Publications

2018

• Non Thermal Plasmas interacting with surfaces at elevated pressures
  
  • Guaitella Olivier
  , 2018.
• Experimental investigation of the mean turbulent structure tilt angle in the ASDEX Upgrade tokamak
  
  • Pinzón J R
  • Angioni C.
  • Happel T.
  • Hennequin Pascale
  • Blanco E.
  • Estrada T.
  • Stroth U.
  • The Asdex Upgrade Mast
  • Tcv Teams
  , 2018.
• Poloidal asymmetry and dynamics of perpendicular flow in Tore Supra plasmas
  
  • Vermare Laure
  • Hennequin Pascale
  • Gürcan Özgür D.
  • Honoré Cyrille
  • Morel Pierre
  • Storelli A.
  • Donnel Peter
  • Garbet X.
  • Giacalone J-C.
  • Tore Supra Team And
  , 2018, pp.P5.1062.
• Turbulence measurements and gyrokinetic validation at ASDEX Upgrade
  
  • Freethy Simon
  • Görler T.
  • Creely A. J.
  • Conway G. D.
  • Denk S.
  • Happel T.
  • Hennequin Pascale
  • White A. E.
  • Asdex Upgrade Team The
  , 2018, pp.O4.109.
• Studying ELM filaments with Doppler reflectometry in ASDEX Upgrade
  
  • Trier Elisée
  • Hennequin Pascale
  • Pinzón J R
  • Hoelzl M.
  • Conway G. D.
  • Happel T.
  • Harrer G.
  • Mink F.
  • Orain F.
  • Wolfrum E.
  • Asdex Upgrade Team The
  • Mst1 Eurofusion Team The
  , 2018, 42A, pp.P1.1023.
• Experimental separation of core transport and edge pedestal isotope dependencies by variation of the plasma shape
  
  • Schneider P.
  • Angioni C.
  • Dunne M.
  • Cavedon M.
  • Hennequin Pascale
  • Kurzan B.
  • Manas P.
  • Mink F.
  • Mcdermott R.M.
  • Ryter F.
  • Willensdorfer M.
  • Wolfrum E.
  • Asdex Upgrade Team The
  , 2018, pp.P5.1078.
• Detailed Properties of Equatorial Noise With Quasiperiodic Modulation
  
  • Němec F.
  • Santolik O.
  • Hayosh M.
  • Darrouzet F.
  • Cornilleau-Wehrlin N.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2018, 123 (7), pp.5344-5355. (10.1029/2018JA025382)
  DOI : 10.1029/2018JA025382
• Internal plasma source requirement for geospace storms
  
  • Fok Mei-Ching
  • Moore Thomas E.
  • Garcia-Sage Katherine
  • Delcourt Dominique
  • Buzulukova N. Y.
  , 2018.
• Dependence on the ion mass and charge of a Fermi-like acceleration mechanism in the Earth’s magnetotail
  
  • Catapano Filomena
  • Zimbardo Gaetano
  • Perri Silvia
  • Greco Antonella
  • Delcourt Dominique
  • Retino Alessandro
  , 2018.
• Statistical Study of the Properties of Magnetosheath Lion Roars
  
  • Giagkiozis Stefanos
  • Wilson Lynn
  • Burch James
  • Le Contel Olivier
  • Ergun Robert
  • Gershman Daniel
  • Lindqvist Per-Arne
  • Mirioni Laurent
  • Moore Thomas
  • Strangeway Robert
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2018, 123 (7), pp.5435-5451. (10.1029/2018JA025343)
  DOI : 10.1029/2018JA025343
• INDEMN, a long-term collision risk prediction tool for constellation design
  
  • Lucken Romain
  • Giolito Damien
  , 2018.
• Fast and Widely-tunable, VBG Spectrally Narrowed, Picosecond Optical Parametric Oscillator for Backscatter Absorption Gas Imaging
  
  • Walter Guillaume
  • Dherbecourt Jean-Baptiste
  • Melkonian Jean-Michel
  • Raybaut Myriam
  • Henry Didier
  • Drag Cyril
  • Godard Antoine
  , 2018. We implement a fast and widely tunable picosecond OPO, based on an aperiodicallypoled ,nonlinear crystal, tuned and spectrally narrowed by a chirped VBG, for backscatter absorption gas imaging of N2O around 3.82 μm. (10.1364/LACSEA.2018.LM5C.3)
  DOI : 10.1364/LACSEA.2018.LM5C.3
• High-resolution VUV absorption diagnostics of discharges in oxygen
  
