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, 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, 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
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
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.
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. 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. 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. 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. 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.
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. 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. 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 ?0.33, and the large curvature has a scaling as ?-2.16. 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
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
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
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
Electron impact dissociation of CO2
- 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 CO2 electron impact dissociation cross sections are available in the literature, different in magnitude and threshold, hindering the understanding of CO2 dissociation mechanisms under gas discharges. This work reports the experimental validation of the electron impact CO2 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 CO2 molecules under electrical discharges. (10.1088/1361-6595/ab6075)
DOI : 10.1088/1361-6595/ab6075
N2-H2 capacitively 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 NHx 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
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

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