Publications

2020

• Electromagnetic radiation from upper-hybrid wave turbulence in inhomogeneous solar plasmas
  
  • Krafft C
  • Volokitin A
  Plasma Physics and Controlled Fusion, IOP Publishing, 2020, 62 (2), pp.024007. Type III solar radio bursts have been commonly observed in the solar wind and coronal plasmas. Electron beams accelerated in the Sun's atmosphere generate weakly magnetized Langmuir (upper-hybrid) wave turbulence producing in turn electromagnetic emissions at the electron plasma frequency ωp and its harmonic 2ωp, via successive processes involving interactions between the background plasma, the waves and the beam particles. The impact of the random density fluctuations inherent to the background plasma on these processes requires the development of novel approaches and models. Owing to a new theoretical modeling, the radiation efficiency of electromagnetic waves radiated at ωp from a plasma source with random density fluctuations and developed upper-hybrid wave turbulence is calculated analytically and numerically. It is shown that the maximum radiation efficiency at frequency ωp scales as the average level of density fluctuations and as the ratio (c/vT)–2 (where vT is the thermal velocity). These scaling laws are found owing to two different and novel methods of determination of the electromagnetic radiation by turbulent inhomogeneous plasma sources through waves' transformations on randomly fluctuating density irregularities. These results contribute significantly to the understanding of the processes involved in the generation of Type III solar radio bursts. Their presentation is preceded by a summary of previous studies on the dynamics of beam-driven Langmuir turbulence in inhomogeneous solar plasmas. (10.1088/1361-6587/ab569d)
  DOI : 10.1088/1361-6587/ab569d
• The Solar Probe ANalyzers-Electrons on the Parker Solar Probe
  
  • Whittlesey Phyllis L
  • Larson Davin
  • Kasper Justin
  • Halekas Jasper
  • Abatcha Mamuda
  • Abiad Robert
  • Berthomier Matthieu
  • Case A. W
  • Chen Jianxin
  • Curtis David
  • Dalton Gregory
  • Klein Kristopher G
  • Korreck Kelly E
  • Livi Roberto
  • Ludlam Michael
  • Marckwordt Mario
  • Rahmati Ali
  • Robinson Miles
  • Slagle Amanda
  • Stevens M. L.
  • Tiu Chris
  • Verniero J. L
  The Astrophysical Journal Supplement, American Astronomical Society / IOP Science, 2020, 246 (2), pp.74. Electrostatic analyzers of different designs have been used since the earliest days of the space age, beginning with the very earliest solar-wind measurements made by Mariner 2 en route to Venus in 1962. The Parker Solar Probe (PSP) mission, NASA's first dedicated mission to study the innermost reaches of the heliosphere, makes its thermal plasma measurements using a suite of instruments called the Solar Wind Electrons, Alphas, and Protons (SWEAP) investigation. SWEAP's electron PSP Analyzer (Solar Probe ANalyzer-Electron (SPAN-E)) instruments are a pair of top-hat electrostatic analyzers on PSP that are capable of measuring the electron distribution function in the solar wind from 2 eV to 30 keV. For the first time, in situ measurements of thermal electrons provided by SPAN-E will help reveal the heating and acceleration mechanisms driving the evolution of the solar wind at the points of acceleration and heating, closer than ever before to the Sun. This paper details the design of the SPAN-E sensors and their operation, data formats, and measurement caveats from PSP's first two close encounters with the Sun. (10.3847/1538-4365/ab7370)
  DOI : 10.3847/1538-4365/ab7370
• Wave turbulence: the case of capillary waves (a review)
  
  • Galtier Sébastien
  Geophysical and Astrophysical Fluid Dynamics, Taylor & Francis, 2020, pp.1-24. Capillary waves are perhaps the simplest example to consider for an introduction to wave turbulence. Since the first paper by Zakharov and Filonenko [1], capillary wave turbulence has been the subject of many studies but a didactic derivation of the kinetic equation is still lacking. It is the objective of this paper to present such a derivation in absence of gravity and in the approximation of deep water. We use the Eulerian method and a Taylor expansion around the equilibrium elevation for the velocity potential to derive the kinetic equation. The use of directional polarities for three-wave interactions leads to a compact form for this equation which is fully compatible with previous work. The exact solutions are derived with the so-called Zakharov transformation applied to wavenumbers and the nature of these solutions is discussed. Experimental and numerical works done in recent decades are also reviewed. (10.1080/03091929.2020.1715966)
  DOI : 10.1080/03091929.2020.1715966
• Electrons in the Young Solar Wind: First Results from the Parker Solar Probe
  
