Publications

2015

• Anisotropy of Third-order Structure Functions in MHD Turbulence
  
  • Verdini Andrea
  • Grappin Roland
  • Hellinger P.
  • Landi Simone
  • Müller Wolf-Christian
  The Astrophysical Journal, American Astronomical Society, 2015, 804, pp.119. The measure of the third-order structure function, \boldsymbolY , is employed in the solar wind to compute the cascade rate of turbulence. In the absence of a mean field B<SUB>0</SUB>=0, \boldsymbolY is expected to be isotropic (radial) and independent of the direction of increments, so its measure yields directly the cascade rate. For turbulence with mean field, as in the solar wind, \boldsymbolY is expected to become more two-dimensional (2D), that is, to have larger perpendicular components, losing the above simple symmetry. To get the cascade rate, one should compute the flux of \boldsymbolY , which is not feasible with single-spacecraft data thus, measurements rely on assumptions about the unknown symmetry. We use direct numerical simulations (DNSs) of magnetohydrodynamic (MHD) turbulence to characterize the anisotropy of \boldsymbolY . We find that for strong guide field B<SUB>0</SUB>=5 the degree of two-dimensionalization depends on the relative importance of shear-Alfvén and pseudo-Alfvén polarizations (the two components of an Alfvén mode in incompressible MHD). The anisotropy also shows up in the inertial range. The more \boldsymbolY is 2D, the more the inertial range extent differs along parallel and perpendicular directions. We finally test the two methods employed in observations and find that the so-obtained cascade rate may depend on the angle between B<SUB>0</SUB> and the direction of increments. Both methods yield a vanishing cascade rate along the parallel direction, contrary to observations, suggesting a weaker anisotropy of solar wind turbulence compared to our DNSs. This could be due to a weaker mean field and/or to solar wind expansion. (10.1088/0004-637X/804/2/119)
  DOI : 10.1088/0004-637X/804/2/119
• A Review of General Physical and Chemical Processes Related to Plasma Sources and Losses for Solar System Magnetospheres
  
  • Seki K.
  • Nagy A.
  • Jackman C. M.
  • Crary F.
  • Fontaine Dominique
  • Zarka P.
  • Wurz Peter
  • Milillo A.
  • Slavin J. A.
  • Delcourt Dominique C.
  • Wiltberger M.
  • Ilie R.
  • Jia X.
  • Ledvina S. A.
  • Liemohn M. W.
  • Schunk R. W.
  Space Science Reviews, Springer Verlag, 2015, 192 (1-4), pp.27-89. The aim of this paper is to provide a review of general processes related to plasma sources, their transport, energization, and losses in the planetary magnetospheres. We provide background information as well as the most up-to-date knowledge of the comparative studies of planetary magnetospheres, with a focus on the plasma supply to each region of the magnetospheres. This review also includes the basic equations and modeling methods commonly used to simulate the plasma sources of the planetary magnetospheres. In this paper, we will describe basic and common processes related to plasma supply to each region of the planetary magnetospheres in our solar system. First, we will describe source processes in Sect. 1. Then the transport and energization processes to supply those source plasmas to various regions of the magnetosphere are described in Sect. 2. Loss processes are also important to understand the plasma population in the magnetosphere and Sect. 3 is dedicated to the explanation of the loss processes. In Sect. 4, we also briefly summarize the basic equations and modeling methods with a focus on plasma supply processes for planetary magnetospheres. (10.1007/s11214-015-0170-y)
  DOI : 10.1007/s11214-015-0170-y
• Wide-banded NTC radiation: local to remote observations by the four Cluster satellites
  
