Publications

2013

A double-plasma source of continuous bipolar ion-ion beam
- Dudin S.V.
- Rafalskyi D.V.
Applied Physics Letters, American Institute of Physics, 2013, 102, pp.034102. A double-plasma source capable of the generation of a continuous bipolar ion-ion beam is described. The quasi-neutral ion-ion flow to an extraction electrode is formed in the system containing primary inductively coupled plasma separated from a secondary plasma by an electrostatic grid-type filter. The total current of each ion species to the 250 mm diameter extraction electrode is about 80 mA; the electron current does not exceed 30% of the ion current. Method of positive/negative ion current ratio control is proposed, allowing the ion currents ratio variation in wide range. (10.1063/1.4788711)
DOI : 10.1063/1.4788711
Secondary electron induced asymmetry in capacitively coupled plasmas
- Lafleur Trevor
- Chabert Pascal
- Booth Jean-Paul
Journal of Physics D: Applied Physics, IOP Publishing, 2013, 46, pp.135201. Using a simple analytical model, together with a 1D particle-in-cell simulation, we show that it is possible to generate an asymmetric plasma response in a sinusoidally excited, geometrically symmetric, capacitively coupled plasma (CCP). The asymmetric response is produced using rf electrodes of differing materials, and hence different secondary electron emission coefficients. This asymmetry in the emission coefficients can produce a significant, measurable dc bias voltage (Vbias /Vrf ∼ 00.2), together with an asymmetry in the plasma density profiles and ion flux to each electrode. The dc bias formation can be understood from a particle-flux balance applied to each electrode, and results from two main effects: (1) the larger effective ion flux at each electrode due to the emission of secondary electrons and (2) ion-flux multiplication within the sheath due to ionization from these emitted secondary electrons. By making use of an empirical fit to the simulation data, the possibility of non-invasively estimating secondary electron emission coefficients in CCP systems is discussed. (10.1088/0022-3727/46/13/135201)
DOI : 10.1088/0022-3727/46/13/135201
Particle-in-cell simulation of an electronegative plasma under direct current bias studied in a large range of electronegativity
- Oudini N.
- Raimbault Jean-Luc
- Chabert Pascal
- Meige A.
- Aanesland Ane
Physics of Plasmas, American Institute of Physics, 2013, 20, pp.043501. A one-dimensional electronegative plasma situated between two symmetrical parallel electrodes under DC bias is studied by Particle-In-Cell simulation with Monte Carlo Collisions. By varying the electronegativity α ≡ n−/ne from the limit of electron-ion plasmas (negative ion free) to ion-ion plasmas (electron free), the sheaths formation, the negative ion flux flowing towards the electrodes, and the particle velocities at the sheath edges are investigated. Depending on α, it is shown that the electronegative plasma behavior can be described by four regimes. In the lowest regime of α, i.e., α < 50, negative ions are confined by two positive sheaths within the plasma, while in the higher regimes of α, a negative sheath is formed and the negative ion flux can be extracted from the bulk plasma. In the two intermediate regimes of α, i.e., 50 < α < 10⁵, both the electron and the negative ion fluxes are involved in the neutralization of the positive ions flux that leaves the plasma. In particular, we show that the velocity of the negative ions entering the negative sheath is affected by the presence of the electrons, and is not given by the modified Bohm velocity generally accepted for electronegative plasmas. For extremely high electronegativity, i.e., α > 10⁵, the presence of electrons in the plasma is marginal and the electronegative plasma can be considered as an ion-ion plasma (electron free). (10.1063/1.4798501)
DOI : 10.1063/1.4798501
Comparison between hybrid and fully kinetic models of asymmetric magnetic reconnection: Coplanar and guide field configurations
- Aunai Nicolas
- Hesse Michael
- Zenitani Seiji
- Kuznetsova M. M.
