Publications

2020

• Average cometary ion flow pattern in the vicinity of comet 67P from moment data
  
  • Nilsson Hans
  • Williamson Hayley
  • Bergman Sofia
  • Stenberg Wieser Gabriella
  • Wieser Martin
  • Behar Etienne
  • Eriksson Anders I.
  • Johansson Fredrik L.
  • Richter Ingo
  • Goetz Charlotte
  Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP): Policy P - Oxford Open Option A, 2020, 498, pp.5263. Average flow patterns of ions around comet 67P detected by the RPC-ICA instrument onboard Rosetta are presented both as a time series and as a spatial distribution of the average flow in the plane perpendicular to the comet - Sun direction (Y-Z plane in the coordinate systems used). Cometary ions in the energy range up to 60 eV flow radially away from the nucleus in the Y-Z plane, irrespective of the direction of the magnetic field, throughout the mission. These ions may however be strongly affected by the spacecraft potential, the uncertainty due to this is briefly discussed. Inside the solar wind ion cavity and in the periods just before and after, the cometary pick up ions moving antisunward are deflected against the inferred solar wind electric field direction. This is opposite to what is observed for lower levels of mass-loading. These pick up ions are behaving in a similar way to the solar wind ions and are deflected due to mass-loading. A spatial asymmetry can be seen in the observations of deflected pick up ions, with motion against the electric field primarily within a radius of 200 km of the nucleus and also in the negative electric field hemisphere. Cometary ions observed by RPC-ICA typically move in the antisunward direction throughout the mission. These are average patterns, full-resolution data show very much variability. (10.1093/mnras/staa2613)
  DOI : 10.1093/mnras/staa2613
• Observational Evidence for Stochastic Shock Drift Acceleration of Electrons at the Earth's Bow Shock
  
  • Amano T.
  • Katou T.
  • Kitamura N.
  • Oka M.
  • Matsumoto Y.
  • Hoshino M.
  • Saito Y.
  • Yokota S.
  • Giles B.L.
  • Paterson W.R.
  • Russell C.T.
  • Le Contel O.
  • Ergun R.E.
  • Lindqvist P.-A.
  • Turner D.L.
  • Fennell J.F.
  • Blake J.B.
  Physical Review Letters, American Physical Society, 2020, 124, pp.065101. The first-order Fermi acceleration of electrons requires an injection of electrons into a mildly relativistic energy range. However, the mechanism of injection has remained a puzzle both in theory and observation. We present direct evidence for a novel stochastic shock drift acceleration theory for the injection obtained with Magnetospheric Multiscale (MMS) observations at Earth's bow shock. The theoretical model can explain electron acceleration to mildly relativistic energies at high-speed astrophysical shocks, which may provide a solution to the long-standing issue of electron injection. (10.1103/PhysRevLett.124.065101)
  DOI : 10.1103/PhysRevLett.124.065101
• Foundations of optical diagnostics in low-temperature plasmas
  
  • Engeln Richard
  • Klarenaar Bart
  • Guaitella Olivier
  Plasma Sources Science and Technology, IOP Publishing, 2020, 29, pp.063001. Over the past few decades many diagnostics have been developed to study the non-equilibrium nature of plasma. These developments have given experimentalists the possibility to measure in situ molecular and atomic densities, electron and ion densities, temperatures and velocities of species in the plasma, to just name a few. Many of the diagnostic techniques are based on the 'photon-in, photon-out' principle and were at first developed to perform spectroscopy on atoms and molecules. Much later they were introduced in the research of plasmas. In this foundation paper we will focus on optical-based diagnostics that are now for quite some time common use in the field of low-temperature plasma physics research. The basic principles of the diagnostics will be outlined and references will be given to papers where these techniques were successfully applied. For a more comprehensive understanding of the techniques the reader will be referred to textbooks. (10.1088/1361-6595/ab6880)
  DOI : 10.1088/1361-6595/ab6880
• Quiet Time Ionopheric Irregularities Over the African Equatorial Ionization Anomaly Region
  
