Publications

2024

• Dynamique de la couronne de transition et génération du vent solaire
  
  • Pellegrin-Franchon Théo
  , 2024. Dans un contexte programmatique riche avec le lancement de Parker Solar Probe en 2018 et celui de Solar Orbiter en 2020, la question fondamentale de l’origine coronale du vent solaire est au cœur des problématiques scientifiques de la communauté solaire et héliosphérique.La couronne solaire est structurée par le champ magnétique qui se décline en champ fermé, formant des boucles connectant la surface solaire, et en champ ouvert avec un pieds ancré à la surface et l’autre s’étendant dans l’héliosphère. L’interface entre les champs ouverts et les champs fermés constitue une zone particulière favorable au développement de la reconnexion magnétique dite d’interchange, qui échange dynamiquement la connectivité magnétique entre le champ ouvert et le champ fermé. Cet échange de connectivité permet de restructurer le champ magnétique coronal à grande échelle et de laisser s’échapper le long des lignes nouvellement ouvertes, le plasma initialement confiné dans la couronne fermée. La reconnexion d’interchange est à ce titre l’une des théories expliquant la génération du vent solaire lent, l’une des deux catégories de vent solaire définies par les observations. Le vent lent, très variable, est composé d’un plasma aux propriétés typiques de la basse couronne fermée, à l’inverse du vent rapide, régulier, qui possède les propriétés des régions de champ magnétique ouvert. Parmi les origines potentielles du vent lent, plusieurs observations EUV et rayons X associées au champ magnétique coronal extrapolé à partir de magnétogrammes observationnels associent le vent lent avec les structures de pseudo-streamer. Ces structures magnétiques sont fréquemment observées dans la couronne lors des phases d'activité solaire maximale. Leur topologie magnétique formée de champ magnétique fermé bordé de champ magnétique ouvert en fait des structures idéales pour les modèles de reconnexion d'interchange. Le travail mené dans cette thèse vise à développer un modèle dynamique de reconnexion d’interchange au sein d’un pseudo-streamer. Elle apporte une description de la dynamique fine du champ magnétique coronal dans ces structures grâce à des simulations numériques 3D de la couronne pour un soleil entier. Le code utilisé, ARMS, est un code à raffinement de maille adaptatif qui résout les équations de la magnétohydrodynamique 3D pour un plasma d’hydrogène. En analysant précisément l’état de connectivité de centaines de lignes de champ magnétique à chaque pas de temps de la simulation, j’ai identifié plusieurs scénarios d’ouverture du champ fermé coronal susceptibles de participer à la variabilité du vent lent. Je distingue notamment un scénario en une étape où la reconnexion d’interchange a lieu au sein du pseudo-streamer, d’avec un scénario en deux étapes initié par une interaction entre pseudo-streamer et helmet streamer, une structure coronale permanente, suivie d’une ouverture par reconnexion d’interchange à l’apex du helmet streamer. Ces différences de scénario suggèrent des différences dans les propriétés du vent généré par ces reconnexions magnétiques. En analysant les propriétés du plasma le long des lignes de champ magnétique ouvertes par reconnexion d'interchange j’ai identifié et caractérisé des flots de plasma injectés dans l'héliosphère. J’ai observé ainsi des lignes de champ magnétique présentant des flots de plasma et d’autres n’en présentant pas. Ces résultats montrent que la reconnexion d’interchange ne garantit pas systématiquement l’injection de plasma dans l’héliosphère, c’est-à-dire de la génération de vent lent. L’extension de cette étude pourra permettre d'apporter des contraintes identifiables dans les observations EUV et mesures in situ afin d'apporter de nouveaux arguments en faveur du modèle de reconnexion d'interchange pour la génération du vent solaire lent, et ainsi d'en améliorer sa compréhension.
• Scaling laws of the plasma velocity in visco-resistive magnetohydrodynamic systems
  
  • Krupka A.
  • Firpo M.-C.
  Fundamental Plasma Physics, Elsevier, 2024, 10, pp.100044. We consider a visco-resistive magnetohydrodynamic modeling of a steady-state incompressible tokamak plasma with a prescribed toroidal current drive, featuring constant resistivity η and viscosity ν. It is shown that the plasma velocity root-mean-square behaves as η f (H) as long as the inertial term remains negligible, where H stands for the Hartmann number H ≡ (ην)^-1/2 , and that f (H) exhibits power-law behaviours in the limits H ≪ 1 and H ≫ 1. In the latter limit, we establish that f (H) scales as H^1/4 , which is consistent with numerical results. (10.1016/j.fpp.2024.100044)
  DOI : 10.1016/j.fpp.2024.100044
• Second Harmonic Electromagnetic Wave Emissions from a Turbulent Plasma with Random Density Fluctuations
  