  • Décréau Pierrette
  • Aoutou S.
  • Denazelle A.
  • Galkina I.
  • Rauch Jean-Louis
  • Vallières Xavier
  • Canu Patrick
  • Rochel Grimald S.
  • El-Lemdani Mazouz Farida
  • Darrouzet F.
  Annales Geophysicae, European Geosciences Union, 2015, 33 (10), pp.1285-1300. The Cluster multi-point mission offers a unique collection of non-thermal continuum (NTC) radio waves observed in the 2-80 kHz frequency range over almost 15 years, from various view points over the radiating plasmasphere. Here we present rather infrequent case events, such as when primary electrostatic sources of such waves are embedded within the plasmapause boundary far from the magnetic equatorial plane. The spectral signature of the emitted electromagnetic waves is structured as a series of wide harmonic bands within the range covered by the step in plasma frequency encountered at the boundary. Developing the concept that the frequency distance df between harmonic bands measures the magnetic field magnitude B at the source (df = F<SUB>ce</SUB>, electron gyrofrequency), we analyse three selected events. The first one (studied in Grimald et al., 2008) presents electric field signatures observed by a Cluster constellation of small size (~ 200 to 1000 km spacecraft separation) placed in the vicinity of sources. The electric field frequency spectra display frequency peaks placed at frequencies fs = n df (n being an integer), with df of the order of F<SUB>ce</SUB> values encountered at the plasmapause by the spacecraft. The second event, taken from the Cluster tilt campaign, leads to a 3-D view of NTC waves ray path orientations and to a localization of a global source region at several Earth radii (R<SUB>E</SUB>) from Cluster (Décréau et al., 2013). The measured spectra present successive peaks placed at fs ~ (n 1/2) df. Next, considering if both situations might be two facets of the same phenomenon, we analyze a third event. The Cluster fleet, configured into a constellation of large size (~ 8000 to 25 000 km spacecraft separation), allows us to observe wide-banded NTC waves at different distances from their sources. Two new findings can be derived from our analysis. First, we point out that a large portion of the plasmasphere boundary layer, covering a large range of magnetic latitudes, is radiating radio waves. The radio waves are issued from multiple sources of small size, each related to a given fs series and radiating inside a beam of narrow cone angle, referred to as a beamlet. The beamlets illuminate different satellites simultaneously, at different characteristic fs values, according to the latitude at which the satellite is placed. Second, when an observing satellite moves away from its assumed source region (the plasmapause surface), it is illuminated by several beamlets, issued from nearby sources with characteristic fs values close to each other. The addition of radio waves blurs the spectra of the overall received electric field. It can move the signal peaks such that their position fs satisfiesfs = (n alpha) df, with 0 < alpha < 1. These findings open new perspectives for the interpretation of NTC events displaying harmonic signatures. (10.5194/angeo-33-1285-2015)
  DOI : 10.5194/angeo-33-1285-2015
• Strong Ionization Asymmetry in a Geometrically Symmetric Radio Frequency Capacitively Coupled Plasma Induced by Sawtooth Voltage Waveforms
  
  • Bruneau Bastien
  • Gans T.
  • O'Connell D.
  • Greb Arthur
  • Johnson E.V.
  • Booth Jean-Paul
  Physical Review Letters, American Physical Society, 2015, 114, pp.125002. The ionization dynamics in geometrically symmetric parallel plate capacitively coupled plasmas driven by radio frequency tailored voltage waveforms is investigated using phase resolved optical emission spectroscopy (PROES) and particle-in-cell (PIC) simulations. Temporally asymmetric waveforms induce spatial asymmetries and offer control of the spatiotemporal dynamics of electron heating and associated ionization structures. Sawtooth waveforms with different rise and fall rates are employed using truncated Fourier series approximations of an ideal sawtooth. Experimental PROES results obtained in argon plasmas are compared with PIC simulations, showing excellent agreement. With waveforms comprising a fast voltage drop followed by a slower rise, the faster sheath expansion in front of the powered electrode causes strongly enhanced ionization in this region. The complementary waveform causes an analogous effect in front of the grounded electrode. (10.1103/PhysRevLett.114.125002)
  DOI : 10.1103/PhysRevLett.114.125002
• Direct identification of predator-prey dynamics in gyrokinetic simulations
  
