Publications

2014

Mars-Solar Wind Interaction: Coupling Between Hybrid, Ionospheric, Thermospheric and Exospheric Models
- Leblanc François
- Chaufray Jean-Yves
- Modolo Ronan
- Hess Sebastien
- Yagi M.
- Mancini M.
- Forget François
- Gonzalez-Galindo Francisco
- Lorenzato L.
- Mazelle Christian
- Chanteur Gérard
, 2014. The solar wind interaction with the Martian neutral envi- ronment is investigated by means of three dimensional hybrid magnetospheric simulations. In such formal- ism, ions have a kinetic description while electrons are treated as an inertialess fluid, ensuring the neutrality of the plasma and contributing to currents and pressure terms. This model has been successfully used to de- scribe the near ionized environment of Mars
Experimental and numerical study of fast gas heating and O atom production in a capillary nanosecond discharge
- Klochko A.V.
- Salmon A.
- Lemainque J.
- Popov N.A.
- Booth Jean-Paul
- Xiong Z.
- Kushner M.J.
- Starikovskaia Svetlana
, 2014, pp.2014-1030.
Ignition of CH4:O2:Ar and n-C4H10:O2:Ar(N2) mixtures with initial temperatures between 650-950 K by a surface pulsed discharge
- Stepanyan S.A.
- Boumehdi M.A.
- Vanhove G.
- Desgroux Pascale
- Starikovskaia Svetlana
- Popov N.A.
, 2014. (10.2514/6.2014-0665)
DOI : 10.2514/6.2014-0665
Adsorption, desorption and reactivity of O and N atoms on SiO2 surface
- Rousseau Antoine
, 2014.
New ferromagnetic core shapes for induction sensors
- Coillot Christophe
- Moutoussamy Joël
- Boda Mathieu
- Leroy Paul
Journal of Sensors and Sensor Systems, Copernicus Publ, 2014, pp.1-8. Induction sensors are used in a wide range of scientific and industrial applications. One way to improve these is rigorous modelling of the sensor combined with a low voltage and current input noise preamplifier aiming to optimize the whole induction magnetometer. In this paper, we explore another way, which consists in the use of original ferromagnetic core shapes of induction sensors, which bring substantial improvements. These new configurations are the cubic, orthogonal and coiled-core induction sensors. For each of them we give modelling elements and discuss their benefits and drawbacks with respect to a given noise-equivalent magnetic induction goal. Our discussion is supported by experimental results for the cubic and orthogonal configurations, while the coiled-core configuration remains open to experimental validation. The transposition of these induction sensor configurations to other magnetic sensors (fluxgate and giant magneto-impedance) is an exciting prospect of this work. (10.5194/jsss-3-1-2014)
DOI : 10.5194/jsss-3-1-2014
Multi Water Bag modelling of drift kinetic electrons and ions plasmas
- Morel Pierre
- Dreydemy Ghiro Florent
- Berionni Vincent
- Gürcan Özgür D.
, 2014.
Spatial Propagation of Turbulence and Formation of Mesoscopic Structures in Plasma Turbulence
- Dif-Pradalier Guilhem
- Ghendrih Ph.
- Diamond P.H.
- Garbet X.
- Grandgirard V.
- Norscini C.
- Palermo F.
- Sarazin Y.
- Abiteboul J.
- Dong Yue
- Gürcan Özgür D.
- Hennequin Pascale
- Morel Pierre
- Vermare Laure
- Kosuga Y.
, 2014.
Radiation sources with planar wire arrays and planar foils for inertial confinement fusion and high energy density physics research
- Kantsyrev Viktor L.
- Chuvatin Alexandre S.
- Safronova Alla S.
- Rudakov Leonid I.
- Esaulov A. A.
- Velikovich A. L.
- Shrestha Ishor
- Astanovitsky A.
- Osborne Glenn C.
- Shlyaptseva V. V.
- Weller Michael E.
- Keim S.
- Stafford A.
