Publications

2022 | 2021 | 2020 | 2019

Below, by year, are the publications listed in the HAL open archive.

2019

Filamentary nanosecond surface dielectric barrier discharge. Plasma properties in the filaments
- Shcherbanev S.A.
- Ding Chenyang
- Starikovskaia Svetlana
- Popov N.A.
Plasma Sources Science and Technology, IOP Publishing, 2019, 28 (6), pp.065013. Streamer-to-filament transition is a general feature of nanosecond discharges at elevated pressure. The transition is observed in different discharges by different groups: in the nanosecond surface dielectric barrier discharges (nSDBDs) in a single shot regime at high pressure (2-15 bar), in the point-to-point or point-to-plane open electrodes discharges at high repetitive frequency (so-called nanosecond repetitive pulsed discharges, NRPDs) at atmospherics pressure. The present paper contains experimental analysis of plasma properties in the filamentary nSDBD: the electrical current, the specific deposited energy, the electron density and the electron temperature were measured for a wide range of pressures and voltages. A model explaining plasma properties in filamentary nanosecond discharges and the role of excited species in streamer-to-filament transition is suggested and discussed. (10.1088/1361-6595/ab2230)
DOI : 10.1088/1361-6595/ab2230
Experimental study of pulsed microwave discharges at pressures ranging over five orders of magnitude
- Shcherbanev S.A.
- Ali Cherif Mhedine
- Starikovskaia Svetlana
- Ikeda Yuji
Plasma Sources Science and Technology, IOP Publishing, 2019, 28, pp.045009 (10pp). Microwave discharge igniter (MDI) is a discharge system developed to initiate combustion in automotive engines. The MDI uses a sequence of N = 700 microwave (2.45 GHz) pulses 100 ns in duration separated by 1 μs. The initial breakdown is provided by the ﬁrst microwave pulse, 5 μs in duration. The aim of pulsing the microwave signal is to keep an optimal combination of parameters when, even at elevated pressures, (i) the discharge propagates over the largest possible volume; (ii) the plasma is non-equilibrium. Properties of plasma produced by MDI igniter in non-combustible gas mixtures at ambient gas temperature and gas pressure in the range between 0.2 mbar and 8 bar were studied experimentally. Discharge spatial structure was analyzed with the help of time-resolved ICCD imaging. Near-UV optical emission spectra taken in different pulses provided the information about rotational and vibrational temperatures. The electric ﬁeld was estimated on the basis of ratio of emission of the second positive and the ﬁrst negative systems of molecular nitrogen. (10.1088/1361-6595/aae765)
DOI : 10.1088/1361-6595/aae765
Nonlinear interaction of whistler waves in a magnetized plasma with density ducts
- Zaboronkova T. M.
- Krafft Catherine
- Yashina N. F.
Physics of Plasmas, American Institute of Physics, 2019, 26, pp.102104. The nonlinear resonant interactions between whistler waves guided bydensity ducts surrounded by a uniform magnetized plasma are studied. Itis shown that, under specific conditions that are determined, a time-harmonic external electromagnetic field can drive the parametricinstability of guided whistlers. Both cases of cylindrical and planarducts are considered, of either decreased or increased plasma density.The frequency interval where the magnetized plasma may be resonant isanalyzed. The growth rate and the threshold of the parametricinstability are determined. Numerical calculations are presented forparameters typical of "space plasmas and" modeling laboratoryexperiments where guided whistler propagation was observed. (10.1063/1.5110958)
DOI : 10.1063/1.5110958
Solar Wind Properties and Geospace Impact of Coronal Mass Ejection‐Driven Sheath Regions: Variation and Driver Dependence
- Kilpua E. K. J.
- Fontaine D.
- Moissard C.
- Ala‐lahti M.
- Palmerio E.
- Yordanova E.
- Good S.
- Kalliokoski M. M. H.
- Lumme E.
- Osmane A.
- Palmroth M.
- Turc L.
Space Weather: The International Journal of Research and Applications, American Geophysical Union (AGU), 2019, 17 (8), pp.1257-1280. We present a statistical study of interplanetary conditions and geospace response to 89 coronal mass ejection‐driven sheaths observed during Solar Cycles 23 and 24. We investigate in particular the dependencies on the driver properties and variations across the sheath. We find that the ejecta speed principally controls the sheath geoeffectiveness and shows the highest correlations with sheath parameters, in particular in the region closest to the shock. Sheaths of fast ejecta have on average high solar wind speeds, magnetic (B) field magnitudes, and fluctuations, and they generate efficiently strong out‐of‐ecliptic fields. Slow‐ejecta sheaths are considerably slower and have weaker fields and field fluctuations, and therefore they cause primarily moderate geospace activity. Sheaths of weak and strong B field ejecta have distinct properties, but differences in their geoeffectiveness are less drastic. Sheaths of fast and strong ejecta push the subsolar magnetopause significantly earthward, often even beyond geostationary orbit. Slow‐ejecta sheaths also compress the magnetopause significantly due to their large densities that are likely a result of their relatively long propagation times and source near the streamer belt. We find the regions near the shock and ejecta leading edge to be the most geoeffective parts of the sheath. These regions are also associated with the largest B field magnitudes, out‐of‐ecliptic fields, and field fluctuations as well as largest speeds and densities. The variations, however, depend on driver properties. Forecasting sheath properties is challenging due to their variable nature, but the dependence on ejecta properties determined in this work could help to estimate sheath geoeffectiveness through remote‐sensing coronal mass ejection observations (10.1029/2019SW002217)
DOI : 10.1029/2019SW002217
Measuring the magnetic structure velocity for the 11 July 2017 magnetotail reconnection event
- Denton R. E.
