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
• 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
• 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
• 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
• 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
• 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.
• Ionospheric and Magnetic Signatures of a Space Weather Event on 25–29 August 2018: CME and HSSWs
  
  • Younas W.
  • Amory-Mazaudier Christine
  • Khan Majid
  • Fleury Rolland
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2020, 125 (8), pp.e2020JA027981. We present a study concerning a space weather event on 25–29 August 2018, accounting for its ionospheric and magnetic signatures at low latitudes and midlatitudes. The effects of a storm in several longitudinal sectors (Asia, Africa, America, and the Pacific) have been analyzed using various parameters such as total electron content (TEC), geomagnetic field, and column [O/N2] ratio. Positive ionospheric storms are found in all the longitudinal sectors having its maximum effects in the Asian sector, whereas the negative ionospheric storms have been observed in the summer hemisphere (Northern Hemisphere). A large decrease in [O/N2] ratio in the Northern Hemisphere is a possible cause of the observed negative storm effects. Ionospheric F2 region maximum electron density (NmF2) and TEC have shown a positive correlation during this storm. The study suggests that storm time‐generated wind does not have a uniform planetary extension and mainly affects dayside (America and Pacific) and duskside (Africa) sectors. During the space weather event, we observe an asymmetric variation of the magnetic field as a function of the longitude. On the other hand, the magnetic variations at midlatitudes are found to be symmetric in both hemispheres. A signature of the disturbance dynamo (anti‐Sq circulation) has been observed, mainly at low latitudes. We emphasize that the partial ring current (PRC), estimated by the ASYM‐H magnetic index, must also be taken into account along with the SYM‐H index for a better approximation of ionospheric currents. The study further suggests existence of several electric current cells in the ionosphere, which is consistent with the Blanc‐Richmond model. (10.1029/2020JA027981)
  DOI : 10.1029/2020JA027981
• Magnetic field fluctuation properties of coronal mass ejection-driven sheath regions in the near-Earth solar wind
  
  • Kilpua Emilia K J
  • Fontaine Dominique
  • Good Simon W
  • Ala-Lahti Matti
  • Osmane Adnane
  • Palmerio Erika
  • Yordanova Emiliya
  • Moissard C.
  • Hadid Lina
  • Janvier Miho
  Annales Geophysicae, European Geosciences Union, 2020, 38, pp.999 - 1017. In this work, we investigate magnetic field fluctuations in three coronal mass ejection (CME)-driven sheath regions at 1 AU, with their speeds ranging from slow to fast. The data set we use consists primarily of high-resolution (0.092 s) magnetic field measurements from the Wind spacecraft. We analyse magnetic field fluctuation amplitudes, com-pressibility, and spectral properties of fluctuations. We also analyse intermittency using various approaches; we apply the partial variance of increments (PVIs) method, investigate probability distribution functions of fluctuations, including their skewness and kurtosis, and perform a structure function analysis. Our analysis is conducted separately for three different subregions within the sheath and one in the solar wind ahead of it, each 1 h in duration. We find that, for all cases, the transition from the solar wind ahead to the sheath generates new fluctuations, and the intermittency and com-pressibility increase, while the region closest to the ejecta leading edge resembled the solar wind ahead. The spectral indices exhibit large variability in different parts of the sheath but are typically steeper than Kolmogorov's in the inertial range. The structure function analysis produced generally the best fit with the extended p model, suggesting that turbulence is not fully developed in CME sheaths near Earth's orbit. Both Kraichnan-Iroshinikov and Kolmogorov's forms yielded high intermittency but different spectral slopes, thus questioning how well these models can describe turbulence in sheaths. At the smallest timescales investigated, the spectral indices indicate shallower than expected slopes in the dissipation range (between −2 and −2.5), suggesting that, in CME-driven sheaths at 1 AU, the energy cascade from larger to smaller scales could still be ongoing through the ion scale. Many turbulent properties of sheaths (e.g. spectral indices and compressibility) resemble those of the slow wind rather than the fast. They are also partly similar to properties reported in the terrestrial magnetosheath, in particular regarding their intermittency, compressibility, and absence of Kolmogorov's type turbulence. Our study also reveals that turbulent properties can vary considerably within the sheath. This was particularly the case for the fast sheath behind the strong and quasi-parallel shock, including a small, coherent structure embedded close to its midpoint. Our results support the view of the complex formation of the sheath and different physical mechanisms playing a role in generating fluctuations in them. (10.5194/angeo-38-999-2020)
  DOI : 10.5194/angeo-38-999-2020
• Helium in the Earth's foreshock: a global Vlasiator survey
  
