Publications

2021

• Low-frequency Whistler Waves Modulate Electrons and Generate Higher-frequency Whistler Waves in the Solar Wind
  
  • Yao S.
  • Shi Q.
  • Zong Q.
  • Degeling A.
  • Guo R.
  • Li L.
  • Li J.
  • Tian A.
  • Zhang H.
  • Yao Z.
  • Fu H.
  • Liu C.
  • Sun W.
  • Niu Z.
  • Li W.
  • Liu Z.
  • Le Contel O.
  • Zhang S.
  • Xiao C.
  • Shang W.
  • Torbert R.
  • Ergun R.
  • Lindqvist P.-A.
  • Pollock C.
  The Astrophysical Journal, American Astronomical Society, 2021, 923 (2), pp.216. Abstract The role of whistler-mode waves in the solar wind and the relationship between their electromagnetic fields and charged particles is a fundamental question in space physics. Using high-temporal-resolution electromagnetic field and plasma data from the Magnetospheric MultiScale spacecraft, we report observations of low-frequency whistler waves and associated electromagnetic fields and particle behavior in the Earth’s foreshock. The frequency of these whistler waves is close to half the lower-hybrid frequency (∼2 Hz), with their wavelength close to the ion gyroradius. The electron bulk flows are strongly modulated by these waves, with a modulation amplitude comparable to the solar wind velocity. At such a spatial scale, the electron flows are forcibly separated from the ion flows by the waves, resulting in strong electric currents and anisotropic ion distributions. Furthermore, we find that the low-frequency whistler wave propagates obliquely to the background magnetic field ( B 0 ), and results in spatially periodic magnetic gradients in the direction parallel to B 0 . Under such conditions, large pitch-angle electrons are trapped in wave magnetic valleys by the magnetic mirror force, and may provide free perpendicular electron energy to excite higher-frequency whistler waves. This study offers important clues and new insights into wave–particle interactions, wave generation, and microscale energy conversion processes in the solar wind. (10.3847/1538-4357/ac2e97)
  DOI : 10.3847/1538-4357/ac2e97
• Transient variations of vertical total electron content at low latitude during the period 2013–2017
  
  • Hammou Ali O
  • Zaourar N.
  • Fleury R.
  • Amory-Mazaudier C.
  Advances in Space Research, Elsevier, 2021, 68 (12), pp.4857-4871. We use GPS networks to measure the vertical Total Electron Content (VTEC) variations at low latitude, in three longitude sectors: America, Europe-Africa and Asia, collected during the period 2013-2017. This period corresponds to the increasing phase of the solar cycle 24 (SC#24) observed around 2013-2014 as well as the decreasing phase around 2014-2017. Our results discussed a morphological analysis of regular variations in ionization during different phases of solar activity: daytime variations, seasonal and semiannual variations and variations based on the solar cycle 24 in three longitude sectors. In all longitude sectors, the highest VTEC values are displayed during the two months of the spring, located after sunrise and before sunset. The lowest values are found during the summer and winter seasons. We found that the winter anomaly and the presence of equinoxial peaks are the most pronounced effects in VTECs in the increasing and decreasing phase of the SC#24. A strong asymmetry is detected between equinoxial peaks and the location of peaks occurring in March/April and October/November at maximum in the solar flux variations during the increase phase. We show that the daily VTEC maximum values were registered between 14:00 and 16:00 LT and the minimum values between 4:00 and 6:00 LT. Double ionization peak in the morning and evening is observed in VTEC annual variations, due to the proximity of the equatorial fountain stations. From the statistical analysis part, we observed practically the same distribution of the different classes of VTEC (two peaks, bell-shaped and plateau-shaped) variations in the three sectors of longitude. These observations indicate longitudinal variation in the presence of the winter anomaly in the Equatorial Ionized Anomaly (EIA) region. Additionally, we can note a longitudinal variation of the spring-autumn VTEC asymmetry in the EIA region during the five years 2013-2017. We observe also that the occurrence of nocturnal peak recorded around 19 local time (LT) shows the same characteristics as the vertical drift E x B (B: magnetic field is perpendicular to E: electric field.) with respect to solar cycle, season and longitude. Three essential characteristics we noted: 1) the occurrence of the nocturnal peak generally follows the solar cycle. 2) The occurrence of the nocturnal peak is generally stronger at the equinoxes than at the solstices. 3) The occurrence of the nocturnal peak is stronger in the Europe-Africa and America sectors than in the Asia sector. As a result, nocturnal peak occurrence is well related to the PRE at the origin of the GNSS signal scintillations. (10.1016/j.asr.2021.02.039)
  DOI : 10.1016/j.asr.2021.02.039
• Fluid Energy Cascade Rate and Kinetic Damping: New Insight from 3D Landau-fluid Simulations
  
  • Ferrand R.
  • Sahraoui Fouad
  • Laveder D.
  • Passot T.
  • Sulem P.
  • Galtier S.
  The Astrophysical Journal, American Astronomical Society, 2021, 923 (1), pp.122. Abstract Using an exact law for incompressible Hall magnetohydrodynamics (HMHD) turbulence, the energy cascade rate is computed from three-dimensional HMHD-CGL (biadiabatic ions and isothermal electrons) and Landau-fluid numerical simulations that feature different intensities of Landau damping over a broad range of wavenumbers, typically 0.05 ≲ k ⊥ d i ≲ 100. Using three sets of cross-scale simulations where turbulence is initiated at large, medium, and small scales, the ability of the fluid energy cascade to “sense” the kinetic Landau damping at different scales is tested. The cascade rate estimated from the exact law and the dissipation calculated directly from the simulation are shown to reflect the role of Landau damping in dissipating energy at all scales, with an emphasis on the kinetic ones. This result provides new prospects on using exact laws for simplified fluid models to analyze dissipation in kinetic simulations and spacecraft observations, and new insights into theoretical description of collisionless magnetized plasmas. (10.3847/1538-4357/ac2bfb)
  DOI : 10.3847/1538-4357/ac2bfb
• Dynamics of Langmuir Wave Spectra in Randomly Inhomogeneous Solar Wind Plasmas
  
  • Krafft C.
  • Volokitin A.
  The Astrophysical Journal, American Astronomical Society, 2021, 923 (1), pp.103. Abstract Solar coronal and wind plasmas often contain density fluctuations of various scales and amplitudes. The scattering of Langmuir wave turbulence on these inhomogeneities modifies the properties of the radiated electromagnetic emissions traveling from the Sun to the Earth. This paper shows the similarities between the physical results obtained by (i) a model based on the Zakharov equations, describing the self-consistent dynamics of Langmuir wave turbulence spectra in a plasma with external density fluctuations, and (ii) a modeling, within the framework of geometric optics approximation, of quasi-particles (representing plasmon quanta) moving in a fluctuating potential. It is shown that the dynamics of the Langmuir spectra is governed by anomalous diffusion processes, as a result of multiple scattering of waves on the density fluctuations; the same dynamics are observed in the momenta distributions of quasi-particles moving in potential structures with random inhomogeneities. These spectra and distributions are both characterized by a fast broadening during which energy is transported to larger wavevectors and momenta, exhibiting nonlinear time dependence of the average squares of wavevectors and quasi-particle momenta as well as non-Gaussian tails in the asymptotic stage. The corresponding diffusion coefficients depend on the time and are proportional to the square of the average level of density (or potential) fluctuations. It appears that anomalous transport and superdiffusion phenomena are responsible for the spectral broadening. (10.3847/1538-4357/ac2153)
  DOI : 10.3847/1538-4357/ac2153
• Dissociation of carbon dioxide in pulsed plasma at high electric fields : role of energy exchange with electronically excited species.
  
