Publications

2016

• 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
• 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.
• 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
• 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
• 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
• 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
• 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
• 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
• 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.
• 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
• 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
• Differential kinetic dynamics and heating of ions in the turbulent solar wind
  
  • Valentini F.
  • Perrone D.
  • Stabile S.
  • Pezzi O.
  • Servidio S.
  • de Marco R.
  • Marcucci M. F.
  • Bruno Roberto
  • Lavraud B.
  • de Keyser J.
  • Consolini G.
  • Brienza D.
  • Sorriso-Valvo L.
  • Retinò Alessandro
  • Vaivads A.
  • Salatti M.
  • Veltri P.
  New Journal of Physics, Institute of Physics: Open Access Journals, 2016, 18, pp.125001. The solar wind plasma is a fully ionized and turbulent gas ejected by the outer layers of the solar corona at very high speed, mainly composed by protons and electrons, with a small percentage of helium nuclei and a significantly lower abundance of heavier ions. Since particle collisions are practically negligible, the solar wind is typically not in a state of thermodynamic equilibrium. Such a complex system must be described through self-consistent and fully nonlinear models, taking into account its multi-species composition and turbulence. We use a kinetic hybrid Vlasov-Maxwell numerical code to reproduce the turbulent energy cascade down to ion kinetic scales, in typical conditions of the uncontaminated solar wind plasma, with the aim of exploring the differential kinetic dynamics of the dominant ion species, namely protons and alpha particles. We show that the response of different species to the fluctuating electromagnetic fields is different. In particular, a significant differential heating of alphas with respect to protons is observed. Interestingly, the preferential heating process occurs in spatial regions nearby the peaks of ion vorticity and where strong deviations from thermodynamic equilibrium are recovered. Moreover, by feeding a simulator of a top-hat ion spectrometer with the output of the kinetic simulations, we show that measurements by such spectrometer planned on board the Turbulence Heating ObserveR (THOR mission), a candidate for the next M4 space mission of the European Space Agency, can provide detailed three-dimensional ion velocity distributions, highlighting important non-Maxwellian features. These results support the idea that future space missions will allow a deeper understanding of the physics of the interplanetary medium. (10.1088/1367-2630/18/12/125001)
  DOI : 10.1088/1367-2630/18/12/125001
• Velocity diffusion of energetic electrons in the solar wind
  
  • Volokitin A.
  • Krafft C.
  AIP Conference Proceedings, American Institute of Physics, 2016, 1720 (1), pp.070007. Particle diffusion in velocity space is studied on the basis of 1D simulations of Langmuir turbulence generated by electron beams in solar wind plasmas. Using a large amount of particle trajectories calculated with a great accuracy and over long times and analyzing them with statistical algorithms, the diffusion coefficients of particles in wave packets are estimated, as well as their relation to the waves' intensities and spectra and their dependence on the average level of background plasma density fluctuations. Results are compared with analytical solutions provided by the quasilinear theory of weak turbulence. (10.1063/1.4943844)
  DOI : 10.1063/1.4943844
• Two interacting X lines in magnetotail: Evolution of collision between the counterstreaming jets
  
  • Alexandrova Alexandra
  • Nakamura R.
  • Panov Evgeny V.
  • Sasunov Yury L.
  • Nakamura T. K. M.
  • Vörös Z.
  • Retinò Alessandro
  • Semenov Vladimir S.
  Geophysical Research Letters, American Geophysical Union, 2016, 43 (15), pp.7795-7803. We study the process of collision between the counterstreaming jets flowing out from two reconnection sites in the Earth's magnetotail. The X lines, bracketing the region of jets collision, were passing by two Cluster probes successively in tailward direction. Two probes observed two different stages of the collision process. At the jets collision site, a probe first observed an ion-scale current sheet-like structure, while the other probe observed more compressed one later. The strong wave activities on both ion and electron scales were seen within the compressed layer. Such evolution of the jets collision resulting in the formation of the compressed boundary between the active X lines shows an example of interaction between the X lines during multiple reconnection. (10.1002/2016GL069823)
  DOI : 10.1002/2016GL069823
• The Search-Coil Magnetometer for MMS
  
