Publications

2014

Finite ballooning angle effects on ion temperature gradient driven mode in gyrokinetic flux tube simulations
- Singh Rameswar
- Brunner Stephan
- Ganesh R.
- Jenko F.
Physics of Plasmas, American Institute of Physics, 2014, 21 (3), pp.032115. This paper presents effects of finite ballooning angles on linear ion temperature gradient (ITG) driven mode and associated heat and momentum flux in Gyrokinetic flux tube simulation GENE. It is found that zero ballooning angle is not always the one at which the linear growth rate is maximum. The ITG mode acquires a short wavelength (SW) branch (k⊥ρi > 1) when growth rates maximized over all ballooning angles are considered. However, the SW branch disappears on reducing temperature gradient showing characteristics of zero ballooning angle SWITG in case of extremely high temperature gradient. Associated heat flux is even with respect to ballooning angle and maximizes at nonzero ballooning angle while the parallel momentum flux is odd with respect to the ballooning angle. (10.1063/1.4868425)
DOI : 10.1063/1.4868425
Momentum transport in the vicinity of qmin in reverse shear tokamaks due to ion temperature gradient turbulence
- Singh Rameswar
- Singh R.
- Jhang Hogun
- Diamond P.H.
Physics of Plasmas, American Institute of Physics, 2014, 21 (1), pp.012302. This paper presents effects of finite ballooning angles on linear ion temperature gradient (ITG) driven mode and associated heat and momentum flux in Gyrokinetic flux tube simulation GENE. It is found that zero ballooning angle is not always the one at which the linear growth rate is maximum. The ITG mode acquires a short wavelength (SW) branch (k⊥ρi > 1) when growth rates maximized over all ballooning angles are considered. However, the SW branch disappears on reducing temperature gradient showing characteristics of zero ballooning angle SWITG in case of extremely high temperature gradient. Associated heat flux is even with respect to ballooning angle and maximizes at nonzero ballooning angle while the parallel momentum flux is odd with respect to the ballooning angle. (10.1063/1.4861625)
DOI : 10.1063/1.4861625
The double well mass filter
- Gueroult R
- Fisch Nathaniel J.
- Rax Jean-Marcel
Physics of Plasmas, American Institute of Physics, 2014, 21 (2), pp.020701. Various mass filter concepts based on rotating plasmas have been suggested with the specific purpose of nuclear waste remediation. We report on a new rotating mass filter combining radial separation with axial extraction. The radial separation of the masses is the result of a “double-well” in effective radial potential in rotating plasma with a sheared rotation profile. (10.1063/1.4864325)
DOI : 10.1063/1.4864325
Pulsed discharges in a wide density range: plasma development and media excitation
- Starikovskaia Svetlana
- Starikovskii A.Yu.
, 2014. The Chapter demonstrates the peculiarities of pulsed nonequilibrium plasma generation in different media by nano- and picosecond high-voltage discharges. Fast ionization waves in long tubes at low pressures, streamers and dielectric barrier discharges at moderate and atmospheric pressures, surface dielectric barrier discharges at elevated pressures are considered. Special attention is given to start of picoseconds and nanosecond discharges in liquid media. The data used were consciously restricted to ICCD fast imaging of picoseconds and nanosecond discharges, to underline the dynamics of pulsed discharge development and the importance of spatial distribution of the discharge energy.
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
Experimental characterization of plasma formation and shockwave propagation induced by high power pulsed underwater electrical discharge
- Claverie Alain
- Deroy Julien
- Boustié Michel
- Avrillaud Gilles
- Chuvatin Alexandre S.
- Mazanchenko Ekaterina
- Demol G.
- Dramane B.
Review of Scientific Instruments, American Institute of Physics, 2014, 85 (06), pp.063701. High power pulsed electrical discharges into liquids are investigated for new industrial applications based on the efficiency of controlled shock waves. We present here new experimental data obtained by combination of detailed high speed imaging equipments. It allows the visualization of the very first instants of plasma discharge formation, and then the pulsations of the gaseous bubble with an accurate timing of events. The time history of the expansion/compression of this bubble leads to an estimation of the energy effectively transferred to water during the discharge. Finally, the consecutive shock generation driven by this pulsating bubble is optically monitored by shadowgraphs and schlieren setup. These data provide essential information about the geometrical pattern and chronometry associated with the shock wave generation and propagation. (10.1063/1.4879715)
DOI : 10.1063/1.4879715
Propagation of lower-band whistler-mode waves in the outer Van Allen belt: Systematic analysis of 11 years of multi-component data from the Cluster spacecraft
- Santolík O.
