Publications

2014

• 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
• 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
• 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
• 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
• 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
• Electron energy distributions in a magnetized inductively coupled plasma
  
  • Song Sang-Heon
  • Yang Yang
  • Chabert Pascal
  • Kushner M.J.
  Physics of Plasmas, American Institute of Physics, 2014, 21 (9), pp.093512. Optimizing and controlling electron energy distributions (EEDs) is a continuing goal in plasma materials processing as EEDs determine the rate coefficients for electron impact processes. There are many strategies to customize EEDs in low pressure inductively coupled plasmas (ICPs), for example, pulsing and choice of frequency, to produce the desired plasma properties. Recent experiments have shown that EEDs in low pressure ICPs can be manipulated through the use of static magnetic fields of sufficient magnitudes to magnetize the electrons and confine them to the electromagnetic skin depth. The EED is then a function of the local magnetic field as opposed to having non-local properties in the absence of the magnetic field. In this paper, EEDs in a magnetized inductively coupled plasma (mICP) sustained in Ar are discussed with results from a two-dimensional plasma hydrodynamics model. Results are compared with experimental measurements. We found that the character of the EED transitions from non-local to local with application of the static magnetic field. The reduction in cross-field mobility increases local electron heating in the skin depth and decreases the transport of these hot electrons to larger radii. The tail of the EED is therefore enhanced in the skin depth and depressed at large radii. Plasmas densities are non-monotonic with increasing pressure with the external magnetic field due to transitions between local and non-local kinetics. (10.1063/1.4896711)
  DOI : 10.1063/1.4896711
• Les débris spatiaux : le revers de l'ère spatiale
  
  • Aanesland Ane
  • Grondein Pascaline
  Flash X - La revue scientifique de l'Ecole polytechnique, Ecole polytechnique, 2014 (16), pp.12.
• E x B shear pattern formation by radial propagation of heat flux waves
  
  • Kosuga Y.
  • Diamond P.H.
  • Dif-Pradalier Guilhem
  • Gürcan Özgür D.
  Physics of Plasmas, American Institute of Physics, 2014, 21 (5). A novel theory to describe the formation of E x B flow patterns by radially propagating heat flux waves is presented. A model for heat avalanche dynamics is extended to include a finite delay time between the instantaneous heat flux and the mean flux, based on an analogy between heat avalanche dynamics and traffic flow dynamics. The response time introduced here is an analogue of the drivers' response time in traffic dynamics. The microscopic foundation for the time delay is the time for mixing of the phase space density. The inclusion of the finite response time changes the model equation for avalanche dynamics from Burgers equation to a nonlinear telegraph equation. Based on the telegraph equation, the formation of heat flux jams is predicted. The growth rate and typical interval of jams are calculated. The connection of the jam interval to the typical step size of the E x B staircase is discussed. (C) 2014 AIP Publishing LLC. (10.1063/1.4872018)
  DOI : 10.1063/1.4872018
• Quantified energy dissipation rates in the terrestrial bow shock: 1. Analysis techniques and methodology
  
  • Wilson Iii L. B.
  • Sibeck David G.
  • Breneman A. W.
  • Le Contel Olivier
  • Cully C. M.
  • Turner D. L.
  • Angelopoulos V.
  • Malaspina D. M.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2014, 119 (8), pp.6455-6474. We present a detailed outline and discussion of the analysis techniques used to compare the relevance of different energy dissipation mechanisms at collisionless shock waves. We show that the low-frequency, quasi-static fields contribute less to ohmic energy dissipation, (-j·E), than their high-frequency counterparts. In fact, we found that high-frequency, large-amplitude (>100 mV/m and/or >1 nT) waves are ubiquitous in the transition region of collisionless shocks. We quantitatively show that their fields, through wave-particle interactions, cause enough energy dissipation to regulate the global structure of collisionless shocks. The purpose of this paper, part one of two, is to outline and describe in detail the background, analysis techniques, and theoretical motivation for our new results presented in the companion paper. The companion paper presents the results of our quantitative energy dissipation rate estimates and discusses the implications. Together, the two manuscripts present the first study quantifying the contribution that high-frequency waves provide, through wave-particle interactions, to the total energy dissipation budget of collisionless shock waves. (10.1002/2014JA019929)
  DOI : 10.1002/2014JA019929
• Observational evidence of electron pitch angle scattering driven by ECH waves
  
