Publications

2011

• Observation and theoretical modeling of electron scale solar wind turbulence
  
  • Sahraoui Fouad
  • Goldstein M. L.
  • Abdul-Kader K.
  • Belmont Gérard
  • Rezeau Laurence
  • Robert Patrick
  • Canu Patrick
  Comptes Rendus. Physique, Académie des sciences (Paris), 2011, 12 (2), pp.132-140. Turbulence at MagnetoHydroDynamics (MHD) scales in the solar wind has been studied for more than three decades, using data analysis, theoretical and numerical modeling. However, smaller scales have not been explored until very recently. Here, we review recent results on the first observation of cascade and dissipation of the solar wind turbulence at the electron scales. Thanks to the high resolution magnetic and electric field data of the Cluster spacecraft, we computed the spectra of turbulence up to (in the spacecraft reference frame) and found evidence of energy dissipation around the Doppler-shifted electron gyroscale . Before its dissipation, the energy is shown to undergo two cascades: a Kolmogorov-like cascade with a scaling above the proton gyroscale, and a new cascade at the sub-proton and electron gyroscales. Above the spectrum has a steeper power law down to the noise level of the instrument. Solving numerically the linear MaxwellVlasov equations combined with recent theoretical predictions of the Gyro-Kinetic theory, we show that the present results are consistent with a scenario of a quasi-two-dimensional cascade into Kinetic Alfvén modes (KAW). New analyses of other data sets, where the Cluster separation (of about ) allowed us to explore the sub-proton scales using the k-filtering technique, and to confirm the 2D nature of the turbulence at those scales. (10.1016/j.crhy.2010.11.008)
  DOI : 10.1016/j.crhy.2010.11.008
• Physics of Radio-Frequency Plasmas
  
  • Chabert Pascal
  • Braithwaite Nicholas
  , 2011. Low-temperature radio frequency plasmas are essential in various sectors of advanced technology, from micro-engineering to spacecraft propulsion systems and efficient sources of light. The subject lies at the complex interfaces between physics, chemistry and engineering. Focusing mostly on physics, this book will interest graduate students and researchers in applied physics and electrical engineering. The book incorporates a cutting-edge perspective on RF plasmas. It also covers basic plasma physics including transport in bounded plasmas and electrical diagnostics. Its pedagogic style engages readers, helping them to develop physical arguments and mathematical analyses. Worked examples apply the theories covered to realistic scenarios, and over 100 in-text questions let readers put their newly acquired knowledge to use and gain confidence in applying physics to real laboratory situations.
• Gas sensing properties of multiwall carbon nanotubes decorated with rhodium nanoparticles
  
  • Leghrib R
  • Dufour Thierry
  • Demoisson F
  • Claessens N
  • Reniers F
  • Llobet E
  Sensors and Actuators B: Chemical, Elsevier, 2011, B160, pp.974-980. In the present work, multiwalled carbon nanotubes were decorated with rhodium nanoparticles using a colloidal solution in the post-discharge of an RF atmospheric plasma of argon (Ar) or argon/oxygen (Ar:O 2). The properties of these hybrid materials towards the room temperature detection of NO 2 , C 2 H 4 , CO, C 6 H 6 and moisture were investigated and discussed in view of compositional and morphological studies. It was found that the presence of oxygen in the plasma treatment is essential to significantly enhance the gas response of Rh-decorated multiwalled carbon nanotubes and to avoid response saturation even at low gas/vapor concentrations. These desirable effects are attributed to the presence of oxygen during the CNT plasma treatment since oxygenated vacancies act both as active adsorption sites for gases and as anchoring sites for Rh nanoparticles (the presence of Rh nanoclusters is nearly doubled in Ar:O 2 treated samples as compared to Ar treated samples). The oxygen treatment also makes easier the charge transfer between Rh nanoparticles and carbon nanotubes upon gas adsorption. The method for treating and decorating multiwalled carbon nanotubes used here is simple, fast and scalable for producing gas sensitive nanohybrid materials with uniform and well-controlled properties. (10.1016/j.snb.2011.09.014)
  DOI : 10.1016/j.snb.2011.09.014
• Turbulence propagation in heat flux-driven plasmas: implications for temperature profile structure
  