  • Halekas J.
  • Whittlesey P.
  • Larson D.
  • Mcginnis D.
  • Maksimovic M.
  • Berthomier Matthieu
  • Kasper J.
  • Case A.
  • Korreck K.
  • Stevens M.
  • Klein K.
  • Bale S.
  • Macdowall R.
  • Pulupa M.
  • Malaspina D.
  • Goetz K.
  • Harvey P.
  The Astrophysical Journal Supplement, American Astronomical Society / IOP Science, 2020, 246 (2), pp.22. The Solar Wind Electrons Alphas and Protons experiment on the Parker Solar Probe (PSP) mission measures the three-dimensional electron velocity distribution function. We derive the parameters of the core, halo, and strahl populations utilizing a combination of fitting to model distributions and numerical integration for ∼100,000 electron distributions measured near the Sun on the first two PSP orbits, which reached heliocentric distances as small as ∼0.17 au. As expected, the electron core density and temperature increase with decreasing heliocentric distance, while the ratio of electron thermal pressure to magnetic pressure (βe) decreases. These quantities have radial scaling consistent with previous observations farther from the Sun, with superposed variations associated with different solar wind streams. The density in the strahl also increases; however, the density of the halo plateaus and even decreases at perihelion, leading to a large strahl/halo ratio near the Sun. As at greater heliocentric distances, the core has a sunward drift relative to the proton frame, which balances the current carried by the strahl, satisfying the zero-current condition necessary to maintain quasi-neutrality. Many characteristics of the electron distributions near perihelion have trends with solar wind flow speed, βe, and/or collisional age. Near the Sun, some trends not clearly seen at 1 au become apparent, including anticorrelations between wind speed and both electron temperature and heat flux. These trends help us understand the mechanisms that shape the solar wind electron distributions at an early stage of their evolution. (10.3847/1538-4365/ab4cec)
  DOI : 10.3847/1538-4365/ab4cec
• Picosecond synchronously pumped optical parametric oscillator based on chirped quasi-phase matching
  
  • Walter Guillaume
  • Descloux Delphine
  • Dherbecourt Jean-Baptiste
  • Melkonian Jean-Michel
  • Raybaut Myriam
  • Drag Cyril
  • Godard Antoine
  Journal of the Optical Society of America B, Optical Society of America, 2020, 37 (2), pp.552-563. We investigate and model a picosecond synchronously pumped optical parametric oscillator (OPO) based on an aperiodically poled lithium niobate (APPLN) nonlinear crystal with a chirped quasi-phase-matching (QPM) grating. We observe remarkable spectral features with an asymmetric OPO spectrum consisting of a main peak with lower side-lobes. Depending on the sign of the QPM chirp rate, the side-lobes are located either on the red or on the blue side of the main peak. Meanwhile, side-bands develop in the depleted pump spectrum. We attribute these features to cascaded sum-/difference-frequency generation processes which are quasi-phase matched at different positions in the APPLN crystal. A terahertz-generation cascading effect is also observed and characterized at high pump power. (10.1364/JOSAB.380605)
  DOI : 10.1364/JOSAB.380605
• Comment on “Measurement of the electron affinity of the lanthanum atom”
  
  • Blondel Christophe
  Physical Review A, American Physical Society, 2020, 101 (1). The electron affinity of the lanthanum atom was recently measured by slow-electron velocity map imaging in a photodetachment experiment [Y. Lu et al., Phys. Rev. A 99, 062507 (2019)]. Several detachment threshold energies have been measured, which correspond to different energy levels of the initial ion and/or final atom. Only one measurement, however, has been exploited to determine the electron affinity. Applying the ordinary spectroscopic method to the complete set of data presented by the authors, one obtains a slightly different, more precise and more consistent value of the electron affinity of La: 449 691(17) instead of 449 697(20) m−1, i.e., 0.557 546(20) instead of 0.557 553(25) eV. (10.1103/PhysRevA.101.016501)
  DOI : 10.1103/PhysRevA.101.016501
• Electron Bernstein waves driven by electron crescents near the electron diffusion region
  