  • Kurita S.
  • Miyoshi Y.
  • Cully C. M.
  • Angelopoulos V.
  • Le Contel Olivier
  • Hikishima M.
  • Misawa H.
  Geophysical Research Letters, American Geophysical Union, 2014. Using the plasma wave and electron data obtained from Time History of Events and Macroscale Interactions during Substorms, we show a signature of electron pitch angle scattering driven by Electrostatic Cyclotron Harmonic (ECH) waves in the velocity distribution function (VDF). The diffusion curve of whistler mode waves is used as a proxy to identify changes in VDFs due to wave-particle interactions. We confirm that the shape of the VDF well agrees with the diffusion curve of whistler mode waves when whistler mode chorus alone is active. On the other hand, we find that the shape of the VDF deviates from the diffusion curves at low pitch angles when ECH waves are active following the inactivation of chorus waves. The result is observational support for electron pitch angle scattering caused by ECH waves and suggests that ECH waves can contribute to generation of diffuse auroras. (10.1002/2014GL061927)
  DOI : 10.1002/2014GL061927
• Theory and Modeling for the Magnetospheric Multiscale Mission
  
  • Hesse Michael
  • Aunai Nicolas
  • Birn Joachim
  • Cassak P.
  • Denton R.~e.
  • Drake J. F.
  • Gombosi Tamas I.
  • Hoshino M.
  • Matthaeus W.
  • Sibeck David G.
  • Zenitani Seiji
  Space Science Reviews, Springer Verlag, 2014. The Magnetospheric Multiscale (MMS) mission will provide measurement capabilities, which will exceed those of earlier and even contemporary missions by orders of magnitude. MMS will, for the first time, be able to measure directly and with sufficient resolution key features of the magnetic reconnection process, down to the critical electron scales, which need to be resolved to understand how reconnection works. Owing to the complexity and extremely high spatial resolution required, no prior measurements exist, which could be employed to guide the definition of measurement requirements, and consequently set essential parameters for mission planning and execution. Insight into expected details of the reconnection process could hence only been obtained from theory and modern kinetic modeling. This situation was recognized early on by MMS leadership, which supported the formation of a fully integrated Theory and Modeling Team (TMT). The TMT participated in all aspects of mission planning, from the proposal stage to individual aspects of instrument performance characteristics. It provided and continues to provide to the mission the latest insights regarding the kinetic physics of magnetic reconnection, as well as associated particle acceleration and turbulence, assuring that, to the best of modern knowledge, the mission is prepared to resolve the inner workings of the magnetic reconnection process. The present paper provides a summary of key recent results or reconnection research by TMT members. (10.1007/s11214-014-0078-y)
  DOI : 10.1007/s11214-014-0078-y
• Comment on "Micronewton electromagnetic thruster
  
  • Lafleur Trevor
  Applied Physics Letters, American Institute of Physics, 2014, 105, pp.146101. ... (10.1063/1.4897967)
  DOI : 10.1063/1.4897967
• Numerical simulations used for a validity check on the laser induced photo-detachment diagnostic method in electronegative plasmas
  