- Black Carrie
- Evans Rebekah
- Smets Roch
Physics of Plasmas, American Institute of Physics, 2013, 20, pp.022902. Magnetic reconnection occurring in collisionless environments is a multi-scale process involving both ion and electron kinetic processes. Because of their small mass, the electron scales are difficult to resolve in numerical and satellite data, it is therefore critical to know whether the overall evolution of the reconnection process is influenced by the kinetic nature of the electrons, or is unchanged when assuming a simpler, fluid, electron model. This paper investigates this issue in the general context of an asymmetric current sheet, where both the magnetic field amplitude and the density vary through the discontinuity. A comparison is made between fully kinetic and hybrid kinetic simulations of magnetic reconnection in coplanar and guide field systems. The models share the initial condition but differ in their electron modeling. It is found that the overall evolution of the system, including the reconnection rate, is very similar between both models. The best agreement is found in the guide field system, which confines particle better than the coplanar one, where the locality of the moments is violated by the electron bounce motion. It is also shown that, contrary to the common understanding, reconnection is much faster in the guide field system than in the coplanar one. Both models show this tendency, indicating that the phenomenon is driven by ion kinetic effects and not electron ones. (10.1063/1.4792250)
DOI : 10.1063/1.4792250
Dipolarization fronts as a consequence of transient reconnection: In situ evidence
- Fu H.S.
- Cao J.B.
- Khotyaintsev Y. V.
- Sitnov M. I.
- Runov A.
- Fu S. Y.
- Hamrin M.
- André M.
- Retinò Alessandro
- Ma Y. D.
- Lu H. Y.
- Wei X.H.
- Huang S. Y.
Geophysical Research Letters, American Geophysical Union, 2013, 40 (23), pp.6023-6027. Dipolarization fronts (DFs) are frequently detected in the Earth's magnetotail from XGSM = −30 RE to XGSM = −7 RE. How these DFs are formed is still poorly understood. Three possible mechanisms have been suggested in previous simulations: (1) jet braking, (2) transient reconnection, and (3) spontaneous formation. Among these three mechanisms, the first has been verified by using spacecraft observation, while the second and third have not. In this study, we show Cluster observation of DFs inside reconnection diffusion region. This observation provides in situ evidence of the second mechanism: Transient reconnection can produce DFs. We suggest that the DFs detected in the near-Earth region (XGSM > −10 RE) are primarily attributed to jet braking, while the DFs detected in the mid- or far-tail region (XGSM < −15 RE) are primarily attributed to transient reconnection or spontaneous formation. In the jet-braking mechanism, the high-speed flow pushes the preexisting plasmas to produce the DF so that there is causality between high-speed flow and DF. In the transient-reconnection mechanism, there is no causality between high-speed flow and DF, because the frozen-in condition is violated. (10.1002/2013GL058620)
DOI : 10.1002/2013GL058620
Radiation from Ag High Energy Density Z-pinch Plasmas with Applications to Lasing
- Weller M. E.
- Safronova Alla S.
- Kantsyrev Viktor L.
- Esaulov A. A.
- Shrestha Ishor
- Apruzese J. P.
- Giuliani J. L.
- Chuvatin Alexandre S.
- Stafford A.
- Keim S. F.
- Shlyaptseva V. V.
- Osborne Glenn C.
- Petkov E. E.
, 2013.
ROLE OF REACTOR CAPACITANCE ON THE PROPAGATION OF IONISATION WAVES
- Guaitella Olivier
- Sobota Ana
- Rousseau Antoine
, 2013.
Cluster Observations of Ion-Scale Magnetic Structures and their Coupling with Whistler Waves During the August 17th 2003 Substorm Event
- Tenerani Anna
- Le Contel Olivier
- Califano F.
- Robert Patrick
- Fontaine Dominique
- Cornilleau-Wehrlin Nicole
- Sauvaud J.-A.
Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2013, 118, pp.6072-6089. We provide evidence of the simultaneous occurrence of large-amplitude, quasi-parallel whistler mode waves and ion-scale magnetic structures, which have been observed by the Cluster spacecraft in the plasma sheet at 17 Earth radii, during a substorm event. It is shown that the magnetic structures are characterized by both a magnetic field strength minimum and a density hump and that they propagate in a direction quasi-perpendicular to the average magnetic field. The observed whistler mode waves are efficiently ducted by the inhomogeneity associated with such ion-scale magnetic structures. The large amplitude of the confined whistler waves suggests that electron precipitations could be enhanced locally via strong pitch angle scattering. Furthermore, electron distribution functions indicate that a strong parallel heating of electrons occurs within these ion-scale structures. This study provides new insights on the possible multiscale coupling of plasma dynamics during the substorm expansion, on the basis of the whistler mode wave trapping by coherent ion-scale structures. (10.1002/jgra.50562)
DOI : 10.1002/jgra.50562
Sahraoui et al. Reply:
- Sahraoui Fouad
- Robert Patrick
- Goldstein M. L.
- Khotyaintsev Y. V.