  • Pokrovskiy Georgy
  , 2021. The Thesis is devoted to study of dissociation of carbon dioxide at moderate pressures in nanosecond capillary pulsed discharges at high levels of reduced electric field and specific deposited energy. The main purpose of the research was to focus on such a discharge regime that facilitates dominationof excitation of electronic degrees of freedom of active species over vibrational ones. The experimental studies have been done in two different types of capillaries – the so called ’thin’ and FTIR’ capillaries. It has been shown that the discharge develops as a stable fast ionization wave (FIW) in CO2 in both types of capillaries. Any portion of gas was being treated by train of three high voltage pulses separated by 250 ns in each experiment. The main discharge characteristics such as electric current, reduced electric field and specific deposited energy have been measured in all three pulses. The electron density as a function of time has been measured in the thin capillary. The peak electron density was found to be 2×1015cm−3 in the first high voltage pulse. This value corresponds to the ionization degree of 0.5% at the pressure of 15.5 mbar. Since it was technically possible to obtain time-resolved profile of the reduced electric field E/n in the thin capillary, the exact measurements of E/n as a function of time have been done in it. The values of the reduced electric field in the thin capillary were about 1000 Td in the FIW and 300 Td behind the front of the FIW. The specific deposited energy was found to be (≈1.5eV/particle). As for the FTIR capillary, it was only possible to estimate E/n and specific deposited energy. It can be still concluded that both values are two times higher than in thethin capillary. Measurements of steady-state values of the dissociation fraction α and the energy efficiency of the dissociation η have been done in the FTIR capillary in effluent gas. FTIR has been used for their measurements.The values of α and η were around 20% at low frequency pulse regime. When the frequency of pulses increased, the α value tended to a saturation threshold of 92%, η of the process was around 8 %.Optical emission spectroscopy (OES) in both thin and FTIR capillaries hasn’t revealed any qualitative difference between the acquired spectra. The emission spectra demonstrate an abundant presence of electronically excited states of CO2+ ion and C atom lying between 18 and 25 eV with respect to the ground state of CO2. It has been shown that the excitation of electronic degrees of freedom does dominate over vibrational ones and supplies high values of dissociation fraction of CO2 during the discharge. Presence of dissociation of CO onto C and O has been noticed as well. Measurements of radial profile of the electron density by ICCD imaging in the middle of the discharge have been done. The profile has been shown to have a maximum in the axis of the capillary and to monotonously decrease with respect to direction of walls. Moreover, the behaviour of the profile didn’t change within the high voltage pulses and between them. Gas temperature has been measured by OES of second positive system of nitrogen which has been added to CO2 as a small admixture. The relevance of rotational temperature of nitrogen and gas temperature has been justified. The measurements of temperature have been done both in the FTIR and thin capillary in all high voltage pulses. The gas temperature was equal to 2000 K after the third pulse. The thin capillary has been heated up to 1100 K. The phenomenon of fast heating of CO2 in a nanosecond discharge has been therefore confirmed. Zero-dimensional numerical modeling of the discharge has been also done. It has shown a good agreement between experimental and calculated results. It has been shown that the temporal dynamics of CO2+, O2+ and C2O4+ ions as well as electronic states CO(a3Π), O(1D,1S) define the most important kinetic processes and heating of the gas during and between the pulses.
• Particle energization in space plasmas: towards a multi-point, multi-scale plasma observatory
  
  • Retinò Alessandro
  • Khotyaintsev Yuri
  • Le Contel Olivier
  • Marcucci Maria Federica
  • Plaschke Ferdinand
  • Vaivads Andris
  • Angelopoulos Vassilis
  • Blasi Pasquale
  • Burch Jim
  • de Keyser Johan
  • Dunlop Malcolm
  • Dai Lei
  • Eastwood Jonathan
  • Fu Huishan
  • Haaland Stein
  • Hoshino Masahiro
  • Johlander Andreas
  • Kepko Larry
  • Kucharek Harald
  • Lapenta Gianni
  • Lavraud Benoit
  • Malandraki Olga
  • Matthaeus William
  • Mcwilliams Kathryn
  • Petrukovich Anatoli
  • Pinçon Jean-Louis
  • Saito Yoshifumi
  • Sorriso-Valvo Luca
  • Vainio Rami
  • Wimmer-Schweingruber Robert
  Experimental Astronomy, Springer Link, 2021, pp.45 pages. Abstract This White Paper outlines the importance of addressing the fundamental science theme “ How are charged particles energized in space plasmas ” through a future ESA mission. The White Paper presents five compelling science questions related to particle energization by shocks, reconnection, waves and turbulence, jets and their combinations. Answering these questions requires resolving scale coupling, nonlinearity, and nonstationarity, which cannot be done with existing multi-point observations. In situ measurements from a multi-point, multi-scale L-class Plasma Observatory consisting of at least seven spacecraft covering fluid, ion, and electron scales are needed. The Plasma Observatory will enable a paradigm shift in our comprehension of particle energization and space plasma physics in general, with a very important impact on solar and astrophysical plasmas. It will be the next logical step following Cluster, THEMIS, and MMS for the very large and active European space plasmas community. Being one of the cornerstone missions of the future ESA Voyage 2050 science programme, it would further strengthen the European scientific and technical leadership in this important field. (10.1007/s10686-021-09797-7)
  DOI : 10.1007/s10686-021-09797-7
• First dust measurements with the Solar Orbiter Radio and Plasma Wave instrument
  
  • Zaslavsky Arnaud
  • Mann Ingrid
  • Souček Jan
  • Czechowski Andrzej
  • Píša David
  • Vaverka Jakub
  • Meyer-Vernet Nicole
  • Maksimovic Milan
  • Lorfèvre Eric
  • Issautier Karine
  • Racković Babić Kristina
  • Bale Stuart D
  • Morooka Michiko
  • Vecchio Antonio
  • Chust Thomas
  • Khotyaintsev Yu. V.
  • Krasnoselskikh Vladimir
  • Kretzschmar Matthieu
  • Plettemeier Dirk
  • Steller Manfred
  • Štverák Štěpán
  • Travnicek Petr
  • Vaivads Andris
  Astronomy & Astrophysics - A&A, EDP Sciences, 2021, 656, pp.A30. Context. Impacts of dust grains on spacecraft are known to produce typical impulsive signals in the voltage waveform recorded at the terminals of electric antennas. Such signals (as may be expected) are routinely detected by the Time Domain Sampler (TDS) system of the Radio and Plasma Waves (RPW) instrument on board Solar Orbiter.Aims. We investigate the capabilities of RPW in terms of interplanetary dust studies and present the first analysis of dust impacts recorded by this instrument. Our purpose is to characterize the dust population observed in terms of size, flux, and velocity.Methods. We briefly discuss previously developed models of voltage pulse generation after a dust impact onto a spacecraft and present the relevant technical parameters for Solar Orbiter RPW as a dust detector. Then we present the statistical analysis of the dust impacts recorded by RPW/TDS from April 20, 2020 to February 27, 2021 between 0.5 AU and 1 AU.Results. The study of the dust impact rate along Solar Orbiter’s orbit shows that the dust population studied presents a radial velocity component directed outward from the Sun. Its order of magnitude can be roughly estimated as vr, dust ≃ 50 km s−1, which is consistent with the flux of impactors being dominated by β-meteoroids. We estimate the cumulative flux of these grains at 1 AU to be roughly Fβ ≃ 8 × 10−5 m−2 s−1 for particles of a radius r ≳ 100 nm. The power law index δ of the cumulative mass flux of the impactors is evaluated by two differents methods, namely: direct observations of voltage pulses and indirect effect on the impact rate dependency on the impact speed. Both methods give the following result: δ ≃ 0.3 − 0.4.Conclusions. Solar Orbiter RPW proves to be a suitable instrument for interplanetary dust studies, and the dust detection algorithm implemented in the TDS subsystem an efficient tool for fluxes estimation. These first results are promising for the continuation of the mission, in particular, for the in situ study of the inner Solar System dust cloud outside of the ecliptic plane, which Solar Orbiter will be the first spacecraft to explore. (10.1051/0004-6361/202140969)
  DOI : 10.1051/0004-6361/202140969
• Solar Orbiter’s first Venus flyby
  