- Cooper M. C.
Physics of Plasmas, American Institute of Physics, 2014, 21 (03), pp.031204. This article reports on the joint success of two independent lines of research, each of them being a multi-year international effort. One of these is the development of innovative sources, such as planar wire arrays (PWAs). PWAs turned out to be a prolific radiator, which act mainly as a resistor, even though the physical mechanism of efficient magnetic energy conversion into radiation still remains unclear. We review the results of our extensive studies of PWAs. We also report the new results of the experimental comparison PWAs with planar foil liners (another promising alternative to wire array loads at multi-mega-ampere generators). Pioneered at UNR, the PWA Z-pinch loads have later been tested at the Sandia National Laboratories (SNL) on the Saturn generator, on GIT-12 machine in Russia, and on the QiangGuang-1 generator in China, always successfully. Another of these is the drastic improvement in energy efficiency of pulsed-power systems, which started in early 1980s with Zucker's experiments at Naval Research Laboratory (NRL). Successful continuation of this approach was the Load Current Multiplier (LCM) proposed by Chuvatin in collaboration with Rudakov and Weber from NRL. The 100 ns LCM was integrated into the Zebra generator, which almost doubled the plasma load current, from 0.9 to 1.7 MA. The two above-mentioned innovative approaches were used in combination to produce a new compact hohlraum radiation source for ICF, as jointly proposed by SNL and UNR [Jones et al., Phys. Rev. Lett. 104, 125001 (2010)]. The first successful proof-of-the-principle experimental implementation of new hohlraum concept at university-scale generator Zebra/LCM is demonstrated. A numerical simulation capability with VisRaD code (from PRISM Co.) established at UNR allowed for the study of hohlraum coupling physics and provides the possibility of optimization of a new hohlraum. Future studies are discussed. (10.1063/1.4865367)
DOI : 10.1063/1.4865367
Turbulence elasticity-A new mechanism for transport barrier dynamics
- Guo Z. B.
- Diamond P.H.
- Kosuga Y.
- Gürcan Özgür D.
Physics of Plasmas, American Institute of Physics, 2014, 21 (9). We present a new, unified model of transport barrier formation in ``elastic'' drift wave-zonal flow (DW-ZF) turbulence. A new physical quantity-the delay time (i.e., the mixing time for the DW turbulence)-is demonstrated to parameterize each stage of the transport barrier formation. Quantitative predictions for the onset of limit-cycle-oscillation (LCO) among DW and ZF intensities (also denoted as I-mode) and I-mode to high-confinement mode (H-mode) transition are also given. The LCO occurs when the ZF shearing rate (vertical bar (ZF)'vertical bar) enters the regime Delta omega(k) < vertical bar < V >(ZF)'vertical bar < tau(-1)(cr), where Delta omega(k) is the local turbulence decorrelation rate and tau(cr) is the threshold delay time. In the basic predator-prey feedback system, tau(cr) is also derived. The I-H transition occurs when vertical bar < V >(ExB)'vertical bar > tau(-1)(cr), where the mean E x B shear flow driven by ion pressure ``locks'' the DW-ZF system to the H-mode by reducing the delay time below the threshold value. (C) 2014 AIP Publishing LLC. (10.1063/1.4894695)
DOI : 10.1063/1.4894695
Complete multi-field characterization of the geodesic acoustic mode in the TCV tokamak
- de Meijere C. A.
- Coda S.
- Huang Z.
- Vermare Laure
- Vernay T.
- Vuille V.
- Brunner Stephan
- Dominski J.
- Hennequin Pascale
- Kraemer-Flecken A.
- Merlo G.
- Porte L.