Physical Review Letters, American Physical Society, 2013, 111, pp.149002. A Reply to the Comment by O. Alexandrova, S. D. Bale, and C. Lacombe.
Magnetic field and dynamic pressure ULF fluctuations in coronal-mass-ejection-driven sheath regions
- Kilpua E. K. J.
- Hietala H.
- Koskinen H. E. J.
- Fontaine Dominique
- Turc Lucile
Annales Geophysicae, European Geosciences Union, 2013, 31, pp.1559-1567. Compressed sheath regions form ahead of interplanetary coronal mass ejections (ICMEs) that are sufficiently faster than the preceding solar wind. The turbulent sheath regions are important drivers of magnetospheric activity, but due to their complex internal structure, relatively little is known on the distribution of the magnetic field and plasma variations in them. In this paper we investigate ultra low frequency (ULF) fluctuations in the interplanetary magnetic field (IMF) and in dynamic pressure (Pdyn) using a superposed epoch analysis of 41 sheath regions observed during solar cycle 23. We find strongest fluctuation power near the shock and in the vicinity of the ICME leading edge. The IMF and Pdyn ULF power have different profiles within the sheath; the former is enhanced in the leading part of the sheath, while the latter is increased in the trailing part of the sheath. We also find that the ICME properties affect the level and distribution of the ULF power in sheath regions. For example, sheath regions associated with strong or fast ICMEs, or those that are crossed at intermediate distances from the center, have strongest ULF power and large variation in the power throughout the sheath region. The weaker or slower ICMEs, or those that are crossed centrally, have in general considerably weaker ULF power with relatively smooth profiles. The strong and abrupt decrease of the IMF ULF power at the ICME leading edge could be used to distinguish the ICME from the preceding sheath plasma. (10.5194/angeo-31-1559-2013)
DOI : 10.5194/angeo-31-1559-2013
First demonstration of an asymmetric kinetic equilibrium for a thin current sheet
- Aunai Nicolas
- Belmont Gérard
- Smets Roch
Physics of Plasmas, American Institute of Physics, 2013, 20 (11), pp.110702. The modeling of steady state collisionless asymmetric tangential current layers is a challenging and poorly understood problem. For decades now, this difficulty has been limiting numerical models to approximate equilibria built with locally Maxwellian current layers and theoretical analyses to the very restricted Harris equilibrium. We show how the use of any distribution functions depending only on local macroscopic quantities results in a strong alteration of the current layer internal structure, which converges toward an unpredictable quasi-steady state with emission of ion scale perturbations. This transient can be explained in terms of ion kinetic and electron fluid physics. We demonstrate, for the first time, the validity of an asymmetric kinetic equilibrium model as well as its usability as an initial condition of hybrid kinetic simulations. This offers broad perspectives for the current sheet modeling, for which the early phase of instabilities can be studied within the kinetic formalism. (10.1063/1.4833679)
DOI : 10.1063/1.4833679
Enhanced Magnetic Compressibility and Isotropic Scale Invariance at Sub-ion Larmor Scales in Solar Wind Turbulence
- Kiyani K. H.
- Chapman S. C.
- Sahraoui Fouad
- Hnat B.
- Fauvarque O.
- Khotyaintsev Y. V.
The Astrophysical Journal, American Astronomical Society, 2013, 763 (1), pp.10. The anisotropic nature of solar wind magnetic turbulence fluctuations is investigated scale by scale using high cadence in situ magnetic field measurements from the Cluster and ACE spacecraft missions. The data span five decades in scales from the inertial range to the electron Larmor radius. In contrast to the inertial range, there is a successive increase toward isotropy between parallel and transverse power at scales below the ion Larmor radius, with isotropy being achieved at the electron Larmor radius. In the context of wave-mediated theories of turbulence, we show that this enhancement in magnetic fluctuations parallel to the local mean background field is qualitatively consistent with the magnetic compressibility signature of kinetic Alfvén wave solutions of the linearized Vlasov equation. More generally, we discuss how these results may arise naturally due to the prominent role of the Hall term at sub-ion Larmor scales. Furthermore, computing higher-order statistics, we show that the full statistical signature of the fluctuations at scales below the ion Larmor radius is that of a single isotropic globally scale-invariant process distinct from the anisotropic statistics of the inertial range. (10.1088/0004-637X/763/1/10)
DOI : 10.1088/0004-637X/763/1/10
Electron acceleration to relativistic energies at a strong quasi-parallel shock wave
- 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.