  • Oudini N.
  • Taccogna F.
  • Bendib A.
  • Aanesland Ane
  Physics of Plasmas, American Institute of Physics, 2014, 21 (6), pp.063515. Laser photo-detachment is used as a method to measure or determine the negative ion density and temperature in electronegative plasmas. In essence, the method consists of producing an electropositive channel (negative ion free region) via pulsed laser photo-detachment within an electronegative plasma bulk. Electrostatic probes placed in this channel measure the change in the electron density. A second pulse might be used to track the negative ion recovery. From this, the negative ion density and temperature can be determined. We study the formation and relaxation of the electropositive channel via a two-dimensional Particle-In-Cell/Mote Carlo collision model. The simulation is mainly carried out in a Hydrogen plasma with an electronegativity of &#945;&#8201;=&#8201;1, with a parametric study for &#945; up to 20. The temporal and spatial evolution of the plasma potential and the electron densities shows the formation of a double layer (DL) confining the photo-detached electrons within the electropositive channel. This DL evolves into two fronts that move in the opposite directions inside and outside of the laser spot region. As a consequence, within the laser spot region, the background and photo-detached electron energy distribution function relaxes/thermalizes via collisionless effects such as Fermi acceleration and Landau damping. Moreover, the simulations show that collisional effects and the DL electric field strength might play a non-negligible role in the negative ion recovery within the laser spot region, leading to a two-temperature negative ion distribution. The latter result might have important effects in the determination of the negative ion density and temperature from laser photo detachment diagnostic. (10.1063/1.4886144)
  DOI : 10.1063/1.4886144
• Radiation from mixed multi-planar wire arrays
  
  • Safronova Alla S.
  • Kantsyrev Viktor L.
  • Esaulov A. A.
  • Chuvatin Alexandre S.
  • Weller Michael E.
  • Shlyaptseva V. V.
  • Shrestha Ishor
  • Keim S. F.
  • Stafford A.
  • Coverdale C. A.
  • Apruzese J. P.
  • Ouart N. D.
  • Giuliani J. L.
  Physics of Plasmas, American Institute of Physics, 2014, 21 (03), pp.031205. The study of radiation from different wire materials in wire array Z-pinch plasma is a very challenging topic because it is almost impossible to separate different plasmas at the stagnation. A new approach is suggested based on planar wire array (PWA) loads to assess this problem. Multi-planar wire arrays are implemented that consist of few planes, each with the same number of wires and masses but from different wire materials, arranged in parallel rows. In particular, the experimental results obtained with triple PWAs (TPWAs) on the UNR Zebra generator are analyzed with Wire Ablation Dynamics Model, non-local thermodynamic equilibrium kinetic model, and 2D radiation magneto-hydrodynamic to illustrate this new approach. In TPWAs, two wire planes were from mid-atomic-number wire material and another plane was from alloyed Al, placed either in the middle or at the edge of the TPWA. Spatial and temporal properties of K-shell Al and L-shell Cu radiations were analyzed and compared from these two configurations of TPWAs. Advantages of the new approach are demonstrated and future work is discussed. (10.1063/1.4864335)
  DOI : 10.1063/1.4864335
• CLUSTER-STAFF search coil magnetometer calibration - comparisons with FGM
  
  • Robert Patrick
  • Cornilleau-Wehrlin Nicole
  • Piberne Rodrigue
  • de Conchy Y.
  • Lacombe C.
  • Bouzid V.
  • Grison B.
  • Alison Dominique
  • Canu Patrick
  Geoscientific Instrumentation, Methods and Data Systems, European Geosciences Union, 2014, 3, pp.153-177. The main part of the Cluster Spatio-Temporal Analysis of Field Fluctuations (STAFF) experiment consists of triaxial search coils allowing the measurements of the three magnetic components of the waves from 0.1 Hz up to 4 kHz. Two sets of data are produced, one by a module to filter and transmit the corresponding waveform up to either 10 or 180 Hz (STAFF-SC), and the second by the onboard Spectrum Analyser (STAFF-SA) to compute the elements of the spectral matrix for five components of the waves, 3 × B and 2 × E (from the EFW experiment), in the frequency range 8 Hz to 4 kHz. In order to understand the way the output signals of the search coils are calibrated, the transfer functions of the different parts of the instrument are described as well as the way to transform telemetry data into physical units across various coordinate systems from the spinning sensors to a fixed and known frame. The instrument sensitivity is discussed. Cross-calibration inside STAFF (SC and SA) is presented. Results of cross-calibration between the STAFF search coils and the Cluster Fluxgate Magnetometer (FGM) data are discussed. It is shown that these cross-calibrations lead to an agreement between both data sets at low frequency within a 2% error. By means of statistics done over 10 yr, it is shown that the functionalities and characteristics of both instruments have not changed during this period. (10.5194/gi-3-153-2014)
  DOI : 10.5194/gi-3-153-2014
• Theory for helical turbulence under fast rotation
  
