Publications

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Sont listées ci-dessous, par année, les publications figurant dans l'archive ouverte HAL.

2013

Radiation from Ag High Energy Density Z-pinch Plasmas with Applications to Lasing
- Weller M. E.
- Safronova Alla S.
- Kantsyrev Viktor L.
- Esaulov A. A.
- Shrestha Ishor
- Apruzese J. P.
- Giuliani J. L.
- Chuvatin Alexandre S.
- Stafford A.
- Keim S. F.
- Shlyaptseva V. V.
- Osborne Glenn C.
- Petkov E. E.
, 2013.
ROLE OF REACTOR CAPACITANCE ON THE PROPAGATION OF IONISATION WAVES
- Guaitella Olivier
- Sobota Ana
- Rousseau Antoine
, 2013.
Direction for the future - Successive acceleration of positive and negative ions applied to space propulsion
- Aanesland Ane
- Bredin Jérôme
- Popelier Lara
- Chabert Pascal
, 2013 (CERN-2013-007).
A double-plasma source of continuous bipolar ion-ion beam
- Dudin S.V.
- Rafalskyi D.V.
Applied Physics Letters, American Institute of Physics, 2013, 102, pp.034102. A double-plasma source capable of the generation of a continuous bipolar ion-ion beam is described. The quasi-neutral ion-ion flow to an extraction electrode is formed in the system containing primary inductively coupled plasma separated from a secondary plasma by an electrostatic grid-type filter. The total current of each ion species to the 250 mm diameter extraction electrode is about 80 mA; the electron current does not exceed 30% of the ion current. Method of positive/negative ion current ratio control is proposed, allowing the ion currents ratio variation in wide range. (10.1063/1.4788711)
DOI : 10.1063/1.4788711
Normal regime of the weak-current mode of an rf capacitive discharge
- Lisovskiy V. A.
- Yegorenkov V. D.
- Artushenko E.
- Booth Jean-Paul
- Martins S.
- Landry K.
- Douai D.
- Cassagne V.
Plasma Sources Science and Technology, IOP Publishing, 2013, 22 (1), pp.015018. This paper studies the normal and abnormal regimes of a weak-current rf discharge in ammonia, nitrogen, hydrogen and N 2 O for the rf electric field frequencies of 13.56 and 27.12 MHz. We reveal that only the abnormal regime of burning is observed at low pressures when the current growth is accompanied by an rf voltage increase while the surface of the electrodes is completely covered with the discharge. The normal regime occurs at higher gas pressures when the current growth is due to the increase in the surface area occupied by the discharge on the electrodes. The discharge burns in the abnormal mode after the surface of the electrodes is completely covered with the discharge. We demonstrate that the normal current density is directly proportional to the gas pressure and it depends approximately on the square of the rf electric field frequency. We present an analytical model for two limiting cases: constant free path length and constant mobility of positive ions furnishing a satisfactory description of the experimental data. (10.1088/0963-0252/22/1/015018)
DOI : 10.1088/0963-0252/22/1/015018
Ozone kinetics in low-pressure discharges: vibrationally excited ozone and molecule formation on surfaces
- Marinov Daniil
- Guerra V.
- Guaitella Olivier
- Booth Jean-Paul
- Rousseau Antoine
Plasma Sources Science and Technology, IOP Publishing, 2013, 22, pp.055018. A combined experimental and modeling investigation of the ozone kinetics in the afterglow of pulsed direct current discharges in oxygen is carried out. The discharge is generated in a cylindrical silica tube of radius 1 cm, with short pulse durations between 0.5 and 2 ms, pressures in the range 15 Torr and discharge currents ∼40120 mA. Time-resolved absolute concentrations of ground-state atoms and ozone molecules were measured simultaneously in situ, by two-photon absorption laser-induced fluorescence and ultraviolet absorption, respectively. The experiments were complemented by a self-consistent model developed to interpret the results and, in particular, to evaluate the roles of vibrationally excited ozone and of ozone formation on surfaces. It is found that vibrationally excited ozone, O∗ 3, plays an important role in the ozone kinetics, leading to a decrease in the ozone concentration and an increase in its formation time. In turn, the kinetics of O∗ 3 is strongly coupled with those of atomic oxygen and O2(a 1g) metastables. Ozone formation at the wall does not contribute significantly to the total ozone production under the present conditions. Upper limits for the effective heterogeneous recombination probability of O atoms into ozone are established. (10.1088/0963-0252/22/5/055018)
DOI : 10.1088/0963-0252/22/5/055018
Particle-in-cell simulation of an electronegative plasma under direct current bias studied in a large range of electronegativity
- Oudini N.
