Publications

2012

• Device convolution effects on the collective scattering signal of the E x B mode from Hall thruster experiments: 2D dispersion relation
  
  • Grésillon D.
  • Cavalier J.
  • Lemoine N.
  • Bonhomme Gildas
  • Tsikata Sedina
  • Honoré Cyrille
  Physics of Plasmas, American Institute of Physics, 2012, 19, pp.082117. The effect of the collective light scattering diagnostic transfer function is considered in the context of the dispersion relation of the unstable E×B mode previously reported. This transfer function is found to have a contribution to the measured frequencies and mode amplitudes which is more or less significant depending on the measurement wavenumbers and angles. After deconvolution, the experimental data are found to be possibly compatible with the idea that the mode frequency in the jet frame (after subtraction of the Doppler effect due to the plasma motion along the thruster axis) is independent of the orientation of the wave vector in the plane orthogonal to the local magnetic field. (10.1063/1.4748286)
  DOI : 10.1063/1.4748286
• Implosions of larger size wire arrays at enhanced current of 1.51.7 MA on Zebra with LCM
  
  • Safronova Alla S.
  • Esaulov A. A.
  • Kantsyrev Viktor L.
  • Stafford A.
  • Weller Michael E.
  • Shlyaptseva V. V.
  • Zunino H. A.
  • Shrestha Ishor
  • Osborne Glenn C.
  • Keim S. F.
  • Chuvatin Alexandre S.
  • Coverdale C. A.
  , 2012, pp.6C7. Experiments on Zebra with a Load Current Multiplier (LCM, which provides an enhanced current of 1.5-1.7 MA) allow the implosion of larger wire array loads than possible with the standard current of 1 MA. Advantages of the larger wire arrays include enhanced energy coupling to plasmas and better diagnostic access to observable plasma regions. Diagnostics, fielded on 10 beam lines, included PCD, XRD, and EUV detectors, X-ray/EUV spectrometers and X-ray pinhole cameras, and laser shadowgraphy. For this work, we collected and analyzed the experimental results from standard and modified triple planar wire arrays (TPWA), as well as cylindrical wire arrays (CWA). The anode-cathode gap in these experiments with LCM was 1 cm, which is half the gap used in the standard mode. For TPWAs, two outer wire planes were made out of mid-atomic-number wire material (Ni or Cu) with the inter-row gap increased from 1.5 or 3 mm (usually used at 1 MA current) up to 4.5 mm. The different designs of a central wire plane from Al were implemented to investigate its role as a magnetic field extruder to prevent the formation of closed magnetic configurations around each wire plane. Previous work has shown that larger double planar wire arrays (at a standard current) can block the inward motion of ablated plasma jets. Therefore, multi-planar wire arrays provide a new test bed to study jet formations in larger wire arrays for laboratory astrophysics. In addition, we measured higher linear radiation yield and the high-temperature precursor Al plasmas, not previously observable in experiments on Zebra at 1 Ma current. However, the observation of high-temperature precursor plasmas from Cu CWAs at enhanced current was consistent with previous findings at a standard current of 1 MA. (10.1109/PLASMA.2012.6384037)
  DOI : 10.1109/PLASMA.2012.6384037
• Upper ionosphere of Mars is not axially symmetrical
  
  • Dubinin E.
  • Fraenz M.
  • Woch J.
  • Modolo Ronan
  • Chanteur Gérard
  • Duru F.
  • Gurnett D. A.
  • Barabash S.
  • Lundin R.
  Earth Planets and Space, Springer / Terra Scientific Publishing Company, 2012, 64 (2), pp.113-120. The measurements carried out by the ASPERA-3 and MARSIS experiments on board the Mars Express (MEX) spacecraft show that the upper Martian ionosphere (h ≥ 400 km) is strongly azimuthally asymmetrical. There are several factors, e.g., the crustal magnetization on Mars and the orientation of the interplanetary magnetic field (IMF) which can give rise to formation of ionospheric swells and valleys. It is shown that expansion of the ionospheric plasma along the magnetic field lines of crustal origin can produce bulges in the plasma density. The absense of a magnetometer on MEX makes the retrieval of an asymmetry caused by the IMF more difficult. However hybrid simulations give a hint that the ionosphere in the hemisphere (E-) to which the motional electric field is pointed occurs more inflated than the ionosphere in the opposite (E+) hemisphere. (10.5047/eps.2011.05.022)
  DOI : 10.5047/eps.2011.05.022
• Analytical-numerical global model of atmospheric-pressure radio-frequency capacitive discharges
  