- Hasegawa H.
- Torbert R. B.
- Manuzzo Roberto
- Sonnerup B. U. Ö.
- Genestreti K. J.
- Dors I.
- Belmont Gérard
- Rezeau Laurence
- Califano F.
, 2019. Velocities in magnetic reconnection events, such as those of particles, are best understood in the frame of reference of the magnetic structure that is ultimately responsible for the reconnection process. We discuss four different methods for evaluating the velocity of the magnetic structure, and use those methods to find the magnetic structure velocity for the 11 July 2017 magnetotail reconnection event studied by Torbert et al. (Science, 2018). The four methods are timing analysis, the SpatioTemporal Difference (STD) method of Shi et al. (JGR, 2006), Electron Magnetohydrodynamic (EMHD) reconstruction (Sonnerup et al., JGR, 2016), and polynomial reconstruction of the magnetic field in the vicinity of the spacecraft using the magnetic field and particle current density as input to the model. The relative merits of the different techniques will be discussed, and the different results compared.
Waves in Kinetic-Scale Magnetic Dips: MMS Observations in the Magnetosheath
- Yao S. T.
- Shi Q. Q.
- Yao Z. H.
- Li J. X.
- Yue C.
- Tao X.
- Degeling A. W.
- Zong Q. G.
- Wang X. G.
- Tian A. M.
- Russell C. T.
- Zhou X. Z.
- Guo R. L.
- Rae I. J.
- Fu H.S.
- Zhang H.
- Li L.
- Le Contel Olivier
- Torbert R. B.
- Ergun R. E.
- Lindqvist P.-A.
- Pollock C. J.
- Giles B. L.
Geophysical Research Letters, American Geophysical Union, 2019, 46 (2), pp.523-533. Kinetic-scale magnetic dips (KSMDs), with a significant depression in magnetic field strength, and scale length close to and less than one proton gyroradius, were reported in the turbulent plasmas both in recent observation and numerical simulation studies. These KSMDs likely play important roles in energy conversion and dissipation. In this study, we present observations of the KSMDs that are labeled whistler mode waves, electrostatic solitary waves, and electron cyclotron waves in the magnetosheath. The observations suggest that electron temperature anisotropy or beams within KSMD structures provide free energy to generate these waves. In addition, the occurrence rates of the waves are higher in the center of the magnetic dips than at their edges, implying that the KSMDs might be the origin of various kinds of waves. We suggest that the KSMDs could provide favorable conditions for the generation of waves and transfer energy to the waves in turbulent magnetosheath plasmas. (10.1029/2018GL080696)
DOI : 10.1029/2018GL080696
Nonlinear Diffusion Models for Gravitational Wave Turbulence
- Galtier Sébastien
- Nazarenko Sergey V.
- Buchlin Éric
- Thalabard Simon
Physica D: Nonlinear Phenomena, Elsevier, 2019, 390, pp.84-88. A fourth-order and a second-order nonlinear diffusion model in spectral space are proposed to describe gravitational wave turbulence in the approximation of strongly local interactions. We show analytically that the model equations satisfy the conservation of energy and wave action, and reproduce the power law solutions previously derived from the kinetic equations with a direct cascade of energy and an explosive inverse cascade of wave action. In the latter case, we show numerically by computing the second-order diffusion model that the non-stationary regime exhibits an anomalous scaling which is understood as a self-similar solution of the second kind with a front propagation following the law kf∼(t∗−t)3.296 , with t<t∗ . These results are relevant to better understand the dynamics of the primordial universe where potent sources of gravitational waves may produce space–time turbulence. (10.1016/j.physd.2019.01.007)
DOI : 10.1016/j.physd.2019.01.007
Single‑mode scannable nanosecond Ti:sapphire laser forhigh‑resolution two‑photon absorption laser‑induced fluorescence (TALIF)
- Lottigier Pierre
- Jucha Alain
- Cabaret Louis
- Blondel Christophe
- Drag Cyril
Applied Physics B - Laser and Optics, Springer Verlag, 2019 (125), pp.14. A pulsed Ti:sapphire laser has been developed so as to operate over a wide range of frequencies, even far from the optimum wavelength (790 nm), as a narrow-band light source for TALIF experiments on O, Cl, N and H. The coupling of the optical cavity, both to its injection seeder and to the laser output beam, relies on a reflecting plate, which makes it fundamentally easier to control the coupling coefficient over a wider spectral range than with an ordinary transmission coupler. Two intra- cavity prisms are used to bring the green pumping light longitudinally coincident with the cavity axis, inside the Ti:sapphire crystal. Seeding by a CW Ti:sapphire laser has made it possible to obtain single-mode emission over the whole range of tunability, thanks to the spectral selection of the prisms and to a specifically developed digital/analog controller. Experiments carried out with the system on oxygen atoms inside an oxygen plasma show that the experimental bandwidth is limited essentially by the collisional dephasing rate and the finite pulse duration. (10.1007/s00340-018-7124-5)
DOI : 10.1007/s00340-018-7124-5
Physics research on the TCV tokamak facility: from conventional to alternative scenarios and beyond
- Coda S.
- Agostini M.
- Albanese R.
- Alberti S.
- Alessi E.
- Allan S.
- Allcock J.
- Ambrosino R.
- Anand H.
- Andrèbe Y.
- Arnichand H.
- Auriemma F.
- Ayllon-Guerola J.M.
- Bagnato F.
- Ball J.
- Baquero-Ruiz M.
- Beletskii A.A.
- Bernert M.