  • Battarbee Markus
  • Blanco-Cano Xóchitl
  • Turc Lucile
  • Kajdič Primož
  • Johlander Andreas
  • Tarvus Vertti
  • Fuselier Stephen
  • Trattner Karlheinz
  • Alho Markku
  • Brito Thiago
  • Ganse Urs
  • Pfau-Kempf Yann
  • Akhavan-Tafti Mojtaba
  • Karlsson Tomas
  • Raptis Savvas
  • Dubart Maxime
  • Grandin Maxime
  • Suni Jonas
  • Palmroth Minna
  Annales Geophysicae, European Geosciences Union, 2020, 38 (5), pp.1081-1099. The foreshock is a region of space upstream of the Earth's bow shock extending along the interplanetary magnetic field (IMF). It is permeated by shock-reflected ions and electrons, low-frequency waves, and various plasma transients. We investigate the extent of the He2+ foreshock using Vlasiator, a global hybrid-Vlasov simulation. We perform the first numerical global survey of the helium foreshock and interpret some historical foreshock observations in a global context. The foreshock edge is populated by both proton and helium field-aligned beams, with the proton foreshock extending slightly further into the solar wind than the helium foreshock and both extending well beyond the ultra-low frequency (ULF) wave foreshock. We compare our simulation results with Magnetosphere Multiscale (MMS) Hot Plasma Composition Analyzer (HPCA) measurements, showing how the gradient of suprathermal ion densities at the foreshock crossing can vary between events. Our analysis suggests that the IMF cone angle and the associated shock obliquity gradient can play a role in explaining this differing behaviour. We also investigate wave–ion interactions with wavelet analysis and show that the dynamics and heating of He2+ must result from proton-driven ULF waves. Enhancements in ion agyrotropy are found in relation to, for example, the ion foreshock boundary, the ULF foreshock boundary, and specular reflection of ions at the bow shock. We show that specular reflection can describe many of the foreshock ion velocity distribution function (VDF) enhancements. Wave–wave interactions deep in the foreshock cause de-coherence of wavefronts, allowing He2+ to be scattered less than protons. (10.5194/angeo-38-1081-2020)
  DOI : 10.5194/angeo-38-1081-2020
• Solar Orbiter Observations of Waves and Structures from the Tail of Comet ATLAS
  
  • Matteini L.
  • Horbury T. S.
  • Woodham L. D.
  • Bale S. D.
  • Hellinger P.
  • Galand M. F.
  • Jones G. H.
  • O'Brien H.
  • Evans V.
  • Angelini V.
  • Maksimovic M.
  • Chust Thomas
  • Khotyaintsev Y.
  • Krasnoselskikh V.
  • Kretzschmar Matthieu
  • Lorfevre E.
  • Plettemeier D.
  • Soucek J.
  • Steller M.
  • Stverak S.
  • Travnicek P.
  • Vaivads A.
  • Vecchio A.
  • Bruno R.
  • Fedorov A.
  • Livi S. A.
  • Louarn P.
  • Owen C. J.
  , 2020, 2020, pp.18 pp.. Comet ATLAS disintegrated into several fragments while reaching its most recent perihelion at approximately 0.25AU in April 2020. Solar Orbiter is predicted to have crossed both the ion and dust tails of the comet between 31 May and 6 June 2020, when the spacecraft was close to 0.5AU. This constituted a unique opportunity to make in situ measurements of distinct cometary fragments at such a close distance from the Sun and to study the interaction of cometary pick-up ions with the solar wind plasma. In this study, we present and discuss possible signatures of this interaction as seen in various Solar Orbiter in situ sensors (MAG, RPW, SWA). We mainly focus on properties of a wide range of both structures and low-frequency electromagnetic waves that are supposedly driven by cometary pick-up ion instabilities and intermittently observed over several days during the encounter. These include trains of phase-steepened Alfvén waves propagating in both directions along the magnetic field, sharp discontinuities and current sheets, and precessing linearly polarised waves possibly suggesting the presence of non-gyrotropic sources of heavier pick-up ions. Observed wave properties are discussed and compared with expectations from linear theory and numerical simulations.
• A reaction mechanism for vibrationally-cold low-pressure CO<SUB>2</SUB> plasmas
  