  • Kobayashi Sumire
  • Gürcan Özgür D.
  • Diamond P.H.
  Physics of Plasmas, American Institute of Physics, 2015, 22 (9), pp.090702. The interaction between spontaneously formed zonal flows and small-scale turbulence in nonlinear gyrokinetic simulations is explored in a shearless closed field line geometry. It is found that when clear limit cycle oscillations prevail, the observed turbulent dynamics can be quantitatively captured by a simple Lotka-Volterra type predator-prey model. Fitting the time traces of full gyrokinetic simulations by such a reduced model allows extraction of the model coefficients. Scanning physical plasma parameters, such as collisionality and density gradient, it was observed that the effective growth rates of turbulence (i.e., the prey) remain roughly constant, in spite of the higher and varying level of primary mode linear growth rates. The effective growth rate that was extracted corresponds roughly to the zonal-flow-modified primary mode growth rate. It was also observed that the effective damping of zonal flows (i.e., the predator) in the parameter range, where clear predator-prey dynamics is observed, (i.e., near marginal stability) agrees with the collisional damping expected in these simulations. This implies that the Kelvin-Helmholtz-like instability may be negligible in this range. The results imply that when the tertiary instability plays a role, the dynamics becomes more complex than a simple Lotka-Volterra predator prey. (10.1063/1.4930127)
  DOI : 10.1063/1.4930127
• Predator-prey model for the self-organization of stochastic oscillators in dual populations.
  
  • Moradi S.
  • Anderson J.
  • Gürcan Özgür D.
  Physical Review E, American Physical Society (APS), 2015, 92, pp.06293. A predator-prey model of dual populations with stochastic oscillators is presented. A linear cross-coupling between the two populations is introduced following the coupling between the motions of a Wilberforce pendulum in two dimensions: one in the longitudinal and the other in torsional plain. Within each population a Kuramoto-type competition between the phases is assumed. Thus, the synchronization state of the whole system is controlled by these two types of competitions. The results of the numerical simulations show that by adding the linear cross-coupling interactions predator-prey oscillations between the two populations appear, which results in self-regulation of the system by a transfer of synchrony between the two populations. The model represents several important features of the dynamical interplay between the drift wave and zonal flow turbulence in magnetically confined plasmas, and a novel interpretation of the coupled dynamics of drift wave-zonal flow turbulence using synchronization of stochastic oscillator is discussed. (10.1103/PhysRevE.92.062930)
  DOI : 10.1103/PhysRevE.92.062930
• Turbulence elasticity: a key concept to a unified paradigm of L -> I -> H transition
  
  • Guo Z. B.
  • Diamond P.H.
  • Kosuga Y.
  • Gürcan Özgür D.
  Nuclear Fusion, IOP Publishing, 2015, 55 (4), pp.043022. We present a theory of turbulence elasticity, which follows from delayed response of drift waves (DWs) to zonal flow (ZF) shears. It is shown that when |&#12296;V&#12297;'ZF|/&#916;&#969;k &#8805; 1, with |&#12296;V&#12297;'ZF| the ZF shearing rate and &#916;&#969;k the local turbulence decorrelation rate, the ZF evolution equation is converted from a diffusion equation to a telegraph equation. This insight provides a natural framework for understanding temporally periodic ZF structures, e.g., propagation of the ZF/turbulence intensity fronts. Furthermore, by incorporating the elastic property of the DWZF turbulence, we propose a unified paradigm of low-confinement-mode to intermediate-confinement-mode to high-confinement-mode (L &#8594; I &#8594; H) transitions. In particular, we predict the onset and termination conditions of the limit cycle oscillations, i.e. the I-mode. The transition from an unstable L-mode to I-mode is predicted to occur when &#916;&#969;k < |&#12296;V&#12297;'ZF|<&#12296;V&#12297;'cr, where &#12296;V&#12297;'cr is a critical flow shearing rate and is derived explicitly. If |&#12296;V&#12297;'E×B| > &#12296;V&#12297;'cr(&#12296;V&#12297;E×B is mean E × B shear flow driven by edge radial electrostatic field), the I-mode will terminate and spiral into the H-mode. (10.1088/0029-5515/55/4/043022)
  DOI : 10.1088/0029-5515/55/4/043022
• Asymmetric kinetic equilibria: Generalization of the BAS model for rotating magnetic profile and non-zero electric field
  