- Macusova E.
- Kolmasova Ivana
- Cornilleau-Wehrlin Nicole
- Conchy Y.
Geophysical Research Letters, American Geophysical Union, 2014, 41, pp.2729-2737. Lower-band whistler-mode emissions can influence the dynamics of the outer Van Allen radiation belts. We use 11 years of measurements of the STAFF-SA instruments onboard the four Cluster spacecraft to systematically build maps of wave propagation parameters as a function of position. We determine probability distributions of wave vector angle weighted by the wave intensity. The results show that wave vector directions of intense waves are close to a Gaussian-shaped peak centered on the local magnetic field line. The width of this peak is between 10 and 20 degrees. The cumulative percentage of oblique waves is below 1015%. This result is especially significant for an important class of whistler-mode emissions of lower-band chorus at higher latitudes, well outside their source region, where a simple ray tracing model fails and another mechanism is necessary to keep the wave vectors close to the field-aligned direction. (10.1002/2014GL059815)
DOI : 10.1002/2014GL059815
Investigation of Switch Designs for the Dynamic Load Current Multiplier Scheme on the SPHYNX Microsecond Linear Transformer Driver
- Maysonnave Thomas
- Bayol Frédéric
- Demol Gauthier
- d'Almeida Thierry
- Lassalle Francis
- Morell Alain
- Grunenwald Julien
- Chuvatin Alexandre S.
- Pecastaing Laurent
- de Ferron Antoine Silvestre
IEEE Transactions on Plasma Science, Institute of Electrical and Electronics Engineers, 2014, 42 (10), pp.2974-2980. SPHINX is a microsecond linear transformer driver LTD, used essentially for implosion of Z-pinch loads in direct drive mode. It can deliver a 6-MA current pulse within 800 ns into a Z-pinch load. The dynamic load current multiplier concept enables the current pulse to be modified by increasing its amplitude while reducing its rise time before being delivered to the load. This compact system is made up of concentric electrodes (autotransformer), a dynamic flux extruder (cylindrical wire array), a vacuum convolute (eight postholes), and a vacuum closing switch, which is the key component of the system. Several different schemes are investigated for designing a vacuum switch suitable for operating the dynamic load current multiplier on the SPHINX generator for various applications, including isentropic compression experiments and Z-pinch radiation effects studies. In particular, the design of a compact vacuum surface switch and a multichannel vacuum switch, located upstream of the load are studied. Electrostatic simulations supporting the switch designs are presented along with test bed experiments. Initial results from shots on the SPHINX driver are also presented. (10.1109/TPS.2014.2313372)
DOI : 10.1109/TPS.2014.2313372
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
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
Kelvin-Helmholtz Vortices and Double Mid-Latitude Reconnection at the Earth's Magnetopause: comparison between observations and simulations
- Faganello Matteo
- Califano F.
- Pegoraro F.
- Retinò Alessandro
EPL - Europhysics Letters, European Physical Society / EDP Sciences / Società Italiana di Fisica / IOP Publishing, 2014. Observational signatures of Kelvin-Helmholtz (K-H) vortices and of double mid-latitude reconnection are highlighted in satellite data of the THEMIS mission. It is shown that the plasma fluid quantities at the low-latitude flank of the Earth's magnetosphere are compatible with K-H vortices, as described by three-dimensional simulations. At the same time it is shown that the particle fluxes are compatible with the presence of magnetic field lines, embedded in the K-H vortices, that close on Earth but are connected to the solar wind at low-latitude. These field lines are generated during the K-H evolution by magnetic reconnection proceeding spontaneously in both hemispheres at mid-latitudes, allowing the solar wind plasma to enter the Earth's magnetosphere directly.
Wave normal angles of whistler-mode chorus rising and falling tones
- Taubenschuss U.
- Khotyaintsev Y. V.
- Santolík O.
- Vaivads A.
- Cully C. M.
- Le Contel Olivier
- Angelopoulos V.
Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2014. We present a study of wave normal angles (θk) of whistler mode chorus emission as observed by Time History of Events and Macroscale Interactions during Substorms (THEMIS) during the year 2008. The three inner THEMIS satellites THA, THD, and THE usually orbit Earth close to the dipole magnetic equator (±20°), covering a large range of L shells from the plasmasphere out to the magnetopause. Waveform measurements of electric and magnetic fields enable a detailed polarization analysis of chorus below 4 kHz. When displayed in a frequency-θk histogram, four characteristic regions of occurrence are evident. They are separated by gaps at f/fc,e≈0.5 (f is the chorus frequency, fc,e is the local electron cyclotron frequency) and at θk∼40°. Below θk∼40°, the average value for θk is predominantly field aligned, but slightly increasing with frequency toward half of fc,e (θk up to 20°). Above half of fc,e, the average θk is again decreasing with frequency. Above θk∼40°, wave normal angles are usually close to the resonance cone angle. Furthermore, we present a detailed comparison of electric and magnetic fields of chorus rising and falling tones. Falling tones exhibit peaks in occurrence solely for θk>40° and are propagating close to the resonance cone angle. Nevertheless, when comparing rising tones to falling tones at θk>40°, the ratio of magnetic to electric field shows no significant differences. Thus, we conclude that falling tones are generated under similar conditions as rising tones, with common source regions close to the magnetic equatorial plane. (10.1002/2014JA020575)
DOI : 10.1002/2014JA020575
Weak turbulence theory for rotating magnetohydrodynamics and planetary flows
- Galtier Sébastien
Journal of Fluid Mechanics, Cambridge University Press (CUP), 2014, 757, pp.114-154. A weak turbulence theory is derived for magnetohydrodynamics (MHD) under rapid rotation and in the presence of a uniform large-scale magnetic field which is associated with a constant Alfvén velocity . The angular velocity is assumed to be uniform and parallel to . Such a system exhibits left and right circularly polarized waves which can be obtained by introducing the magneto-inertial length . In the large-scale limit ( , with being the wavenumber) the left- and right-handed waves tend to the inertial and magnetostrophic waves, respectively, whereas in the small-scale limit ( ) pure Alfvén waves are recovered. By using a complex helicity decomposition, the asymptotic weak turbulence equations are derived which describe the long-time behaviour of weakly dispersive interacting waves via three-wave interaction processes. It is shown that the nonlinear dynamics is mainly anisotropic, with a stronger transfer perpendicular than parallel to the rotation axis. The general theory may converge to pure weak inertial/magnetostrophic or Alfvén wave turbulence when the large- or small-scale limits are taken, respectively. Inertial wave turbulence is asymptotically dominated by the kinetic energy/helicity, whereas the magnetostrophic wave turbulence is dominated by the magnetic energy/helicity. For both regimes, families of exact solutions are found for the spectra, which do not correspond necessarily to a maximal helicity state. It is shown that the hybrid helicity exhibits a cascade whose direction may vary according to the scale at which the helicity flux is injected, with an inverse cascade if and a direct cascade otherwise. The theory is relevant to the magnetostrophic dynamo, whose main applications are the Earth and the giant planets, such as Jupiter and Saturn, for which a small ( ) Rossby number is expected. (10.1017/jfm.2014.490)
DOI : 10.1017/jfm.2014.490
Dynamics of plasma evolution in a nanosecond underwater discharge
- Marinov Ilya
- Starikovskaia Svetlana
- Rousseau Antoine
Journal of Physics D: Applied Physics, IOP Publishing, 2014, 47 (22), pp.224017. A positive discharge in water is generated by applying a 30 ns high-voltage (HV) pulse on a micrometre scale electrode. The applied voltage ranges from 6 to 15 kV and a fast plasma propagating mode is launched with a velocity of up to 60 km s−1 . Time-resolved shadowgraphy and spectroscopy are performed to monitor the time evolution of the discharge structure and of the plasma emission spectra. By analysing the dynamics of the shock front velocity and the lateral expansion of the plasma channel, it is possible to estimate the pressure at the ignition of the plasma by two independent methods: very good agreement is found at 6 kV giving initial pressures of 0.4 GPa and 0.3 GPa, respectively. At 15 kV, only the shock front velocity method is applicable under our experimental conditions, giving an estimate of the initial pressure of 5.8 GPa. Such high initial pressures show that, under a nanosecond HV pulse, the plasma is ignited directly in the dense phase. Emission spectra show a strong continuum emission as well as a broad Balmer α line with a strong red shift, with an estimate of the initial plasma density of 1.3 × 1026 m−3. The relaxation of discharge pressure and plasma density is studied under a series of six successive pulses. (10.1088/0022-3727/47/22/224017)
DOI : 10.1088/0022-3727/47/22/224017
Time-resolved imaging of nanosecond-pulsed micro-discharges in heptane
- Hamdan A.