  • Li W.Y.
  • Graham D. B
  • Khotyaintsev Yu V
  • Vaivads A.
  • André M.
  • Min K.
  • Liu K.
  • Tang B. B
  • Wang C.
  • Fujimoto K.
  • Norgren C.
  • Toledo-Redondo S.
  • Lindqvist P.-A.
  • Ergun R. E
  • Torbert R. B
  • Rager A. C
  • Dorelli J.C.
  • Gershman D.J.
  • Giles B.L.
  • Lavraud B.
  • Plaschke F.
  • Magnes W.
  • Le Contel O.
  • Russell C. T.
  • Burch J.L.
  Nature Communications, Nature Publishing Group, 2020, 11 (1). The Magnetospheric Multiscale (MMS) spacecraft encounter an electron diffusion region (EDR) of asymmetric magnetic reconnection at Earth's magnetopause. The EDR is characterized by agyrotropic electron velocity distributions on both sides of the neutral line. Various types of plasma waves are produced by the magnetic reconnection in and near the EDR. Here we report large-amplitude electron Bernstein waves (EBWs) at the electron-scale boundary of the Hall current reversal. The finite gyroradius effect of the outflow electrons generates the crescent-shaped agyrotropic electron distributions, which drive the EBWs. The EBWs propagate toward the central EDR. The amplitude of the EBWs is sufficiently large to thermalize and diffuse electrons around the EDR. The EBWs contribute to the cross-field diffusion of the electron-scale boundary of the Hall current reversal near the EDR. (10.1038/s41467-019-13920-w)
  DOI : 10.1038/s41467-019-13920-w
• N-atom Production at High Electric Fields: E-FISH and TALIF Experiments for Understanding Fast Ionization Wave Kinetics
  
  • Chng Tat Loon
  • Orel Inna S
  • Adamovich Igor V
  • Popov Nikolay A
  • Starikovskaia Svetlana
  , 2020. This work forms part of a larger effort to develop a suite of diagnostics for making measurements in non-equilibrium, nanosecond pulse discharges, so as to facilitate an improved understanding of the plasma kinetics. Electric field induced second harmonic (E-FISH) generation, is used to probe the electric field in a fast ionization wave, nanosecond pulse discharge in pure N2 at a pressure of 20 mbar. The field evolution during the fast ionization wave development is clearly captured in the form of three distinct phases. An initial field overshoot ahead of the front to about 10.5 kV/cm (or about 2 kTd), followed by a field drop as the wave traverses the measurement location, and finally a subsequent rise as a quasi-steady state regime is established. TALIF measurements of N-atom density are also performed with a view to understanding the impact of the reduced electric field on the consequent atomic species production. These measurements are limited to the post-discharge phase, mainly due to the poor signal to raise ratio associated with the lower atomic densities and strong fluorescence-overlapping plasma emission. A relatively low peak N-atom density of about 5.5 x 10 12 cm-3 is obtained, in line with the low specific deposited energy of this discharge (0.01 eV/molecule). Finally, attempts to model this plasma show that the results of simulations are strongly influenced by the radial non-uniformity of the discharge.
• Experimental study of energy delivered to the filaments in high pressure nanosecond surface discharge
  
  • Ding Chenyang
  • Jean Antonin
  • Shcherbanev S.A.
  • Selivonin Igor
  • Moralev Ivan
  • Popov Nikolay
  • Starikovskaia Svetlana
  , 2020. (10.2514/6.2020-1662)
  DOI : 10.2514/6.2020-1662
• In-situ monitoring of an organic sample with electric field determination during cold plasma jet exposure
  
  • Slikboer Elmar
  • Sobota Ana
  • Garcia-Caurel Enric
  • Guaitella Olivier
  Scientific Reports, Nature Publishing Group, 2020, 10, pp.13580. Pockels-based Mueller polarimetry is presented as a novel diagnostic technique for studying time and space-resolved and in-situ the interaction between an organic sample (a layer of onion cells) and non-thermal atmospheric pressure plasma. The effect of plasma is complex, as it delivers electric field, radicals, (UV) radiation, non-uniform in time nor in space. This work shows for the first time that the plasma-surface interaction can be characterized through the induced electric field in an electro-optic crystal (birefringence caused by the Pockels effect) while at the same moment the surface evolution of the targeted sample is monitored (depolarization) which is attached to the crystal. As Mueller polarimetry allows for separate detection of depolarization and birefringence, it is possible to decouple the entangled effects of the plasma. In the sample three spatial regions are identified where the surface evolution of the sample differs. This directly relates to the spatial in-homogeneity of the plasma at the surface characterized through the detected electric field. The method can be applied in the future to investigate plasma-surface interactions for various targets ranging from bio-films, to catalytic surfaces and plastics/polymers. (10.1038/s41598-020-70452-w)
  DOI : 10.1038/s41598-020-70452-w
• Italian Solar Orbiter-SWA Working Group on "Multiscale Physics
  