  • Amaechi Paul O
  • Oyeyemi Elijah O
  • Akala Andrew O
  • Falayi Elijah O
  • Kaab Mohammed
  • Benkhaldoun Zouhair
  • Amory-Mazaudier Christine
  Radio Science, American Geophysical Union, 2020, 55 (8), pp.e2020RS007077. This paper investigated variations of quiet time ionospheric irregularities over the African equatorial ionization anomaly using the rate of change of total electron content index. Irregularities were quantified in terms of percentage occurrence and examined along with parameter of the anomaly, mainly its strength and the asymmetry of the crests as well as equatorial electric field derived from the real‐time equatorial electric field model and meridional wind obtained from the horizontal wind model. Irregularities occurred from 19:30 to 03:00 LT with a time difference of 1 hr between both crests. The highest occurrences were registered in April: 91.67%, 75.00%, and 96.43% for the northern crest, trough, and southern crest, respectively. Seasonally, stronger anomaly (>20 total electron content unit) in addition to the highest equatorial electric field value in the dusk sector corresponded with the equinoctial higher occurrence rate in both hemispheres, while stronger meridional wind and farthest crests location accounted for the least occurrence in winter. The summer occurrence rate was favored by reduced meridional wind, smaller crests location, and late time of prereversal enhancement at the magnetic equator. There was a significant asymmetry in irregularities over the crests in both hemispheres with stronger and greater occurrence rate over the southern crest. Also, irregularities strength and occurrence rate were similar over the northern crest and trough in summer. In addition to dusk‐sector activity, irregularities occurred during postmidnight in summer. Simultaneous variations of irregularities at the crests and trough also highlighted the contribution of nonequatorial processes to their formation at the crests. (10.1029/2020RS007077)
  DOI : 10.1029/2020RS007077
• Italian SWA-Solar Orbiter Working Group on "Particle Energization
  
  • Perri S.
  • Bemporad A.
  • Benella S.
  • Bruno R.
  • Catapano F.
  • d'Amicis R.
  • de Marco R.
  • Frassati F.
  • Grimani C.
  • Ippolito A.
  • Jagarlamudi V. K.
  • Laurenza M.
  • Lepreti F.
  • Nisticò G.
  • Pecora F.
  • Perrone D.
  • Pezzi O.
  • Plainaki C.
  • Prete G.
  • Pucci F.
  • Retino A.
  • Servidio S.
  • Susino R.
  • Trotta D.
  • Valentini F.
  • Zimbardo G.
  , 2020, 2020. One of the outstanding scientific questions in space physics is how charged particles are accelerated up to supra-thermal energies and how they are transported through the inner heliosphere. Such problems match some of the scientific objectives of the Solar Orbiter Science Activity Plan and represent the main scientific cases discussed in the Italian SWA-Solar Orbiter Working Group (WG) on "Particle Energization" (https://sites.google.com/view/italian-solar-orbiter-swa/research-interests/particle-energization?authuser=0). <P />The WG started its activities on May 2020 and gathers experts of in-situ observations, remote sensing, and numerical simulations. This variety of expertises is fundamental for reaching the science objectives. <P />Indeed, candidates for particle acceleration are shocks driven by eruptive phenomena in the solar corona as the coronal mass ejections (CMEs). Thanks to the joint combination between in-situ (as MAG, SWA, EPD) and remote sensing (EUI, METIS) instruments on board Solar Orbiter and to its vicinity to the Sun, we will have the opportunity to study, with unprecedented precision, the onset of CMEs and the properties of the induced shocks propagating in the interplanetary medium. Thus, parameters as the sonic Mach number, the compression ratio and the shock geometry (both when shocks form in the corona and then propagate in the interplanetary space) will give a quantitative estimation of the shocks evolution and their capability to accelerate particles. Then, the investigation of the phenomena involved in the acceleration and propagation of solar energetic particles (SEPs) that were difficult to resolve from prior observations, will be carried out. Further, being close to the source of acceleration, it will be possible to investigate the properties of the local energetic particle "seed" population. <P />In this abstract we would like to present the ongoing activity of the Italian SWA WG on "Particle Energization", pointing out the physical problems discussed during the last months, with particular focus on the possible analysis of Solar Orbiter data (both in-situ and remote sensing) in the framework of particle energization, which we propose to carry out once the data will be available to the scientific community.
• The Radio and Plasma Waves (RPW) Instrument on Solar Orbiter : Capabilities, Performance and First results.
  
  • Maksimovic Milan
  • Souček Jan
  • Bale Stuart D.
  • Bonnin Xavier
  • Chust Thomas
  • Khotyaintsev Yuri
  • Kretzschmar Matthieu
  • Plettemeier Dirk
  • Steller Manfred
  • Štverák Štěpán
  , 2020. We will review the instrumental capabilities of the Radio and Plasma Waves (RPW) Instrument on Solar Orbiter which at the time of writing this abstract is planned for a launch on February 5th 2020. 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. If everything goes well after the launch, we will hopefully be able to present the first RPW data and results gathered during the commissioning. (10.5194/egusphere-egu2020-5800)
  DOI : 10.5194/egusphere-egu2020-5800
• A multi-fluid model of the magnetopause
  
