Publications

2011

Three-dimensional spatial structures of solar wind turbulence from 10 000-km to 100-km scales
- Narita Y.
- Glassmeier K.-H.
- Goldstein M. L.
- Motschmann U.
- Sahraoui Fouad
Annales Geophysicae, European Geosciences Union, 2011, 29, pp.1731-1738. Using the four Cluster spacecraft, we have determined the three-dimensional wave-vector spectra of fluctuating magnetic fields in the solar wind. Three different solar wind intervals of Cluster data are investigated for this purpose, representing three different spatial scales: 10 000 km, 1000 km, and 100 km. The spectra are determined using the wave telescope technique (k-filtering technique) without assuming the validity of Taylor's frozen-in-flow hypothesis nor are any assumptions made as to the symmetry properties of the fluctuations. We find that the spectra are anisotropic on all the three scales and the power is extended primarily in the directions perpendicular to the mean magnetic field, as might be expected of two-dimensional turbulence, however, the analyzed fluctuations are not axisymmetric. The lack of axisymmetry invalidates some earlier techniques using single spacecraft observations that were used to estimate the percentage of magnetic energy residing in quasi-two-dimensional power. However, the dominance of two-dimensional turbulence is consistent with the relatively long mean free paths of cosmic rays in observed in the heliosphere. On the other hand, the spectra also exhibit secondary extended structures oblique from the mean magnetic field direction. We discuss possible origins of anisotropy and asymmetry of solar wind turbulence spectra. (10.5194/angeo-29-1731-2011)
DOI : 10.5194/angeo-29-1731-2011
Numerical analysis of electronegative plasma in the extraction region of negative hydrogen ion sources
- Kuppel S.
- Matsushita D.
- Hatayama A.
- Bacal M.
Journal of Applied Physics, American Institute of Physics, 2011, 109 (1), pp.013305. This numerical study focuses on the physical mechanisms involved in the extraction of volume-produced H− ions from a steady state laboratory negative hydrogen ion source with one opening in the plasma electrode (PE) on which a dc-bias voltage is applied. A weak magnetic field is applied in the source plasma transversely to the extracted beam. The goal is to highlight the combined effects of the weak magnetic field and the PE bias voltage (upon the extraction process of H− ions and electrons). To do so, we focus on the behavior of electrons and volume-produced negative ions within a two-dimensional model using the particle-in-cell method. No collision processes are taken into account, except for electron diffusion across the magnetic field using a simple random-walk model at each time step of the simulation. The results show first that applying the magnetic field (without PE bias) enhances H− ion extraction, while it drastically decreases the extracted electron current. Secondly, the extracted H− ion current has a maximum when the PE bias is equal to the plasma potential, while the extracted electron current is significantly reduced by applying the PE bias. The underlying mechanism leading to the above results is the gradual opening by the PE bias of the equipotential lines towards the parts of the extraction region facing the PE. The shape of these lines is due originally to the electron trapping by the magnetic field. (10.1063/1.3530454)
DOI : 10.1063/1.3530454
Electron-cylotron maser radiation from electron holes: upward current region
- Treumann R. A.
- Baumjohann W.
- Pottelette R.
Annales Geophysicae, European Geosciences Union, 2011, 29, pp.1885-1904. Electron holes are suggested to be an important source for generation of electron-cyclotron maser radiation. We demonstrate that electron holes generated in a ring-horseshoe distribution in the auroral-kilometric radiation source region have the capacity to emit band-limited radiation. The radiation is calculated in the proper frame of a circular model hole and shown to be strictly perpendicular in this frame. Its bandwidth under auroral conditions is of the order of ~1 kHz, which is a reasonable value. It is also shown that much of the drift of fine structure in the radiation can be interpreted as Doppler shift. Estimates based on data are in good agreement with theory. Growth and absorption rates have been obtained for the emitted radiation. However, the growth rate of a single hole obtained under conservative conditions is small, too small for reproducing the observed fine structure flux. Trapping of radiation inside the hole for the hole's lifetime helps amplifying the radiation additionally but introduces other problems. This entire set of questions is discussed at length and compared to radiation from the global horseshoe distribution. The interior of the hole produces a weak absorption at slightly higher frequency than emission. The absorptivity is roughly two orders of magnitude below the growth rate of the radiation thus being weak even when the emission and absorption bands overlap. Transforming to the stationary observer's frame it is found that the radiation becomes oblique against the magnetic field. For approaching holes the radiated frequencies may even exceed the local electron cyclotron frequency. (10.5194/angeo-29-1885-2011)
DOI : 10.5194/angeo-29-1885-2011
Multi-spacecraft investigation of space turbulence: lessons from Cluster and input to the Cross- Scale mission
- Sahraoui Fouad
- Goldstein M.L.
