Publications

2019

• A rotational Raman study under non-thermal conditions in pulsed CO2−N2 and CO2−O2 glow discharges
  
  • Grofulovic Marija
  • Klarenaar Bart
  • Guaitella Olivier
  • Guerra V.
  • Engeln Richard
  Plasma Sources Science and Technology, IOP Publishing, 2019, 28 (4), pp.045014. This work employs in situ rotational Raman spectroscopy to study the effect of N2 and O2 addition to CO2 in pulsed glow discharges in the mbar range. The spatiotemporally resolved measurements are performed in CO2 and 25%, 50% and 75% of N2 or O2 admixture, in a 510 ms on-off cycle, 50 mA plasma current and 6.7 mbar total pressure. The rotational temperature profile is not affected by adding N2, ranging from 400 to 850 K from start to end of the discharge pulse, while the addition of O2 decreases the temperature at corresponding time points. Molecular number densities of CO2, CO, O2 and N2 are determined, showing the spatial homogeneity along the axis of the reactor and uniformity during the cycle. The measurements in the N2 containing mixtures show that CO2 conversion factor α increases from 0.15 to 0.33 when the content of N2 is increased from 0% to 75%, demonstrating the potential of N2 addition to enhance the vibrational pumping of CO2 and its beneficial effect on CO2 dissociation. Furthermore, the influence of admixtures on CO2 vibrations is examined by analysing the vibrationally averaged nuclear spin degeneracy. The difference between the fitted odd averaged degeneracy and the calculated odd degeneracy assuming thermal conditions increases with the addition of N2, demonstrating the growth of vibrational temperatures in CO2. On the other hand, the addition of O2 leads to a decrease of α, which might be attributed to quenched vibrations of CO2, and/or to the influence of the back reaction in the presence of O2. (10.1088/1361-6595/ab1240)
  DOI : 10.1088/1361-6595/ab1240
• Stationarity of I-mode operation and I-mode divertor heat fluxes on the ASDEX Upgrade tokamak
  
  • Happel T.
  • Griener M.
  • Silvagni D.
  • Freethy S. J.
  • Hennequin Pascale
  • Janky F.
  • Manz P.
  • Prisiazhniuk D.
  • Ryter F.
  • Bernert M.
  • Brida D.
  • Eich T.
  • Faitsch M.
  • Gil L.
  • Guimarais L.
  • Merle A.
  • Nille D.
  • Pinzón J R
  • Sieglin B.
  • Stroth U.
  • Viezzer E.
  Nuclear Materials and Energy, Elsevier, 2019, 18, pp.159 - 165. Recent I-mode investigations from the ASDEX Upgrade tokamak are reported. It is shown that neutral-beam-injection heated I-modes can be stationary, which is important in terms of extrapolability towards future fusion devices. Furthermore, detailed studies on the weakly coherent mode are reported. In particular, experimental observations point towards its existence in L-mode, before I-mode starts. Moreover, its impact on density and temperature fluctuations is evaluated. Studies of stationary divertor heat fluxes show that in I-mode, the upstream power fall-off length is between those observed in L-mode and H-mode, and it is connected to the scrape-off layer temperature fall-off length. Moreover, analysis of transient divertor heat loads shows that intermittent turbulent events, observed in the confinement region and linked to the weakly coherent mode, are responsible for a significant part of divertor heat loads. (10.1016/j.nme.2018.12.022)
  DOI : 10.1016/j.nme.2018.12.022
• Whistler Waves Driven by Field-Aligned Streaming Electrons in the Near-Earth Magnetotail Reconnection
  
  • Ren Y.
  • Dai L.
  • Li W.
  • Tao X.
  • Wang C.
  • Tang B.
  • Lavraud B.
  • Wu Y.
  • Burch J. L.
  • Giles B. L.
  • Le Contel Olivier
  • Torbert R. B.
  • Russell C. T.
  • Strangeway R. J.
  • Ergun R. E.
  • Lindqvist P.-A.
  Geophysical Research Letters, American Geophysical Union, 2019, 46 (10), pp.5045-5054. We analyze Magnetospheric Multiscale Mission observations of whistler waves and associated electron field-aligned crescent distribution in the vicinity of the magnetotail near-Earth X-line. The whistler waves propagate outward from the X-line in the neutral sheet. The associated field-aligned streaming electrons exhibit a crescent-like shape, with an inverse slope (df/d|v<SUB>||</SUB>|>0) at 1-5 keV. The parallel phase velocity of the waves is in the range (1-5 keV) of the inverse slope of the field-aligned crescents in the velocity space. We demonstrate that the observed whistler waves are driven by the electron field-aligned crescents through Landau resonance. The cyclotron resonance is at the high-energy tail with negligible free energy of pitch angle anisotropy in these events. (10.1029/2019GL083283)
  DOI : 10.1029/2019GL083283
• Evidence of Electron Acceleration at a Reconnecting Magnetopause
  