- Raimbault Jean-Luc
- Chabert Pascal
- Meige A.
- Aanesland Ane
Physics of Plasmas, American Institute of Physics, 2013, 20, pp.043501. A one-dimensional electronegative plasma situated between two symmetrical parallel electrodes under DC bias is studied by Particle-In-Cell simulation with Monte Carlo Collisions. By varying the electronegativity α ≡ n−/ne from the limit of electron-ion plasmas (negative ion free) to ion-ion plasmas (electron free), the sheaths formation, the negative ion flux flowing towards the electrodes, and the particle velocities at the sheath edges are investigated. Depending on α, it is shown that the electronegative plasma behavior can be described by four regimes. In the lowest regime of α, i.e., α < 50, negative ions are confined by two positive sheaths within the plasma, while in the higher regimes of α, a negative sheath is formed and the negative ion flux can be extracted from the bulk plasma. In the two intermediate regimes of α, i.e., 50 < α < 10⁵, both the electron and the negative ion fluxes are involved in the neutralization of the positive ions flux that leaves the plasma. In particular, we show that the velocity of the negative ions entering the negative sheath is affected by the presence of the electrons, and is not given by the modified Bohm velocity generally accepted for electronegative plasmas. For extremely high electronegativity, i.e., α > 10⁵, the presence of electrons in the plasma is marginal and the electronegative plasma can be considered as an ion-ion plasma (electron free). (10.1063/1.4798501)
DOI : 10.1063/1.4798501
Secondary electron induced asymmetry in capacitively coupled plasmas
- Lafleur Trevor
- Chabert Pascal
- Booth Jean-Paul
Journal of Physics D: Applied Physics, IOP Publishing, 2013, 46, pp.135201. Using a simple analytical model, together with a 1D particle-in-cell simulation, we show that it is possible to generate an asymmetric plasma response in a sinusoidally excited, geometrically symmetric, capacitively coupled plasma (CCP). The asymmetric response is produced using rf electrodes of differing materials, and hence different secondary electron emission coefficients. This asymmetry in the emission coefficients can produce a significant, measurable dc bias voltage (Vbias /Vrf ∼ 00.2), together with an asymmetry in the plasma density profiles and ion flux to each electrode. The dc bias formation can be understood from a particle-flux balance applied to each electrode, and results from two main effects: (1) the larger effective ion flux at each electrode due to the emission of secondary electrons and (2) ion-flux multiplication within the sheath due to ionization from these emitted secondary electrons. By making use of an empirical fit to the simulation data, the possibility of non-invasively estimating secondary electron emission coefficients in CCP systems is discussed. (10.1088/0022-3727/46/13/135201)
DOI : 10.1088/0022-3727/46/13/135201
Absolute atomic oxygen and nitrogen densities in radio-frequency driven atmospheric pressure cold plasmas: Synchrotron vacuum ultra-violet high-resolution Fourier-transform absorption measurements
- Niemi K.
- O'Connell D.
- de Oliveira N.
- Joyeux D.
- Nahon L.
- Booth Jean-Paul
- Gans T.