  • Dorville Nicolas
  • Belmont Gérard
  • Aunai Nicolas
  • Dargent Jérémy
  • Rezeau Laurence
  Physics of Plasmas, American Institute of Physics, 2015, 22 (9), pp.092904. Finding kinetic equilibria for non-collisional/collisionless tangential current layers is a key issue as well for their theoretical modeling as for our understanding of the processes that disturb them, such as tearing or Kelvin Helmholtz instabilities. The famous Harris equilibrium [E. Harris, Il Nuovo Cimento Ser. 10 23, 115121 (1962)] assumes drifting Maxwellian distributions for ions and electrons, with constant temperatures and flow velocities; these assumptions lead to symmetric layers surrounded by vacuum. This strongly particular kind of layer is not suited for the general case: asymmetric boundaries between two media with different plasmas and different magnetic fields. The standard method for constructing more general kinetic equilibria consists in using Jeans theorem, which says that any function depending only on the Hamiltonian constants of motion is a solution to the steady Vlasov equation [P. J. Channell, Phys. Fluids (19581988) 19, 1541 (1976); M. Roth et al., Space Sci. Rev. 76, 251317 (1996); and F. Mottez, Phys. Plasmas 10, 15411545 (2003)]. The inverse implication is however not true: when using the motion invariants as variables instead of the velocity components, the general stationary particle distributions keep on depending explicitly of the position, in addition to the implicit dependence introduced by these invariants. The standard approach therefore strongly restricts the class of solutions to the problem and probably does not select the most physically reasonable. The BAS (Belmont-Aunai-Smets) model [G. Belmont et al., Phys. Plasmas 19, 022108 (2012)] used for the first time the concept of particle accessibility to find new solutions: considering the case of a coplanar-antiparallel magnetic field configuration without electric field, asymmetric solutions could be found while the standard method can only lead to symmetric ones. These solutions were validated in a hybrid simulation [N. Aunai et al., Phys. Plasmas (1994-present) 20, 110702 (2013)], and more recently in a fully kinetic simulation as well [J. Dargent and N. Aunai, Phys. Plasmas (submitted)]. Nevertheless, in most asymmetric layers like the terrestrial magnetopause, one would indeed expect a magnetic field rotation from one direction to another without going through zero [J. Berchem and C. T. Russell, J. Geophys. Res. 87, 81398148 (1982)], and a non-zero normal electric field. In this paper, we propose the corresponding generalization: in the model presented, the profiles can be freely imposed for the magnetic field rotation (although restricted to a 180 rotation hitherto) and for the normal electric field. As it was done previously, the equilibrium is tested with a hybrid simulation. (10.1063/1.4930210)
  DOI : 10.1063/1.4930210
• Distribution of energetic oxygen and hydrogen in the near-Earth plasma sheet
  
  • Kronberg E. A.
  • Grigorenko E. E.
  • Haaland S. E.
  • Daly P. W.
  • Delcourt Dominique C.
  • Luo H.
  • Kistler L. M.
  • Dandouras I.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2015, 120 (5), pp.3415-3431. The spatial distributions of different ion species are useful indicators for plasma sheet dynamics. In this statistical study based on 7 years of Cluster observations, we establish the spatial distributions of oxygen ions and protons at energies from 274 to 955 keV, depending on geomagnetic and solar wind (SW) conditions. Compared with protons, the distribution of energetic oxygen has stronger dawn-dusk asymmetry in response to changes in the geomagnetic activity. When the interplanetary magnetic field (IMF) is directed southward, the oxygen ions show significant acceleration in the tail plasma sheet. Changes in the SW dynamic pressure (P<SUB>dyn</SUB>) affect the oxygen and proton intensities in the same way. The energetic protons show significant intensity increases at the near-Earth duskside during disturbed geomagnetic conditions, enhanced SW P<SUB>dyn</SUB>, and southward IMF, implying there location of effective inductive acceleration mechanisms and a strong duskward drift due to the increase of the magnetic field gradient in the near-Earth tail. Higher losses of energetic ions are observed in the dayside plasma sheet under disturbed geomagnetic conditions and enhanced SW P<SUB>dyn</SUB>. These observations are in agreement with theoretical models. (10.1002/2014JA020882)
  DOI : 10.1002/2014JA020882
• Magnetic noise contribution of the ferromagnetic core of induction magnetometers
  
