Publications

2016

• A Review of General Physical and Chemical Processes Related to Plasma Sources and Losses for Solar System Magnetospheres
  
  • Seki K.
  • Nagy A.
  • Jackman C. M.
  • Crary F.
  • Fontaine Dominique
  • Zarka P.
  • Wurz Peter
  • Milillo A.
  • Slavin J. A.
  • Delcourt Dominique
  • Wiltberger M.
  • Ilie R.
  • Jia X.
  • Ledvina S. A.
  • Liemohn M. W.
  • Schunk R. W.
  • Blanc Michel
  • Chappell Charles R.
  • Krupp N.
  , 2016, pp.27-89. The aim of this paper is to provide a review of general processes related to plasma sources, their transport, energization, and losses in the planetary magnetospheres. We provide background information as well as the most up-to-date knowledge of the comparative studies of planetary magnetospheres, with a focus on the plasma supply to each region of the magnetospheres. This review also includes the basic equations and modeling methods commonly used to simulate the plasma sources of the planetary magnetospheres. In this paper, we will describe basic and common processes related to plasma supply to each region of the planetary magnetospheres in our solar system. First, we will describe source processes in Sect. 1. Then the transport and energization processes to supply those source plasmas to various regions of the magnetosphere are described in Sect. 2. Loss processes are also important to understand the plasma population in the magnetosphere and Sect. 3 is dedicated to the explanation of the loss processes. In Sect. 4, we also briefly summarize the basic equations and modeling methods with a focus on plasma supply processes for planetary magnetospheres.
• Mars-solar wind interaction: LatHyS, an improved parallel 3-D multispecies hybrid model
  
  • Modolo Ronan
  • Hess Sebastien
  • Mancini Marco
  • Leblanc François
  • Chaufray Jean-Yves
  • Brain David
  • Leclercq Ludivine
  • Esteban Hernandez Rosa
  • Chanteur Gérard
  • Weill Philippe
  • González-Galindo Francisco
  • Forget François
  • Yagi Manabu
  • Mazelle Christian
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2016, 121 (7), pp.6378–6399. In order to better represent Mars-Solar wind interaction, we present an unprecedented model achieving spatial resolution down to 50 km, a so far unexplored resolution for global kinetic models of the Martian ionized environment. Such resolution approaches the ionospheric plasma scale height. In practice, the model is derived from a first version described in Modolo et al. [2005]. An important effort of parallelization has been conducted and is presented here. A better description of the ionosphere was also implemented including ionospheric chemistry, electrical conductivities and a drag force modelling the ion-neutral collisions in the ionosphere. This new version of the code, named LatHyS (Latmos Hybrid Simulation), is here used to characterize the impact of various spatial resolutions on simulation results. In addition, and following a global model challenge effort [Brain et al., 2010], we present the results of simulation run for three cases which allows addressing the effect of the supra-thermal corona and of the solar EUV activity on the magnetospheric plasma boundaries and on the global escape. Simulation results showed that global patterns are relatively similar for the different spatial resolution runs but finest grid runs provide a better representation of the ionosphere and display more details of the planetary plasma dynamic. Simulation results suggest that a significant fraction of escaping O+ ions is originated from below 1200 km altitude. (10.1002/2015JA022324)
  DOI : 10.1002/2015JA022324
• Tailored voltage waveform capacitively coupled plasmas in electronegative gases: frequency dependence of asymmetry effects
  
  • Schüngel E.
  • Korolov Ihor
  • Bruneau Bastien
  • Derzsi A.
  • Johnson E.V.
  • O'Connell D.
  • Gans T.
  • Booth Jean-Paul
  • Donkó Z.
  • Schulze J.
  Journal of Physics D: Applied Physics, IOP Publishing, 2016, 49 (26), pp.265203. Capacitively coupled radio frequency plasmas operated in an electronegative gas (CF 4 ) and driven by voltage waveforms composed of four consecutive harmonics are investigated for different fundamental driving frequencies using PIC/MCC simulations and an analytical model. As has been observed previously for electropositive gases, the application of peak-shaped waveforms (that are characterized by a strong amplitude asymmetry) results in the development of a DC self-bias due to the electrical asymmetry effect (EAE), which increases the energy of ions arriving at the powered electrode. In contrast to the electropositive case (Korolov et al 2012 J. Phys. D: Appl. Phys . 45 465202) the absolute value of the DC self-bias is found to increase as the fundamental frequency is reduced in this electronegative discharge, providing an increased range over which the DC self-bias can be controlled. The analytical model reveals that this increased DC self-bias is caused by changes in the spatial profile and the mean value of the net charge density in the grounded electrode sheath. The spatio-temporally resolved simulation data show that as the frequency is reduced the grounded electrode sheath region becomes electronegative. The presence of negative ions in this sheath leads to very different dynamics of the power absorption of electrons, which in turn enhances the local electronegativity and plasma density via ionization and attachment processes. The ion flux to the grounded electrode (where the ion energy is lowest) can be up to twice that to the powered electrode. At the same time, while the mean ion energies at both electrodes are quite different, their ratio remains approximately constant for all base frequencies studied here. (10.1088/0022-3727/49/26/265203)
  DOI : 10.1088/0022-3727/49/26/265203
• Electron density measurements in highly electronegative plasmas
  
