Publications

2013

• Progress on theoretical issues in modelling turbulent transport
  
  • Kosuga Y.
  • Diamond P.H.
  • Wang L.
  • Gürcan Özgür D.
  • Hahm T.S.
  Nuclear Fusion, IOP Publishing, 2013, 53 (4), pp.043008. We discuss theoretical progress in turbulent transport modelling in tokamaks. In particular, we address issues that the conventional quasilinear type calculation cannot confront, such as (i) the nature of turbulence in the edge-core coupling region of tokamaks (i.e. the so-called no mans land'), and the dynamics of incoming structures coupled to zonal flows, (ii) nonlinear dynamics of zonal flows and (iii) transport by drift wave turbulence with strong waveparticle interaction. A unifying theme of these studies is their formulation in terms of the phase space density correlation evolution. (10.1088/0029-5515/53/4/043008)
  DOI : 10.1088/0029-5515/53/4/043008
• How the Propagation of Heat-Flux Modulations Triggers ExB Flow Pattern Formation
  
  • Kosuga Y.
  • Diamond P.H.
  • Gürcan Özgür D.
  Physical Review Letters, American Physical Society, 2013, 110, pp.105002. We propose a novel mechanism to describe E×B flow pattern formation based upon the dynamics of propagation of heat-flux modulations. The E×B flows of interest are staircases, which are quasiregular patterns of strong, localized shear layers and profile corrugations interspersed between regions of avalanching. An analogy of staircase formation to jam formation in traffic flow is used to develop an extended model of heat avalanche dynamics. The extension includes a flux response time, during which the instantaneous heat flux relaxes to the mean heat flux, determined by symmetry constraints. The response time introduced here is the counterpart of the drivers response time in traffic, during which drivers adjust their speed to match the background traffic flow. The finite response time causes the growth of mesoscale temperature perturbations, which evolve to form profile corrugations. The length scale associated with the maximum growth rate scales as Δ2∼(vthi/λTi)ρi√χneoτ, where λTi is a typical heat pulse speed, χneo is the neoclassical thermal diffusivity, and τ is the response time of the heat flux. The connection between the scale length Δ2 and the staircase interstep scale is discussed. (10.1103/PhysRevLett.110.105002)
  DOI : 10.1103/PhysRevLett.110.105002
• Transport of radial heat flux and second sound in fusion plasmas
  
  • Gürcan Özgür D.
  • Diamond P.H.
  • Garbet X.
  • Berionni Vincent
  • Dif-Pradalier Guilhem
  • Hennequin Pascale
  • Morel Pierre
  • Kosuga Y.
  • Vermare Laure
  Physics of Plasmas, American Institute of Physics, 2013, 20, pp.022307. Simple flux-gradient relations that involve time delay and radial coupling are discussed. Such a formulation leads to a rather simple description of avalanches and may explain breaking of gyroBohm transport scaling. The generalization of the flux-gradient relation (i.e., constitutive relation), which involve both time delay and spatial coupling, is derived from drift-kinetic equation, leading to kinetic definitions of constitutive elements such as the flux of radial heat flux. This allows numerical simulations to compute these cubic quantities directly. The formulation introduced here can be viewed as an extension of turbulence spreading to include the effect of spreading of cross-phase as well as turbulence intensity, combined in such a way to give the flux. The link between turbulence spreading and entropy production is highlighted. An extension of this formulation to general quasi-linear theory for the distribution function in the phase space of radial position and parallel velocity is also discussed. (10.1063/1.4792161)
  DOI : 10.1063/1.4792161
• Interplanetary Nanodust Detection by the Solar Terrestrial Relations Observatory/WAVES Low Frequency Receiver
  
  • Le Chat G.
  • Zaslavsky A.
  • Meyer-Vernet N.
  • Issautier K.
  • Belheouane S.
  • Pantellini F.
  • Maksimovic M.
  • Zouganelis I.
  • Bale S. D.
  • Kasper J. C.
  Solar Physics, Springer Verlag, 2013, 286 (2), pp.549-559. New measurements using radio and plasma-wave instruments in interplanetary space have shown that nanometer-scale dust, or nanodust, is a significant contributor to the total mass in interplanetary space. Better measurements of nanodust will allow us to determine where it comes from and the extent to which it interacts with the solar wind. When one of these nanodust grains impacts a spacecraft, it creates an expanding plasma cloud, which perturbs the photoelectron currents. This leads to a voltage pulse between the spacecraft body and the antenna. Nanodust has a high charge/mass ratio, and therefore can be accelerated by the interplanetary magnetic field to the speed of the solar wind: significantly faster than the Keplerian orbital speeds of heavier dust. The amplitude of the signal induced by a dust grain grows much more strongly with speed than with mass of the dust particle. As a result, nanodust can produce a strong signal despite its low mass. The WAVES instruments on the twin Solar TErrestrial RElations Observatory spacecraft have observed interplanetary nanodust particles since shortly after their launch in 2006. After describing a new and improved analysis of the last five years of STEREO/WAVES Low Frequency Receiver data, we present a statistical survey of the nanodust characteristics, namely the rise time of the pulse voltage and the flux of nanodust. We show that previous measurements and interplanetary dust models agree with this survey. The temporal variations of the nanodust flux are also discussed. (10.1007/s11207-013-0268-x)
  DOI : 10.1007/s11207-013-0268-x
• Generation mechanism of the whistler-mode waves in the plasma sheet prior to magnetic reconnection
  
