Publications

2015

• The Earth: Plasma Sources, Losses, and Transport Processes
  
  • Welling D. T.
  • André M.
  • Dandouras Iannis
  • Delcourt Dominique C.
  • Fazakerley A.
  • Fontaine Dominique
  • Foster John
  • Ilie R.
  • Kistler L. M.
  • Lee J. H.
  • Liemohn M. W.
  • Slavin J. A.
  • Wang Chih-Ping
  • Wiltberger M.
  • Yau Andrew
  Space Science Reviews, Springer Verlag, 2015, 192 (1-4), pp.145-208. This paper reviews the state of knowledge concerning the source of magnetospheric plasma at Earth. Source of plasma, its acceleration and transport throughout the system, its consequences on system dynamics, and its loss are all discussed. Both observational and modeling advances since the last time this subject was covered in detail (Hultqvist et al., Magnetospheric Plasma Sources and Losses, 1999) are addressed. (10.1007/s11214-015-0187-2)
  DOI : 10.1007/s11214-015-0187-2
• How to find magnetic nulls and reconstruct field topology with MMS data?
  
  • Fu H.S.
  • Vaivads A.
  • Khotyaintsev Y. V.
  • Olshevsky V.
  • André M.
  • Cao J.B.
  • Huang S. Y.
  • Retinò Alessandro
  • Lapenta G.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2015, 120 (5), pp.3758-3782. In this study, we apply a new method―-the first-order Taylor expansion (FOTE)―-to find magnetic nulls and reconstruct magnetic field topology, in order to use it with the data from the forthcoming MMS mission. We compare this method with the previously used Poincare index (PI), and find that they are generally consistent, except that the PI method can only find a null inside the spacecraft (SC) tetrahedron, while the FOTE method can find a null both inside and outside the tetrahedron and also deduce its drift velocity. In addition, the FOTE method can (1) avoid limitations of the PI method such as data resolution, instrument uncertainty (Bz offset), and SC separation; (2) identify 3-D null types (A, B, As, and Bs) and determine whether these types can degenerate into 2-D (X and O); (3) reconstruct the magnetic field topology. We quantitatively test the accuracy of FOTE in positioning magnetic nulls and reconstructing field topology by using the data from 3-D kinetic simulations. The influences of SC separation (0.05~1 d<SUB>i</SUB>) and null-SC distance (0~1 d<SUB>i</SUB>) on the accuracy are both considered. We find that (1) for an isolated null, the method is accurate when the SC separation is smaller than 1 d<SUB>i</SUB>, and the null-SC distance is smaller than 0.25~0.5 d<SUB>i</SUB>; (2) for a null pair, the accuracy is same as in the isolated-null situation, except at the separator line, where the field is nonlinear. We define a parameter xi &#8801; |( lambda<SUB>1</SUB> lambda<SUB>2</SUB> lambda<SUB>3</SUB> )|/|lambda|<SUB>max</SUB> in terms of the eigenvalues (lambda<SUB>i</SUB>) of the null to quantify the quality of our method―-the smaller this parameter the better the results. Comparing to the previously used parameter (eta&#8801;|&#8711; s B|/|&#8711; × B|), xi is more relevant for null identification. Using the new method, we reconstruct the magnetic field topology around a radial-type null and a spiral-type null, and find that the topologies are well consistent with those predicted in theory. We therefore suggest using this method to find magnetic nulls and reconstruct field topology with four-point measurements, particularly from Cluster and the forthcoming MMS mission. For the MMS mission, this null-finding algorithm can be used to trigger its burst-mode measurements. (10.1002/2015JA021082)
  DOI : 10.1002/2015JA021082
• Sub-nanosecond delays of light emitted by streamer in atmospheric pressure air: Analysis of N<SUB>2</SUB>(C<SUP>3</SUP>Pi<SUB>u</SUB>) and N<SUB>2</SUB><SUP>+</SUP>(B<SUP>2</SUP>Sigma<SUB>u</SUB><SUP>+</SUP>) emissions and fundamental streamer structure
  