- Bin W.
- Blanchard P.
- Blanken T.C.
- Boedo J.A.
- Bogar O.
- Bolzonella T.
- Bombarda F.
- Bonanomi N.
- Bouquey F.
- Bowman C.
- Brida D.
- Bucalossi J.
- Buermans J.
- Bufferand H.
- Buratti P.
- Calabró G.
- Calacci L.
- Camenen Y.
- Carnevale D.
- Carpanese F.
- Carr M.
- Carraro L.
- Casolari A.
- Causa F.
- Čeřovský J.
- Chellaï O.
- Chmielewski P.
- Choi D.
- Christen N.
- Ciraolo G.
- Cordaro L.
- Costea S.
- Cruz N.
- Czarnecka A.
- Molin A. Dal
- David P.
- Decker J.
- Oliveira H. De
- Douai D.
- Dreval M.B.
- Dudson B.
- Dunne M.
- Duval B.P.
- Eich T.
- Elmore S.
- Embréus O.
- Esposito B.
- Faitsch M.
- Farník M.
- Fasoli A.
- Fedorczak N.
- Felici F.
- Feng S.
- Feng X.
- Ferro G.
- Février O.
- Ficker O.
- Fil Alexandre
- Fontana M.
- Frassinetti L.
- Furno I.
- Gahle D.S.
- Galassi D.
- Ga\lązka K.
- Gallo A.
- Galperti C.
- Garavaglia S.
- Garcia J.
- Garcia-Muñoz M.
- Garrido A.J.
- Garrido I.
- Gath J.
- Geiger B.
- Giruzzi G.
- Gobbin M.
- Goodman T.P.
- Gorini G.
- Gospodarczyk M.
- Granucci G.
- Graves J.P.
- Gruca M.
- Gyergyek T.
- Hakola A.
- Happel T.
- Harrer G.F.
- Harrison J.
- Havlíčková E.
- Hawke J.
- Henderson S.
- Hennequin P.
- Hesslow L.
- Hogeweij D.
- Hogge J.-Ph.
- Hopf C.
- Hoppe M.
- Horáček J.
- Huang Z.
- Hubbard A.
- Iantchenko A.
- Igochine V.
- Innocente P.
- Schrittwieser C. Ionita
- Isliker H.
- Jacquier R.
- Jardin A.
- Kappatou A.
- Karpushov A.
- Kazantzidis P.-V.
- Keeling D.
- Kirneva N.
- Komm M.
- Kong M.
- Kovacic J.
- Krawczyk N.
- Kudlacek O.
- Kurki-Suonio T.
- Kwiatkowski R.
- Labit B.
- Lazzaro E.
- Linehan B.
- Lipschultz B.
- Llobet X.
- Lombroni R.
- Loschiavo V.P.
- Lunt T.
- Macusova E.
- Madsen J.
- Maljaars E.
- Mantica P.
- Maraschek M.
- Marchetto C.
- Marco A.
- Mariani A.
- Marini C.
- Martin Y.
- Matos F.
- Maurizio R.
- Mavkov B.
- Mazon D.
- Mccarthy P.
- Mcdermott R.
- Menkovski V.
- Merle A.
- Meyer H.
- Micheletti D.
- Militello F.
- Mitosinkova K.
- Mlynář J.
- Moiseenko V.
- Cabrera P.A. Molina
- Morales J.
- Moret J.-M.
- Moro A.
- Mumgaard R.T.
- Naulin V.
- Nem R.D.
- Nespoli F.
- Nielsen A.H.
- Nielsen S.K.
- Nocente M.
- Nowak S.
- Offeddu N.
- Orsitto F.P.
- Paccagnella R.
- Palha A.
- Papp G.
- Pau A.
- Pavlichenko R.O.
- Perek A.
- Ridolfini V. Pericoli
- Pesamosca F.
- Piergotti V.
- Pigatto L.
- Piovesan P.
- Piron C.
- Plyusnin V.
- Poli E.
- Porte L.
- Pucella G.
- Puiatti M.E.
- Pütterich T.
- Rabinski M.
- Rasmussen J. Juul
- Ravensbergen T.
- Reich M.
- Reimerdes H.
- Reimold F.
- Reux C.
- Ricci D.
- Ricci P.
- Rispoli N.
- Rosato J.
- Saarelma S.
- Salewski M.
- Salmi A.
- Sauter O.
- Scheffer M.
- Schlatter Ch.
- Schneider B.S.
- Schrittwieser R.
- Sharapov S.
- Sheeba R.R.
- Sheikh U.
- Shousha R.
- Silva M.
- Sinha J.
- Sozzi C.
- Spolaore M.
- Stipani L.
- Strand P.
- Tala T.
- Tema Biwole A.S.
- Teplukhina A.A.
- Testa D.
- Theiler C.
- Thornton A.
- Tomaž G.
- Tomes M.
- Tran M.Q.
- Tsironis C.
- Tsui C.K.
- Urban Joanna M
- Valisa M.
- Valla M.
- Vugt D. Van
- Vartanian S.
- Vasilovici O.
- Verhaegh K.
- Vermare L.
- Vianello N.
- Viezzer E.
- Vijvers W.A.J.
- Villone F.
- Voitsekhovitch I.
- Vu N.M.T.
- Walkden N.
- Wauters T.
- Weiland M.
- Weisen H.
- Wensing M.
- Wiesenberger M.
- Wilkie G.
- Wischmeier M.
- Wu K.
- Yoshida M.
- Zagorski R.
- Zanca P.
- Zebrowski J.
- Zisis A.
- Zuin M.