  • Galtier Sébastien
  Physical Review E, American Physical Society (APS), 2014, 89, pp.41001. Recent numerical simulations have shown the strong impact of helicity on homogeneous rotating hydrodynamic turbulence. The main effect can be summarized through the law n ñ=-4, where n and ñ are the power law indices of the one-dimensional energy and helicity spectra, respectively. We investigate this rotating turbulence problem in the small Rossby number limit by using the asymptotic weak turbulence theory derived previously. We show that the empirical law is an exact solution of the helicity equation where the power law indices correspond to perpendicular (to the rotation axis) wave number spectra. It is proposed that when the cascade towards small scales tends to be dominated by the helicity flux the solution tends to ñ=-2, whereas it is ñ=-3/2 when the energy flux dominates. The latter is compatible with the solution previously observed numerically and derived theoretically in the weak turbulence regime when only the energy equation is used, whereas the former solution is constrained by a locality condition. (10.1103/PhysRevE.89.041001)
  DOI : 10.1103/PhysRevE.89.041001
• Investigation of Switch Designs for the Dynamic Load Current Multiplier Scheme on the SPHYNX Microsecond Linear Transformer Driver
  
  • Maysonnave Thomas
  • Bayol Frédéric
  • Demol Gauthier
  • d'Almeida Thierry
  • Lassalle Francis
  • Morell Alain
  • Grunenwald Julien
  • Chuvatin Alexandre S.
  • Pecastaing Laurent
  • de Ferron Antoine Silvestre
  IEEE Transactions on Plasma Science, Institute of Electrical and Electronics Engineers, 2014, 42 (10), pp.2974-2980. SPHINX is a microsecond linear transformer driver LTD, used essentially for implosion of Z-pinch loads in direct drive mode. It can deliver a 6-MA current pulse within 800 ns into a Z-pinch load. The dynamic load current multiplier concept enables the current pulse to be modified by increasing its amplitude while reducing its rise time before being delivered to the load. This compact system is made up of concentric electrodes (autotransformer), a dynamic flux extruder (cylindrical wire array), a vacuum convolute (eight postholes), and a vacuum closing switch, which is the key component of the system. Several different schemes are investigated for designing a vacuum switch suitable for operating the dynamic load current multiplier on the SPHINX generator for various applications, including isentropic compression experiments and Z-pinch radiation effects studies. In particular, the design of a compact vacuum surface switch and a multichannel vacuum switch, located upstream of the load are studied. Electrostatic simulations supporting the switch designs are presented along with test bed experiments. Initial results from shots on the SPHINX driver are also presented. (10.1109/TPS.2014.2313372)
  DOI : 10.1109/TPS.2014.2313372
• Quantified energy dissipation rates in the terrestrial bow shock: 2. Waves and dissipation
  