- Villard Laurent
Plasma Physics and Controlled Fusion, IOP Publishing, 2014, 56 (7), pp.072001. The geodesic acoustic mode (GAM) is a coherently oscillating zonal flow that may regulate turbulence in toroidal plasmas. Uniquely, the complete poloidal and toroidal structure of the magnetic component of the turbulence-driven GAM has been mapped in the TCV tokamak. Radially localized measurements of the fluctuating density, ECE radiative temperature and poloidal flow show that the GAM is a fully coherent, radially propagating wave. These observations are consistent with electrostatic, gyrokinetic simulations. (10.1088/0741-3335/56/7/072001)
DOI : 10.1088/0741-3335/56/7/072001
The FIELDS Instrument Suite on MMS: Scientific Objectives, Measurements, and Data Products
- Torbert R. B.
- Russell C. T.
- Magnes W.
- Ergun R. E.
- Lindqvist P.-A.
- Le Contel Olivier
- Vaith H.
- Macri J.
- Myers S.
- Rau D.
- Needell J.
- King B.
- Granoff M.
- Chutter M.
- Dors I.
- Olsson G.
- Khotyaintsev Y. V.
- Eriksson A.
- Kletzing C. A.
- Bounds S.
- Anderson B.
- Baumjohann W.
- Steller M.
- Bromund K.
- Le G.
- Nakamura R.
- Strangeway R. J.
- Leinweber H. K.
- Tucker S.
- Westfall J.
- Fischer D.
- Plaschke F.
- Porter J.
- Lappalainen K.
Space Science Reviews, Springer Verlag, 2014, pp.1-31. Not Available (10.1007/s11214-014-0109-8)
DOI : 10.1007/s11214-014-0109-8
Circulation of Heavy Ions and Their Dynamical Effects in the Magnetosphere: Recent Observations and Models
- Kronberg E. A.
- Ashour-Abdalla M.
- Dandouras I.
- Delcourt Dominique C.
- Grigorenko E. E.
- Kistler L. M.
- Kuzichev I. V.
- Liao J.
- Maggiolo R.
- Malova H. V.
- Orlova K. G.
- Peroomian V.
- Shklyar D. R.
- Shprits Y. Y.
- Welling D. T.
- Zelenyi L. M.
Space Science Reviews, Springer Verlag, 2014, 184 (1-4), pp.173-235. Knowledge of the ion composition in the near-Earths magnetosphere and plasma sheet is essential for the understanding of magnetospheric processes and instabilities. The presence of heavy ions of ionospheric origin in the magnetosphere, in particular oxygen (O ), influences the plasma sheet bulk properties, current sheet (CS) thickness and its structure. It affects reconnection rates and the formation of Kelvin-Helmholtz instabilities. This has profound consequences for the global magnetospheric dynamics, including geomagnetic storms and substorm-like events. The formation and demise of the ring current and the radiation belts are also dependent on the presence of heavy ions. In this review we cover recent advances in observations and models of the circulation of heavy ions in the magnetosphere, considering sources, transport, acceleration, bulk properties, and the influence on the magnetospheric dynamics. We identify important open questions and promising avenues for future research. (10.1007/s11214-014-0104-0)
DOI : 10.1007/s11214-014-0104-0
On the origin of falling-tone chorus elements in Earth's inner magnetosphere
- Breuillard H
- Agapitov O
- Artemyev A
- Krasnoselskikh V
- Le Contel Olivier
- Cully C. M.
- Angelopoulos V
- Zaliznyak Y
- Rolland G
Annales Geophysicae, European Geosciences Union, 2014, 32, pp.1477-1485. Generation of extremely/very low frequency (ELF/VLF) chorus waves in Earth's inner magnetosphere has received increased attention recently because of their significance for radiation belt dynamics. Though past theoretical and numerical models have demonstrated how rising-tone chorus elements are produced, falling-tone chorus element generation has yet to be explained. Our new model proposes that weak-amplitude falling-tone chorus elements can be generated by magnetospheric reflection of rising-tone elements. Using ray tracing in a realistic plasma model of the inner magnetosphere, we demonstrate that rising-tone elements originating at the magnetic equator propagate to higher latitudes. Upon reflection there, they propagate to lower L-shells and turn into oblique falling tones of reduced power, frequency, and bandwidth relative to their progenitor rising tones. Our results are in good agreement with comprehensive statistical studies of such waves, notably using magnetic field measurements from THEMIS (Time History of Events and Macroscale Interactions during Substorms) spacecraft. Thus, we conclude that the proposed mechanism can be responsible for the generation of weak-amplitude falling-tone chorus emissions. (10.5194/angeo-32-1477-2014)
DOI : 10.5194/angeo-32-1477-2014
Ion flux asymmetry in radiofrequency capacitively-coupled plasmas excited by sawtooth-like waveforms
- Bruneau Bastien
- Novikova T.
