Publications

2013

• Isopropanol saturated TiO<SUB>2</SUB> surface regeneration by non-thermal plasma : Influence of air relative humidity
  
  • Sivachandiran Loganathan
  • Thévenet Frédéric
  • Gravejat Paul
  • Rousseau Antoine
  Chemical Engineering Journal, Elsevier, 2013, 214, pp.17-26. Environmental regulation on air quality requires the development of energetic efficient volatile organic compounds (VOCs) abatement techniques. Adsorption, photocatalysis, non-thermal plasma and their combinations have been widely studied for VOC treatment. Even if the plasma material (sorbent or catalyst) association appears as one of the most efficient configuration for VOC removal, it mainly consists in operating continuously the discharge on the material surface as long as the effluent flows across the reactor. This work aims at investigating another approach of plasma material association for VOC removal: in a first step, the material is used as a sorbent until the complete coverage of adsorption sites; in a second step, once VOC saturation is achieved, the discharge is ignited on the material surface. During both steps, the influence of air relative humidity (RH) is investigated in order to evaluate its impact on the process. The objectives of our approach are: (i) the reduction of energy consumption; (ii) the increase of sorbent life-times by efficient regeneration; (iii) the investigation of plasma interaction with VOC saturated materials; (iv) the investigation of air RH influence on such VOC treatment process. A packed bed reactor coated with TiO2 has been designed. IPA is used as a model VOC. First, injected power in the packed-bed reactor is characterized as a function of air RH. Complete coverage of TiO2 surface over 35% RH is suggested as a significant parameter. Then, adsorption of IPA on TiO2 was monitored until IPA breakthrough. The amount of IPA adsorbed per TiO2 surface unit is compared to values reported by other authors. The influence of air RH on reversibly and irreversibly adsorbed IPA fractions is investigated. Over 35% RH irreversible adsorption is favored, adsorption modes are discussed. Plasma regeneration of IPA saturated TiO2 surface leads simultaneously to IPA desorption and mineralization. Increasing air RH favors IPA mineralization and diminishes acetone production. Carbon balance obtained after 1 h plasma treatment reaches 91% in the presence of 50% RH. A thermal treatment is performed after each plasma treatment in order to evidence plasma insensitive adsorbed species and to restore TiO2 initial surface state. 97% of the carbon balance is collected under 50% RH after thermal treatment. During the thermal step, acetone and CO2 are mainly produced, their formation pathways are discussed. (10.1016/j.cej.2012.10.022)
  DOI : 10.1016/j.cej.2012.10.022
• Dynamics of tilted eddies in a transversal flow at the edge of tokamak plasmas and the consequences for L-H transition
  
  • Fedorczak N.
  • Ghendrih Philippe
  • Hennequin Pascale
  • Tynan G.R.
  • Diamond P.H.
  • Manz P.
  Plasma Physics and Controlled Fusion, IOP Publishing, 2013, 55 (12), pp.124024. The dynamical interaction between eddies and shear flow is investigated through a simplified model of vorticity conservation with tilted eddies. Energy is transferred either to the flow or to eddies, depending on the eddy tilt with respect to the flow shear. When eddies are tilted in the shear direction, the system is favorable to shear increase: tilt instability (TI) or the negative viscosity phenomenon. When eddies are tilted in the opposite direction, the shear flow is damped via a Kelvin-Helmholtz (KH) process. The TI generally dominates the interaction on the largest radial scale, but a fraction of the energy cascades to smaller radial scales through the alternation of tilting and KH dynamics. Within this eddy description, we show that the symmetry breaking required to generate a net residual stress is set by the intrinsic eddy tilt. We recall that magnetic shear can provide an intrinsic tilt to ballooning modes at the edge of tokamak plasmas, with an orientation which depends on flux surface geometry. In L-mode weak shear regimes, this residual stress can dominate the Reynolds stress. Coupled to momentum sources acting in the scrape-off layer, it can induce a significant difference of the edge radial electric field between lower single null and upper single null geometries. A comparison with experimental profiles measured across the edge of Tore Supra L-mode plasmas is discussed. (10.1088/0741-3335/55/12/124024)
  DOI : 10.1088/0741-3335/55/12/124024
• Radio-frequency capacitively coupled plasmas excited by tailored voltage waveforms: comparison of experiment and particle-in-cell simulations
  
