Publications

2015

• Plasma acceleration using a radio frequency self-bias effect
  
  • Rafalskyi D.V.
  • Aanesland Ane
  Physics of Plasmas, American Institute of Physics, 2015, 22 (6), pp.063502. In this work plasma acceleration using a RF self-bias effect is experimentally studied. The experiments are conducted using a novel plasma accelerator system, called Neptune, consisting of an inductively coupled plasma source and a RF-biased set of grids. The plasma accelerator can operate in a steady state mode, producing a plasma flow with separately controlled plasma flux and velocity without any magnetic configuration. The operating pressure at the source output is as low as 0.2 mTorr and can further be decreased. The ion and electron flows are investigated by measuring the ion and electron energy distribution functions both space resolved and with different orientations with respect to the flow direction. It is found that the flow of electrons from the source is highly anisotropic and directed along the ion flow and this global flow of accelerated plasma is well localized in the plasma transport chamber. The maximum flux is about 7.5·1015 ions s−1 m−2 (at standard conditions) on the axis and decreasing to almost zero at a radial distances of more than 15 cm from the flow axis. Varying the RF acceleration voltage in the range 20350 V, the plasma flow velocity can be changed between 10 and 35 km/s. The system is prospective for different technology such as space propulsion and surface modification and also interesting for fundamental studies for space-related plasma simulations and investigation of the dynamo effect using accelerated rotating plasmas. I. INTRODUCT (10.1063/1.4922065)
  DOI : 10.1063/1.4922065
• Reply to Comment on "A review on ion-ion plasmas created in weakly magnetized electronegative plasmas
  
  • Aanesland Ane
  • Bredin Jérôme
  • Chabert Pascal
  Plasma Sources Science and Technology, IOP Publishing, 2015, 24 (3), pp.038002. This is a reply to the comments made by Bogdanov et al on our paper entitled ?A review on ion?ion plasmas created in weakly magnetized electronegative plasmas?. We have clarified some issues regarding the electronegative plasma stratification and the definition of an ion?ion plasma, and we discuss the issue of extracting negative ions from a steady-state ion?ion plasma formed at the periphery or downstream a magnetized electronegative plasma. (10.1088/0963-0252/24/3/038002)
  DOI : 10.1088/0963-0252/24/3/038002
• WEST Physics Basis
  
  • Bourdelle C.
  • Artaud J.F.
  • Basiuk Vincent
  • Bécoulet M.
  • Brémond S.
  • Bucalossi J.
  • Bufferand H.
  • Ciraolo G.
  • Colas L.
  • Corre Y.
  • Courtois X.
  • Decker J.
  • Delpech L.
  • Devynck P.
  • Dif-Pradalier Guilhem
  • Doerner R.P.
  • Douai D.
  • Dumont Rémi
  • Ekedahl A.
  • Fedorczak N.
  • Fenzi C.
  • Firdaouss M.
  • Garcia J.
  • Ghendrih Philippe
  • Gil C.
  • Giruzzi G.
  • Goniche M.
  • Grisolia C.
  • Grosman A.
  • Guilhem D.
  • Guirlet R.
  • Gunn J.
  • Hennequin Pascale
  • Hillairet J.
  • Hoang T.
  • Imbeaux Frédéric
  • Ivanova-Stanik Irena
  • Joffrin E.
  • Kallenbach A.
  • Linke J.
  • Loarer T.
  • Lotte P.
  • Maget P.
  • Marandet Yannick
  • Mayoral M.L.
  • Meyer O.
  • Missirlian M.
  • Mollard P.
  • Monier-Garbet P.
  • Moreau P.
  • Nardon Eric
  • Pégourié B.
  • Peysson Y.
  • Sabot R.
  • Saint-Laurent F.
  • Schneider M.
  • Travère J. M.
  • Tsitrone E.
  • Vartanian S.
  • Vermare Laure
  • Yoshida M.
  • Zagorski R.
  • Jet Contributors
  Nuclear Fusion, IOP Publishing, 2015, 55 (6), pp.063017. With WEST (Tungsten Environment in Steady State Tokamak) (Bucalossi et al 2014 Fusion Eng. Des. 89 [http://dx.doi.org/10.1016/j.fusengdes.2014.01.062] 907?12 ), the Tore Supra facility and team expertise (Dumont et al 2014 Plasma Phys. Control. Fusion 56 [http://dx.doi.org/10.1088/0741-3335/56/7/075020] 075020 ) is used to pave the way towards ITER divertor procurement and operation. It consists in implementing a divertor configuration and installing ITER-like actively cooled tungsten monoblocks in the Tore Supra tokamak, taking full benefit of its unique long-pulse capability. WEST is a user facility platform, open to all ITER partners. This paper describes the physics basis of WEST: the estimated heat flux on the divertor target, the planned heating schemes, the expected behaviour of the L?H threshold and of the pedestal and the potential W sources. A series of operating scenarios has been modelled, showing that ITER-relevant heat fluxes on the divertor can be achieved in WEST long pulse H-mode plasmas. (10.1088/0029-5515/55/6/063017)
  DOI : 10.1088/0029-5515/55/6/063017
• Systematic analysis of occurrence of equatorial noise emissions using 10 years of data from the Cluster mission
  
