Publications

2020

• Generalized curvature modified plasma dispersion functions and Dupree renormalization of toroidal ITG
  
  • Gültekin Ö
  • Gürcan Özgür D.
  Plasma Physics and Controlled Fusion, IOP Publishing, 2020, 62 (2), pp.025018. A new generalization of curvature modified plasma dispersion functions is introduced in order to express Dupree renormalized dispersion relations used in quasi-linear theory. For instance the Dupree renormalized dispersion relation for gyrokinetic, toroidal ion temperature gradient driven (ITG) modes, where the Dupree's diffusion coefficient is assumed to be a low order polynomial of the velocity, can be written entirely using generalized curvature modified plasma dispersion functions: Knm's. Using those, Dupree's formulation of renormalized quasi-linear theory is revisited for the toroidal ITG mode. The Dupree diffusion coefficient has been obtained as a function of velocity using an iteration scheme, first by assuming that the diffusion coefficient is constant at each v (i.e. applicable for slow dependence), and then substituting the resulting v dependence in the form of complex polynomial coefficients into the Knm's for verification. The algorithm generally converges rapidly after only a few iterations. Since the quasi-linear calculation relies on an assumed form for the wave-number spectrum, especially around its peak, practical usefulness of the method is to be determined in actual applications. A parameter scan of ηi shows that the form of the diffusion coefficient is better represented by the polynomial form as ηi is increased. (10.1088/1361-6587/ab56a7)
  DOI : 10.1088/1361-6587/ab56a7
• 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
• Corrigendum: Non-isothermal sheath model for low pressure plasmas (2019 Plasma Sources Sci. Technol. 28 075007)
  
  • Tavant Antoine
  • Lucken Romain
  • Bourdon Anne
  • Chabert Pascal
  Plasma Sources Science and Technology, IOP Publishing, 2020, 29, pp.039501. (10.1088/1361-6595/ab74b7)
  DOI : 10.1088/1361-6595/ab74b7
• An Active Plume Eruption on Europa During Galileo Flyby E26 as Indicated by Energetic Proton Depletions
  
  • Huybrighs H. L. F.
  • Roussos E.
  • Blöcker A.
  • Krupp N.
  • Futaana Y.
  • Barabash S.
  • Hadid Lina
  • Holmberg M. K. G.
  • Lomax O.
  • Witasse O.
  Geophysical Research Letters, American Geophysical Union, 2020, 47 (10), pp.e2020GL087806. Strong depletions of energetic protons (115–244 keV) were observed during Galileo flyby E26 of Europa. We simulate the flux of energetic protons using a Monte Carlo particle backtracing code and show that energetic proton depletions during E26 are reproduced by taking into account the perturbations of the electromagnetic fields calculated by magnetohydrodynamic (MHD) simulations and charge exchange with a global atmosphere and plume. A depletion feature occurring shortly after closest approach is driven by plume associated charge exchange, or a combination with plume associated field perturbations. We therefore conclude, with a new method and independent data set, that Galileo could have encountered a plume during E26. (10.1029/2020GL087806)
  DOI : 10.1029/2020GL087806
• Interaction of an atmospheric pressure plasma jet with grounded and floating metallic targets: simulations and experiments
  
  • Viegas Pedro
  • Hofmans Marlous
  • van Rooij Olivier
  • Obrusník Adam
  • L M Klarenaar Bart
  • Bonaventura Zdenek
  • Guaitella Olivier
  • Sobota Ana
  • Bourdon Anne
  Plasma Sources Science and Technology, IOP Publishing, 2020, 29 (9), pp.095011. The interaction of kHz μs-pulsed atmospheric pressure He jets with metallic targets is studied through simulations and experiments, focusing on the differences between floating and grounded targets. It is shown that the electric potential of the floating target is close to grounded in the instants after the impact of the discharge, but rises to a high voltage, potentially more than half of the applied voltage, at the end of the 1 μs pulse. As a result, a return stroke takes place after the discharge impact with both grounded and floating targets, as a redistribution between the high voltage electrode and the low voltage target. Electric field, electron temperature and electron density in the plasma plume are higher during the pulse with grounded target than with floating target, as gradients of electric potential progressively dissipate in the latter case. Finally, at the fall of the pulse, another electrical redistribution takes place, with higher intensity with the highly-charged floating target than with the grounded target. It is shown that this phenomenon can lead to an increase in electric field, electron temperature and electron density in the plume with floating target. (10.1088/1361-6595/aba7ec)
  DOI : 10.1088/1361-6595/aba7ec
• Cancer-associated fibroblasts in cholangiocarcinoma
  