  • Delattre Pierre-Alexandre
  • Lafleur Trevor
  • Johnson Erik
  • Booth Jean-Paul
  Journal of Physics D: Applied Physics, IOP Publishing, 2013, 46, pp.235201. Using a range of different diagnostics we have performed a detailed experimental characterization of a capacitively coupled rf plasma discharge excited by tailored voltage waveforms in argon (3?13 Pa). The applied pulse-type tailored waveforms consist of between 1 and 5 harmonics (with a fundamental of 15 MHz), and are used to generate an electrically asymmetric plasma response, manifested by the formation of a strong dc bias in the geometrically symmetric reactor used. Experimental measurements of the dc bias, electron density, ion current density, ion-flux energy distributions at the electrodes and discharge current waveforms, are compared with a one-dimensional particle-in-cell simulation for the same operating conditions. The experimental and simulation results are found to be in good agreement over the range of parameters investigated, and demonstrate a number of unique features present with pulse-type tailored waveforms, including: increased plasma density and ion flux with the number of harmonics, and a broader control range of the ion bombarding energy. (10.1088/0022-3727/46/23/235201)
  DOI : 10.1088/0022-3727/46/23/235201
• Negative ion extraction from hydrogen plasma bulk
  
  • Oudini N.
  • Taccogna F.
  • Minelli P.
  • Aanesland Ane
  • Raimbault Jean-Luc
  Physics of Plasmas, American Institute of Physics, 2013, 20 (10), pp.103506. A two-dimensional particle-in-cell/Monte Carlo collision model has been developed and used to study low electronegative magnetized hydrogen plasma. A configuration characterized by four electrodes is used: the left electrode is biased at Vl&#8201;=&#8201;&#8722;100&#8201;V, the right electrode is grounded, while the upper and lower transversal electrodes are biased at an intermediate voltage Vud between 0 and &#8722;100&#8201;V. A constant and homogeneous magnetic field is applied parallel to the lateral (left/right) electrodes. It is shown that in the magnetized case, the bulk plasma potential is close to the transversal electrodes bias inducing then a reversed sheath in front of the right electrode. The potential drop within the reversed sheath is controlled by the transversal electrodes bias allowing extraction of negative ions with a significant reduction of co-extracted electron current. Furthermore, introducing plasma electrodes, between the transversal electrodes and the right electrode, biased with a voltage just above the plasma bulk potential, increases the negative ion extracted current and decreases significantly the co-extracted electron current. The physical mechanism on basis of this phenomenon has been discussed. (10.1063/1.4825246)
  DOI : 10.1063/1.4825246
• ECH effects on toroidal rotation: KSTAR experiments, intrinsic torque modelling and gyrokinetic stability analyses
  
  • Shi Y. J.
  • Ko W. H.
  • Kwon J.M.
  • Diamond P.H.
  • Lee S. G.
  • Ko S. H.
  • Wang L.
  • Yi Sukyoung
  • Ida K.
  • Terzolo L.
  • Yoon S. W.
  • Lee K. D.
  • Lee J. H.
  • Nam U. N.
  • Bae Y. S.
  • Oh Y. K.
  • Kwak J. G.
  • Bitter M.
  • Hill K.
  • Gürcan Özgür D.
  • Hahm T.S.
  Nuclear Fusion, IOP Publishing, 2013, 53 (11). Toroidal rotation profiles have been investigated in KSTAR H-mode plasma using combined auxiliary heating by co-neutral beam injection (NBI) and electron cyclotron resonance heating (ECH). The ion temperature and toroidal rotation are measured with x-ray imaging crystal spectroscopy and charge exchange recombination spectroscopy. H-mode plasma is achieved using co-current 1.3MW NBI, and a 0.35MW ECH pulse is added to the flat-top of H-mode. The core rotation profiles, which are centrally peaked in the pure NBI heating phase, flatten when ECH is injected, while the edge pedestal is unchanged. Dramatic decreases in the core toroidal rotation values (Delta V-tor/V-tor similar to -30%) are observed when on-axis ECH is added to H-mode. The experimental data show that the decrease of core rotation velocity and its gradient are correlated with the increase of core electron temperature and its gradient, and also with the likely steepening of the density gradient. We thus explore the viability of a hypothesized ITG (ITG ion temperature gradient instability) -> TEM (trapped electron mode instability) transition as the explanation of the observed counter-current flow induced by ECH. However, the results of linear microstability analyses using inferred profiles suggest that the TEM is excited only in the deep core, so the viability of the hypothesized explanation is not yet clear. (10.1088/0029-5515/53/11/113031)
  DOI : 10.1088/0029-5515/53/11/113031
• 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.
• Electrical characteristics of micro-hollow cathode discharges
  