  • Wang Z.H.
  • Diamond P.H.
  • Gürcan Özgür D.
  • Garbet X.
  • Wang X.G.
  Nuclear Fusion, IOP Publishing, 2011, 51, pp.073009. Turbulence propagation and temperature profile evolution are studied in heat flux-driven plasmas. A simple model consisting of coupled non-linear reactiondiffusion equations for both turbulence and heat transport is proposed to elucidate several aspects of apparent non-local profile dynamics. Self-consistent E × B shear feedback on turbulence intensity growth and transport is also included in the model. Temperature profile evolution is studied in the presence of an intensity pulse propagating inwards but also interacting with an outward propagating heat pulse. It is found that as the heat flux Q increases, the intensity pulse speed first grows as √ Q and then decays as 1/Q, while the heat pulse speed finally saturates at the level given by neoclassical transport. Intensity pulse propagation can be effectively saturated at or above a critical heat flux, so that the formation of an internal transport barrier (ITB) can be triggered. This suggests that the ITB location is ultimately determined by both heat flux and edge turbulence conditions, and thus the ITB inhibits both the inward turbulence propagation and the outward turbulent heat transport. As a test of turbulence spreading dynamics, the intensity pulse propagation through gaps in turbulence excitation and its implications for profile response to off-axis heat deposition are also investigated. It is shown that the profile resilience phenomena can be recovered by taking into account intensity pulse propagation. (10.1088/0029-5515/51/7/073009)
  DOI : 10.1088/0029-5515/51/7/073009
• Triple Q : A three channel quantum cascade laser absorption spectrometer for fast multiple species concentration measurements
  
  • Hübner M.
  • Welzel S.
  • Marinov Daniil
  • Guaitella Olivier
  • Glitsch S.
  • Rousseau Antoine
  • Röpcke J.
  Review of Scientific Instruments, American Institute of Physics, 2011, 82, pp.093102. A compact and transportable three channel quantum cascade laser system (TRIPLE Q) based on mid-infrared absorption spectroscopy has been developed for time-resolved plasma diagnostics. The TRIPLE Q spectrometer encompasses three independently controlled quantum cascade lasers (QCLs), which can be used for chemical sensing, particularly for gas phase analysis of plasmas. All three QCLs are operated in the intra-pulse mode with typical pulse lengths of the order of 150 ns. Using a multiplexed detection, a time resolution shorter than 1 μs can be achieved. Hence, the spectrometer is well suited to study kinetic processes of multiple infrared active compounds in reactive plasmas. A special data processing and analysis technique has been established to account for time jitter effects of the infrared emission of the QCLs. The performance of the TRIPLE Q system has been validated in pulsed direct current plasmas containing N2O/air and NO2/air. (10.1063/1.3633952)
  DOI : 10.1063/1.3633952
• Control of Nanocrystalline Silicon Growth Phase and Deposition Rate through Voltage Waveform Tailoring during PECVD
  
  • Johnson E.V.
  • Pouliquen S.
  • Delattre Pierre-Alexandre
  • Booth Jean-Paul
  MRS Online Proceedings Library, Cambridge University Press, 2011, 1339, pp.mrss11-1339-s04-5. The use of Voltage Waveform Tailoring (VWT) that is the use of non-sinusoidal waveforms with a period equivalent to RF frequencies is shown to be effective in modifying the electric field distribution in a parallel plate, capacitively coupled laboratory plasma deposition reactor, and thus in changing the growth mode of silicon thin films from amorphous to nanocrystalline. The use of the VWT technique allows one to decouple the power injected into the plasma from the ion-bombardment energy at the film surface without changing any other deposition parameters, such as pressure or gas mixture. Material results are presented for an H2/SiH4 gas composition. A peaks type waveform increases the ion-bombardment energy at the RF electrode and reduces it at the substrate, resulting in more nanocrystalline growth. The use of a valleys-type waveform has the opposite effect, and results in more amorphous growth. We show the dependence of the process on silane dilution and pressure, including results on changes to the deposition rate when changing the excitation voltage waveform. (10.1557/opl.2011.993)
  DOI : 10.1557/opl.2011.993
• Successive Nanosecond Discharges in Water
  