Nature Physics, Nature Publishing Group [2005-....], 2013, 9, pp.164-167. Electrons can be accelerated to ultrarelativistic energies at strong (high Mach number) collisionless shock waves that form when stellar debris rapidly expands after a supernova. Collisionless shock waves also form in the flow of particles from the Sun (the solar wind), and extensive spacecraft observations have established that electron acceleration at these shocks is effectively absent whenever the upstream magnetic field is roughly parallel to the shock-surface normal (quasi-parallel conditions). However, it is unclear whether this magnetic dependence of electron acceleration also applies to the far stronger shocks around young supernova remnants, where local magnetic conditions are poorly understood. Here we present Cassini spacecraft observations of an unusually strong solar system shock wave (Saturn's bow shock) where significant local electron acceleration has been confirmed under quasi-parallel magnetic conditions for the first time, contradicting the established magnetic dependence of electron acceleration at solar system shocks. Furthermore, the acceleration led to electrons at relativistic energies (about megaelectronvolt), comparable to the highest energies ever attributed to shock acceleration in the solar wind. These observations suggest that at high Mach numbers, such as those of young supernova remnant shocks, quasi-parallel shocks become considerably more effective electron accelerators. (10.1038/nphys2541)
DOI : 10.1038/nphys2541
Frequency dependence of the electrical asymmetry effect in dual-frequency capacitively coupled discharges
- Booth Jean-Paul
- Lafleur Trevor
Applied Physics Letters, American Institute of Physics, 2013, 102, pp.154104. Using experimental measurements complemented with particle-in-cell (PIC) simulations, we demonstrate a reduction in the electrical asymmetry effect in capacitively coupled discharges for low excitation frequencies (0.8 MHz < f<10 MHz). These results confirm PIC simulation predictions made by [I. Korolov, Z. Donkó, U. Czarnetzki, and J. Schulze, J. Phys. D: Appl. Phys. 45, 465205 (2012)], where this effect was investigated for dual-frequency discharges in which the driving frequencies are phase-shifted harmonics. Because the reduction in electrical asymmetry is a sensitive function of the secondary electron emission coefficient, we are able to non-invasively estimate this coefficient as 0.035 for argon ions incident on aluminium electrodes. (10.1063/1.4802241)
DOI : 10.1063/1.4802241
Non thermal Pasma regeneration of Acetone adsorbed TiO2 Surface
- Sivachandiran Loganathan
- Thévenet Frédéric
- Rousseau Antoine
Plasma Chemistry and Plasma Processing, Springer Verlag, 2013. Improvement of indoor air quality regarding volatile organic compounds (VOCs) requires the development of innovative oxidation processes. This paper investigates the coupling of a metal oxide sorbent with non-thermal plasma (NTP) in an especially designed reactor. TiO2 was selected as model sorbent and acetone was used as model VOC. The analyses of gas phase species at the reactor downstream have been performed using FTIR spectroscopy. In a first step, acetone adsorption on TiO2 surface under dry air was characterized in terms of total amount adsorbed, as well as reversibly and irreversibly adsorbed fractions. Obtained results were compared and discussed with literature in terms of acetone reactive adsorption on TiO2 surface. Mesityloxide was proposed as the major compound in the irreversibly adsorbed fraction. In a second time, acetone saturated TiO2 surface was exposed to NTP surface discharge. Irrespectively of the injected power, <30 % of the initially adsorbed acetone has been recovered as CO, CO2 and desorbed acetone. Finally, thermal desorptions have been performed. They evidenced that (1) NTP treatment modifies the nature of the adsorbed organic species, (2) mineralization rate is considerably improved. Based on desorbed species temporal profile analysis, carboxylates and more especially formates are suggested as major adsorbed species after NTP treatment (Pinj > 0.2 W). This hypothesis has been evaluated and confirmed. This paper finally evidenced that NTP can be used as an efficient pretreatment technique to promote the mineralization of adsorbed acetone for further thermal treatment (10.1007/s11090-013-9463-7)
DOI : 10.1007/s11090-013-9463-7
Modes of underwater discharge propagation in a series of nanosecond successive pulses
- Marinov Ilya
- Guaitella Olivier
- Rousseau Antoine
- Starikovskaia Svetlana