  • Wilson Iii L. B.
  • Sibeck David G.
  • Breneman A. W.
  • Le Contel Olivier
  • Cully C. M.
  • Turner D. L.
  • Angelopoulos V.
  • Malaspina D. M.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2014, 119 (8), pp.6475-6495. We present the first quantified measure of the energy dissipation rates, due to wave-particle interactions, in the transition region of the Earth's collisionless bow shock using data from the Time History of Events and Macroscale Interactions during Substorms spacecraft. Our results show that wave-particle interactions can regulate the global structure and dominate the energy dissipation of collisionless shocks. In every bow shock crossing examined, we observed both low-frequency (<10 Hz) and high-frequency (&#8819;10 Hz) electromagnetic waves throughout the entire transition region and into the magnetosheath. The low-frequency waves were consistent with magnetosonic-whistler waves. The high-frequency waves were combinations of ion-acoustic waves, electron cyclotron drift instability driven waves, electrostatic solitary waves, and whistler mode waves. The high-frequency waves had the following: (1) peak amplitudes exceeding deltaB 10 nT and deltaE 300 mV/m, though more typical values were deltaB 0.1-1.0 nT and deltaE 10-50 mV/m; (2) Poynting fluxes in excess of 2000 muW m<SUP>-2</SUP> (typical values were 1-10 muW m<SUP>-2</SUP>); (3) resistivities > 9000 Omega m; and (4) associated energy dissipation rates >10 muW m<SUP>-3</SUP>. The dissipation rates due to wave-particle interactions exceeded rates necessary to explain the increase in entropy across the shock ramps for 90% of the wave burst durations. For 22% of these times, the wave-particle interactions needed to only be <= 0.1% efficient to balance the nonlinear wave steepening that produced the shock waves. These results show that wave-particle interactions have the capacity to regulate the global structure and dominate the energy dissipation of collisionless shocks. (10.1002/2014JA019930)
  DOI : 10.1002/2014JA019930
• Finite ballooning angle effects on ion temperature gradient driven mode in gyrokinetic flux tube simulations
  
  • Singh Rameswar
  • Brunner Stephan
  • Ganesh R.
  • Jenko F.
  Physics of Plasmas, American Institute of Physics, 2014, 21 (3), pp.032115. This paper presents effects of finite ballooning angles on linear ion temperature gradient (ITG) driven mode and associated heat and momentum flux in Gyrokinetic flux tube simulation GENE. It is found that zero ballooning angle is not always the one at which the linear growth rate is maximum. The ITG mode acquires a short wavelength (SW) branch (k&#8869;&#961;i&#8201;>&#8201;1) when growth rates maximized over all ballooning angles are considered. However, the SW branch disappears on reducing temperature gradient showing characteristics of zero ballooning angle SWITG in case of extremely high temperature gradient. Associated heat flux is even with respect to ballooning angle and maximizes at nonzero ballooning angle while the parallel momentum flux is odd with respect to the ballooning angle. (10.1063/1.4868425)
  DOI : 10.1063/1.4868425
• Momentum transport in the vicinity of q<SUB>min</SUB> in reverse shear tokamaks due to ion temperature gradient turbulence
  
  • Singh Rameswar
  • Singh R.
  • Jhang Hogun
  • Diamond P.H.
  Physics of Plasmas, American Institute of Physics, 2014, 21 (1), pp.012302. This paper presents effects of finite ballooning angles on linear ion temperature gradient (ITG) driven mode and associated heat and momentum flux in Gyrokinetic flux tube simulation GENE. It is found that zero ballooning angle is not always the one at which the linear growth rate is maximum. The ITG mode acquires a short wavelength (SW) branch (k&#8869;&#961;i&#8201;>&#8201;1) when growth rates maximized over all ballooning angles are considered. However, the SW branch disappears on reducing temperature gradient showing characteristics of zero ballooning angle SWITG in case of extremely high temperature gradient. Associated heat flux is even with respect to ballooning angle and maximizes at nonzero ballooning angle while the parallel momentum flux is odd with respect to the ballooning angle. (10.1063/1.4861625)
  DOI : 10.1063/1.4861625
• Numerical computation of the modified plasma dispersion function with curvature
  
  • Gürcan Özgür D.
  Journal of Computational Physics, Elsevier, 2014, 269, pp.156-167. A particular generalization of the plasma dispersion function, which is linked to the regular plasma dispersion function via recurrence relations is discussed. The generalization allows a fast numerical implementation of a certain two-dimensional integral that appears in the description of the plasma dispersion in curved geometry, by reducing it to a single integral over a function involving the generalized plasma dispersion function. The local dielectric function of the toroidal ion temperature gradient driven mode can be written in terms of these integral functions. A matrix method is proposed to combine the consecutive integrals as a single 1D integral over a single integrand. The method allows two orders of magnitude speed up over the 2D integral implementation. Using various optimizations and an efficient implementation of the regular plasma dispersion function, further speed up is obtained. (C) 2014 Elsevier Inc. All rights reserved. (10.1016/j.jcp.2014.03.017)
  DOI : 10.1016/j.jcp.2014.03.017
• Experimental characterization of plasma formation and shockwave propagation induced by high power pulsed underwater electrical discharge
  