- Marinov Ilya
- Belmonte Thierry
- Rousseau A.
Journal of Physics D: Applied Physics, IOP Publishing, 2014, 47 (5). Nanosecond-pulsed micro-discharges in heptane are studied by time-resolved imaging in pin-to-plate configuration. When a voltage of +5 kV is applied to the pin electrode, the discharge exhibits one maximum in light intensity. At +15 kV, filtered images show that up to three maxima can be identified. These maxima are associated with local electron-ion recombination and bremsstrahlung emission and attributed to the development of a complex space-charge field. In the post-discharge, the dynamics of the gas bubble can be simulated by the Gilmore model, and the pressure evolution in this bubble is predicted. From our results, it seems reasonable to think that the gas bubble develops from the post-discharge of the spark. Results obtained by using the double-pulse technique show that light emission during the post-discharge of the second discharge lasts 10 times longer than the post-discharge of the first spark. The pressure drop in the gas bubble, predicted by the Gilmore model, is used to explain this result and it provides a control method by optical diagnostics in liquids. (10.1088/0022-3727/47/5/055203)
DOI : 10.1088/0022-3727/47/5/055203
Fourier spectrum and phases for a signal in a finite interval
- Dorville Nicolas
- Belmont Gérard
- Sahraoui Fouad
- Rezeau Laurence
, 2014, 13, pp.SH13B-4086. When investigating the physics of turbulent media, as the solar wind or the magnetosheath plasmas, obtaining accurate Fourier spectra and phases is a crucial issue. For the different fields, the spectra allow in particular verifying whether one or several power laws can be determined in different frequency ranges. Accurate phases are necessary as well for all the "higher order statistics" studies in Fourier space, the coherence ones and for the polarization studies. Unfortunately, the Fourier analysis is not unique for a finite time interval of duration T: the frequencies lower than 1/T have a large influence on the result, which can hardly be controlled. This unknown "trend" has in particular the effect of superposing jumps at the edges of the interval, for the function under study itself, as well as for all its derivatives. The Fourier transform obtained directly by FFT (Fast Fourier Transform) is generally much influenced by these effects and cannot be used without care for wide band signals. The interferences between the jumps and the signal itself also provide "hairs" on the spectrum, which are clearly visible fluctuations with df≈1/T. These fluctuations are usually eliminated by smoothing the spectrum, or by averaging several successive spectra. Nevertheless, such smoothing introduces uncertainties on the spectral laws and it makes the phases lost. Windowing is also a method currently used to suppress the jumps, but it modifies the signal (the windowed trend has a spectrum, which is convolved with the searched one) and the phases are also lost to a large extent. Here, we present a new data processing technique to circumvent these difficulties. It takes advantage of the fact that the signal is generally not unknown out of the interval under study: the complete signal is tapered to this interval of interest thanks to a new kind of window, sharp but not square. This kind of window is such that the spectrum obtained can then be deconvolved almost exactly, through a minimization procedure based on the weak- hypothesis that it is smooth at the scale of a few successive spectral points. Then, a later step allows reconstructing the phases. Tests with synthetic data are presented, that demonstrate the efficiency of the method, and first results from Cluster data are also shown.
Equivalence of the hard-wall and kinetic-fluid models of collisionless electron heating in capacitively coupled discharges
- Lafleur Trevor
- Chabert Pascal
- Turner Miles
- Booth Jean-Paul
Plasma Sources Science and Technology, IOP Publishing, 2014, 23 (1), pp.015016. By re-evaluating the hard-wall collisionless electron heating model from first principles, we show that despite previous criticisms (Gozadinos et al 2001 Phys. Rev. Lett. 87 [http://dx.doi.org/10.1103/PhysRevLett.87.135004] 135004 ), this model can in general be made consistent with the requirement of radio frequency (rf) current continuity at the sheath edge, while still producing a net heating effect. In addition, we demonstrate that the hard-wall and kinetic-fluid heating models stem from the same basic physical mechanism, and are in many ways the same theory; they differ only in the spatial region where electron heating is assumed to occur, and the way in which the effective electron distribution function is determined. Fundamentally, both models predict that collisionless heating occurs because of a non-isothermal compression and expansion of the plasma electrons by an oscillating rf sheath. (10.1088/0963-0252/23/1/015016)
DOI : 10.1088/0963-0252/23/1/015016
In situ spatiotemporal measurements of the detailed azimuthal substructure of the substorm current wedge
- Forsyth C.