  • Hrbackova Z.
  • Santolík O.
  • Nemec F.
  • Macusova E.
  • Cornilleau-Wehrlin Nicole
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2015, 120, pp.1007-1021. We report results of a systematic analysis of equatorial noise (EN) emissions which are also known as fast magnetosonic waves. EN occurs in the vicinity of the geomagnetic equator at frequencies between the local proton cyclotron frequency and the lower hybrid frequency. Our analysis is based on the data collected by the Spatio-Temporal Analysis of Field Fluctuations-Spectrum Analyzer instruments on board the four Cluster spacecraft. The data set covers the period from January 2001 to December 2010. We have developed selection criteria for the visual identification of these emissions, and we have compiled a list of more than 2000 events identified during the analyzed time period. The evolution of the Cluster orbit enables us to investigate a large range of McIlwain's parameter from about L1.1 to L10. We demonstrate that EN can occur at almost all analyzed L shells. However, the occurrence rate is very low (<6%) at L shells below L=2.5 and above L=8.5. EN mostly occurs between L=3 and L=5.5, and within 7° of the geomagnetic equator, reaching 40% occurrence rate. This rate further increases to more than 60% under geomagnetically disturbed conditions. Analysis of occurrence rates as a function of magnetic local time (MLT) shows strong variations outside of the plasmasphere (with a peak around 15 MLT), while the occurrence rate inside the plasmasphere is almost independent on MLT. This is consistent with the hypothesis that EN is generated in the afternoon sector of the plasmapause region and propagates both inward and outward. (10.1002/2014JA020268)
  DOI : 10.1002/2014JA020268
• Solar illumination control of ionospheric outflow above polar cap arcs
  
  • Maes Lukas
  • Maggiolo R.
  • de Keyser J.
  • Dandouras I.
  • Fear R. C.
  • Fontaine Dominique
  • Haaland S.
  Geophysical Research Letters, American Geophysical Union, 2015, 42 (5), pp.1304-1311. We measure the flux density, composition, and energy of outflowing ions above the polar cap, accelerated by quasi-static electric fields parallel to the magnetic field and associated with polar cap arcs, using Cluster. Mapping the spacecraft position to its ionospheric foot point, we analyze the dependence of these parameters on the solar zenith angle (SZA). We find a clear transition at SZA between 94° and 107°, with the O<SUP> </SUP> flux higher above the sunlit ionosphere. This dependence on the illumination of the local ionosphere indicates that significant O<SUP> </SUP> upflow occurs locally above the polar ionosphere. The same is found for H<SUP> </SUP>, but to a lesser extent. This effect can result in a seasonal variation of the total ion upflow from the polar ionosphere. Furthermore, we show that low-magnitude field-aligned potential drops are preferentially observed above the sunlit ionosphere, suggesting a feedback effect of ionospheric conductivity. (10.1002/2014GL062972)
  DOI : 10.1002/2014GL062972
• Structure of a laser-driven radiative shock
  