  • Krafft C.
  • Volokitin A.
  The Astrophysical Journal, American Astronomical Society, 2024, 964 (1), pp.65. Abstract In the solar wind, electromagnetic waves at the harmonic plasma frequency 2 ω p can be generated as a result of coalescence between forward- and backward-propagating Langmuir waves. A new approach to calculate their radiation efficiency in plasmas with external background density fluctuations is developed. The evolution of Langmuir wave turbulence is studied by solving numerically the Zakharov equations in a two-dimensional randomly inhomogeneous plasma. Then, the dynamics of the nonlinear electric currents modulated at frequencies close to 2 ω p are calculated, as well as their radiation into harmonic electromagnetic waves. In the frame of this non-self-consistent approach where all transformations of Langmuir waves on density inhomogeneities are taken into account, the electromagnetic wave radiation rate (emissivity) is determined numerically as well as analytically, providing in both cases similar results. Moreover, scaling laws of the harmonic wave emissivity as a function of the ratio of the light velocity to the electron plasma thermal velocity are found. It is also shown how the emissivity depends on the average level of density fluctuations and on the isotropic/anisotropic character of the Langmuir waves’ and density fluctuations’ spectra. (10.3847/1538-4357/ad20ee)
  DOI : 10.3847/1538-4357/ad20ee
• Global Magnetic Reconnection During Sustained Sub‐Alfvénic Solar Wind Driving
  
  • Burkholder B.
  • Chen L.‐j.
  • Sarantos M.
  • Gershman D.
  • Argall M.
  • Chen Y.
  • Dong C.
  • Wilder F.
  • Le Contel O.
  • Gurram H.
  Geophysical Research Letters, American Geophysical Union, 2024, 51 (6). Abstract When the solar wind speed falls below the local Alfvén speed, the magnetotail transforms into an Alfvén wing configuration. A Grid Agnostic Magnetohydrodynamics for Extended Research Applications (GAMERA) simulation of Earth's magnetosphere using solar wind parameters from the 24 April 2023 sub‐Alfvénic interval is examined to reveal modifications of Dungey‐type magnetotail reconnection during sustained sub‐Alfvénic solar wind. The simulation shows new magnetospheric flux is generated via reconnection between polar cap field lines from the northern and southern hemisphere, similar to Dungey‐type magnetotail reconnection between lobe field lines mapping to opposite hemispheres. The key feature setting the Alfvén wing reconnection apart from the typical Dungey‐type is that the majority of new magnetospheric flux is added to the polar cap at local times 1–3 (21‐23) in the northern (southern) hemisphere. During most of the sub‐Alfvénic interval, reconnection mapping to midnight in the polar cap generates relatively little new magnetospheric flux. (10.1029/2024GL108311)
  DOI : 10.1029/2024GL108311
• Electron moments derived from the Mercury Electron Analyzer during the cruise phase of BepiColombo
  
  • Rojo M.
  • Persson M.
  • Sauvaud J.-A.
  • Aizawa Sae
  • Nicolaou G.
  • Penou E.
  • Barthe A.
  • André N.
  • Mazelle C.
  • Fedorov A.
  • Yokota S.
  • Saito Y.
  • Heyner D.
  • Richter I.
  • Auster U.
  • Schmid D.
  • Fischer D.
  • Horbury T.
  • Owen C.
  • Maksimovic M.
  • Khotyaintsev Y.
  • Louarn P.
  • Murakami G.
  Astronomy & Astrophysics - A&A, EDP Sciences, 2024, 683, pp.A99. Aims. We derive electron density and temperature from observations obtained by the Mercury Electron Analyzer on board Mio during the cruise phase of BepiColombo while the spacecraft is in a stacked configuration. Methods. In order to remove the secondary electron emission contribution, we first fit the core electron population of the solar wind with a Maxwellian distribution. We then subtract the resulting distribution from the complete electron spectrum, and suppress the residual count rates observed at low energies. Hence, our corrected count rates consist of the sum of the fitted Maxwellian core electron population with a contribution at higher energies. We finally estimate the electron density and temperature from the corrected count rates using a classical integration method. We illustrate the results of our derivation for two case studies, including the second Venus flyby of BepiColombo when the Solar Orbiter spacecraft was located nearby, and for a statistical study using observations obtained to date for distances to the Sun ranging from 0.3 to 0.9 AU. Results. When compared either to measurements of Solar Orbiter or to measurements obtained by HELIOS and Parker Solar Probe, our method leads to a good estimation of the electron density and temperature. Hence, despite the strong limitations arising from the stacked configuration of BepiColombo during its cruise phase, we illustrate how we can retrieve reasonable estimates for the electron density and temperature for timescales from days down to several seconds. (10.1051/0004-6361/202347843)
  DOI : 10.1051/0004-6361/202347843
• Reversal of the Parallel Drift Frequency in Anomalous Transport of Impurity Ions
  