  • Vaquero Javier
  • Aoudjehane Lynda
  • Fouassier Laura
  Current Opinion in Gastroenterology, Lippincott, Williams & Wilkins, 2020, 36 (2), pp.63-69. Purpose of review: To give a state-of-art knowledge regarding cancer-associated fibroblasts (CAF) in cholangiocarcinoma (CCA) based both on direct evidence and studies on other desmoplastic cancers. High contingency of CAF characterizes CCA, a tumor with a biliary epithelial phenotype that can emerge anywhere in the biliary tree. Current treatments are very limited, the surgical resection being the only effective treatment but restricted to a minority of patients, whereas the remaining patients undergo palliative chemotherapy regimens. In cancer, CAF shape the tumor microenvironment, drive cancer growth and progression, and contribute to drug resistance. All these functions are accomplished through an interplay network between CAF and surrounding cells including tumor and other stromal cells, i.e. immune and endothelial cells. Recent findings: Several studies have pointed out the existence of CAF sub-populations carrying out several and opposite functions, cancer-promoting or cancer-restraining as shown in pancreatic cancer, another prototypic desmoplastic tumor in which heterogeneity of CAF is well demonstrated. Summary: New CAF functions are now emerging in pancreatic and breast cancers like the modulation of immune responses or tumor metabolism, opening new area for treatments. (10.1097/MOG.0000000000000609)
  DOI : 10.1097/MOG.0000000000000609
• Interaction dust – plasma in Titan's ionosphere: An experimental simulation of aerosols erosion
  
  • Chatain Audrey
  • Carrasco Nathalie
  • Ruscassier N.
  • Gautier Thomas
  • Vettier Ludovic
  • Guaitella Olivier
  Icarus, Elsevier, 2020, 345, pp.113741. Organic aerosols accumulated in Titan's orange haze start forming in its ionosphere. This upper part of the atmosphere is highly reactive and complex ion chemistry takes place at altitudes from 1200 to 900 km. The ionosphere is a nitrogen plasma with a few percent of methane and hydrogen. Carbon from methane enables the formation of macromolecules with long organic chains, finally leading to the organic aerosols. On the other hand, we suspect that hydrogen and the protonated ions have a different erosive effect on the aerosols.Here we experimentally studied the effect of hydrogen and protonated species on organic aerosols. Analogues of Titan's aerosols were formed in a radiofrequency capacitively coupled plasma (RF CCP) discharge in 95% N2 and 5% CH4. Thereafter, the aerosols were exposed to a DC plasma in 99% N2 and 1% H2. Samples were analysed by scanning electron microscopy and in situ infrared transmission spectroscopy. Two pellet techniques – KBr pressed pellets and thin metallic grids - were compared to confirm that modifications seen are not due to the material used to make the pellet.We observed that the spherical aerosols of ~500 nm in diameter were eroded under N2-H2 plasma exposure, with the formation of holes of ~10 nm at their surface. Aerosols were globally removed from the pellet by the plasma. IR spectra showed a faster disappearance of isonitriles and/or carbo-diimides compared to the global band of nitriles. The opposite effect was seen with β-unsaturated nitriles and/or cyanamides. Double bonds as CC and CN were more affected than amines and CH bonds. NH and CH absorption bands kept a similar ratio in intensity and their shape did not vary.Therefore, it seems that carbon and hydrogen play opposite roles in Titan's ionosphere: the carbon from methane leads to organic growth while hydrogen and protonated species erode the aerosols and react preferentially with unsaturated chemical functions. (10.1016/j.icarus.2020.113741)
  DOI : 10.1016/j.icarus.2020.113741
• 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
• 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
• Cluster and MMS Simultaneous Observations of Magnetosheath High Speed Jets and Their Impact on the Magnetopause
  