  • Le Contel Olivier
  • Leroy Paul
  • Roux A.
  • Coillot Christophe
  • Alison Dominique
  • Bouabdellah Abdel
  • Mirioni Laurent
  • Meslier L.
  • Galic A.
  • Vassal M. C.
  • Torbert R. B.
  • Needell J.
  • Rau D.
  • Dors I.
  • Ergun R. E.
  • Westfall J.
  • Summers D.
  • Wallace J.
  • Magnes W.
  • Valavanoglou A.
  • Olsson G.
  • Chutter M.
  • Macri J.
  • Myers S.
  • Turco S.
  • Nolin J.
  • Bodet D.
  • Rowe K.
  • Tanguy M.
  • de La Porte B.
  Space Science Reviews, Springer Verlag, 2016, 199 (1-4), pp.257-282. The tri-axial search-coil magnetometer (SCM) belongs to the FIELDS instrumentation suite on the Magnetospheric Multiscale (MMS) mission (Torbert et al. in Space Sci. Rev. (2014), this issue). It provides the three magnetic components of the waves from 1 Hz to 6 kHz in particular in the key regions of the Earth’s magnetosphere namely the subsolar region and the magnetotail. Magnetospheric plasmas being collisionless, such a measurement is crucial as the electromagnetic waves are thought to provide a way to ensure the conversion from magnetic to thermal and kinetic energies allowing local or global reconfigurations of the Earth’s magnetic field. The analog waveforms provided by the SCM are digitized and processed inside the digital signal processor (DSP), within the Central Electronics Box (CEB), together with the electric field data provided by the spin-plane double probe (SDP) and the axial double probe (ADP). On-board calibration signal provided by DSP allows the verification of the SCM transfer function once per orbit. Magnetic waveforms and on-board spectra computed by DSP are available at different time resolution depending on the selected mode. The SCM design is described in details as well as the different steps of the ground and in-flight calibrations. (10.1007/s11214-014-0096-9)
  DOI : 10.1007/s11214-014-0096-9
• Multispacecraft analysis of dipolarization fronts and associated whistler wave emissions using MMS data
  
  • Breuillard Hugo
  • Le Contel Olivier
  • Retinò Alessandro
  • Chasapis A.
  • Chust Thomas
  • Mirioni Laurent
  • Graham D. B.
  • Wilder F. D.
  • Cohen I.
  • Vaivads A.
  • Khotyaintsev Y. V.
  • Lindqvist P.-A.
  • Marklund G. T.
  • Burch J. L.
  • Torbert R. B.
  • Ergun R. E.
  • Goodrich K. A.
  • Macri J.
  • Needell J.
  • Chutter M.
  • Rau D.
  • Dors I.
  • Russell C. T.
  • Magnes W.
  • Strangeway R. J.
  • Bromund K. R.
  • Plaschke F.
  • Fischer D.
  • Leinweber H. K.
  • Anderson B. J.
  • Le G.
  • Slavin J. A.
  • Kepko E. L.
  • Baumjohann W.
  • Mauk B.
  • Fuselier S. A.
  • Nakamura R.
  Geophysical Research Letters, American Geophysical Union, 2016, 43 (14), pp.7279-7286. Dipolarization fronts (DFs), embedded in bursty bulk flows, play a crucial role in Earth's plasma sheet dynamics because the energy input from the solar wind is partly dissipated in their vicinity. This dissipation is in the form of strong low-frequency waves that can heat and accelerate energetic electrons up to the high-latitude plasma sheet. However, the dynamics of DF propagation and associated low-frequency waves in the magnetotail are still under debate due to instrumental limitations and spacecraft separation distances. In May 2015 the Magnetospheric Multiscale (MMS) mission was in a string-of-pearls configuration with an average intersatellite distance of 160 km, which allows us to study in detail the microphysics of DFs. Thus, in this letter we employ MMS data to investigate the properties of dipolarization fronts propagating earthward and associated whistler mode wave emissions. We show that the spatial dynamics of DFs are below the ion gyroradius scale in this region (500 km), which can modify the dynamics of ions in the vicinity of the DF (e.g., making their motion nonadiabatic). We also show that whistler wave dynamics have a temporal scale of the order of the ion gyroperiod (a few seconds), indicating that the perpendicular temperature anisotropy can vary on such time scales. (10.1002/2016GL069188)
  DOI : 10.1002/2016GL069188
• Observations of whistler mode waves with nonlinear parallel electric fields near the dayside magnetic reconnection separatrix by the Magnetospheric Multiscale mission
  