  • Fu H.S.
  • Peng F. Z.
  • Liu C. M.
  • Burch J. L.
  • Gershman D. G.
  • Le Contel Olivier
  Geophysical Research Letters, American Geophysical Union, 2019, 46 (11), pp.5645-5652. It is still unknown nowadays whether magnetic reconnection−-a process occurring both in the magnetotail and at the magnetopause−-can intrinsically accelerate energetic electrons. Observations in the Earth's magnetotail usually indicate strong electron acceleration during magnetic reconnection, while observations at the Earth's magnetopause rarely show such features. With the recently launched Magnetospheric Multiscale (MMS) mission, here we report the first evidence of energetic-electron acceleration at a reconnecting magnetopause. We find that the acceleration of electrons, with energy up to 70 times their thermal energy, occurs in the magnetosheath side of the ion diffusion region and is associated with strong whistler waves. Such acceleration−-not contaminated by the magnetospheric population−-is attributed to nonadiabatic wave-particle interactions, as supported by analyses of the resonance condition. It manifests that energetic-electron acceleration can happen at the reconnecting magnetopause, like that in the tail. (10.1029/2019GL083032)
  DOI : 10.1029/2019GL083032
• Electron-Driven Dissipation in a Tailward Flow Burst
  
  • Chen Z. Z.
  • Fu H.S.
  • Liu C. M.
  • Wang T. Y.
  • Ergun R. E.
  • Cozzani Giulia
  • Huang S. Y.
  • Khotyaintsev Y. V.
  • Le Contel Olivier
  • Giles B. L.
  • Burch J. L.
  Geophysical Research Letters, American Geophysical Union, 2019, 46 (11), pp.5698-5706. Traditionally, the magnetotail flow burst outside the diffusion region is known to carry ions and electrons together (V<SUB>i</SUB> = V<SUB>e</SUB>), with the frozen-in condition well satisfied (E V<SUB>e</SUB> × B = 0). Such picture, however, may not be true, based on our analyses of the high-resolution MMS (Magnetospheric Multiscale mission) data. We find that inside the flow burst the electrons and ions can be decoupled (V<SUB>e</SUB> != V<SUB>i</SUB>), with the electron speed 5 times larger than the ion speed. Such super-Alfvenic electron jet, having scale of 10 d<SUB>i</SUB> (ion inertial length) in X<SUB>GSM</SUB> direction, is associated with electron demagnetization (E V<SUB>e</SUB> × B != 0), electron agyrotropy (crescent distribution), and O-line magnetic topology but not associated with the flow reversal and X-line topology; it can cause strong energy dissipation and electron heating. We quantitatively analyze the dissipation and find that it is primarily attributed to lower hybrid drift waves. These results emphasize the non-MHD (magnetohydrodynamics) behaviors of magnetotail flow bursts and the role of lower hybrid drift waves in dissipating energies. (10.1029/2019GL082503)
  DOI : 10.1029/2019GL082503
• Erratum: Multi frequency matching for voltage waveform tailoring <A href="/abs/">(2018 Plasma Sources Sci. Technol. 27 095012</A>)
  
  • Schmidt Frederik
  • Schulze Julian
  • Johnson Erik
  • Booth Jean-Paul
  • Keil Douglas
  • French David M.
  • Trieschmann Jan
  • Mussenbrock Thomas
  Plasma Sources Science and Technology, IOP Publishing, 2019, 28, pp.019601. (10.1088/1361-6595/aaeb4b)
  DOI : 10.1088/1361-6595/aaeb4b
• Groupe de Travail Soleil Heliosphere-Magnetospheres (SHM)
  
  • Auchère F.
  • Astafyeva E.
  • Baudin F.
  • Briand C.
  • Brun S.
  • Célestin Sebastien
  • Génot V.
  • Kretzschmar Matthieu
  • Leblanc François
  • Rouillard A.
  • Sahraoui F.
  CNES: Rapport du Groupe de Travail Soleil Heliosphere-Magnetospheres (SHM), 2019, pp.1-28. Les grandes questions scientifiques abordées dans le cadre de la thématique Soleil Héliosphère et Magnétosphères (SHM) couvrent l'ensemble des problématiques liées aux relations entre notre étoile et le système solaire. Cela commence par l'étude de la structure interne du Soleil à travers l'observation multi-spectrales, l'hélio-sismologie et la modélisation ; par l'étude de l'origine de la couronne solaire, son chauffage et l'accélération du vent solaire et des particules énergétiques solaires lors d'événements énergétiques solaires ; et enfin par l'étude de la propagation du vent solaire et des mécanismes de chauffage de celui-ci par dissipation turbulente.
• Universality of Lower Hybrid Waves at Earth's Magnetopause
  