Applied Physics Letters, American Institute of Physics, 2013, 103 (3), pp.034102. Reactive atomic species play a key role in emerging cold atmospheric pressure plasma applications, in particular, in plasma medicine. Absolute densities of atomic oxygen and atomic nitrogen were measured in a radio-frequency driven non-equilibrium plasma operated at atmospheric pressure using vacuum ultra-violet (VUV) absorption spectroscopy. The experiment was conducted on the DESIRS synchrotron beamline using a unique VUV Fourier-transform spectrometer. Measurements were carried out in plasmas operated in helium with air-like N2/O2 (4:1) admixtures. A maximum in the O-atom concentration of (9.1 ± 0.7)×1020 m−3 was found at admixtures of 0.35 vol. %, while the N-atom concentration exhibits a maximum of (5.7 ± 0.4)×1019 m−3 at 0.1 vol. %. (10.1063/1.4813817)
DOI : 10.1063/1.4813817
Structure of nonlocality of plasma turbulence
- Gürcan Özgür D.
- Vermare Laure
- Hennequin Pascale
- Berionni Vincent
- Diamond P.H.
- Dif-Pradalier Guilhem
- Garbet X.
- Ghendrih Philippe
- Grandgirard Virginie
- Mcdevitt C.J.
- Morel Pierre
- Sarazin Y.
- Storelli A.
- Bourdelle C.
- Tore Supra Team
Nuclear Fusion, IOP Publishing, 2013, 53, pp.073029. Various indications on the weakly nonlocal character of turbulent plasma transport both from experimental fluctuation measurements from Tore Supra and observations from the full-f, flux-driven gyrokinetic code GYSELA are reported. A simple Fisher equation model of this weakly nonlocal dynamics can be formulated in terms of an evolution equation for the turbulent entropy density, which contains the basic phenomenon of radial turbulence spreading in addition to avalanche-like dynamics via coupling to profile modulations. A derivation of this model, which contains the so-called beach effect, a diffusive and convective flux components for the flux of turbulence intensity, in addition to linear group propagation is given, starting from the drift-kinetic equation. The proposed model has the form of a transport equation for turbulence intensity, and may be considered as an addition to transport modelling. The kinetic fluxes given, can be computed using model closures, or local gyrokinetics. The model is also used in a particular setup that represents the near edge region as a relatively stable zone between the core and edge region where the energy injection is locally more substantial. It is observed that with constant, physical coefficients, the model gives a convincing qualitative profile of fluctuation intensity when the turbulence is coming from the core region with either a group velocity or a convective flux. (10.1088/0029-5515/53/7/073029)
DOI : 10.1088/0029-5515/53/7/073029
Localizing Transport Barriers in Degenerate 3/2 D.O.F. Hamiltonian Systems with Applications to Magnetic Confinement Fusion
- Constantinescu D.
- Firpo Marie-Christine
International journal of bifurcation and chaos in applied sciences and engineering, World Scientific Publishing, 2013, 23, pp.1350034. The existence of transport barriers in 3/2 degrees of freedom degenerate Hamiltonian systems is studied using the associated stroboscopic maps. For small enough amplitudes of the perturbations, a transport barrier (formed by infinitely many invariant rotational circles) is proven to exist and to form in the degenerate annulus. These results are applied to Hamiltonian models which describe some magnetic configurations in tokamak plasmas. Read More: http://www.worldscientific.com/doi/abs/10.1142/S021812741350034X (10.1142/S021812741350034X)
DOI : 10.1142/S021812741350034X
Redistribution of high energy alpha particles due to sawteeth with partial reconnection
- Farengo R.
- Ferrari H.E.
- García-Martínez P.L.
- Firpo Marie-Christine
- Ettoumi Wahb
- Lifschitz A.F.