  • Wilder F. D.
  • Ergun R. E.
  • Goodrich K. A.
  • Goldman M. V.
  • Newman D. L.
  • Malaspina D. M.
  • Jaynes A. N.
  • Schwartz S. J.
  • Trattner K. J.
  • Burch J. L.
  • Argall M. R.
  • Torbert R. B.
  • Lindqvist P.-A.
  • Marklund G.
  • Le Contel Olivier
  • Mirioni Laurent
  • Khotyaintsev Y. V.
  • Strangeway R. J.
  • Russell C. T.
  • Pollock C. J.
  • Giles B. L.
  • Plaschke F.
  • Magnes W.
  • Eriksson S.
  • Stawarz J. E.
  • Sturner A. P.
  • Holmes J. C.
  Geophysical Research Letters, American Geophysical Union, 2016, 43 (12), pp.5909-5917. We show observations from the Magnetospheric Multiscale (MMS) mission of whistler mode waves in the Earth's low-latitude boundary layer (LLBL) during a magnetic reconnection event. The waves propagated obliquely to the magnetic field toward the X line and were confined to the edge of a southward jet in the LLBL. Bipolar parallel electric fields interpreted as electrostatic solitary waves (ESW) are observed intermittently and appear to be in phase with the parallel component of the whistler oscillations. The polarity of the ESWs suggests that if they propagate with the waves, they are electron enhancements as opposed to electron holes. The reduced electron distribution shows a shoulder in the distribution for parallel velocities between 17,000 and 22,000 km/s, which persisted during the interval when ESWs were observed, and is near the phase velocity of the whistlers. This shoulder can drive Langmuir waves, which were observed in the high-frequency parallel electric field data. (10.1002/2016GL069473)
  DOI : 10.1002/2016GL069473
• Experimental investigation of electron transport across a magnetic field barrier in electropositive and electronegative plasmas
  
  • Thomas M B
  • Rafalskyi D.V.
  • Lafleur Trevor
  • Aanesland Ane
  Plasma Sources Science and Technology, IOP Publishing, 2016, 25 (4), pp.045018. In this paper we experimentally investigate the drift of electrons in low temperature plasmas containing a magnetic field barrier; a plasma configuration commonly used in gridded negative ion sources. A planar Langmuir probe array is developed to quantify the drift of electrons over the cross-section of the ion-extraction region of an ionion plasma source. The drift is studied as a function of pressure using both electropositive plasmas (Ar), as well electronegative plasmas (Ar and SF 6 mixtures), and is demonstrated to result from an interaction of the applied magnetic field and the electric fields in the sheath and pre-sheath near the transverse boundaries. The drift enhances electron transport across the magnetic field by more than two orders of magnitude compared with simple collisional transport, and is found to be strongly dependant on pressure. The lowest pressure resulted in the highest influence of the drift across the extraction area and is found to be 30%. (10.1088/0963-0252/25/4/045018)
  DOI : 10.1088/0963-0252/25/4/045018
• MMS observations of ion-scale magnetic island in the magnetosheath turbulent plasma
  
