Publications

2012

• 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
• 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
• 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
• 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.
• 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.
• 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
• 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
• 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
• Analysis of Ni-60 alloy precursor wire array experiments on the 1.7 MA Zebra generator at UNR
  
  • Stafford A.
  • Safronova Alla S.
  • Kantsyrev Viktor L.
  • Esaulov A. A.
  • Weller Michael E.
  • Osborne Glenn C.
  • Shrestha Ishor
  • Keim S. F.
  • Shlyaptseva V. V.
  • Zunino H. A.
  • Coverdale C. A.
  • Chuvatin Alexandre S.
  , 2012, pp.2P88. Previous experiments on the 1 MA Zebra generator at UNR were dedicated to studies of precursor plasmas with Ni-60 alloy (96% Cu) cylindrical wire arrays (CWA). Those precursor plasmas were shown to consistently have electron temperatures >; 400 eV 1. Continuing research at 1 MA on Zebra found precursors for Cu, Brass, and Alumel CWAs to be consistent with Ni-60 results2. Recent Ni-60 CWA experiments have been performed on Zebra using a Load Current Multiplier (LCM) that raises the current up to 1.7 MA. A full set of diagnostics included 10 beam lines. These CWAs consist of 6 wires evenly spaced in a 12 mm diameter as before, but with a linear mass density of 100 μg/cm, more than double the mass density in 1 MA experiments. The radiation yield per unit length in the LCM shots, 16 kJ/cm, (with decreased 1 cm anode-cathode gap) has approximately doubled the previous Ni-60 yield per unit length. The total integrated PCD energy (filtered with 8 μm Be) increases up to 750 J (compared to the previous ~500 J). The percentage of the PCD due to the precursor has remained relatively constant. Non-LTE kinetic models of Cu and Ni have been applied to account for the L-shell radiation from the precursor and main x-ray burst plasmas. The resulting plasma parameters from modeling of TGSI and TISR spectra together with analysis of corresponding images allow for the study of precursor plasma formation in time and in space, respectively. (10.1109/PLASMA.2012.6383644)
  DOI : 10.1109/PLASMA.2012.6383644
• In Situ Observations of Reconnection and Associated Particle Energization in Turbulent Plasmas
  
  • Retinò Alessandro
  • Vaivads A.
  • Chasapis A.
  • Sundkvist D.
  • Sahraoui Fouad
  , 2012.
• EIDOSCOPE: particle acceleration at plasma boundaries
  
  • Vaivads A.
  • Andersson G.
  • Bale S. D.
  • Cully C. M.
  • de Keyser J.
  • Fujimoto M.
  • Grahn S.
  • Haaland S.
  • Ji H.
  • Khotyaintsev Y. V.
  • Lazarian A.
  • Lavraud B.
  • Mann I. R.
  • Nakamura R.
  • Nakamura T. K. M.
  • Narita Y.
  • Retinò Alessandro
  • Sahraoui Fouad
  • Schekochihin A.
  • Schwartz S. J.
  • Shinohara I.
  • Sorriso-Valvo L.
  Experimental Astronomy, Springer Link, 2012, 33 (2-3), pp.491-527. We describe the mission concept of how ESA can make a major contribution to the Japanese Canadian multi-spacecraft mission SCOPE by adding one cost-effective spacecraft EIDO (Electron and Ion Dynamics Observatory), which has a comprehensive and optimized plasma payload to address the physics of particle acceleration. The combined mission EIDOSCOPE will distinguish amongst and quantify the governing processes of particle acceleration at several important plasma boundaries and their associated boundary layers: collisionless shocks, plasma jet fronts, thin current sheets and turbulent boundary layers. Particle acceleration and associated cross-scale coupling is one of the key outstanding topics to be addressed in the Plasma Universe. The very important science questions that only the combined EIDOSCOPE mission will be able to tackle are: 1) Quantitatively, what are the processes and efficiencies with which both electrons and ions are selectively injected and subsequently accelerated by collisionless shocks? 2) How does small-scale electron and ion acceleration at jet fronts due to kinetic processes couple simultaneously to large scale acceleration due to fluid (MHD) mechanisms? 3) How does multi-scale coupling govern acceleration mechanisms at electron, ion and fluid scales in thin current sheets? 4) How do particle acceleration processes inside turbulent boundary layers depend on turbulence properties at ion/electron scales? EIDO particle instruments are capable of resolving full 3D particle distribution functions in both thermal and suprathermal regimes and at high enough temporal resolution to resolve the relevant scales even in very dynamic plasma processes. The EIDO spin axis is designed to be sun-pointing, allowing EIDO to carry out the most sensitive electric field measurements ever accomplished in the outer magnetosphere. Combined with a nearby SCOPE Far Daughter satellite, EIDO will form a second pair (in addition to SCOPE Mother-Near Daughter) of closely separated satellites that provides the unique capability to measure the 3D electric field with high accuracy and sensitivity. All EIDO instrumentation are state-of-the-art technology with heritage from many recent missions. The EIDOSCOPE orbit will be close to equatorial with apogee 25-30 RE and perigee 8-10 RE. In the course of one year the orbit will cross all the major plasma boundaries in the outer magnetosphere; bow shock, magnetopause and magnetotail current sheets, jet fronts and turbulent boundary layers. EIDO offers excellent cost/benefits for ESA, as for only a fraction of an M-class mission cost ESA can become an integral part of a major multi-agency L-class level mission that addresses outstanding science questions for the benefit of the European science community. (10.1007/s10686-011-9233-6)
  DOI : 10.1007/s10686-011-9233-6
• The 2012 Plasma Roadmap (Invited Review Article)
  