  • Coillot C
  • El Moussalim M
  • Brun E
  • Rhouni A
  • Lebourgeois R
  • Sou Gérard
  • Mansour Malik
  Journal of Sensors and Sensor Systems, Copernicus Publ, 2015, 4, pp.229 - 237. The performance of induction magnetometers, in terms of resolution, depends both on the induction sensor and the electronic circuit. To investigate accurately the sensor noise sources, an induction sensor, made of a ferrite ferromagnetic core, is combined with a dedicated low voltage and current noise preamplifier, designed in CMOS 0.35 µm technology. A modelling of the contribution of the ferromagnetic core to the noise through the complex permeability formalism is performed. Its comparison with experimental measurements highlight another possible source for the dominating noise near the resonance. (10.5194/jsss-4-229-2015)
  DOI : 10.5194/jsss-4-229-2015
• Geodesic acoustic modes in a fluid model of tokamak plasma: the effects of finite beta and collisionality
  
  • Singh Rameswar
  • Storelli A.
  • Gürcan Özgür D.
  • Hennequin Pascale
  • Vermare Laure
  • Morel Pierre
  • Singh R.
  Plasma Physics and Controlled Fusion, IOP Publishing, 2015, 57, pp.125002. Starting from the Braginskii equations, relevant for the tokamak edge region, a complete set of nonlinear equations for the geodesic acoustic modes (GAM) has been derived which includes collisionality, plasma beta and external sources of particle, momentum and heat. Local linear analysis shows that the GAM frequency increases with collisionality at low radial wave number and decreases at high . GAM frequency also decreases with plasma beta. Radial profiles of GAM frequency for two Tore Supra shots, which were part of a collisionality scan, are compared with these calculations. A discrepancy between experiment and theory is observed, which seems to be explained by a finite for the GAM when flux surface averaged density \langle n\rangle and temperature are assumed to vanish. It is shown that this agreement is incidental and self-consistent inclusion of and responses enhances the disagreement more with at high . So the discrepancy between the linear GAM calculation and experiment, (which also persist for more 'complete' linear models such as gyrokinetics) can probably not be resolved by simply adding a finite . (10.1088/0741-3335/57/12/125002)
  DOI : 10.1088/0741-3335/57/12/125002
• 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
• 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
• Magnetic reconnection in th Solar System
  
  • Aunai N.
  , 2015.
• Numerical experiment to estimate the validity of negative ion diagnostic using photo-detachment combined with Langmuir probing
  