  • Chaulagain Uddhab
  • Stehle Chantal
  • Larour Jean
  • Kozlová Michaela
  • Suzuki-Vidal Francisco
  • Barroso Patrice
  • Cotelo M.
  • Velarde P.
  • Rodriguez R.
  • Gil J. M.
  • Ciardi Andrea
  • Acef Ouali
  • Nejdl Jaroslav
  • de Sá Lionel
  • Singh Raj Laxmi
  • Ibgui Laurent
  • Champion Norbert
  High Energy Density Physics, Elsevier, 2015, 17, pp.106-113. Radiative shocks are ubiquitous in stellar environments and are characterized by high temperature plasma emitting a considerable fraction of their energy as radiation. The physical structure of these shocks is complex and experimental benchmarks are needed to provide a deeper understanding of the physics at play. In addition, experiments provide unique data for testing radiation hydrodynamics codes which, in turn, are used to model astrophysical phenomena.
• Production of nongyrotropic and gyrotropic backstreaming ion distributions in the quasi-perpendicular ion foreshock region
  
  • Savoini Philippe
  • Lembège Bertrand
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2015, 120 (9), pp.7154–7171. A curved shock is analyzed in the whole quasi-perpendicular propagation region (90° ≥ θBn≥45°) in a supercritical regime with the help of a 2-D particle-in-cell code including self-consistent effects such as the shock front curvature and the time-of-flight effects. Two distinct ion populations are observed within the foreshock: a (gyrotropic) field-aligned beam population, hereafter named “FAB,” and a (nongyrotropic) gyrophase bunched population, hereafter named “GPB.” The origin of these high-energy particles and their corresponding acceleration mechanisms are analyzed in details in the present paper. Both FAB and GPB populations are shown to be produced by the shock front itself and more important, do have exactly the same origin. At the shock front, the two populations gain a nongyrotropic distribution, but FAB population loses its initial phase coherency after suffering several bounces along the curved front. This result has one main consequence: the time evolution of the two populations does not involve some distinct reflection processes as often claimed in the literature, but results only from the particle time history at the shock front. This important result was not expected and greatly simplifies the question of their origin. More precisely, a new parameter, the injection angle θinj has been defined between the shock normal direction and the ion gyrating velocity vector. We found that the FAB population is formed by ions injected almost along the shock front, while GPB population is formed by ions injected almost along the shock normal. (10.1002/2015JA021018)
  DOI : 10.1002/2015JA021018
• Finding the Elusive E × B Staircase in Magnetized Plasmas
  
  • Dif-Pradalier Guilhem
  • Hornung G
  • Ghendrih Philippe
  • Sarazin Yanick
  • Clairet F
  • Vermare L
  • Diamond P H
  • Abiteboul J
  • Cartier-Michaud T
  • Ehrlacher C
  • Estève Daniel
  • Garbet Xavier
  • Grandgirard Virginie
  • Gürcan Özgür D.
  • Hennequin P
  • Kosuga Y
  • Latu Guillaume
  • Maget P
  • Morel Pierre
  • Norscini C
  • Sabot R
  • Storelli A.
  Physical Review Letters, American Physical Society, 2015, 114, pp.085004. Turbulence in hot magnetized plasmas is shown to generate permeable localized transport barriers that globally organize into the so-called "ExB staircase" [G. Dif-Pradalier et al., Phys. Rev. E, 82, 025401(R) (2010)]. Its domain of existence and dependence with key plasma parameters is discussed theoretically. Based on these predictions, staircases are observed experimentally in the Tore Supra tokamak by means of high-resolution fast-sweeping X-mode reflectometry. This observation strongly emphasizes the critical role of mesoscale self-organization in plasma turbulence and may have far-reaching consequences for turbulent transport models and their validation. (10.1103/PhysRevLett.114.085004)
  DOI : 10.1103/PhysRevLett.114.085004
• Imprints of Expansion on the Local Anisotropy of Solar Wind Turbulence
  
  • Verdini Andrea
  • Grappin Roland
  The Astrophysical Journal Letters, Bristol : IOP Publishing, 2015, 808, pp.L34. We study the anisotropy of II-order structure functions (SFs) defined in a frame attached to the local mean field in three-dimensional (3D) direct numerical simulations of magnetohydrodynamic turbulence, with the solar wind expansion both included and not included. We simulate spacecraft flybys through the numerical domain by taking increments along the radial (wind) direction that form an angle of 45° with the ambient magnetic field. We find that only when expansion is taken into account do the synthetic observations match the 3D anisotropy observed in the solar wind, including the change of anisotropy with scale. Our simulations also show that the anisotropy changes dramatically when considering increments oblique to the radial directions. Both results can be understood by noting that expansion reduces the radial component of the magnetic field at all scales, thus confining fluctuations in the plane perpendicular to the radial. Expansion is thus shown to affect not only the (global) spectral anisotropy, but also the local anisotropy of second-order SF by influencing the distribution of the local mean field, which enters this higher-order statistics. (10.1088/2041-8205/808/2/L34)
  DOI : 10.1088/2041-8205/808/2/L34
• Experimental turbulence studies for gyro-kinetic code validation using advanced microwave diagnostics
  