  • Lazzaroni Claudia
  • Chabert Pascal
  • Lieberman M.A.
  • Lichtenberg A.J.
  • Leblanc A.
  Plasma Sources Science and Technology, IOP Publishing, 2012, 21, pp.035013. A one-dimensional hybrid analyticalnumerical global model of atmospheric-pressure, radio-frequency (rf) driven capacitive discharges is developed. The feed gas is assumed to be helium with small admixtures of oxygen or nitrogen. The electrical characteristics are modeled analytically as a current-driven homogeneous discharge. The electron power balance is solved analytically to determine a time-varying Maxwellian electron temperature, which oscillates on the rf timescale. Averaging over the rf period yields effective rate coefficients for gas phase activated processes. The particle balance relations for all species are then integrated numerically to determine the equilibrium discharge parameters. The coupling of analytical solutions of the time-varying discharge and electron temperature dynamics, and numerical solutions of the discharge chemistry, allows for a fast solution of the discharge equilibrium. Variations of discharge parameters with discharge composition and rf power are determined. Comparisons are made to more accurate but numerically costly fluid models, with space and time variations, but with the range of parameters limited by computational time. (10.1088/0963-0252/21/3/035013)
  DOI : 10.1088/0963-0252/21/3/035013
• Microcrystalline silicon solar cells deposited using a plasma process excited by tailored voltage waveforms
  
  • Johnson E.V.
  • Delattre Pierre-Alexandre
  • Booth Jean-Paul
  Applied Physics Letters, American Institute of Physics, 2012, 100, pp.133504. Thin film solar cells in a p-i-n structure with an absorbing layer of intrinsic hydrogenated microcrystalline silicon (μc-Si:H) deposited through plasma enhanced chemical vapour deposition excited by tailored voltage waveforms have been prepared. The use of an asymmetric voltage waveform decouples the ion-bombardment energy at the growth surface from the injected power and allows the growth of good quality μc-Si:H at reasonable deposition rates (3 Å/s) using low pressure, powder-free conditions. Unoptimized photovoltaic devices with an efficiency of 6.1% are demonstrated using an i-layer deposited at 1.3 Å/s and a process pressure of 500 mTorr. (10.1063/1.3699222)
  DOI : 10.1063/1.3699222
• A load current multiplier of the MIG terawatt generator
  
  • Chaikovsky S. A.
  • Chuvatin Alexandre S.
  • Oreshkin V. I.
  Instruments and Experimental Techniques, MAIK Nauka/Interperiodica, 2012, 55 (2), pp.209-217. The design of the load current multiplier with a 1.75-current enlargement factor, when the pulse amplitude of the current through a 3-MA load of the MIG terawatt pulse generator (multifunction pulse generator), is described, and its operation is demonstrated. The design of the multiplier is sufficiently simple, and it is easily demounted, allowing one to use the MIG generator in other operation modes with different-impedance loads. It is shown that it is expedient to use the multiplier for operation with static low-inductance loads, e.g., in studies of the skin electric explosion or nonlinear diffusion of megagauss magnetic fields. In this case, the multiplier application is intended to ensure a one-and-one-half increase in the current through the load as compared to the standard operation mode of the МИГ generator.
• VOC elimination using plasma enhanced catalysis in a post situ configuration
  
  • Barakat Christelle
  • Gravejat Paul
  • Guaitella Olivier
  • Rousseau Antoine
  , 2012.
• Adsorption and reactivity of nitrogen atoms on dielectric surfaces under
  
  • Marinov Daniil
  • Guaitella Olivier
  • Rousseau Antoine
  , 2012.
• Multiple scattering of electromagnetic waves by an array of parallel gyrotropic rods
  
  • Es'Kin V. A.
  • Kudrin A. V.
  • Zaboronkova T. M.
  • Krafft C.
  Physical Review E, American Physical Society (APS), 2012, 86, pp.067601. We study multiple scattering of electromagnetic waves by an array of parallel gyrotropic circular rods and show that such an array can exhibit fairly unusual scattering properties and provide, under certain conditions, a giant enhancement of the scattered field. Among the scattering patterns of such an array at its resonant frequencies, the most interesting is the distribution of the total field in the form of a perfect self-similar structure of chessboard type. The scattering characteristics of the array are found to be essentially determined by the resonant properties of its gyrotropic elements and cannot be realized for arrays of nongyrotropic rods. It is expected that the results obtained can lead to a wide variety of practical applications. (10.1103/PhysRevE.86.067601)
  DOI : 10.1103/PhysRevE.86.067601
• Reflection of solar wind protons on the Martian bow shock: Investigations by means of 3-dimensional simulations
  