  • Xu Shaokang
  • Maeyama Shinya
  • Watanabe Tomo-Hiko
  • Gürcan Özgür D.
  Physical Review Letters, American Physical Society, 2024, 132 (10), pp.105101. We study the heavy ion transport with the gyrokinetic simulation and find that when the gradient of the turbulence intensity is enhanced along the magnetic field line, part of the particles in velocity space reverses the parallel drift frequency. As a result, the particle transport related to the parallel dynamics is strongly enhanced. The parallel drift frequency is derived and shows that the frequency reversal is due to the amplitude effect of the turbulence on the plasma parallel structure and occurs when the gradient of turbulence intensity becomes large along the magnetic field line. (10.1103/PhysRevLett.132.105101)
  DOI : 10.1103/PhysRevLett.132.105101
• Gradient pulsed transient plasma for initiation of detonation
  
  • Lafaurie Victor
  • Shu Zhan
  • Vidal Pierre
  • Starikovskaia Svetlana
  Combustion and Flame, Elsevier, 2024, 261, pp.113311. The formation of a gradient of atomic oxygen is demonstrated by means of a nanosecond non-equilibrium plasma for a varying gap size plane-to-plane electrode. Using a flat high-voltage electrode in front of a rounded triangle a 2.9 to 5 cm gap is formed over a 9.8 cm span. ICCD imaging determined an adequate ground electrode shape and slope to create a gradient. The plasma is formed by three consecutive high voltage pulses of -30, -40 and -50 kV in 100 mbar of air. O-TALIF measurements confirm that atomic oxygen production changed with gap size within the same plasma. This setup will be used to test detonation initiation by Zel’dovich gradient mechanisms in stoichiometric H₂:O₂ mixtures. Novelty and Significance: A novel configuration of a nanosecond non-equilibrium discharge was developed to create a controllable gradient of atomic oxygen. This was achieved by using varying gap plane-to-plane electrodes to generate an electric field of varying strength along the length of the gap. This setup will be tested in combustible mixtures to initiate a detonation wave using a gradient mechanism of Zel’dovich. (10.1016/j.combustflame.2024.113311)
  DOI : 10.1016/j.combustflame.2024.113311
• Cold plasma treatment boosts barley germination and seedling vigor: Insights into soluble sugar, starch, and protein modifications
  
  • Benabderrahim Mohamed Ali
  • Bettaieb Imen
  • Hannachi Hédia
  • Rejili Mokhtar
  • Dufour Thierry
  Journal of Cereal Science, Elsevier, 2024, 116, pp.103852. (10.1016/j.jcs.2024.103852)
  DOI : 10.1016/j.jcs.2024.103852
• Stability analysis of WEST L-mode discharges with improved confinement from boron powder injection
  