  • Stroth U.
  • Bañón Navarro A.
  • Conway G. D.
  • Görler T.
  • Happel T.
  • Hennequin Pascale
  • Lechte C.
  • Manz P.
  • Simon P.
  • Biancalani A.
  • Blanco E.
  • Bottereau C.
  • Clairet F.
  • Coda S.
  • Eibert T.
  • Estrada T.
  • Fasoli A.
  • Guimarais L.
  • Gürcan Özgür D.
  • Huang Z.
  • Jenko F.
  • Kasparek W.
  • Koenen C.
  • Krämer-Flecken A.
  • Manso M.-E.
  • Medvedeva A.
  • Molina D.
  • Nikolaeva V.
  • Plaum B.
  • Porte L.
  • Prisiazhniuk D.
  • Ribeiro T.
  • Scott B.D.
  • Siart U.
  • Storelli A.
  • Vermare Laure
  • Wolf S.
  Nuclear Fusion, IOP Publishing, 2015, 55 (8), pp.083027. For a comprehensive comparison with theoretical models and advanced numerical turbulence simulations, a large spectrum of fluctuation parameters was measured on the devices ASDEX Upgrade, TCV, and Tore-Supra. Radial profiles of scale-resolved turbulence levels in H-mode discharges are measured and compared with GENE simulations in the transition range from ion-temperature-gradient to trapped-electron-mode turbulence. Correlation reflectometry is used to study the microscopic structure of turbulence and GAMs in discharges where poloidal flow damping was varied by means of variations of the shape of the poloidal plasma cross-section and collisionality. Full-wave codes and synthetic diagnostics are applied for the interpretation of the data. (10.1088/0029-5515/55/8/083027)
  DOI : 10.1088/0029-5515/55/8/083027
• Comprehensive comparisons of geodesic acoustic mode characteristics and dynamics between Tore Supra experiments and gyrokinetic simulations
  
  • Storelli A.
  • Vermare Laure
  • Hennequin Pascale
  • Gürcan Özgür D.
  • Dif-Pradalier Guilhem
  • Sarazin Y.
  • Garbet X.
  • Görler T.
  • Singh Rameswar
  • Morel Pierre
  • Grandgirard Virginie
  • Ghendrih Philippe
  • Tore Supra Team
  Physics of Plasmas, American Institute of Physics, 2015, 22 (6). In a dedicated collisionality scan in Tore Supra, the geodesic acoustic mode (GAM) is detected and identified with the Doppler backscattering technique. Observations are compared to the results of a simulation with the gyrokinetic code GYSELA. We found that the GAM frequency in experiments is lower than predicted by simulation and theory. Moreover, the disagreement is higher in the low collisionality scenario. Bursts of non harmonic GAM oscillations have been characterized with filtering techniques, such as the Hilbert-Huang transform. When comparing this dynamical behaviour between experiments and simulation, the probability density function of GAM amplitude and the burst autocorrelation time are found to be remarkably similar. In the simulation, where the radial profile of GAM frequency is continuous, we observed a phenomenon of radial phase mixing of the GAM oscillations, which could influence the burst autocorrelation time. (10.1063/1.4922845)
  DOI : 10.1063/1.4922845
• Towards an emerging understanding of non-locality phenomena and non-local transport
  