  • Lazzaroni Claudia
  • Chabert Pascal
  Journal of Physics D: Applied Physics, IOP Publishing, 2013, 46, pp.455203. A cathode sheath model of micro-hollow cathode discharges is proposed to calculate the voltagecurrent characteristics and discuss the physics of the discharge resistance. Three different approaches are compared: (i) a self-consistent model where the electric field is determined self-consistently with the electron flux, (ii) a matrix sheath model where the electric field profile in the sheath is imposed, (iii) a constant electric field model where the electric field in the sheath is assumed to be equal to a constant fraction of the electric field at the cathode. The sheath size is found to decrease with the pressure, the voltage and the secondary emission coefficient. There is a strong effect of the secondary emission coefficient and the pressure on the voltagecurrent characteristics. The discharge resistance is found to be several hundreds of k&#937; and decreases with the discharge current, the pressure and the secondary emission coefficient. A comparison between the matrix sheath model and experiments suggests that both the secondary emission coefficient and the surface area on which the current is collected at the cathode increase with the discharge current. This increase is related to a transition between a discharge confined in the hole at low current and a plasma abruptly expanded on the cathode backside at higher current. (10.1088/0022-3727/46/45/455203)
  DOI : 10.1088/0022-3727/46/45/455203
• 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
• 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
• 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
• 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
• 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
• 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.
• 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
• 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
• Hysteresis effects in the formation of a neutralizing beam plasma at low ion energy
  
  • Rafalskyi D.V.
  • Aanesland Ane
  EPL - Europhysics Letters, European Physical Society / EDP Sciences / Società Italiana di Fisica / IOP Publishing, 2013, 104 (3), pp.35004. In this paper, the PEGASES II thruster prototype is used as an ion source generating low-energy positive Ar ion beam, extracted without an external neutralizer. The ions are extracted and accelerated from the source using a two-grid system. The extracted positive ion beam current is measured on a large beam target that can be translated along the acceleration axis. The ion beam current shows a stepwise transition from a low-current to a high-current extraction regime with hysteresis. The hysteresis region depends strongly upon the beam target position. Langmuir probe measurements in the plume show high plasma potentials and low plasma densities in the low-current mode, while the plasma potential drops and the density increases in the high-current mode. The ion energy distribution functions of the beam are measured for different regimes of ion extraction. The ion beam extracted in the high-current mode is indicated by the presence of an additional low-energy peak corresponding to ions from an ion-beam plasma created in the downstream chamber, as well as 1020 times higher intensity of the primary ion beam peak. The hysteresis behavior is explained by the formation of a downstream neutralizing beam plasma, that depends on the target position and pressure in agreement with a Paschen-like breakdown by secondary electrons. The obtained results are of high relevance for further development of the PEGASES thruster, as well as for improving existing neutralizer-free concepts of the broad-beam ion sources. (10.1209/0295-5075/104/35004)
  DOI : 10.1209/0295-5075/104/35004
• 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 &#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
• 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
• 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
• Fine-structure-resolved electron collisions from chlorine atoms in the (3p<SUP>5</SUP>)<SUP>2</SUP>P<SUB>3/2</SUB><SUP>o</SUP> and (3p<SUP>5</SUP>)<SUP>2</SUP>P<SUB>1/2</SUB><SUP>o</SUP> states
  
  • Wang Yang
  • Zatsarinny Oleg
  • Bartschat Klaus
  • Booth Jean-Paul
  Physical Review A : Atomic, molecular, and optical physics [1990-2015], American Physical Society, 2013, 87, pp.022703. The B-spline R-matrix method is employed to calculate elastic electron scattering from chlorine atoms in the (3p5)2P3/2,1/2o states and electron-induced collisions between these two finestructure levels. The polarizability of the target states is accounted for by including polarized pseudostates in the close-coupling expansion, while relativistic effects are treated at the level of the semirelativistic Breit-Pauli approximation. We find the Ramsauer minimum in the elastic channels at a significantly lower projectile energy (&#8776;0.2 eV) than previous calculations, due to an apparent strong sensitivity of the theoretical predictions on the details of the model, especially the target structure. The present results are relevant to the determination of chlorine atomic densities in Cl2-containing industrial plasma etch reactors. (10.1103/PhysRevA.87.022703)
  DOI : 10.1103/PhysRevA.87.022703
• Solar wind fluctuations and solar wind activity long-term swing 1963-2012
  
  • Zerbo J.-L.
  • Amory-Mazaudier Christine
  • Ouattara Frédéric Martial
  , 2013, 1301161.
• 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.