  • Wei X.H.
  • Cao J.B.
  • Zhou G.C.
  • Fu H.S.
  • Santolík O.
  • Rème H.
  • Dandouras I.
  • Cornilleau-Wehrlin Nicole
  • Fazakerley A.
  Advances in Space Research, Elsevier, 2013, 52 (1), pp.205-210. The whistler-mode waves and electron temperature anisotropy play a key role prior to and during magnetic reconnection. On August 21, 2002, the Cluster spacecrafts encountered a quasi-collisionless magnetic reconnection event when they crossed the plasma sheet. Prior to the southward turning of magnetospheric magnetic field and high speed ion flow, the whistler-mode waves and positive electron temperature anisotropy are simultaneously observed. Theoretic analysis shows that the electrons with positive temperature anisotropy can excite the whistler-mode waves via cyclotron resonances. Using the data of particles and magnetic field, we estimated the whistler-mode wave growth rate and the ratio of whistler-mode growth rate to wave frequency. They are 0.0016fce (Electron cyclotron frequency) and 0.0086fce, respectively. Therefore the whistler-mode waves can grow quickly in the current sheet. The combined observations of energetic electron beams and waves show that after the southward turning of magnetic field, energetic electrons in the reconnection process are accelerated by the whistler-mode waves. (10.1016/j.asr.2013.02.016)
  DOI : 10.1016/j.asr.2013.02.016
• Reinterpretation of Slowdown of Solar Wind Mean Velocity in Nonlinear Structures Observed Upstream of Earth's Bow Shock
  
  • Parks G. K.
  • Lee E.
  • Lin N.
  • Fu S. Y.
  • Mccarthy M.
  • Cao J.B.
  • Hong J.
  • Liu Y.
  • Shi J. K.
  • Goldstein M. L.
  • Canu Patrick
  • Dandouras I.
  • Rème H.
  The Astrophysical Journal Letters, Bristol : IOP Publishing, 2013, 771, pp.L39. Two of the many features associated with nonlinear upstream structures are (1) the solar wind (SW) mean flow slows down and deviates substantially and (2) the temperature of the plasma increases in the structure. In this Letter, we show that the SW beam can be present throughout the entire upstream event maintaining a nearly constant beam velocity and temperature. The decrease of the velocity is due to the appearance of new particles moving in the opposite direction that act against the SW beam and reduce the mean velocity as computed via moments. The new population, which occupies a larger velocity space, also contributes to the second moment, increasing the temperature. The new particles include the reflected SW beam at the bow shock and another population of lower energies, accelerated nearby at the shock or at the boundary of the nonlinear structures. (10.1088/2041-8205/771/2/L39)
  DOI : 10.1088/2041-8205/771/2/L39
• A comparison of bow shock models with Cluster observations during low Alfvén Mach number magnetic clouds
  
  • Turc Lucile
  • Fontaine Dominique
  • Savoini Philippe
  • Hietala H.
  • Kilpua E. K. J.
  Annales Geophysicae, European Geosciences Union, 2013, 31 (6), pp.1011-019. Magnetic clouds (MCs) are very geoeffective solar wind structures. Their properties in the interplanetary medium have been extensively studied, yet little is known about their characteristics in the Earth's magnetosheath. The Cluster spacecraft offer the opportunity to observe MCs in the magnetosheath, but before MCs reach the magnetosphere, their structure is altered when they interact with the terrestrial bow shock (BS). The physics taking place at the BS strongly depends on ΘBn, the angle between the shock normal and the interplanetary magnetic field. However, in situ observations of the BS during an MC's crossing are seldom available. In order to relate magnetosheath observations to solar wind conditions, we need to rely on a model to determine the shock's position and normal direction. Yet during MCs, the models tend to be less accurate, because the Alfvén Mach number (MA) is often significantly lower than in regular solar wind. On the contrary, the models are generally optimised for high MA conditions. In this study, we compare the predictions of four widely used models available in the literature (Wu et al., 2000; Chapman and Cairns, 2003; Jeřáb et al., 2005; Měrka et al., 2005b) to Cluster's dayside BS crossings observed during five MC events. Our analysis shows that the ΘBn angle is well predicted by all four models. On the other hand, the Jeřáb et al. (2005) model yields the best estimates of the BS position during low MA MCs. The other models locate the BS either too far from or too close to Earth. The results of this paper can be directly used to estimate the BS parameters in all studies of MC interaction with Earth's magnetosphere. (10.5194/angeo-31-1011-2013)
  DOI : 10.5194/angeo-31-1011-2013
• In situ observations of high-Mach number collisionless shocks in space plasmas
  