  • d'Amicis R.
  • Alberti T.
  • Bruno R.
  • Califano F.
  • Carnevale G.
  • Catapano F.
  • Cerri S. S.
  • Coco I.
  • del Zanna L.
  • de Marco R.
  • Di Matteo S.
  • Franci L.
  • Greco A.
  • Jagarlamudi V. K.
  • Landi S.
  • Lepreti F.
  • Malara F.
  • Marcucci M. F.
  • Marino R.
  • Matteini L.
  • Nieves-Chinchilla T.
  • Nigro G.
  • Nisticò G.
  • Papini E.
  • Pecora F.
  • Perri S.
  • Pezzi O.
  • Perrone D.
  • Primavera L.
  • Qamili E.
  • Retino A.
  • Servidio S.
  • Sorriso-Valvo L.
  • Innocenti M. E.
  • Telloni D.
  • Tenerani A.
  • Trenchi L.
  • Valentini F.
  • Velli M. C. M.
  • Veltri P.
  • Verdini A.
  • Villante U.
  • Zimbardo G.
  , 2020, 2020. Despite more than a half-century of study, the basic physical processes responsible for heating and accelerating the solar wind are still not fully understood. These phenomena are at the center of a hot debate that is of great interest for the Solar Orbiter mission (as discussed in details in the Science Activity Plan, SAP) and are strictly linked to the turbulent nature of solar wind fluctuations which cover an extended range of spatial and temporal scales. So the identification of these physical processes is of primary importance for understanding the origins and evolution of the solar wind and its impact on the different bodies of the solar system. Moreover, in a broader context, it would allow also to achieve significant progress in our understanding of stellar astrophysics. <P />Within this context, the Italian Solar Orbiter-SWA Working Group (WGs) on `Multiscale Physics' was created in response to the interest manifested by scientists from several Italian and international institutions on some important topics such as radial evolution of turbulence and Alfvénicity and link between fluid and kinetic scales; solar wind origin; reconnection, intermittency and particle acceleration in the turbulent solar wind (just to cite some of them), with a particular attention to the synergies with other in-situ and remote sensing instruments on board Solar Orbiter and also with other ESA and NASA missions (e.g. L1 observatories and Parker Solar Probe). The `Multiscale Physics' WG involves scientists with an extensive experience in solar wind turbulence and reconnection processes including expertise in data analysis, simulations and modeling. <P />In this contribution, we present the activity developed so far with a particular focus on the scientific cases identified.
• Italian SWA-Solar Orbiter Working Group on "Kinetic Processes
  
  • Valentini F.
  • Califano F.
  • Camporeale E.
  • Carbone V.
  • Cerri S. S.
  • d'Amicis R.
  • del Sarto D.
  • Franci L.
  • Innocenti M. E.
  • Landi S.
  • Lepreti F.
  • Malara F.
  • Matteini L.
  • Nigro G.
  • Papini E.
  • Pegoraro F.
  • Perri S.
  • Pezzi O.
  • Pucci F.
  • Retino A.
  • Servidio S.
  • Settino A.
  • Sorriso-Valvo L.
  • Telloni D.
  • Vecchio A.
  • Veltri P.
  • Verdini A.
  • Perrone D.
  • Bruno R.
  • de Marco R.
  • Pecora F.
  • Trotta D.
  • Lapenta G.
  • Marcucci M. F.
  • Jagarlamudi V. K.
  • Carnevale G.
  , 2020, 2020. Since inter-particle collisions are to a large extent negligible, the solar wind plasma is typically observed in a state far from thermodynamic equilibrium, meaning that the velocity distributions of particles of different species display significant deviations from a single Maxwellian. These deviations retain the whole history of the interaction of particles with the turbulent electromagnetic fields. Simultaneous measurements of fields and particle velocity distributions at kinetic scales made at different radial distances can help in tracking this history backwards allowing one to identify the physical mechanisms at play to heat and accelerate particles in the interplanetary medium close to the Sun and all along solar wind expansion. <P />In this scenario, data from the Solar Wind Analyzer instrument onboard the ESA Solar Orbiter mission are very promising in addressing the kinetic physics of protons, ions and electrons in the solar wind close to the Sun. The Italian SWA-Solar Orbiter Working Group entitled "Kinetic Processes" has been formed in May 2020 and gathers scientists from several Italian and international institutions and with different expertises (theoretical modeling, observational data analysis and numerical simulations), who convene periodically to discuss these scientific subjects. <P />The main scientific goals of this working group are (i) to maximize the scientific return of Solar Orbiter data within the Heliospheric communities and (ii) to identify open scientific questions and relevant physical problems for which Solar Orbiter data could play a key role and help scientists to find answers and explanations. <P />Exploitation of combined measurements from the in-situ instruments (SWA, MAG, EPD and RPW) onboard Solar Orbiter will provide the unique opportunity of attacking fundamental plasma physics processes responsible for energy exchanges between fluctuations and particles. <P />In this Abstract, we will present some of the activities carried on within the Italian SWA-Solar Orbiter WG "Kinetic Processes" in the last few months, with the aim of engaging the broader scientific community into the discussion and in preparation of the release of the first Orbiter data.
• Performances and First Results from the RPW/Search Coil Magnetometer onboard Solar Orbiter
  