  • Booth Jean-Paul
  , 2018. Electrical discharges in oxygen gas are widespread in nature and occur in many plasma applications such as surface treatment and plasma medicine. They are also an ideal archetype for the understanding of molecular plasmas, showing the effects of dissociation/surface recombination, electron attachment, high densities of molecular and atomic metastable states, vibrational excitation and gas heating. Nevertheless, many uncertainties remain concerning the cross-section and reaction sets, as well as surface processes, all necessary for reliable modelling. We are making comprehensive measurements of transient species absolute densities and kinetics in a well-characterised and reproducible system, a DC positive column in pure O2.. This provides a uniform plasma column with constant reduced field over a wide range of gas pressure and electron density (pressure 0.2-10 Torr, current 5-40 mA), ideal for model validation. We employ a range of powerful diagnostic techniques, including vacuum ultraviolet absorption spectroscopy (120-200nm) using the unique DESIRS beamline at synchrotron Soleil. The Fourier-Transform branch was used to record absorption spectra with a resolution of 106, giving complete high-resolution spectra of O2 in the X, a and b states. The absorption cross-sections of O2 X and a are known, allowing absolute densities to be determined. However, some differences in the spectra are seen due to our superior resolution. Using a combination of ab-initio calculations and absolute emission spectrometry, we have derived the first absolute absorption cross-sections of O2 b, and therefore the absolute density of this state. The absolute density of oxygen atoms is a critical but hard to measure parameter. It is needed to calculate the electron-impact dissociation cross-section. Unfortunately, the resonance lines at 130nm are entirely saturated and therefore useless. However, we able to demonstrate absorption via the forbidden 5S203P2 transition at 135.56nm, allowing relative [O] measurements by other techniques (actinometry, TALIF) to be calibrated. We also performed time-resolved measurements of O2 X, a and b during both full and partial modulation of the discharge current, using the monochromatic branch of the VUV beamline, allowing their creation and loss kinetics (in the gas phase and on the tube surface) to be probed. However, interpretation of this data is complicated by both gas temperature variations and spectral overlap, causing both gas density modulation and possibly spectral shape changes. An improved, dual-beam setup is under development to address these issues. Measurements were also performed in a low-pressure (10-50 mTorr) ICP discharge, giving the absolute O2 X, a and b densities as a function of pressure and RF power, allowing recent speculation on the role of metastable states to be tested.
• High−resolution VUV absorption diagnostics of discharges in oxygen
  
  • Booth Jean-Paul
  • Chatterjee Abhyuday
  • Guaitella Olivier
  • de Oliveira N.
  • Nahon L.
  • Western Colin
  , 2018.
• The I-mode confinement regime on the ASDEX Upgrade tokamak: scrape-off layer properties and investigation of stationary and transient divertor heat loads
  
  • Happel T.
  • Griener M.
  • Silvagni D.
  • Freethy Simon
  • Hennequin Pascale
  • Janky F.
  • Manz P.
  • Nille D.
  • Ryter F.
  • Asdex Upgrade Team The
  , 2018.
• Determination of charge density in an atmospheric pressure plasma jet via electric field measurements and simulations
  