- Belmont Gérard
- Roux A.
- Rezeau Laurence
- Canu Patrick
- Robert Patrick
- Cornilleau-Wehrlin Nicole
- Le Contel Olivier
- Dudok de Wit Thierry
- Pinçon Jean-Louis
- Kiyani K.
Planetary and Space Science, Elsevier, 2011, 59 (7), pp.Pages 585-591. Investigating space plasma turbulence from single-point measurements is known to be characterized by unavoidable ambiguities in disentangling temporal and spatial variations. Solving this problem has been one of the major goals of the Cluster mission. For that purpose multipoint measurements techniques, such as the $k$-filtering, have been developed. Such techniques combine several time series recorded simultaneously at different points in space to estimate the corresponding energy density in the wavenumber space. Here we apply the technique to both simulated and Cluster magnetometer data in the solar wind (SW) and investigate the errors and limitations that arise due to the separation of the spacecraft and the quality of the tetrahedral configuration. Specifically, we provide an estimation of the minimum and maximum scales that can be accurately measured given a specific distance between the satellites and show the importance of the geometry of the tetrahedron and the relationship of that geometry to spatial aliasing. We also present recent results on characterizing small scale SW turbulence and provide scientific arguments supporting the need of new magnetometers having better sensitivity than the existing ones. Throughout the paper we emphasize technical challenges and their solutions that can be considered for a better preparation of the Cross- Scale mission. (10.1016/j.pss.2010.06.001)
DOI : 10.1016/j.pss.2010.06.001
Landau and Non-Landau Linear Damping: Physics of the Dissipation
- Belmont Gérard
- Chust Thomas
- Mottez Fabrice
- Hess S.
Transport Theory and Statistical Physics, Taylor & Francis, 2011, 40 (6-7), pp.419-424. The linear Landau effect is revisited by the means of numerical simulations and analytical calculations. The existence of non-Landau solutions to the Vlasov-Poisson system is emphasized and the consistency of these solutions with respect to the arguments based on energy is investigated. The present article briefly summarizes the content of two articles already published on the subject and introduces a discussion based on the exchanges that occurred at Marseille during the Vlasovia meeting. (10.1080/00411450.2011.651055)
DOI : 10.1080/00411450.2011.651055
Energy budgets in collisionless magnetic reconnection: Ion heating and bulk acceleration
- Aunai Nicolas
- Belmont Gérard
- Smets Roch
Physics of Plasmas, American Institute of Physics, 2011, 18, pp.122901. This paper investigates the energy transfer in the process of collisionless antiparallel magnetic reconnection. Using two-dimensional hybrid simulations, we measure the increase of the bulk and thermal kinetic energies and compare it to the loss of magnetic energy through a contour surrounding the ion decoupling region. It is shown, for both symmetric and asymmetric configurations, that the loss of magnetic energy is not equally partitioned between heating and acceleration. The heating is found to be dominant and the partition ratio depends on the asymptotic parameters, and future investigations will be needed to understand this dependence. (10.1063/1.3664320)
DOI : 10.1063/1.3664320
Evolution of micro-turbulence characteristics with collisionality at the tokamak core-edge interface
- Vermare Laure
- Hennequin Pascale
- Gürcan Özgür D.
- Honoré Cyrille
- Berionni Vincent
- Bourdelle C.
- Casati A.
- Clairet F.
- Garbet X.
- Giacalone J-C.
- Sabot R.
- Tore Supra Team
, 2011, oral.
A generalization of the rocket formula and its application to advanced space propulsion systems
- Nasi L.
- Raimbault Jean-Luc
Acta Astronautica, Elsevier, 2011, 68 (1-2), pp.34-38. A generalized rocket formula is derived from a first principles approach. The resulting expression of the thrust is applied to advanced space propulsion systems and a possible link between the asymptotic propellant velocity and the velocity at thruster exit is given. An estimation of the thrust modification due to spacecraftplume interactions is also considered. (10.1016/j.actaastro.2010.07.015)
DOI : 10.1016/j.actaastro.2010.07.015
Oxidation of NO into NO2 by surface adsorbed O atoms
- Guaitella Olivier
- Hübner M.