  • Kretzschmar Matthieu
  • Krasnoselskikh V.
  • Dudok de Wit Thierry
  • Froment C.
  • Jean-Yves B.
  • Jannet G.
  • Le Contel O.
  • Maksimovic M.
  • Chust T.
  • Soucek J.
  • Vecchio A.
  • Bale S. D.
  • Khotyaintsev Y.
  • Lorfevre E.
  • Plettemeier D.
  • Steller M.
  • Stverak S.
  • Travnicek P.
  • Vaivads A.
  , 2020, 2020, pp.18 pp.. The Search Coil Magnetometer (SCM) onboard Solar Orbiter is part of the Radio and Plasma Waves (RPW) experiment. It measures magnetic field fluctuations in the frequency range from a few Hz to 50 kHz on three axes and between 1 kHz and 1MHz in one axis. RPW has been working nearly continuously and SCM has recorded many interesting features, including whistler and other types of waves as well as local characteristics of turbulence. We will provide an overview of these observations as well as a description of the in flight performances of SCM.
• Electric Field Vector Measurements Via Nanosecond Electric Field Induced Second Harmonic Generation
  
  • Chng Tat Loon
  • Naphade Maya
  • Goldberg Benjamin M
  • Adamovich Igor V
  • Starikovskaia Svetlana
  Optics Letters, Optical Society of America - OSA Publishing, 2020, 45 (7), pp.1942. (10.1364/OL.45.001942)
  DOI : 10.1364/OL.45.001942
• Observations of Magnetic Field Line Curvature and Its Role in the Space Plasma Turbulence
  
  • Huang S. Y.
  • Zhang Jing
  • Sahraoui Fouad
  • Yuan Z. G.
  • Deng X. H.
  • Jiang K.
  • Xu S. B.
  • Wei Y. Y.
  • He L. H.
  • Zhang Z. H.
  The Astrophysical Journal, American Astronomical Society, 2020, 898, pp.L18. Recent numerical simulations of plasma turbulence showed that magnetic field line curvature plays a key role in particle energization. Based on in situ high-resolution data provided by the four Magnetospheric Multiscale spacecraft, we investigate the magnetic field line curvature and its role in the turbulent magnetosheath plasma. Our analysis reveals that the curvature exhibits two power-law distributions: the low curvature follows the scaling as ?<SUP>0.33</SUP>, and the large curvature has a scaling as ?<SUP>-2.16</SUP>. The curvature is anticorrelated with the magnitude of the magnetic field, but positively related to the normal force, the drift electric current, and the curvature drift acceleration term, indicating that intense energy dissipation due to the curvature drift occurs in the large curvature region. One typical example shows a localized increase of electron temperature that coincides with a peak in the curvature and the curvature drift acceleration term, which supports the role of the latter in local energization of electrons, in agreement with simulation results. These observations allow us to better understand the connection between magnetic field line curvature, energy dissipation, and particle energization in space and astrophysical plasmas. (10.3847/2041-8213/aba263)
  DOI : 10.3847/2041-8213/aba263
• Electron impact dissociation of CO<SUB>2</SUB>
  