  • Samukawa S.
  • Hori M.
  • Rauf S.
  • Tachibana K.
  • Bruggeman P.
  • Kroesen G.
  • Whitehead J.C.
  • Murphy A.B.
  • Gutsol A.F.
  • Starikovskaia Svetlana
  • Kortshagen U.
  • Buf J.-P.
  • Sommerer T.J.
  • Kushner M.J.
  • Czarnetzki U.
  • Mason N.
  Journal of Physics D: Applied Physics, IOP Publishing, 2012, 45, pp.253001. Low-temperature plasma physics and technology are diverse and interdisciplinary fields. The plasma parameters can span many orders of magnitude and applications are found in quite different areas of daily life and industrial production. As a consequence, the trends in research, science and technology are difficult to follow and it is not easy to identify the major challenges of the field and their many sub-fields. Even for experts the road to the future is sometimes lost in the mist. Journal of Physics D: Applied Physics is addressing this need for clarity and thus providing guidance to the field by this special Review article, The 2012 Plasma Roadmap. Although roadmaps are common in the microelectronic industry and other fields of research and development, constructing a roadmap for the field of low-temperature plasmas is perhaps a unique undertaking. Realizing the difficulty of this task for any individual, the plasma section of the Journal of Physics D Board decided to meet the challenge of developing a roadmap through an unusual and novel concept. The roadmap was divided into 16 formalized short subsections each addressing a particular key topic. For each topic a renowned expert in the sub-field was invited to express his/her individual visions on the status, current and future challenges, and to identify advances in science and technology required to meet these challenges. Together these contributions form a detailed snapshot of the current state of the art which clearly shows the lifelines of the field and the challenges ahead. Novel technologies, fresh ideas and concepts, and new applications discussed by our authors demonstrate that the road to the future is wide and far reaching. We hope that this special plasma science and technology roadmap will provide guidance for colleagues, funding agencies and government institutions. If successful in doing so, the roadmap will be periodically updated to continue to help in guiding the field. (10.1088/0022-3727/45/25/253001)
  DOI : 10.1088/0022-3727/45/25/253001
• Surface vibrational relaxation of N<SUB>2</SUB> studied by CO<SUB>2</SUB> titration with time-resolved quantum cascade laser absorption spectroscopy
  