  • Ida K.
  • Shi Z.
  • Sun H. J.
  • Inagaki S.
  • Kamiya K.
  • Rice J.E.
  • Tamura N.
  • Diamond P.H.
  • Dif-Pradalier Guilhem
  • Zou X. L.
  • Itoh K.
  • Sugita S.
  • Gürcan Özgür D.
  • Estrada T.
  • Hidalgo C.
  • Hahm T.S.
  • Field A.
  • Ding X. T.
  • Sakamoto Y.
  • Oldenburger S.
  • Yoshinuma M.
  • Kobayashi T.
  • Jiang M.
  • Hahn S. -H.
  • Jeon Y. M.
  • Hong S. H.
  • Kosuga Y.
  • Dong J.
  • Itoh S. I.
  Nuclear Fusion, IOP Publishing, 2015, 55 (1), pp.013022. In this paper, recent progress on experimental analysis and theoretical models for non-local transport (non-Fickian fluxes in real space) is reviewed. The non-locality in the heat and momentum transport observed in the plasma, the departures from linear flux-gradient proportionality, and externally triggered non-local transport phenomena are described in both L-mode and improved-mode plasmas. Ongoing evaluation of 'fast front' and 'intrinsically non-local' models, and their success in comparisons with experimental data, are discussed (10.1088/0029-5515/55/1/013022)
  DOI : 10.1088/0029-5515/55/1/013022
• Some statistical equilibrium mechanics and stability properties of a class of two-dimensional Hamiltonian mean-field models
  
  • Maciel J. M.
  • Firpo Marie-Christine
  • Amato M. A.
  Physica A: Statistical Mechanics and its Applications, Elsevier, 2015, 424, pp.34-43. Abstract A two-dimensional class of mean-field models that may serve as a minimal model to study the properties of long-range systems in two space dimensions is considered. The statistical equilibrium mechanics is derived in the microcanonical ensemble using Monte Carlo simulations for different combinations of the coupling constants in the potential leading to fully repulsive, fully attractive and mixed attractive?repulsive potential along the Cartesian axis and diagonals. Then, having in mind potential realizations of long-range systems using cold atoms, the linear theory of this two-dimensional mean-field Hamiltonian models is derived in the low temperature limit. (10.1016/j.physa.2014.12.030)
  DOI : 10.1016/j.physa.2014.12.030
• Different types of whistler mode chorus in the equatorial source region
  
  • Taubenschuss U.
  • Santolík O.
  • Graham Daniel B.
  • Fu H.S.
  • Khotyaintsev Y. V.
  • Le Contel Olivier
  Geophysical Research Letters, American Geophysical Union, 2015, 42 (20), pp.8271-8279. The Time History of Events and Macroscale Interactions during Substorms-D spacecraft crossed an active equatorial source region of whistler mode chorus rising tones on 23 October 2008. Rising tones are analyzed in terms of spectral and polarization characteristics, with special emphasis on wave normal angles. The latter exhibit large variations from quasi-parallel to oblique, even within single bursts, but seem to follow a definite pattern, which enables an unambiguous classification into five different groups. Furthermore, we discuss the frequently observed splitting of chorus bursts into a lower and an upper band around one half of the local electron cyclotron frequency. At chorus frequencies close to the gap, we find significantly lowered wave planarities and a tendency of wave normal angles to approach the Gendrin angle. (10.1002/2015GL066004)
  DOI : 10.1002/2015GL066004
• Thin Current Sheets and Associated Electron Heating in Turbulent Space Plasma
  
  • Chasapis A.
  • Retinò Alessandro
  • Sahraoui Fouad
  • Vaivads A.
  • Khotyaintsev Y. V.
  • Sundkvist D.
  • Greco A.
  • Sorriso-Valvo L.
  • Canu Patrick
  The Astrophysical Journal Letters, Bristol : IOP Publishing, 2015, 804 (1). Intermittent structures, such as thin current sheets, are abundant in turbulent plasmas. Numerical simulations indicate that such current sheets are important sites of energy dissipation and particle heating occurring at kinetic scales. However, direct evidence of dissipation and associated heating within current sheets is scarce. Here, we show a new statistical study of local electron heating within proton-scale current sheets by using high-resolution spacecraft data. Current sheets are detected using the Partial Variance of Increments (PVI) method which identifies regions of strong intermittency. We find that strong electron heating occurs in high PVI (>3) current sheets while no significant heating occurs in low PVI cases (<3), indicating that the former are dominant for energy dissipation. Current sheets corresponding to very high PVI (>5) show the strongest heating and most of the time are consistent with ongoing magnetic reconnection. This suggests that reconnection is important for electron heating and dissipation at kinetic scales in turbulent plasmas. (10.1088/2041-8205/804/1/L1)
  DOI : 10.1088/2041-8205/804/1/L1
• Entanglement of helicity and energy in kinetic Alfvén wave/whistler turbulence
  