  • Hoder Tomas
  • Bonaventura Zdenek
  • Bourdon Anne
  • Simek Milan
  Journal of Applied Physics, American Institute of Physics, 2015, 117, pp.073302. Theoretical analysis of ultra-short phenomena occurring during the positive streamer propagation in atmospheric pressure air is presented. Motivated by experimental results obtained with tens-of picoseconds and tens-of-microns precision, it is shown that when the streamer head passes a spatial coordinate, emission maxima from N2 and N2 radiative states follow with different delays. Thesedifferent delays are caused by differences in the dynamics of populating the radiative states, due to different excitation and quenching rates. Associating the position of the streamer head with the maximum value of the self-enhanced electric field, a delay of 160 ps was experimentally found for the peak emission of the first negative system of N2 . A delay dilatation was observed experimentally on early-stage streamers and the general mechanism of this phenomenon is clarified theoretically. In the case of the second positive system of N2, the delay can reach as much as 400 ps. In contrast to the highly nonlinear behavior of streamer events, it is shown theoretically that emission maximum delays linearly depend on the ratio of the streamer radius and its velocity. This is found to be one of the fundamental streamer features and its use in streamer head diagnostics is proposed. Moreover,radially resolved spectra are synthesized for selected subsequent picosecond moments in order to visualize spectrometric fingerprints of radial structures of N2(C3Piu) and N2 (B2Sigma u) populations created by streamer-head electrons (10.1063/1.4913215)
  DOI : 10.1063/1.4913215
• Fourier spectrum and phases for a signal in a finite interval
  
  • Belmont Gérard
  • Dorville Nicolas
  • Sahraoui Fouad
  • Rezeau Laurence
  , 2015, 17, pp.5320. 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 introducing 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 interference between the jumps and the signal itself provide in particular characteristic "hairs" on the spectrum, which are clearly visible on it with df&#8776;1/T. These fluctuations are usually eliminated by smoothing the spectrum, or by averaging several successive spectra. Nevertheless, such treatments introduce uncertainties on the spectral laws (the phases being anyway completely lost). Windowing is also a method currently used to suppress or decrease the jumps, but it modifies the signal (the windowed trend has a spectrum, which is convolved with the searched one) and the phases are generally much altered. 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 window function, sharp but not square. This window function is chosen such that the spectrum obtained can 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 and first applications to Cluster data are presented, which demonstrate the capability of the method to better estimate the Fourier spectra.
• Une énergie, des énergies. Comment fonctionne le monde ?
  
  • Aanesland Ane
  • Rezeau Laurence
  , 2015. Se chauffer, se déplacer, communiquer, créer? Toutes nos actions « consomment » de l'énergie. Omniprésente dans les débats géopolitiques, galvaudée par les slogans publicitaires, l'énergie hante notre société. Elle se conserve, mais s'épuise. Elle se manifeste partout, dans l'eau qui coule, dans les atomes qui se désintègrent ou fusionnent, mais pas toujours sous la forme qui conviendrait au moment voulu. Et pire, la voilà désormais associée aux pollutions ! La première partie de cet ouvrage fait le tour des signes perceptibles de l'énergie dans notre vie quotidienne (feu, vapeur?), puis ceux qui se produisent en nous et autour de nous, du vivant végétal jusqu'aux confins de l'Univers. La deuxième montre la manière dont les humains utilisent ces transformations énergétiques pour se nourrir, se déplacer, se loger, fabriquer des objets, alimenter leurs industries, créer ou communiquer. La troisième et dernière partie, plus théorique, donne les clés de l'énergie en se référant à l'histoire des sciences, l'épistémologie et la science contemporaine. À l'écart des jugements de valeur, ce livre rassemble les connaissances les plus actuelles, émanant de nombreux chercheurs de toutes disciplines.
• ICAN: High power neutral beam generation
  
  • Moustaizis Stavros
  • Lalousis P.
  • Perrakis K.
  • Auvray Philippe
  • Larour Jean
  • Ducret J.-E.
  • Balcou Philippe
  The European Physical Journal. Special Topics, EDP Sciences / Springer Verlag, 2015, 224, pp.2639 - 2643. During the last few years there is an increasing interest on the development of alternative high power new negative ion source for Tokamak applications. The proposed new neutral beam device presents a number of advantages with respect to: the density current, the acceleration voltage, the relative compact dimension of the negative ion source, and the coupling of a high power laser beam for photo-neutralization of the negative ion beam. Here we numerically investigate, using a multifluid 1-D code, the acceleration and the extraction of high power ion beam from a Magnetically Insulated Diode (MID). The diode configuration will be coupled to a high power device capable of extracting a current up to few kA with an accelerating voltage up to MeV. An efficiency of up to 92% of the coupling of the laser beam, is required in order to obtain a high power, up to GW, neutral beam. The new high energy, high average power, high efficiency (up to 30%) ICAN fiber laser is proposed for both the plasma generation and the photo-neutralizer configuration [1]. (10.1140/epjst/e2015-02576-6)
  DOI : 10.1140/epjst/e2015-02576-6
• Mid-Atomic-Number Cylindrical Wire Array Precursor Plasma Studies on Zebra
  