  • Rafalskyi D.V.
  • Lafleur Trevor
  • Aanesland Ane
  Plasma Sources Science and Technology, IOP Publishing, 2016, 25 (4), pp.047001. In this paper we present experimental measurements of the electron density in very electronegative ionion ArSF 6 plasmas where previous investigations using Langmuir probes have observed electronegativities of up to 5000. The electron density is measured using a short matched dipole probe technique that provides a tolerance better than  ±2 · 10 13 m −3 . The results demonstrate that the electron density in the low pressure plasma source (which contains a magnetic filter) can be reduced to around 2.7 · 10 13 m −3 with a corresponding plasma electronegativity of about 4000; close to that from fluid simulation predictions. The highest electronegativity, and lowest electron density, is achieved with a pure SF 6 plasma, while adding only 6% SF 6 to Ar allows the electronegativity to be increased from 0 to a few hundred with a corresponding decrease in the electron density by more than a thousand. The impedance probe based on a short matched dipole appears to be a practical diagnostic that can be used for independent measurements of the electron density in very electronegative plasmas, and opens up the possibility to further investigate and optimize electronegative plasma sources. (10.1088/0963-0252/25/4/047001)
  DOI : 10.1088/0963-0252/25/4/047001
• Optimized merging of search coil and fluxgate data for MMS
  
  • Fischer David
  • Magnes Werner
  • Hagen Christian
  • Dors Ivan
  • Chutter Mark W.
  • Needell Jerry
  • Torbert Roy B.
  • Le Contel Olivier
  • Strangeway Robert J.
  • Kubin Gernot
  • Valavanoglou Aris
  • Plaschke Ferdinand
  • Nakamura R.
  • Mirioni Laurent
  • Russell Christopher T.
  • Leinweber Hannes K.
  • Bromund Kenneth R.
  • Le Guan
  • Kepko Lawrence
  • Anderson Brian J.
  • Slavin J. A.
  • Baumjohann W.
  Geoscientific Instrumentation, Methods and Data Systems, European Geosciences Union, 2016, 5, pp.521-530. The Magnetospheric Multiscale mission (MMS) targets the characterization of fine-scale current structures in the Earth's tail and magnetopause. The high speed of these structures, when traversing one of the MMS spacecraft, creates magnetic field signatures that cross the sensitive frequency bands of both search coil and fluxgate magnetometers. Higher data quality for analysis of these events can be achieved by combining data from both instrument types and using the frequency bands with best sensitivity and signal-to-noise ratio from both sensors. This can be achieved by a model-based frequency compensation approach which requires the precise knowledge of instrument gain and phase properties. We discuss relevant aspects of the instrument design and the ground calibration activities, describe the model development and explain the application on in-flight data. Finally, we show the precision of this method by comparison of in-flight data. It confirms unity gain and a time difference of less than 100 µs between the different magnetometer instruments. (10.5194/gi-5-521-2016)
  DOI : 10.5194/gi-5-521-2016
• Transport in the barrier billiard
  
  • Saberi Fathi S. M.
  • Ettoumi W.
  • Courbage M.
  Physical Review E, American Physical Society (APS), 2016, 93. We investigate transport properties of an ensemble of particles moving inside an infinite periodic horizontal planar barrier billiard. A particle moves among bars and elastically reflects on them. The motion is a uniform translation along the bars' axis. When the tangent of the incidence angle, alpha , is fixed and rational, the second moment of the displacement along the orthogonal axis at time n , , is either bounded or asymptotic to K n<SUP>2</SUP> , when n -->&infin; . For irrational alpha , the collision map is ergodic and has a family of weakly mixing observables, the transport is not ballistic, and autocorrelation functions decay only in time average, but may not decay for a family of irrational alpha 's. An exhaustive numerical computation shows that the transport may be superdiffusive or subdiffusive with various rates or bounded strongly depending on the values of alpha . The variety of transport behaviors sounds reminiscent of well-known behavior of conservative systems. Considering then an ensemble of particles with nonfixed alpha , the system is nonergodic and certainly not mixing and has anomalous diffusion with self-similar space-time properties. However, we verified that such a system decomposes into ergodic subdynamics breaking self-similarity. (10.1103/PhysRevE.93.062216)
  DOI : 10.1103/PhysRevE.93.062216
• Comment on "Insight into hydrogenation of graphene: Effect of hydrogen plasma chemistry" [Appl. Phys. Lett. 105, 183104 (2014)]
  