  • Galtier Sébastien
  • Meyrand Romain
  Journal of Plasma Physics, Cambridge University Press (CUP), 2015, 81 (1), pp.325810106. The role of magnetic helicity is investigated in kinetic Alfvén wave and oblique whistler turbulence in presence of a relatively intense external magnetic field b <SUB>0</SUB> e <SUB>||</SUB>. In this situation, turbulence is strongly anisotropic and the fluid equations describing both regimes are the reduced electron magnetohydrodynamics (REMHD) whose derivation, originally made from the gyrokinetic theory, is also obtained here from compressible Hall magnetohydrodynamics (MHD). We use the asymptotic equations derived by Galtier and Bhattacharjee (2003 Phys. Plasmas 10, 3065-3076) to study the REMHD dynamics in the weak turbulence regime. The analysis is focused on the magnetic helicity equation for which we obtain the exact solutions: they correspond to the entanglement relation, n ñ = -6, where n and ñ are the power law indices of the perpendicular (to b <SUB>0</SUB>) wave number magnetic energy and helicity spectra, respectively. Therefore, the spectra derived in the past from the energy equation only, namely n = -2.5 and ñ = -3.5, are not the unique solutions to this problem but rather characterize the direct energy cascade. The solution ñ = -3 is a limit imposed by the locality condition; it is also the constant helicity flux solution obtained heuristically. The results obtained offer a new paradigm to understand solar wind turbulence at sub-ion scales where it is often observed that -3 < n < -2.5. (10.1017/S0022377814000774)
  DOI : 10.1017/S0022377814000774
• Observations of discrete harmonics emerging from equatorial noise
  
  • Balikhin M. A.
  • Shprits Y. Y.
  • Walker S. N.
  • Chen Lunjin
  • Cornilleau-Wehrlin Nicole
  • Dandouras Iannis
  • Santolík O.
  • Carr Christopher
  • Yearby K. H.
  • Weiss Benjamin
  Nature Communications, Nature Publishing Group, 2015, 6. A number of modes of oscillations of particles and fields can exist in space plasmas. Since the early 1970s, space missions have observed noise-like plasma waves near the geomagnetic equator known as `equatorial noise'. Several theories were suggested, but clear observational evidence supported by realistic modelling has not been provided. Here we report on observations by the Cluster mission that clearly show the highly structured and periodic pattern of these waves. Very narrow-banded emissions at frequencies corresponding to exact multiples of the proton gyrofrequency (frequency of gyration around the field line) from the 17th up to the 30th harmonic are observed, indicating that these waves are generated by the proton distributions. Simultaneously with these coherent periodic structures in waves, the Cluster spacecraft observes `ring' distributions of protons in velocity space that provide the free energy for the waves. Calculated wave growth based on ion distributions shows a very similar pattern to the observations. (10.1038/ncomms8703)
  DOI : 10.1038/ncomms8703
• Further details on the plasma E × B staircase
  
  • Dif-Pradalier Guilhem
  • Hornung G
  • Ghendrih Philippe
  • Sarazin Yanick
  • Clairet F
  • Vermare L
  • Diamond P H
  • Abiteboul J
  • Cartier-Michaud T
  • Ehrlacher C
  • Esteve D
  • Garbet Xavier
  • Grandgirard Virginie
  • Gürcan Özgür D.
  • Hennequin P
  • Kosuga A
  • Latu Guillaume
  • Morel Pierre
  • Norscini C
  • Sabot R
  • Storelli A.
  , 2015. Turbulence in hot magnetised plasmas spontaneously has been shown to spontaneously organise on global scales into the so-called " E × B staircase ". Further characterisation of this structure is detailed below.
• Nature of the MHD and Kinetic Scale Turbulence in the Magnetosheath of Saturn: Cassini Observations
  
  • Hadid Lina
  • Sahraoui Fouad
  • Kiyani K. H.
  • Retinò Alessandro
  • Modolo Ronan
  • Canu Patrick
  • Masters Adam
  • Dougherty Michele K.
  The Astrophysical Journal Letters, Bristol : IOP Publishing, 2015, 813 (2), pp.L29. Low-frequency turbulence in Saturn's magnetosheath is investigated using in situ measurements of the Cassini spacecraft. Focus is put on the magnetic energy spectra. A set of 42 time intervals in the magnetosheath were analyzed, and three main results that contrast with known features of solar wind turbulence are reported. (10.1088/2041-8205/813/2/L29)
  DOI : 10.1088/2041-8205/813/2/L29
• Equatorial noise emissions with quasiperiodic modulation of wave intensity
  