  • 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.
  Plasma Physics and Controlled Fusion, IOP Publishing, 2013, 55 (12), pp.124035. Shock waves are widespread in collisionless space plasmas throughout the Universe. How particles are accelerated at these shocks has been the subject of much research attention. The dominant source of the high-energy particles that pervade our Galaxy (cosmic rays) is thought to be the high-Mach number collisionless shocks that form around young supernova remnants, but it is unclear how much the lower Mach number collisionless shock waves frequently encountered by spacecraft in Solar System space plasmas can tell us about particle acceleration in the higher Mach number regime. Here we review recent studies of the shock wave that stands in the solar wind in front of the planet Saturn (Saturn's bow shock), based on Cassini spacecraft observations. This review represents a new direction of shock physics research, with the potential to bridge the gap between Solar System and astrophysical shocks. These studies have confirmed that Saturn's bow shock is one of the strongest shocks in the Solar System, and a recent discovery indicates that electron acceleration at high-Mach numbers may occur irrespective of the upstream magnetic field geometry. This is important because astrophysical shocks can often only be studied remotely via emissions associated with accelerated electrons. We discuss possible future directions of this emerging sub-field of collisionless space plasma shock physics. (10.1088/0741-3335/55/12/124035)
  DOI : 10.1088/0741-3335/55/12/124035
• In Situ Cassini Spacecraft Observations of Turbulence in Saturn's Magnetosheath
  
  • Hadid L. Z.
  • Sahraoui Fouad
  • Retinò Alessandro
  • Modolo Ronan
  • Canu Patrick
  • Jackman C. M.
  • Masters A.
  • Dougherty M. K.
  • Gurnett D. A.
  , 2013, 8, pp.EPSC2013-1056. Throughout this work we investigate, the properties of turbulence in the Magnetosheath of Saturn. To do so, we computed Power Spectral Densities (PSD) based on Cassini interplanetary magnetic field data between 2004 and 2007. As a preliminary result, we show the absence of the Kolmogorov scale ~ f-5/3 in the inertial range whereas only the f-1 scale is present.
• Vibrational relaxation of N2 on catalytic surfaces studied by infrared titration with time resolved Quantum Cascade Laser diagnostics
  
  • Marinov Daniil
  • Guaitella Olivier
  • Lopatik D.
  • Hübner M.
  • Ionikh Y.
  • Roepcke J.
  • Rousseau Antoine
  , 2013.
• Atmospheric Pressure Townsend Discharges in nitrogen with small admixtures of oxygen: discussion on the origin of the memory effect
  
  • Naudé Nicolas
  • Bouzidi Mohamed Cherif
  • Dang V.S.
  • Dang van Sung Mussard Marguerite
  • Puechagut Loïc
  • Belinger Antoine
  • Ségur Pierre
  • Gherardi Nicolas
  , 2013.
• SPACE RESEARCH IN AFRICA SOME ACHIEVEMENTS FROM 2007 to 2012
  
  • Amory-Mazaudier Christine
  • Fleury Rolland
  Sun and Geosphere, BBC SWS Regional Network, 2013, 1, pp.ISSN : I819-0839. This article presents the results of a research network Europe Africa established in 1995 after the International Electrojet Equatorial Year (1992-1994). During the last decade, this research network has been involved in two international projects: the International Heliophysical Year (2007-2009) and International Space Weather Initiative (2010-2012).The participation in these international projects increased the number of PhD and multiplied the number of scientific papers. Many scientific results have been obtained. Teaching and working methods have been also developed. We emphasize in this article the last two points.
• Solar wind fluctuations and solar wind activity long-term swing 1963-2012
  
  • Zerbo J.-L.
  • Amory-Mazaudier Christine
  • Ouattara Frédéric Martial
  , 2013, 1301161.
• ROLE OF REACTOR CAPACITANCE ON THE PROPAGATION OF IONISATION WAVES
  
  • Guaitella Olivier
  • Sobota Ana
  • Rousseau Antoine
  , 2013.
• 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 R<SUB>E</SUB>. 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
• 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.
• 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).
• 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&#8201;±&#8201;0.7)×1020&#8201;m&#8722;3 was found at admixtures of 0.35&#8201;vol.&#8201;%, while the N-atom concentration exhibits a maximum of (5.7&#8201;±&#8201;0.4)×1019&#8201;m&#8722;3 at 0.1&#8201;vol.&#8201;%. (10.1063/1.4813817)
  DOI : 10.1063/1.4813817
• 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&#8201;=&#8201;&#8722;30 RE to XGSM&#8201;=&#8201;&#8722;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&#8201;>&#8201;&#8722;10 RE) are primarily attributed to jet braking, while the DFs detected in the mid- or far-tail region (XGSM&#8201;<&#8201;&#8722;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
• 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
• 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
• 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 &#8764; 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
• 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 &#945; &#8801; n&#8722;/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 &#945;, it is shown that the electronegative plasma behavior can be described by four regimes. In the lowest regime of &#945;, i.e., &#945; < 50, negative ions are confined by two positive sheaths within the plasma, while in the higher regimes of &#945;, a negative sheath is formed and the negative ion flux can be extracted from the bulk plasma. In the two intermediate regimes of &#945;, i.e., 50 < &#945; < 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., &#945; > 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
• 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