  • Graham D. B.
  • Khotyaintsev Yu. V.
  • Norgren C.
  • Vaivads A.
  • André M.
  • Drake J. F.
  • Egedal J.
  • Zhou M.
  • Le Contel O.
  • Webster J. M.
  • Lavraud B.
  • Kacem I.
  • Génot V.
  • Jacquey C.
  • Rager A. C.
  • Gershman D. J.
  • Burch J. L.
  • Ergun R. E.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2019, 124, pp.8727-8760. Waves around the lower hybrid frequency are frequently observed at Earth's magnetopause and readily reach very large amplitudes. Determining the properties of lower hybrid waves is crucial because they are thought to contribute to electron and ion heating, cross-field particle diffusion, anomalous resistivity, and energy transfer between electrons and ions. All these processes could play an important role in magnetic reconnection at the magnetopause and the evolution of the boundary layer. In this paper, the properties of lower hybrid waves at Earth's magnetopause are investigated using the Magnetospheric Multiscale mission. For the first time, the properties of the waves are investigated using fields and direct particle measurements. The highest-resolution electron moments resolve the velocity and density fluctuations of lower hybrid waves, confirming that electrons remain approximately frozen in at lower hybrid wave frequencies. Using fields and particle moments, the dispersion relation is constructed and the wave-normal angle is estimated to be close to 90° to the background magnetic field. The waves are shown to have a finite parallel wave vector, suggesting that they can interact with parallel propagating electrons. The observed wave properties are shown to agree with theoretical predictions, the previously used single-spacecraft method, and four-spacecraft timing analyses. These results show that single-spacecraft methods can accurately determine lower hybrid wave properties. (10.1029/2019JA027155)
  DOI : 10.1029/2019JA027155
• Electron Distribution Functions Around a Reconnection X-Line Resolved by the FOTE Method
  
  • Wang Z.
  • Fu H. S.
  • Liu C. M.
  • Liu Y. Y.
  • Cozzani G.
  • Giles B. L.
  • Hwang K. -J.
  • Burch J. L.
  Geophysical Research Letters, American Geophysical Union, 2019, 46, pp.1195. Using data from the MMS mission and the First-Order Taylor Expansion(FOTE) method, here we reveal electron distribution functions around areconnection X-line at the Earth's magnetopause. We find cigardistribution of electrons in both the magnetosphere-side andmagnetosheath-side inflow regions, isotropic distribution of electronsat the separatrix, and loss of high-energy electrons in the antiparalleldirection in the magnetosheath-side inflow region. We interpret theformation of cigar distribution in the inflow regions using the Fermimechanism?as suggested in previous simulations, the loss of high-energyelectrons in the magnetosheath side using the parallel electricfields?which evacuate electrons to escape the diffusion region along theantiparallel direction, and the isotropic distribution at the separatrixusing the pitch angle scattering by whistler waves?which existfrequently at the separatrix. We also find that the electrondistribution functions can change rapidly (within 60 ms) from isotropicto cigar as the spacecraft moves slightly away from the separatrix. (10.1029/2018GL081708)
  DOI : 10.1029/2018GL081708
• Sign singularity of the local energy transfer in space plasma turbulence
  