  • Richer Emilie
  • Chanteur Gérard
  • Modolo Ronan
  • Dubinin Eduard
  Geophysical Research Letters, American Geophysical Union, 2012, 39, pp.L17101. The reflection of solar wind protons on the Martian bow shock (BS) is investigated by means of three-dimensional simulation models. A two steps approach is adopted to allow a detailed analysis of the reflected population. Firstly, the 3-dimensional hybrid model of Modolo et al. (2005) is used to compute a stationary state of the interaction of the solar wind (SW) with Mars. Secondly, the motion of test particles is followed in the electromagnetic field computed by the hybrid simulation meanwhile detection criteria defined to identify reflected protons are applied. This study demonstrates some effects of the large curvature of a planetary BS on the structure of the foreshock. Reflected protons encounter the BS in a region encompassing parts of the quasi-perpendicular and quasi-parallel shocks, and exit the shock mainly from the quasi-parallel region. The energy spectrum of all reflected protons extends from 0 to almost 15keV. A virtual omnidirectional detector (VOD) is used to compute the local omnidirectional flux of reflected protons at various locations upstream of the BS. Spatial variations of this omnidirectional flux indicate the location and spatial extent of the proton foreshock and demonstrate its shift, increasing with the distance downstream, in the direction opposite to the motional electric field of the SW. Local energy spectra computed from the VOD observations demonstrate the existence of an energy gradient along the direction of the convection electric field. (10.1029/2012GL052858)
  DOI : 10.1029/2012GL052858
• Polar cap arcs from the magnetosphere to the ionosphere: kinetic modelling and observations by Cluster and TIMED
  
  • Maggiolo R
  • Echim M
  • Wedlund Simon C.
  • Zhang Y.
  • Fontaine Dominique
  • Lointier G
  • Trotignon Jean-Gabriel
  Annales Geophysicae, European Geosciences Union, 2012, 30, pp.283–302. On 1 April 2004 the GUVI imager onboard the TIMED spacecraft spots an isolated and elongated polar cap arc. About 20 min later, the Cluster satellites detect an isolated upflowing ion beam above the polar cap. Cluster observations show that the ions are accelerated upward by a quasi-stationary electric field. The field-aligned potential drop is estimated to about 700 V and the upflowing ions are accompanied by a tenuous population of isotropic protons with a temperature of about 500 eV. The magnetic footpoints of the ion outflows observed by Cluster are situated in the prolongation of the polar cap arc observed by TIMED GUVI. The upflowing ion beam and the polar cap arc may be different signatures of the same phenomenon , as suggested by a recent statistical study of polar cap ion beams using Cluster data. We use Cluster observations at high altitude as input to a quasi-stationary magnetosphere-ionosphere (MI) coupling model. Using a Knight-type current-voltage relationship and the current continuity at the topside ionosphere, the model computes the energy spectrum of precipitating electrons at the top of the ionosphere corresponding to the generator electric field observed by Cluster. The MI coupling model provides a field-aligned potential drop in agreement with Cluster observations of upflowing ions and a spatial scale of the polar cap arc consistent with the optical observations by TIMED. The computed energy spectrum of the precipitating electrons is used as input to the Trans4 ionospheric transport code. This 1-D model, based on Boltzmann's kinetic formalism, takes into account ionospheric processes such as photoion-ization and electron/proton precipitation, and computes the optical and UV emissions due to precipitating electrons. The emission rates provided by the Trans4 code are compared to the optical observations by TIMED. They are similar in size and intensity. Data and modelling results are consistent with the scenario of quasi-static acceleration of electrons that generate a polar cap arc as they precipitate in the ionosphere. The detailed observations of the acceleration region by Cluster and the large scale image of the polar cap arc provided by TIMED are two different features of the same phenomenon. Combined together, they bring new light on the configuration of the high-latitude magnetosphere during prolonged periods of Northward IMF. Possible implications of the modelling results for optical observations of polar cap arcs are also discussed . (10.5194/angeo-30-283-2012)
  DOI : 10.5194/angeo-30-283-2012
• A global model of the self-pulsing regime of micro-hollow cathode discharges
  
