Publications

2024

• Magnetospheric Time‐History in Storm‐Time Magnetic Flux Dynamics: A Global Simulation Campaign
  
  • Atilaw T.
  • Akhavan-Tafti M.
  • Al Shidi Q.
  • Pulkkinen T.
  • Fontaine D.
  • Le Contel Olivier
  • Slavin J.
  • Le G.
  • Chen L.‐j.
  • Reiff P.
  • Alqeeq S.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2024, 129 (5). Abstract This paper aims to quantify the magnetospheric magnetic flux contents under moderate to intense space weather conditions using global simulations. This study is a companion to Akhavan‐Tafti, Atilaw, et al. (2023, https://doi.org/10.1029/2023JA031832 ) where magnetic flux evolution is presented for a catalog of storm events, using Heliophysics System Observatory (HSO) observations. For this study, we used the Space Weather Modeling Framework (SWMF) in Geospace configuration to study magnetic flux dynamics for a subset of their storm events (15 events). Simulations reliably resolve the storm‐time magnetic flux Bz and current density |J| asymmetries across the different storm phases. It is revealed that: relative to the quiet period, flux content is enhanced during the storm sudden commencement (SSC) phase in the dayside by ΔBz/Bz, quiet = +17%, and reduced in the nightside magnetosphere (r[R E ] < −6 R E ) by −15%. At the same time, the cross‐tail current is found to enhance (|J| = 2 nA/m 2 ), which suggests the storm impact in the nightside magnetosphere is much earlier in the storm cycle than previously shown. Concurring with previous studies, a significant depletion of magnetic flux by up to −40%, with day‐night and dawn‐dusk asymmetries, can be seen during the main and recovery phases. This corresponds to the enhanced current density (|J| = 5–8 nA/m 2 ) at ∼6 R E further confirming the role of ring current in driving magnetospheric dynamics during the main and recovery phases. This is in contrast with the SSC phase wherein the Chapman‐Ferraro and cross‐tail currents are the dominant current systems. (10.1029/2023JA031997)
  DOI : 10.1029/2023JA031997
• Energy Transport and Conversion Within Earth's Supercritical Bow Shock: The Role of Intense Lower‐Hybrid Whistler Waves
  
  • Hull Arthur J
  • Muschietti Laurent
  • Agapitov Oleksiy V
  • Chaston Christopher C
  • Le Contel Olivier
  • Lindqvist Per‐arne
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2024, 129 (5), pp.e2023JA031630. Detailed analysis of a high Mach number quasiperpendicular Earth bow shock crossing by the Magnetospheric Multiscale (MMS) spacecraft fleet reveal that lower‐hybrid (LH) whistler waves generated in the shock foot region transport energy predominately along the shock surface and slightly toward the shock ramp in the shock normal incidence frame, where wave energy accumulates and is dissipated into the plasma. This suggests the LH whistlers play an integral role in energy reconfiguration at high Mach number collisionless shocks with ramifications to plasma heating. The multipoint observations are used to quantify the wave characteristic parameters (via interferometry), Poynting fluxes, and energy conversion rates D, and to assess their scale dependencies and spatial and temporal properties. The whistler associated energy transport and conversion are found to depend on scale and location within the layer. High‐frequency electrostatic waves yield largest values of D. However, the dominant net energy exchange contribution is from the LH whistlers. In the foot spatially temporally coherent net energy exchange from the plasma to whistlers is observed, whereas deeper in the ramp net wave energy dissipation to the plasma is observed exhibiting significant space‐time variability. These results are consistent with the modified two stream instability driven by the relative drift between reflected ions and electrons as the mechanism for wave growth in the foot. Owing to strong electron heating, whistler energy dissipation in the ramp is attributed to Landau damping, which out‐competes the destabilizing effect of the reflected ion and electron drift. (10.1029/2023JA031630)
  DOI : 10.1029/2023JA031630
• Nitrogen atoms ps-TALIF in atmospheric pressure nanosecond volume DBD plasma
  
  • Kreyder G
  • Stefas D
  • Invernizzi L
  • Lombardi G
  • Gazeli K
  • Prasanna S
  • Starikovskaia S M
  , 2024.
• Transient gradient nanosecond plasmas for the initiation of a detonation wave: plasma characterisation with OES and O-TALIF
  