  • Volwerk M.
  • Horbury T. S.
  • Woodham L. D.
  • Bale S. D.
  • Simon Wedlund C.
  • Schmid D.
  • Allen R. C.
  • Angelini V.
  • Baumjohann W.
  • Berger L.
  • Edberg N. J. T.
  • Evans V.
  • Hadid L. Z.
  • Ho G. C.
  • Khotyaintsev Yu. V.
  • Magnes W.
  • Maksimovic M.
  • O’brien H.
  • Steller M. B.
  • Rodriguez-Pacheco J.
  • Wimmer-Scheingruber R. F.
  Astronomy & Astrophysics - A&A, EDP Sciences, 2021, 656, pp.A11. Context. The induced magnetosphere of Venus is caused by the interaction of the solar wind and embedded interplanetary magnetic field with the exosphere and ionosphere of Venus. Solar Orbiter entered Venus’s magnetotail far downstream, > 70 Venus radii, of the planet and exited the magnetosphere over the north pole. This offered a unique view of the system over distances that had only been flown through before by three other missions, Mariner 10, Galileo, and BepiColombo. Aims. In this study, we study the large-scale structure and activity of the induced magnetosphere as well as the high-frequency plasma waves both in the magnetosphere and in a limited region upstream of the planet where interaction with Venus’s exosphere is expected. Methods. The large-scale structure of the magnetosphere was studied with low-pass filtered data and identified events are investigated with a minimum variance analysis as well as combined with plasma data. The high-frequency plasma waves were studied with spectral analysis. Results. We find that Venus’s magnetotail is very active during the Solar Orbiter flyby. Structures such as flux ropes and reconnection sites were encountered, in addition to a strong overdraping of the magnetic field downstream of the bow shock and planet. High-frequency plasma waves (up to six times the local proton cyclotron frequency) are observed in the magnetotail, which are identified as Doppler-shifted proton cyclotron waves, whereas in the upstream solar wind, these waves appear just below the proton cyclotron frequency (as expected) but are very patchy. The bow shock is quasi-perpendicular, however, expected mirror mode activity is not found directly behind it; instead, there is strong cyclotron wave power. This is most likely caused by the relatively low plasma-β behind the bow shock. Much further downstream, magnetic hole or mirror mode structures are identified in the magnetosheath. (10.1051/0004-6361/202140910)
  DOI : 10.1051/0004-6361/202140910
• Kinetic electrostatic waves and their association with current structures in the solar wind
  
  • Graham D. B. B
  • Khotyaintsev Yu V
  • Vaivads A.
  • Edberg N. J. T. J T
  • Eriksson A. I. I
  • Johansson E.
  • Sorriso-Valvo L.
  • Maksimovic M.
  • Souček J.
  • Píša D.
  • Bale S. D. D
  • Chust Thomas
  • Kretzschmar M.
  • Krasnoselskikh V.
  • Lorfèvre E.
  • Plettemeier D.
  • Steller M.
  • Štverák Š.
  • Trávníček P.
  • Vecchio A.
  • Horbury T. S. S
  • O'Brien H.
  • Evans V.
  • Angelini V.
  Astronomy & Astrophysics - A&A, EDP Sciences, 2021, 656, pp.A23. Context. A variety of kinetic electrostatic and electromagnetic waves develop in the solar wind and the relationship between these waves and larger scale structures, such as current sheets and ongoing turbulence, remain a topic of investigation. Similarly, the instabilities producing ion-acoustic waves in the solar wind are still an open question. Aims. The goals of this paper are to investigate electrostatic Langmuir and ion-acoustic waves in the solar wind at 0.5 AU and determine whether current sheets and associated streaming instabilities can produce the observed waves. The relationship between these waves and currents observed in the solar wind is investigated statistically. Methods. Solar Orbiter’s Radio and Plasma Waves instrument suite provides high-resolution snapshots of the fluctuating electric field. The Low Frequency Receiver resolves the waveforms of ion-acoustic waves and the Time Domain Sampler resolves the waveforms of both ion-acoustic and Langmuir waves. Using these waveform data, we determine when these waves are observed in relation to current structures in the solar wind, estimated from the background magnetic field. Results. Langmuir and ion-acoustic waves are frequently observed in the solar wind. Ion-acoustic waves are observed about 1% of the time at 0.5 AU. The waves are more likely to be observed in regions of enhanced currents. However, the waves typically do not occur at current structures themselves. The observed currents in the solar wind are too small to drive instability by the relative drift between single ion and electron populations. When multi-component ion or electron distributions are present, the observed currents may be sufficient for instabilities to occur. Ion beams are the most plausible source of ion-acoustic waves in the solar wind. The spacecraft potential is confirmed to be a reliable probe of the background electron density when comparing the peak frequencies of Langmuir waves with the plasma frequency calculated from the spacecraft potential. (10.1051/0004-6361/202140943)
  DOI : 10.1051/0004-6361/202140943
• First observations and performance of the RPW instrument on board the Solar Orbiter mission
  