  • Lazzaroni Claudia
  • Chabert Pascal
  Journal of Applied Physics, American Institute of Physics, 2012, 111, pp.053305. A global (volume-averaged) model of the self-pulsing regime of micro-hollow cathode discharges working in argon gas is proposed. The power balance is done using an equivalent circuit model of the discharge that allows the current and voltage dynamics to be calculated. The fraction of the total power dissipated in the discharge that contributes to electron heating is deduced from a sheath model previously described. The particle balance is first done in a very simplified reaction scheme involving only electrons, argon atomic ions, and argon molecular ions. In a second step, the excited states (the metastable state Ar*(3P2) and the resonant state Ar*(3P1)) are included in the particle balance equations. The models are compared to experiments and several conclusions are drawn. The model without excited states underestimates the electron density and does not capture well the trends in pressure. The model with the excited states is in better agreement which shows that multi-step ionization plays a significant role. The time-evolution of the electron density follows closely that of the discharge current but the excited states density presents two peaks: (i) the first at the early stage of the current peak due to direct excitation with high electron temperature, (ii) the second at the end of the current (and electron density) peak due to large production of excited states by electron-ion recombination at very low electron temperature. (10.1063/1.3690943)
  DOI : 10.1063/1.3690943
• A nanosecond surface dielectric barrier discharge at elevated pressures : time-resolved electric field and efficiency of initiation of combustion
  
  • Kosarev I.N.
  • Khorunzhenko V.I.
  • Mintoussov E.I.
  • Sagulenko P.N.
  • Popov N.A.
  • Starikovskaia Svetlana
  Plasma Sources Science and Technology, IOP Publishing, 2012, 21, pp.045012. We study a nanosecond surface dielectric barrier discharge (SDBD) initiated by negative or positive polarity pulses 1015 kV in amplitude in a cable, 2530 ns FWHM, 5 ns rise time, in the regime of a single shot or 3 Hz repetitive frequency. Discharge parameters, namely spatial structure of the discharge and time- and space-resolved electric field are studied in a N2 : O2 = 4 : 1 mixture for P = 15 atm. The possibility of igniting a combustible mixture with the help of an SDBD is demonstrated using the example of a stoichiometric C2H6 : O2 mixture at ambient initial temperature and at 1 atm pressure. Flame propagation and ignited volume as a function of time are compared experimentally for two discharge geometries: SDBD and pin-to-pin configurations at the same shape and amplitude of the incident pulse. It is shown that the SDBD can be considered as a multi-point ignition system with maximum energy release near the high-voltage electrode. Numerical modeling of the discharge and subsequent combustion kinetics for the SDBD conditions is performed. The discharge action leads to the production of atoms and radicals as well as to fast gas heating, due to the relaxation of electronic and vibrational degrees of freedom. The calculated ignition delay time is in reasonable agreement with the experimental results. (10.1088/0963-0252/21/4/045012)
  DOI : 10.1088/0963-0252/21/4/045012
• Plasma decay in air and O<SUB>2</SUB> after a high-voltage nanosecond discharge
  
  • Aleksandrov N.L.
  • Anokhin E.M.
  • Kindysheva S.V.
  • Kirpichnikov A.A.
  • Kosarev I.N.
  • Nudnova M.M.
  • Starikovskaia Svetlana
  • Starikovskii A.Yu.
  Journal of Physics D: Applied Physics, IOP Publishing, 2012, 45, pp.255202. This paper presents the results of experimental and theoretical studies of an afterglow in room temperature air and O2 excited by a high-voltage nanosecond discharge for pressures between 1 and 10 Torr. We measured time-resolved electron density by a microwave interferometer for initial electron densities in the range (23) × 1012 cm&#8722;3. Discharge uniformity was investigated by optical methods. The balance equations for charged particles and electron temperature were numerically solved to describe the temporal evolution of the densities of electrons and ions in the discharge afterglow. It was shown that the loss of electrons is governed by dissociative and three-body electron recombination with \rm O₂^ ions under the conditions considered. Good agreement between the calculated and measured electron density histories could be obtained only when the rate of three-body recombination was increased by an order of magnitude and when the dependence of the recombination rate on electron temperature was changed. This could testify that the well-understood mechanism of three-body electron recombination with atomic ions could be noticeably modified in the case of molecular ions. (10.1088/0022-3727/45/25/255202)
  DOI : 10.1088/0022-3727/45/25/255202
• Coupling Between Whistler Waves and Ion-Scale Solitary Waves: Cluster Measurements in the Magnetotail During a Substorm
  
