Publications

2013

• Controlled deposition of sulphur-containing semiconductor and dielectric nano-structured films on metals in SF<SUB>6</SUB> ion-ion plasma
  
  • Rafalskyi D.V.
  • Bredin Jérôme
  • Aanesland Ane
  Journal of Applied Physics, American Institute of Physics, 2013, 114 (21), pp.213303. In the present paper, the deposition processes and formation of films in SF6 ion-ion plasma, with positive and negative ion flows accelerated to the surface, are investigated. The PEGASES (acronym for Plasma Propulsion with Electronegative GASES) source is used as an ion-ion plasma source capable of generating almost ideal ion-ion plasma with negative ion to electron density ratio more than 2500. It is shown that film deposition in SF6 ion-ion plasma is very sensitive to the polarity of the incoming ions. The effect is observed for Cu, W, and Pt materials. The films formed on Cu electrodes during negative and positive ion assisted deposition were analyzed. Scanning electron microscope analysis has shown that both positive and negative ion fluxes influence the copper surface and leads to film formation, but with different structures of the surface: the low-energy positive ion bombardment causes the formation of a nano-pored film transparent for ions, while the negative ion bombardment leads to a continuous smooth insulating film. The transversal size of the pores in the porous film varies in the range 50500&#8201;nm, and further analysis of the film has shown that the film forms a diode together with the substrate preventing positive charge drain, and positive ions are neutralized by passing through the nano-pores. The film obtained with the negative ion bombardment has an insulating surface, but probably with a multi-layer structure: destroying the top surface layer allows to measure similar diode IV-characteristics as for the nano-pored film case. Basing on results, practical conclusions for the probes and electrodes cleaning in ion-ion SF6 plasmas have been made. Different applications are proposed for the discovered features of the controlled deposition from ion-ion plasmas, from Li-sulphur rechargeable batteries manufacturing and nanofluidics issues to the applications for microelectronics, including low-k materials formation. (10.1063/1.4842915)
  DOI : 10.1063/1.4842915
• On the reactivity of plasma-treated photo-catalytic TiO<SUB>2</SUB> surfaces for oxidation of C<SUB>2</SUB>H<SUB>2</SUB> and CO
  
  • Lopatik D.
  • Marinov Daniil
  • Guaitella Olivier
  • Rousseau Antoine
  • Roepcke J.
  Journal of Physics D: Applied Physics, IOP Publishing, 2013, 46, pp.255203. The objective of this study is to understand fundamental aspects of interactions of plasmas with catalytic surfaces. Based on this approach the reactivity of plasma treated and stimulated catalytic surfaces of TiO2 is studied by analysing the oxidation (i) of C2H2 to CO and CO2 and (ii) of CO to CO2. The inner surface of a Pyrex discharge tube is coated with TiO2 films impregnated with TiO2 nanoparticles, which provides a surface area of about 4 m2. In addition to the exposure of the TiO2 surface by low-pressure radio-frequency plasmas using O2, Ar or N2 (f = 13.56 MHz, p = 0.53 mbar, P = 17 W) the surfaces are stimulated by heating and UV radiation treatment. The temporal development of the concentrations of the precursor gases C2H2 or CO and of the reaction products is monitored using quantum cascade laser absorption spectroscopy, which provides multi-component detection in the mid-infrared spectral range. The C2H2 concentration was found to be nearly constant over time after a pre-treatment with Ar or N2 discharges using an initial gas mixture of 1% C2H2 in Ar. However, a strong decay of the concentration of C2H2 is observed for pure O2 plasma pre-treatment. In general, the decay is found to be nearly exponential with time constant in the order of about 10 min. The reactive adsorption of C2H2 molecules on the inner surface of the tube reactor showed a density of about 7.5 × 1012 C2H2 molecules cm&#8722;2. This behaviour demonstrates that the reaction (\rm O_\rm ads \rm C_2 \rm H_2)_\rm TiO_2 produces some adsorbed intermediates, which can be thermally or photo-catalytically oxidized to CO2. In contrast, when 1% CO in Ar is used as an initial gas mixture no adsorption processes on the TiO2 surface could be detected. An effective destruction of CO took part via photo-catalytic oxidation. (10.1088/0022-3727/46/25/255203)
  DOI : 10.1088/0022-3727/46/25/255203
• 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.
• 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
• Cell death induced on cell cultures and nude mouse skin by non-thermal, nanosecond-pulsed generated plasma
  