  • Bodner Grant
  • Bourdelle Clarisse
  • Manas Pierre
  • Gallo Alberto
  • Afonin Kirill
  • Diallo Ahmed
  • Lunsford Robert
  • Moreau Philippe
  • Nagy Alexander
  • Clairet Frederic
  • Gil Christophe
  • Tsitrone Emmanuelle
  • Vermare L
  Plasma Physics and Controlled Fusion, IOP Publishing, 2024. WEST L-mode plasmas with dominant electron heating and no core torque source have observed improvements in confinement during boron (B) powder injection. These results are reminiscent of previous powder injection experiments on other devices and gaseous impurity seeding experiments on WEST. During powder injection, the stored energy increased up to 25% due to enhanced ion and electron heat and particle confinement. The improvements in confinement were not indicative of an L-H transition. To identify the dominant mechanisms and the causality chain behind these improvements in confinement, we employ interpretative modelling using METIS, predictive integrated modelling using a high-fidelity plasma simulator (HFPS), and stand-alone gyrokinetic simulations using QuaLiKiz. Interpretative modelling with METIS allowed for the estimation of missing data while maintaining good overall consistency with experiment. These results provided the initial conditions for fully predictive flux driven simulations using the HFPS. From these simulations, quasi-linear gyrokinetic analysis was performed at ρ=0.5 and ρ=0.65. Collisionality was found to be a strong candidate for turbulence suppression at ρ=0.5, while a combination of collisionality and the $T_e$ /$T_i$ ratio was found to be the likely mechanism at ρ=0.65. The results additionally suggested that increased $Z_{eff}$ (through main ion dilution) could play a role in the improved confinement, but this could not be confirmed due to a lack of experimental measurements. The modelling framework established here can now be used to evaluate and exploit a variety of future powder injection experiments. (10.1088/1361-6587/ad2c29)
  DOI : 10.1088/1361-6587/ad2c29
• Absolute calibration of the ratio of Xe/O two-photon absorption cross-sections for O-TALIF applications
  
  • Shu Z
  • Popov N
  • Starikovskaia S
  Plasma Sources Science and Technology, IOP Publishing, 2024, 33 (2), pp.025019. Abstract The paper presents a calibration of the ratio of two-photon absorption cross-sections, σ X e ( 2 ) / σ O ( 2 ) , necessary for the absolute O-atom density measurements by two-photon absorption laser-induced fluorescence (TALIF) technique. To calibrate the ratio of the cross-sections, a special discharge with 100% dissociation of molecular oxygen, and so with a known ‘reference’ density of O-atom [O] r e f = 2 ⋅ [O 2 ] was suggested. This is a nanosecond capillary discharge in N 2 :O 2 mixtures with a few percent of oxygen at a reduced electric field of a few hundred of Townsend and specific deposited energy of about 1 eV mol −1 . Voltage at the electrodes, electrical current in the plasma, longitudinal electric field and energy delivered to the gas were measured with 0.2 ns synchronisation. Additionally, radial distribution of emission of excited nitrogen molecules and gas temperature in the discharge and afterglow were obtained experimentally. Detailed 1D kinetic modeling was suggested to confirm complete O 2 dissociation and to analyse the main reactions. By comparing the data measured by TALIF technique with the ‘reference’ density of oxygen atoms [O] r e f , the ratio of the two-photon absorption cross-sections σ X e ( 2 ) / σ O ( 2 ) was determined. (10.1088/1361-6595/ad270f)
  DOI : 10.1088/1361-6595/ad270f
• Study of the breathing mode development in Hall thrusters using hybrid simulations
  
  • Petronio Federico
  • Alvarez Laguna Alejandro
  • Bourdon Anne
  • Chabert Pascal
  Journal of Applied Physics, American Institute of Physics, 2024, 135 (7). We use a 2.5D hybrid simulation to study the breathing mode (BM) dynamics in Hall thrusters (HTs). This involves a 1D Euler fluid simulation for neutral dynamics in the axial direction, coupled with a 2D axial–azimuthal Particle-in-Cell (PIC) simulation for charged species. The simulation also includes an out-of-plane virtual dimension for wall losses. This setup allows us to replicate the BM’s macroscopic features observed in experiments. A comprehensive analysis of plasma parameters in BM’s phases divides it into two growth and two decay sub-phases. Examining 1D axial profiles of electron temperature, gas and plasma densities, and particle creation rate shows that an increase in electron temperature alone cannot sustain ionization. Ionization seems to be influenced by the spatial correlation between electron and gas densities and the ionization rate coefficient. Investigating ion back-flow reveals its impact on modulating neutral flux entering the ionization region. The hybrid simulation’s outcomes let us assess the usual 0D predator–prey model’s validity and identify its limitations. The ionization and ion convection term approximations hold, but the gas convective term approximation does not. Introducing an alternative gas convective term approximation involving constant density ejection from the ionization region constructs an unstable BM model consistent with simulation results. In addition, this paper explores how varying the imposed voltage and mass flow rate impacts the BM. The BM frequency increases with imposed voltage, aligning with theoretical predictions. The mass flow rate variation has a limited effect on BM frequency, following the theoretical model’s trend. (10.1063/5.0188859)
  DOI : 10.1063/5.0188859
• Transport and staircase formation in competing flux-driven interchange & drift waves turbulence
  