  • Lafaurie V
  • Shu Z
  • Sadauskaite M
  • Vidal Pierre
  • Starikovkaia S M
  , 2024.
• Gravitational wave turbulence: A multiple time scale approach for quartic wave interactions
  
  • Gay Benoît
  • Galtier Sébastien
  Physical Review D, American Physical Society, 2024, 109 (8), pp.083531. (10.1103/PhysRevD.109.083531)
  DOI : 10.1103/PhysRevD.109.083531
• Unveiling the Initiation Route of Coronal Mass Ejections through Their Slow Rise Phase
  
  • Xing Chen
  • Aulanier Guillaume
  • Cheng Xin
  • Xia Chun
  • Ding Mingde
  The Astrophysical Journal, American Astronomical Society, 2024. Understanding the early evolution of coronal mass ejections (CMEs), in particular their initiation, is the key to forecasting solar eruptions and induced disastrous space weather. Although many initiation mechanisms have been proposed, a full understand- ing of CME initiation, which is identified as a slow rise of CME progenitors in kine- matics before the impulsive acceleration, remains elusive. Here, with a state-of-the-art thermal-magnetohydrodynamics simulation, we determine a complete CME initiation route in which multiple mainstream mechanisms occur in sequence yet are tightly cou- pled. The slow rise is first triggered and driven by the developing hyperbolic flux tube (HFT) reconnection. Subsequently, the slow rise continues as driven by the coupling of the HFT reconnection and the early development of torus instability. The end of the slow rise, i.e., the onset of the impulsive acceleration, is induced by the start of the fast magnetic reconnection coupled with the torus instability. These results unveil that the CME initiation is a complicated process involving multiple physical mechanisms, thus being hardly resolved by a single initiation mechanism. (10.3847/1538-4357/ad2ea9)
  DOI : 10.3847/1538-4357/ad2ea9
• The inviscid incompressible limit of Kelvin–Helmholtz instability for plasmas
  
  • Briard A.
  • Ripoll J.-F.
  • Michael A.
  • Gréa B.-J.
  • Peyrichon G.
  • Cosmides M.
  • El-Rabii Hazem
  • Faganello M.
  • Merkin V.
  • Sorathia K.
  • Ukhorskiy A.
  • Lyon J.
  • Retino A.
  • Bouffetier V.
  • Ceurvorst L.
  • Sio H.
  • Hurricane O.
  • Smalyuk V.
  • Casner A.
  Frontiers in Physics, Frontiers, 2024, 12. <b>Introduction:</b> The Kelvin–Helmholtz Instability (KHI) is an interface instability that develops between two fluids or plasmas flowing with a common shear layer. KHI occurs in astrophysical jets, solar atmosphere, solar flows, cometary tails, planetary magnetospheres. Two applications of interest, encompassing both space and fusion applications, drive this study: KHI formation at the outer flanks of the Earth’s magnetosphere and KHI growth from non-uniform laser heating in magnetized direct-drive implosion experiments. Here, we study 2D KHI with or without a magnetic field parallel to the flow. We use both the GAMERA code, which solves the compressible Euler equations, and the STRATOSPEC code, which solves the Navier-Stokes equations under the Boussinesq approximation, coupled with the magnetic field dynamics. GAMERA is a global three-dimensional MHD code with high-order reconstruction in arbitrary nonorthogonal curvilinear coordinates, which is developed for a large range of astrophysical applications. STRATOSPEC is a three-dimensional pseudo-spectral code with an accuracy of infinite order (no numerical diffusion). Magnetized KHI is a canonical case for benchmarking hydrocode simulations with extended MHD options. <b>Methods:</b> An objective is to assess whether or not, and under which conditions, the incompressibility hypothesis allows to describe a dynamic compressible system. For comparing both codes, we reach the inviscid incompressible regime, by decreasing the Mach number in GAMERA, and viscosity and diffusion in STRATOSPEC. Here, we specifically investigate both single-mode and multi-mode initial perturbations, either with or without magnetic field parallel to the flow. The method relies on comparisons of the density fields, 1D&nbsp;profiles of physical quantities averaged along the flow direction, and scale-by-scale spectral densities. We also address the triggering, formation and damping of filamentary structures under varying Mach number or Atwood number, with or without a parallel magnetic field. <b>Results:</b> Comparisons show very satisfactory results between the two codes. The vortices dynamics is well reproduced, along with the breaking or damping of small-scale structures. We end with the extraction of growth rates of magnetized KHI from the compressible regime to the incompressible limit in the linear regime assessing the effects of compressibility under increasing magnetic field. <b>Discussion:</b> The observed differences between the two codes are explained either from diffusion or non-Boussinesq effects. (10.3389/fphy.2024.1383514)
  DOI : 10.3389/fphy.2024.1383514
• Energy conversion in a compressed magnetospheric separatrix: Observations and simulations
  