  • Marinov Daniil
  Applied Physics Letters, American Institute of Physics, 2016, 108. Not Available (10.1063/1.4953260)
  DOI : 10.1063/1.4953260
• The Mass Spectrum Analyzer (MSA) on board the BepiColombo MMO
  
  • Delcourt Dominique C.
  • Saito Y.
  • Leblanc Frédéric
  • Verdeil Christophe
  • Yokota S.
  • Fraenz M.
  • Fischer H.
  • Fiethe B.
  • Katra Bruno
  • Fontaine Dominique
  • Illiano Jean-Marie
  • Berthelier Jean-Jacques
  • Krupp N.
  • Buhrke U.
  • Bubenhagen F.
  • Michalik H.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2016, 121 (7), pp.6749-6761. Observations from the MESSENGER spacecraft have considerably enhanced our understanding of the plasma environment at Mercury. In particular, measurements from the Fast Imaging Plasma Spectrometer (FIPS) provide evidences of a variety of ion species of planetary origin (He+, O+, Na+) in the northern dayside cusp and in the nightside plasma sheet. A more comprehensive view of Mercury's plasma environment will be provided by the Bepi Colombo mission that will be launched in 2018. Onboard the Bepi Colombo MMO spacecraft, the MPPE (Mercury Plasma/Particle Experiment) consortium gathers different sensors dedicated to particle measurements. Among these sensors, the Mass Spectrum Analyzer (MSA) is the instrument dedicated to plasma composition analysis. It consists of a top-hat for energy analysis followed by a Time-Of-Flight (TOF) chamber to derive the ion mass. Taking advantage of the spacecraft rotation, MSA will measure three-dimensional distribution functions in one spin (4 s), from energies characteristic of exospheric populations (in the eV range) up to plasma sheet energies (up to ~38 keV/q). A notable feature of the MSA instrument is that the TOF chamber is polarized with a linear electric field that leads to isochronous TOFs and enhanced mass resolution (typically, m/∆m ≈ 40 for ions with energies up to 13 keV/q). At Mercury, this capability is of paramount importance to thoroughly characterize the wide variety of ion species originating from the planet surface. It is thus anticipated that MSA will provide unprecedented information on ion populations in the Hermean environment and hence improve our understanding of the coupling processes at work. (10.1002/2016JA022380)
  DOI : 10.1002/2016JA022380
• Day-to-day variability of VTEC and ROTI in October 2012 with impact of high-speed solar wind stream on 13 October 2012
  
  • Azzouzi Ilyasse
  • Migoya-Orué Yenca
  • Coïsson Pierdavide
  • Amory-Mazaudier Christine
  • Fleury Rolland
  • Radicella Sandro
  Sun and Geosphere, BBC SWS Regional Network, 2016, 11 (1), pp.7-22. This paper presents the day-today variability of the Vertical Total Electron Content (VTEC) and the Rate of change of TEC Index (ROTI) in October 2012. We focused our attention to the impact of a high-speed solar wind stream (HSSWS) on the ionosphere in middle and low latitudes on 13 October 2012. This event was preceded by two other disturbances caused by a Coronal Mass Ejection (CME) at 05:26UT on 8 October and a HSSWS around 19:00UT on 9 October. The changes in the VTEC observed during the period between 8 and 12 October preceding the 13 October case showed a comparable response of the ionosphere in both hemispheres, varying mainly with latitude and presenting a stronger impact in the Northern hemisphere. The VTEC increased at the arrival of the CME on 8 October, then decreased, and increased again on 13 October. The solar wind speed associated with the second HSSWS reached its peak, 580 km/s around 17:00UT during the recovery phase of a geomagnetic storm started around 00:00UT on 13 October. Its impact was observed in Africa and in Eastern South America on the ROTI, an indicator of ionospheric scintillation. On 13 October, the ROTI was small over whole Africa and in Eastern South America at the moment the impact of the second HSSWS. These observations are interpreted as due to the ionospheric disturbance dynamo electric field associated with the Joule heating produced in the auroral zone by the HSSWS.
• Long-lived plasma and fast quenching of N<SUB>2</SUB>(C<SUP>3</SUP>P<SUB>u</SUB>) by electrons in the afterglow of a nanosecond capillary discharge in nitrogen
  