  • Panico Olivier
  • Sarazin Y
  • Hennequin P
  • Gürcan Ö D
  , 2024.
• PHARE: Parallel hybrid particle-in-cell code with patch-based adaptive mesh refinement
  
  • Aunai Nicolas
  • Smets Roch
  • Ciardi Andrea
  • Deegan Philip
  • Jeandet Alexis
  • Payet Thibault
  • Guyot Nathan
  • Darrieumerlou Loic
  Computer Physics Communications, Elsevier, 2024, 295, pp.108966. Modeling multi-scale collisionless magnetized processes constitutes an important numerical challenge. By treating electrons as a fluid and ions kinetically, the so-called hybrid Particle-In-Cell (PIC) codes represent a promising intermediary between fully kinetic codes, limited to model small scales and short durations, and magnetohydrodynamic codes used large scale. However, simulating processes at scales significantly larger than typical ion particle dynamics while resolving sub-ion dissipative current sheets remain extremely difficult. This paper presents a new hybrid PIC code with patch-based adaptive mesh refinement. Here, hybrid PIC equations are solved on a hierarchy of an arbitrary number of Cartesian meshes of incrementally finer resolution dynamically mapping regions of interest, and with a refined time stepping. This paper presents how the hybrid PIC algorithm is adapted to evolve such mesh hierarchy and the validation of the code on a uniform mesh, fixed refined mesh and dynamically refined mesh. (10.1016/j.cpc.2023.108966)
  DOI : 10.1016/j.cpc.2023.108966
• Skewness and kurtosis of solar wind proton distribution functions: The normal inverse-Gaussian model and its implications
  
  • Louarn P.
  • Fedorov A.
  • Prech L.
  • Owen C J
  • D’amicis R.
  • Bruno R.
  • Livi S.
  • Lavraud B.
  • Rouillard A P
  • Génot V.
  • André N.
  • Fruit G.
  • Réville Victor
  • Kieokaew R.
  • Plotnikov I.
  • Penou E.
  • Barthe A.
  • Lewis G.
  • Berthomier M.
  • Allegrini F.
  • Alterman B L
  • Lepri S T
  • Raines J M
  • Verscharen D.
  • Mele G.
  • Fargette N.
  • Horbury T S
  • Maksimovic M.
  • Kasper J C
  • Bale S D
  Astronomy & Astrophysics - A&A, EDP Sciences, 2024, 682, pp.A44. Context. In the solar wind (SW), the particle distribution functions are generally not Gaussian. They present nonthermal features that are related to underlying acceleration and heating processes. These processes are critical in the overall dynamics of this expanding astrophysical fluid. Aims. The Proton Alpha Sensor (PAS) on board Solar Orbiter commonly observes skewed proton distributions, with a more populated high-energy side in the magnetic field direction than the Gaussian distribution. Our objectives are: (1) to identify a theoretical statistical function that adequately models the observed distributions and (2) to use its statistical interpretation to constrain the acceleration and heating processes. Methods. We analyzed the 3D velocity distribution functions (VDFs) measured by PAS and compared them to model statistical functions. Results. We show that the normal inverse Gaussian (NIG), a type of hyperbolic statistical distribution, provides excellent fits of skewed and leptokurtic proton distributions. NIG can model both the core distribution and the beam, if present. We propose an interpretation that is inspired by the mathematical formulation of the NIG. It assumes that the acceleration or heating mechanism can be modeled as a drifting diffusion process in velocity space, controlled (or subordinated) by the time of interaction of the particles with “accelerating structures”. The probability function of the interaction time is an inverse Gaussian (IG), obtained by considering a random drift across structures of a given size. The control of the diffusion by interaction times that follow an IG probability function formally defines the NIG distribution. Following this model, we show that skewness and kurtosis can be used to estimate the kinetic and thermal energy gains provided by the interaction with structures. For example, in the case studies presented here, the analyzed populations would have gained kinetic energy representing approximately two to four times their thermal energy, with an increase in velocity – due to acceleration – of from one-tenth to one-third of the observed flow velocity. We also show that the model constrains the initial temperature of the populations. Conclusions. Overall, the NIG model offers excellent fits of the observed proton distributions. Combining the skewness and the kurtosis, it also leads to constraints in the part of acceleration and heating due to the interactions with structures in the formation of the proton populations. We suggest that these effects add to the classical thermal evolution of the bulk velocity and temperature resulting from SW expansion. (10.1051/0004-6361/202347874)
  DOI : 10.1051/0004-6361/202347874
• Kinetic effects in thin layers: effects on jump conditions and discontinuity properties
  