Nuclear Fusion, IOP Publishing, 2013, 53, pp.043012. The redistribution of high energy alpha particles due to internal kink modes is studied in plasmas with ITER-like parameters. The exact particle trajectories in the total fields, equilibrium plus perturbation, are calculated. The equilibrium magnetic field is obtained by analytically solving the GradShafranov equation and the perturbed electric and magnetic fields are reconstructed using ideal MHD and the experimental information about the displacement eigenfunction. The (1, 1), (2, 2) and (2, 1) modes are included and the effect of changing their amplitude and frequency is determined. The results show that if the conditions are similar to those reported in Igochine et al (2007 Nucl. Fusion 47 23), the peak density of counter-passing particles decreases between 25% and 40% (depending on the energy); the peak of the trapped particles density shifts outwards by approximately 10% of the minor radius and the total on axis density decreases by more than 25%. This redistribution occurs inside the q = 1 surface. The addition of a (2, 1) mode, which can produce the stochastization of the magnetic field, significantly increases particle redistribution and allows particles to spread beyond the q = 1 surface. Different groups of particles (co-passing, counter-passing, trapped) respond differently to the perturbations. (10.1088/0029-5515/53/4/043012)
DOI : 10.1088/0029-5515/53/4/043012
Design and Testing of a Surface Switch for the Dynamic Load Current Multiplier on the SPHINX Microsecond LTD
- Maysonnave Thomas
- Bayol Frédéric
- Demol Gauthier
- d'Almeida Thierry
- Morell Alain
- Lassalle Francis
- Grunenwald Julien
- Chuvatin Alexandre S.
- Pecastaing Laurent
- de Ferron Antoine Silvestre
IEEE Transactions on Plasma Science, Institute of Electrical and Electronics Engineers, 2013, 41 (10), pp.2593 - 2599. SPHINX is a microsecond linear transformer driver located at Atomic Energy Comission (CEA) Gramat (France), which can deliver a current pulse of 6 MA within 800 ns in a Z -pinch load. Using the concept of the dynamic load current multiplier (DLCM), which was proposed by Chuvatin, we expect to increase the load current above 6 MA, while decreasing its rise time to ~ 300 ns. The DLCM developed by the CEA Gramat and International Technologies for High Pulsed Power (ITHPP) is a compact system made up of concentric electrodes (autotransformer), a dynamic flux extruder (cylindrical wire array), a vacuum convolute (eight post-hole rods), and a closing switch (compact vacuum surface switch). The latter is a key component of the system, which is used to prevent the current from flowing into the load until the inductance builds up due to the implosion of the wire array. This paper presents the design and testing of the DLCM surface switch, resulting from both electrostatic simulations and experiments on the SPHINX generator. These studies, carried out either with or without load (open circuit), were valuable for a first experimental evaluation of the DLCM scheme in a microsecond regime and provided detailed information on the surface switch behavior. (10.1109/TPS.2013.2245148)
DOI : 10.1109/TPS.2013.2245148
Nonturbulent stabilization of ion fluxes by the fan instability
- Krafft C.
- Volokitin A.
Physics Letters A, Elsevier, 2013, 377 (16-17), pp.1189-1198. Resonant interactions between energetic ion fluxes and wave packets they excite through fan instability are studied using self-consistent 3D simulations to explain the nonlinear wave-particle mechanisms at work and to estimate the energy lost by the flux and its sharing between wave emission and particle heating. The saturation of waves and the relaxation of particles are studied over long time periods. The ions are not only diffusing in the waves but are also trapped simultaneously by several potential wells of large amplitude overlapping waves. Estimates of the ion heating energy and rate are given and compared with space observations. (10.1016/j.physleta.2013.03.011)
DOI : 10.1016/j.physleta.2013.03.011
Asymmetric distribution of reconnection jet fronts in the Jovian nightside magnetosphere
- Kasahara S.
- Kronberg E. A.
- Kimura T.
- Tao C.
- Badman S. V.
- Masters A.
- Retinò Alessandro
- Krupp N.
- Fujimoto M.
Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2013, 118, pp.375-384. Magnetic reconnection plays important roles in mass transport and energy conversion in planetary magnetospheres. It is considered that transient reconnection causes localized auroral arcs or spots in the Jovian magnetosphere, by analogy to the case in the Earth's magnetosphere. However, the local structures of transient reconnection events (i.e., magnetospheric plasma parameters) and their spatial distribution have not been extensively investigated for the Jovian magnetosphere. Here we examine plasma velocity and density during strong north-south magnetic field events in the Jovian nightside magnetosphere, which may be associated with tail reconnection. We find prominent reconnection jet fronts predominantly on the dawnside of the nightside magnetosphere, which would be a signature unique to rotation-dominant planetary magnetospheres. The observed plasma structures are consistent with significant field-aligned currents which would generate localized aurora. (10.1029/2012JA018130)
DOI : 10.1029/2012JA018130
Comparison between hybrid and fully kinetic models of asymmetric magnetic reconnection: Coplanar and guide field configurations
- Aunai Nicolas
- Hesse Michael
- Zenitani Seiji
- Kuznetsova M. M.