  • Maksimovic M.
  • Souček J.
  • Chust Thomas
  • Khotyaintsev Y.
  • Kretzschmar M.
  • Bonnin X.
  • Vecchio A.
  • Alexandrova O.
  • Bale S. D.
  • Bérard D.
  • Brochot J.-Y.
  • Edberg N. J. T.
  • Eriksson A.
  • Hadid L. Z.
  • Johansson E. P. G.
  • Karlsson T.
  • Katra Bruno
  • Krasnoselskikh V.
  • Krupař V.
  • Lion S.
  • Lorfèvre E.
  • Matteini L.
  • Nguyen Q. N.
  • Píša D.
  • Piberne Rodrigue
  • Plettemeier D.
  • Rucker H. O.
  • Santolík O.
  • Steinvall K.
  • Steller M.
  • Štverák Š.
  • Trávníček P.
  • Vaivads A.
  • Zaslavsky A.
  • Chaintreuil S.
  • Dekkali M.
  • Astier P.-A.
  • Barbary G.
  • Boughedada K.
  • Cecconi B.
  • Chapron F.
  • Collin C.
  • Dias D.
  • Guéguen L.
  • Lamy L.
  • Leray V.
  • Malac-Allain L. R.
  • Pantellini F.
  • Parisot J.
  • Plasson P.
  • Thijs S.
  • Fratter I.
  • Bellouard E.
  • Danto P.
  • Julien S.
  • Guilhem E.
  • Fiachetti C.
  • Sanisidro J.
  • Laffaye C.
  • Gonzalez F.
  • Pontet B.
  • Quéruel N.
  • Jannet G.
  • Fergeau P.
  • Dudok de Wit T.
  • Vincent T.
  • Agrapart C.
  • Pragout J.
  • Bergerard-Timofeeva M.
  • Delory G. T.
  • Turin P.
  • Jeandet A.
  • Leroy P.
  • Pellion J.-C.
  • Bouzid V.
  • Recart W.
  • Kolmašová I.
  • Krupařová O.
  • Uhlíř L.
  • Lán R.
  • Baše J.
  • André M.
  • Bylander L.
  • Cripps V.
  • Cully C.
  • Jansson S.-E.
  • Puccio W.
  • Břínek J.
  • Ottacher H.
  • Angelini V.
  • Berthomier M.
  • Evans V.
  • Goetz K.
  • Hellinger P.
  • Horbury T. S.
  • Issautier K.
  • Kontar E.
  • Le Contel O.
  • Louarn P.
  • Martinović M.
  • Müller D.
  • O’brien H.
  • Owen C. J.
  • Retino A.
  • Rodríguez-Pacheco J.
  • Sahraoui Fouad
  • Sanchez L.
  • Walsh A. P.
  • Wimmer-Schweingruber R. F.
  • Zouganelis I.
  Astronomy & Astrophysics - A&A, EDP Sciences, 2021, 656, pp.1-12. The Radio and Plasma Waves (RPW) instrument on the ESA Solar Orbiter mission is designed to measure in situ magnetic and electric fields and waves from the continuum up to several hundred kHz. The RPW also observes solar and heliospheric radio emissions up to 16 MHz. It was switched on and its antennae were successfully deployed two days after the launch of Solar Orbiter on February 10, 2020. Since then, the instrument has acquired enough data to make it possible to assess its performance and the electromagnetic disturbances it experiences. In this article, we assess its scientific performance and present the first RPW observations. In particular, we focus on a statistical analysis of the first observations of interplanetary dust by the instrument’s Thermal Noise Receiver. We also review the electro-magnetic disturbances that RPW suffers, especially those which potential users of the instrument data should be aware of before starting their research work. (10.1051/0004-6361/202141271)
  DOI : 10.1051/0004-6361/202141271
• Solar Orbiter’s first Venus flyby: Observations from the Radio and Plasma Wave instrument
  
  • Hadid L. Z.
  • Edberg N.
  • Chust Thomas
  • Píša D.
  • Dimmock A.
  • Morooka M.
  • Maksimovic M.
  • Khotyaintsev Yu.
  • Souček J.
  • Kretzschmar M.
  • Vecchio A.
  • Le Contel O.
  • Retino A.
  • Allen R.
  • Volwerk M.
  • Fowler C.
  • Sorriso-Valvo L.
  • Karlsson T.
  • Santolík O.
  • Kolmašová I.
  • Sahraoui F.
  • Stergiopoulou K.
  • Moussas X.
  • Issautier K.
  • Dewey R.
  • Klein Wolt M.
  • Malandraki O.
  • Kontar E.
  • Howes G.
  • Bale S.
  • Horbury T.
  • Martinović M.
  • Vaivads A.
  • Krasnoselskikh V.
  • Lorfèvre E.
  • Plettemeier D.
  • Steller M.
  • Štverák Š.
  • Trávníček P.
  • O’brien H.
  • Evans V.
  • Angelini V.
  • Velli M.
  • Zouganelis I.
  Astronomy & Astrophysics - A&A, EDP Sciences, 2021, 656, pp.A18. Context. On December 27, 2020, Solar Orbiter completed its first gravity assist manoeuvre of Venus (VGAM1). While this flyby was performed to provide the spacecraft with sufficient velocity to get closer to the Sun and observe its poles from progressively higher inclinations, the Radio and Plasma Wave (RPW) consortium, along with other operational in situ instruments, had the opportunity to perform high cadence measurements and study the plasma properties in the induced magnetosphere of Venus. Aims. In this paper, we review the main observations of the RPW instrument during VGAM1. They include the identification of a number of magnetospheric plasma wave modes, measurements of the electron number densities computed using the quasi-thermal noise spectroscopy technique and inferred from the probe-to-spacecraft potential, the observation of dust impact signatures, kinetic solitary structures, and localized structures at the bow shock, in addition to the validation of the wave normal analysis on-board from the Low Frequency Receiver. Methods. We used the data products provided by the different subsystems of RPW to study Venus’ induced magnetosphere. Results. The results include the observations of various electromagnetic and electrostatic wave modes in the induced magnetosphere of Venus: strong emissions of ∼100 Hz whistler waves are observed in addition to electrostatic ion acoustic waves, solitary structures and Langmuir waves in the magnetosheath of Venus. Moreover, based on the different levels of the wave amplitudes and the large-scale variations of the electron number densities, we could identify different regions and boundary layers at Venus. Conclusions. The RPW instrument provided unprecedented AC magnetic and electric field measurements in Venus’ induced magnetosphere for continuous frequency ranges and with high time resolution. These data allow for the conclusive identification of various plasma waves at higher frequencies than previously observed and a detailed investigation regarding the structure of the induced magnetosphere of Venus. Furthermore, noting that prior studies were mainly focused on the magnetosheath region and could only reach 10–12 Venus radii ( R V ) down the tail, the particular orbit geometry of Solar Orbiter’s VGAM1, allowed the first investigation of the nature of the plasma waves continuously from the bow shock to the magnetosheath, extending to ∼70 R V in the far distant tail region. (10.1051/0004-6361/202140934)
  DOI : 10.1051/0004-6361/202140934
• Density fluctuations associated with turbulence and waves
  
  • Khotyaintsev Yu V
  • Graham D. B
  • Vaivads A.
  • Steinvall K.
  • Edberg N. J T
  • Eriksson A. I
  • Johansson E. P G
  • Sorriso-Valvo L.
  • Maksimovic M.
  • Bale S. D
  • Chust Thomas
  • Krasnoselskikh V.
  • Kretzschmar M.
  • Lorfèvre E.
  • Plettemeier D.
  • Souček J.
  • Steller M.
  • Štverák Š.
  • Trávníček P.
  • Vecchio A.
  • Horbury T. S
  • O’brien H.
  • Evans V.
  • Angelini V.
  Astronomy & Astrophysics - A&A, EDP Sciences, 2021, 656, pp.A19. Aims. The aim of this work is to demonstrate that the probe-to-spacecraft potential measured by RPW on Solar Orbiter can be used to derive the plasma (electron) density measurement, which exhibits both a high temporal resolution and a high level of accuracy. To investigate the physical nature of the solar wind turbulence and waves, we analyze the density and magnetic field fluctuations around the proton cyclotron frequency observed by Solar Orbiter during the first perihelion encounter (∼0.5 AU away from the Sun). Methods. We used the plasma density based on measurements of the probe-to-spacecraft potential in combination with magnetic field measurements by MAG to study the fields and density fluctuations in the solar wind. In particular, we used the polarization of the wave magnetic field, the phase between the compressible magnetic field and density fluctuations, and the compressibility ratio (the ratio of the normalized density fluctuations to the normalized compressible fluctuations of B) to characterize the observed waves and turbulence. Results. We find that the density fluctuations are 180° out of phase (anticorrelated) with the compressible component of magnetic fluctuations for intervals of turbulence, whereas they are in phase for the circular-polarized waves. We analyze, in detail, two specific events with a simultaneous presence of left- and right-handed waves at different frequencies. We compare the observed wave properties to a prediction of the three-fluid (electrons, protons, and alphas) model. We find a limit on the observed wavenumbers, 10 −6 < k < 7 × 10 −6 m −1 , which corresponds to a wavelength of 7 × 10 6 > λ > 10 6 m. We conclude that it is most likely that both the left- and right-handed waves correspond to the low-wavenumber part (close to the cut-off at Ω c He + + ) of the proton-band electromagnetic ion cyclotron (left-handed wave in the plasma frame confined to the frequency range Ω c He + + < ω < Ω cp ) waves propagating in the outwards and inwards directions, respectively. The fact that both wave polarizations are observed at the same time and the identified wave mode has a low group velocity suggests that the double-banded events occur in the source regions of the waves. (10.1051/0004-6361/202140936)
  DOI : 10.1051/0004-6361/202140936
• Magnetic reconnection as a mechanism to produce multiple thermal proton populations and beams locally in the solar wind
  