  • Belmont G
  • Ballerini G
  • Rezeau L
  • Califano F
  , 2024. In plasmas as in neutral fluids, there are a few types of well-established kinds of discontinuities: shocks, rotational discontinuities, etc., whose properties are based on the so-called "Rankine-Hugoniot" jump relations. In the classic theory, these relations are based only on universal conservation laws so that they are independent of the physics occurring inside the layer and of the theory used for describing it, fluid or kinetic. We will highlight what are the underlying assumptions behind the classic theory and show its limits. We will first make explicit the role of the pressure anisotropy, which is ubiquitous in magnetized plasmas. It makes in particular "evolutionary" the rotational discontinuity, so justifying its existence through wave steepening. Furthermore, we will show that the Finite Larmor radius (FLR) effects, implying non-gyrotropic pressure tensors, are of primary importance for the plasma equilibrium at thin layers, and that they can determine their stationary widths. Taking FLR effects into account results in discontinuity properties that are notably different from the classic ones in the quasi-tangential limit and can explain the observations at the terrestrial magnetopause. We show that the change concerning the rotational discontinuity is comparable to the change of the MHD Alfvén wave into a Kinetic Alfvén wave for the linear modes.
• Experimental evidence of the role of non-gyrotropy in magnetopause equilibrium
  
  • Ballerini Giulio
  • Rezeau Laurence
  • Belmont Gérard
  • Califano Francesco
  , 2024.
• Identifying footpoints of pre-eruptive and coronal mass ejection flux ropes with sunspot scars
  
  • Xing Chen
  • Aulanier Guillaume
  • Schmieder Brigitte
  • Cheng Xin
  • Ding Mingde
  Astronomy & Astrophysics - A&A, EDP Sciences, 2024, 682, pp.A3. Context. The properties of pre-eruptive structures and coronal mass ejections (CMEs) are characterized by those of their footpoints, the latter of which attract a great deal of interest. However, the matter of how to identify the footpoints of pre-eruptive structures and how to do so with the use of ground-based instruments still remains elusive. Aims. In this work, we study an arc-shaped structure intruding in the sunspot umbra. It is located close to the (pre-)eruptive flux rope footpoint and it is expected to help identify the footpoint. Methods. We analyzed this arc-shaped structure, which we call a “sunspot scar”, in a CME event on July 12, 2012, and in two CME events from observationally inspired magnetohydrodynamic simulations performed by OHM and MPI-AMRVAC. Results. The sunspot scar displays a more inclined magnetic field with a weaker vertical component and a stronger horizontal component relative to that in the surrounding umbra and is manifested as a light bridge in the white light passband. The hot field lines anchored in the sunspot scar are spatially at the transition between the flux rope and the background coronal loops and temporally in the process of the slipping reconnection which builds up the flux rope. Conclusions. The sunspot scar and its related light bridge mark the edge of the CME flux rope footpoint and particularly indicate the edge of the pre-eruptive flux rope footpoint in the framework of “pre-eruptive structures being flux ropes”. Therefore, they provide a new perspective for the identification of pre-eruptive and CME flux rope footpoints, as well as new methods for studying the properties and evolution of pre-eruptive structures and CMEs with photospheric observations only. (10.1051/0004-6361/202347053)
  DOI : 10.1051/0004-6361/202347053
• Acceleration of an interplanetary shock through the magnetosheath: a global hybrid simulation
  
  • Moissard C.
  • Savoini P.
  • Fontaine D.
  • Modolo Ronan
  Frontiers in Astronomy and Space Sciences, Frontiers Media, 2024, 11, pp.1330397. According to most observations and simulations, interplanetary shocks slow down when they propagate through the magnetosheath. In this article, we present results from a self-consistent global hybrid PIC simulation of an interplanetary shock which, by contrast, accelerates as it propagates through the magnetosheath. In this simulation, the solar wind upstream of the interplanetary shock is set up with an Alfvén Mach number M A = 4.5 and the interplanetary magnetic field (IMF) is set up to be almost parallel to the y direction in GSE coordinate system. The ‘planet’ is modelled as a magnetic dipole with no tilt: the dipole is in the GSE’s z direction. In the ecliptic plane (Oxy), which contains the interplanetary magnetic field (IMF), the magnetic field lines are piling up against the magnetopause, and the velocity of the interplanetary shock decreases from 779 ± 48 km/s in the solar wind down to 607 ± 48 km/s in the magnetosheath. By contrast, in the noon-meridian plane (Oxz), which is perpendicular to the IMF, the velocity of the interplanetary shock in the magnetosheath can reach values up to 904 ± 48 km/s. This study suggests that interplanetary shocks can accelerate as they propagate through the magnetosheath. This finding, reported here for the first time, could have important implications for space weather, as it corresponds to the case where an interplanetary shock catches up with a low Alfvén Mach number solar transient such as an interplanetary coronal mass ejection. (10.3389/fspas.2024.1330397)
  DOI : 10.3389/fspas.2024.1330397
• The radial localization of the transition from low to high confinement mode in the ASDEX Upgrade tokamak
  