  • Manuzzo Roberto
  • Califano Francesco
  • Belmont Gérard
  • Rezeau Laurence
  Annales Geophysicae, European Geosciences Union, 2020, 38 (2), pp.275 - 286. Observation of the solar wind-magnetosphere boundary provides a unique opportunity to investigate the physics underlying the interaction between two collisionless magnetized plasmas with different temperature, density and magnetic field topology. Their mixing across the interface as well as the boundary dynamics are affected by the development of fluid (and kinetic) instabilities driven by large-scale inhomogeneities in particle and electromagnetic fields. Building up a realistic initial equilibrium state of the magne-topause according to observations is still a challenge nowadays. In this paper, we address the modeling of the particles and electromagnetic field configuration across the Earth's magnetopause by means of a three-fluid analytic model. The model relies on one hot and one cold ion population as well as a neutralizing electron population. The goal is to create an analytic model that is able to reproduce the observations as closely as possible. Some parameters of the model are set using a fitting procedure that aims to minimize their difference with respect to experimental data provided by the Magne-tospheric MultiScale (MMS) mission. All of the other profiles , concerning the electron pressure and the relative densities of the cold and hot ion populations, are calculated in order to satisfy the fluid equilibrium equations. Finally, using a new tri-fluid code, we check the stability of the large-scale equilibrium model for a given experimental case and provide proof that the system is unstable to reconnection. This model could be of interest for the interpretation of satellite results and for the study of the dynamics at the magnetosphere-solar wind boundary. (10.5194/angeo-38-275-2020)
  DOI : 10.5194/angeo-38-275-2020
• Fast Camera Analysis of Plasma Instabilities in Hall Effect Thrusters Using a POD Method under Different Operating Regimes
  
  • Désangles Victor
  • Shcherbanev S.A.
  • Charoy Thomas
  • Clément Noé
  • Deltel Clarence
  • Richard Pablo
  • Vincent Simon
  • Chabert Pascal
  • Bourdon Anne
  Atmosphere, MDPI, 2020, 11 (5), pp.518. Even after half a century of development, many phenomena in Hall Effect Thrusters are still not well-understood. While numerical studies are now widely used to study this highly non-linear system, experimental diagnostics are needed to validate their results and identify specific oscillations. By varying the cathode heating current, its emissivity is efficiently controlled and a transition between two functioning regimes of a low power thruster is observed. This transition implies a modification of the axial electric field and of the plasma plume shape. High-speed camera imaging is performed and the data are analysed using a Proper Orthogonal Decomposition method to isolate the different types of plasma fluctuations occurring simultaneously. The low-frequency breathing mode is observed, along with higher frequency rotating modes that can be associated to rotating spokes or gradient-induced instabilities. These rotating modes are observed while propagating outside the thruster channel. The reduction of the cathode emissivity beyond the transition comes along with a disappearance of the breathing mode, which could improve the thruster performance and stability. (10.3390/atmos11050518)
  DOI : 10.3390/atmos11050518
• Numerical Study of Jet-Target Interaction: Influence of Dielectric Permittivity on the Electric Field Experienced by the Target
  
  • Viegas Pedro
  • Bourdon Anne
  Plasma Chemistry and Plasma Processing, Springer Verlag, 2020, 40, pp.661–683. This work presents a study of the influence of dielectric permittivity on the interaction between a positive pulsed He plasma jet and a 0.5 mm-thick dielectric target, using a validated two-dimensional numerical model. Six different targets are studied: five targets at floating potential with relative permittivities &#1013;r= 1, 4, 20, 56 and 80; and one grounded target of permittivity &#1013;r=56. The temporal evolution of the charging of the target and of the electric field inside the target are described, during the pulse of applied voltage and after its fall. It is found that the order of magnitude of the electric field inside the dielectric targets is the same for all floating targets with &#1013;r&#8805;4. For all these targets, during the pulse of applied voltage, the electric field perpendicular to the target and averaged through the target thickness, at the point of discharge impact, is between 1 and 5 kV cm&#8722;1. For the two remaining targets (&#1013;r=1 and grounded target with &#1013;r=56), the field is significantly higher than for all the other floating targets. (10.1007/s11090-019-10033-6)
  DOI : 10.1007/s11090-019-10033-6
• The RPW Time Domain Sampler (TDS) on Solar Orbiter: In-flight performance and first data
  