  • Lavraud B.
  • Kieokaew R.
  • Fargette N.
  • Louarn P.
  • Fedorov A.
  • André N.
  • Fruit G.
  • Génot V.
  • Réville V.
  • Rouillard A. P.
  • Plotnikov I.
  • Penou E.
  • Barthe A.
  • Prech L.
  • Owen C. J.
  • Bruno R.
  • Allegrini F.
  • Berthomier M.
  • Kataria D.
  • Livi S.
  • Raines J. M.
  • D’amicis R.
  • Eastwood J. P.
  • Froment C.
  • Laker R.
  • Maksimovic M.
  • Marcucci F.
  • Perri S.
  • Perrone D.
  • Phan T. D.
  • Stansby D.
  • Stawarz J.
  • Toledo-Redondo S.
  • Vaivads A.
  • Verscharen D.
  • Zouganelis I.
  • Angelini V.
  • Evans V.
  • Horbury T. S.
  • O’brien H.
  Astronomy & Astrophysics - A&A, EDP Sciences, 2021, 656, pp.A37. Context. Spacecraft data revealed early on the frequent observation of multiple near-thermal proton populations in the solar wind. Decades of research on their origin have focused on processes such as magnetic reconnection in the low corona and wave-particle interactions in the corona and locally in the solar wind.Aims. This study aims to highlight the fact that such multiple thermal proton populations and beams are also produced by magnetic reconnection occurring locally in the solar wind.Methods. We used high-resolution Solar Orbiter proton velocity distribution function measurements, complemented by electron and magnetic field data, to analyze the association of multiple thermal proton populations and beams with magnetic reconnection during a period of slow Alfvénic solar wind on 16 July 2020.Results. At least six reconnecting current sheets with associated multiple thermal proton populations and beams, including a case of magnetic reconnection at a switchback boundary, were found on this day. This represents 2% of the measured distribution functions. We discuss how this proportion may be underestimated, and how it may depend on solar wind type and distance from the Sun.Conclusions. Although suggesting a likely small contribution, but which remains to be quantitatively assessed, Solar Orbiter observations show that magnetic reconnection must be considered as one of the mechanisms that produce multiple thermal proton populations and beams locally in the solar wind. (10.1051/0004-6361/202141149)
  DOI : 10.1051/0004-6361/202141149
• Multiscale views of an Alfvénic slow solar wind: 3D velocity distribution functions observed by the Proton-Alpha Sensor of Solar Orbiter
  
  • Louarn P.
  • Fedorov A.
  • Prech L.
  • Owen C. J.
  • Bruno R.
  • Livi S.
  • Lavraud B.
  • Rouillard A. P.
  • Génot V.
  • André N.
  • Fruit G.
  • Réville V.
  • Kieokaew R.
  • Plotnikov I.
  • Penou E.
  • Barthe A.
  • Khataria D.
  • Berthomier M.
  • D’amicis R.
  • Sorriso-Valvo L.
  • Allegrini F.
  • Raines J.
  • Verscharen D.
  • Fortunato V.
  • Mele G.
  • Horbury T. S.
  • O’brien H.
  • Evans V.
  • Angelini V.
  • Maksimovic M.
  • Kasper J. C.
  • Bale S. D.
  Astronomy & Astrophysics - A&A, EDP Sciences, 2021, 656, pp.A36. Context. The Alfvénic slow solar wind is of particular interest, as it is often characterized by intense magnetic turbulence, complex proton 3D velocity distribution functions (VDF), and an ensuing richness of kinetic and dynamic processes.Aims. We take advantage of the fast time cadence of measurements taken by the Proton-Alpha Sensor (PAS) on board Solar Orbiter to analyze the kinetic properties of the proton population, the variability of their VDFs, and the possible link with propagating magnetic structures. We also study the magnetic (B) and velocity (V) correlation that characterizes this type of wind down to the ion gyroperiod.Methods. We analyzed the VDFs measured by PAS, a novelty that take advantages of the capability of 3D measurements at a 4 Hz cadence. In addition, we considered MAG observations.Results. We first show that there is a remarkable correlation between the B and V components observed down to timescales approaching the ion gyrofrequency. This concerns a wide variety of fluctuations, such as waves, isolated peaks, and discontinuities. The great variability of the proton VDFs is also documented. The juxtaposition of a core and a field-aligned beam is the norm but the relative density of the beam, drift speed, and temperatures can considerably change on scales as short as as a few seconds. The characteristics of the core are comparatively more stable. These variations in the beam characteristics mostly explain the variations in the total parallel temperature and, therefore, in the total anisotropy of the proton VDFs. Two magnetic structures that are associated with significant changes in the shape of VDFs, one corresponding to relaxation of total anisotropy and the other to its strong increase, are analyzed here. Our statistical analysis shows a clear link between total anisotropy (and, thus, beam characteristics) and the direction of B with respect to the Parker spiral. In the present case, flux tubes aligned with Parker spiral contain an average proton VDF with a much more developed beam (thus, with larger total anisotropy) than those that are inclined, perpendicular, or even reverse with regard to the outward direction.Conclusions. These observations document the variability of the proton VDF shape in relation to the propagation of magnetic structures. This is a key area of interest for understanding of the effect of turbulence on solar wind dynamics. (10.1051/0004-6361/202141095)
  DOI : 10.1051/0004-6361/202141095
• Whistler waves observed by Solar Orbiter/RPW between 0.5 AU and 1 AU
  