- Lafleur Trevor
- Booth Jean-Paul
- Johnson E.V.
Plasma Sources Science and Technology, IOP Publishing, 2014, 23 (6), pp.065010. Using particle-in-cell simulations, we predict that it is possible to obtain a significant difference between the ion flux to the powered electrode and that to the grounded electrode?with about 50% higher ion flux on one electrode?in a geometrically symmetric, radiofrequency capacitively-coupled plasma reactor by applying a non-sinusoidal, ?Tailored? voltage waveform. This sawtooth-like waveform presents different rising and falling slopes over one cycle. We show that this effect is due to differing plasma sheath motion in front of each electrode, which induces a higher ionization rate in front of the electrode which has the fastest positive rising voltage. Together with the higher ion flux comes a lower voltage drop across the sheath, and therefore a reduced maximum ion bombardment energy; a result in contrast to typical process control mechanisms. (10.1088/0963-0252/23/6/065010)
DOI : 10.1088/0963-0252/23/6/065010
Plasma-assisted ignition and combustion: nanosecond discharges and development of kinetic mechanisms
- Starikovskaia Svetlana
Journal of Physics D: Applied Physics, IOP Publishing, 2014, 47 (35), pp.353001 (34pp). This review covers the results obtained in the period 20062014 in the field of plasma-assisted combustion, and in particular the results on ignition and combustion triggered or sustained by pulsed nanosecond discharges in different geometries. Some benefits of pulsed high voltage discharges for kinetic study and for applications are demonstrated. The necessity of and the possibility of building a particular kinetic mechanism of plasma-assisted ignition and combustion are discussed. The most sensitive regions of parameters for plasmacombustion kinetic mechanisms are selected. A map of the pressure and temperature parameters (PT diagram) is suggested, to unify the available data on ignition delay times, ignition lengths and densities of intermediate species reported by different authors. (10.1088/0022-3727/47/35/353001)
DOI : 10.1088/0022-3727/47/35/353001
What is the size of a floating sheath?
- Chabert Pascal
Plasma Sources Science and Technology, IOP Publishing, 2014, 23 (6), pp.065042. The size of the positive space charge sheath that forms in front of an object immersed in a plasma and not dc-connected to ground with an external circuit (a floating sheath) is calculated numerically. If the sheath edge is defined as the position at which the ion fluid speed equals the Bohm speed, it is shown that the sheath size varies significantly with the discharge parameters, typically from s float ≈ 7 λ Des to s float ≈ 14 λ Des , where s float is the floating sheath size and λ Des is the Debye length at the sheath edge. However, if the sheath edge is defined as a significant departure from quasi-neutrality, then the floating sheath size is almost independent of the discharge parameters and may be approximated by s float ≈ 5 λ Des . (10.1088/0963-0252/23/6/065042)
DOI : 10.1088/0963-0252/23/6/065042
Evolution of Turbulence in the Expanding Solar Wind, a Numerical Study
- Dong Yue
- Verdini Andrea
- Grappin Roland
The Astrophysical Journal, American Astronomical Society, 2014, 793, pp.118. We study the evolution of turbulence in the solar wind by solving numerically the full three-dimensional (3D) magnetohydrodynamic (MHD) equations embedded in a radial mean wind. The corresponding equations (expanding box model or EBM) have been considered earlier but never integrated in 3D simulations. Here, we follow the development of turbulence from 0.2 AU up to about 1.5 AU. Starting with isotropic spectra scaling as k -1, we observe a steepening toward a k -5/3 scaling in the middle of the wave number range and formation of spectral anisotropies. The advection of a plasma volume by the expanding solar wind causes a non-trivial stretching of the volume in directions