  • Soucek Jan
  • Uhlir Ludek
  • Lan Radek
  • Pisa David
  • Kolmasova Ivana
  • Santolik Ondrej
  • Kruparova Oksana
  • Maksimovic Milan
  • Kretzschmar Matthieu
  • Khotyaintsev Yuri
  • Chust Thomas
  , 2020. The Radio and Plasma Wave instrument (RPW) for Solar Orbiter includes a Time Domain Sampler sub-unit (TDS) designed to capture electromagnetic waveform measurements of high-frequency plasma waves and antenna voltage spikes associated with dust impacts. TDS will digitize three components of the electric field and one magnetic component at 524 kHz sampling rate and scan the obtained signal for plasma waves and dust impact signatures. The main science target of TDS are Langmuir waves observed in the solar wind in association with Type II and Type III solar bursts, interplanetary shocks, magnetic holes, and other phenomena. In this poster, we present the scientific data products provided by the TDS instrument and discuss the first data obtained during the commissioning phase. The first data will be used to evaluate the actual performance of the RPW TDS instrument. (10.5194/egusphere-egu2020-18888)
  DOI : 10.5194/egusphere-egu2020-18888
• MMS observations of intense whistler waves within Earth's supercritical bow shock: Source mechanism and impact on shock structure and plasma transport
  
  • Hull A.
  • Muschietti Laurent
  • Le Contel O.
  • Dorelli J.
  • Lindqvist P.-E.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2020, 125 (7), pp.e2019JA027290. The properties of whistler waves near lower‐hybrid frequencies within Earth's quasiperpendicular bow shock are examined using data from the Magnetospheric Multiscale (MMS) mission. These waves appear as right‐hand polarized wave packets propagating upstream obliquely to the magnetic field and shock normal with phase speeds from a few hundred up to 1600 km/s. The wavelengths are near the ion inertial length scale (λ~0.3‐1.3 λi). Detailed analysis finds characteristics consistent with the modified two‐stream instability mechanism driven by the reflected ion and electron drift. Correlations between wave and electron anisotropy variations reveal that the whistlers are affecting electron dynamics and thus their perpendicular and parallel temperatures. The electron signatures are explainable via the interaction of magnetized electrons in the whistler induced non‐monotonic magnetic fields. These waves have intense magnetic fields (δB/Bo~0.1‐1.) and carry sizable currents that are a significant fraction of the thermal current (|J/Jvte|~0.1‐0.5). The whistler induced currents and the electron anisotropies are sufficiently large to respectively excite high‐frequency (HF) electrostatic (> 100 Hz) and HF whistler waves (f~0.1‐0.5 fce). Energy dissipation J•E from whistlers at 30 Hz and below range from a few thousandths to few hundredths of μW/m3. Comparisons reveal that plasma energy is converted to wave energy in the foot, whereas wave energy gets dissipated into the plasma in the ramp, where irreversible heating occurs. These observed features are indicative of an intricate coupling between small‐scale interaction processes and larger‐scale structure transpiring within the layer. Such a characterization is only made possible now with the MMS high‐time‐resolution measurements. (10.1029/2019JA027290)
  DOI : 10.1029/2019JA027290
• Analysis of Turbulence Properties in the Mercury Plasma Environment Using MESSENGER Observations
  
  • Huang S.
  • Wang Q. A.
  • Sahraoui F.
  • Yuan Z.
  • Liu Y.
  • Deng X.
  • Sun W.
  • Jiang K.
  • Xu S.
  • Yu X.
  • Wei Y.
  • Zhang J.
  The Astrophysical Journal, American Astronomical Society, 2020, 891 (2), pp.159. Turbulence is ubiquitous in space and astrophysical plasmas, such as the solar wind, planetary magnetospheres, and the interstellar medium. It plays a key role in converting electric and magnetic energies into kinetic energy of the plasma particles. Here, the properties of MHD and kinetic-scale magnetic fluctuations in the Mercury environment are investigated using data collected by the MESSENGER spacecraft from 2011 March 23 to 2015 April 28. It is found that spectral indices at MHD scales vary from ∼−5/3 in the near-Planet solar wind (possibly the foreshock) to ∼−1.3 within the magnetosheath close to bow shock. The spectra steepen further in the magnetosheath close to magnetopause, and reach ∼−2.2 within the magnetosphere. Only 15% of events were found to have the Kolmogorov scaling ∼−5/3 in the magnetosheath. The high variability of the spectral indices implies that the scaling of turbulent fluctuations in the magnetosheath is not universal, and it emphasizes the role of the bow shock on the turbulence dynamics, at least at the largest scales. Analysis of the magnetic compressibility shows that only ∼30% of events with Kolmogorov inertial range in the magnetosheath are dominated by (shear) Alfvénic fluctuations, which contrasts with well-known features of solar wind turbulence. At kinetic scales, the steepest spectra (slopes ∼−2.8) occur in the solar wind, before flattening to ∼−2 near the bow shock, then steepening again to ∼−2.8 in the magnetosheath. The spectral indices at kinetic scales are close to the ones at large scales in the magnetosphere, which may be caused by the presence of heavy ions in the latter. The statistical results are compared with previous observations reported in other planetary plasma environments. (10.3847/1538-4357/ab7349)
  DOI : 10.3847/1538-4357/ab7349
• Seed-packed dielectric barrier device for plasma agriculture: Understanding its electrical properties through an equivalent electrical model
  