  • Baraka Mohammed
  • Le Contel Olivier
  • Canu Patrick
  • Alqeeq Soboh
  • Akhavan-Tafti Mojtaba
  • Retino Alessandro
  • Chust Thomas
  • Toledo-Redondo Sergio
  • Dargent Jeremy
  • Beck Arnaud
  • Cozzani Giulia
  • Norgren Cecilia
  , 2024. Magnetic reconnection is a fundamental process that is ubiquitous in the universe. It converts magnetic field energy into heating and acceleration of plasma. On the dayside of the Earth’s magnetosphere, it is responsible for the dominant transport of plasma, momentum, and energy across the magnetopause from the solar wind into the Earth’s magnetosphere. The present study reports on a magnetic reconnection event with a guide field (BM=0.5 B) detected by the Magnetospheric Multiscale mission (MMS) on October 21, 2015, around 04:39:24 UT. The MMS traversed the compressed magnetospheric separatrix and the reconnection jet far from the diffusion regions and in specific conditions: observing magnetospheric cold ions and a large magnetosheath density of up to 150 p/cc. We investigate the generalized Ohm’s law and the energy conversion process in the spacecraft frame (J.E) and in the fluid frame (J.E`) associated with the separatrix crossing under such conditions. We further validate and compare our results using 2D fully kinetic simulation. (10.5194/egusphere-egu24-9641)
  DOI : 10.5194/egusphere-egu24-9641
• Interaction between non-linear plasma structures and collisionless shocks: magnetic holes vs cometary shock
  
  • Wedlund Cyril Simon
  • Pucci Francesco
  • Preisser Luis
  • Henri P.
  • Behar Etienne
  • Ballerini Giulio
  • Califano Francesco
  • Passot T.
  • Sulem Pierre-Louis
  • Settino Adriana
  , 2024. Linear Magnetic Holes (LMHs) are magnetic field depressions generated in the solar wind upstream of planetary and cometary shock. Some of those structures are reminiscent of mirror modes, thus possibly linked to the mirror mode instability driven by a temperature anisotropy in a large plasma beta environment. LMHs have also been found downstream of the shock, which suggests that they can survive its crossing (Karlsson et al. 2022). Using the new GPU-intensive kinetic hybrid model Menura (Behar et al. 2022), we present two-dimensional (2D 3V) simulations of individual solar-wind LMHs impacting a shock in quasi-perpendicular conditions. First, we feed an analytical model of stable LMHs of various size and depth with magnetic field and density variations in antiphase, oriented along the solar wind magnetic field, into the simulation. The LMHs are then left to propagate with and into the plasma flow, eventually impacting the shock, where they may cross into the induced magnetosheath. We look at the global and local effects of such crossings and how the structures' characteristics and their immediate vicinity change over time. We apply this setup to (i) a local quasi-perpendicular shock structure created by one reflecting boundary and (ii) a global simulation of a cometary environment, and compare with observational findings. This work is part of preliminary modelling efforts preparing for the upcoming ESA/JAXA Comet Interceptor mission. (10.5194/egusphere-egu24-6135)
  DOI : 10.5194/egusphere-egu24-6135
• On the influence of solar wind turbulence on the Earth's foreshock dynamics
  