transverse to radial and the selective decay of the components of velocity and magnetic fluctuations. These two effects combine to yield the following results. (1) Spectral anisotropy: gyrotropy is broken, and the radial wave vectors have most of the power. (2) Coherent structures: radial streams emerge that resemble the observed microjets. (3) Energy spectra per component: they show an ordering in good agreement with the one observed in the solar wind at 1 AU. The latter point includes a global dominance of the magnetic energy over kinetic energy in the inertial and f -1 range and a dominance of the perpendicular-to-the-radial components over the radial components in the inertial range. We conclude that many of the above properties are the result of evolution during transport in the heliosphere, and not just the remnant of the initial turbulence close to the Sun. (10.1088/0004-637X/793/2/118)
DOI : 10.1088/0004-637X/793/2/118
The influence of the geometry and electrical characteristics on the formation of the atmospheric pressure plasma jet
- Sobota Ana
- Guaitella Olivier
- Rousseau Antoine
Plasma Sources Science and Technology, IOP Publishing, 2014, 23, pp.025016. An extensive electrical study was performed on a coaxial geometry atmospheric pressure plasma jet source in helium, driven by 30 kHz sine voltage. Two modes of operation were observed, a highly reproducible low-power mode that features the emission of one plasma bullet per voltage period and an erratic high-power mode in which micro-discharges appear around the grounded electrode. The minimum of power transfer efficiency corresponds to the transition between the two modes. Effective capacitance was identified as a varying property influenced by the discharge and the dissipated power. The charge carried by plasma bullets was found to be a small fraction of charge produced in the source irrespective of input power and configuration of the grounded electrode. The biggest part of the produced charge stays localized in the plasma source and below the grounded electrode, in the range 1.23.3 nC for ground length of 38 mm. (10.1088/0963-0252/23/2/025016)
DOI : 10.1088/0963-0252/23/2/025016
Ionospheric disturbance dynamo associated to a coronal hole: Case study of 5-10 April 2010
- Fathy Ibrahim
- Amory-Mazaudier Christine
- Fathy A.
- Mahrous A. M.
- Yumoto K.
- Ghamry E.
Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2014, 119 (5), pp.4120–4133. In this paper we study the planetary magnetic disturbance during the magnetic storm occurring on 5 April 2010 associated with high-speed solar wind stream due to a coronal hole following a coronal mass ejection. We separate the magnetic disturbance associated to the ionospheric disturbance dynamo (Ddyn) from the magnetic disturbance associated to the prompt penetration of magnetospheric electric field (DP2). This event exhibits different responses of ionospheric disturbance dynamo in the different longitude sectors (European-African, Asian, and American). The strongest effect is observed in the European-African sector. The Ddyn disturbance reduces the amplitude of the daytime H component at low latitudes during four consecutive days in agreement with the Blanc and Richmond's model of ionospheric disturbance dynamo. The amplitude of Ddyn decreased with time during the 4 days. We discuss its diverse worldwide effects. The observed signature of magnetic disturbance process in specific longitude sector is strongly dependent on which Earth's side faces the magnetic storms (i.e., there is a different response depending on which longitude sector is at noon when the SSC hits). Finally, we determined an average period of 22 h for Ddyn using wavelet analysis. (10.1002/2013JA019510)
DOI : 10.1002/2013JA019510
A nanosecond surface dieletric barrier discharge in air at high pressure and different polarities of applied pulses. Transition to filamentary mode
- Stepanyan S.A.
- Starikovskiy a Yu
- Popov N.A.