  • Damany Xavier
  • Viegas Pedro
  • Pouvesle Jean-Michel
  • Dozias Sébastien
  • Bourdon Anne
  • Eric Robert
  , 2018. Atmospheric pressure plasma jets have been extensively studied for several years as they showed very promising results in numerous fields such as material processing or plasma medicine. What makes cold plasma interesting is the presence of electrons, ions, reactive oxygen and nitrogen species, visible and UV light and high transient electric fields (EF). Even if the latter play a key role, from the production and propagation of the plasma to the efficiency of applications, they are far from being fully understood. This work focuses on the comparison of measurements of EF produced by a Plasma Gun (PG) discharge with an electro-optic probe based on Pockels effect [1] with 2D simulations of atmospheric pressure discharges propagating in a geometry close to the Plasma Gun’s one. Plasma Gun consists in a vertically downward oriented capillary with an inner high-voltage electrode and an outer grounded one. Plasma is powered with μs-duration voltage pulses from single shot to 4kHz. In [2] the electric field is evaluated by the simulations inside the capillary, in the glass and outside. The aim of this work is to compare the radial profile of the electric field outside the capillary between experiments and simulations to get information on the plasma inside it. The electro-optic probe was placed at different levels alongside the capillary and was getting far from it. Measurements were executed every 5mm over 5cm. At the middle of the capillary a decrease inversely proportional to the distance has been found. It reminds the shape of an EF produced by an infinite uniformly charged cylinder. 2D simulations were in a good agreement finding also the same slope for EF. But simulations permit also to get information on the distribution of charge density and especially to know if the main contribution is from volume or surface charge density. Results show that the radial profile of EF outside the tube is mostly determined by the volume charge density in positive polarity while in negative polarity the surface charge density is dominant. Simulations have provided values of average volume charge density in the order of 7.5 nC/cm3 in positive polarity and of average surface charge density around 1nC/cm² in negative polarity. Near the electrodes, a decrease inversely proportional to the square of the distance has been found, showing that there is an axial position dependence. A time dependence investigation will also be presented. X.D. acknowledges his grant funding Thermofisher Scientific INEL/Région Centre Val de Loire. References [1] G. Gaborit et al., IEEE Trans. Plasma Sci., 42 (2014). [2] P. Viegas, F. Pechereau and A. Bourdon, Plasma Source Science and Technology, in press (2018)
• Turbulence compressible aux échelles MHD et cinétiques dans les plasmas spatiaux: théories et observations in-situ
  
  • Sahraoui Fouad
  , 2018.
• Echelles et dynamique de la turbulence, observations par diffusion de la lumière dans les plasmas de tokamak
  
  • Hennequin Pascale
  , 2018.
• Wavenumber space patterns in fluid and plasma turbulence
  
  • Gürcan Özgür D.
  , 2018.
• The effect of alternative propellants on the electron drift instability in Hall-effect thrusters: Insight from 2D particle-in-cell simulations
  
  • Croes Vivien
  • Tavant Antoine
  • Lucken Romain
  • Martorelli Roberto
  • Lafleur Trevor
  • Bourdon Anne
  • Chabert Pascal
  Physics of Plasmas, American Institute of Physics, 2018, 25 (6). Hall-effect thrusters (HETs) operated with xenon are one of the most commonly used electric propulsion technologies for a wide range of space missions, including drag compensation in low Earth orbit, station-keeping, and orbital insertion, as access to space becomes more affordable. Although anomalous electron transport, the electron drift instability (EDI), and secondary electron emission (SEE) have been studied experimentally and numerically in xenon-based HETs, the impact of alternative propellants is still poorly characterized. In this work, a two-dimensional particle-in-cell/Monte Carlo collision code is used to model the (r – θ) plane of a HET operated separately with four different noble gases: xenon, krypton, argon, and helium. Models for electron induced secondary electron emission (SEE) and dielectric walls are implemented in order to investigate the coupling between the propellant choice and the radial thruster walls. For all conditions and propellants studied, an EDI and enhanced electron cross-field transport are observed. The frequency of the instability, as well as the electron mobility, is compared with analytical expressions from a recently developed kinetic theory. Confirming this theory, it is shown that while the frequency of the EDI depends on the propellant mass, the electron mobility appears to be almost independent of the propellant choice. (10.1063/1.5033492)
  DOI : 10.1063/1.5033492
• Fluctuations measurements from core to edge: examples of constraints for confrontation to simulations
  
  • Hennequin Pascale
  , 2018.
• Multi-species experimental validation of plasma chemistry models at atmospheric pressure
  
  • Schröter Sandra
  • Wijiakaum A.
  • Gibson Andrew
  • Bredin Jérôme
  • Niemi K.
  • West A.
  • Gorbanev Y.
  • Davies H.
  • Minesi Nicolas
  • de Oliveira N.
  • Nahon L.
  • Dedrick J.
  • Booth Jean-Paul
  • Chechik V.
  • Kushner M.J.
  • Wagenaars E.
  • Gans T.
  • O'Connell D.
  , 2018.
• Advances in turbulence measurements using new Correlation ECE and nT-phase diagnostics at ASDEX Upgrade
  