  • Kretzschmar Matthieu
  • Chust T.
  • Krasnoselskikh V.
  • Graham D.
  • Colomban L.
  • Maksimovic M.
  • Khotyaintsev Yu.
  • Soucek J.
  • Steinvall K.
  • Santolík O.
  • Jannet G.
  • Brochot J.-Y.
  • Le Contel O.
  • Vecchio A.
  • Bonnin X.
  • Bale S.
  • Froment C.
  • Larosa A.
  • Bergerard-Timofeeva M.
  • Fergeau P.
  • Lorfevre E.
  • Plettemeier D.
  • Steller M.
  • Štverák Š.
  • Trávníček P.
  • Vaivads A.
  • Horbury T.
  • O’brien H.
  • Evans V.
  • Angelini V.
  • Owen C.
  • Louarn P.
  Astronomy & Astrophysics - A&A, EDP Sciences, 2021, 656, pp.A24. Context. Solar wind evolution differs from a simple radial expansion, while wave-particle interactions are assumed to be the major cause for the observed dynamics of the electron distribution function. In particular, whistler waves are thought to inhibit the electron heat flux and ensure the diffusion of the field-aligned energetic electrons (Strahl electrons) to replenish the halo population. Aims. The goal of our study is to detect and characterize the electromagnetic waves that have the capacity to modify the electron distribution functions, with a special focus on whistler waves. Methods. We carried out a detailed analysis of the electric and magnetic field fluctuations observed by the Solar Orbiter spacecraft during its first orbit around the Sun, between 0.5 and 1 AU. Using data from the Search Coil Magnetometer and electric antenna, both part of the Radio and Plasma Waves (RPW) instrumental suite, we detected the electromagnetic waves with frequencies above 3 Hz and determined the statistical distribution of their amplitudes, frequencies, polarization, and k -vector as a function of distance. Here, we also discuss the relevant instrumental issues regarding the phase between the electric and magnetic measurements as well as the effective length of the electric antenna. Results. An overwhelming majority of the observed waves are right-handed circularly polarized in the solar wind frame and identified as outwardly propagating quasi-parallel whistler waves. Their occurrence rate increases by a least a factor of 2 from 1 AU to 0.5 AU. These results are consistent with the regulation of the heat flux by the whistler heat flux instability. Near 0.5 AU, whistler waves are found to be more field-aligned and to have a smaller normalized frequency ( f / f ce ), larger amplitude, and greater bandwidth than at 1 AU. (10.1051/0004-6361/202140945)
  DOI : 10.1051/0004-6361/202140945
• Observations of whistler mode waves by Solar Orbiter's RPW Low Frequency Receiver (LFR): In-flight performance and first results
  
  • Chust T.
  • Kretzschmar Matthieu
  • Graham D. B.
  • Le Contel O.
  • Retino A.
  • Alexandrova A.
  • Berthomier Matthieu
  • Hadid L. Z.
  • Sahraoui F
  • Jeandet Alexis
  • Leroy P
  • Pellion J-C
  • Bouzid V.
  • Katra Bruno
  • Piberne R
  • Khotyaintsev Yu V
  • Vaivads A
  • Krasnoselskikh V
  • Souček J
  • Santolík O
  • Lorfèvre E
  • Plettemeier D
  • Steller M
  • Štverák Š
  • Trávníček P
  • Vecchio A
  • Maksimovic M.
  • Bale S D
  • Horbury T S
  • O'Brien H
  • Evans V
  • Angelini V
  Astronomy & Astrophysics - A&A, EDP Sciences, 2021, 656 (A17), pp.18. Context. The Radio and Plasma Waves (RPW) instrument is one of the four in situ instruments of the ESA/NASA Solar Orbiter mission, which was successfully launched on February 10, 2020. The Low Frequency Receiver (LFR) is one of its subsystems, designed to characterize the low frequency electric (quasi-DC-10 kHz) and magnetic (∼1 Hz-10 kHz) fields that develop, propagate, interact, and dissipate in the solar wind plasma. Combined with observations of the particles and the DC magnetic field, LFR measurements will help to improve the understanding of the heating and acceleration processes at work during solar wind expansion. Aims. The capability of LFR to observe and analyze a variety of low frequency plasma waves can be demontrated by taking advantage of whistler mode wave observations made just after the near-Earth commissioning phase of Solar Orbiter. In particular, this is related to its capability of measuring the wave normal vector, the phase velocity, and the Poynting vector for determining the propagation characteristics of the waves. Methods. Several case studies of whistler mode waves are presented, using all possible LFR onboard digital processing products, waveforms, spectral matrices, and basic wave parameters. Results. Here, we show that whistler mode waves can be very properly identified and characterized, along with their Doppler-shifted frequency, based on the waveform capture as well as on the LFR onboard spectral analysis. Conclusions. Despite the fact that calibrations of the electric and magnetic data still require some improvement, these first whistler observations show a good overall consistency between the RPW LFR data, indicating that many science results on these waves, as well as on other plasma waves, can be obtained by Solar Orbiter in the solar wind. (10.1051/0004-6361/202140932)
  DOI : 10.1051/0004-6361/202140932
• Solar Orbiter Radio and Plasma Waves – Time Domain Sampler: In-flight performance and first results
  
  • Soucek J.
  • Píša D.
  • Kolmasova I.
  • Uhlir L.
  • Lan R.
  • Santolík O.
  • Krupar V.
  • Kruparova O.
  • Baše J.
  • Maksimovic M.
  • Bale S. D.
  • Chust Thomas
  • Khotyaintsev Yu V.
  • Krasnoselskikh V.
  • Kretzschmar Matthieu
  • Lorfèvre E.
  • Plettemeier D.
  • Steller M.
  • Štverák Š.
  • Vaivads A.
  • Vecchio A.
  • Bérard D.
  • Bonnin X.
  Astronomy & Astrophysics - A&A, EDP Sciences, 2021, 656, pp.A26. Context. The Radio and Plasma Waves (RPW) instrument on board Solar Orbiter has been operating nearly continuously since the launch in February 2020. The Time Domain Sampler (TDS) receiver of the RPW instrument is dedicated to waveform measurements of plasma waves and dust impact signatures in an intermediate frequency range from 0.2 to 200 kHz. Aims. This article presents the first data from the RPW-TDS receiver and discusses the in-flight performance of the instrument and, in particular, the on-board wave and dust detection algorithm. We present the TDS data products and its scientific operation. We demonstrate the content of the dataset on several examples. In particular, we study the distribution of solar Langmuir waves in the first year of observations and one Type III burst event. Methods. The on-board detection algorithm is described in detail in this article and classifies the observed waveform snapshots, identifying plasma waves and dust impacts based on the ratio of their maximum amplitude to their median and on the spectral bandwidth. The algorithm allows TDS to downlink the most scientifically relevant waveforms and to perform an on-board statistical characterization of the processed data. Results. The detection algorithm of TDS is shown to perform very well in its detection of plasma waves and dust impacts with a high accuracy. The initial analysis of statistical data returned by TDS shows that sporadic Langmuir waves that are not associated with Type III events are routinely observed in the inner heliosphere, with a clear increase in occurrence rate closer to the Sun. We also present an example of RPW observations during an encounter of the source region of a Type III burst, which exploits the on-board calculated histograms data. (10.1051/0004-6361/202140948)
  DOI : 10.1051/0004-6361/202140948
• Interaction between an interplanetary shock and the geomagnetic frontiers: Hybrid PIC simulations
  