  • Pucci Francesco
  • Behar Etienne
  • Henri P.
  • Wedlund Cyril Simon
  • Preisser Luis
  • Ballerini Giulio
  • Califano Francesco
  , 2024. We present the results of two numerical simulations of the interaction between the solar wind and a planetary Earth-like magnetosphere. We use the hybrid particle-in-cell (PIC) code Menura, which allows for injecting a turbulent solar wind [1]. The two numerical simulations we present only differ one from the other on the nature of the solar wind, which is laminar in one case and turbulent in the other. Even though we poorly resolve ion scales because of computational constraints, we observe the development of a foreshock in the quasi-parallel shock region formed by kinetic effects due to the presence of reflected particles. We focus our analysis on the spatial properties of the reflected ion beams and compare them in the case of laminar and turbulent solar wind. In the laminar case, we observe the presence of fast modes excited by reflected particles and find homogeneous density and temperature of the ion beam in the foreshock region. Instead, in the turbulent case, we find that fluctuations in the foreshock are not simple fast waves but result from the interaction between solar wind turbulence and reflected particles. We also observe that density and temperature are modulated in space in contrast with the laminar case. We argue that this modulation arises from the complex shape of the magnetic field, in which field line random walk and perpendicular diffusion are enhanced with respect to the laminar case. [1] Behar, E., Fatemi, S., Henri, P., &amp; Holmström, M. (2022, May). Menura: a code for simulating the interaction between a turbulent solar wind and solar system bodies. In Annales Geophysicae (Vol. 40, No. 3, pp. 281-297). Copernicus GmbH. (10.5194/egusphere-egu24-9845)
  DOI : 10.5194/egusphere-egu24-9845
• The French contribution for the NASA HelioSwarm mission
  
  • Le Contel Olivier
  • Lavraud Benoit
  • Retino Alessandro
  • Kretzschmar Matthieu
  • Génot Vincent
  • Alexandrova Olga
  • Mansour Malik
  • Amoros Carine
  • Jannet Guillaume
  • Baruah Rituparna
  • Mehrez Fatima
  • Camus Thierry
  • Alison Dominique
  • Grigoriev Alexander
  • Revillet Claire
  • Studniarek Marina
  • Mirioni Laurent
  • Agrapart Clémence
  • Sou Gérard
  • Geyskens Nicolas
  , 2024. The HelioSwarm mission was selected as a MIDEX mission by NASA in February 2022 for launch in 2029 with a nominal duration of 15 months. Its main objectives are to reveal the 3D spatial structure and dynamics of turbulence in a weakly collisional plasma and to investigate the mutual impact of turbulence near boundaries (e. g., Earth's bow shock and magnetopause) and large-scale structures evolving in the solar wind (e. g., coronal mass ejection, corotating interaction region). The HelioSwarm mission will also contribute to the space weather science and to a better understanding of the Sun-Earth relationship. It consists of a platform (Hub) and eight smaller satellites (nodes) evolving along an elliptical orbit with an apogee ~ 60 and a perigee ~15 Earth radii. These 9 satellites, three-axis stabilised, will provide 36 pair combinations and 126 tetrahedral configurations covering the scales from 50~km (subion scale) to 3000 km (MHD scale). It will be the first mission able to investigate the physical processes related to cross-scale couplings between ion and MHD scales by measuring, simultaneously at these two scales, the magnetic field, ion density and velocity variations. Thus each satellite is equipped with the same instrument suite. A fluxgate magnetometer (MAG from Imperial College, UK) and a search-coil magnetometer (SCM) provide the 3D measurements of the magnetic field fluctuations whereas a Faraday cup (FC, SAO, USA) performs the ion density and velocity measurements. In addition, the ion distribution function is measured at a single point onboard the Hub by the iESA instrument, allowing to investigate the ion heating in particular. The SCM for HelioSwarm provided by LPP and LPC2E is strongly inherited of the SCM designed for the ESA JUICE mission. It will be mounted at the tip of a 3m boom and will cover the frequency range associated with the ion and subion scales in the near-Earth environment [0.1-16Hz] with the following sensitivities [15pT/√Hz at 1 Hz and 1.5 pT/√Hz at 10 Hz]. The iESA, developped by IRAP and LAB, is inherited from the PAS instrument operating on the ESA Solar Orbiter mission. It will provide the ion distribution function at high time and angular resolutions, respectively 0.150 s and 3°. Furthermore the energy range will be ~200 eV to 20 keV with 8% energy resolution. Status of the development of SCM and iESA prototypes will be presented. (10.5194/egusphere-egu24-9272)
  DOI : 10.5194/egusphere-egu24-9272
• Feedback Effects in Positive Corona and Relativistic Runaway Discharges
  