  • Oudini N.
  • Sirse Nishant
  • Benallal R.
  • Taccogna F.
  • Aanesland Ane
  • Bendib A.
  • Ellingboe A. R.
  Physics of Plasmas, American Institute of Physics, 2015, 22 (7), pp.073509. This paper presents a critical assessment of the theory of photo-detachment diagnostic method used to probe the negative ion density and electronegativity &#945;&#8201;=&#8201;n-/ne. In this method, a laser pulse is used to photo-detach all negative ions located within the electropositive channel (laser spot region). The negative ion density is estimated based on the assumption that the increase of the current collected by an electrostatic probe biased positively to the plasma is a result of only the creation of photo-detached electrons. In parallel, the background electron density and temperature are considered as constants during this diagnostics. While the numerical experiments performed here show that the background electron density and temperature increase due to the formation of an electrostatic potential barrier around the electropositive channel. The time scale of potential barrier rise is about 2&#8201;ns, which is comparable to the time required to completely photo-detach the negative ions in the electropositive channel (&#8764;3&#8201;ns). We find that neglecting the effect of the potential barrier on the background plasma leads to an erroneous determination of the negative ion density. Moreover, the background electron velocity distribution function within the electropositive channel is not Maxwellian. This is due to the acceleration of these electrons through the electrostatic potential barrier. In this work, the validity of the photo-detachment diagnostic assumptions is questioned and our results illustrate the weakness of these assumptions. (10.1063/1.4926826)
  DOI : 10.1063/1.4926826
• 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&#8201;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&#8722;1 m&#8722;2 (at standard conditions) on the axis and decreasing to almost zero at a radial distances of more than 15&#8201;cm from the flow axis. Varying the RF acceleration voltage in the range 20350&#8201;V, the plasma flow velocity can be changed between 10 and 35&#8201;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
• 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
• Is collisionless heating in capacitively coupled plasmas really collisionless?
  
  • Lafleur Trevor
  • Chabert Pascal
  Plasma Sources Science and Technology, IOP Publishing, 2015, 24 (4), pp.044002. By performing a combination of test-particle and particle-in-cell simulations, we investigate electron heating in single frequency capacitively coupled plasmas (CCPs). In agreement with previous theoretical considerations highlighted in Kaganovich et al (1996 Appl. Phys. Lett. 69 3818), we show that the level of true collisionless/stochastic heating in typical CCPs is significantly smaller than that due to collisional interactions; even at very low pressures and wide gap lengths. Fundamentally electron heating is a collisional phenomenon whereby particle collisions provide the vital phase randomization and stochastization mechanism needed to generate both a local (or ohmic) heating component, and a non-local (or hybrid) heating component. (10.1088/0963-0252/24/4/044002)
  DOI : 10.1088/0963-0252/24/4/044002
• 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
• 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.
• 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
• Negative hydrogen ion production mechanisms
  
  • Bacal M.
  • Wada M.
  Applied Physics Reviews, AIP Publishing, 2015, 2 (2), pp.021305. Negative hydrogen/deuterium ions can be formed by processes occurring in the plasma volume and on surfaces facing the plasma. The principal mechanisms leading to the formation of these negative ions are dissociative electron attachment to ro-vibrationally excited hydrogen/deuterium molecules when the reaction takes place in the plasma volume, and the direct electron transfer from the low work function metal surface to the hydrogen/deuterium atoms when formation occurs on the surface. The existing theoretical models and reported experimental results on these two mechanisms are summarized. Performance of the negative hydrogen/deuterium ion sources that emerged from studies of these mechanisms is reviewed. Contemporary negative ion sources do not have negative ion production electrodes of original surface type sources but are operated with caesium with their structures nearly identical to volume production type sources. Reasons for enhanced negative ion current due to caesium addition to these sources are discussed. (31 pages, 265 refs) (10.1063/1.4921298)
  DOI : 10.1063/1.4921298
• Isopropanol removal using Mn<SUB>X</SUB>O<SUB>Y</SUB> packed bed non-thermal plasma reactor: Comparison between continuous treatment and sequential sorption/regeneration
  