  • Freethy Simon
  • Görler T.
  • Creely A. J.
  • Conway G. D.
  • Happel T.
  • Könen C.
  • Hennequin Pascale
  • White A. E.
  • Asdex Upgrade Team The
  , 2018.
• Backscatter Absorption Gas Imaging with a Narrow-Linewidth Picosecond Optical Parametric Oscillator
  
  • Walter Guillaume
  • Dherbecourt Jean-Baptiste
  • Melkonian Jean-Michel
  • Raybaut Myriam
  • Henry Didier
  • Drag Cyril
  • Godard Antoine
  , 2018.
• Étude numérique dans une décharge capillaire nanoseconde et dans la décharge contrôlée par barrière diélectrique surfacique : Cinétiques, Transport et Réponses de fluide
  
  • Zhu Yifei
  , 2018. Nanosecond pulsed discharges are characterized by high reduced electric fields (hundreds of Td) and strong nonequilibrium. They have characteristic electron energies of a few to tens of eV and specific energy deposition ranging from 10⁻³ eV/mol to a few eV/mol. The energetic electrons can efficiently generate chemical active species, lead to fast gas heating. These discharges are found in a growing list of successful practical applications: gas pollution control, surface treatment, plasma assisted aerodynamics, plasma assisted biology and medicine and plasma assisted combustion.Two particular configurations are studied in present work: (i) nanosecond capillary discharge (nCD) operated at moderate pressures and high specific deposited energy, and (ii) nanosecond surface dielectric barrier discharge (nSDBD) operated at atmospheric or higher pressures and relatively low specific deposited energy.Nanosecond capillary discharge is an experimental tool to analyse nanosecond plasma in some limit extreme conditions. Recent nCD experiments revealed that, plasma kinetics changes dramatically at high specific energy deposition. One of the aims of the present work, is to study numerically the effects of the changed kinetics to the classical actinometry measurement technique, and the spatial-temporal evolution of plasmas during discharge and afterglow. Nanosecond surface dielectric barrier discharge has been widely studied in the community of aerodynamics. However, at the moment of starting the thesis, the parameters of nSDBD plasma were not yet clearly understood, detailed comparison of numerical calculations and experiments were not available. Therefore, modelling of nSDBD and comparison with experiments performed for the same parameters is another object of the presented thesis.The results in the thesis are presented in three parts. In the first part, numerical modelling and experiment of Ar-based actinometry are used to study the atomic oxygen density in nanosecond capillary discharge. A kinetic scheme describing consistent behavior of the set of the experimental data is developed. The main processes responsible for population and decay of the three species of interest are selected on the basis of sensitivity and rate analysis. The role of the reactions between excited species and electrons in early afterglow for pulsed discharges at high electric fields and high values of specific deposited energy is discussed. Density of O-atoms in the ground state is obtained from the calculations.The second part is devoted to study, analyse and predict the features of the discharge and afterglow of nCD under different specific energy deposition based on a two--dimensional self-consistent code, nonPDPsim. Propagation of the discharge have been modelled. Two modes of propagation were identified, three shapes of ionization waves are found with various tube radius. The decay rate and radial distribution of electrons and N₂(C³Πu) in the afterglow are studied with respect to specific energy deposition. Finally, a two--dimensional parallel PASSKEy ("PArallel Streamer Solver with KinEtics") code coupling plasma and hydrodynamics has been developed and validated to model nSDBD. Series of numerical calculations for a single pulse nSDBD in atmospheric pressure air at 24~kV voltage amplitude has been performed, the results were compared with experiments in the same conditions. Calculated and measured velocity of the discharge front, electrical current, 2D map of emission of N₂(C³Πu)→ N₂(B³Πg), and hydrodynamic perturbations caused by the discharge on the time scale 0.2-5~µs are analysed. The effect of different kinetics processes in 2D distribution of heat release is studied. The data are presented and analyzed for negative and positive polarity of voltages. A set of parametric calculations with different dielectric permittivity, the thickness of dielectric and ambient pressures are presented.