  • Lepikhin N D
  • Klochko A.V.
  • Popov N A
  • Starikovskaia Svetlana
  Plasma Sources Science and Technology, IOP Publishing, 2016, 25 (4), pp.045003. Quenching of electronically excited nitrogen state, ##IMG## [http://ej.iop.org/images/0963-0252/25/4/045003/psstaa2269ieqn003.gif] \textN_2≤ft(\textC^3Π_u,v^\prime=0\right) , in the afterglow of nanosecond capillary discharge in pure nitrogen is studied. It is found experimentally that an additional collisional mechanism appears and dominates at high specific deposited energies leading to the anomalously fast quenching of the ##IMG## [http://ej.iop.org/images/0963-0252/25/4/045003/psstaa2269ieqn004.gif] \textN_2≤ft(\textC^3Π_u\right) in the afterglow. On the basis of obtained experimental data and of the analysis of possible quenching agents, it is concluded that the anomalously fast deactivation of the ##IMG## [http://ej.iop.org/images/0963-0252/25/4/045003/psstaa2269ieqn005.gif] \textN_2≤ft(\textC^3Π_u\right) can be explained by quenching by electrons. Long-lived plasma at time scale of hundreds nanoseconds after the end of the pulse is observed. High electron densities, about 10 14 cm &#1074;3 at 27 mbar, are sustained by reactions of associative ionization. Kinetic 1D numerical modeling and comparison of calculated results with experimentally measured electric fields in the second high-voltage pulse 250 ns after the initial pulse, and electron density measurements in the afterglow confirm the validity of the suggested mechanism. (10.1088/0963-0252/25/4/045003)
  DOI : 10.1088/0963-0252/25/4/045003
• Linear electromagnetic excitation of an asymmetric low pressure capacitive discharge with unequal sheath widths
  
  • Lieberman M.A.
  • Lichtenberg A.J.
  • Kawamura E.
  • Chabert Pascal
  Physics of Plasmas, American Institute of Physics, 2016, 23 (1), pp.013501. It is well-known that standing waves having radially center-high radio frequency (rf) voltage profiles exist in high frequency capacitive discharges. In this work, we determine the symmetric and antisymmetric radially propagating waves in a cylindrical capacitive discharge that is asymmetrically driven at the lower electrode by an rf voltage source. The discharge is modeled as a uniform bulk plasma which at lower frequencies has a thicker sheath at the smaller area powered electrode and a thinner sheath at the larger area grounded electrode. These are self-consistently determined at a specified density using the Child law to calculate sheath widths and the electron power balance to calculate the rf voltage. The fields and the system resonant frequencies are determined. The center-to-edge voltage ratio on the powered electrode is calculated versus frequency, and central highs are found near the resonances. The results are compared with simulations in a similar geometry using a two-dimensional hybrid fluid-analytical code, giving mainly a reasonable agreement. The analytic model may be useful for finding good operating frequencies for a given discharge geometry and power. (10.1063/1.4938204)
  DOI : 10.1063/1.4938204
• Kinetic studies of NO formation in pulsed air-like low-pressure dc plasmas
  
  • Hübner M.
  • Gortschakow S.
  • Guaitella Olivier
  • Marinov Daniil
  • Rousseau Antoine
  • Röpcke J.
  • Loffhagen D.
  Plasma Sources Science and Technology, IOP Publishing, 2016, 25 (3), pp.035005. The kinetics of the formation of NO in pulsed air-like dc plasmas at a pressure of 1.33 mbar and mean currents between 50 and 150 mA of discharge pulses with 5&#8201;ms duration has been investigated both experimentally and by self-consistent numerical modelling. Using time-resolved quantum cascade laser absorption spectroscopy, the densities of NO, NO2 and N2O have been measured in synthetic air as well as in air with 0.8% of NO2 and N2O, respectively. The temporal evolution of the NO density shows four distinct phases during the plasma pulse and the early afterglow in the three gas mixtures that were used. In particular, a steep density increase during the ignition phase and after termination of the discharge current pulse has been detected. The NO concentration has been found to reach a constant value of , , and for mean plasma currents of 50 mA, 100 mA and 150 mA, respectively, in the afterglow. The measured densities of NO2 and N2O in the respective mixture decrease exponentially during the plasma pulse and remain almost constant in the afterglow, especially where the admixture of NO2 has a remarkable impact on the NO production during the ignition. The numerical results of the coupled solution of a set of rate equations for the various heavy particles and the time-dependent Boltzmann equation of the electrons agree quite well with the experimental findings for the different air-like plasmas. The main reaction processes have been analysed on the basis of the model calculations and the remaining differences between the experiment and modelling especially during the afterglow are discussed. (10.1088/0963-0252/25/3/035005)
  DOI : 10.1088/0963-0252/25/3/035005
• Evolution of nanosecond surface dielectric barrier discharge for negative polarity of voltage pulse
  