  • Sivachandiran Loganathan
  • Thévenet Frédéric
  • Rousseau Antoine
  Chemical Engineering Journal, Elsevier, 2015, 270, pp.327-335. MnXOY coated glass beads packed bed non-thermal plasma (NTP) reactor has been designed and operated for isopropanol (IPA) removal close to indoor air conditions. The IPA removal efficiency of continuous NTP treatment is compared with the sequential approach, i.e. adsorption of IPA on MnXOY and subsequent regeneration of the saturated MnXOY surface by non-thermal plasma. The comparison between both approaches has been achieved with the same packed bed reactor and model VOC under equivalent indoor air conditions. Firstly, based on carbon mass balance calculations, the continuous treatment has shown better performances from an IPA abatement point of view, as well as from a mineralization point of view. However, the characterization of ppb level side-products evidenced that the continuous treatment leads to a more significant release of organic side products which may impact indoor air quality. Secondly, both processes have been compared in terms of energetic costs regarding (i) IPA removal, and (ii) CO2 forma- tion. Interestingly, it is evidenced that, to treat the same amount of IPA, the sequential approach requires 14.5 times less energy than the continuous NTP treatment process. Similarly, to produce the same amount of CO2, the sequential approach consumes 10 times less energy. This comparison evidences the interest of adsorption combined with subsequent non-thermal plasma regeneration for indoor air effluent treatment. (10.1016/j.cej.2015.01.055)
  DOI : 10.1016/j.cej.2015.01.055
• Matched dipole probe for magnetized low electron density laboratory plasma diagnostics
  
  • Rafalskyi D.V.
  • Aanesland Ane
  Physics of Plasmas, American Institute of Physics, 2015, 22 (7), pp.073504. In this paper, a diagnostic method for magnetized and unmagnetized laboratory plasma is proposed, based on impedance measurements of a short matched dipole. The range of the measured electron densities is limited to low density plasmas (10121015&#8201;m&#8722;3), where other diagnostic methods have strong limitations on the magnetic field strength and topology, plasma dimensions, and boundary conditions. The method is designed for use in both large- and small-dimension plasma (<10&#8201;cm) without or with strong non-homogeneous magnetic field, which can be undefined within the probe size. The design of a matched dipole probe allows to suppress the sheath resonance effects and to reach high sensitivity at relatively small probe dimensions. Validation experiments are conducted in both magnetized (B&#8201;&#8764;&#8201;170&#8201;G) and unmagnetized (B&#8201;=&#8201;0) low density (7&#8201;×&#8201;1012&#8201;m&#8722;37&#8201;×&#8201;1013&#8201;m&#8722;3) low pressure (1 mTorr) 10&#8201;cm scale plasmas. The experimentally measured data show very good agreement with an analytical theory both for a non-magnetized and a magnetized case. The electron density measured by the matched dipole and Langmuir probes in the range of 7&#8201;×&#8201;1012&#8201;m&#8722;37&#8201;×&#8201;1013&#8201;m&#8722;3 show less than 30% difference. An experimentally measured tolerance/uncertainty of the dipole probe method is estimated to ±1% for plasma densities above 2&#8201;×&#8201;1013&#8201;m&#8722;3. A spatial resolution is estimated from the experiments to be about 3d, where d is the dipole diameter. The diagnostic method is also validated by comparing the measured plasma impedance curves with results of analytical modelling. (10.1063/1.4926447)
  DOI : 10.1063/1.4926447
• The impingement of a kHz helium atmospheric pressure plasma jet on a dielectric surface
  
  • Guaitella Olivier
  • Sobota Ana
  Journal of Physics D: Applied Physics, IOP Publishing, 2015, 48 (25), pp.255202. A parametric study of the impingement of a helium kHz atmospheric pressure plasma jet on a flat glass surface was performed by means of time-resolved intensified charge-coupled device imaging. The development of the plasma on the target is linked to the plasma evolution in the source and governed by the power supply. The glass surface takes part in the elongation of the plasma jet by the virtue of two mechanisms: the local enhancement of the electric field and the supply of pre-deposited charge. The evidence for the pre-deposited charge is the formation of a sheath on the glass surface, and the faint discharge formed on the glass surface during the negative voltage slope starting at the maximum of the negative current peak. The influence of the gas flow dynamics taking into account various gas flows, incident angles and distances is more important for the behaviour of the discharge on the surface than the voltage amplitude or the geometry of the source. The capacitance of the target strongly modifies the interaction with the plasma jet and increases the deposited surface charge density, featuring a streamer-like propagation mechanism in the case of high electric field enhancement at the surface. (10.1088/0022-3727/48/25/255202)
  DOI : 10.1088/0022-3727/48/25/255202