  • Stafford A.
  • Safronova Alla S.
  • Kantsyrev Viktor L.
  • Weller Michael E.
  • Shrestha Ishor
  • Shlyaptseva V. V.
  • Coverdale C. A.
  • Chuvatin Alexandre S.
  IEEE Transactions on Plasma Science, Institute of Electrical and Electronics Engineers, 2015, 43 (8), pp.2497 - 2502. Precursor plasmas from low wire number cylindrical wire arrays (CWAs) were previously shown to radiate at temperatures >300 eV for Ni-60 (94% Cu and 6% Ni) wires in experiments on the 1-MA Zebra generator. Continued research into precursor plasmas has studied additional midatomic-number materials including Cu and Alumel (95% Ni, 2% Al, 2% Mn, and 1% Si) to determine if the >300 eV temperatures are common for midatomic-number materials. In addition, current scaling effects were observed by performing CWA precursor experiments at an increased current of 1.5 MA using a load current multiplier. The results show an increase in a linear radiation yield of ~50% (16 versus 10 kJ/cm) for the experiments at increased current. However, plasma conditions inferred through the modeling of X-ray time-gated spectra are very similar for the precursor plasma in both current conditions. (10.1109/TPS.2014.2382072)
  DOI : 10.1109/TPS.2014.2382072
• Scaling and anisotropy of magnetohydrodynamic turbulence in a strong mean magnetic field
  
  • Mueller W.
  • Grappin Roland
  AGU Fall Meeting Abstracts, AGU, 2010, 51, pp.03. We present a new analysis of the anisotropic spectral energy distribution in incompressible magnetohydrodynamic (MHD) turbulence permeated by a strong mean magnetic field. The turbulent flow is generated by high-resolution pseudo-spectral direct numerical simulations with large-scale isotropic forcing. Examining the radial energy distribution for various angles theta with respect to B reveals a specific structure which remains hidden when not taking axial symmetry with respect to B0 into account. For each direction, starting at the forced large-scales, the spectrum first exhibits an amplitude drop around a wavenumber k0 which marks the start of a scaling range and goes on up to a dissipative wavenumber kd(theta). The 3D spectrum for k >= k0 is described by a single theta-independent functional form F(k/kd), the scaling law being the same in every direction. The previous properties still hold when increasing the mean field from B0=5 up to B0=10 (in units of brms), as well as when passing from resistive to ideal flows. We conjecture that at fixed B0 the direction-independent scaling regime is reached when increasing the Reynolds number above a threshold which raises with increasing B0.
• Anisotropy of Third-order Structure Functions in MHD Turbulence
  
  • Verdini Andrea
  • Grappin Roland
  • Hellinger P.
  • Landi Simone
  • Müller Wolf-Christian
  The Astrophysical Journal, American Astronomical Society, 2015, 804, pp.119. The measure of the third-order structure function, \boldsymbolY , is employed in the solar wind to compute the cascade rate of turbulence. In the absence of a mean field B<SUB>0</SUB>=0, \boldsymbolY is expected to be isotropic (radial) and independent of the direction of increments, so its measure yields directly the cascade rate. For turbulence with mean field, as in the solar wind, \boldsymbolY is expected to become more two-dimensional (2D), that is, to have larger perpendicular components, losing the above simple symmetry. To get the cascade rate, one should compute the flux of \boldsymbolY , which is not feasible with single-spacecraft data thus, measurements rely on assumptions about the unknown symmetry. We use direct numerical simulations (DNSs) of magnetohydrodynamic (MHD) turbulence to characterize the anisotropy of \boldsymbolY . We find that for strong guide field B<SUB>0</SUB>=5 the degree of two-dimensionalization depends on the relative importance of shear-Alfvén and pseudo-Alfvén polarizations (the two components of an Alfvén mode in incompressible MHD). The anisotropy also shows up in the inertial range. The more \boldsymbolY is 2D, the more the inertial range extent differs along parallel and perpendicular directions. We finally test the two methods employed in observations and find that the so-obtained cascade rate may depend on the angle between B<SUB>0</SUB> and the direction of increments. Both methods yield a vanishing cascade rate along the parallel direction, contrary to observations, suggesting a weaker anisotropy of solar wind turbulence compared to our DNSs. This could be due to a weaker mean field and/or to solar wind expansion. (10.1088/0004-637X/804/2/119)
  DOI : 10.1088/0004-637X/804/2/119