  • Nemec F.
  • Santolík O.
  • Hrbackova Z.
  • Pickett J. S.
  • Cornilleau-Wehrlin Nicole
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2015, 120, pp.2649-2661. Equatorial noise (EN) emissions are electromagnetic wave events at frequencies between the proton cyclotron frequency and the lower hybrid frequency observed in the equatorial region of the inner magnetosphere. They propagate nearly perpendicular to the ambient magnetic field, and they exhibit a harmonic line structure characteristic of the proton cyclotron frequency in the source region. However, they were generally believed to be continuous in time. We investigate more than 2000 EN events observed by the Spatio-Temporal Analysis of Field Fluctuations and Wide-Band Data Plasma Wave investigation instruments on board the Cluster spacecraft, and we show that this is not always the case. A clear quasiperiodic (QP) time modulation of the wave intensity is present in more than 5% of events. We perform a systematic analysis of these EN events with QP modulation of the wave intensity. Such events occur usually in the noon-to-dawn magnetic local time sector. Their occurrence seems to be related to the increased geomagnetic activity, and it is associated with the time intervals of enhanced solar wind flow speeds. The modulation period of these events is on the order of minutes. Compressional ULF magnetic field pulsations with periods about double the modulation periods of EN wave intensity and magnitudes on the order of a few tenths of nanotesla were identified in about 46% of events. We suggest that these compressional magnetic field pulsations might be responsible for the observed QP modulation of EN wave intensity, in analogy to formerly reported VLF whistler mode QP events. (10.1002/2014JA020816)
  DOI : 10.1002/2014JA020816
• 3D hybrid simulations of the interaction of a magnetic cloud with a bow shock
  
  • Turc Lucile
  • Fontaine Dominique
  • Savoini Philippe
  • Modolo Ronan
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2015, 120 (8), pp.6133-6151. In this paper, we investigate the interaction of a magnetic cloud (MC) with a planetary bow shock using hybrid simulations. It is the first time to our knowledge that this interaction is studied using kinetic simulations which include self-consistently both the ion foreshock and the shock wave dynamics. We show that when the shock is in a quasi-perpendicular configuration, the MC's magnetic structure in the magnetosheath remains similar to that in the solar wind, whereas it is strongly altered downstream of a quasi-parallel shock. The latter can result in a reversal of the magnetic field north-south component in some parts of the magnetosheath. We also investigate how the MC affects in turn the outer parts of the planetary environment, i.e., from the foreshock to the magnetopause. We find the following: (i) The decrease of the Alfvén Mach number at the MC's arrival causes an attenuation of the foreshock region because of the weakening of the bow shock. (ii) The foreshock moves along the bow shock's surface, following the rotation of the MC's magnetic field. (iii) Owing to the low plasma beta, asymmetric flows arise inside the magnetosheath, due to the magnetic tension force which accelerates the particles in some parts of the magnetosheath and slows them down in others. (iv) The quasi-parallel region forms a depression in the shock's surface. Other deformations of the magnetopause and the bow shock are also highlighted. All these effects can contribute to significantly modify the solar wind/magnetosphere coupling during MC events. (10.1002/2015JA021318)
  DOI : 10.1002/2015JA021318
• The Plasma E × B Staircase: Turbulence Self-Regulation through Spontaneous Flow Patterning
  
  • Dif-Pradalier Guilhem
  • Hornung G
  • Ghendrih Philippe
  • Clairet R
  • Diamond P H
  • Sarazin Yanick
  • Vermare L
  • Abiteboul J
  • Cartier-Michaud T
  • Ehrlacher C
  • Estève D
  • Garbet Xavier
  • Grandgirard Virginie
  • Gürcan Özgür D.
  • Hennequin P
  • Kosuga Y
  • Latu Guillaume
  • Morel Pierre
  • Norscini C
  • Sabot R
  , 2015. The E × B staircase [1, 2] is a spontaneously formed, turbulence-driven self-organising pattern of quasi-regular, long-lived and localised shear flow [3] and stress layers. These layers coincide with long-lived pressure corrugations and are interspersed between regions of turbulent avalanching. The typical spacing between these layers is mesoscale, noted ∆ ∼ 25 − 30ρ i [1, 4] —in-between the turbulence auto-correlation length c ∼ 5ρ i at micro scales and the profile macroscale L 100ρ i , see e.g. Fig.2 in [1]— and sets the outer scale of the turbulent avalanching. Here ρ i is ion Larmor radius. Whilst arresting, statistically, to mesoscales the detrimental avalanching these layers, located at the " steps of the staircase " are beneficial to confinement. The E×B staircase is thus best understood as a self-organising and dynamical set of weak or permeable transport barriers. Strong mean zonal flows are generated and endure at the steps of the staircase, resulting in localised deviations of the poloidal flow from its oft-assumed neoclassical prediction [5].
• Kinetic simulations of secondary reconnection in the reconnection jet
  