  • Tenerani Anna
  • Le Contel Olivier
  • Califano F.
  • Pegoraro F.
  • Robert Patrick
  • Cornilleau-Wehrlin Nicole
  • Sauvaud J.-A.
  Physical Review Letters, American Physical Society, 2012, 109, pp.155005. We present a new model of self-consistent coupling between low frequency, ion-scale coherent structures with high frequency whistler waves in order to interpret Cluster data. The idea relies on the possibility of trapping whistler waves by inhomogeneous external fields where they can be spatially confined and propagate for times much longer than their characteristic electronic time scale. Here we take the example of a slow magnetosonic soliton acting as a wave guide in analogy with the ducting properties of an inhomogeneous plasma. The soliton is characterized by a magnetic dip and density hump that traps and advects high frequency waves over many ion times. The model represents a new possible way of explaining space measurements often detecting the presence of whistler waves in correspondence to magnetic depressions and density humps. This approach, here given by means of slow solitons, but more general than that, is alternative to the standard approach of considering whistler wave packets as associated with nonpropagating magnetic holes resulting from a mirror-type instability. (10.1103/PhysRevLett.109.155005)
  DOI : 10.1103/PhysRevLett.109.155005
• La science au service du développement
  
  • Amory-Mazaudier Christine
  , 2012. Dans cet ouvrage est présentée une expérience humaine d'un réseau de scientifiques, GIRGEA, qui a réuni, et qui réunit toujours plusieurs centaines d'étudiants, ingénieurs, techniciens, chercheurs, enseignants, etc. autour d'un objectif central : développer la recherche en sciences de l'espace en Afrique en installant des instruments, en formant des chercheurs de niveau international qui pourront constituer des équipes de recherche dans leur pays et assurer ainsi la pérennité du réseau. Il semble impensable, et pourtant, qu'au XXIe siècle un scientifique puisse prétendre développer des études planétaires des phénomènes physiques de l'environnement terrestre sans mesures sur l'ensemble du globe. Le Nord est indispensable au Sud et le Sud est indispensable au Nord. L'éruption du volcan Eyjafjöll en 2010 a révélé la fragilité des pays du Nord techniquement avancés. Le tsunami du 26 décembre 2004 a mis en évidence la grande vulnérabilité des habitants de certaines régions du Sud ayant des réseaux d'alerte au tsunami défaillants ou inexistants. Mais ces événements ont aussi surtout démontré nos liens, nous vivons tous sur la même planète : la Terre est un petit village et nous dépendons les uns des autres. Le GIRGEA propose donc une méthode pour allier science de l'espace au niveau international et règles éthiques afin de favoriser une recherche à l'échelle planétaire indispensable à l'avancée des connaissances et profitable à tous.
• On the reactivity of C<SUB>2</SUB>H<SUB>2</SUB> on plasma pretreated TiO<SUB>2</SUB> surface
  
  • Marinov Daniil
  • Lopatik D.
  • Hübner M.
  • Guaitella Olivier
  • Roepcke J.
  • Rousseau Antoine
  , 2012.
• New probing techniques of radiative shocks
  
  • Stehlé Chantal
  • Kozlova Michaela
  • Larour Jean
  • Nejdl Jaroslav
  • Champion Norbert
  • Barroso Patrice
  • Suzuki-Vidal Francisco
  • Acef Ouali
  • Delattre Pierre-Alexandre
  • Dostal Jan
  • Krus Miroslav
  • Chièze Jean-Pierre
  Optics Communications, Elsevier, 2012, 285, pp.64-69. Radiative shock waves propagating in xenon at a low pressure have been produced using 60 joules of iodine laser (&#955; = 1.315 &#956;m) at PALS center. The shocks have been probed by XUV imaging using a Zn X-raylaser (&#955; = 21 nm) generated with a 20-ns delay after the shock creating pulse. Auxiliary high-speed silicon diodes allowed performing space- and time-resolved measurement of plasma self-emission in the visible and XUV. The results show the generation of a shock wave propagating at 60 km/s preceded by a radiative precursor. This demonstrates the feasibility of radiative shock generation using high power infrared lasers and the use of XRL backlighting as a suitable diagnostic for shock imaging. (10.1016/j.optcom.2011.09.008)
  DOI : 10.1016/j.optcom.2011.09.008
• Detection of geodesic acoustic mode oscillations, using multiple signal classification analysis of doppler backscattering signal on tore supra
  