  • Marinov Daniil
  • Lopatik D.
  • Guaitella Olivier
  • Hübner M.
  • Ionikh Y.
  • Röpcke J.
  • Rousseau Antoine
  Journal of Physics D: Applied Physics, IOP Publishing, 2012, 45, pp.175201. A new method for determination of the wall de-excitation probability γ _\rm N₂ of vibrationally excited N2 on different surfaces exposed to low-pressure plasmas has been developed. A short dc discharge pulse of only a few milliseconds was applied to a mixture containing 0.051% of CO2 in N2 at a pressure of 133 Pa. Due to a nearly resonant fast vibrational transfer between N2(v) and the asymmetric &#957;3 mode of CO2 the vibrational excitation of these titrating molecules is an image of the degree of vibrational excitation of N2. In the afterglow, the vibrational relaxation of CO2 was monitored in situ using quantum cascade laser absorption spectroscopy. The experimental results were interpreted in terms of a numerical model of non-equilibrium vibrational kinetics in CO2N2 mixtures. Heterogeneous relaxation was the main quenching process of N2(v) under the conditions of this study, which allowed determination of the value of γ _\rm N₂ from the best agreement between the experiment and the model. The new method is suitable for γ _\rm N₂ determination in a single plasma pulse with the discharge tube surface pretreated by a low-pressure plasma. The relaxation probability of the first vibrational level of nitrogen &#947;1 = (1.1 ± 0.15) × 10&#8722;3 found for Pyrex and silica is in reasonable agreement with the literature data. Using the new technique the N2(v = 1) quenching probability was measured on TiO2 surface, &#947;1 = (9 ± 1) × 10&#8722;3. A linear enhancement of the N2(v) wall deactivation probability with an increase in the admixture of CO2 was observed for all studied materials. In order to explain this effect, a vibrational energy transfer mechanism between N2(v) and adsorbed CO2 is proposed. (10.1088/0022-3727/45/17/175201)
  DOI : 10.1088/0022-3727/45/17/175201
• Comparative study of Positive and Negative ion flows extracted from downstream plasmas beyond magnetic and electrostatic filters
  
  • Dudin S.
  • Rafalskyi D.V.
  • Popelier Lara
  • Aanesland Ane
  Physical Surface Engineering, 2012, 10, pp.22-28. In the present paper we compare the positive and negative ion flows created using a recently developed electrostatic grid-type filter with the flows formed using a magnetic filter. Langmuir probe measurements show electron cooling with both filters, allowing effective formation of negative ions via electron dissociative attachment in the region of low electron temperature. The energy distribution functions of positive and negative ions extracted from the filtered plasmas are measured in both systems showing an almost monoenergetic nature of the ions with the energy corresponding to the imposed extraction potential. It is shown that in both cases strongly electronegative plasmas where the negative ion density is much larger than the electron density can be formed downstream of the filter. Biasing an internal electrode or the electrostatic filter grid allows control of the plasma potential. In the case of the electrostatic filter the plasma could be biased negatively compared to ground and effective extraction of negative ion was achieved.
• Geomagnetism during solar cycle 23: Characteristics
  
  • Zerbo Jean-Louis
  • Amory-Mazaudier Christine
  • Ouattara F.
  Journal of Advanced Research, Elsevier, 2012, pp.1-25. On the basis of more than 48 years of morphological analysis of yearly and monthly values of the sunspot number, the aa index, the solar wind speed and interplanetary magnetic field, we point out the particularities of geomagnetic activity during the period 1996-2009. We especially investigate the last cycle 23 and the long minimum which followed it. During this period, the lowest values of the yearly averaged IMF (3nT) and yearly averaged solar wind speed (364km/s) are recorded in 1996, and 2009 respectively. The year 2003 shows itself particular by recording the highest value of the averaged solar wind (568 km/s), associated to the highest value of the yearly averaged aa index (37nT). We also find that observations during the year 2003 seem to be related to several coronal holes which are known to generate high-speed wind stream. From the long time (more than one century) study of solar variability, the present period is similar to the beginning of twentieth century. We especially present the morphological features of solar cycle 23 which is followed by a deep solar minimum. (10.1016/j.jare.2012.08.010)
  DOI : 10.1016/j.jare.2012.08.010
• SOLAR WIND TURBULENT SPECTRUM AT PLASMA KINETIC SCALES
  