  • Silva A. F.
  • Morillo-Candas A. S.
  • Tejero-Del-Caz A.
  • Alves L. L.
  • Guaitella Olivier
  • Guerra V.
  Plasma Sources Science and Technology, IOP Publishing, 2020, 29, pp.125020. The use of plasmas for CO<SUB>2</SUB> utilization has been under investigation in recent years following a wave of environmental awareness. In this work, previously published experimental results on vibrationally cold CO<SUB>2</SUB> plasmas are modelled to define a reaction mechanism, i.e. a set of reactions and rate coefficients validated against benchmark experiments. The model couples self-consistently the electron and heavy particle kinetics. In turn, the simulated results are validated against measurements taken in CO<SUB>2</SUB> DC glow discharges in a relatively large range of experimental conditions: at pressures from 0.4 to 5 Torr, reduced electric fields ranging from 50 to 100 Td and gas flowing from 2 to 8 sccm. The model predicts the measured values of product formation (CO and O) as well as discharge power and electric field. After validation, a thorough analysis of the model's results is presented, including: electron properties, species densities, power distribution into different excitation channels and main creation and destruction mechanisms of the main species. It is shown that, although vibrational populations are low, they have a significant effect on the electron properties and thus on the electric field and conversion. Moreover, the shape of the EEDF is significantly dependent on the dissociation degree. The role of electronically excited states on CO<SUB>2</SUB> dissociation is also analyzed, showing that the first electronic excited state of CO can have a beneficial or detrimental effect in further producing CO and O in the discharge. (10.1088/1361-6595/abc818)
  DOI : 10.1088/1361-6595/abc818
• Investigating Mercury's Environment with the Two-Spacecraft BepiColombo Mission
  
  • Milillo A.
  • Fujimoto M.
  • Murakami G.
  • Benkhoff J.
  • Zender J.
  • Aizawa S.
  • Dósa M.
  • Griton L.
  • Heyner D.
  • Ho G.
  • Imber S. M.
  • Jia X.
  • Karlsson T.
  • Killen R. M.
  • Laurenza M.
  • Lindsay S. T.
  • Mckenna-Lawlor S.
  • Mura A.
  • Raines J. M.
  • Rothery D. A.
  • André N.
  • Baumjohann W.
  • Berezhnoy A.
  • Bourdin P. A.
  • Bunce E. J.
  • Califano F.
  • Deca Jan
  • de La Fuente S.
  • Dong C.
  • Grava C.
  • Fatemi S.
  • Henri Pierre
  • Ivanovski S. L.
  • Jackson B. V.
  • James M.
  • Kallio E.
  • Kasaba Y.
  • Kilpua E.
  • Kobayashi M.
  • Langlais Benoit
  • Leblanc François
  • Lhotka C.
  • Mangano V.
  • Martindale A.
  • Massetti S.
  • Masters A.
  • Morooka M.
  • Narita Y.
  • Oliveira J. S.
  • Odstrcil D.
  • Orsini S.
  • Pelizzo M. G.
  • Plainaki C.
  • Plaschke F.
  • Sahraoui F.
  • Seki K.
  • Slavin J. A.
  • Vainio R.
  • Wurz P.
  • Barabash S.
  • Carr C. M.
  • Delcourt Dominique
  • Glassmeier K.-H.
  • Grande M.
  • Hirahara M.
  • Huovelin J.
  • Korablev Oleg
  • Kojima H.
  • Lichtenegger H.
  • Livi S.
  • Matsuoka A.
  • Moissl R.
  • Moncuquet Michel
  • Muinonen K.
  • Quémerais Eric
  • Saito Y.
  • Yagitani S.
  • Yoshikawa I.
  • Wahlund J.-E.
  Space Science Reviews, Springer Verlag, 2020, 216, pp.93. The ESA-JAXA BepiColombo mission will provide simultaneous measurements from two spacecraft, offering an unprecedented opportunity to investigate magnetospheric The BepiColombo mission to Mercury Edited A. Milillo et al. and exospheric dynamics at Mercury as well as their interactions with the solar wind, radiation , and interplanetary dust. Many scientific instruments onboard the two spacecraft will be completely, or partially devoted to study the near-space environment of Mercury as well as the complex processes that govern it. Many issues remain unsolved even after the MESSENGER mission that ended in 2015. The specific orbits of the two spacecraft, MPO and Mio, and the comprehensive scientific payload allow a wider range of scientific questions to be addressed than those that could be achieved by the individual instruments acting alone, or by previous missions. These joint observations are of key importance because many phenomena in Mercury's environment are highly temporally and spatially variable. Examples of possible coordinated observations are described in this article, analysing the required geometrical conditions, pointing, resolutions and operation timing of different BepiColombo instruments sensors. (10.1007/s11214-020-00712-8)
  DOI : 10.1007/s11214-020-00712-8
• 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
• 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
• 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
• 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.
• 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
• 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
• 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.