  • Sorriso-Valvo L.
  • de Vita Gaetano
  • Fraternale Federico
  • Gurchumelia Alexandre
  • Perri S.
  • Nigro Giuseppina
  • Catapano F.
  • Retinò Alessandro
  • Chen Christopher H. K.
  • Yordanova E.
  • Pezzi O.
  • Chargazia Khatuna
  • Kharshiladze Oleg
  • Kvaratskhelia Diana
  • Vásconez Christian L.
  • Marino Raffaele
  • Le Contel Olivier
  • Giles B. L.
  • Moore T. E.
  • Torbert Roy B.
  • Burch James L.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2019, 7, pp.108. In weakly collisional space plasmas, the turbulent cascade provides most of the energy that is dissipated at small scales by various kinetic processes. Understanding the characteristics of such dissipative mechanisms requires the accurate knowledge of the fluctuations that make energy available for conversion at small scales, as different dissipation processes are triggered by fluctuations of a different nature. The scaling properties of different energy channels are estimated here using a proxy of the local energy transfer, based on the third-order moment scaling law for magnetohydrodynamic turbulence. In particular, the sign-singularity analysis was used to explore the scaling properties of the alternating positive-negative energy fluxes, thus providing information on the structure and topology of such fluxes for each of the different type of fluctuations. The results show the highly complex geometrical nature of the flux, and that the local contributions associated with energy and cross-helicity nonlinear transfer have similar scaling properties. Consequently, the fractal properties of current and vorticity structures are similar to those of the Alfvénic fluctuations. (10.3389/fphy.2019.00108)
  DOI : 10.3389/fphy.2019.00108
• Evolution of Turbulence in the Kelvin-Helmholtz Instability in the Terrestrial Magnetopause
  
  • Di Mare Francesca
  • Sorriso-Valvo L.
  • Retinò Alessandro
  • Malara Francesco
  • Hasegawa H.
  Atmosphere, MDPI, 2019, 10 (9), pp.561. The dynamics occurring at the terrestrial magnetopause are investigated by using Geotail and THEMIS spacecraft data of magnetopause crossings during ongoing KelvinHelmholtz instability. Properties of plasma turbulence and intermittency are presented, with the aim of understanding the evolution of the turbulence as a result of the development of KelvinHelmholtz instability. The data have been tested against standard diagnostics for intermittent turbulence, such as the autocorrelation function, the spectral analysis and the scale-dependent statistics of the magnetic field increments. A quasi-periodic modulation of different scaling exponents may exist along the direction of propagation of the KelvinHelmholtz waves along the Geocentric Solar Magnetosphere coordinate system (GSM), and it is visible as a quasi-periodic modulation of the scaling exponents we have studied. The wave period associated with such oscillation was estimated to be approximately 6.4 Earth Radii ( RE ). Furthermore, the amplitude of such modulation seems to decrease as the measurements are taken further away from the Earth along the magnetopause, in particular after X(GSM)&#8818;&#8722;15RE . The observed modulation seems to persist for most of the parameters considered in this analysis. This suggests that a kind of signature related to the development of the KelvinHelmholtz instabilities could be present in the statistical properties of the magnetic turbulence. (10.3390/atmos10090561)
  DOI : 10.3390/atmos10090561
• Single&#8209;mode scannable nanosecond Ti:sapphire laser for&#57375;high&#8209;resolution two&#8209;photon absorption laser&#8209;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
• 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^+&gt;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
• 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 (SF<SUB>B</SUB>) is consistent with tube-like structures for strong expansion. When passing to weak expansion, structures become ribbon-like because of the flattening of SF<SUB>B</SUB> 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 (SF<SUB>V</SUB>) 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 SF<SUB>V</SUB> is generally flatter than SF<SUB>B</SUB>. When expansion passes from strong to weak, a further flattening of the perpendicular SF<SUB>V</SUB> occurs and the small-scale anisotropy switches from tube-like to ribbon-like structures. These two types of anisotropy, common to SF<SUB>V</SUB> and SF<SUB>B</SUB>, are associated with distinct large-scale variance anisotropies of deltaB in the strong- and weak-expansion data sets. We conclude that SF<SUB>V</SUB> show anisotropic three-dimensional scaling similar to SF<SUB>B</SUB>, with however systematic flatter scalings, reflecting the difference between global spectral slopes. (10.1093/mnras/stz1041)
  DOI : 10.1093/mnras/stz1041
• 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
• 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&#8722;1 for the freely expanding jet to 32.6 kV cm&#8722;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&#8722;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
• 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
• 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 d<SUB>0</SUB> of the irregularities.Irregularities with small density enhancements around 10-20% andtransverse sizes larger than d<SUB>0</SUB>?1 km can serve as separatewaveguides for VLF waves. In their turn, single irregularities narrowerthan d<SUB>0</SUB> 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 d<SUB>0</SUB> 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 aboutd<SUB>0</SUB> the original density distribution. (10.1029/2019JA026637)
  DOI : 10.1029/2019JA026637
• 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, 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 &#956;s. The initial breakdown is provided by the &#64257;rst microwave pulse, 5 &#956;s 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 &#64257;eld was estimated on the basis of ratio of emission of the second positive and the &#64257;rst negative systems of molecular nitrogen. (10.1088/1361-6595/aae765)
  DOI : 10.1088/1361-6595/aae765
• 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
• 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
• 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
• 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
• 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