  • Escoubet Philippe C.
  • Hwang K-J
  • Toledo-Redondo S.
  • Turc L
  • Haaland S E
  • Aunai N
  • Dargent J
  • Eastwood Jonathan P
  • Genestreti K. J.
  • Graham D.B.
  • Khotyaintsev Y.
  • Dimmock A.P.
  • Bogdanova Y.
  • Fear R C
  • Fu H
  • Lapenta G
  • Lavraud Benoit
  • Norgren C
  • Sibeck D.
  • Varsani A.
  • Berchem J
  • Paschmann G.
  • Dunlop M
  • Roberts Owen
  • Laakso H
  • Masson Arnaud
  • Taylor M G G T
  • Kajdič P
  • Carr C.
  • Dandouras I.
  • Fazakerley A.
  • Nakamura R.
  • Burch Jim L
  • Giles B L
  • Pollock C.
  • Russell C T
  • Torbert R B
  Frontiers in Astronomy and Space Sciences, Frontiers Media, 2020, 6, pp.78. When the supersonic solar wind encounters the Earth's magnetosphere a shock, called bow shock, is formed and the plasma is decelerated and thermalized in the magnetosheath downstream from the shock. Sometimes, however, due to discontinuities in the solar wind, bow shock ripples or ionized dust clouds carried by the solar wind, high speed jets (HSJs) are observed in the magnetosheath. These HSJs have typically a V x component larger than 200 km s −1 and their dynamic pressure can be a few times the solar wind dynamic pressure. They are typically observed downstream from the quasi-parallel bow shock and have a typical size around one Earth radius (R E) in X GSE. We use a conjunction of Cluster and MMS, crossing simultaneously the magnetopause, to study the characteristics of these HSJs and their impact on the magnetopause. Over 1 h 15 min interval in the magnetosheath, Cluster observed 21 HSJs. During the same period, MMS observed 12 HSJs and entered the magnetosphere several times. A jet was observed simultaneously by both MMS and Cluster and it is very likely that they were two distinct HSJs. This shows that HSJs are not localized into small regions but could span a region larger than 10 R E , especially when the quasi-parallel shock is covering the entire dayside magnetosphere under radial IMF. During this period, two and six magnetopause crossings were observed, respectively, on Cluster and MMS with a significant angle between the observation and the expected normal deduced from models. The angles observed range between from 11◦ up to 114◦. One inbound magnetopause crossing observed by Cluster (magnetopause moving out at 142 km s−1) was observed simultaneous to an outbound magnetopause crossing observed by MMS (magnetopause moving in at −83 km s−1), showing that the magnetopause can have multiple local indentation places, most likely independent from each other. Under the continuous impacts of HSJs, the magnetopause is deformed significantly and can even move in opposite directions at different places. It can therefore not be considered as a smooth surface anymore but more as surface full of local indents. Four dust impacts were observed on MMS, although not at the time when HSJs are observed, showing that dust clouds would have been present during the observations. No dust cloud in the form of Interplanetary Field Enhancements was however observed in the solar wind which may exclude large clouds of dust as a cause of HSJs. Radial IMF and Alfvén Mach number above 10 would fulfill the criteria for the creation of bow shock ripples and the subsequent crossing of HSJs in the magnetosheath. (10.3389/fspas.2019.00078)
  DOI : 10.3389/fspas.2019.00078
• 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
• 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
• 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
• 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