  • Pasko Victor
  • Celestin Sebastien
  • Bourdon Anne
  • Janalizadeh Reza
  • Jansky Jaroslav
  , 2024. We discuss characteristic scales and direct physical analogy between the photoionization feedback in conventional positive corona discharges in air and the photoelectric feedback in discharges driven by relativistic runaway electrons in air. In a positive corona system the avalanche of electrons in bulk of discharge volume is initiated by specific distribution of photoionization far away from the electrode. Under inception conditions in positive corona each electron arriving at the anode creates on average just enough seed electrons in discharge volume through photoionization to replicate itself. Under these self-sustained steady state conditions, photoionization feedback produces just enough secondary electrons upstream of the avalanche to maintain the system in steady state. Analogically, in case of relativistic electron avalanches a feedback process is realized when X-rays emitted by these electrons travel backwards with respect to the electron motion and generate new relativistic electron seeds due to the photoelectric absorption in air. It is demonstrated that terrestrial gamma-ray flashes are produced by growth of long bidirectional lightning leader system consisting of positive and stepping negative leaders. The spatial extent of streamer zones of a typical lightning leader with tip potential exceeding several tens of megavolts is on the order of 10-100 m. The photoelectric absorption of bremsstrahlung radiation generated by avalanching relativistic runaway electrons occurs efficiently on the same spatial scales. The intense multiplication of these electrons is triggered when the size of the negative leader streamer zone crosses a threshold of approximately 100 m (for sea-level air pressure conditions) allowing self-replication of these avalanches due to the upstream relativistic electron seeds generated by the photoelectric absorption.References: Pasko et al., GRL, 50, e2022GL102710, 2023, https://doi.org/10.1029/2022GL102710Pasko et al., PSST, 32, 075014, 2023, https://doi.org/10.1088/1361-6595/ace6d0 (10.5194/egusphere-egu24-11937)
  DOI : 10.5194/egusphere-egu24-11937
• BepiColombo observations of cold oxygen and carbon ions in the flank of the induced magnetosphere of Venus
  
  • Hadid L Z
  • Delcourt Dominique
  • Saito Y
  • Fränz M
  • Yokota S
  • Fiethe B
  • Verdeil C
  • Katra B
  • Leblanc François
  • Fischer H
  • Persson M
  • Aizawa S
  • André N
  • Harada Y
  • Fedorov A
  • Fontaine D
  • Krupp N
  • Michalik H
  • Berthelier Jean-Jacques
  • Krüger H
  • Murakami G
  • Matsuda S
  • Heyner D
  • Auster H-U
  • Richter I
  • Mieth J Z D
  • Schmid D
  • Fischer D
  Nature Astronomy, Nature Publishing Group, 2024, 8, pp.716-724. On 10 August 2021, the Mercury-bound BepiColombo spacecraft performed its second y-by of Venus and provided a short-lived observation of its induced magnetosphere. Here we report results recorded by the Mass Spectrum Analyzer on board Mio, which reveal the presence of cold O+ and C+ with an average total ux of ~4 ± 1 × 104 cm−2 s−1 at a distance of about six planetary radii in a region that has never been explored before. The ratio of escaping C+ to O+ is at most 0.31 ± 0.2, implying that, in addition to atomic O+ ions, CO group ions or water group ions may be a source of the observed O+. Simultaneous magnetometer observations suggest that these planetary ions were in the magnetosheath ank in the vicinity of the magnetic pileup boundary downstream. These results have important implications regarding the evolution of Venus’s atmosphere and, in particular, the evolution of water on the surface of the planet. (10.1038/s41550-024-02247-2)
  DOI : 10.1038/s41550-024-02247-2
• Treatment of seeds by cold ambient air plasma: combining impedance measurements with water sorption modeling to understand the impact of seed hydration
  