- Black Carrie
- Evans Rebekah
- Smets Roch
Physics of Plasmas, American Institute of Physics, 2013, 20, pp.022902. Magnetic reconnection occurring in collisionless environments is a multi-scale process involving both ion and electron kinetic processes. Because of their small mass, the electron scales are difficult to resolve in numerical and satellite data, it is therefore critical to know whether the overall evolution of the reconnection process is influenced by the kinetic nature of the electrons, or is unchanged when assuming a simpler, fluid, electron model. This paper investigates this issue in the general context of an asymmetric current sheet, where both the magnetic field amplitude and the density vary through the discontinuity. A comparison is made between fully kinetic and hybrid kinetic simulations of magnetic reconnection in coplanar and guide field systems. The models share the initial condition but differ in their electron modeling. It is found that the overall evolution of the system, including the reconnection rate, is very similar between both models. The best agreement is found in the guide field system, which confines particle better than the coplanar one, where the locality of the moments is violated by the electron bounce motion. It is also shown that, contrary to the common understanding, reconnection is much faster in the guide field system than in the coplanar one. Both models show this tendency, indicating that the phenomenon is driven by ion kinetic effects and not electron ones. (10.1063/1.4792250)
DOI : 10.1063/1.4792250
Dipolarization fronts as a consequence of transient reconnection: In situ evidence
- Fu H.S.
- Cao J.B.
- Khotyaintsev Y. V.
- Sitnov M. I.
- Runov A.
- Fu S. Y.
- Hamrin M.
- André M.
- Retinò Alessandro
- Ma Y. D.
- Lu H. Y.
- Wei X.H.
- Huang S. Y.
Geophysical Research Letters, American Geophysical Union, 2013, 40 (23), pp.6023-6027. Dipolarization fronts (DFs) are frequently detected in the Earth's magnetotail from XGSM = −30 RE to XGSM = −7 RE. How these DFs are formed is still poorly understood. Three possible mechanisms have been suggested in previous simulations: (1) jet braking, (2) transient reconnection, and (3) spontaneous formation. Among these three mechanisms, the first has been verified by using spacecraft observation, while the second and third have not. In this study, we show Cluster observation of DFs inside reconnection diffusion region. This observation provides in situ evidence of the second mechanism: Transient reconnection can produce DFs. We suggest that the DFs detected in the near-Earth region (XGSM > −10 RE) are primarily attributed to jet braking, while the DFs detected in the mid- or far-tail region (XGSM < −15 RE) are primarily attributed to transient reconnection or spontaneous formation. In the jet-braking mechanism, the high-speed flow pushes the preexisting plasmas to produce the DF so that there is causality between high-speed flow and DF. In the transient-reconnection mechanism, there is no causality between high-speed flow and DF, because the frozen-in condition is violated. (10.1002/2013GL058620)
DOI : 10.1002/2013GL058620
Azimuthal directions of equatorial noise propagation determined using 10 years of data from the Cluster spacecraft
- Nemec F.
- Santolík O.
- Pickett J. S.
- Hrbackova Z.
- Cornilleau-Wehrlin Nicole
Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2013, 118, pp.7160-7169. Equatorial noise (EN) emissions are electromagnetic waves at frequencies between the proton cyclotron frequency and the lower hybrid frequency routinely observed within a few degrees of the geomagnetic equator at radial distances from about 2 to 6 RE. They propagate in the extraordinary (fast magnetosonic) mode nearly perpendicularly to the ambient magnetic field. We conduct a systematic analysis of azimuthal directions of wave propagation, using all available Cluster data from 2001 to 2010. Altogether, combined measurements of the Wide-Band Data and Spectrum Analyzer of the Spatio-Temporal Analysis of Field Fluctuations instruments allowed us to determine azimuthal angle of wave propagation for more than 100 EN events. It is found that the observed propagation pattern is mostly related to the plasmapause location. While principally isotropic azimuthal directions of EN propagation were detected inside the plasmasphere, wave propagation in the plasma trough was predominantly found directed to the West or East, perpendicular to the radial direction. The observed propagation pattern can be explained using a simple propagation analysis, assuming that the emissions are generated close to the plasmapause. (10.1002/2013JA019373)
DOI : 10.1002/2013JA019373
Multi-dipolar microwave plasmas and their application to negative ion production
- Béchu Stéphane
- Soum-Glaude A.