  • Marinov Ilya
  • Guaitella Olivier
  • Rousseau Antoine
  • Starikovskaia Svetlana
  IEEE Transactions on Plasma Science, Institute of Electrical and Electronics Engineers, 2011, 39 (11), pp.2672-2673. Successive discharges of alternating polarities in distilled water have been studied. Cathode-initiated discharges develop in two possible configurations: slow and weakly luminescent bushlike mode or fast and luminous treelike mode with well-pronounced branching. Under our experimental conditions, the two modes originate with approximately equal probability. Positive discharge demonstrates only one discharge morphology with two hemispherical weakly luminescent structures. Successive negative pulse results in the formation of one of the negative modes, bushlike or treelike. (10.1109/TPS.2011.2147337)
  DOI : 10.1109/TPS.2011.2147337
• Lower hybrid resonances stimulated by the four CLUSTER relaxation sounders deep inside the plasmasphere: observations and inferred plasma characteristics
  
  • Kougblénou S
  • Lointier G
  • Décréau Pierrette
  • Trotignon Jean-Gabriel
  • Rauch Jean-Louis
  • Vallières Xavier
  • Canu Patrick
  • Masson A
  • Pickett J
  Annales Geophysicae, European Geosciences Union, 2011, 29, pp.2003–2018. The frequency range of the WHISPER relaxation sounder instrument on board CLUSTER, 4–80 kHz, has been chosen so as to encompass the electron gyro-frequency, F ce , and the electron plasma frequency, F p , in most regions to be explored. Measurement of those frequencies, which are triggered as resonances by the sounder, provides a direct estimation of in situ fundamental plasma characteristics: electron density and magnetic field intensity. In the late mission phase, CLUSTER penetrated regions deep inside the plas-masphere where F ce and F p are much higher than the upper frequency of the sounder's range. However, they are of the right order of magnitude as to place the lower hybrid frequency , F lh , in the 4–15 kHz band. This characteristic frequency , placed at a resonance of the medium, is triggered by the sounder's transmitter and shows up as an isolated peak in the received spectrum, not present in spectra of naturally occuring VLF waves. This paper illustrates, from analysis of case events, how measured F lh values give access to a plasma diagnostic novel of its kind. CLUSTER, travelling along its orbit, encounters favourable conditions where F ce is increasing and F p decreasing, such that F ce /F p increases from values below unity to values above unity. Measured F lh values thus give access, in turn, to the effective mass, M eff , indicative of plasma ion composition, and to the core plasma-sphere electron density value, a parameter difficult to measure. The analysed case events indicate that the estimated quantities (M eff in the 1.0–1.4 range, N e in the 5 × 10 2 – 10 4 cm −3 range) are varying with external factors (altitude, L value, geomagnetic activity) in a plausible way. Although covering only a restricted region (mid-latitude, low altitude inner plasmasphere), these measurements are available, since Correspondence to: S. Kougblénou (sena.kougblenou@cnrs-orleans.fr) late 2009, for all CLUSTER perigee passes not affected by eclipses (on average, roughly a third of a total of ∼200 passes per year) and offer multipoint observations previously unavailable in this region. (10.5194/angeo-29-2003-2011)
  DOI : 10.5194/angeo-29-2003-2011
• Cluster Observations of Magnetopause Reconnection at Sub-Proton Scales
  
  • Retinò Alessandro
  • Vaivads A.
  • Sahraoui Fouad
  • Le Contel Olivier
  • Zieger B.
  • Nakamura R.
  • Mozer F. S.
  , 2011.
• Edge Temperature Gradient as Intrinsic Rotation Drive in Alcator C-Mod Tokamak Plasmas
  
  • Rice J.E.
  • Hughes J.W.
  • Diamond P.H.
  • Kosuga Y.
  • Podpaly Y.A.
  • Reinke M.L.
  • Greenwald M.J.
  • Gürcan Özgür D.
  • Hahm T.S.
  • Hubbard A.E.
  • Marmar E.S.
  • Mcdevitt C.J.
  • Whyte D.G.
  Physical Review Letters, American Physical Society, 2011, 106, pp.215001. Intrinsic rotation has been observed in I-mode plasmas from the C-Mod tokamak, and is found to be similar to that in H mode, both in its edge origin and in the scaling with global pressure. Since both plasmas have similar edge ∇T, but completely different edge ∇n, it may be concluded that the drive of the intrinsic rotation is the edge ∇T rather than ∇P. Evidence suggests that the connection between gradients and rotation is the residual stress, and a scaling for the rotation from conversion of free energy to macroscopic flow is calculated. (10.1103/PhysRevLett.106.215001)
  DOI : 10.1103/PhysRevLett.106.215001
• Reactivity and adsorption of N atoms on catalytic surfaces
  