- Eurofusion Mst1 Team The
Nuclear Fusion, IOP Publishing, 2019, 59 (11), pp.112023. The research program of the TCV tokamak ranges from conventional to advanced-tokamak scenarios and alternative divertor configurations, to exploratory plasmas driven by theoretical insight, exploiting the device’s unique shaping capabilities. Disruption avoidance by real-time locked mode prevention or unlocking with electron-cyclotron resonance heating (ECRH) was thoroughly documented, using magnetic and radiation triggers. Runaway generation with high-Z noble-gas injection and runaway dissipation by subsequent Ne or Ar injection were studied for model validation. The new 1 MW neutral beam injector has expanded the parameter range, now encompassing ELMy H-modes in an ITER-like shape and nearly non-inductive H-mode discharges sustained by electron cyclotron and neutral beam current drive. In the H-mode, the pedestal pressure increases modestly with nitrogen seeding while fueling moves the density pedestal outwards, but the plasma stored energy is largely uncorrelated to either seeding or fueling. High fueling at high triangularity is key to accessing the attractive small edge-localized mode (type-II) regime. Turbulence is reduced in the core at negative triangularity, consistent with increased confinement and in accord with global gyrokinetic simulations. The geodesic acoustic mode, possibly coupled with avalanche events, has been linked with particle flow to the wall in diverted plasmas. Detachment, scrape-off layer transport, and turbulence were studied in L- and H-modes in both standard and alternative configurations (snowflake, super-X, and beyond). The detachment process is caused by power ‘starvation’ reducing the ionization source, with volume recombination playing only a minor role. Partial detachment in the H-mode is obtained with impurity seeding and has shown little dependence on flux expansion in standard single-null geometry. In the attached L-mode phase, increasing the outer connection length reduces the in–out heat-flow asymmetry. A doublet plasma, featuring an internal X-point, was achieved successfully, and a transport barrier was observed in the mantle just outside the internal separatrix. In the near future variable-configuration baffles and possibly divertor pumping will be introduced to investigate the effect of divertor closure on exhaust and performance, and 3.5 MW ECRH and 1 MW neutral beam injection heating will be added. (10.1088/1741-4326/ab25cb)
DOI : 10.1088/1741-4326/ab25cb
Cavity-enhanced photodetachment of H$^-$as a means to produce energetic neutral beams for phasma Heating
- Blondel Christophe
- Bresteau David
- Drag Cyril
Atoms, MDPI, 2019, 7 (1), pp.32. Neutral beam injection, for plasma heating, will supposedly be achieved, in ITER, by collisional detachment of a pre-accelerated D− beam. Collisional detachment, however, makes use of a D2-filled neutralisation chamber, which has severe drawbacks, including the necessity to set the D− -ion source at −1 MV. Photodetachment, in contradistinction, would have several advantages as a neutralisation method, including the absence of gas injection, and the possibility to set the ion source close to the earth potential. Photodetachment, however, requires a very high laser flux. The presented work has consisted in implementing an optical cavity, with a finesse greater than 3000, to make such a high illumination possible with a state-of-the-art CW (continuous-wave) laser. A 1.2 keV 1H− -beam (only 20 times slower than the 1 MeV 2D− ion beams to be prepared for ITER) was photodetached with more-than-50% efficiency, with only 24 W of CW laser input. This experimental demonstration paves the way for developing real-size photoneutralizers, based on the implementation of refolded optical cavities around the ion beams of neutral beam injectors. Depending on whether the specifications of the laser power or the cavity finesse will be more difficult to achieve in real scale, different architectures can be considered, with greater or smaller numbers of optical refoldings or (inclusively) optical cavities in succession, on the beam to be neutralised. (10.3390/atoms7010032)
DOI : 10.3390/atoms7010032
Plasma-surface interaction: dielectric and metallic targets and their influence on the electric field profile in a kHz AC-driven He plasma jet
- Sobota Ana
- Guaitella Olivier
- Sretenović G. B.
- Kovačević V. V.
- Slikboer Elmar
- Krstić I. B.
- Obradović B. M.
- Kuraica M. M.
Plasma Sources Science and Technology, IOP Publishing, 2019, 28 (4), pp.045003. Plasma catalysis, biomedical applications or atomic layer deposition at atmospheric pressure all make use of non-thermal plasmas in contact with a wide variety of surfaces. As the presence of a target (substrate) has been shown to modify the plasma in addition to the plasma modifying the target, it is reasonable to describe and study the plasma-surface as one system. This work shows how the presence of dielectric and metallic targets influences a kHz AC-driven discharge in a He plasma jet. Next to bringing the absolute values of the axial electric field along the plume of the jet, the presence of the surface has been shown to significantly elongate both the plume and the electric field profile. In addition, when a dielectric target is placed closer than the maximum length of the freely expanding jet, the electric field profile is enhanced only in the vicinity of the dielectric, typically between 0.3 and 2 mm above the target surface. The maximum measured relative increase is 31%, for 1000 SCCM flow with the target at 7 mm distance, when the electric field increased from 14.1 kV cm−1 for the freely expanding jet to 32.6 kV cm−1 when the jet was impinging on glass. Finally, a grounded metallic target enhances the electric field compared to the glass target only within a very thin layer just above the surface, typically about 0.2 mm. The highest measured electric field was 40.1 kV cm−1 at a grounded metallic target 12 mm away from the nozzle, for 1000 SCCM of helium flow. The discussion on the effects of the flow on the electric field profile are supported by the visualization of the flow. The discussion brings, among other, the comparison of properties between the 30 kHz AC-driven system and the 5 kHz pulsed jet. (10.1088/1361-6595/ab0c6a)
DOI : 10.1088/1361-6595/ab0c6a
Numerical simulations of high cross-helicity turbulence from 0.2 to 1 AU
- Verdini Andrea
- Grappin Roland
- Montagud-Camps Victor
- Landi Simone
- Franci Luca
- Papini Emanuele
Il Nuovo cimento della Societa italiana di fisica. C, Springer-Verlag, 2019, 42, pp.17. Turbulence in the fast stream of the solar wind is maintained despitethe small compressibility and a dominance of outward-propagatingfluctuations ( z^+>z^- , in contrast to its rapid decay in imbalancedhomogenous MHD turbulence. We numerically study if the inhomogeneityintroduced by solar wind expansion can be an effective source of z^-that maintains turbulence. Starting at 0.2 AU with z^-=0 , we obtain adamping with distance of z^+ and a quasi-steady level of z^- . The z^+spectrum steepens with distance toward a -1.4 power-law at 1 AU, whilethe z^- spectrum has a -5/3 power-law index at all distances. Theseproperties are robust against variations of the input spectrum andexpansion rate and are in agreement with in-situ data, suggesting thatimbalanced turbulence can be maintained by expansion alone. (10.1393/ncc/i2019-19017-x)
DOI : 10.1393/ncc/i2019-19017-x
Whistler Waves' Propagation in Plasmas With Systems of Small-Scale Density Irregularities: Numerical Simulations and Theory
- Zudin I. Yu.
