Publications

Sont listées ci-dessous, par année, les publications figurant dans l'archive ouverte HAL.

2019

High-Frequency Wave Generation in Magnetotail Reconnection: Linear Dispersion Analysis
- Burch J. L.
- Dokgo K.
- Hwang K.-J.
- Torbert R. B.
- Graham D. B.
- Webster J. M.
- Ergun R. E.
- Giles B. L.
- Allen R. C.
- Chen L.-J.
- Wang S.
- Genestreti K. J.
- Russell C. T.
- Strangeway R. J.
- Le Contel Olivier
Geophysical Research Letters, American Geophysical Union, 2019, 46 (8), pp.4089-4097. Plasma and wave measurements from the NASA Magnetospheric Multiscale mission are presented for magnetotail reconnection events on 3 July and 11 July 2017. Linear dispersion analyses were performed using distribution functions comprising up to six drifting bi-Maxwellian distributions. In both events electron crescent-shaped distributions are shown to be responsible for upper hybrid waves near the X-line. In an adjacent location within the 3 July event a monodirectional field-aligned electron beam drove parallel-propagating beam-mode waves. In the 11 July event an electron distribution consisting of a drifting core and two crescents was shown to generate upper-hybrid and beam-mode waves at three different frequencies, explaining the observed broadband waves. Multiple harmonics of the upper hybrid waves were observed but cannot be explained by the linear dispersion analysis since they result from nonlinear beam interactions. (10.1029/2019GL082471)
DOI : 10.1029/2019GL082471
Turbulent Heating in the Accelerating Region Using a Multishell Model
- Verdini Andrea
- Grappin Roland
- Montagud-Camps Victor
Solar Physics, Springer Verlag, 2019, 294. Recent studies of turbulence-driven solar winds indicate that fast winds are obtained only at the price of unrealistic bottom boundary conditions: too large wave amplitudes and small frequencies. In this work, the incompressible turbulent dissipation is modeled with a large-scale von Karman-Howarth-Kolmogorov-like phenomenological expression (Q_K410). An evaluation of the phenomenology is thus necessary to understand if unrealistic boundary conditions result from physical or model limitations. To assess the validity of the Kolmogorov-like expression, Q_K410, one needs to compare it to exact heating, which requires describing the cascade in detail. This has been done in the case of homogeneous MHD turbulence, including expansion, but not in the critical accelerating region. To assess the standard incompressible turbulent heating in the accelerating region, we use a reduced MHD model (multishell model) in which the perpendicular turbulent cascade is described by a shell model, allowing to reach a Reynolds number of 106. We first consider the homogeneous and expanding cases, and find that primitive MHD and multishell equations give remarkably similar results. We thus feel free to use the multishell model in the accelerating region. The results indicate that the large-scale phenomenology is inaccurate and it overestimates the heating by a factor at least 20, thus invalidating earlier studies of winds driven by incompressible turbulence. We conclude that realistic 1D wind models cannot be based solely on incompressible turbulence, but probably need an addition of compressible turbulence and shocks to increase the wave reflection and thus the heating. (10.1007/s11207-019-1458-y)
DOI : 10.1007/s11207-019-1458-y
Non-Isothermal Sheath Model for Low Pressure Plasmas
- Tavant Antoine
- Lucken Romain
- Bourdon Anne
- Chabert Pascal
Plasma Sources Science and Technology, IOP Publishing, 2019, 28 (7), pp.075007. The evolution of the electron mean energy in the pre-sheath and the sheath of a low pressure plasma bounded by two planes is investigated with 1D particle in cell simulations. We observed that the electron mean energy is not constant in the sheath, but instead decreases significantly from the bulk towards the wall. From the simulations, a polytropic state law is proposed, allowing us to close the fluid equations for the electrons without the isothermal hypothesis. A comparison between the fluid model and the simulations show that the non-isothermal sheath model is more accurate than the isothermal model. The impact of the electron mean energy variation on the potential sheath drop and the electron particle and heat flux is evaluated. (10.1088/1361-6595/ab279b)
DOI : 10.1088/1361-6595/ab279b
The Radio and Plasma Waves (RPW) Instrument on Solar Orbiter : Capabilities and Performance
- Maksimovic M.
- Soucek J.
- Bale S. D.
- Bonnin X.
- Chust Thomas
- Khotyaintsev Y.
- Kretzschmar Matthieu
- Plettemeier D.
- Steller M.
- Štverák S.
, 2019, 2019, pp.15 pp.. We will review the instrumental capabilities of the Radio and Plasma Waves (RPW) Instrument on Solar Orbiter. This instrument is designed to measure in-situ magnetic and electric fields and waves from 'DC' to a few hundreds of kHz. RPW will also observe solar radio emissions up to 16 MHz. The RPW instrument is of primary importance to the Solar Orbiter mission and science requirements, since it is essential to answer three of the four mission overarching science objectives. In addition, RPW will exchange on-board data with the other in-situ instruments, in order to process algorithms for interplanetary shocks and type III Langmuir waves detections.