- Bès A.
- Lacoste A.
- Svarnas P.
- Aleiferis S.
- Ivanov Jr. A.A.
- Bacal M.
Physics of Plasmas, American Institute of Physics, 2013, 20, pp.101601. (10.1063/1.4823466)
DOI : 10.1063/1.4823466
First demonstration of an asymmetric kinetic equilibrium for a thin current sheet
- Aunai Nicolas
- Belmont Gérard
- Smets Roch
Physics of Plasmas, American Institute of Physics, 2013, 20 (11), pp.110702. The modeling of steady state collisionless asymmetric tangential current layers is a challenging and poorly understood problem. For decades now, this difficulty has been limiting numerical models to approximate equilibria built with locally Maxwellian current layers and theoretical analyses to the very restricted Harris equilibrium. We show how the use of any distribution functions depending only on local macroscopic quantities results in a strong alteration of the current layer internal structure, which converges toward an unpredictable quasi-steady state with emission of ion scale perturbations. This transient can be explained in terms of ion kinetic and electron fluid physics. We demonstrate, for the first time, the validity of an asymmetric kinetic equilibrium model as well as its usability as an initial condition of hybrid kinetic simulations. This offers broad perspectives for the current sheet modeling, for which the early phase of instabilities can be studied within the kinetic formalism. (10.1063/1.4833679)
DOI : 10.1063/1.4833679
Magnetic field and dynamic pressure ULF fluctuations in coronal-mass-ejection-driven sheath regions
- Kilpua E. K. J.
- Hietala H.
- Koskinen H. E. J.
- Fontaine Dominique
- Turc Lucile
Annales Geophysicae, European Geosciences Union, 2013, 31, pp.1559-1567. Compressed sheath regions form ahead of interplanetary coronal mass ejections (ICMEs) that are sufficiently faster than the preceding solar wind. The turbulent sheath regions are important drivers of magnetospheric activity, but due to their complex internal structure, relatively little is known on the distribution of the magnetic field and plasma variations in them. In this paper we investigate ultra low frequency (ULF) fluctuations in the interplanetary magnetic field (IMF) and in dynamic pressure (Pdyn) using a superposed epoch analysis of 41 sheath regions observed during solar cycle 23. We find strongest fluctuation power near the shock and in the vicinity of the ICME leading edge. The IMF and Pdyn ULF power have different profiles within the sheath; the former is enhanced in the leading part of the sheath, while the latter is increased in the trailing part of the sheath. We also find that the ICME properties affect the level and distribution of the ULF power in sheath regions. For example, sheath regions associated with strong or fast ICMEs, or those that are crossed at intermediate distances from the center, have strongest ULF power and large variation in the power throughout the sheath region. The weaker or slower ICMEs, or those that are crossed centrally, have in general considerably weaker ULF power with relatively smooth profiles. The strong and abrupt decrease of the IMF ULF power at the ICME leading edge could be used to distinguish the ICME from the preceding sheath plasma. (10.5194/angeo-31-1559-2013)
DOI : 10.5194/angeo-31-1559-2013
Electron acceleration to relativistic energies at a strong quasi-parallel shock wave
- Masters A.
- Stawarz L.
- Fujimoto M.
- Schwartz S. J.
- Sergis N.
- Thomsen M. F.
- Retinò Alessandro
- Hasegawa H.
- Zieger B.
- Lewis G. R.
- Coates A. J.
- Canu Patrick
- Dougherty M. K.