- Marinov Daniil
- Guerra V.
- Pintassilgo C.D.
- Welzel S.
- Röpcke J.
- Rousseau Antoine
Contributions to Plasma Physics, Wiley-VCH Verlag, 2011, 51 (2-3), pp.176-181. Plasma-surface interactions are increasingly recognised as a key factor in explaining molecule production and conversion processes. In order to scrutinise such effects well-defined surface and gas phase conditions are required. Hence, the inner surface of a Pyrex tube was treated by a capacitively coupled RF plasma at low pressure. The post-plasma oxidation of gas mixtures containing 1 % NO into NO2 has been studied by means of quantum cascade laser absorption spectroscopy in the mid-infrared spectral range. The plasma pre-treatment experiments with oxygen containing precursors suggest O atom adsorption on the Pyrex tube with a surface density of 2.7 x 1014 cm2. A simple kinetic model was developed and shows good agreement with the measured NO and NO2 gas phase concentrations. In the model a fraction of the surface is considered to be covered with chemisorption sites where atoms and molecules can be adsorbed, whereas they can be removed only by recombination (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) (10.1002/ctpp.201000068)
DOI : 10.1002/ctpp.201000068
Compressible Kelvin-Helmholtz instability in supermagnetosonic regimes
- Palermo F.
- Faganello M.
- Califano F.
- Pegoraro F.
- Le Contel Olivier
Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2011, 116, pp.4223. We investigate the transition from submagnetosonic to supermagnetosonic regimes in the presence of a sheared flow and density variations typically observed between the solar wind and the Earth's magnetosphere. In particular, we show the possibility of generating quasi-perpendicular magnetosonic shock structures under typical conditions that can be realized at the magnetosphere flanks. Here the Kelvin-Helmholtz instability generates rolled-up, large- scale vortices that propagate along the flanks of the magnetosphere. The shocks are generated by those vortices for which the magnetosonic Mach number turns out to be of the order of unity or larger. (10.1029/2010JA016400)
DOI : 10.1029/2010JA016400
A mechanism for heating electrons in the magnetopause current layer and adjacent regions
- Roux A.
- Robert Patrick
- Le Contel Olivier
- Angelopoulos V.
- Auster U.
- Bonnell J. W.
- Cully C. M.
- Ergun R. E.
- Mcfadden J. P.
Annales Geophysicae, European Geosciences Union, 2011, 29, pp.2305-2316. Taking advantage of the string-of-pearls configuration of the five THEMIS spacecraft during the early phase of their mission, we analyze observations taken simultaneously in the magnetosheath, the magnetopause current layer and the magnetosphere. We find that electron heating coincides with ultra low frequency waves. It seems unlikely that electrons are heated by these waves because the electron thermal velocity is much larger than the Alfvén velocity (Va). In the short transverse scale (k\botrhoi >> 1) regime, however, short scale Alfvén waves (SSAWs) have parallel phase velocities much larger than Va and are shown to interact, via Landau damping, with electrons thereby heating them. The origin of these waves is also addressed. THEMIS data give evidence for sharp spatial gradients in the magnetopause current layer where the highest amplitude waves have a large component deltaB perpendicular to the magnetopause and k azimuthal. We suggest that SSAWs are drift waves generated by temperature gradients in a high beta, large Ti/Te magnetopause current layer. Therefore these waves are called SSDAWs, where D stands for drift. SSDAWs have large k\bot and therefore a large Doppler shift that can exceed their frequencies in the plasma frame. Because they have a small but finite parallel electric field and a magnetic component perpendicular to the magnetopause, they could play a key role at reconnecting magnetic field lines. The growth rate depends strongly on the scale of the gradients; it becomes very large when the scale of the electron temperature gradient gets below 400 km. Therefore SSDAW's are expected to limit the sharpness of the gradients, which might explain why Berchem and Russell (1982) found that the average magnetopause current sheet thickness to be ~400-1000 km (~500 km in the near equatorial region). (10.5194/angeo-29-2305-2011)
DOI : 10.5194/angeo-29-2305-2011
Ion acceleration in antiparallel collisionless magnetic reconnection: Kinetic and fluid aspects
- Aunai Nicolas
- Belmont Gérard
- Smets Roch
Comptes Rendus. Physique, Académie des sciences (Paris), 2011, 12, pp.141-150. Not Available (10.1016/j.crhy.2010.11.004)
DOI : 10.1016/j.crhy.2010.11.004
Modeling the superstorm in November 2003
- Fok M.-C. H.
