Publications

2013

• Goniopolarimetry with Coupled Electric and Magnetic Measurements
  
  • Cecconi B.
  • Gautier A.-L.
  • Bergman J.E.S
  • Chust Thomas
  • Marchaudon A.
  • Cavoit C.
  • Santolík O.
  , 2013.
• Nonlinear saturation of wave packets excited by low-energy electron horseshoe distributions
  
  • Krafft C.
  • Volokitin A.
  Physical Review E, American Physical Society (APS), 2013, 87, pp.053107. Horseshoe distributions are shell-like particle distributions that can arise in space and laboratory plasmas when particle beams propagate into increasing magnetic fields. The present paper studies the stability and the dynamics of wave packets interacting resonantly with electrons presenting low-energy horseshoe or shell-type velocity distributions in a magnetized plasma. The linear instability growth rates are determined as a function of the ratio of the plasma to the cyclotron frequencies, of the velocity and the opening angle of the horseshoe, and of the relative thickness of the shell. The nonlinear stage of the instability is investigated numerically using a symplectic code based on a three-dimensional Hamiltonian model. Simulation results show that the dynamics of the system is mainly governed by wave-particle interactions at Landau and normal cyclotron resonances and that the high-order normal cyclotron resonances play an essential role. Specific features of the dynamics of particles interacting simultaneously with two or more waves at resonances of different natures and orders are discussed, showing that such complex processes determine the main characteristics of the wave spectrum's evolution. Simulations with wave packets presenting quasicontinuous spectra provide a full picture of the relaxation of the horseshoe distribution, revealing two main phases of the evolution: an initial stage of wave energy growth, characterized by a fast filling of the shell, and a second phase of slow damping of the wave energy, accompanied by final adjustments of the electron distribution. The influence of the density inhomogeneity along the horseshoe on the wave-particle dynamics is also discussed. (10.1103/PhysRevE.87.053107)
  DOI : 10.1103/PhysRevE.87.053107
• Anisotropy of radiation emitted from planar wire arrays
  
  • Kantsyrev Viktor L.
  • Chuvatin Alexandre S.
  • Esaulov A. A.
  • Safronova Alla S.
  • Rudakov Leonid I.
  • Velikovich A. L.
  • Williamson Kenneth M.
  • Osborne Glenn C.
  • Shrestha I. K.
  • Weller Michael E.
  • Shlyaptseva V. V.
  Physics of Plasmas, American Institute of Physics, 2013, 20 (07), pp.070702. The planar wire array (PWA) is a promising load for new multi-source inertial confinement fusion (ICF) hohlraums [B. Jones et al. Phys. Rev. Lett. 104 125001 (2010)]. The hohlraum radiation symmetry is an important issue for ICF. It was found that extreme ultraviolet and sub-keV photon emission from PWAs may have considerable anisotropy in the load azimuthal plane. This experimental result is obtained on the UNR 11.7 MA Zebra generator. The time-dependent anisotropy effect is detected. This feature is studied in 2D numerical simulations and can be explained by initial anisotropy of implosion of those non-cylindrical loads radiating essentially as surface sources in sub-keV quanta and also by radiation absorption in cold magnetized plasma tails forming in the direction of magnetic compression. (10.1063/1.4817023)
  DOI : 10.1063/1.4817023
• A spectroscopic study of ethylene destruction and by-product generation using a three-stage atmospheric packed-bed plasma reactor
  