  • Judée Florian
  • Dufour Thierry
  Journal of Applied Physics, American Institute of Physics, 2020, 128 (4), pp.044901. Seeds have been packed in a dielectric barrier device where cold atmospheric plasma has been generated to improve their germinative properties. A special attention has been paid on understanding the resulting plasma electrical properties through an equivalent electrical model whose experimental validity has been demonstrated here. In this model, the interelectrode gap is subdivided into 4 types of elementary domains, according to whether they contain electric charges (or not) and according to their type of medium (gas, seed or insulator). The model enables to study the influence of seeds on the plasma electrical properties by measuring and deducing several parameters (charge per filament, gas capacitance, plasma power, …) either in no-bed configuration (i.e. no seed in the reactor) or in packed-bed configuration (seeds in the reactor). In that second case, we have investigated how seeds can influence the plasma electrical parameters considering six specimens of seeds (beans, radishes, corianders, lentils, sunflowers and corns). The influence of molecular oxygen (0-100 sccm) mixed with a continuous flow rate of helium (2 slm) is also investigated, especially through filaments breakdown voltages, charge per filament and plasma power. It is demonstrated that such bed-packing drives to an increase in the gas capacitance (ξOFF), to a decrease in the β-parameter and to variations of the filaments' breakdown voltages in a seed-dependent manner. Finally, we show how the equivalent electrical model can be used to assess the total volume of the contact points, the capacitance of the seeds in the packed-bed configuration and we demonstrate that germinative effects can be induced by plasma on four of the six agronomical specimens. (10.1063/1.5139889)
  DOI : 10.1063/1.5139889
• Target Design for XUV Probing of Radiative Shock Experiments
  
  • Chaulagain U.
  • Stehlé C.
  • Barroso P.
  • Kozlova M.
  • Nejdl J.
  • Suzuki Vidal F.
  • Larour Jean
  Journal of Nepal Physical Society, Nepal Physical Society, 2020, 6 (1), pp.30-41. Radiative shocks are strong shocks characterized by plasma at a high temperature emitting an important fraction of its energy as radiation. Radiative shocks are commonly found in many astrophysical systems and are templates of radiative hydrodynamic flows, which can be studied experimentally using high-power lasers. This is not only important in the context of laboratory astrophysics but also to benchmark numerical studies. We present details on the design of experiments on radiative shocks in xenon gas performed at the kJ scale PALS laser facility. It includes technical specifications for the tube targets design and numerical studies with the 1-D radiative hydrodynamics code MULTI. Emphasis is given to the technical feasibility of an XUV imaging diagnostic with a 21 nm (~58 eV) probing beam, which allows to probe simultaneously the post-shock and the precursor region ahead of the shock. The novel design of the target together with the improved X-ray optics and XUV source allow to show both the dense post-shock structure and the precursor of the radiative shock. (10.3126/jnphyssoc.v6i1.30514)
  DOI : 10.3126/jnphyssoc.v6i1.30514
• The 2020 plasma catalysis roadmap
  
  • Bogaerts Annemie
  • Tu Xin
  • Whitehead J Christopher
  • Centi Gabriele
  • Lefferts Leon
  • Guaitella Olivier
  • Azzolina-Jury Federico
  • Kim Hyun-Ha
  • Murphy Anthony
  • Schneider William
  • Nozaki Tomohiro
  • Hicks Jason
  • Rousseau Antoine
  • Thevenet Frederic
  • Khacef Ahmed
  • Carreon Maria
  Journal of Physics D: Applied Physics, IOP Publishing, 2020, 53 (44), pp.443001. Plasma catalysis is gaining increasing interest for various gas conversion applications, such as CO2 conversion into value-added chemicals and fuels, CH4 activation into hydrogen, higher hydrocarbons or oxygenates, and NH3 synthesis. Other applications are already more established, such as for air pollution control, e.g. volatile organic compound remediation, particulate matter and NOx removal. In addition, plasma is also very promising for catalyst synthesis and treatment. Plasma catalysis clearly has benefits over 'conventional' catalysis, as outlined in the Introduction. However, a better insight into the underlying physical and chemical processes is crucial. This can be obtained by experiments applying diagnostics, studying both the chemical processes at the catalyst surface and the physicochemical mechanisms of plasma-catalyst interactions, as well as by computer modeling. The key challenge is to design cost-effective, highly active and stable catalysts tailored to the plasma environment. Therefore, insight from thermal catalysis as well as electro- and photocatalysis is crucial. All these aspects are covered in this Roadmap paper, written by specialists in their field, presenting the state-of-the-art, the current and future challenges, as well as the advances in science and technology needed to meet these challenges. (10.1088/1361-6463/ab9048)
  DOI : 10.1088/1361-6463/ab9048
• Turbulence as a Network of Fourier Modes
  