  • Huang S. Y.
  • Sahraoui Fouad
  • Retinò Alessandro
  • Le Contel Olivier
  • Yuan Z. G.
  • Chasapis A.
  • Aunai Nicolas
  • Breuillard Hugo
  • Deng X. H.
  • Zhou M.
  • Fu H.S.
  • Pang Y.
  • Wang D. D.
  • Torbert R. B.
  • Goodrich K. A.
  • Ergun R. E.
  • Khotyaintsev Y. V.
  • Lindqvist P.-A.
  • Russell C. T.
  • Strangeway R. J.
  • Magnes W.
  • Bromund K.
  • Leinweber H.
  • Plaschke F.
  • Anderson B. J.
  • Pollock C. J.
  • Giles B. L.
  • Moore T. E.
  • Burch J. L.
  Geophysical Research Letters, American Geophysical Union, 2016, 43 (15), pp.7850-7858. In this letter, first observations of ion-scale magnetic island from the Magnetospheric Multiscale mission in the magnetosheath turbulent plasma are presented. The magnetic island is characterized by bipolar variation of magnetic fields with magnetic field compression, strong core field, density depletion, and strong currents dominated by the parallel component to the local magnetic field. The estimated size of magnetic island is about 8 d<SUB>i</SUB>, where d<SUB>i</SUB> is the ion inertial length. Distinct particle behaviors and wave activities inside and at the edges of the magnetic island are observed: parallel electron beam accompanied with electrostatic solitary waves and strong electromagnetic lower hybrid drift waves inside the magnetic island and bidirectional electron beams, whistler waves, weak electromagnetic lower hybrid drift waves, and strong broadband electrostatic noise at the edges of the magnetic island. Our observations demonstrate that highly dynamical, strong wave activities and electron-scale physics occur within ion-scale magnetic islands in the magnetosheath turbulent plasma. (10.1002/2016GL070033)
  DOI : 10.1002/2016GL070033
• Turbulence intermittency linked to the weakly coherent mode in ASDEX Upgrade I-mode plasmas
  
  • Happel T.
  • Manz P.
  • Ryter F.
  • Hennequin Pascale
  • Hetzenecker A.
  • Conway G. D.
  • Guimarais L.
  • Honoré Cyrille
  • Stroth U.
  • Viezzer E.
  • The Asdex Upgrade Team
  Nuclear Fusion, IOP Publishing, 2016, 56 (6), pp.064004. This letter shows for the first time a pronounced increase of extremely intermittent edge density turbulence behavior inside the confinement region related to the I-mode confinement regime in the ASDEX Upgrade tokamak. With improving confinement, the perpendicular propagation velocity of density fluctuations in the plasma edge increases together with the intermittency of the observed density bursts. Furthermore, it is shown that the weakly coherent mode, a fluctuation feature generally observed in I-mode plasmas, is connected to the observed bursts. It is suggested that the large amplitude density bursts could be generated by a non-linearity similar to that in the Korteweg?de-Vries equation which includes the radial temperature gradient. (10.1088/0029-5515/56/6/064004)
  DOI : 10.1088/0029-5515/56/6/064004
• The Alfvén Mission for the ESA M5 Call: Mission Concept
  
  • Fazakerley A.
  • Berthomier Matthieu
  • Pottelette Raymond
  • Forsyth C.
  , 2016, 18, pp.EPSC2016-16890. This poster will present the proposed Alfvén mission concept and is complemented by a presentation of the mission scientific goals planned for the ST1.5 session. The Alfvén mission has the scientific objective of studying particle acceleration and other forms of electromagnetic energy conversion in a collisionless low beta plasma. The mission is proposed to operate in the Earth's Auroral Acceleration Region (AAR), the most accessible laboratory for investigating plasmas at an interface where ideal magneto-hydrodynamics does not apply. Alfvén is designed to answer questions about where and how the particles that create the aurorae are accelerated, how and why they emit auroral kilometric radiation, what creates and maintains large scale electric fields aligned with the magnetic field, and to elucidate the ion outflow processes which are slowly removing the Earth's atmosphere. The mission will provide the required coordinated two-spacecraft observations within the AAR several times a day. From well designed separations along or across the magnetic field lines, using a comprehensive suite of inter-calibrated particles and field instruments, it will measure the parallel electric fields, variations in particle flux, and wave energy that will answer open questions on energy conversion. It will use onboard auroral imagers to determine how this energy conversion occurs in the regional context and, together with its orbit design, this makes the mission ideally suited to resolving spatio-temporal ambiguities that have plagued previous auroral satellite studies. The spacecraft observations will be complemented by coordinated observations with the existing dense network of ground based observatories, for more detailed ionospheric and auroral information when Alfvén overflights occur.
• Near-field plume properties of an ion beam formed by alternating extraction and acceleration of oppositely charged ions
  
