3000&#8201;s, propellant utilizations above 90%, and thruster efficiencies of about 30%. (10.1063/1.4871727)
  DOI : 10.1063/1.4871727