  • Moissard Clement
  • Savoini Philippe
  • Fontaine Dominique
  • Modolo Ronan
  , 2021, 25, pp.SM25B-2008.. In the hybrid PIC code LatHyS - which is used to simulate the interaction between the solar wind and planetary magnetic environments - we injected a fast magnetic cloud which self consistently leads to the formation of an interplanetary shock. The interaction of the latter with an obstacle representing the geomagnetic environments gives us, for the first time, a kinetic global simulation of the interaction between an interplanetary shock followed by a sheath and the geomagnetic frontiers. This allows us to lift two common limitations of global simulations of such an interaction: the interplanetary shock is not artificially injected using the Rankine-Hugoniot equations, and the motion of the magnetopause is not imposed by any model (usually fixed or of constant velocity). We found that interplanetary shocks could be accelerated as they travel through the magnetosheath, as they ride on a fast bulk plasma. To explain this, we show that the velocity of the interplanetary shock in the plasma frame is actually constant. This means that in the plane of the IMF, both the plasma and the interplanetary shock are slowed down as they propagate in the magnetosheath; and that, conversely, they both accelerate in the plane orthogonal to it. In our simulations, we observe a strong asymmetry downstream of the interplanetary shock when particles were deviated by traversing the quasi-periodic pressure waves and ensuing oscillatory electric field that can be found behind the shock when the plasma beta is low. This suggests that the Rankine-Hugoniot equations may, under certain conditions, fail even at large scales. Furthermore, this asymmetry in the sheath leads to an asymmetric compression of the magnetosheath. We also studied the origin of the back-and-forth motion of the bow shock following its collision with the interplanetary shock. We show that this motion is due to a reflection on the magnetopause. Lastly, we explain the existence of a trough on the interplanetary shock by the appearance of a wave expanding outward from the magnetopause after its encounter with the transmitted interplanetary shock.
• BepiColombo and Solar Orbiter VGAM2 : Coordinated observations of the ion composition and total ion flux in the induced magnetosphere of Venus
  
  • Hadid L. Z.
  • Delcourt Dominique
  • Saito Yoshifumi
  • Fraenz Markus
  • Yokota Shoichiro
  • Fiethe Bjoern
  • Verdeil Christophe
  • Katra Bruno
  • Leblanc Frédéric
  • Fischer Henning
  , 2021.
• Étude de l’interaction des plasmas hors-équilibre et des détonation : réduction de la largueur des cellules et longueur de transition.
  
  • Ali Cherif Mhedine
  , 2021. La thèse présente une étude de l’interaction entre les plasmas froids nanosecondes et les ondes de combustion en vue d'améliorer la détonabilité de mélanges gazeux. Elle rapproche deux domaines de la physique aux échelles de temps caractéristiques différentes (nanoseconde vs. micro/milliseconde). Elle vise à démontrer l'existence d'un lien de causalité entre la pré-dissociation d’un mélange gazeux par plasma et la réduction des temps et longueur caractéristiques des réactions de combustion. Cette étude de l'effet du plasma sur la déflagration et la détonation est expérimentale et numérique. Après des rappels contextuels et des travaux antérieurs, nous donnons un bref résumé des phénoménologies de la détonation et de la déflagration dans les gaz et les deux définitions la détonabilité, soit, (1) la facilité pour la détonation à se propager dans des conditions données de confinement et (2) la rapidité avec laquelle la détonation s’établit à partir d’une flamme. La première est liée à la taille de la cellule de détonation caractérisant l'instabilité intrinsèque de sa zone de réaction établie. La deuxième est liée à la longueur de transition déflagration-détonation. Nous analysons également le plasma nanoseconde et son rôle dans la dissociation d’espèces dans un gaz. Nous proposons et testons un schéma cinétique, et sa procédure numérique, pour simuler l’effet du plasma dans un mélange combustible. Nous utilisons ces résultats de simulation comme paramètres initiaux d'un code de calcul de longueurs chimiques de la zone de réaction selon le modèle ZND de la détonation. Nous réalisons nos expériences dans des tubes de section carrée. Les méthodes de mesure sont l'imagerie ICCD, la strioscopie, la chimiluminescence, des enregistrements sur plaque à dépôt de carbone et des capteurs de pression dynamique, et un shunt avec courant de retour (BCS). Dans la série d'expériences à la cellule de détonation, nous démontrons que l’application d’un plasma nanoseconde devant un front de détonation établi diminue d'un facteur 2 la largeur des cellules de détonation de mélanges H2:O2:Ar, H2:O2, CH4:H2:O2:Ar et CH4:O2:AR à des pressions initiales entre 100 et 200 mbar. Dans la série d'expériences dédiée à la TDD, nous développons un système d’électrodes multi-canaux pour l’amorçage de la déflagration. Nous comparons la flamme qu’elle génère à celle issue d’une bougie d’allumage classique. La flamme induite par le plasma évolue vers le régime de détonation plus rapidement, à des distance plus courtes et à des pressions plus basses pour des mélanges H2:O2 à des pressions entre 200 mbar à 600 mbar. Pour les deux séries d’expériences nous avons caractérisé le plasma en portant une attention particulière à son efficacité (dépôt d’énergie et homogénéité) en fonction de la pression initiale. Nous démontrons ainsi une causalité entre plasma, temps d’induction chimique et détonabilité. Notre étude approfondit la compréhension du rôle des plasmas nanosecondes couplé aux ondes de combustion. Elle souligne l’intérêt de poursuivre cette approche nécessaire à la mise au point de dispositifs plasmas adaptés aux phénomènes de dynamique des détonations.Mots clés : Plasma nanoseconde, détonation, déflagration, détonabilité, temps d’induction chimique.
• In-situ optical diagnostics of plasma-water interfaces for applications in graphene synthesis
  
  • Pai David Z
  • Thomas Orrière
  • Francesca Caeilli
  • Karthik Thyagarajan
  • Darwin Kurniawan
  • Yi-Chen Chang
  • Jhih-Siang Yang
  • Wei-Hung Chiang
  , 2021. Many approaches to graphene synthesis can require high temperature, strong/toxic reducing agents, or are expensive. The microplasma-electrochemical reactor (MEC), composed of an atmospheric-pressure microplasma with an aqueous solution as an electrode, may overcome these difficulties by providing physico-chemical conditions that are difficult to achieve otherwise. They can initiate non-equilibrium electrochemistry and nucleation in solution without additional heating or reducing agents, improving the efficiency of synthesis. In addition, the technological barrier to implementing MECs is low. MECs have successfully synthesized graphene quantum dot (GQD) synthesis in aqueous solution [1,2]. One of the main challenges going forward is to develop a detailed mechanism of GQD growth, which is a general difficulty in plasma-based nanomaterials synthesis due to the complexity of non-equilibrium plasma chemistry and interactions with surfaces. So far the relevant species and reactions have mainly been inferred from ex situ or macroscopic effects, with a limited degree of detail and certainty. The liquid-phase diagnostics of the plasma-water interfacial region can provide new insight into how the MEC transforms the precursor into GQDs. Current experimental techniques used for the analysis of liquid chemistry suffer from a lack of selectivity and/or degradation of dyes, chemical probes, or spin traps/probes introduced into the liquid. The spatial distribution of species is not often accessible. Most importantly, the majority of the diagnostics must be performed ex situ, removed from the plasma reactor and after treatment. To address this challenge, we have developed an in situ multi-diagnostics approach to encompass a wide range of physical and chemical properties at the plasma-water interface. The centerpiece of this platform is in situ spontaneous Raman microspectroscopy, which offers several important advantages over the aforementioned diagnostic tools: non-intrusiveness, selectivity, versatility, and straightforward calibration. By developing a light-sheet technique, we have experimentally investigated the interfacial region with a spatial resolution as high as several tens of microns. To gain insight into the physical state of the solvent, we tracked the Raman spectrum of water. In particular, changes to the –OH stretch band shape indicate a weakening of the hydrogen bonding network of water with. These changes to the Raman spectra over the course of plasma treatment occur at both fast and slow time scales and become more pronounced as the detection volume approaches the interface. We also tracked the aqueous species H2O2 and NO3-, whose concentrations both increase when approaching the interface to within several tens of µm [3]. An interfacial layer of excess NO3- concentration was found to extend 28 µm in depth. Similar interfacial layers have been modeled for transient species such as OH radicals but not for NO3-, a stable product of plasma-activated water. Raman spectroscopy of the liquid environment was complemented by in situ photoluminescence (PL) spectroscopy to track the appearance of GQDs in real time. The PL spectrum evolves differently according to the depth of detection in the liquid, and so particle image velocimetry of the liquid flow field was performed to gain an understanding of possible transport mechanisms. These measurements of the liquid phase were complemented by optical emission spectroscopy of plasma properties such as the electron number density and presence of excited species as a function of the distance from the interface. Together, these experimental results represent the fullest description to date of the physico-chemical environment enabling GQD synthesis and mark an important step towards the discovery of the reaction mechanism. Acknowledgments Financial support: ANR grants ANR-15-CE06-0007-01 and ANR-11-LABX-0017-01, PHC Orchid 40938YL, CNRS-IEA “GRAFMET”. References [1] Orrière, T., Kurniawan, D., Chang, Y. C., Pai, D. Z., & Chiang, W. H. (2020). Nanotechnology 31 (485001). [2] Yang, J. S., Pai, D. Z., & Chiang, W. H. (2019). Carbon 153, 315-319. [3] Pai, D. Z. (2021) J. Phys. D. : Appl. Phys. 54, 355201
• In-orbit demonstration of an iodine electric propulsion system
  