Nature Physics, Nature Publishing Group [2005-....], 2013, 9, pp.164-167. Electrons can be accelerated to ultrarelativistic energies at strong (high Mach number) collisionless shock waves that form when stellar debris rapidly expands after a supernova. Collisionless shock waves also form in the flow of particles from the Sun (the solar wind), and extensive spacecraft observations have established that electron acceleration at these shocks is effectively absent whenever the upstream magnetic field is roughly parallel to the shock-surface normal (quasi-parallel conditions). However, it is unclear whether this magnetic dependence of electron acceleration also applies to the far stronger shocks around young supernova remnants, where local magnetic conditions are poorly understood. Here we present Cassini spacecraft observations of an unusually strong solar system shock wave (Saturn's bow shock) where significant local electron acceleration has been confirmed under quasi-parallel magnetic conditions for the first time, contradicting the established magnetic dependence of electron acceleration at solar system shocks. Furthermore, the acceleration led to electrons at relativistic energies (about megaelectronvolt), comparable to the highest energies ever attributed to shock acceleration in the solar wind. These observations suggest that at high Mach numbers, such as those of young supernova remnant shocks, quasi-parallel shocks become considerably more effective electron accelerators. (10.1038/nphys2541)
DOI : 10.1038/nphys2541
Enhanced Magnetic Compressibility and Isotropic Scale Invariance at Sub-ion Larmor Scales in Solar Wind Turbulence
- Kiyani K. H.
- Chapman S. C.
- Sahraoui Fouad
- Hnat B.
- Fauvarque O.
- Khotyaintsev Y. V.
The Astrophysical Journal, American Astronomical Society, 2013, 763 (1), pp.10. The anisotropic nature of solar wind magnetic turbulence fluctuations is investigated scale by scale using high cadence in situ magnetic field measurements from the Cluster and ACE spacecraft missions. The data span five decades in scales from the inertial range to the electron Larmor radius. In contrast to the inertial range, there is a successive increase toward isotropy between parallel and transverse power at scales below the ion Larmor radius, with isotropy being achieved at the electron Larmor radius. In the context of wave-mediated theories of turbulence, we show that this enhancement in magnetic fluctuations parallel to the local mean background field is qualitatively consistent with the magnetic compressibility signature of kinetic Alfvén wave solutions of the linearized Vlasov equation. More generally, we discuss how these results may arise naturally due to the prominent role of the Hall term at sub-ion Larmor scales. Furthermore, computing higher-order statistics, we show that the full statistical signature of the fluctuations at scales below the ion Larmor radius is that of a single isotropic globally scale-invariant process distinct from the anisotropic statistics of the inertial range. (10.1088/0004-637X/763/1/10)
DOI : 10.1088/0004-637X/763/1/10
Sahraoui et al. Reply:
- Sahraoui Fouad
- Robert Patrick
- Goldstein M. L.
- Khotyaintsev Y. V.
Physical Review Letters, American Physical Society, 2013, 111, pp.149002. A Reply to the Comment by O. Alexandrova, S. D. Bale, and C. Lacombe.
Frequency dependence of the electrical asymmetry effect in dual-frequency capacitively coupled discharges
- Booth Jean-Paul
- Lafleur Trevor
Applied Physics Letters, American Institute of Physics, 2013, 102, pp.154104. Using experimental measurements complemented with particle-in-cell (PIC) simulations, we demonstrate a reduction in the electrical asymmetry effect in capacitively coupled discharges for low excitation frequencies (0.8 MHz < f<10 MHz). These results confirm PIC simulation predictions made by [I. Korolov, Z. Donkó, U. Czarnetzki, and J. Schulze, J. Phys. D: Appl. Phys. 45, 465205 (2012)], where this effect was investigated for dual-frequency discharges in which the driving frequencies are phase-shifted harmonics. Because the reduction in electrical asymmetry is a sensitive function of the secondary electron emission coefficient, we are able to non-invasively estimate this coefficient as 0.035 for argon ions incident on aluminium electrodes. (10.1063/1.4802241)
DOI : 10.1063/1.4802241

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