  • Morillo-Candas A. S.
  • Silva T.
  • Klarenaar B. L. M.
  • Grofulović M.
  • Guerra V.
  • Guaitella Olivier
  Plasma Sources Science and Technology, IOP Publishing, 2020, 29, pp.01LT01. Several CO&lt;SUB&gt;2&lt;/SUB&gt; electron impact dissociation cross sections are available in the literature, different in magnitude and threshold, hindering the understanding of CO&lt;SUB&gt;2&lt;/SUB&gt; dissociation mechanisms under gas discharges. This work reports the experimental validation of the electron impact CO&lt;SUB&gt;2&lt;/SUB&gt; dissociation cross section using two complementary methods: through the comparison of the measured rate coefficients with those derived from cross sections available in literature; and through the comparison of the experimental time evolution of the dissociation fraction with the simulations of a 0D model. A careful experimental approach was designed to avoid any influence from other dissociation mechanisms or chemical reactions. The experimental results match remarkably well the theoretical predictions from Polak and Slovetsky and establish the validity of the dissociation rate coefficients derived from their cross section. This validation supports the use of Polak and Slovetsky's cross section in any theoretical or modelling approach involving CO&lt;SUB&gt;2&lt;/SUB&gt; molecules under electrical discharges. (10.1088/1361-6595/ab6075)
  DOI : 10.1088/1361-6595/ab6075
• N₂-H₂capacitively coupled radio-frequency discharges at low pressure. Part II. Modelling results: the relevance of plasma-surface interaction.
  
  • Jiménez-Redondo Miguel
  • Chatain Audrey
  • Guaitella Olivier
  • Cernogora Guy
  • Carrasco Nathalie
  • Alves Luis Lemos
  • Marques Luis Silvino Alves
  Plasma Sources Science and Technology, IOP Publishing, 2020, 29 (8), pp.085023. In this work, we present the results of simulations carried out for N₂-H₂ capacitively coupled radio-frequency discharges, running at low pressure (0.3–0.9 mbar), low power (5–20 W), and for amounts of H₂ up to 5%. Simulations are performed using a hybrid code that couples a two-dimensional time-dependent fluid module, describing the dynamics of the charged particles in the discharge, to a zero-dimensional kinetic module, that solves the Boltzmann equation and describes the production and destruction of neutral species. The model accounts for the production of several vibrationally and electronic excited states, and contains a detailed surface chemistry that includes recombination processes and the production of NH_x molecules. The results obtained highlight the relevance of the interactions between plasma and surface, given the role of the secondary electron emission in the electrical parameters of the discharge and the critical importance of the surface production of ammonia to the neutral and ionic chemistry of the discharge. (10.1088/1361-6595/ab9b1b)
  DOI : 10.1088/1361-6595/ab9b1b
• Initial in-flight performance results from Solar Orbiter RPW/BIAS
  
  • Khotyaintsev Yuri V.
  • Vaivads Andris
  • Graham Daniel B.
  • Edberg Niklas J. T.
  • Johansson Erik P. G.
  • Maksimovic Milan
  • Bale Stuart D.
  • Chust Thomas
  • Kretzschmar Matthieu
  • Soucek Jan
  , 2020. The BIAS subsystem is a part of the Radio and Plasma Waves (RPW) instrument on the ESA Solar Orbiter mission. It allows sending bias current to each of the three RPW antennas. By setting the appropriate bias current the antenna potential can be shifted closer to the local plasma potential. This allows us to measure the floating potential of the spacecraft, as well as the electric field in the DC/LF frequency range with higher accuracy and lower noise level. Here we present the very initial results on RPW/BIAS in-flight performance based on the operations during the instrument commissioning. (10.5194/egusphere-egu2020-14874)
  DOI : 10.5194/egusphere-egu2020-14874
• Effect of non-equilibrium plasma on decreasing the detonation cell size
  
  • Ali cherif Mhedine
  • Shcherbanev Sergey a.
  • Starikovskaia Svetlana m.
  • Vidal Pierre
  Combustion and Flame, Elsevier, 2020, 217, pp.1-3. The effect of a volumetric nanosecond discharge on detonation cell size was demonstrated experimentally in a detonation tube test rig. The experiments were performed in CH 4 :O 2 :Ar=1:2:2 mixture, at initial pressure 180 mbar and ambient temperature. The plasma was generated by two consecutive pulses of −50 and −32 kV amplitude on the high-voltage electrode and 25 ns pulse duration. The analysis of the detonation cell size with and without plasma generation was performed via sootedplate technique. The detonation cell size was reduced by a factor of 1.5 − 2, while passing through the region of the discharge. (10.1016/j.combustflame.2020.03.014)
  DOI : 10.1016/j.combustflame.2020.03.014
• 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
• 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
• 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
• 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.
• 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
• 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