  • Marinov Daniil
  • Guaitella Olivier
  • Rousseau Antoine
  , 2011.
• Reactivity of atoms adsorbed on catalytic surfaces under plasma exposure
  
  • Marinov Daniil
  • Guaitella Olivier
  • Rousseau Antoine
  , 2011.
• Global distribution of electrostatic electron cyclotron harmonic waves observed on THEMIS
  
  • Ni B.
  • Thorne R. M.
  • Liang Jun
  • Angelopoulos V.
  • Cully C. M.
  • Li W.
  • Zhang Xiaojia
  • Hartinger Michael
  • Le Contel Olivier
  • Roux A.
  Geophysical Research Letters, American Geophysical Union, 2011, 38, pp.17105. A global, statistical analysis of electrostatic electron cyclotron harmonic (ECH) waves is performed using THEMIS wave data. Our results confirm the high occurrence of <1 mV/m ECH emissions throughout the outer magnetosphere (L > 5). The strongest (>=1 mV/m) ECH waves are enhanced during geomagnetically disturbed periods, and are mainly confined close to the magnetic equator (|lambda| < 3°) over the region L <= 10 in the night and dawn MLT sector. ECH wave intensities within 3° <= |lambda| < 6° are generally much weaker but not negligible especially for L < 12 on the midnight side. Furthermore, the occurrence rates and variability of moderately intense (>=0.1 mV/m) ECH emissions suggest that ECH wave scattering could contribute to diffuse auroral precipitation in the outer (L > 8) magnetosphere where chorus emissions are statistically weak. (10.1029/2011GL048793)
  DOI : 10.1029/2011GL048793
• Plasmoid Releases in the Heliospheric Current Sheet and Associated Coronal Hole Boundary Layer Evolution
  
  • Foullon C.
  • Lavraud B.
  • Luhmann J. G.
  • Farrugia C. J.
  • Retinò Alessandro
  • Simunac K. D. C.
  • Wardle N. C.
  • Galvin A. B.
  • Kucharek H.
  • Owen C. J.
  • Popecki M.
  • Opitz A.
  • Sauvaud J.-A.
  The Astrophysical Journal, American Astronomical Society, 2011, 737, pp.16. As the heliospheric current sheet (HCS) is corotating past STEREO-B, near-Earth spacecraft ACE, Wind and Cluster, and STEREO-A over more than three days between 2008 January 10 and 14, we observe various sections of (near-pressure-balanced) flux-rope- and magnetic-island-type plasmoids in the associated heliospheric plasma sheet (HPS). The plasmoids can qualify as slow interplanetary coronal mass ejections and are relatively low proton beta (<0.5) structures, with small length scales (an order of magnitude lower than typical magnetic cloud values) and low magnetic field strengths (2-8 nT). One of them, in particular, detected at STEREO-B, corresponds to the first reported evidence of a detached plasmoid in the HPS. The in situ signatures near Earth are associated with a long-decay X-ray flare and a slow small-scale streamer ejecta, observed remotely with white-light coronagraphs aboard STEREO-B and SOHO and tracked by triangulation. Before the arrival of the HPS, a coronal hole boundary layer (CHBL) is detected in situ. The multi-spacecraft observations indicate a CHBL stream corotating with the HCS but with a decreasing speed distribution suggestive of a localized or transient nature. While we may reasonably assume that an interaction between ejecta and CHBL provides the source of momentum for the slow ejecta's acceleration, the outstanding composition properties of the CHBL near Earth provide here circumstantial evidence that this interaction or possibly an earlier one, taking place during streamer swelling when the ejecta rises slowly, results in additional mixing processes. (10.1088/0004-637X/737/1/16)
  DOI : 10.1088/0004-637X/737/1/16
• Space Exploration Technologies Pegases A new promising electric propulsion concept
  