  • Hubner Antoine
  • Guaitella Olivier
  • Rousseau Antoine
  • Roepcke J.
  Journal of Applied Physics, American Institute of Physics, 2013, 114, pp.033301. Using a three-stage dielectric packed-bed plasma reactor at atmospheric pressure, the destruction of ethylene, a typical volatile organic compound, and the generation of major by-products have been studied by means of Fourier Transform Infrared Spectroscopy. A test gas mixture air at a gas flow of 1 slm containing 0.12% humidity with 0.1% ethylene has been used. In addition to the fragmentation of the precursor gas, the evolution of the concentration of ten stable reaction products, CO, CO2, O3, NO2, N2O, HCN, H2O, HNO3, CH2O, and CH2O2 has been monitored. The concentrations of the by-products range between 5 ppm, in the case of NO2, and 1200 ppm, for H2O. By the application of three sequentially working discharge cells at a frequency of f = 4 kHz and voltage values between 9 and 12 kV, a nearly complete decomposition of C2H4 could be achieved. Furthermore, the influence of the specific energy deposition (SED) on the destruction process has been studied and the maximum value of SED was about 900 J l−1. The value of the characteristic energy β, characterizing the energy efficiency of the ethylene destruction in the reactor, was found to be 330 J l−1. It was proven that the application of three reactor stages suppresses essentially the production of harmful by-products as formaldehyde, formic acid, and NO2 compared to the use of only one or two stages. Based on the multi-component detection, the carbon balance of the plasma chemical conversion of ethylene has been analyzed. The dependence of the fragmentation efficiencies of ethylene (RF(C2H4) = 5.5 × 1019 molecules J−1) and conversion efficiencies to the produced molecular species (RC = (0.13) × 1016 molecules J−1) on the discharge conditions could be estimated in the multistage plasma reactor. (10.1063/1.4813409)
  DOI : 10.1063/1.4813409
• Physics of Stimulated L->H Transitions
  
  • Miki K.
  • Diamond P.H.
  • Hahn S. -H.
  • Xiao W. W.
  • Gürcan Özgür D.
  • Tynan G.R.
  Physical Review Letters, American Physical Society, 2013, 110, pp.195002. We report on model studies of stimulated L&#8594;H transitions. These studies use a novel reduced mesoscale model. Studies reveal that L&#8594;H transitions can be triggered by particle injection into a subcritical state (i.e., P<PThresh). Particle injection alters the edge mean flow shear via changes of density and temperature gradients. The change of edge mean flow shear is critical to turbulence collapse and the subsequent stimulated transition. For low ambient heating, strong injection is predicted to trigger a transient turbulence collapse. We predict that repetitive injection can maintain the turbulence collapse and so sustain a driven H-mode-like state. The total number of particles required to induce a transition by either injection or gas puffing is estimated. Results indicate that the total number of injected particles required is much smaller than that required for inducing a transition by gas puffing. Thus, we show that internal injection is more efficient than gas puffing of comparable strength. We also observe that zonal flows do not play a critical role in stimulated transitions. (10.1103/PhysRevLett.110.195002)
  DOI : 10.1103/PhysRevLett.110.195002
• CLUSTER observation of polar electron precipitation above the polar caps during periods of Northward IMF
  
  • Fontaine Dominique
  • Maggiolo R.
  AGU Fall Meeting Abstracts, AGU, 2013, 21, pp.07. The CLUSTER spacecraft revealed the presence of successive current sheets of opposite polarity above the polar caps during periods of northward or weak IMF. We first present the general electrodynamical context. At CLUSTER altitude (5-7 RE), the upward part of this current system consists of ion beams accelerated by quasi-static electric fields, associated with precipitating electrons. They are surrounded by low energy upflowing electron beams carrying a downward current. We then focus on the precipitating electrons above the polar cap which form acceleration structures at about 100 - 300 eV. This acceleration is interpreted as the effect of an electrostatic potential along magnetic field lines located above CLUSTER altitude, i.e. typically above 5-7 RE. We present statistics on the characteristics of these precipitating electron structures and we discuss the source regions and the mechanisms possibly at their origin.
• Building small scales in MHD turbulence
  
  • Verdini Andrea
  • Grappin Roland
  • Pinto Rui
  • Velli Marco
  , 2013, 1539, pp.74-77. Magneto-hydrodynamic turbulence (MHD) with a mean large-scale field is known to produce an anisotropic cascade, with energy mostly in perpendicular scales. We use a shell-model version of the Reduced MHD equations to simulate turbulence in homogeneous periodic conditions, in coronal loops, and in the solar wind. We compare the perpendicular and parallel spectra and show that different regimes of weak turbulence develop in loops and in the solar wind. We briefly comment on the way their characteristic large-scale features influence the weak turbulence spectra and their transition to strong turbulence. (10.1063/1.4810993)
  DOI : 10.1063/1.4810993
• Solar wind turbulence: the fight between the direct turbulent cascade and the (anisotropic) expansion
  