  • Vermare Laure
  • Hennequin Pascale
  • Gürcan Özgür D.
  • Tore Supra Team
  Nuclear Fusion, IOP Publishing, 2012, 52, pp.063008. This paper presents the first observation of geodesic acoustic modes (GAMs) on Tore Supra plasmas. Using the Doppler backscattering system, the oscillations of the plasma flow velocity, localized between r/a = 0.85 and r/a = 0.95, and with a frequency, typically around 10 kHz, have been observed at the plasma edge in numerous discharges. When the additional heating power is varied, the frequency is found to scale with Cs/R. The MUltiple SIgnal Classification (MUSIC) algorithm is employed to access the temporal evolution of the perpendicular velocity of density fluctuations. The method is presented in some detail, and is validated and compared against standard methods, such as the conventional fast Fourier transform method, using a synthetic signal. It stands out as a powerful data analysis method to follow the Doppler frequency with a high temporal resolution, which is important in order to extract the dynamics of GAMs. (10.1088/0029-5515/52/6/063008)
  DOI : 10.1088/0029-5515/52/6/063008
• Numerical modelling of the properties of an ion beam extracted from a low-pressure wire discharge
  
  • Gueroult R
  • Elias Paul-Quentin
  • Packan Denis
  • Rax Jean-Marcel
  Journal of Physics D: Applied Physics, IOP Publishing, 2012, 45 (24), pp.245203. The combination of a dedicated acceleration stage with direct extraction of ions from a low-pressure wire discharge enables one to generate a narrow band ion beam of tunable energy. In order to optimize this ion source concept, we conduct a numerical study emphasizing the main physical processes and the parameters controlling them. An analysis of the three-dimensional non-collisional ion trajectories inside the ion source reveals that the total beam current can be tuned by modifying the depth and radius of the diaphragm connecting the wire discharge chamber to the acceleration chamber, while the inter-electrode distance controls the beam focusing. A particle-in-cell (PIC) modelling of the beam acceleration and propagation indicates that, despite the low operating pressure (~10−2 mbar), elastic and charge-exchange collisions are responsible for a decrease in the beam current by a factor of four. Charge-exchange collisions are also shown to be accountable for the existence of a low-energy ion population being non-uniform throughout a beam cross section. (10.1088/0022-3727/45/24/245203)
  DOI : 10.1088/0022-3727/45/24/245203
• Producing Kiloelectronvolt L-Shell Plasmas on Zebra at UNR
  
  • Safronova Alla S.
  • Kantsyrev Viktor L.
  • Esaulov A. A.
  • Shrestha Ishor
  • Shlyapstseva V. V.
  • Weller Michael E.
  • Ouart N. D.
  • Osborne Glenn C.
  • Stafford A.
  • Keim S. F.
  • Velikovich A. L.
  • Giuliani J. L.
  • Chuvatin Alexandre S.
  IEEE Transactions on Plasma Science, Institute of Electrical and Electronics Engineers, 2012, 40 (12), pp.3347-3353. Experiments with various wire loads from mid-atomic-number wires, which were performed on the university-scale 1-MA Zebra generator at the University of Nevada, Reno, during the last few years, are analyzed to assess the highest electron temperature reached. In particular, the results from experiments with planar wire arrays (PWAs) were considered. Load materials from mid-atomic-number such as stainless steel, Alumel, Cu, brass, Mo, and up to Ag were used to generate L-shell plasmas and to study plasma parameters. Though the full diagnostic set was utilized, the main focus was on X-ray spectroscopic data and on the non-local thermodynamic equilibrium kinetic modeling. As a result, the scaling of the maximum Te with the load material atomic number is presented for the first time in the range from Fe to Ag for L-shell plasmas from PWAs. The highest values of the electron temperature in L-shell plasmas, which are estimated from the modeling, were from both Ag PWAs and X-pinches. This work is important for the development of efficient X-ray radiators on university-scale Z-pinch generators. (10.1109/TPS.2012.2222451)
  DOI : 10.1109/TPS.2012.2222451
• Negative hydrogen ion production in fusion dedicated ion sources
  