  • Gürcan Özgür D.
  • Li Yang
  • Morel Pierre
  Mathematics, MDPI, 2020, 8 (4), pp.530. Turbulence is the duality of chaotic dynamics and hierarchical organization of a field over a large range of scales due to advective nonlinearities. Quadratic nonlinearities (e.g., advection) in real space, translates into triadic interactions in Fourier space. Those interactions can be computed using fast Fourier transforms, or other methods of computing convolution integrals. However, more generally, they can be interpreted as a network of interacting nodes, where each interaction is between a node and a pair. In this formulation, each node interacts with a list of pairs that satisfy the triadic interaction condition with that node, and the convolution becomes a sum over this list. A regular wavenumber space mesh can be written in the form of such a network. Reducing the resolution of a regular mesh and combining the nearby nodes in order to obtain the reduced network corresponding to the low resolution mesh, we can deduce the reduction rules for such a network. This perspective allows us to develop network models as approximations of various types of turbulent dynamics. Various examples, such as shell models, nested polyhedra models, or predator-prey models, are briefly discussed. A prescription for setting up a small world variants of these models are given. (10.3390/math8040530)
  DOI : 10.3390/math8040530
• Electron Heating by Debye-Scale Turbulence in Guide-Field Reconnection
  
  • Khotyaintsev Yu. v.
  • Graham D. b.
  • Steinvall K.
  • Alm L.
  • Vaivads A.
  • Johlander A.
  • Norgren C.
  • Li W.
  • Divin A.
  • Fu H. s.
  • Hwang K.-J.
  • Burch J. l.
  • Ahmadi N.
  • Le Contel O.
  • Gershman D. j.
  • Russell C. t.
  • Torbert R. b.
  Physical Review Letters, American Physical Society, 2020, 124 (4). (10.1103/PhysRevLett.124.045101)
  DOI : 10.1103/PhysRevLett.124.045101
• The study of low-frequency waves in the solar wind by the RPW/TDS instrument onboard Solar Orbiter
  
  • Pisa D.
  • Soucek J.
  • Santolik O.
  • Maksimovic M.
  • Bale S. D.
  • Chust T.
  • Khotyaintsev Y.
  • Krasnoselskikh V.
  • Kretzschmar Matthieu
  • Lorfevre E.
  • Plettemeier D.
  • Steller M.
  • Štverák Š.
  • Travnicek P.
  • Vaivads A.
  • Vecchio A.
  • Horbury T. S.
  • Angelini V.
  • O'Brien H.
  • Evans V.
  , 2020, 2020, pp.18 pp.. The Time Domain Sampler (TDS) receiver is a part of the Radio and Plasma Wave instrument (RPW) onboard Solar Orbiter, sampling three electric and one magnetic field components at frequencies up to 524 kHz. The RPW instrument has been operating almost continuously during the commissioning phase of the mission and through the first perihelion in June 2020, covering an interval of heliocentric distances between 0.5 AU to 1 AU. The most common plasma phenomena observed by TDS are low-frequency electrostatic waves at frequencies between hundreds of Hertz and 10 kHz. These are interpreted as strongly Doppler-shifted ion-acoustic waves, generated by solar wind ion beams and often accompanying large scale solar wind structures. In this initial study, we performed a statistical investigation of the waves, studying their modulation and polarization.
• Early results from the Proton Alfa Sensor (PAS/SWA) onboard Solar Orbiter: the Solar Wind at different scales.
  
  • Louarn P.
  • Fedorov A.
  • Prech L.
  • Lavraud B.
  • Rouillard A. P.
  • Genot V. N.
  • Plotnikov I.
  • Penou E.
  • Barthe A.
  • Owen C. J.
  • Berthomier M.
  • Kataria D. O.
  • Bruno R.
  • Livi S. A.
  • Evans V.
  • Raines J. M.
  • Horbury T. S.
  • O'Brien H.
  • Angelini V.
  • Maksimovic M.
  • Bale S. D.
  • Chust T.
  • Khotyaintsev Y.
  • Krasnoselskikh V.
  • Kretzschmar Matthieu
  • Plettemeier D.
  • Soucek J.
  • Steller M.
  • Stverak S.
  • Travnicek P.
  • Vaivads A.
  • Vecchio A.
  , 2020, 2020. Solar Orbiter is designed to discover the fundamental connections between the rapidly varying solar atmosphere and the solar wind. In operations since mid-2020, the Solar Wind Analyzer (SWA) plasma package is now providing comprehensive in-situ measurements of the solar wind. In particular, the Proton-Alpha Sensor (PAS) is determining the properties of the dominant solar wind ion populations through the measurements of the 3D distribution functions, density, bulk velocities, temperatures, and heat fluxes, at temporal cadences ranging from 4 s to ~0.1 s. This offers the possibility of analyzing the solar wind dynamics at vastly different scales, from days to fractions of seconds. Specifically, kinetic structures can thus be described at unprecedented resolution, both in time or spatial scales and phase space organization of the associated ion populations. We will report on observations of various structures that propagate in the solar wind (large amplitude waves, solitary structures, discontinuities between different types of solar winds...) with a focus on the formation of non-thermal distribution functions, the associated wave activity and magnetic perturbations.
• Italian Solar Orbiter-SWA Working Group on Machine Learning and Artificial Intelligence
  