  • August Jonas
  • Bailly Christophe
  • Dufour Thierry
  Journal of Physics D: Applied Physics, IOP Publishing, 2024, 57 (26), pp.265203. In this article, we focus on the plasma seed interaction and more specifically-on the feedback exerted by the seeds on the plasma properties. Dormant Arabidopsis seeds with different water contents (WC), namely 3% DW , 10% DW and 30% DW were exposed to cold ambient air plasma (C2AP) generated in a dielectric barrier device (DBD). It is found that increasing WC enhances the capacitive current of the DBD, generates a greater number of low energy streamers (characterized by current peaks lower than 10 mA) that preferentially interplay with the seeds. Since the resistive and capacitive components of the seeds modify the C2AP electrical properties, impedance measurements (also called LCRmetry) have been carried out to measure their main dielectric parameters before/after plasma exposure (seeds resistance, capacitance, complex relative permittivity, tangent loss and conductivity). It appears that WC significantly changes dielectric losses at low frequencies (<1 kHz) due to polarization relaxation of the polar molecules (i.e. water). LCRmetry further reveals that C2AP does not substantially alter seeds dielectric parameters, i.e. it neither adds or removes significant amounts of new materials, meaning that the relative starch, protein and lipid contents remain essentially unaffected. However, it cannot be discounted that some bulk properties of the Arabidopsis seeds may be modified, especially regarding their porosity. This characteristic could facilitate penetration of plasma-generated reactive oxygen species into the internal seed tissues, leading to the grafting of oxygenated groups. To corroborate this theory, water sorption isotherms have been achieved on Arabidopsis seeds and fitted with four thermodynamic models, including the Brunauer–Emmett–Teller model and the Generalized D’Arcy and Watt model. It is demonstrated that C2AP primarily strengthens water-seed affinity by modifying molecular interactions rather than changing the seed’s moisture layer. This occurs despite a potential decrease in the number of adsorption sites, indicating a significant increase in overall seed hydrophilicity after plasma treatment. (10.1088/1361-6463/ad3838)
  DOI : 10.1088/1361-6463/ad3838
• Investigation of the directional Faraday cup and improvement of the comparison between direct and indirect thrust measurements of a magnetic nozzle ECR thruster
  
  • Pioch Romain
  • Désangles Victor
  • Chabert Pascal
  Physics of Plasmas, American Institute of Physics, 2024, 31 (4), pp.043516. The thrust of an electric propulsion device estimated from electrostatic probe measurements may be different from direct thrust measurements. In order to reduce this discrepancy for electron cyclotron resonance thrusters (ECRT), a new diagnostic is presented: the directional Faraday cup (FCDi). Thanks to a peculiar design, it assesses the angular distribution of ion current density in the plume of plasma thrusters. First, a theoretical model of the angular selectivity of the FCDi is introduced. It is validated with both simulations and experiments. Guidelines are given to use the FCDi in the plume of ECRT. Second, the observed discrepancies between direct thrust measurements made on a thrust stand and indirect ones are reduced when using the FCDi instead of a planar Faraday probe with a guard ring (FPGR). Relative errors come down to 10% with the FCDi, which are compared to 20%–30% observed with the FPGR. An analysis demonstrates that it is not due to the effect of local ion trajectories but comes from the magnitude of the ion current measured. A large sheath in front of the negatively biased FPGR seems to be the cause of this phenomenon. The grounded opening of the FCDi reduces this phenomenon and improves the ion flux measurement accuracy. This new probe, with angular selectivity characteristics, allows for the comparison of the ion flux ejection direction with the magnetic field line and contributes to a better description of ion population dynamic in the magnetic nozzle of the thruster. (10.1063/5.0190318)
  DOI : 10.1063/5.0190318
• Quantifying the diffusion of suprathermal electrons by whistler waves between 0.2 and 1 AU with Solar Orbiter and Parker Solar Probe
  
  • Colomban L.
  • Kretzschmar Matthieu
  • Krasnoselkikh V.
  • Agapitov O. V.
  • Froment C.
  • Maksimovic M.
  • Berthomier M.
  • Khotyaintsev Yu. V.
  • Graham D. B.
  • Bale S.
  Astronomy & Astrophysics - A&A, EDP Sciences, 2024, 684, pp.A143. Context. The evolution of the solar wind electron distribution function with heliocentric distance exhibits different features that are still unexplained, in particular, the fast decrease in the electron heat flux and the increase in the Strahl pitch angle width. Wave-particle interactions between electrons and whistler waves are often proposed to explain these phenomena.Aims. We aim to quantify the effect of whistler waves on suprathermal electrons as a function of heliocentric distance.Methods. We first performed a statistical analysis of whistler waves (occurrence and properties) observed by Solar Orbiter and Parker Solar Probe between 0.2 and 1 AU. The wave characteristics were then used to compute the diffusion coefficients for solar wind suprathermal electrons in the framework of quasi-linear theory. These coefficients were integrated to deduce the overall effect of whistler waves on electrons along their propagation.Results. About 110 000 whistler wave packets were detected and characterized in the plasma frame, including their direction of propagation with respect to the background magnetic field and their radial direction of propagation. Most waves are aligned with the magnetic field and only ∼0.5% of them have a propagation angle greater than 45°. Beyond 0.3 AU, it is almost exclusively quasi-parallel waves propagating anti-sunward (some of them are found sunward but are within switchbacks with a change of sign of the radial component of the background magnetic) that are observed. Thus, these waves are found to be Strahl-aligned and not counter-streaming. At 0.2 AU, we find both Strahl-aligned and counter-streaming quasi-parallel whistler waves.Conclusions. Beyond 0.3 AU, the integrated diffusion coefficients show that the observed waves are sufficient to explain the measured Strahl pitch angle evolution and effective in isotropizing the halo. Strahl diffusion is mainly attributed to whistler waves with a propagation angle of θ ∈ [15.45]°, although their origin has not yet been fully determined. Near 0.2 AU, counter-streaming whistler waves are able to diffuse the Strahl electrons more efficiently than the Strahl-aligned waves by two orders of magnitude. (10.1051/0004-6361/202347489)
  DOI : 10.1051/0004-6361/202347489
• Electrostatic Wave Decay in the Randomly Inhomogeneous Solar Wind
  