  • Aanesland Ane
  • Mazouffre S.
  • Chabert Pascal
  Europhysics News, EDP Sciences, 2011, 42 (6), pp.28-31. This article has no abstract (10.1051/epn/2011604)
  DOI : 10.1051/epn/2011604
• Solar wind, mass and momentum losses during the solar cycle
  
  • Pinto Rui
  • Brun Allan Sacha
  • Jouve Laurène
  • Grappin Roland
  , 2011, 271 (2010-06-21 / 2010-06-25), pp.395-396. We study the connections between the sun's convection zone evolution and the dynamics of the solar wind and corona. We input the magnetic fields generated by a 2.5D axisymmetric kinematic dynamo code (STELEM) into a 2.5D axisymmetric coronal MHD code (DIP). The computations were carried out for an 11 year cycle. We show that the solar wind's velocity and mass flux vary in latitude and in time in good agreement with the well known time-latitude assymptotic wind speed diagram. Overall sun's mass loss rate, momentum flux and magnetic breaking torque are maximal near the solar minimum. (10.1017/S1743921311017960)
  DOI : 10.1017/S1743921311017960
• Impact of collisionality on fluctuation characteristics of micro-turbulence
  
  • Vermare Laure
  • Hennequin Pascale
  • Gürcan Özgür D.
  • Bourdelle C.
  • Clairet F.
  • Garbet X.
  • Sabot R.
  • Tore Supra Team
  Physics of Plasmas, American Institute of Physics, 2011, 18, pp.012306. The influence of changing collisionality on density fluctuation characteristics is studied during dedicated &#957;&#8727; scaling experiments, using Doppler backscattering system. First, the repartition of fluctuation energy over different spatial scales, as represented by the wavenumber spectrum, is investigated and a modification of the shape of the perpendicular wavenumber spectrum in the low wavenumber part of the spectrum is observed when changing collisionality. In addition, a new procedure to evaluate the dispersion relation of micro-turbulence is presented. From the behavior of the perpendicular mean velocity of density fluctuations with the perpendicular wavenumber, different dispersion relations are obtained between low and high collisionality cases. (10.1063/1.3536648)
  DOI : 10.1063/1.3536648
• Observational evidence of the generation mechanism for rising-tone chorus
  
  • Cully C. M.
  • Angelopoulos V.
  • Auster U.
  • Bonnell J. W.
  • Le Contel Olivier
  Geophysical Research Letters, American Geophysical Union, 2011, 38, pp.1106. Chorus emissions are a striking feature of the electromagnetic wave environment in the Earth's magnetosphere. These bursts of whistler-mode waves exhibit characteristic frequency sweeps (chirps) believed to result from wave-particle trapping of cyclotron-resonant particles. Based on the theory of Omura et al. (2008), we predict the sweep rates of chorus elements observed by the THEMIS satellites. The predictions use independent observations of the electron distribution functions and have no free parameters. The predicted chirp rates are a function of wave amplitude, and this relation is clearly observed. The predictive success of the theory lends strong support to its underlying physical mechanism: cyclotron-resonant wave-particle trapping. (10.1029/2010GL045793)
  DOI : 10.1029/2010GL045793
• A model of electromagnetic electron phase-space holes and its application
  
  • Tao J. B.
  • Ergun R. E.
  • Andersson L.
  • Bonnell J. W.
  • Roux A.
  • Le Contel Olivier
  • Angelopoulos V.
  • Mcfadden J. P.
  • Larson D. E.
  • Cully C. M.
  • Auster H.-U.
  • Glassmeier K.-H.
  • Baumjohann W.
  • Newman D. L.
  • Goldman M. V.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2011, 116, pp.11213. Electron phase-space holes (EHs) are indicators of nonlinear activities in space plasmas. Most often they are observed as electrostatic signals, but recently Andersson et al. [2009] reported electromagnetic EHs observed by the THEMIS mission in the Earth's plasma sheet. As a follow-up to Andersson et al. [2009], this paper presents a model of electromagnetic EHs where the deltaE × B<SUB>0</SUB> drift of electrons creates a net current. The model is examined with test-particle simulations and compared to the electromagnetic EHs reported by Andersson et al. [2009]. As an application of the model, we introduce a more accurate method than the simplified Lorentz transformation of Andersson et al. [2009] to derive EH velocity (v<SUB>EH</SUB>). The sizes and potentials of EHs are derived from v<SUB>EH</SUB>, so an accurate derivation of v<SUB>EH</SUB> is important in analyzing EHs. In general, our results are qualitatively consistent with those of Andersson et al. [2009] but generally with smaller velocities and sizes. (10.1029/2010JA016054)
  DOI : 10.1029/2010JA016054
• On the effect of IMF turning on ion dynamics at Mercury
  