  • Duval Arnaud
  • Marinov Ilya
  • Bousquet Guilhem
  • Gapihan Guillaume
  • Starikovskaia Svetlana
  • Rousseau Antoine
  • Janin Anne
  PLoS ONE, Public Library of Science, 2013, 8 (12), pp.e83001. Non-thermal plasmas are gaseous mixtures of molecules, radicals, and excited species with a small proportion of ions and energetic electrons. Non-thermal plasmas can be generated with any high electro-magnetic field. We studied here the pathological effects, and in particular cell death, induced by nanosecond-pulsed high voltage generated plasmas homogeneously applied on cell cultures and nude mouse skin. In vitro, Jurkat cells and HMEC exhibited apoptosis and necrosis, in dose-dependent manner. In vivo, on nude mouse skin, cell death occurred for doses above 113 J/cm(2) for the epidermis, 281 J/cm(2) for the dermis, and 394 J/cm(2) for the hypodermis. Using electron microscopy, we characterized apoptosis for low doses and necrosis for high doses. We demonstrated that these effects were not related to thermal, photonic or pH variations, and were due to the production of free radicals. The ability of cold plasmas to generate apoptosis on cells in suspension and, without any sensitizer, on precise skin areas, opens new fields of application in dermatology for extracorporeal blood cell treatment and the eradication of superficial skin lesions. (10.1371/journal.pone.0083001)
  DOI : 10.1371/journal.pone.0083001
• 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
• 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
• 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 &#916;2&#8764;(vthi/&#955;Ti)&#961;i&#8730;&#967;neo&#964;, where &#955;Ti is a typical heat pulse speed, &#967;neo is the neoclassical thermal diffusivity, and &#964; is the response time of the heat flux. The connection between the scale length &#916;2 and the staircase interstep scale is discussed. (10.1103/PhysRevLett.110.105002)
  DOI : 10.1103/PhysRevLett.110.105002
• 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.
• 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
• Solar wind fluctuations and solar wind activity long-term swing 1963-2012
  
  • Zerbo J.-L.
  • Amory-Mazaudier Christine
  • Ouattara Frédéric Martial
  , 2013, 1301161.
• 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.
• A study of helium atmospheric-pressure guided streamers for potential biological applications
  
  • Gazeli Kristacq
  • Noel Cédric
  • Clement Franck
  • Dauge C.
  • Svarnas P.
  • Belmonte Thierry
  Plasma Sources Science and Technology, IOP Publishing, 2013, 22 (2), pp.025020. The origin of differences in the rotational temperatures of various molecules and ions (N-2(+)(B), OH(A) and N-2(C)) is studied in helium atmospheric-pressure guided streamers. The rotational temperature of N-2(+)(B) is room temperature. It is estimated from the emission band of the first negative system at 391.4 nm, and it is governed by the temperature of N-2(X) in the surrounding air. N-2(X) is ionized by direct electron impact in the outer part of the plasma. N-2(+)(B) is deactivated by collisions with N-2 and O-2. The rotational temperature of OH(A), estimated from the OH band at 306.4 nm, is slightly higher than that of N-2(+)(B). OH(A) is excited by electron impact with H2O during the first 100 ns of the applied voltage pulse. Next, OH(A) is produced by electron impact with OH(X) created by the quenching of OH(A) by N-2 and O-2. H2O diffuses deeper than N-2 into the plasma ring and the rotational temperature of OH(A) is slightly higher than that of N-2(+)(B). The rotational temperature of N-2(C), estimated from the emission of the second positive system at 315.9 nm, is governed by its collisions with helium. The gas temperature of helium at the beginning of the pulse is predicted to be several hundred kelvin higher than room temperature. (10.1088/0963-0252/22/2/025020)
  DOI : 10.1088/0963-0252/22/2/025020
• 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).
• 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
• 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
• 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
• 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
• 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 &#8764;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&#8727; 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&#8727; 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
• 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
• 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
• 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
• 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&#8201;mm diameter extraction electrode is about 80&#8201;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