- Starikovskaia Svetlana
Plasma Sources Science and Technology, IOP Publishing, 2014, 23 (4), pp.045003. The development of a nanosecond surface dielectric barrier discharge in air at pressures 16 bar is studied. At atmospheric pressure, the discharge develops as a set of streamers starting synchronously from the high-voltage electrode and propagating along the dielectric layer. Streamers cover the dielectric surface creating a 'quasi-uniform' plasma layer. At high pressures and high voltage amplitudes on the cathode, filamentation of the discharge is observed a few nanoseconds after the discharge starts. Parameters of the observed 'streamers-to-filaments' transition are measured; physics of transition is discussed on the basis of theoretical estimates and numerical modeling. Ionization-heating instability on the boundary of the cathode layer is suggested as a mechanism of filamentation. (10.1088/0963-0252/23/4/045003)
DOI : 10.1088/0963-0252/23/4/045003
Oxidation of isopropanol and acetone adsorbed on TiO2 under plasma generated ozone flow: Gas phase and adsorbed species monitoring
- Barakat Christelle
- Gravejat Paul
- Guaitella Olivier
- Thévenet Frédéric
- Rousseau Antoine
Applied Catalysis B: Environmental, Elsevier, 2014, 147, pp.302-313. The regeneration of isopropanol (IPA) and/or acetone saturated TiO2 surface by ozone is investigated. TiO2 catalyst is placed downstream a dielectric barrier discharge and is subsequently exposed to ozone considered as the main oxidative species generated by non-thermal plasma and able to interact with the material surface at room temperature. The oxidation of isopropanol and/or acetone is monitored using two parallel and complementary infrared diagnostics: (1) Fourier Transform Infrared Spectroscopy for the analysis of the gas phase composition; and (2) Diffuse Reflectance Infrared Fourier Transform Spectroscopy for the in situ analysis of the adsorbent/catalyst surface. In this study, the pollutant is first adsorbed on the TiO2 surface, the plasma being switched off. The irreversibly adsorbed amounts of isopropanol and acetone have been respectively quantified as 5.3 μmol/m2 and 1.9 μmol/m2. In a second step, the plasma is switched on to regenerate the surface by mineralization of the adsorbed organic species. A 70-min plasma phase, with approximately 20 ppm of ozone constantly flowing through the adsorbent bed yields 8.5 nmol and 8.9 nmol of CO2 per injected joule of energy for isopropanol and acetone saturated surfaces, respectively. Acetone has been evidenced as the main oxidation intermediate of isopropanol on TiO2 surface. It has been proven that the complete oxidation of isopropanol and acetone is mainly limited by the acetone oxidation rate. Competitive adsorption on the surface of the catalyst between both compounds has been studied. Results obtained are compared with those observed in the photocatalytic oxidation of the same species. (10.1016/j.apcatb.2013.09.008)
DOI : 10.1016/j.apcatb.2013.09.008
Surface deactivation of vibrationally excited N2 studied using infrared titration combined with quantum cascade laser absorption spectroscopy
- Marinov Daniil
- Lopatik D.
- Guaitella Olivier
- Ionikh Y.
- Röpcke J.