Journal of Physics D: Applied Physics, IOP Publishing, 2013, 46, pp.464013. Initiation and development of nanosecond electric discharges in deionized water was studied by time-resolved shadowgraphy and emission imaging. Pulses of 410 kV in amplitude, 5 ns rise time and 30 ns duration were applied to a high-voltage (HV) pin-like electrode with the diameter of the pin tip about 2μm. Two distinct bush-like and tree-like modes of the discharge propagation were observed in the same conditions already at the rising slope of HV pulse. Both the modes are supersonic. The probability of finding one of them depends on applied voltage. Bush-mode propagates at 4 kms−1 at the initial stage; the deposited energy is less than 0.05 mJ. For the tree-like mode, propagation velocity, number of branches and deposited energy show well-prononced dependence on applied voltage. It is suggested that the bush-like discharge ignites in the gaseous cavity, whereas the tree-like discharge propagates in bulk liquid. The role of electrostriciton in the initiation and propagation of two modes is discussed, and comparison with microsecond discharges is given. Transition from bush-like discharge to tree-like mode may occur in successive positive pulse coming 500 ns after initial pulse. (10.1088/0022-3727/46/46/464013)
DOI : 10.1088/0022-3727/46/46/464013
Investigation of NO and NO2 adsorption mechanisms on TiO2 at room temperature
- Sivachandiran Loganathan
- Thévenet Frédéric
- Gravelat Paul
- Rousseau Antoine
Applied Catalysis B: Environmental, Elsevier, 2013, 142-143, pp.196-204. In this study, NO and NO2 adsorption mechanisms on TiO2 at room temperature have been investigated separately. Atmospheric pressure gas phase Fourier Transform Infrared Spectroscopy (FTIR) coupled to adsorption and temperature programmed desorption (TPD) experiments have been used to characterize gas phase and adsorbed phase species. TiO2 coated glass beads packed-bed reactor has been designed and used for NO and NO2 adsorption and storage capacity under dark and gas-flowing conditions at room temperature. For NO adsorption, experimental data suggests that, at room temperature, NO shows no significant adsorption on TiO2. On the other hand NO2 adsorbs in a reactive way by evolving NO in the gas phase. We quantitatively evidenced that, the ratio between consumed NO2, desorbed NO2 by TPD after adsorption and produced NO during NO2 adsorption is 3:2:1, by a qualitative and quantitative analysis performed downstream the reactor. Based on the quantitative analysis, a new NO2 adsorption mechanism on TiO2 at room temperature has been proposed, and validated for various NO2 inlet concentrations. The proposed mechanism is valid on the investigated NO2 inlet concentration range. In addition, it was found that, NO formation time, during NO2 adsorption, is rather controlled by TiO2 surface coverage than NO2 inlet concentration; similarly, adsorption time i.e. surface coverage, significantly modifies the nature of adsorbed species on TiO2 surface. (10.1016/j.apcatb.2013.04.073)
DOI : 10.1016/j.apcatb.2013.04.073
Radio frequency current-voltage probe for impedance and power measurements in multi-frequency unmatched loads
- Lafleur Trevor
- Delattre Pierre-Alexandre
- Johnson E.V.
- Booth Jean-Paul
- Diné Sébastien
Review of Scientific Instruments, American Institute of Physics, 2013, 84, pp.015001. A broad-band, inline current-voltage probe, with a characteristic impedance of 50 Ω, is presented for the measurement of voltage and current waveforms, impedance, and power in rf systems. The probe, which uses capacitive and inductive sensors to determine the voltage and current, respectively, can be used for the measurement of single or multi-frequency signals into both matched and unmatched loads, over a frequency range of about 1100 MHz. The probe calibration and impedance/power measurement technique are described in detail, and the calibrated probe results are compared with those obtained from a vector network analyzer and other commercial power meters. Use of the probe is demonstrated with the measurement of power into an unmatched capacitively coupled plasma excited by multi-frequency tailored voltage waveforms. (10.1063/1.4773540)
DOI : 10.1063/1.4773540
First Realistic validation of Plasma Air treatment with QCL-OFCEAS detection of formaldehyde below ppb range
- Guaitella Olivier
- Barakat Christelle
- Fasci Eugenio
- Rousseau Antoine
- Gorrotxategi Carbajo P.
- Ventrillard I.
- Carras M.
- Maisons G.
- Romanini D.
, 2013.
Collisionless Plasmas in Astrophysics
- Belmont Gérard
- Grappin Roland
- Mottez Fabrice
- Pantellini F.
- Pelletier Guy
, 2013 (ISBN: 978-3-527-41074-3).

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