  • Soloviev V.R.
  • Krivtsov V.M.
  • Shcherbanev S.A.
  • Starikovskaia Svetlana
  Plasma Sources Science and Technology, IOP Publishing, 2016, 26 (1), pp.014001 (12pp). Surface dielectric barrier discharge, initiated by a high-voltage pulse of negative polarity in atmospheric pressure air, is studied numerically and experimentally. At a pulse duration of a few tens of nanoseconds, two waves of optical emission propagate from the high-voltage electrode corresponding to the leading and trailing edges of the high-voltage pulse. It is shown by means of numerical modeling that a glow-like discharge slides along the surface of the dielectric at the leading edge of the pulse, slowing down on the plateau of the pulse. When the trailing edge of the pulse arrives to the high-voltage electrode, a second discharge starts and propagates in the same direction. The difference is that the discharge corresponding to the trailing edge is not diffuse and demonstrates a well-pronounced streamer-like shape. The 2D (in numerical modeling) streamer propagates above the dielectric surface, leaving a gap of about 0.05 mm between the streamer and the surface. The calculated and experimentally measured emission picture, waveform of the electrical current, and deposited energy, qualitatively coincide. The sensitivity of the numerical solution to unknown physical parameters of the model is discussed. (10.1088/0963-0252/26/1/014001)
  DOI : 10.1088/0963-0252/26/1/014001
• Poynting vector and wave vector directions of equatorial chorus
  
  • Taubenschuss U.
  • Santolík O.
  • Breuillard Hugo
  • Li W.
  • Le Contel Olivier
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2016, 121 (12), pp.11,912-11,928. We present new results on wave vectors and Poynting vectors of chorus rising and falling tones on the basis of 6 years of THEMIS (Time History of Events and Macroscale Interactions during Substorms) observations. The majority of wave vectors is closely aligned with the direction of the ambient magnetic field (B<SUB>0</SUB>). Oblique wave vectors are confined to the magnetic meridional plane, pointing away from Earth. Poynting vectors are found to be almost parallel to B<SUB>0</SUB>. We show, for the first time, that slightly oblique Poynting vectors are directed away from Earth for rising tones and toward Earth for falling tones. For the majority of lower band chorus elements, the mutual orientation between Poynting vectors and wave vectors can be explained by whistler mode dispersion in a homogeneous collisionless cold plasma. Upper band chorus seems to require inclusion of collisional processes or taking into account azimuthal anisotropies in the propagation medium. The latitudinal extension of the equatorial source region can be limited to ±6<SUP>o</SUP> around the B<SUB>0</SUB> minimum or approximately ±5000 km along magnetic field lines. We find increasing Poynting flux and focusing of Poynting vectors on the B<SUB>0</SUB> direction with increasing latitude. Also, wave vectors become most often more field aligned. A smaller group of chorus generated with very oblique wave normals tends to stay close to the whistler mode resonance cone. This suggests that close to the equatorial source region (within 20<SUP>o</SUP> latitude), a wave guidance mechanism is relevant, for example, in ducts of depleted or enhanced plasma density. (10.1002/2016JA023389)
  DOI : 10.1002/2016JA023389
• Ionospheric and magnetic signatures of a high speed solar wind in low latitudes on 13 October 2012
  
  • Migoya-Orué Yenca
  • Azzouzi Ilyasse
  • Coisson Pierdavide
  • Amory-Mazaudier Christine
  • Fleury Rolland
  • Radicella Sandro M.
  Sun and Geosphere, BBC SWS Regional Network, 2016, 11 (1), pp.23-35. This paper presents the impact of a fast solar wind on the ionosphere, in low latitudes, on 13 October 2012. On that day, the high speed solar wind reached the Earth around 16:00UT, during the recovery phase of a geomagnetic storm which started around 00:00UT. The solar wind speed was determined to be 580km/s, on the same day, around 17:00UT. Its impact was observed in low and equatorial latitudes, in Africa and in Eastern South America, on the F layer and on the geomagnetic field variations. Through the analysis of magnetic indices, ionosonde characteristics and the horizontal component of the geomagnetic field, we found that the 13 October 2012 event exhibited a local impact, affecting the observatories situated in a longitude sector between 315°E and 45°E. Particularly, the F layer in Africa (observed by the ionosonde at Ascension Island) did not present any lift, and there was a delay for approximately two hours of the ascent of the F layer in America (the ionosonde at Fortaleza). In this case, there was an evident inhibition on the development of spread F at the time of the Pre Reversal Enhancement (PRE) in Africa and Eastern America, while the ionograms of the days before and after presented clear spread F traces. The disturbances of the ionospheric equivalent electric current (Diono) deduced from the variations of the geomagnetic field at M'Bour near Dakar (Africa) and at Kourou (Eastern America) exhibited on the dayside, an anti Sq current which is signature of the influence of the Disturbance Dynamo Electric Field (DDEF).
• Theory for the anomalous electron transport in Hall effect thrusters. I. Insights from particle-in-cell simulations
  