- Fazakerley A.
- Rae I. J.
- Watt C. E. J.
- Murphy K.
- Wild James A.
- Karlsson T.
- Mutel R. L.
- Owen C. J.
- Ergun R.
- Masson A.
- Berthomier Matthieu
- Donovan E.
- Frey H.~u.
- Matzka J.
- Stolle C.
- Zhang Y.
Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2014, 119 (2), pp.927-946. The substorm current wedge (SCW) is a fundamental component of geomagnetic substorms. Models tend to describe the SCW as a simple line current flowing into the ionosphere toward dawn and out of the ionosphere toward dusk, linked by a westward electrojet. We use multispacecraft observations from perigee passes of the Cluster 1 and 4 spacecraft during a substorm on 15 January 2010, in conjunction with ground-based observations, to examine the spatial structuring and temporal variability of the SCW. At this time, the spacecraft traveled east-west azimuthally above the auroral region. We show that the SCW has significant azimuthal substructure on scales of 100 km at altitudes of 40007000 km. We identify 26 individual current sheets in the Cluster 4 data and 34 individual current sheets in the Cluster 1 data, with Cluster 1 passing through the SCW 120240 s after Cluster 4 at 13002000 km higher altitude. Both spacecraft observed large-scale regions of net upward and downward field-aligned current, consistent with the large-scale characteristics of the SCW, although sheets of oppositely directed currents were observed within both regions. We show that the majority of these current sheets were closely aligned to a north-south direction, in contrast to the expected east-west orientation of the preonset aurora. Comparing our results with observations of the field-aligned current associated with bursty bulk flows (BBFs), we conclude that significant questions remain for the explanation of SCW structuring by BBF-driven wedgelets. Our results therefore represent constraints on future modeling and theoretical frameworks on the generation of the SCW. (10.1002/2013JA019302)
DOI : 10.1002/2013JA019302
Ground state bromine atom density measurements by two-photon absorption laser-induced fluorescence
- Sirse Nishant
- Foucher Mickaël
- Chabert Pascal
- Booth Jean-Paul
Plasma Sources Science and Technology, IOP Publishing, 2014, 23 (6), pp.062003. Ground state bromine atom detection by two-photon absorption laser-induced fluorescence (TALIF) is demonstrated. The bromine atoms are excited by two-photon absorption at 252.594 nm to the state and detected by 635.25 nm fluorescence to the (5s) 4 P 5/2 state. The atoms are generated in a radio-frequency inductively-coupled plasma in pure HBr. The excitation laser also causes some photodissociation of HBr molecules, but this can be minimized by not focussing the laser beam, still giving adequate signal levels. We determined the natural lifetime of the emitting state, and the rate constant for quenching of this state by collision with HBr molecules, ... (10.1088/0963-0252/23/6/062003)
DOI : 10.1088/0963-0252/23/6/062003
Neutralizer-free gridded ion thruster
- Rafalskyi D.V.
- Aanesland Ane
American Institute of Aeronautics and Astronautics paper, 2014, Propulsion and Energy Forum. (10.2514/6.2014-3423)
DOI : 10.2514/6.2014-3423
Kinetic Turbulence in the Terrestrial Magnetosheath: Cluster Observations
- Huang S. Y.
- Sahraoui Fouad
- Deng X. H.
- He J. S.
- Yuan Z. G.
- Zhou M.
- Pang Y.
- Fu H.S.