Experimental investigation of the tilt angle of turbulent structures in the core of fusion plasmas
- Pinzon Javier
- Happel T.
- Hennequin Pascale
- Angioni Clemente
- Estrada Teresa
- Lebschy Alexander
- Stroth Ulrich
- Asdex Upgrade Team The
Nuclear Fusion, IOP Publishing, 2019, 59, pp.074002. The tilt angle of turbulent structures stands for the anisotropy of turbulence which is essential for understanding the dynamics of magnetized plasmas. It is a quantity predicted by theory and simulations, that provides information on the interplay between turbulence, micro-instabilities and plasma flows. A new method for measuring the tilt angle of turbulent structures in the core region of fusion plasmas using Doppler reflectometry is presented. First measurements of this type on the ASDEX Upgrade tokamak have shown a significant difference of tilt angle for different plasma conditions. The dominance of sheared flows in determining the structure tilt is experimentally demonstrated for different turbulence regimes. (10.1088/1741-4326/ab227e)
DOI : 10.1088/1741-4326/ab227e
Introduction to plasma physics
- Belmont Gérard
- Rezeau Laurence
- Riconda C.
- Zaslavsky A.
, 2019.
Electric field induced second harmonic (E-FISH) generation for characterization of fast ionization wave discharges at moderate and low pressures
- Chng Tat Loon
- Orel Inna
- Starikovskaia Svetlana
- Adamovich I.V.
Plasma Sources Science and Technology, IOP Publishing, 2019, 28 (4), pp.045004 (8pp). The electric ﬁeld in an ionization wave discharge in nitrogen at 20100 mbar, initiated by positive polarity, high-voltage, ns duration pulses, is measured by ps second harmonic generation. The axial electric ﬁeld component is determined both during the propagation of the ionization wave along the discharge tube, and after the wave reaches the grounded electrode, spanning the entire discharge gap. The temporal resolution of the present measurements is 200 ps, with the spatial resolution in the axial direction of approximately 0.5 mm. The second harmonic signal exhibits a quadratic dependence on the Laplacian electric ﬁeld but indicates that in this pressure range most of the signal is generated within the wall of the tube. Absolute calibration of the signal is obtained from the current shunt data, after the ionization wave has reached the grounded electrode. Comparison of the data taken at different pressures shows that the peak value of the axial electric ﬁeld in the wave front, 811 kV cm−1, has a fairly weak dependence on pressure, with the peak reduced electric ﬁeld reaching ≈2000 Td at 20 mbar. Reducing the pressure from 100 to 20 mbar, while keeping the discharge pulse voltage waveform the same, steepens the ionization wave front considerably, from 3.0 to 1.0 ns full width at half maximum. The results demonstrate that ps second harmonic generation may be employed for electric ﬁeld measurements in low-pressure discharges, discharges sustained in small diameter capillary tubes, and discharges sustained in gas mixtures with low nonlinear susceptibility, at the conditions when the detection of the signal generated directly in the plasma is challenging. High temporal resolution of the present measurements indicates a possibility of detection of non-local electron kinetics effects induced by a rapidly va (10.1088/1361-6595/ab0b22)
DOI : 10.1088/1361-6595/ab0b22
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
Signatures of Cold Ions in a Kinetic Simulation of the Reconnecting Magnetopause
- Dargent Jérémy
- Aunai Nicolas
- Lavraud B.
- Toledo-Redondo Sergio
- Califano F.
Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2019, 124 (4), pp.2497-2514. Abstract At the Earth's magnetopause, a low-energy ion population of ionospheric origin is commonly observed at the magnetospheric side. In this work we use a 2-D fully kinetic simulation to identify several original signatures related to the dynamics of cold ions involved in magnetic reconnection at the asymmetric dayside magnetopause. We identify several original signatures of the cold ions dynamics driven by the development of magnetic reconnection at the asymmetric dayside magnetopause. We find that cold ions tend to rarefy in the diffusion region, while their density is enhanced as a result of compression along magnetospheric separatrices. We also observe the formation of crescent-shaped cold ion distribution functions along the separatrices in the near-exhaust region, and we present an analytical model to explain this signature. Finally, we give evidence of a localized parallel heating of cold ions. These signatures should be detected with the magnetospheric multiscale mission high-resolution observations. (10.1029/2018JA026343)
DOI : 10.1029/2018JA026343

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