  • Delcourt Dominique C.
  • Moore T. E.
  • Fok M.-C. H.
  Annales Geophysicae, European Geosciences Union, 2011, 29, pp.987-996. We investigate the effect of a rotation of the Interplanetary Magnetic Field (IMF) on the transport of magnetospheric ion populations at Mercury. We focus on ions of planetary origin and investigate their large-scale circulation using three-dimensional single-particle simulations. We show that a nonzero B<SUB>X</SUB> component of the IMF leads to a pronounced asymmetry in the overall circulation pattern. In particular, we demonstrate that the centrifugal acceleration due to curvature of the E × B drift paths is more pronounced in one hemisphere than the other, leading to filling of the magnetospheric lobes and plasma sheet with more or less energetic material depending upon the hemisphere of origin. Using a time-varying electric and magnetic field model, we investigate the response of ions to rapid (a few tens of seconds) re-orientation of the IMF. We show that, for ions with gyroperiods comparable to the field variation time scale, the inductive electric field should lead to significant nonadiabatic energization, up to several hundreds of eVs or a few keVs. It thus appears that IMF turning at Mercury should lead to localized loading of the magnetosphere with energetic material of planetary origin (e.g., Na<SUP> </SUP>). (10.5194/angeo-29-987-2011)
  DOI : 10.5194/angeo-29-987-2011
• Estimation of magnetic field mapping accuracy using the pulsating aurora-chorus connection
  
  • Nishimura Y.
  • Bortnik J.
  • Li W.
  • Thorne R. M.
  • Lyons L.R.
  • Angelopoulos V.
  • Mende S. B.
  • Bonnell J. W.
  • Le Contel Olivier
  • Cully C. M.
  • Ergun R.
  • Auster U.
  Geophysical Research Letters, American Geophysical Union, 2011, 38, pp.14110. Although magnetic field models are widely used in magnetosphere-ionosphere coupling studies to perform field-line mapping, their accuracy has been difficult to estimate experimentally. Taking advantage of the high correlation between lower-band chorus and pulsating aurora, we located the THEMIS spacecraft footprint within km accuracy and calculated the differences from mappings given in widely-used Tsyganenko models. Using 13 conjunctions of the THEMIS spacecraft and ground-based imagers, we found that the Tsyganenko model footprints were located within 1°-2° magnetic latitude and 0.1-0.2 h magnetic local time of our derived footprint. The deviation between the footprints has a consistent dependence on geomagnetic activity. Our results showed that the real magnetic field tends to be less stretched than that in the Tsyganenko models during quiet times and comparable to or more stretched during disturbed times. This approach can be used to advance modeling of field lines that connect to the near-Earth plasma sheet. (10.1029/2011GL048281)
  DOI : 10.1029/2011GL048281
• Polar cap ion beams during periods of northward IMF: Cluster statistical results
  