- Moore T. E.
- Slinker Steve P.
- Fedder Joel A.
- Delcourt Dominique C.
- Nosé Masahito
- Chen Sheng-Hsien
Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2011, 116. The superstorm on 20-21 November 2003 was the largest geomagnetic storm in solar cycle 23 as measured by Dst, which attained a minimum value of -422 nT. We have simulated this storm to understand how particles originating from the solar wind and ionosphere get access to the magnetosphere and how the subsequent transport and energization processes contribute to the buildup of the ring current. The global electromagnetic configuration and the solar wind H distribution are specified by the Lyon-Fedder-Mobarry (LFM) magnetohydrodynamics model. The outflow of H and O ions from the ionosphere are also considered. Their trajectories in the magnetosphere are followed by a test-particle code. The particle distributions at the inner plasma sheet established by the LFM model and test-particle calculations are then used as boundary conditions for a ring current model. Our simulations reproduce the rapid decrease of Dst during the storm main phase and the fast initial phase of recovery. Shielding in the inner magnetosphere is established at early main phase. This shielding field lasts several hours and then breaks down at late main phase. At the peak of the storm, strong penetration of ions earthward to L shell of 1.5 is revealed in the simulation. It is surprising that O is significant but not the dominant species in the ring current in our calculation for this major storm. It is very likely that substorm effects are not well represented in the models and O energization is underestimated. Ring current simulation with O energy density at the boundary set comparable to Geotail observations produces excellent agreement with the observed symH. As expected in superstorms, ring current O is the dominant species over H during the main to midrecovery phase of the storm. (10.1029/2010JA015720)
DOI : 10.1029/2010JA015720
Whistler eigenmodes of magnetic flux tubes in a magnetoplasma
- Kudrin A. V.
- Bakharev P. V.
- Zaboronkova T. M.
- Krafft C.
Plasma Physics and Controlled Fusion, IOP Publishing, 2011, 53, pp.065005. Guided propagation of whistler waves along cylindrical non-uniformities of a dc magnetic field is studied within the framework of a full-wave approach. Conditions are revealed under which such guiding structures, commonly known as magnetic flux tubes, can support volume and surface eigenmodes in the whistler range. The dispersion properties and field structures of whistler eigenmodes guided by flux tubes with an enhanced magnetic field are calculated and analysed for plasma parameters typical of laboratory experiments. The results obtained are useful in understanding the basic features of whistler wave guidance by magnetic flux tubes and can be applied to interpreting the data of the relevant experiments. (10.1088/0741-3335/53/6/065005)
DOI : 10.1088/0741-3335/53/6/065005
Predator prey oscillations in a simple cascade model of drift wave turbulence
- Berionni Vincent
- Gürcan Özgür D.
Physics of Plasmas, American Institute of Physics, 2011, 18, pp.112301. A reduced three shell limit of a simple cascade model of drift wave turbulence, which emphasizes nonlocal interactions with a large scale mode, is considered. It is shown to describe both the well known predator prey dynamics between the drift waves and zonal flows and to reduce to the standard three wave interaction equations. Here, this model is considered as a dynamical system whose characteristics are investigated. The analytical solutions for the purely nonlinear limit are given in terms of the Jacobi elliptic functions. An approximate analytical solution involving Jacobi elliptic functions and exponential growth is computed using scale separation for the case of unstable solutions that are observed when the energy injection rate is high. The fixed points of the system are determined, and the behavior around these fixed points is studied. The system is shown to display periodic solutions corresponding to limit cycle oscillations, apparently chaotic phase space orbits, as well as unstable solutions that grow slowly while oscillating rapidly. The period doubling route to transition to chaos is examined. (10.1063/1.3656953)
DOI : 10.1063/1.3656953
Wavenumber spectrum of micro-turbulence in tokamak plasmas / Spectre en nombre d'onde de la micro-turbulence dans les plasmas de tokamak
- Vermare Laure
- Gürcan Özgür D.