  • Lafleur Trevor
  • Baalrud S. D.
  • Chabert Pascal
  Physics of Plasmas, American Institute of Physics, 2016, 23 (5), pp.053502. Using a 1D particle-in-cell simulation with perpendicular electric, E0, and magnetic, B0, fields, and modelling the azimuthal direction (i.e., the E0&#8201;×&#8201;B0 direction), we study the cross-field electron transport in Hall effect thrusters (HETs). For low plasma densities, the electron transport is found to be well described by classical electron-neutral collision theory, but at sufficiently high densities (representative of typical HETs), a strong instability is observed to significantly enhance the electron mobility, even in the absence of electron-neutral collisions. This instability is associated with correlated high-frequency (of the order of MHz) and short-wavelength (of the order of mm) fluctuations in both the electric field and the plasma density, which are shown to be the cause of the anomalous transport. Saturation of the instability is observed to occur due to a combination of ion-wave trapping in the E0&#8201;×&#8201;B0 direction, and convection in the E0 direction. (10.1063/1.4948495)
  DOI : 10.1063/1.4948495
• Theory for the anomalous electron transport in Hall effect thrusters. II. Kinetic model
  
  • Lafleur Trevor
  • Baalrud S. D.
  • Chabert Pascal
  Physics of Plasmas, American Institute of Physics, 2016, 23 (5), pp.053503. In Paper I [T. Lafleur et al., Phys. Plasmas 23, 053502 (2016)], we demonstrated (using particle-in-cell simulations) the definite correlation between an anomalously high cross-field electron transport in Hall effect thrusters (HETs), and the presence of azimuthal electrostatic instabilities leading to enhanced electron scattering. Here, we present a kinetic theory that predicts the enhanced scattering rate and provides an electron cross-field mobility that is in good agreement with experiment. The large azimuthal electron drift velocity in HETs drives a strong instability that quickly saturates due to a combination of ion-wave trapping and wave-convection, leading to an enhanced mobility many orders of magnitude larger than that expected from classical diffusion theory. In addition to the magnetic field strength, B0, this enhanced mobility is a strong function of the plasma properties (such as the plasma density) and therefore does not, in general, follow simple 1/B20 or 1/B0 scaling laws. (10.1063/1.4948496)
  DOI : 10.1063/1.4948496
• Time-resolved electric field measurements during and after the initialization of a kHz plasma jetfrom streamers to guided streamers
  
  • Slikboer Elmar
  • Guaitella Olivier
  • Sobota Ana
  Plasma Sources Science and Technology, IOP Publishing, 2016, 25 (3), pp.03LT04. This work presents the investigation of a 30&#8201;kHz operated atmospheric pressure plasma jet impinging a dielectric BSO-crystal, allowing time-resolved electric field measurements based on the Pockels effect. Observations indicate that from the time the voltage is applied, the plasma first develops through unstable branching before a stable periodic behavior is established. This initialization of the plasma jet suggests the importance of the build-up of leftover ionization, which creates a preferred pathway for the streamer-like discharges. After initialization the time and spatially resolved electric field of guided ionization waves induced in the crystal is obtained, showing a highly periodic charging and discharging at the surface of the crystal. When the ionization wave arrives at the crystal charge is deposited and constant electric fields are generated for approximately 14 &#956;s. Then a (back) discharge will remove the deposited charge at the surface, related to the moment when the applied voltage changes polarity and it agrees with imaging reported on in other literature. (10.1088/0963-0252/25/3/03LT04)
  DOI : 10.1088/0963-0252/25/3/03LT04
• Global model of an iodine gridded plasma thruster
  