  • Rafalskyi Dmytro
  • Martínez Javier Martínez
  • Habl Lui
  • Zorzoli Rossi Elena
  • Proynov Plamen
  • Boré Antoine
  • Baret Thomas
  • Poyet Antoine
  • Lafleur Trevor
  • Dudin Stanislav
  • Aanesland Ane
  Nature, Nature Publishing Group, 2021, 599 (7885), pp.411 - 415. Propulsion is a critical subsystem of many spacecraft1,2,3,4. For efficient propellant usage, electric propulsion systems based on the electrostatic acceleration of ions formed during electron impact ionization of a gas are particularly attractive5,6. At present, xenon is used almost exclusively as an ionizable propellant for space propulsion2,3,4,5. However, xenon is rare, it must be stored under high pressure and commercial production is expensive7,8,9. Here we demonstrate a propulsion system that uses iodine propellant and we present in-orbit results of this new technology. Diatomic iodine is stored as a solid and sublimated at low temperatures. A plasma is then produced with a radio-frequency inductive antenna, and we show that the ionization efficiency is enhanced compared with xenon. Both atomic and molecular iodine ions are accelerated by high-voltage grids to generate thrust, and a highly collimated beam can be produced with substantial iodine dissociation. The propulsion system has been successfully operated in space onboard a small satellite with manoeuvres confirmed using satellite tracking data. We anticipate that these results will accelerate the adoption of alternative propellants within the space industry and demonstrate the potential of iodine for a wide range of space missions. For example, iodine enables substantial system miniaturization and simplification, which provides small satellites and satellite constellations with new capabilities for deployment, collision avoidance, end-of-life disposal and space exploration10,11,12,13,14. (10.1038/s41586-021-04015-y)
  DOI : 10.1038/s41586-021-04015-y
• Titan's Induced magnetosphere from plasma wave, magnetic field and particle observations
  
  • Modolo Ronan
  • Romanelli Norberto
  • Bertucci Cesar
  • Canu Patrick
  • Piberne R.
  • Coates Andrew
  • Leblanc Francois
  • Edberg Niklas
  • Morooka Michiko
  • Holmberg Mika Katharina Göransdotter
  • Dubinin Eduard
  • Regoli Leonardo
  • Kurth William
  • Gurnett Donald
  • Wahlund Jan-Erik
  • Waite Jack Hunter
  • Dougherty Michele
  , 2021. (10.1002/essoar.10505169.1)
  DOI : 10.1002/essoar.10505169.1
• B2 Thickness Parameter Response to Equinoctial Geomagnetic Storms
  
  • Migoya-Orué Yenca
  • Alazo-Cuartas Katy
  • Kashcheyev Anton
  • Amory-Mazaudier Christine
  • Radicella Sandro
  • Nava Bruno
  • Fleury Rolland
  • Ezquer Rodolfo
  Sensors, MDPI, 2021, 21 (21), pp.7369. The thickness parameters that most empirical models use are generally defined by empirical relations related to ionogram characteristics. This is the case with the NeQuick model that uses an inflection point below the F2 layer peak to define a thickness parameter of the F2 bottomside of the electron density profile, which is named B2. This study is focused on the effects of geomagnetic storms on the thickness parameter B2. We selected three equinoctial storms, namely 17 March 2013, 2 October 2013 and 17 March 2015. To investigate the behavior of the B2 parameter before, during and after those events, we have analyzed variations of GNSS derived vertical TEC (VTEC) and maximum electron density (NmF2) obtained from manually scaled ionograms over 20 stations at middle and low latitudes of Asian, Euro-African and American longitude sectors. The results show two main kinds of responses after the onset of the geomagnetic events: a peak of B2 parameter prior to the increase in VTEC and NmF2 (in ~60% of the cases) and a fluctuation in B2 associated with a decrease in VTEC and NmF2 (~25% of the cases). The behavior observed has been related to the dominant factor acting after the CME shocks associated with positive and negative storm effects. Investigation into the time delay of the different measurements according to location showed that B2 reacts before NmF2 and VTEC after the onset of the storms in all the cases. The sensitivity shown by B2 during the studied storms might indicate that experimentally derived thickness parameter B2 could be incorporated into the empirical models such as NeQuick in order to adapt them to storm situations that represent extreme cases of ionospheric weather-like conditions. (10.3390/s21217369)
  DOI : 10.3390/s21217369
• Curlometer Technique and Applications
  
  • Dunlop M. W
  • Dong X.‐c. ‐c
  • Wang T.‐y. ‐y
  • Eastwood J. P
  • Robert P.
  • Haaland S.
  • Yang Y.‐Y.
  • Escoubet P.
  • Rong Z.‐j.
  • Shen C.
  • Fu H.‐s.
  • de Keyser J.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2021, 126 (11). We review the range of applications and use of the curlometer, initially developed to analyze Cluster multi-spacecraft magnetic field data; but more recently adapted to other arrays of spacecraft flying in formation, such as MMS small-scale, 4-spacecraft configurations; THEMIS close constellations of 3–5 spacecraft, and Swarm 2–3 spacecraft configurations. Although magnetic gradients require knowledge of spacecraft separations and the magnetic field, the structure of the electric current density (for example, its relative spatial scale), and any temporal evolution, limits measurement accuracy. Nevertheless, in many magnetospheric regions the curlometer is reliable (within certain limits), particularly under conditions of time stationarity, or with supporting information on morphology (for example, when the geometry of the large scale structure is expected). A number of large-scale regions have been covered, such as: the cross-tail current sheet, ring current, the current layer at the magnetopause and field-aligned currents. Transient and smaller scale current structures (e.g., reconnected flux tube or dipolarisation fronts) and energy transfer processes. The method is able to provide estimates of single components of the vector current density, even if there are only two or three satellites flying in formation, within the current region, as can be the case when there is a highly irregular spacecraft configuration. The computation of magnetic field gradients and topology in general includes magnetic rotation analysis and various least squares approaches, as well as the curlometer, and indeed the added inclusion of plasma measurements and the extension to larger arrays of spacecraft have recently been considered. (10.1029/2021ja029538)
  DOI : 10.1029/2021ja029538