- Hennequin Pascale
- Honoré Cyrille
- Garbet X.
- Giacalone J-C.
- Sabot R.
- Clairet F.
- Tore Supra Team
Comptes Rendus. Physique, Académie des sciences (Paris), 2011, 12 (2), pp.115 - 122. A better understanding of turbulent transport in a tokamak plasma requires precise comparisons between experimental observation and theoretical prediction of micro-turbulence characteristics. The repartition of fluctuation energy over different spatial scales, which contains detailed information about the character of underlying instabilities and the mechanisms involved in energy transfer between different scales, is one of the few quantities allowing a high detail comparison. The present article reports the investigation performed on the Tore Supra tokamak on the wavenumber spectrum of micro-turbulence using Doppler backscattering. The theoretical approach consists of the derivation of spectral models that include interactions between fluctuations and large scale flow structures. Une meilleure compréhension du transport turbulent dans les plasmas de tokamak exige des comparaisons précises entre les observations expérimentales et les prédictions théoriques des caractéristiques de la micro-turbulence. La répartition de lʼénergie des fluctuations sur les différentes échelles spatiales, qui contient des informations sur le type instabilités sous-jacentes et sur les mécanismes de transfert dʼénergie entre échelles spatiales, est lʼune des rares quantités permettant une comparaison de niveau élevé. Cet article présente le travail mené sur le tokamak Tore Supra sur lʼétude du spectre en nombre dʼonde de la micro-turbulence mesuré par rétro-diffusion Doppler. Lʼapproche théorique consiste en la dérivation de modéles spectraux qui inclut les interactions entre les fluctuations et les structures dʼécoulement de grandes échelles. (10.1016/j.crhy.2010.11.003)
DOI : 10.1016/j.crhy.2010.11.003
Collisionality scaling in Tore Supra: detailed energy confinement analysis, turbulence measurements and gyrokinetic modelling
- Bourdelle C.
- Gerbaud T.
- Vermare Laure
- Casati A.
- Aniel Thierry
- Artaud J.F.
- Basiuk Vincent
- Bucalossi J.
- Clairet F.
- Corre Y.
- Devynck P.
- Falchetto G.
- Fenzi C.
- Garbet X.
- Guirlet R.
- Gürcan Özgür D.
- Heuraux S.
- Hennequin Pascale
- Hoang G.T.
- Imbeaux Frédéric
- Manenc L.
- Monier-Garbet P.
- Moreau P.
- Sabot R.
- Segui J.-L.
- Sirinelli A.
- Villegas D.
- Tore Supra Team
Nuclear Fusion, IOP Publishing, 2011, 51, pp.063037. This paper presents the first observation of geodesic acoustic modes (GAMs) on Tore Supra plasmas. Using the Doppler backscattering system, the oscillations of the plasma flow velocity, localized between r/a = 0.85 and r/a = 0.95, and with a frequency, typically around 10 kHz, have been observed at the plasma edge in numerous discharges. When the additional heating power is varied, the frequency is found to scale with Cs/R. The MUltiple SIgnal Classification (MUSIC) algorithm is employed to access the temporal evolution of the perpendicular velocity of density fluctuations. The method is presented in some detail, and is validated and compared against standard methods, such as the conventional fast Fourier transform method, using a synthetic signal. It stands out as a powerful data analysis method to follow the Doppler frequency with a high temporal resolution, which is important in order to extract the dynamics of GAMs. (10.1088/0029-5515/51/6/063037)
DOI : 10.1088/0029-5515/51/6/063037
Stochastic treatment of finite-N effects in mean-field systems and its application to the lifetimes of coherent structures
- Ettoumi Wahb
- Firpo Marie-Christine
Physical Review E, American Physical Society (APS), 2011, 84, pp.030103(R). A stochastic treatment yielding to the derivation of a general Fokker-Planck equation is presented to model the slow convergence toward equilibrium of mean-field systems due to finite-N effects. The thermalization process involves notably the disintegration of coherent structures that may sustain out-of-equilibrium quasistationary states. The time evolution of the fraction of particles remaining close to a mean-field potential trough is analytically computed. This indicator enables to estimate the lifetime of coherent structures and thermalization time scale in mean-field systems. (10.1103/PhysRevE.84.030103)
DOI : 10.1103/PhysRevE.84.030103
Vibrational relaxation of N2 studied by IR titration with time-resolved Qantum Cascade Laser diagnostics
- Marinov Daniil
- Lopatik D.
