Publications

2014

• 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 α0 = 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 α0 > 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 α0 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
• 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
• 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
• 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
• 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
• 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.
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• 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 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
• Experimental validation of the dual positive and negative ion beam acceleration in the plasma propulsion with electronegative gases thruster
  
  • Rafalskyi D.V.
  • Popelier Lara
  • Aanesland Ane
  Journal of Applied Physics, American Institute of Physics, 2014, 115 (5), pp.053301. The PEGASES (Plasma Propulsion with Electronegative Gases) thruster is a gridded ion thruster, where both positive and negative ions are accelerated to generate thrust. In this way, additional downstream neutralization by electrons is redundant. To achieve this, the thruster accelerates alternately positive and negative ions from an ion-ion plasma where the electron density is three orders of magnitude lower than the ion densities. This paper presents a first experimental study of the alternate acceleration in PEGASES, where SF6 is used as the working gas. Various electrostatic probes are used to investigate the source plasma potential and the energy, composition, and current of the extracted beams. We show here that the plasma potential control in such system is key parameter defining success of ion extraction and is sensitive to both parasitic electron current paths in the source region and deposition of sulphur containing dielectric films on the grids. In addition, large oscillations in the ion-ion plasma potential are found in the negative ion extraction phase. The oscillation occurs when the primary plasma approaches the grounded parts of the main core via sub-millimetres technological inputs. By controlling and suppressing the various undesired effects, we achieve perfect ion-ion plasma potential control with stable oscillation-free operation in the range of the available acceleration voltages (±350&#8201;V). The measured positive and negative ion currents in the beam are about 10&#8201;mA for each component at RF power of 100&#8201;W and non-optimized extraction system. Two different energy analyzers with and without magnetic electron suppression system are used to measure and compare the negative and positive ion and electron fluxes formed by the thruster. It is found that at alternate ion-ion extraction the positive and negative ion energy peaks are similar in areas and symmetrical in position with /&#8722; ion energy corresponding to the amplitude of the applied acceleration voltage. (10.1063/1.4863876)
  DOI : 10.1063/1.4863876
• 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
• An electric field in nanosecond surface dielectric barrier discharge at different polarities of the high voltage pulse: spectroscopy measurements and numerical modeling
  
  • Stepanyan S.A.
  • Soloviev Victor
  • Starikovskaia Svetlana
  Journal of Physics D: Applied Physics, IOP Publishing, 2014, 47, pp.485201. The ratio of emission intensities of the second positive N2(C3&#928;u, v' = 0) &#8594; N2(B3&#928;g, v = 0), 337.1 nm and first negative, 391.4 nm systems of nitrogen have been measured in a nanosecond surface dielectric barrier discharge (SDBD). The measurements were carried out in synthetic air for a pressure range 13 bar for different polarities of the high-voltage (HV) pulse. For all the investigated conditions, the ratio of emission intensities at the wavelengthes 391.4 and 337.1 nm, measured experimentally, is systematically higher for the positive polarity of HV electrodes. To analyze the spatial distribution of N2(C3&#928;u) and emissions, comprehensive two-dimensional numerical modeling for P = 1 bar has been performed. The details of the formation of a narrow gap between the dielectric surface and the streamer channel in the case of positive polarity of HV electrodes are discussed. The ratio of integrated over space calculated emission intensities, , has been analyzed and compared with obtained experimental data. A good agreement was obtained for a negative polarity SDBD. For a positive polarity discharge, for all the considered conditions. Explanation for the observed effect is suggested. (10.1088/0022-3727/47/48/485201)
  DOI : 10.1088/0022-3727/47/48/485201
• Investigation of capillary nanosecond discharges in air at moderate pressure: comparison of experiments and 2D numerical modeling
  
  • Klochko A.V.
  • Starikovskaia Svetlana
  • Xiong Z.
  • Kushner M.J.
  Journal of Physics D: Applied Physics, IOP Publishing, 2014, 47, pp.365202. Nanosecond electrical discharges in the form of ionization waves are of interest for rapidly ionizing and exciting complex gas mixtures to initiate chemical reactions. Operating with a small discharge tube diameter can significantly increase the specific energy deposition and so enable optimization of the initiation process. Analysis of the uniformity of energy release in small diameter capillary tubes will aid in this optimization. In this paper, results for the experimentally derived characteristics of nanosecond capillary discharges in air at moderate pressure are presented and compared with results from a two-dimensional model. The quartz capillary tube, having inner and outer diameters of 1.5 and 3.4 mm, is about 80 mm long and filled with synthetic dry air at 27 mbar. The capillary tube with two electrodes at the ends is inserted into a break of the central wire of a long coaxial cable. A metal screen around the tube is connected to the cable ground shield. The discharge is driven by a 19 kV 35 ns voltage pulse applied to the powered electrode. The experimental measurements are conducted primarily by using a calibrated capacitive probe and back current shunts. The numerical modelling focuses on the fast ionization wave (FIW) and the plasma properties in the immediate afterglow after the conductive plasma channel has been established between the two electrodes. The FIW produces a highly focused region of electric field on the tube axis that sustains the ionization wave that eventually bridges the electrode gap. Results from the model predict FIW propagation speed and current rise time that agree with the experiment. (10.1088/0022-3727/47/36/365202)
  DOI : 10.1088/0022-3727/47/36/365202
• Electric field in nanosecond surface dielectric barrier discharge at different polarities of the high voltage pulse: spectroscopy measurements and numerical modeling.
  
  • Stepanyan S.A.
  • Victor Soloviev
  • Starikovskaia Svetlana
  Journal of Physics D: Applied Physics, IOP Publishing, 2014. Has been just accepted
• Pure airplasma bullets propagating inside microcapillaries and in ambient air
  
  • Lacoste D.A.
  • Bourdon Anne
  • Kuribara Koichi
  • Urabe Keiichiro
  • Stauss Sven
  • Terashima Kazuo
  Plasma Sources Science and Technology, IOP Publishing, 2014, 23, pp.062006. This paper reports on the characterization of airplasma bullets in microcapillary tubes and in ambient air, obtained without the use of inert or noble gases. The bullets were produced by nanosecond repetitively pulsed discharges, applied in a dielectric barrier discharge configuration. The anode was a tungsten wire with a diameter of 50&#956;m, centered in the microcapillary, while the cathode was a silver ring, fixed on the outer surface of the fused silica tube. The effects of the applied voltage and the inner diameter of the microcapillary tube on the plasma behavior were investigated. Inside the tubes, while the topology of the bullets seems to be strongly dependent on the diameter, their velocity is only a function of the amplitude of the applied voltage. In ambient air, the propagation of air bullets with a velocity of about 1.25 × 105 ms&#8722;1 is observed. (10.1088/0963-0252/23/6/062006)
  DOI : 10.1088/0963-0252/23/6/062006