  • Maggiolo R.
  • Echim M.
  • de Keyser J.
  • Fontaine Dominique
  • Jacquey C.
  • Dandouras I.
  Annales Geophysicae, European Geosciences Union, 2011, 29, pp.771-787. Above the polar caps and during prolonged periods of northward IMF, the Cluster satellites detect upward accelerated ion beams with energies up to a few keV. They are associated with converging electric field structures indicating that the acceleration is caused by a quasi-static field-aligned electric field that can extend to altitudes higher than 7 R<SUB>E</SUB> (Maggiolo et al., 2006; Teste et al., 2007). Using the AMDA science analysis service provided by the Centre de Données de la Physique des Plasmas, we have been able to extract about 200 events of accelerated upgoing ion beams above the polar caps from the Cluster database. Most of these observations are taken at altitudes lower than 7 R<SUB>E</SUB> and in the Northern Hemisphere. We investigate the statistical properties of these ion beams. We analyze their geometry, the properties of the plasma populations and of the electric field inside and around the beams, as well as their dependence on solar wind and IMF conditions. We show that ~40 % of the ion beams are collocated with a relatively hot and isotropic plasma population. The density and temperature of the isotropic population are highly variable but suggest that this plasma originates from the plasma sheet. The ion beam properties do not change significantly when the isotropic, hot background population is present. Furthermore, during one single polar cap crossing by Cluster it is possible to detect upgoing ion beams both with and without an accompanying isotropic component. The analysis of the variation of the IMF B<SUB>Z</SUB> component prior to the detection of the beams indicates that the delay between a northward/southward turning of IMF and the appearance/disappearance of the beams is respectively ~2 h and 20 min. The observed electrodynamic characteristics of high altitude polar cap ion beams suggest that they are closely connected to polar cap auroral arcs. We discuss the implications of these Cluster observations above the polar cap on the magnetospheric dynamics and configuration during prolonged periods of northward IMF. (10.5194/angeo-29-771-2011)
  DOI : 10.5194/angeo-29-771-2011
• Two-Temperature Models for Polar Plumes: Cooling by Means of Strong Base Heating
  
  • Grappin Roland
  • Wang Y-M
  • Pantellini F.
  The Astrophysical Journal, American Astronomical Society, 2011, 727 (1), pp.30. In earlier one-fluid hydrodynamical calculations incorporating heat conduction and radiative losses, it was shown that the high densities in polar plumes could be reproduced by including a concentrated heat source near the plume base, in addition to the global heating required in both the plume and interplume regions of the coronal hole. The extra heating (attributed to interchange reconnection between the open flux and an underlying magnetic bipole) results in lower flow speeds and temperatures relative to the interplume gas, predictions that have since been confirmed by spectroscopic measurements. Here, the model is extended to the two-fluid case, in which ions and electrons are allowed to have different temperatures, coupling is via Coulomb collisions, and heat transport is mainly by electrons. Again, we find that depositing energy very close to the coronal base, in either the protons or electrons (or both), raises the densities and decreases the flow speeds everywhere along the flux tube. The higher densities in turn act to lower the ion temperatures by coupling the protons more closely to the energy-losing electrons. In addition, we find that energy must be deposited globally in both the electrons and the ions; without this direct heating, the electrons would end up cooler in the interplume region than in the plume, contrary to observations. Increasing the rate of flux-tube expansion has the effect of lowering the electron and ion temperatures and reducing the asymptotic flow speed, both in the plume and the interplume region; the observed densities and temperatures can be matched by taking the magnetic field to fall off with radius roughly as r 4. (10.1088/0004-637X/727/1/30)
  DOI : 10.1088/0004-637X/727/1/30
• Jet front-driven mirror modes and shocklets in the near-Earth flow-braking region
  
  • Zieger B.
  • Retinò Alessandro
  • Nakamura R.
  • Baumjohann W.
  • Vaivads A.
  • Khotyaintsev Y. V.
  Geophysical Research Letters, American Geophysical Union, 2011, 38, pp.22103. We investigate the small-scale structure of jet fronts through a case study of multi-spacecraft Cluster observations in the near-Earth flow-braking region at -10 RE. We find that the interaction between the earthward moving fast plasma jet and the high-&#946; ambient plasma in the plasma sheet results in magnetic pileup and compression ahead of the jet and rarefaction trailing the jet. It is shown that mirror-mode structures of ion gyroradius scale develop within the pileup region due to the observed ion temperature anisotropy (Ti⊥ > Ti\parallel). We suggest that the growth of these mirror modes is driven by the perpendicular total pressure perturbation (&#916;p⊥) generated by the braking jet. When &#916;p⊥ becomes too large, the mirror-mode structure cannot maintain pressure balance any longer, and consequently a shocklet is formed in the pileup region ahead of the jet front. We present the first evidence for such a kinetic shocklet in the flow-braking region. (10.1029/2011GL049746)
  DOI : 10.1029/2011GL049746
• Different regimes of MHD turbulence with mean magnetic field
  
  • Grappin Roland
  , 2011.