- Guaitella Olivier
- Roepcke J.
- Rousseau Antoine
, 2011.
The proton pressure tensor as a new proxy of the proton decoupling region in collisionless magnetic reconnection
- Aunai Nicolas
- Retinò Alessandro
- Belmont Gérard
- Smets Roch
- Lavraud B.
- Vaivads A.
Annales Geophysicae, European Geosciences Union, 2011, 29, pp.1571-1579. Cluster data is analyzed to test the proton pressure tensor variations as a proxy of the proton decoupling region in collisionless magnetic reconnection. The Hall electric potential well created in the proton decoupling region results in bounce trajectories of the protons which appears as a characteristic variation of one of the in-plane off-diagonal components of the proton pressure tensor in this region. The event studied in this paper is found to be consistent with classical Hall field signatures with a possible 20% guide field. Moreover, correlations between this pressure tensor component, magnetic field and bulk flow are proposed and validated, together with the expected counterstreaming proton distribution functions. (10.5194/angeo-29-1571-2011)
DOI : 10.5194/angeo-29-1571-2011
Proton acceleration in antiparallel collisionless magnetic reconnection: Kinetic mechanisms behind the fluid dynamics
- Aunai Nicolas
- Belmont Gérard
- Smets Roch
Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2011, 116, pp.9232. This paper investigates the proton kinetic mechanisms leading to the formation of plasma jets in antiparallel magnetic reconnection. In particular, the interaction of the protons with the Hall electric field in the proton non-ideal region is discussed. The study, based on a two-dimensional hybrid simulation, details the important role of the proton pressure force in the acceleration process and its role in maintaining open and steady the proton outflow channel. When no fluid closure is assumed, it is found that this force arises from a strong anisotropy in velocity space which comes from kinetic effect. By analyzing the distribution functions and the individual particle dynamics, it is shown that the mixing of protons bouncing in a divergent electrostatic potential well associated to the Hall effect statistically couples the two in-plane velocity components of the particles. This coupling results, from the macroscopic point of view, in off-diagonal components of the pressure tensor. (10.1029/2011JA016688)
DOI : 10.1029/2011JA016688
Estimation of the Gas Temperature of NO during a DC Plasma Pulse using Quantum Cascade Laser (QCL) Absorption Spectroscopy
- Hübner M.
- Marinov Daniil
- Guaitella Olivier
- Rousseau Antoine
- Roepcke J.
, 2011.
Experimental and modeling analysis of fast ionization wave discharge propagation in a rectangular geometry
- Takashima K.
- Adamovich I.V.
- Xiong Z.
- Kushner M.J.
- Starikovskaia Svetlana
- Czarnetzki U.
- Luggenhölscher D.
Physics of Plasmas, American Institute of Physics, 2011, 18, pp.083505. Fast ionization wave (FIW), nanosecond pulse discharge propagation in nitrogen and helium in a rectangular geometry channel/waveguide is studied experimentally using calibrated capacitive probe measurements. The repetitive nanosecond pulse discharge in the channel was generated using a custom designed pulsed plasma generator (peak voltage 1040 kV, pulse duration 30100 ns, and voltage rise time ∼1 kV/ns), generating a sequence of alternating polarity high-voltage pulses at a pulse repetition rate of 20 Hz. Both negative polarity and positive polarity ionization waves have been studied. Ionization wave speed, as well as time-resolved potential distributions and axial electric field distributions in the propagating discharge are inferred from the capacitive probe data. ICCD images show that at the present conditions the FIW discharge in helium is diffuse and volume-filling, while in nitrogen the discharge propagates along the walls of the channel. FIW discharge propagation has been analyzed numerically using quasi-one-dimensional and two-dimensional kinetic models in a hydrodynamic (drift-diffusion), local ionization approximation. The wave speed and the electric field distribution in the wave front predicted by the model are in good agreement with the experimental results. A self-similar analytic solution of the fast ionization wave propagation equations has also been obtained. The analytic model of the FIW discharge predicts key ionization wave parameters, such as wave speed, peak electric field in the front, potential difference across the wave, and electron density as functions of the waveform on the high voltage electrode, in good agreement with the numerical calculations and the experimental results. (10.1063/1.3619810)
DOI : 10.1063/1.3619810
Emission and propagation of Saturn kilometric radiation: Magnetoionic modes, beaming pattern, and polarization state
- Lamy L.