  • de Marco R.
  • Alberti T.
  • Amaya J.
  • Bruno R.
  • Califano F.
  • Camporeale E.
  • Consolini G.
  • Foldes R.
  • d'Amicis R.
  • Dupuis R.
  • Franci L.
  • Guedes dos Santos L. F.
  • Innocenti M. E.
  • Jagarlamudi V. K.
  • Lapenta G.
  • Laurenza M.
  • Marcucci M. F.
  • Narock A.
  • Papini E.
  • Perri S.
  • Perrone D.
  • Retino A.
  • Servidio S.
  • Sisti M.
  • Sorriso-Valvo L.
  • Valentini F.
  , 2020, 2020. The exponential growth of data volume experienced by astronomy and astrophysics causes new disciplines like machine learning (ML) and data mining (DM) to gain more and more ground in these fields. Applications like clustering, feature selection, automatic classification of events are proving to be a valuable aid in exploiting space data in the era of the synergy between "pure" science and "data-driven" science. <P />The Italian Solar Orbiter-SWA Working Group on Machine Learning and Artificial Intelligence<SUP>1</SUP> together with the European Commission Horizon 2020 project AIDA<SUP>2</SUP>, has the scope of applying ML and DM analysis techniques to the Solar Orbiter data. The implementations are numerous. First of all these new techniques can be used to discover unexpected relations between data, can automate tasks so that they can be carried out without human intervention, and can help to forecast physical properties and events. A non-exhaustive list of these activities includes automatic detection of coronal holes in images, automatic recognition of plasma regions, prediction of solar wind properties at 1 AU, classification of solar wind type based on new indicators, analysis of particle velocity distribution functions. <P />In addition, this Working Group will integrate the existing software developed in the context of the various heliospheric missions with the parts regarding Solar Orbiter. These packages are able to handle complex data set with ease and provide statistical analysis and visualization tools. Catalogs of scientific data are also produced, which report, among others, magnetic reconnection and particle acceleration events, detected by routines trained to browse data and select physical processes and features of interest. <P />Here we present the project overview along with the ML and DM tools which will be used to handle and analyse Solar Orbiter data. <P />1.https://sites.google.com/view/italian-solar-orbiter-swa/ 2.http://www.aida-space.eu
• Design of a variable frequency comb reflectometer system for the ASDEX Upgrade tokamak
  
  • Happel T.
  • Kasparek W.
  • Hennequin Pascale
  • Höfler K.
  • Honoré Cyrille
  • Team Asdex Upgrade
  Plasma Science and Technology, IOP Publishing, 2020, 22 (6), pp.064002. Comb reflectometers offer the advantage of measuring several radial positions in plasma simultaneously. This allows for the investigation of fast timescales during L-H transitions, I-phases, I-mode bursts, transients during heat wave propagation, etc. A drawback of many present-day systems is that they use a fixed frequency difference between the probing frequencies. Hence, although the central probing frequency can be varied, the probing frequency difference is usually fixed. The new design presented in this work uses an advanced microwave generation and detection scheme, which allows for arbitrary probing frequencies and probing frequency separations. (10.1088/2058-6272/ab618c)
  DOI : 10.1088/2058-6272/ab618c
• Influence of N<SUB>2</SUB> on the CO<SUB>2</SUB> vibrational distribution function and dissociation yield in non-equilibrium plasmas
  