  • Huang S. Y.
  • Zhou M.
  • Yuan Z. G.
  • Fu H.S.
  • He J. S.
  • Sahraoui Fouad
  • Aunai Nicolas
  • Deng X. H.
  • Fu S. Y.
  • Pang Y.
  • Wang D. D.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2015, 120 (8), pp.61886198. Magnetic reconnection, as one important energy dissipation process in plasmas, has been extensively studied in the past several decades. Magnetic reconnection occurring in the downstream of a primary X line is referred to as secondary reconnection. In this paper, we used kinetic simulations to investigate the secondary reconnection in detail. We found that secondary reconnection is reversed by the compression caused by the outflowing jet originating from the primary reconnection site, which results in the erosion of the magnetic island between the two X lines within ~3&#8201;&#969;ci&#8722;1. We show the observational signatures expected in electromagnetic fields and plasma measurements in the Earth's magnetotail, associated with this mechanism. These simulation results could be applied to interpret the signatures associated with the evolution of earthward magnetic islands in the Earth's magnetotail. (10.1002/2014JA020969)
  DOI : 10.1002/2014JA020969
• What is the nature of magnetosheath FTEs?
  
  • Roux A.
  • Robert Patrick
  • Fontaine Dominique
  • Le Contel Olivier
  • Canu Patrick
  • Louarn P.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2015, 120 (6), pp.4576-4595. Cluster multipoint measurements are used to study two successive magnetosheath flux transfer events (FTEs). Magnetic field lines in the leading region are found to be closed magnetospheric field lines. For event 1 these field lines are wounded up by a large current structure oriented eastward and moving poleward. Conversely, the trailing region corresponds to opened magnetic field lines. For both events the leading edge of the FTEs is a tangential discontinuity separating the magnetosheath from closed field lines. In the case of event 1 magnetosheath ions are accelerated through the FTE trailing edge via a rotational discontinuity and penetrate on closed field lines through a second discontinuity. Thus, the ion jet is accelerated equatorward of the spacecraft but the backtracking of the discontinuities and the lack of dispersion show that ion acceleration occurs at less than 2 R<SUB>E</SUB> from Cluster. On the other hand the extrapolation forward indicates that the FTE bulge steepens as in simulations of Dorelli and Bhattacharjee). Evidence is given for the penetration of magnetosheath ions inside the core of the FTE, on closed field lines. Magnetosheath electrons are accelerated in parallel and antiparallel directions on open and on closed field lines, thus breaking the frozen-in condition. Event 2 is also split in two distinct regions but no evidence is found for accelerated bidirectional magnetosheath electrons. For event 2 the two discontinuities at the trailing region are stacked together when they are crossed by the spacecraft, suggesting that the current splitting is a reconnection signature. (10.1002/2015JA020983)
  DOI : 10.1002/2015JA020983
• Kinetic scale turbulence and dissipation in the solar wind: key observational results and future outlook
  
  • Goldstein M. L.
  • Wicks R. T.
  • Perri S.
  • Sahraoui Fouad
  Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, Royal Society, The, 2015, 373, pp.20140147. Turbulence is ubiquitous in the solar wind. Turbulence causes kinetic and magnetic energy to cascade to small scales where they are eventually dissipated, adding heat to the plasma. The details of how this occurs are not well understood. This article reviews the evidence for turbulent dissipation and examines various diagnostics for identifying solar wind regions where dissipation is occurring. We also discuss how future missions will further enhance our understanding of the importance of turbulence to solar wind dynamics. (10.1098/rsta.2014.0147)
  DOI : 10.1098/rsta.2014.0147