- Cecconi B.
- Zarka P.
- Canu Patrick
- Schippers P.
- Kurth W. S.
- Mutel R. L.
- Gurnett D. A.
- Menietti D.
- Louarn P.
Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2011, 116, pp.4212. The Cassini mission crossed the source region of the Saturn kilometric radiation (SKR) on 17 October 2008. On this occasion, the Radio and Plasma Wave Science (RPWS) experiment detected both local and distant radio sources, while plasma parameters were measured in situ by the magnetometer and the Cassini Plasma Spectrometer. A goniopolarimetric inversion was applied to RPWS three-antenna electric measurements to determine the wave vector k and the complete state of polarization of detected waves. We identify broadband extraordinary (X) mode as well as narrowband ordinary (O) mode SKR at low frequencies. Within the source region, SKR is emitted just above the X mode cutoff frequency in a hot plasma, with a typical electron-to-wave energy conversion efficiency of 1% (2% peak). The knowledge of the k vector is then used to derive the locus of SKR sources in the kronian magnetosphere, which shows X and O components emanating from the same regions. We also compute the associated beaming angle at the source theta' = (k, -B) either from (1) in situ measurements or a model of the magnetic field vector (for local to distant sources) or (2) polarization measurements (for local sources). Obtained results, similar for both modes, suggest quasi-perpendicular emission for local sources, whereas the beaming pattern of distant sources appears as a hollow cone with a frequency-dependent constant aperture angle: theta' = 75° ± 15° below 300 kHz, decreasing at higher frequencies to reach theta' (1000 kHz) = 50° ± 25°. Finally, we investigate quantitatively the SKR polarization state, observed to be strongly elliptical at the source, and quasi-purely circular for sources located beyond approximately two kronian radii. We show that conditions of weak mode coupling are achieved along the raypath, under which the magnetoionic theory satisfactorily describes the evolution of the observed polarization. These results are analyzed comparatively with the auroral kilometric radiation at Earth. (10.1029/2010JA016195)
DOI : 10.1029/2010JA016195
Alfvén : Magnetosphere -Ionosphere Connection Explorers
- Berthomier Matthieu
- Fazakerlay, N. A.
- Forsyth C.
- Pottelette Raymond
- Alexandrova Olga
- Anastasiadis A.
- Aruliah A.
- Blelly Pierre-Louis
- Briand Carine
- Bruno R.
- Canu Patrick
- Cecconi Baptiste
- Chust Thomas
- Daglis I.
- Davie J.
- Dunlop M.
- Fontaine Dominique
- Génot Vincent
- Gustavsson B.
- Haerendel G.
- Hamrin M.
- Hapgood M.
- Hess S.
- Kataria D.
- Kauristie K.
- Kemble S.
- Khotyaintsev Y.
- Koskinen H.
- Lamy Laurent
- Lanchester B.
- Louarn P.
- Lucek E.
- Lundin R.
- Maksimovic M.
- Manninen J.
- Marchaudon Aurélie
- Marghitu O.
- Marklund G.
- Milan S.
- Moen J.
- Mottez Fabrice
- Nilsson Hans
- Parrot Michel
- Ostgaard N.
- J. Owen C.
- Pedersen A.
- Perry C.
- Pinçon Jean-Louis
- Pitout Frederic
- Pulkkinen T.
- J. Rae I.
- Rezeau Laurence
- Roux A.
- Sandahl I.
- Sandberg I.
- Turunen E.
- Vogt J.
- Walsh A.
- E. J. Watt C.
- A. Wild J.
- Yamauchi M.
- Zarka Philippe
- Zouganelis I.
Experimental Astronomy, Springer Link, 2011, pp.1. The Alfvén concept is designed specifically to take the next step in studying the aurora, by making the crucial high-time resolution, multi-scale measurements in the AAR, needed to address the key science questions of auroral plasma physics. The new knowledge that the mission will produce will find application in studies of the Sun, the processes that accelerate the solar wind and that produce aurora on other planets. (10.1007/s10686-011-9273-y)
DOI : 10.1007/s10686-011-9273-y

Retour aux années