  • Grappin Roland
  , 2013.
• Structures of dayside whistler-mode waves deduced from conjugate diffuse aurora
  
  • Nishimura Y.
  • Bortnik J.
  • Li W.
  • Thome R.M.
  • Ni B.
  • Lyons L.R.
  • Angelopoulos V.
  • Ebihara Y.
  • Bonnell J. W.
  • Le Contel Olivier
  • Auster U.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2013, 118 (2), pp.664-673. [1] We present simultaneous measurements of dayside diffuse aurora and whistler-mode waves made by the South Pole all-sky imager and two of the THEMIS spacecraft. We found a high correlation between the diffuse aurora intensity at 557.7&#8201;nm near the footprint latitudes of THEMIS and whistler-mode wave intensity measured on board. The power in other wave modes was negligibly small in most cases, indicating that the dayside diffuse aurora is driven by precipitating energetic electrons resonating with whistler-mode waves. The high correlation over a wide L* range (6&#8201;<&#8201;L*&#8201;<&#8201;11) further allowed us to magnetically link the wave and magnetospheric plasma distributions with the auroral patterns. Two distinct regions of whistler-mode waves and ambient plasma density were found outside the plasmasphere near the equator: (1) intense waves in a smooth, low density and (2) moderate waves with enhanced and fluctuating density. The whistler-mode wave intensity in the fluctuating plasma density region is positively correlated with the ambient density variations. The corresponding auroral images show an azimuthally elongated diffuse auroral band on the field lines connected to the low density region, as opposed to a structured diffuse aurora on the fluctuating density field lines. Each structured diffuse auroral patch was stable for a few tens of minutes and slowly drifted azimuthally. The high correlation of waves and auroras indicates that the structured diffuse auroral pattern reflects the spatial distribution of whistler-mode waves and ambient plasma density in space. The enhanced density measured by the spacecraft is quasi-spatial and contributes to enhanced growth of whistler-mode waves. (10.1029/2012JA018242)
  DOI : 10.1029/2012JA018242
• Statistical properties of planetary heavy-ion precipitations toward the Martian ionosphere obtained from Mars Express
  
  • Hara T.
  • Seki K.
  • Futaana Y.
  • Yamauchi M.
  • Barabash S.
  • Fedorov A. O.
  • Yagi M.
  • Delcourt Dominique C.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2013, 118 (8), pp.5348-5357. The interplanetary magnetic field (IMF) embedded in the solar wind interacts with the Martian crustal magnetic field and atmosphere. The IMF orientation is one of the important parameters to control the acceleration and precipitation of planetary heavy ions (PHIs). We statistically investigate the effects of the IMF orientation on PHI precipitations toward the ionosphere based on observations by Mars Express (MEX). We identified 59 PHI precipitation events between July 2007 and September 2009. To estimate the IMF orientation without magnetometer that MEX does not carry, we used the velocity distribution of exospheric-origin pickup protons. We estimated the IMF orientation without its polarity for 10 events. The results show that the precipitations of PHIs tend to be observed around pole regions in the MSE (Mars-centered, solar electrical) coordinates determined from the solar wind electric field (Esw), in which the pole axis directs to the parallel or antiparallel to Esw due to the ambiguity in the IMF polarity determination. The observed precipitating PHIs are accelerated only up to a few keV. This feature may reflect the short distance from the picked-up region. For one of these 10 events, we estimated the IMF polarity by comparing the velocity distribution of exospheric-origin pickup protons observed by MEX with those obtained from statistical trajectory tracing simulations under two cases of possible IMF polarity conditions. The estimated polarity indicates that the PHI precipitation in this event is observed in the downward electric field hemisphere in MSE, where Esw points to Mars in the pole region. (10.1002/jgra.50494)
  DOI : 10.1002/jgra.50494
• Commutation rapide déclenchée par filamentation laser femtoseconde
  