  • Terraz L.
  • Silva T.
  • Morillo-Candas A.
  • Guaitella O.
  • Tejero-Del-Caz A.
  • Alves L. L.
  • Guerra V.
  Journal of Physics D: Applied Physics, IOP Publishing, 2020, 53, pp.094002. This work explores the effect of nitrogen addition on CO<SUB>2</SUB> dissociation under various non-equilibrium plasma conditions. Experiments are performed in non-thermal plasmas sustained by DC pulsed discharges, for pressure and current ranges of 1 to 5 Torr and 20 to 50 mA, respectively. A self-consistent model, previously validated for pure CO<SUB>2</SUB> discharges, is further extended to take into account e-V, V-T and V-V reactions involving N<SUB>2</SUB>. Both model predictions and experimental data reveal a maximum of the asymmetric vibrational temperature T<SUB>3</SUB> at 5 Torr during the discharge around 1 ms, while no such maximum is visible at 1 Torr before the saturation occurs. It is shown that V-T deactivation by O atoms can have a strong influence on the vibrational kinetics, by directly affecting the relaxation of N<SUB>2</SUB> vibrational excited states and, as a consequence, the very important energy transfers between vibrationally excited N<SUB>2</SUB> and CO<SUB>2</SUB> molecules. The experimental results show a twice as large CO<SUB>2</SUB>-conversion rate when N<SUB>2</SUB> gas is added to the plasma. The simulations suggest this effect cannot be the result of an increased dissociation by direct electron impact due to modifications in the reduced electric field, but rather of some other contribution to dissociation and/or inhibition of reactions giving back CO<SUB>2</SUB>. (10.1088/1361-6463/ab55fb)
  DOI : 10.1088/1361-6463/ab55fb
• Negative ion source operation with deuterium
  
  • Bacal M.
  • Wada M
  Plasma Sources Science and Technology, IOP Publishing, 2020, 29 (3), pp.033001. When the working gas of a negative ion source is changed from hydrogen to its isotope, deuterium, an 'isotope effect' is observed; namely, several plasma characteristics such as the electron energy distribution, the atomic fraction and the spectra of rovibrationally excited molecules change. The understanding of the effect becomes more important, as research and development aiming at ITER power level operation is being challenged with feeding deuterium to the ion sources. As a historical review of the effort to develop hydrogen/deuterium negative ion sources, several types of negative ion sources designed for the neutral beam plasma heating are described: double charge exchange sources, volume sources and surface-plasma sources. The early results with volume sources operated with and without cesium are introduced. The characteristics of the source charged with deuterium are compared to those of the source charged with hydrogen. The isotope effect did not appear pronounced as the negative ion density was measured in a small source but became more pronounced when the plasma source size was enlarged and the discharge power density was increased to higher values. Surface plasma sources were optimized for deuterium operation but could not achieve the same performance as a source operated with hydrogen at the same power and pressure. The lower velocity of negative deuterium ions leaving the low work function surface seemed to limit the production efficiency. Fundamental processes causing these differences in negative ion source operation are summarized. After explaining the current status of negative ion source research and development, the acquired knowledge is utilized to the development of large negative ion sources for nuclear fusion research and to the development of compact negative ion sources for neutron source applications. (10.1088/1361-6595/ab6881)
  DOI : 10.1088/1361-6595/ab6881
• On the deviation from Maxwellian of the ion velocity distribution functions in the turbulent magnetosheath
  
  • Perri S.
  • Perrone D.
  • Yordanova E.
  • Sorriso-Valvo L.
  • Paterson W. R.
  • Gershman D. J.
  • Giles B. L.
  • Pollock C. J.
  • Dorelli J. C.
  • Avanov L. A.
  • Lavraud B.
  • Saito Y.
  • Nakamura R.
  • Fischer D.
  • Baumjohann W.
  • Plaschke F.
  • Narita Y.
  • Magnes W.
  • Russell C. T.
  • Strangeway R. J.
  • Contel O. Le
  • Khotyaintsev Y.
  • Valentini F.
  Journal of Plasma Physics, Cambridge University Press (CUP), 2020, 86. The deviation from thermodynamic equilibrium of the ion velocity distribution functions (VDFs), as measured by the Magnetospheric Multiscale (MMS) mission in the Earth's turbulent magnetosheath, is quantitatively investigated. Making use of the unprecedented high-resolution MMS ion data, and together with Vlasov-Maxwell simulations, this analysis aims at investigating the relationship between deviation from Maxwellian equilibrium and typical plasma parameters. Correlations of the non-Maxwellian features with plasma quantities such as electric fields, ion temperature, current density and ion vorticity are found to be similar in magnetosheath data and numerical experiments, with a poor correlation between distortions of ion VDFs and current density, evidence that questions the occurrence of VDF departure from Maxwellian at the current density peaks. Moreover, strong correlation has been observed with the magnitude of the electric field in the turbulent magnetosheath, while a certain degree of correlation has been found in the numerical simulations and during a magnetopause crossing by MMS. This work could help shed light on the influence of electrostatic waves on the distortion of the ion VDFs in space turbulent plasmas. (10.1017/S0022377820000021)
  DOI : 10.1017/S0022377820000021
• Microphysics of Magnetic Reconnection in Near-Earth Space
  
  • Cozzani Giulia
  , 2020. (10.1007/978-3-030-56142-0)
  DOI : 10.1007/978-3-030-56142-0