- Zaboronkova T. M.
- Gushchin M. E.
- Aidakina N. A.
- Korobkov S. V.
- Krafft Catherine
Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2019, 124, pp.4739. The propagation of whistler waves in a magnetized plasma containingmultiple small-scale (100 m to 1 km) field-aligned irregularities ofenhanced electron density is considered analytically and by means ofnumerical simulations. Such systems of irregularities can develop in theupper ionosphere during the generation of density ducts by high-frequency heating facilities and other types of active experiments. Thesimulation parameters are close to those of an active experiment where awhistler wave of 18 kHz emitted by a ground-based very low frequency(VLF) transmitter was received onboard the DEMETER satellite at 700 kmabove the SURA heater. The study reveals a number of remarkableproperties of the VLF waves' propagation, including the existence ofspecific waveguide modes of the small-scale density structures and of acharacteristic transverse size d0 of the irregularities.Irregularities with small density enhancements around 10-20% andtransverse sizes larger than d0?1 km can serve as separatewaveguides for VLF waves. In their turn, single irregularities narrowerthan d0 cannot be considered as individual ductingstructures. Numerical simulations show that, for the analysis of theelectromagnetic whistlers' propagation, a system of closely spacedirregularities with scales narrower than d0 can be modeled byan equivalent ducting structure with a smoothed density profile. Suchequivalent structure has the same ducting properties for whistlers andcan be produced by averaging with a sliding window of a scale aboutd0 the original density distribution. (10.1029/2019JA026637)
DOI : 10.1029/2019JA026637
Three-dimensional local anisotropy of velocity fluctuations in the solar wind
- Verdini Andrea
- Grappin Roland
- Alexandrova Olga
- Franci L.
- Landi S.
- Matteini L.
- Papini E.
Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP): Policy P - Oxford Open Option A, 2019, 486, pp.3006-3018. We analyse velocity fluctuations in the solar wind at magneto-fluid scales in two data sets, extracted from Wind data in the period 2005-2015, that are characterized by strong or weak expansion. Expansion affects measurements of anisotropy because it breaks axisymmetry around the mean magnetic field. Indeed, the small-scale three-dimensional local anisotropy of magnetic fluctuations (deltaB) as measured by structure functions (SFB) is consistent with tube-like structures for strong expansion. When passing to weak expansion, structures become ribbon-like because of the flattening of SFB along one of the two perpendicular directions. The power-law index that is consistent with a spectral slope -5/3 for strong expansion now becomes closer to -3/2. This index is also characteristic of velocity fluctuations in the solar wind. We study velocity fluctuations (deltaV) to understand if the anisotropy of their structure functions (SFV) also changes with the strength of expansion and if the difference with the magnetic spectral index is washed out once anisotropy is accounted for. We find that SFV is generally flatter than SFB. When expansion passes from strong to weak, a further flattening of the perpendicular SFV occurs and the small-scale anisotropy switches from tube-like to ribbon-like structures. These two types of anisotropy, common to SFV and SFB, are associated with distinct large-scale variance anisotropies of deltaB in the strong- and weak-expansion data sets. We conclude that SFV show anisotropic three-dimensional scaling similar to SFB, with however systematic flatter scalings, reflecting the difference between global spectral slopes. (10.1093/mnras/stz1041)
DOI : 10.1093/mnras/stz1041
ViDA: a Vlasov-DArwin solver for plasma physics at electron scales
- Pezzi Oreste
- Cozzani Giulia
- Califano Francesco
- Valentini Francesco
- Guarrasi Massimiliano
- Camporeale Enrico
- Brunetti Gianfranco
- Retinò Alessandro
- Veltri Pierluigi
Journal of Plasma Physics, Cambridge University Press (CUP), 2019, 85 (5), pp.905850506. We present a VlasovDArwin numerical code (ViDA) specifically designed to address plasma physics problems, where small-scale high accuracy is requested even during the nonlinear regime to guarantee a clean description of the plasma dynamics at fine spatial scales. The algorithm provides a low-noise description of proton and electron kinetic dynamics, by splitting in time the multi-advection Vlasov equation in phase space. Maxwell equations for the electric and magnetic fields are reorganized according to the Darwin approximation to remove light waves. Several numerical tests show that ViDA successfully reproduces the propagation of linear and nonlinear waves and captures the physics of magnetic reconnection. We also discuss preliminary tests of the parallelization algorithm efficiency, performed at CINECA on the Marconi-KNL cluster. ViDA will allow the running of Eulerian simulations of a non-relativistic fully kinetic collisionless plasma and it is expected to provide relevant insights into important problems of plasma astrophysics such as, for instance, the development of the turbulent cascade at electron scales and the structure and dynamics of electron-scale magnetic reconnection, such as the electron diffusion region. (10.1017/S0022377819000631)
DOI : 10.1017/S0022377819000631
Energy Conversion and Electron Acceleration in the Magnetopause Reconnection Diffusion Region
- Pritchard K. R.