  • Cavedon M
  • Happel T
  • Hennequin P.
  • Dux R
  • Höfler K
  • Plank U
  • Pütterich T
  • Stroth U
  • Viezzer E
  • Wolfrum E
  Plasma Physics and Controlled Fusion, IOP Publishing, 2024, 66 (2), pp.025011. Abstract A novel experimental method is applied to localize the initial suppression of turbulence, in the form of density fluctuations, at the transition from the low (L-) to the high (H-) confinement mode in toroidal magnetic fusion plasmas. The high radial and temporal resolution, combined with the unprecedented statistical significance, provided the awaited information on a possible dominant E × B shear layer in L-H transition physics. We show, for the first time, that the H-mode turbulence suppression is initiated at the inner E × B shear layer in the ASDEX Upgrade tokamak possibly shedding light on the causality behind the L-H transition process. (10.1088/1361-6587/ad1ae3)
  DOI : 10.1088/1361-6587/ad1ae3
• Measurement of the main neutral species densities and temperatures in iodine plasmas using optical absorption techniques
  
  • Esteves Benjamin
  • Blondel Christophe
  • Chabert Pascal
  • Michel Tanguy
  • Drag Cyril
  Plasma Sources Science and Technology, IOP Publishing, 2024, 33, pp.1. Iodine is a promising propellant for future plasma thrusters used in space propulsion. It is therefore important to understand the basic physics and chemistry of low-pressure iodine plasmas. In the present work, optical absorption methods are used to measure the densities of iodine molecules, I2 , and iodine atoms, I, the translational temperature of the atoms and the dissociation fraction. The plasma is generated in a long quartz tube by a capacitively coupled RF discharge, and the pressure is varied between a few Pa and a few tens of Pa. The translational temperature of the atom vapour increases both with RF power and with pressure and reaches 1000 K at 50 watts and 25 Pa. The molecules appear to be efficiently dissociated, with a dissociation fraction found above 65 %, on average along the line-of-sight, at 120 watts and 5 Pa. The population of the upper, 2P1/2 , fine-structure level of the atomic ground term is found to be negligible, which confirms the existence of a high quenching rate, due to collisions with molecules and/or atoms. These measurements can be helpful for chemistry models of iodine plasmas. (10.1088/1361-6595/ad169d)
  DOI : 10.1088/1361-6595/ad169d
• Spacecraft Outgassing Observed by the BepiColombo Ion Spectrometers
  
  • Fränz M.
  • Rojo M.
  • Cornet T.
  • Hadid L.
  • Saito Y.
  • André N.
  • Varsani A.
  • Schmid D.
  • Krüger H.
  • Krupp N.
  • Delcourt D.
  • Katra B.
  • Harada Y.
  • Yokota S.
  • Verdeil C.
  • Aizawa S.
  • Millilo A.
  • Orsini S.
  • Mangano V.
  • Fiethe B.
  • Benkhoff J.
  • Murakami G.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2024, 129 (1). Abstract During the first flyby of the BepiColombo composite spacecraft at Mercury in October 2021 ion spectrometers observed two intense spectral lines with energies between 10 and 70 eV. The spectral lines persisted also at larger distances from Mercury and were observed again at lower intensity during cruise phase in March 2022 and at the second and third Mercury flyby as a single band. The ion composition indicates that water is the dominant gas source. The outgassing causes the composite spacecraft to charge up to a negative potential of up to −50 V. The distribution and intensity of the lower energy signal depends on the intensity of low energy electron fluxes around the spacecraft which again depend on the magnetic field orientation. We interpret the observation as being caused by water outgassing from different source locations on the spacecraft being ionized in two different regions of the surrounding potential. The interpretation is confirmed by two dimensional particle‐in‐cell simulations. (10.1029/2023JA032044)
  DOI : 10.1029/2023JA032044
• The Magnetopause: an almost tangential interface between the magnetosphere and the magnetosheath
  