  • Larour Jean
  • Arantchouk Léonid
  • Houard Aurélien
  Flash X - La revue scientifique de l'Ecole polytechnique, Ecole polytechnique, 2013, 15, pp.55-57. La revue scientifique de l'Ecole polytechnique (parution annuelle) ISSN : 1775-0385 Le phénomène de filamentation laser dans lair a été décrit dans un précédent numéro (Flash X n° 12) par A. Houard et A. Mysyrowicz, chercheurs du LOA (Laboratoire dOptique appliquée). Rappelons ici quil apparaît spontanément le long dun faisceau laser de durée femtoseconde (fs) quand sa puissance dépasse un seuil critique de quelques GW. un équilibre dynamique entre la diffraction naturelle du faisceau, leffet Kerr, et la défocalisation par lair ionisé, maintient lintensité dans le coeur du faisceau sur une distance qui peut dépasser un mètre, entraînant la formation dun canal de plasma dans le sillage de limpulsion. Le point de démarrage, la longueur des canaux de plasma et leur distribution transverse sont contrôlables en jouant sur les paramètres de limpulsion laser initiale (énergie, durée, diamètre du faisceau).
• Simulation benchmarks for low-pressure plasmas: Capacitive discharges
  
  • Turner M.M.
  • Derzsi A.
  • Donkó Z.
  • Eremin D.
  • Kelly S.J.
  • Lafleur Trevor
  • Mussenbrock T.
  Physics of Plasmas, American Institute of Physics, 2013, 20, pp.013507. Benchmarking is generally accepted as an important element in demonstrating the correctness of computer simulations. In the modern sense, a benchmark is a computer simulation result that has evidence of correctness, is accompanied by estimates of relevant errors, and which can thus be used as a basis for judging the accuracy and efficiency of other codes. In this paper, we present four benchmark cases related to capacitively coupled discharges. These benchmarks prescribe all relevant physical and numerical parameters. We have simulated the benchmark conditions using five independently developed particle-in-cell codes. We show that the results of these simulations are statistically indistinguishable, within bounds of uncertainty that we define. We, therefore, claim that the results of these simulations represent strong benchmarks, which can be used as a basis for evaluating the accuracy of other codes. These other codes could include other approaches than particle-in-cell simulations, where benchmarking could examine not just implementation accuracy and efficiency, but also the fidelity of different physical models, such as moment or hybrid models. We discuss an example of this kind in the Appendix. Of course, the methodology that we have developed can also be readily extended to a suite of benchmarks with coverage of a wider range of physical and chemical phenomena. (10.1063/1.4775084)
  DOI : 10.1063/1.4775084
• Interaction of plasma transport and turbulence on particle fuelling
  
  • Tamain Patrick
  • Bonhomme Gérard
  • Brochard Frédéric
  • Clairet Frédéric
  • Gil C.
  • Gunn J.
  • Hennequin P.
  • Hornung G.
  • Segui J. L.
  • Vermare L.
  • Ghendrih Philippe
  • Team Tore Supra
  Journal of Nuclear Materials, Elsevier, 2013, 438 (S), pp.S148-S154. We report the results of an experimental investigation of the impact of Supersonic Molecular Beam Injection in the Tore Supra tokamak. Several diagnostics were synchronised with the injection to extract a global picture of the physics at play from the time scale of turbulence (similar to 10 mu s) to the full-recovery time (similar to 1 s). As previously reported, a strong impact of the injection on density and temperature profiles is observed. Both fields exhibit a complex dynamic response involving different phases and time scales. In particular, we show that the effective particle fuelling efficiency is determined by a period of degraded confinement that follows the injection, during which the edge density collapses, in some cases, lower than the initial one. This phase is characterised by a dramatic change in the turbulent transport, with a drop of the frequency spectrum and the observation of large coherent structures as opposed to small intermittent fluctuations before the injection. (10.1016/j.jnucmat.2013.01.023)
  DOI : 10.1016/j.jnucmat.2013.01.023
• Anomalous collisionality in low-pressure plasmas
  
  • Lafleur Trevor
  • Chabert Pascal
  • Turner M.M.
  • Booth Jean-Paul
  Physics of Plasmas, American Institute of Physics, 2013, 20 (12), pp.124503. Based on a theoretical argument from fundamental kinetic theory, by way of simple worked examples, and through the use of particle-in-cell simulations of capacitively coupled plasmas, we demonstrate that conventional methods for calculating the momentum transfer collision frequency in low-pressure plasmas can be seriously erroneous. This potentially plays an important and previously unconsidered role in many low-pressure discharges, and at least in part provides a possible explanation for anomalous behaviour often encountered in these plasmas. (10.1063/1.4859155)
  DOI : 10.1063/1.4859155
• Theory for the self-bias formation in capacitively coupled plasmas excited by arbitrary waveforms
  