  • Oudini N.
  • Aanesland Ane
  • Chabert Pascal
  • Lounes-Mahloul S.
  • Bendib A.
  Plasma Sources Science and Technology, IOP Publishing, 2016, 25 (5), pp.055013. This paper is devoted to study the expansion of a beam composed of packets of positively and negatively charged ions generated by alternating extraction and acceleration. This beam is extracted from an ionion plasma, i.e. the electron density is negligible compared to the negative ion density. The alternating acceleration of ions is ensured by two grids placed in the ionion plasma region. The screen grid in contact with the plasma is biased with a square voltage waveform while the acceleration grid is grounded. A two-dimensional particle-in-cell (2D-PIC) code and an analytical model are used to study the properties of the near-field plume downstream of the acceleration grid. It is shown that the possible operating bias frequency is delimited by an upper limit and a lower one that are in the low MHz range. The simulations show that alternating acceleration with bias frequencies close to the upper frequency limit for the system can achieve high ion exhaust velocities, similar to traditional gridded ion thrusters, and with lower beam divergence than in classical systems. Indeed, ionion beam envelope might be reduced to 15° with 70% of ion flux contained within an angle of 3°. Thus, this alternating acceleration method is promising for electric space propulsion. (10.1088/0963-0252/25/5/055013)
  DOI : 10.1088/0963-0252/25/5/055013
• An expression for the h<SUB>l</SUB> factor in low-pressure electronegative plasma discharges
  
  • Chabert Pascal
  Plasma Sources Science and Technology, IOP Publishing, 2016, 25 (2), pp.025010. The positive ion flux exiting a low-pressure plasma discharge is a crucial quantity in global (volume-averaged) models. In discharges containing only electrons and positive ions (electropositive discharges), it is common to write this flux , where is the central positive ion density, is the positive ion fluid speed at the sheath edge (the Bohm speed), and is the positive ion edge-to-centre density ratio. There are well established formulae for in electropositive discharges, but for discharges containing negative ions (electronegative discharges), the analysis is more complicated. The purpose of this paper is to propose a formula for the factor in low-pressure electronegative discharges. We use the numerical solution of fluid equations with Boltzmann negative ions, including Poisson's equation, as a guide to derive an analytical expression that can easily be incorporated in global models. The parameter space in which the derived expression is valid is discussed at the end of the paper. (10.1088/0963-0252/25/2/025010)
  DOI : 10.1088/0963-0252/25/2/025010
• A comparison between micro hollow cathode discharges and atmospheric pressure plasma jets in Ar/O<SUB>2</SUB> gas mixtures
  
  • Lazzaroni Claudia
  • Chabert Pascal
  Plasma Sources Science and Technology, IOP Publishing, 2016, 25 (6), pp.065015. Using global models, micro hollow cathode discharges (MHCDs) are compared to radiofrequency atmospheric pressure plasma jets (APPJs) in terms of reactive oxygen species (ROS) production. Ar/O 2 gas mixtures are investigated, typically with a small percentage of oxygen in argon. The same chemical reaction set, involving 17 species and 128 chemical reactions in the gas phase, is used for both devices, operated in the typical geometries previously published; the APPJ is driven by a radiofrequency voltage across a 1&#8201;mm gap, at atmospheric pressure, while the MHCD is driven by a DC voltage source, at 100 Torr and in a 400 &#956; m hole. The MHCD may be operated either in the self-pulsing or in the normal (stationary) regime, depending on the driving voltage. The comparison shows that in both regimes, the MHCD produces larger amounts of ##IMG## [http://ej.iop.org/images/0963-0252/25/6/065015/psstaa4123ieqn001.gif] \textO_2^\ast , while the APPJ produces predominantly reactive oxygen ground state species, ##IMG## [http://ej.iop.org/images/0963-0252/25/6/065015/psstaa4123ieqn002.gif] \textO and ##IMG## [http://ej.iop.org/images/0963-0252/25/6/065015/psstaa4123ieqn003.gif] \textO_3 . These large differences in ROS composition are mostly due to the higher plasma density produced in the MHCD. The difference in operating pressure is a second order effect. (10.1088/0963-0252/25/6/065015)
  DOI : 10.1088/0963-0252/25/6/065015