  • Bacal M.
  Chemical Physics, Elsevier, 2012, 398, pp.3-6. A brief description is given of the basic processes in negative ion sources dedicated to fusion. It is considered that in these sources negative ions are produced by ions and atoms interacting with a caesiated surface, but this mechanism is not unique: the volume production, based on dissociative electron attachment to rovibrationally excited molecules, is also active. We suggest that in RF sources the acceleration of positive ions to a few tens of eV by the plasma potential difference between the driver and the extraction regions can have an important effect on negative ion production by enhancing the negative ion yield from caesiated surfaces, and by charge exchange reactions with caesium atoms. The presence of energetic positive ions can have other implications (modifying the virtual cathode in front of the plasma grid, participating in caesium ionization). (10.1016/j.chemphys.2011.04.002)
  DOI : 10.1016/j.chemphys.2011.04.002
• Electron acceleration in the reconnection diffusion region: Cluster observations
  
  • Huang S. Y.
  • Vaivads A.
  • Khotyaintsev Y. V.
  • Zhou M.
  • Fu H.S.
  • Retinò Alessandro
  • Deng X. H.
  • André M.
  • Cully C. M.
  • He J. S.
  • Sahraoui Fouad
  • Yuan Z. G.
  • Pang Y.
  Geophysical Research Letters, American Geophysical Union, 2012, 39, pp.11103. We present one case study of magnetic islands and energetic electrons in the reconnection diffusion region observed by the Cluster spacecraft. The cores of the islands are characterized by strong core magnetic fields and density depletion. Intense currents, with the dominant component parallel to the ambient magnetic field, are detected inside the magnetic islands. A thin current sheet is observed in the close vicinity of one magnetic island. Energetic electron fluxes increase at the location of the thin current sheet, and further increase inside the magnetic island, with the highest fluxes located at the core region of the island. We suggest that these energetic electrons are firstly accelerated in the thin current sheet, and then trapped and further accelerated in the magnetic island by betatron and Fermi acceleration. (10.1029/2012GL051946)
  DOI : 10.1029/2012GL051946
• Ionospheric conductivity from the Ionograms recorded at Phu Thuy Hanoï
  
  • Pham Thi Thu Hong
  • Amory-Mazaudier Christine
  • Le Huy Minh
  Journal of Science of the Earth, 2012, 34 (4), pp.524-534. Ionospheric conductivity from the ionograms recorded at Phu Thuy, Hanoi This is the first study result about the structure of the ionospheric conductivity at the northern tropical crest of ionization in Vietnam. This paper presents briefly the theory of the ionospheric conductivity and shows the Pedersen and Hall conductivity profiles derived from ionograms recorded at Phu Thuy, Hanoi during the 1996 - 2004 period and the MISIS90 atmospheric model. We analyzed the diurnal, seasonal and sunspot cycle variations of ionospheric conductivity during magnetically quiet days during the period of interest. The profiles of the Hall and Pedersen ionospheric conductivities showed a maximum at 12.00 LT; Hall conductivity reached to maximum at an altitude of around 107.3±0.5 Km, meanwhile the profiles of the ionospheric Pedersen conductivity reached to maximum at altitude of around 127.1±0.8 Km. Maximum amplitude of Hall conductivity was greater than the one of Pedersen conductivity. Both conductivities varied clearly with the season and the amplitude of these maximums was greater in summer than in other seasons. The Hall and Pedersen ionospheric conductivities varied also on the time depending on the sunspot number.
• Electron-cylotron maser radiation from electron holes: downward current region
  
  • Treumann R. A.
  • Baumjohann W.
  • Pottelette Raymond
  Annales Geophysicae, European Geosciences Union, 2012, 30, pp.119-130. The electron-cyclotron maser emission theory from electron holes is applied to holes generated in the downward current region of the aurora. It is argued that the main background auroral kilometric radiation source may still be located in the upward current region electron-ring (horseshoe) distribution while the fine structure is caused by electron holes predominantly in the downward current region. There the existence of electron holes is well established and electron densities are high enough for substantial maser growth rates. Trapping of radiation by the holes provides strong amplification. Upward motion of holes favours the escape of radiation both, from the holes and from the downward current region, into the upward current region. Since upward and downward current regions always exist simultaneously, they are acting in tandem in generating auroral kilometric radiation and its fine structure by the same mechanism though in different ways. This mechanism solves the long-standing problem of auroral kilometric radiation fine structure. (10.5194/angeo-30-119-2012)
  DOI : 10.5194/angeo-30-119-2012