  • Grondein Pascaline
  • Lafleur Trevor
  • Chabert Pascal
  • Aanesland Ane
  Physics of Plasmas, American Institute of Physics, 2016, 23 (3), pp.033514. Most state-of-the-art electric space propulsion systems such as gridded and Hall effect thrusters use xenon as the propellant gas. However, xenon is very rare, expensive to produce, and used in a number of competing industrial applications. Alternatives to xenon are currently being investigated, and iodine has emerged as a potential candidate. Its lower cost and larger availability, its solid state at standard temperature and pressure, its low vapour pressure and its low ionization potential make it an attractive option. In this work, we compare the performances of a gridded ion thruster operating separately with iodine and xenon, under otherwise identical conditions using a global model. The thruster discharge properties such as neutral, ion, and electron densities and electron temperature are calculated, as well as the thruster performance parameters such as thrust, specific impulse, and system efficiencies. For similar operating conditions, representative of realistic thrusters, the model predicts similar thrust levels and performances for both iodine and xenon. The thruster efficiency is however slightly higher for iodine compared with xenon, due to its lower ionization potential. This demonstrates that iodine could be a viable alternative propellant for gridded plasma thrusters. (10.1063/1.4944882)
  DOI : 10.1063/1.4944882
• Dynamical Monte Carlo methods for plasma-surface reactions
  
  • Guerra V.
  • Marinov Daniil
  Plasma Sources Science and Technology, IOP Publishing, 2016, 25 (4), pp.045001. Different dynamical Monte Carlo algorithms to investigate molecule formation on surfaces are developed, evaluated and compared with the deterministic approach based on reaction-rate equations. These include a null event algorithm, the n-fold way/BKL algorithm and an 'hybrid' variant of the latter. NO2 formation by NO oxidation on Pyrex and O recombination on silica with the formation of O2 are taken as case studies. The influence of the grid size on the CPU calculation time and the accuracy of the results is analysed. The role of LangmuirHinsehlwood recombination involving two physisorbed atoms and the effect of back diffusion and its inclusion in a deterministic formulation are investigated and discussed. It is shown that dynamical Monte Carlo schemes are flexible, simple to implement, describe easily elementary processes that are not straightforward to include in deterministic simulations, can run very efficiently if appropriately chosen and give highly reliable results. Moreover, the present approach provides a relatively simple procedure to describe fully coupled surface and gas phase chemistries. (10.1088/0963-0252/25/4/045001)
  DOI : 10.1088/0963-0252/25/4/045001
• Logarithmic discretization and systematic derivation of shell models in two-dimensional turbulence
  
  • Gürcan Özgür D.
  • Morel Pierre
  • Kobayashi Sumire
  • Singh Rameswar
  • Xu S.
  • Diamond P.H.
  Physical Review E, American Physical Society (APS), 2016, 94, pp.033106. A detailed systematic derivation of a logarithmically discretized model for two-dimensional turbulence is given, starting from the basic fluid equations and proceeding with a particular form of discretization of the wave-number space. We show that it is possible to keep all or a subset of the interactions, either local or disparate scale, and recover various limiting forms of shell models used in plasma and geophysical turbulence studies. The method makes no use of the conservation laws even though it respects the underlying conservation properties of the fluid equations. It gives a family of models ranging from shell models with nonlocal interactions to anisotropic shell models depending on the way the shells are constructed. Numerical integration of the model shows that energy and enstrophy equipartition seem to dominate over the dual cascade, which is a common problem of two-dimensional shell models. (10.1103/PhysRevE.94.033106)
  DOI : 10.1103/PhysRevE.94.033106
• Cluster observations of reflected EMIC-triggered emission
  
  • Grison B.
  • Darrouzet F.
  • Santolík O.
  • Cornilleau-Wehrlin Nicole
  • Masson A.
  Geophysical Research Letters, American Geophysical Union, 2016, 43, pp.4164-4171. On 19 March 2001, the Cluster fleet recorded an electromagnetic rising tone on the nightside of the plasmasphere. The emission was found to propagate toward the Earth and toward the magnetic equator at a group velocity of about 200 km/s. The Poynting vector is mainly oblique to the background magnetic field and directed toward the Earth. The propagation angle thetak,B<SUB>0</SUB> becomes more oblique with increasing magnetic latitude. Inside each rising tone thetak,B<SUB>0</SUB> is more field aligned for higher frequencies. Comparing our results to previous ray tracing analysis we conclude that this emission is a triggered electromagnetic ion cyclotron (EMIC) wave generated at the nightside plasmapause. We detect the wave just after its reflection in the plasmasphere. The reflection makes the tone slope shallower. This process can contribute to the formation of pearl pulsations. (10.1002/2016GL069096)
  DOI : 10.1002/2016GL069096
• Signatures of complex magnetic topologies from multiple reconnection sites induced by Kelvin-Helmholtz instability
  