- Burch J. L.
- Fuselier S. A.
- Webster J. M.
- Torbert R. B.
- Argall M. R.
- Broll J.
- Genestreti K. J.
- Giles B. L.
- Le Contel Olivier
- Mukherjee J.
- Phan T. D.
- Rager A. C.
- Russell C. T.
- Strangeway R. J.
Geophysical Research Letters, American Geophysical Union, 2019, 46 (17-18), pp.10274-10282. Data are analyzed from a Magnetospheric Multiscale encounter with a dayside magnetopause reconnection region on 29 December 2016. The uniqueness of the event stems from the small ( 7 km) average spacecraft separation and the sequential sampling of an electron diffusion region with electron crescent distributions. We quantitatively investigate the earthward acceleration of magnetosheath electrons through the in-plane null by the polarization electric field EN that points radially outward from the magnetopause. The results compare favorably with previous plasma simulations with one important difference that the reconnection electric field (EM) extends throughout the region of strong EN so that both fields energize electrons in the same region. This acceleration is quantified here for the first time. As the spacecraft penetrate deeper into the region of enhanced EN, the magnetic reflection of lower-energy electrons produces a thinner crescent. (10.1029/2019GL084636)
DOI : 10.1029/2019GL084636
Training on GNSS and Space Weather in Africa in the framework of the North-South scientific network GIRGEA
- Amory-Mazaudier Christine
- Fleury Rolland
- Masson F.
- Gadimova S.
- Anas Emran
Sun and Geosphere, BBC SWS Regional Network, 2019, 1 (141), pp.71-79. This paper presents the successful setting up of a research and teaching network for space weather in developed and fragile countries. This development took nearly a quarter of a century with the help of international cooperation. Numerous studies have been developed in different domains of Space Weather concerning the impact of solar events on the ionosphere and the Earth's magnetic field, ionospheric electric currents and the induced currents in the ground (GIC) Other studies have also been conducted on climate change, lightning and the movement of tectonic plates. We underline the importance of Global Navigation Satellite Systems [GNSS] for the development of space weather research and capacity building during the last decades (10.31401/SunGeo.2019.01.10)
DOI : 10.31401/SunGeo.2019.01.10
Crossing of Plasma Structures by spacecraft: a path calculator
- Manuzzo Roberto
- Belmont Gérard
- Rezeau Laurence
- Califano F.
- Denton R E
Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2019, 124 (12), pp.10119-10140. When spacecraft (s/c) missions probe plasma structures (PSs) the relative location of the s/c with respect to the PS is unknown. This information is, however, needed to measure the geometrical features of the PS (orientation and thickness) and to understand the physical processes underlying the PS dynamics. Methods to determine the s/c location exist, but they need strong assumptions to be satisfied (stationarity and special spatial dependencies). The number of cases for which these assumptions are likely to be valid for the entire PS seems to be limited, and even weak departures from these hypotheses may affect the results. For a quasi‐1‐D geometry in particular, the determination of the velocity component along the two quasi‐invariant directions is very inaccurate and the assumption of strict stationarity may lead these quantities to diverge. In this paper we present new methods to compute the s/c trajectory through a PS, without a priori assumption on its spatial geometry, and able to work even in the presence of weak nonstationarities. The methods are tested both on artificial and real data, the latter provided by the Magnetospheric Multiscale mission probing the Earth's magnetopause. The 1‐D and 2‐D trajectories of the Magnetospheric Multiscale are found that can be used as an initial step for future reconstruction studies. Advanced minimization procedures to optimize the results are discussed. (10.1029/2019JA026632)
DOI : 10.1029/2019JA026632
Inverse cascade of hybrid helicity in BΩ-MHD turbulence
- Menu Mélissa
- Galtier Sébastien
- Petitdemange Ludovic
Physical Review Fluids, American Physical Society, 2019, 4, pp.073701. We investigate the impact of a solid-body rotation Ω0 on the large-scale dynamics of an incompressible magnetohydrodynamic turbulent flow in presence of a background magnetic field B0 and at low Rossby number. Three-dimensional direct numerical simulations are performed in a periodic box, at unit magnetic Prandtl number and with a forcing at intermediate wave number kf=20. When Ω0 is aligned with B0 (i.e., θ≡(Ω0,B0)=0), inverse transfer is found for the magnetic spectrum at k<kf. This transfer is stronger when the forcing excites preferentially right-handed (rather than left-handed) fluctuations; it is smaller when θ>0 and becomes weak when θ≥35∘. These properties are understood as the consequence of an inverse cascade of hybrid helicity which is an inviscid/ideal invariant of this system when θ=0. Hybrid helicity emerges, therefore, as a key element for understanding rotating dynamos. Implication of these findings on the origin of the alignment of the magnetic dipole with the rotation axis in planets and stars is discussed. (10.1103/PhysRevFluids.4.073701)
DOI : 10.1103/PhysRevFluids.4.073701
Non-thermal DBD plasma array on seed germination of different plant species
- Liu Bo
- Honnorat Bruno
- Yang Hang
- Arancibia Monreal J.