  • Krafft C.
  • Savoini P.
  The Astrophysical Journal Letters, Bristol : IOP Publishing, 2024, 964 (2), pp.L30. Despite a few space observations where Langmuir and ion acoustic waves are expected to participate in the mechanism of electrostatic decay, this is to date believed to be the main and fastest nonlinear wave process in the solar wind. However, in such a plasma where random density fluctuations are ubiquitous, the question of whether nonlinear wave processes play a significant role in Langmuir wave turbulence generated by electron beams associated with type III solar radio bursts remains still open. This paper provides several answers by studying, owing to two-dimensional challenging particle-in-cell simulations, the dynamics and the properties of the ion acoustic waves excited by such Langmuir wave turbulence and the role they play in the electrostatic decay. The impact on this process of plasma background density fluctuations and electron-to-ion temperature ratio is studied. Moreover, it is shown that, for a typical solar wind plasma with an average level of density fluctuations of a few percent of the ambient density and a temperature ratio of the order of 1, nonlinear induced scattering off ions occurs, with small intensity low-frequency quasi-modes and only in localized plasma regions where density is depleted or weakly perturbed by low-frequency turbulence. (10.3847/2041-8213/ad3449)
  DOI : 10.3847/2041-8213/ad3449
• Statistical Study of the Global Constraints Governing Magnetic Reconnection at the Earth's Magnetopause
  
  • Michotte de Welle Bayane
  , 2024. Magnetic reconnection is the primarymechanism through which the Earth's magnetosphere couples to the surrounding magnetized solar wind. The efficiency of this coupling largely depends on where the reconnection occurs on themagnetopause. Determining the location of so-called reconnection X-lines, as a function of the upstream interplanetary conditions, remains a long-standing challenge in magnetospheric physics due to its multiscale character. Progress is hampered by the fact that the plasma and field properties that constrain where reconnection can develop on the magnetopause are themselves poorly understood, and so far only accessed through global magnetohydrodynamics simulations. This thesis brings new observational constraints to this problem through the reconstruction of 3D global spatial variations of the plasma and magnetic field on the dayside magnetosheath and magnetopause. A newmethodology was developed to collect and process two decades of in-situ measurements from the Cluster, Double Star, THEMIS, andMMS missions. We first reconstructed the global 3Dmagnetic draping of the interplanetary magnetic field (IMF) in the magnetosheath, whose structure is demonstrated to be controlled by the plasma flow in this region in a way that invalidates widely used vacuum magnetostatic draping assumptions in about 30% of the IMF orientations. We then examine the variation of magnetic field amplitude and plasma density in the magnetosheath and their dependence on the IMF orientation, and highlight their nonlinear coupling with magnetopause reconnection. Finally reconstructions of the spatial distributions magnetic shear, current density and reconnection rate on the dayside magnetopause,for different dipole tilts and IMF orientations, allowed us to better understand the interplay between local and global constraints on the location of reconnection X-lines.
• 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
• 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&nbsp;2.9 to 5&nbsp;cm gap is formed over a 9.8&nbsp;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&nbsp;-30, -40 and -50&nbsp;kV in 100&nbsp;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