  • Ballerini Giulio
  • Rezeau Laurence
  • Belmont Gérard
  • Califano Francesco
  , 2024.
• Modeling of mutual impedance experiments and quasi-thermal noise spectroscopy in magnetized plasma
  
  • Dazzi Pietro
  • Henri Pierre
  • Issautier Karine
  • Bucciantini Luca
  • Lavorenti Federico
  • Califano Francesco
  • Wattieaux Gaëtan
  , 2024, pp.500229. Mutual impedance experiments and quasi-thermal noise spectroscopy are two in situ plasma diagnostic techniques. They both rely on electric antennas in contact with the plasma, and both measure electron properties, notably electron density and temperature. They differ in that mutual impedance is an active technique, while quasi-thermal noise is a passive technique. Mutual impedance experiments measure the mutual impedance spectrum between two antennas. This measurement is performed by generating an electric perturbation within the plasma using one antenna, while another antenna simultaneously measures the electric field. Quasi-thermal noise spectroscopy uses one dipolar antenna, connected to a sensitive radio receiver, that measures the electric field fluctuations produced by the thermal motion of the ambient particles of the plasma. Both techniques are included in the scientific payload of past, current, and future NASA, ESA, and JAXA space missions, such as Rosetta, Parker Solar Probe, BepiColombo, JUICE, and Comet Interceptor. Instrumental models for both techniques are needed to interpret the instrumental output and derive measurements of the electron properties. They take into account both the electron plasma dispersion function and the geometry of the instrument. The modelling current state-of-the-art is largely focused on the limit of an unmagnetized plasma, that in this context identifies a plasma where the ratio of plasma to electron cyclotron frequency is much larger than one. We highlight here that the magnetized plasma regime will be of interest for future planetary space missions, including BepiColombo and JUICE, and to prepare future mission in the Earth's magnetosphere. In this context, we provide for the first time a complete diagnostic, in magnetized plasmas, of the plasma electron density and temperature, and the magnetic field magnitude and direction, based on mutual impedance experiments and quasi-thermal noise spectroscopy. For this purpose, we developed numerical models for both mutual impedance experiments and quasi-thermal noise spectroscopy in a magnetized plasma. A diagnostic is derived for the plasma density, the electron temperature, and the magnetic field. We validated these instrumental models against both laboratory and space measurements. The dependency of this diagnostic on the antenna shape and size is investigated, as well as the expected precision of these techniques as plasma diagnostic.
• New insights into the consequences of different interplanetary conditions on the near-Hermean environment
  
  • Cazzola Emanuele
  • Fontaine D.
  • Modolo Ronan
  , 2024. In this work we investigate the effects of different interplanetary conditions on the near-Mercury’s dynamics by means of hybrid simulations. In fact, along its orbit Mercury experiences significantly different environments in terms of interplanetary magnetic field (IMF) intensity and direction, as well as solar wind density and velocity. In particular, we show the variations occurring in the bow-shock / magnetosheath / magnetopause system under a Parker’s spiral IMF configuration as the orbit passes from the Aphelion position at 0.47 AU to the Perihelion position at 0.30 AU, as well as the effects of solar winds at different velocities. We observe these boundaries being significantly compressed towards the planetary surface as result of the interaction with high dynamic pressure and/or high Alfenic Mach number conditions. Moreover, a quasi-radial IMF configuration leads to the formation of an intense foreshock region concurring to further affect the boundaries characteristics. Finally, one of the main consequences of such a variable near-planet magnetic dynamics is the different rate, intensity and energy distribution of the interplanetary particles capable of precipitating onto the planetary surface. These particles are thought to be one of the main source of the neutrals seen in the exosphere. We observe that the precipitation mainly occurs along the open-lines magnetic cusps regions. Unlike what found from some past simulations, these regions show a significant longitudinal displacement from the north-south meridian line probably due to the quasi-radial configuration, as well as a latitudinal displacement towards the equatorial plane as the incoming solar wind compression increases. Additionally, the presence of a compressed magnetosphere / bow-shock scenario concurs to increase the precipitation rate in the equatorial regions.
• SPODIFY: Space Plasma Object Detection Inspired From Yolo
  
  • Nguyen Gautier
  • Bernoux Guillerme
  • Aunai Nicolas
  , 2024.