  • Lafleur Trevor
  • Chabert Pascal
  • Turner M.M.
  • Booth Jean-Paul
  Plasma Sources Science and Technology, IOP Publishing, 2013, 22 (6), pp.065013. We develop a semi-analytical theory for the self-bias formation in capacitively coupled plasmas excited by arbitrary radio-frequency (rf) waveforms. The requirement of rf current continuity and voltage balance across the discharge results in the need for a self-bias voltage to develop with non-sinusoidal excitations, even in geometrically symmetric systems. The theory is compared extensively with a wide range of experimental and particle-in-cell (PIC) simulation data within the literature, and is found to be in excellent agreement. Furthermore, it is shown that the present theory is formally equivalent to the original model proposed by Heil et al (2008 J. Phys. D: Appl. Phys. 41 165202), but goes further by explicitly allowing the time-varying sheath voltages and symmetry parameter to be evaluated without input from PIC simulations. (10.1088/0963-0252/22/6/065013)
  DOI : 10.1088/0963-0252/22/6/065013
• Action diffusion and lifetimes of quasistationary states in the Hamiltonian Mean Field model
  
  • Ettoumi Wahb
  • Firpo Marie-Christine
  Physical Review E, American Physical Society (APS), 2013, 87, pp.030102(R). Out-of-equilibrium quasistationary states (QSSs) are one of the signatures of a broken ergodicity in long-range interacting systems. For the widely studied Hamiltonian Mean-Field model, the lifetime of some QSSs has been shown to diverge with the number N of degrees of freedom with a puzzling N¹.7 scaling law, contradicting the otherwise widespread N scaling law. It is shown here that this peculiar scaling arises from the locality properties of the dynamics captured through the computation of the diffusion coefficient in terms of the action variable. The use of a mean first passage time approach proves to be successful in explaining the non-trivial scaling at stake here, and sheds some light on another case, where lifetimes diverging as e^N above some critical energy have been reported. (10.1103/PhysRevE.87.030102)
  DOI : 10.1103/PhysRevE.87.030102
• Study of reconnection physics using laser-generated B fields
  
  • Smets Roch
  • Belmont Gérard
  • Aunai N.
  • Fuchs J. C.
  • Boniface C.
  • Aulanier G.
  , 2013.
• Capacitively coupled radio-frequency plasmas excited by tailored voltage waveforms
  
  • Lafleur Trevor
  • Delattre Pierre-Alexandre
  • Johnson E.V.
  • Booth Jean-Paul
  Plasma Physics and Controlled Fusion, IOP Publishing, 2013, 55 (12), pp.124002. By applying certain types of ?tailored? voltage waveforms (TVWs) to capacitively coupled plasmas, a dc self-bias and an asymmetric plasma response can be produced, even in geometrically symmetric reactors. Furthermore, these arbitrary applied waveforms can produce a number of interesting phenomena that are not present in typical single-frequency sinusoidal discharges. This electrical asymmetry effect presents emerging possibilities for the improved control of the ion energy and ion flux in these systems; parameters of vital importance to both etching and deposition applications for materials processing. With a combined research approach utilizing both experimental measurements, and particle-in-cell simulations, we review and extend recent investigations that study a particular class of TVW. The waveforms used have a pulse-type shape and are composed of a varying number of harmonic frequencies. This allows a strong self-bias to be produced, and causes most of the applied voltage to be dropped across a single sheath. Additionally, decreasing the pulse width (by increasing the number of harmonics), allows the plasma density and ion flux to be increased. Simulation and experimental results both demonstrate that this type of waveform can be used to separately control the ion flux and ion energy, while still producing a uniform plasma over large area (50 cm diameter) rf electrodes. (10.1088/0741-3335/55/12/124002)
  DOI : 10.1088/0741-3335/55/12/124002
• 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
• 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
• 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
• 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.