- Rousseau Antoine
Journal of Physics D: Applied Physics, IOP Publishing, 2014, 47 (1), pp.015203. The wall de-excitation probability of vibrationally excited nitrogen molecules was determined using infrared (IR) titration with CO, CO 2 and N 2 O. Gas mixtures of N 2 with 0.05?0.5% of CO (CO 2 or N 2 O) were excited by a pulsed dc discharge at p = 133 Pa in a cylindrical discharge tube. During the afterglow, the vibrational relaxation of titrating molecules was monitored in situ with quantum cascade laser absorption spectroscopy. The value of was deduced from measured vibrational relaxation times using a model of vibrational kinetics in N 2 . It was found that adsorption of IR tracers on the surface may increase the value of by a factor up to two, depending on the molecule and the surface material. It was demonstrated that N 2 O is the most inert and reliable tracer and it was used for the determination of on silica, Pyrex, TiO 2 , Al 2 O 3 and anodized aluminum. Pretreatment of the silica surface by low-pressure plasma was found to have a strong effect on the vibrational de-excitation. Values of measured after O 2 , Ar and N 2 plasma pretreatment of the same silica discharge tube were 5.7 × 10 ?4 , 8.2 × 10 ?4 and 11 × 10 ?4 , respectively. This study clearly demonstrates that the presence of adsorbed atoms and molecules on the surface may significantly alter the value of . (10.1088/0022-3727/47/1/015203)
DOI : 10.1088/0022-3727/47/1/015203
Ambipolar and non-ambipolar diffusion in an rf plasma source containing a magnetic filter
- Lafleur Trevor
- Aanesland Ane
Physics of Plasmas, American Institute of Physics, 2014, 21, pp.063510. By placing a magnetic filter across a rectangular plasma source (closed at one end with a ceramic plate and an rf antenna, and terminated at the opposite end by a grounded grid), we experimentally investigate the effect of conducting and insulating source walls on the nature of the plasma diffusion phenomena. The use of a magnetic filter creates a unique plasma, characterized by a high upstream electron temperature (Teu∼5 eV) near the rf antenna and a low downstream electron temperature (Ted∼1 eV) near the grid, which more clearly demonstrates the role of the source wall materials. For conducting walls a net ion current to ground is measured on the grid, and the plasma potential is determined by a mean electron temperature within the source. For insulating walls the plasma potential is determined by the downstream electron temperature (i.e., Vp∼5.2Ted in argon), and the net current to the grid is exactly zero. Furthermore, by inserting a small additional upstream conductor (that can be made floating or grounded through an external circuit switch), we demonstrate that the plasma potential can be controlled and set to a low (Vp∼5.2Ted), or high (Vp∼5.2Teu) value. (10.1063/1.4885109)
DOI : 10.1063/1.4885109
A radio-frequency sheath model for complex waveforms
- Turner M.M.
- Chabert Pascal
Applied Physics Letters, American Institute of Physics, 2014, 104 (16), pp.164102. Plasma sheaths driven by radio-frequency voltages occur in contexts ranging from plasma processing to magnetically confined fusion experiments. An analytical understanding of such sheaths is therefore important, both intrinsically and as an element in more elaborate theoretical structures. Radio-frequency sheaths are commonly excited by highly anharmonic waveforms, but no analytical model exists for this general case. We present a mathematically simple sheath model that is in good agreement with earlier models for single frequency excitation, yet can be solved for arbitrary excitation waveforms. As examples, we discuss dual-frequency and pulse-like waveforms. The model employs the ansatz that the time-averaged electron density is a constant fraction of the ion density. In the cases we discuss, the error introduced by this approximation is small, and in general it can be quantified through an internal consistency condition of the model. This simple and accurate model is likely to have wide application. (10.1063/1.4872172)
DOI : 10.1063/1.4872172
Electron heating in capacitively coupled plasmas revisited
- Lafleur Trevor
- Chabert Pascal
- Booth Jean-Paul
Plasma Sources Science and Technology, IOP Publishing, 2014, 23 (3), pp.035010. We revisit the problem of electron heating in capacitively coupled plasmas (CCPs), and propose a method for quantifying the level of collisionless and collisional heating in plasma simulations. The proposed procedure, based on the electron mechanical energy conservation equation, is demonstrated with particle-in-cell simulations of a number of single and multi-frequency CCPs operated in regimes of research and industrial interest. In almost all cases tested, the total electron heating is comprised of collisional (ohmic) and pressure heating parts. This latter collisionless component is in qualitative agreement with the mechanism of electron heating predicted from the recent re-evaluation of theoretical models. Finally, in very electrically asymmetric plasmas produced in multi-frequency discharges, we observe an additional collisionless heating mechanism associated with electron inertia. (10.1088/0963-0252/23/3/035010)
DOI : 10.1088/0963-0252/23/3/035010

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