  • Vernisse Y.
  • Lavraud B.
  • Eriksson S.
  • Gershman D. J.
  • Dorelli J. C.
  • Pollock C.
  • Giles B. L.
  • Aunai Nicolas
  • Avanov L.
  • Burch J. L.
  • Chandler Michael O.
  • Coffey Victoria
  • Dargent Jérémy
  • Ergun R. E.
  • Farrugia C. J.
  • Génot V.
  • Graham D. B.
  • Hasegawa H.
  • Jacquey C.
  • Kacem I.
  • Khotyaintsev Y. V.
  • Li W.
  • Magnes W.
  • Marchaudon A.
  • Moore T. E.
  • Paterson W. R.
  • Penou E.
  • Phan T. D.
  • Retinò Alessandro
  • Russell C. T.
  • Saito Y.
  • Sauvaud J.-A.
  • Torbert R.
  • Wilder F. D.
  • Yokota S.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2016, 121 (10), pp.9926-9939. The Magnetospheric Multiscale mission has demonstrated the frequent presence of reconnection exhausts at thin current sheets within Kelvin-Helmholtz (KH) waves at the flank magnetopause. Motivated by these recent observations, we performed a statistical analysis of the boundary layers on the magnetosheath side of all KH current sheets on 8 September 2015. We show 86% consistency between the exhaust flows and particle leakage in the magnetosheath boundary layers but further highlight the very frequent presence of additional boundary layer signatures that do not come from the locally observed reconnection exhausts. These additional electron and ion boundary layers, of various durations and at various positions with respect to the leading and trailing boundaries of the KH waves, signal connections to reconnection sites at other locations. Based on the directionality and extent of these layers, we provide an interpretation whereby complex magnetic topologies can arise within KH waves from the combination of reconnection in the equatorial plane and at midlatitudes in the Southern and Northern Hemispheres, where additional reconnection sites are expected to be triggered by the three-dimensional field lines interweaving induced by the KH waves at the flanks (owing to differential flow and magnetic field shear with latitude). The present event demonstrates that the three-dimensional development of KH waves can induce plasma entry (through reconnection at both midlatitude and equatorial regions) already sunward of the terminator where the instability remains in its linear stage. (10.1002/2016JA023051)
  DOI : 10.1002/2016JA023051
• Poynting vector behaviour during the resonance scattering of a plane electromagnetic wave by a gyrotropic cylinder
  
  • Es'Kin V. A.
  • Ivoninsky A. V.
  • Kudrin A. V.
  • Krafft C.
  Physica Scripta, IOP Publishing, 2016, 91 (1), pp.015502. The energy-flow structure during the resonance scattering of a normally incident plane electromagnetic H wave by a gyrotropic cylinder is studied. The main attention is focused on the bifurcations of the time-averaged Poynting vector field at the surface and volume plasmon resonances in the case where the cylinder is aligned with a gyrotropy axis. The behaviour of the Poynting vector field in this case is compared with that observed during the scattering by an isotropic cylinder, and significant differences in the energy-flow structures in the two cases are revealed. Conditions are found under which the maximum magnitude of the Poynting vector at the boundary of a gyrotropic cylinder turns out to be much greater than that at the boundary of an isotropic scatterer of the same shape and size. (10.1088/0031-8949/91/1/015502)
  DOI : 10.1088/0031-8949/91/1/015502
• Cold ion heating at the dayside magnetopause during magnetic reconnection
  
  • Toledo-Redondo Sergio
  • André M.
  • Vaivads A.
  • Khotyaintsev Y. V.
  • Lavraud B.
  • Graham D. B.
  • Divin A. V.
  • Aunai Nicolas
  Geophysical Research Letters, American Geophysical Union, 2016, 43 (1), pp.58-66. Cold ions of ionospheric origin are known to be present in the magnetospheric side of the Earth's magnetopause. They can be very abundant, with densities up to 100 cm<SUP>-3</SUP>. These cold ions can mass load the magnetosphere, changing global parameters of magnetic reconnection, like the Alfvén speed or the reconnection rate. In addition they introduce a new length scale related to their gyroradius and kinetic effects which must be accounted for. We report in situ observations of cold ion heating in the separatrix owing to time and space fluctuations of the electric field. When this occurs, the cold ions are preheated before crossing the Hall electric field barrier. However, when this mechanism is not present cold ions can be observed well inside the reconnection exhaust. Our observations suggest that the perpendicular cold ion heating is stronger close to the X line owing to waves and electric field gradients linked to the reconnection process. (10.1002/2015GL067187)
  DOI : 10.1002/2015GL067187