- Rajjou Loic
- Rousseau Antoine
Journal of Physics D: Applied Physics, IOP Publishing, 2019, 52 (2), pp.025401. A dielectric barrier discharge (DBD) reactor producing cold plasma at atmospheric pressure has been used to treat seeds of eight different species and investigate their responses in term of germination. The device is made of nine cylindrical DBDs organized in a array and partially immersed in water. O2, N2, and air were flown in the device; the cold plasma from such gas is formed in the bubbles and touch liquid surface. Seeds were either located inside the water during plasma treatment process (direct treatment) or were watered by the water exposed to cold plasma beforehand (indirect treatment). Such plasma activated water contains reactive oxygen species and reactive nitrogen species. The statistical analysis shows that the probability of germinating of treated mung bean, mustard and radish is significantly higher than in control groups (p  <  0.05) for indirect treatments. A comparison of different treatment modalities (direct versus indirect treatment and gas composition) on germination boost has been completed on mung bean seeds. It is shown that direct plasma treatment using different gas (O2, N2, and air) give a strong enhancement of the mung bean germination probability compared to the control group; in the case of indirect treatment, only plasma air-treated water lead to a significant germination boost compared to the control group; this effect is still smaller than the one obtained using a direct treatment. (10.1088/1361-6463/aae771)
DOI : 10.1088/1361-6463/aae771
Dependence on plasma shape and plasma fueling for small edge-localized mode regimes in TCV and ASDEX Upgrade
- Labit B.
- Eich T.
- Harrer G.F.
- Wolfrum E.
- Bernert M.
- Dunne M.G.
- Frassinetti L.
- Hennequin Pascale
- Maurizio R.
- Merle A.
- Meyer H.
- Saarelma S.
- Sheikh U.
- Eurofusion Mst1 Team The
Nuclear Fusion, IOP Publishing, 2019, 59 (8), pp.086020. Within the EUROfusion MST1 work package, a series of experiments has been conducted on AUG and TCV devices to disentangle the role of plasma fueling and plasma shape for the onset of small ELM regimes. On both devices, small ELM regimes with high confinement are achieved if and only if two conditions are fulfilled at the same time. Firstly, the plasma density at the separatrix must be large enough (), leading to a pressure profile flattening at the separatrix, which stabilizes type-I ELMs. Secondly, the magnetic configuration has to be close to a double null (DN), leading to a reduction of the magnetic shear in the extreme vicinity of the separatrix. As a consequence, its stabilizing effect on ballooning modes is weakened. (10.1088/1741-4326/ab2211)
DOI : 10.1088/1741-4326/ab2211
Experimental and numerical investigation of the transient charging of a dielectric surface exposed to a plasma jet
- Slikboer Elmar
- Viegas Pedro
- Bonaventura Z.
- Garcia-Caurel Enric
- Sobota Ana
- Bourdon Anne
- Guaitella Olivier
Plasma Sources Science and Technology, IOP Publishing, 2019, 28 (9), pp.095016. This work investigates the dynamical charging of a surface under exposure of a non-equilibrium plasma jet at atmospheric pressure through a quantitative comparison between modeling and experiments. We show using mono-polar pulses with variable pulse duration and amplitude that the charging time (i.e. the time from impact of the ionization wave till the fall of the high voltage pulse) is a crucial element determining the plasma-surface interaction. This is done through direct measurements of the electric field induced inside the target using the optical diagnostic technique called Mueller polarimetry and comparison with the electric field calculated using a 2D fluid model of the plasma jet interaction with the target in the same conditions as in the experiments. When the charging time is kept relatively short (less than 100 ns), the surface spreading of the discharge and consequent surface charge deposition are limited. When it is relatively long (up to microseconds), the increased surface spreading and charge deposition significantly change the electric field to which the target is exposed during the charging time and when the applied voltage returns to zero. (10.1088/1361-6595/ab3c27)
DOI : 10.1088/1361-6595/ab3c27
Plasma gun for medical applications: engineering an equivalent electrical target of human body and deciphering relevant electrical parameters
- Judée Florian
- Dufour Thierry
Journal of Physics D: Applied Physics, IOP Publishing, 2019, 52 (16), pp.16 - 18. Simulations and experimental works have been carried out in a complementary way to engineer a basic material target mimicking the same dielectric properties of the human body. It includes a resistor in parallel with a capacitor, whose values (Rh=1500 Ω and Ch=100 pF) are estimated in regard of parameters commonly utilized upon in vivo campaigns (frequency=30 kHz, gap=10 mm, high voltage electrode surface=12.6 mm 2). This equivalent electrical human body (EEHB) circuit can be used as a reference and realistic target to calibrate electrical properties of therapeutic plasma sources before their utilization on patients. In this letter, we consider a configuration where this EEHB target interacts with a plasma gun (PG). Plasma power measurements performed in such configuration clearly indicate two operating modes depending on the value of the supplied voltage. Hence, the plasma gun generates pulsed atmospheric plasma streams likely to present therapeutic interest for voltages comprised between 3.0 and 8.5 kV while for higher values, transient arcs of thermal plasma are generated and represent substantial risks for the patient. (10.1088/1361-6463/ab03b8)
DOI : 10.1088/1361-6463/ab03b8
Comparison between ad-hoc and instability-induced electron anomalous transport in a 1D fluid simulation of Hall-effect thruster
- Martorelli Roberto
- Lafleur Trevor
- Bourdon Anne
- Chabert Pascal
Physics of Plasmas, American Institute of Physics, 2019, 26 (8), pp.083502. Anomalous electron transport is a long-standing problem in the understanding of Hall-effect thrusters. Recent results have suggested as a possible cause a kinetic instability, but few attempts have succeeded in implementing such phenomena in a fluid simulation of the thruster. The common approach in this case relies on including an ad-hoc model of the anomalous transport and so to fit experimental results. We propose here a comparison between the friction force and the anomalous heating arising from the ad-hoc model, with the corresponding effects coming from the use of the instability-induced transport. The results are obtained through a one-dimensional fluid simulation of the Hall-effect thruster with ad-hoc anomalous transport. The comparison shows good agreement between the two approaches, suggesting indeed that the instability-induced anomalous transport is the good candidate for reproducing the ad-hoc simulations and paving the way for a full self-consistent implementation of the phenomena in a fluid simulation. (10.1063/1.5089008)
DOI : 10.1063/1.5089008
The Space Physics Environment Data Analysis System (SPEDAS)
- Angelopoulos V.