  • Claverie Alain
  • Deroy Julien
  • Boustié Michel
  • Avrillaud Gilles
  • Chuvatin Alexandre S.
  • Mazanchenko Ekaterina
  • Demol G.
  • Dramane B.
  Review of Scientific Instruments, American Institute of Physics, 2014, 85 (06), pp.063701. High power pulsed electrical discharges into liquids are investigated for new industrial applications based on the efficiency of controlled shock waves. We present here new experimental data obtained by combination of detailed high speed imaging equipments. It allows the visualization of the very first instants of plasma discharge formation, and then the pulsations of the gaseous bubble with an accurate timing of events. The time history of the expansion/compression of this bubble leads to an estimation of the energy effectively transferred to water during the discharge. Finally, the consecutive shock generation driven by this pulsating bubble is optically monitored by shadowgraphs and schlieren setup. These data provide essential information about the geometrical pattern and chronometry associated with the shock wave generation and propagation. (10.1063/1.4879715)
  DOI : 10.1063/1.4879715
• Propagation of lower-band whistler-mode waves in the outer Van Allen belt: Systematic analysis of 11 years of multi-component data from the Cluster spacecraft
  
  • Santolík O.
  • Macusova E.
  • Kolmasova Ivana
  • Cornilleau-Wehrlin Nicole
  • Conchy Y.
  Geophysical Research Letters, American Geophysical Union, 2014, 41, pp.2729-2737. Lower-band whistler-mode emissions can influence the dynamics of the outer Van Allen radiation belts. We use 11&#8201;years of measurements of the STAFF-SA instruments onboard the four Cluster spacecraft to systematically build maps of wave propagation parameters as a function of position. We determine probability distributions of wave vector angle weighted by the wave intensity. The results show that wave vector directions of intense waves are close to a Gaussian-shaped peak centered on the local magnetic field line. The width of this peak is between 10 and 20 degrees. The cumulative percentage of oblique waves is below 1015%. This result is especially significant for an important class of whistler-mode emissions of lower-band chorus at higher latitudes, well outside their source region, where a simple ray tracing model fails and another mechanism is necessary to keep the wave vectors close to the field-aligned direction. (10.1002/2014GL059815)
  DOI : 10.1002/2014GL059815
• Ionospheric disturbance dynamo associated to a coronal hole: Case study of 5-10 April 2010
  
  • Fathy Ibrahim
  • Amory-Mazaudier Christine
  • Fathy A.
  • Mahrous A. M.
  • Yumoto K.
  • Ghamry E.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2014, 119 (5), pp.4120–4133. In this paper we study the planetary magnetic disturbance during the magnetic storm occurring on 5 April 2010 associated with high-speed solar wind stream due to a coronal hole following a coronal mass ejection. We separate the magnetic disturbance associated to the ionospheric disturbance dynamo (Ddyn) from the magnetic disturbance associated to the prompt penetration of magnetospheric electric field (DP2). This event exhibits different responses of ionospheric disturbance dynamo in the different longitude sectors (European-African, Asian, and American). The strongest effect is observed in the European-African sector. The Ddyn disturbance reduces the amplitude of the daytime H component at low latitudes during four consecutive days in agreement with the Blanc and Richmond's model of ionospheric disturbance dynamo. The amplitude of Ddyn decreased with time during the 4 days. We discuss its diverse worldwide effects. The observed signature of magnetic disturbance process in specific longitude sector is strongly dependent on which Earth's side faces the magnetic storms (i.e., there is a different response depending on which longitude sector is at noon when the SSC hits). Finally, we determined an average period of 22 h for Ddyn using wavelet analysis. (10.1002/2013JA019510)
  DOI : 10.1002/2013JA019510