  • Alexandrova Olga
  • Lacombe C.
  • Mangeney Anne
  • Grappin Roland
  • Maksimovic M.
  The Astrophysical Journal, American Astronomical Society, 2012, 760 (2), pp.121. The description of the turbulent spectrum of magnetic fluctuations in the solar wind in the kinetic range of scales is not yet completely established. Here, we perform a statistical study of 100 spectra measured by the STAFF instrument on the Cluster mission, which allows us to resolve turbulent fluctuations from ion scales down to a fraction of electron scales, i.e., from ~102 km to ~300 m. We show that for k &#8869;&#961; e in [0.03, 3] (which corresponds approximately to the frequency in the spacecraft frame f in [3, 300] Hz), all the observed spectra can be described by a general law E(k &#8869;)vpropk 8/3 &#8869;exp ( k &#8869;&#961; e ), where k &#8869; is the wavevector component normal to the background magnetic field and &#961; e the electron Larmor radius. This exponential tail found in the solar wind seems compatible with the Landau damping of magnetic fluctuations onto electrons. (10.1088/0004-637X/760/2/121)
  DOI : 10.1088/0004-637X/760/2/121
• IMPALAS: Investigation of MagnetoPause Activity using Longitudinally-Aligned Satellites―-a mission concept proposed for the ESA M3 2020/2022 launch
  
  • Owen C. J.
  • Amm Olaf
  • Bruno Roberto
  • de Keyser J.
  • Dunlop M. W.
  • Eastwood Jonathan P.
  • Fazakerley A.
  • Fontaine Dominique
  • Forsyth C.
  • Hasegawa H.
  • Hellinger P.
  • Hercik David
  • Jacquey C.
  • Milan Steven
  • Raeder Joachim
  • Sibeck David G.
  • Stverak Stepan
  • Travnicek Pavel
  • Walsh Andrew P.
  • Wild James A.
  Experimental Astronomy, Springer Link, 2012, 33 (2-3), pp.365-401. The dayside magnetopause is the primary site of energy transfer from the solar wind into the magnetosphere, and modulates the activity observed within the magnetosphere itself. Specific plasma processes operating on the magnetopause include magnetic reconnection, generation of boundary waves, propagation of pressure-pulse induced deformations of the boundary, formation of boundary layers and generation of Alfvén waves and field-aligned current systems connecting the boundary to the inner magnetosphere and ionosphere. However, many of the details of these processes are not fully understood. For example, magnetic reconnection occurs sporadically, producing flux transfer events, but how and where these arise, and their importance to the global dynamics of the magnetospheric system remain unresolved. Many of these phenomena involve propagation across the magnetopause surface. Measurements at widely-spaced (Delta 5 R<SUB>E</SUB>) intervals along the direction of dayside terrestrial field lines at the magnetopause would be decisive in resolving these issues. We describe a mission carrying a fields and plasmas payload (including magnetometer, ion and electron spectrometer and energetic particle telescopes) on three identical spacecraft in synchronized orbits. These provide the needed separations, with each spacecraft skimming the dayside magnetopause and continuously sampling this boundary for many hours. The orbits are phased such that (i) all three spacecraft maintain common longitude and thus sample along the same magnetopause field line; (ii) the three spacecraft reach local midday when northern European ground-based facilities also lie near local midday, enabling simultaneous sampling of magnetopause field lines and their footprints. (10.1007/s10686-011-9245-2)
  DOI : 10.1007/s10686-011-9245-2
• Time dependent behaviors of ion-ion plasmas exposed to various voltage waveforms in the kilohertz to megahertz frequency range
  
  • Oudini N.
  • Garrigues Laurent
  • Meige A.
  • Raimbault Jean-Luc
  • Chabert Pascal
  • Aanesland Ane
  Physics of Plasmas, American Institute of Physics, 2012, 19, pp.103501. An ion-ion plasma, situated between two parallel electrodes, is studied with the use of a time dependent one-dimensional particle-in-cell Monte-Carlo collisions model. This plasma consists of only positively and negatively singly charged ions with the same order of mass and temperature (the electron density is zero). The right electrode is grounded, and the left electrode is biased with a voltage waveform varying from sinusoidal to square with the frequency in the kHz to MHz range. The sheath evolution and the particle flux towards the electrodes, as a function of both space and time, are investigated for the various waveforms and frequencies. The sheath evolution has a strong influence on the time averaged ion energy distribution function (IEDF). The IEDF is broad with a low energy tail for low frequency sinusoidal biases (25kHz) while peaked at low energy for higher frequencies (2 MHz). For square waveforms, the IEDF is mono-energetic with some broadening when the rise time is faster than the typical time to establish the steady state sheath formation(<0.3 us). (10.1063/1.4762855)
  DOI : 10.1063/1.4762855