- Cruce P.
- Drozdov A.
- Grimes E. W.
- Hatzigeorgiu N.
- King D. A.
- Larson D. E.
- Lewis J. W.
- Mctiernan J. M.
- Roberts D. A.
- Russell C. L.
- Hori T.
- Kasahara Y.
- Kumamoto A.
- Matsuoka A.
- Miyashita Y.
- Miyoshi Y.
- Shinohara I.
- Teramoto M.
- Faden J. B.
- Halford A. J.
- Mccarthy M.
- Millan R. M.
- Sample J. G.
- Smith D. M.
- Woodger L. A.
- Masson A.
- Narock A. A.
- Asamura K.
- Chang T. F.
- Chiang C.-Y.
- Kazama Y.
- Keika K.
- Matsuda S.
- Segawa T.
- Seki K.
- Shoji M.
- Tam S. W. Y.
- Umemura N.
- Wang B.-J.
- Wang S.-Y.
- Redmon R.
- Rodriguez J. V.
- Singer H. J.
- Vandegriff J.
- Abe S.
- Nose M.
- Shinbori A.
- Tanaka Y.-M.
- Ueno S.
- Andersson L.
- Dunn P.
- Fowler C.
- Halekas J. S.
- Hara T.
- Harada Y.
- Lee C. O.
- Lillis R.
- Mitchell D. L.
- Argall M. R.
- Bromund K.
- Burch J. L.
- Cohen I. J.
- Galloy M.
- Giles B. L.
- Jaynes A. N.
- Le Contel Olivier
- Oka M.
- Phan T. D.
- Walsh B. M.
- Westlake J.
- Wilder F. D.
- Bale S. D.
- Livi R.
- Pulupa M.
- Whittlesey P.
- Dewolfe A.
- Harter B.
- Lucas E.
- Auster U.
- Bonnell J. W.
- Cully C. M.
- Donovan E.
- Ergun R. E.
- Frey H. U.
- Jackel B.
- Keiling A.
- Korth H.
- Mcfadden J. P.
- Nishimura Y.
- Plaschke F.
- Robert Patrick
- Turner D. L.
- Weygand J. M.
- Candey R. M.
- Johnson R. C.
- Kovalick T.
- Liu M. H.
- Mcguire R. E.
- Breneman A.
- Kersten K.
- Schroeder P.
Space Science Reviews, Springer Verlag, 2019, 215, pp.9, 46p. With the advent of the Heliophysics/Geospace System Observatory (H/GSO), a complement of multi-spacecraft missions and ground-based observatories to study the space environment, data retrieval, analysis, and visualization of space physics data can be daunting. The Space Physics Environment Data Analysis System (SPEDAS), a grass-roots software development platform (<ExternalRef> <RefSource>www.spedas.org</RefSource> <RefTarget Address="http://www.spedas.org" TargetType="URL"/> </ExternalRef>), is now officially supported by NASA Heliophysics as part of its data environment infrastructure. It serves more than a dozen space missions and ground observatories and can integrate the full complement of past and upcoming space physics missions with minimal resources, following clear, simple, and well-proven guidelines. Free, modular and configurable to the needs of individual missions, it works in both command-line (ideal for experienced users) and Graphical User Interface (GUI) mode (reducing the learning curve for first-time users). Both options have "crib-sheets," user-command sequences in ASCII format that can facilitate record-and-repeat actions, especially for complex operations and plotting. Crib-sheets enhance scientific interactions, as users can move rapidly and accurately from exchanges of technical information on data processing to efficient discussions regarding data interpretation and science. SPEDAS can readily query and ingest all International Solar Terrestrial Physics (ISTP)-compatible products from the Space Physics Data Facility (SPDF), enabling access to a vast collection of historic and current mission data. The planned incorporation of Heliophysics Application Programmer's Interface (HAPI) standards will facilitate data ingestion from distributed datasets that adhere to these standards. Although SPEDAS is currently Interactive Data Language (IDL)-based (and interfaces to Java-based tools such as Autoplot), efforts are under-way to expand it further to work with python (first as an interface tool and potentially even receiving an under-the-hood replacement). We review the SPEDAS development history, goals, and current implementation. We explain its "modes of use" with examples geared for users and outline its technical implementation and requirements with software developers in mind. We also describe SPEDAS personnel and software management, interfaces with other organizations, resources and support structure available to the community, and future development plans. (10.1007/s11214-018-0576-4)
DOI : 10.1007/s11214-018-0576-4

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