The Astrophysical Journal Letters, Bristol : IOP Publishing, 2014, 789, pp.L28. We present a first statistical study of subproton- and electron-scale turbulence in the terrestrial magnetosheath using waveform data measured by the Cluster/STAFF search coil magnetometer in the frequency range [1, 180] Hz. It is found that clear spectral breaks exist near the electron scale, which separate two power-law-like frequency bands referred to as the dispersive and the electron dissipation ranges. The frequencies of the breaks fb are shown to be well correlated with the electron gyroscale rho e rather than with the electron inertial length de . The distribution of the slopes below fb is found to be narrow and peaks near -2.9, while that of the slopes above fb is found to be broader, peaking near -5.2, with values as low as -7.5. This is the first time that such steep power-law spectra are reported in space plasma turbulence. These observations provide new constraints on theoretical modeling of kinetic turbulence and dissipation in collisionless magnetized plasmas. (10.1088/2041-8205/789/2/L28)
DOI : 10.1088/2041-8205/789/2/L28
Characteristics of the flank magnetopause: Cluster observations
- Haaland S.
- Reistad J.
- Tenfjord P.
- Gjerloev J.
- Maes Lukas
- de Keyser J.
- Maggiolo R.
- Anekallu C.
- Dorville Nicolas
Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2014, 119, pp.9019-9037. The magnetopause is a current sheet forming the boundary between the geomagnetic field on one side and the shocked solar wind on the other side. This paper discusses properties of the low-latitude dawn and dusk flanks of the magnetopause. The reported results are based on a large number of measurements obtained by the Cluster satellites during magnetopause traversals. Using a combination of single-spacecraft and multispacecraft techniques, we calculated macroscopic features such as thickness, location, and motion of the magnetopause. The results show that the typical flank magnetopause is significantly thicker than the dayside magnetopause and also possesses a pronounced and persistent dawn-dusk asymmetry. Thicknesses vary from 150 to 5000 km, with an median thickness of around 1400 km at dawn and around 1150 km at dusk. Current densities are on average higher on dusk, suggesting that the total current at dawn and dusk are similar. Solar wind conditions and the interplanetary magnetic field cannot fully explain the observed dawn-dusk asymmetry. For a number of crossings we were also able to derive detailed current density profiles. The profiles show that the magnetopause often consists of two or more adjacent current sheets, each current sheet typically several ion gyroradii thick and often with different current direction. This demonstrates that the flank magnetopause has a structure that is more complex than the thin, one-dimensional current sheet described by a Chapman-Ferraro layer. (10.1002/2014JA020539)
DOI : 10.1002/2014JA020539
Planetary Science Virtual Observatory architecture
- Erard S.
- Cecconi B.
- Le Sidaner P.
- Berthier J.
- Henry F.
- Chauvin C.
- André N.
- Génot V.
- Jacquey C.
- Gangloff M.
- Bourrel N.
- Schmitt B.
- Capria M.-Th.
- Chanteur Gérard
Astronomy and Computing, Elsevier, 2014, 7-8, pp.71-80. In the framework of the Europlanet-RI program, a prototype of Virtual Observatory dedicated to Planetary Science was defined. Most of the activity was dedicated to the elaboration of standards to retrieve and visualize data in this field, and to provide light procedures to teams who wish to contribute with on-line data services. The architecture of this VO system and selected solutions are presented here, together with existing demonstrators. (10.1016/j.ascom.2014.07.005)
DOI : 10.1016/j.ascom.2014.07.005
A review on ion-ion plasmas created in weakly magnetized electronegative plasmas
- Aanesland Ane
- Bredin Jérôme
- Chabert Pascal
Plasma Sources Science and Technology, IOP Publishing, 2014, 23 (4), pp.044003. IonIon plasmas are electronegative plasmas where the electron density is several orders of magnitude lower than the negative ion density. These plasmas have been scarcely observed and investigated since the 1960s and are formed as a transient state of pulsed plasmas or in separate regions in magnetized plasmas. In this review we focus on the latter case of continuous formation of ionion plasmas created at the periphery of magnetized plasma columns or downstream localized magnetic barriers. We bring together and review experimental results already published elsewhere and complement them with new results to illustrate the physics important in ionion plasma formation and highlight in particular unanswered questions. We show that with a good design the density in the ionion region is dropping only by a factor of 23 from the initial plasma density. These plasmas can therefore be well suited for various ion source applications when both fluxes or beams of positive and negative ions are desired, and when electrons can cause harmful effects. (10.1088/0963-0252/23/4/044003)
DOI : 10.1088/0963-0252/23/4/044003

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