Publications

2024

• Reconnection Inside a Dipolarization Front of a Diverging Earthward Fast Flow
  
  • Hosner M.
  • Nakamura R.
  • Schmid D.
  • Nakamura T.
  • Panov E.
  • Volwerk M.
  • Vörös Z.
  • Roberts O.
  • Blasl K.
  • Settino A.
  • Korovinskiy D.
  • Marshall A.
  • Denton R.
  • Burch J.
  • Giles B.
  • Torbert R.
  • Le Contel O.
  • Escoubet C.
  • Dandouras I.
  • Carr C.
  • Fazakerley A.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2024, 129 (1). Abstract We examine a Dipolarization Front (DF) event with an embedded electron diffusion region (EDR), observed by the Magnetospheric Multiscale (MMS) spacecraft on 08 September 2018 at 14:51:30 UT in the Earth's magnetotail by applying multi‐scale multipoint analysis methods. In order to study the large‐scale context of this DF, we use conjunction observations of the Cluster spacecraft together with MMS. A polynomial magnetic field reconstruction technique is applied to MMS data to characterize the embedded electron current sheet including its velocity and the X‐line exhaust opening angle. Our results show that the MMS and Cluster spacecraft were located in two counter‐rotating vortex flows, and such flows may distort a flux tube in a way that the local magnetic shear angle is increased and localized magnetic reconnection may be triggered. Using multi‐point data from MMS we further show that the local normalized reconnection rate is in the range of R ∼ 0.16 to 0.18. We find a highly asymmetric electron in‐ and outflow structure, consistent with previous simulations on strong guide‐field reconnection events. This study shows that magnetic reconnection may not only take place at large‐scale stable magnetopause or magnetotail current sheets but also in transient localized current sheets, produced as a consequence of the interaction between the fast Earthward flows and the Earth's dipole field. (10.1029/2023JA031976)
  DOI : 10.1029/2023JA031976
• CO2/CH4 Glow Discharge Plasma. Part II: Study of Plasma Catalysis Interaction Mechanisms on CeO2
  
  • Garcia-Soto Carolina A.
  • Baratte Edmond
  • Silva Tiago
  • Guerra Vasco
  • Parvulescu Vasile I.
  • Guaitella Olivier
  Plasma Chemistry and Plasma Processing, Springer Verlag, 2024. A fundamental study of CO2/CH4 plasma is performed in a glow discharge at a few Torr. Experimental and numerical results are compared to identify the main reaction pathways. OES-based techniques and FTIR (Fourier Transform Infrared) spectroscopy are used to determine molecules densities and gas temperature. Several conditions of pressure, initial mixture and residence time are measured. The main dissociation products are found to be CO and H2. The LoKI simulation tool was used to build a simplified kinetic scheme to limit the uncertainties on rate coefficients, but sufficient to reproduce the experimental data. To this aim, only molecules containing at most one carbon atom are considered based on the experimental observations. Obtaining a good match between the experimental data and the simulation requires the inclusion of reactions involving the excited state O(1D). The key role of CH3 radical is also emphasized. The good match obtained between the experiment and the simulation allows to draw the main reaction pathways of the low-pressure CO2-CH4 plasmas, in particular to identify the main back reaction mechanisms for CO2. The role of CH2O and H2O in the gas phase is also discussed in depth as they appear to play an important role on catalytic surface studied in the part II of this study (10.1007/s11090-023-10419-7)
  DOI : 10.1007/s11090-023-10419-7
• Study and Modelling of the Impact of June 2015 Geomagnetic Storms on the Brazilian Ionosphere
  
  • Afolabi Oladayo O
  • Candido Claudia Maria Nicoli
  • Becker-Guedes Fabio
  • Amory-Mazaudier Christine
  Atmosphere, MDPI, 2024, 15 (5), pp.597. This study investigated the impact of the June 2015 geomagnetic storms on the Brazilian equatorial and low-latitude ionosphere by analyzing various data sources, including solar wind parameters from the advanced compositional explorer satellite (ACE), global positioning satellite vertical total electron content (GPS-VTEC), geomagnetic data, and validation of the SAMI2 model-VTEC with GPS-VTEC. The effect of geomagnetic disturbances on the Brazilian longitudinal sector was examined by applying multiresolution analysis (MRA) of the maximum overlap discrete wavelet transform (MODWT) to isolate the diurnal component of the disturbance dynamo (Ddyn), DP2 current fluctuations from the ionospheric electric current disturbance (Diono), and semblance cross-correlation wavelet analysis for local phase comparison between the Sq and Diono currents. Our findings revealed that the significant fluctuations in DP2 at the Brazilian equatorial stations (Belem, dip lat: −0.47° and Alta Floresta, dip lat: −3.75°) were influenced by IMF Bz oscillations; the equatorial electrojet also fluctuated in tandem with the DP2 currents, and dayside reconnection generated the field-aligned current that drove the DP2 current system. The short-lived positive ionospheric storm during the main phase on 22 June in the Southern Hemisphere in the Brazilian sector was caused by the interplay between the eastward prompt penetration of the magnetospheric convection electric field and the westward disturbance dynamo electric field. The negative ionospheric storms that occurred during the recovery phase from 23 to 29 June 2015, were attributed to the westward disturbance dynamo electric field, which caused the downward E × B drift of the plasma to a lower height with a high recombination rate. The comparison between the SAMI2 model-VTEC and GPS-VTEC indicates that the SAMI2 model underestimated the VTEC within magnetic latitudes of −9° to −24° in the Brazilian longitudinal sector from 6 to 17 June 2015. However, it demonstrated satisfactory agreement with the GPS-VTEC within magnetic latitudes of −9° to 10° from 8 to 15 June 2015. Conversely, the SAMI2 model overestimated the VTEC between ±10° magnetic latitudes from 16 to 28 June 2015. The most substantial root mean square error (RMSE) values, notably 10.30 and 5.48 TECU, were recorded on 22 and 23 June 2015, coinciding with periods of intense geomagnetic disturbance. (10.3390/atmos15050597)
  DOI : 10.3390/atmos15050597
• Impact of solar-wind turbulence on a planetary bow shock: A global 3D simulation
  
  • Behar E.
  • Pucci F.
  • Simon Wedlund C.
  • Henri P.
  • Ballerini G.
  • Preisser L.
  • Califano F.
  Astronomy & Astrophysics - A&A, EDP Sciences, 2024, 692. Context. The interaction of the solar-wind plasma with a magnetized planet generates a bow-shaped shock ahead of the wind. Over recent decades, near-Earth spacecraft observations have provided insights into the physics of the bow shock, and the findings suggest that solar-wind intrinsic turbulence influences the bow shock dynamics. On the other hand, theoretical studies, primarily based on global numerical simulations, have not yet investigated the global three-dimensional (3D) interaction between a turbulent solar wind and a planetary magnetosphere. This paper addresses this gap for the first time by presenting an investigation of the global dynamics of this interaction that provides new perspectives on the underlying physical processes. Aims. We use the newly developed numerical code MENURA to examine how the turbulent nature of the solar wind influences the 3D structure and dynamics of magnetized planetary environments, such as those of Mercury, Earth, and magnetized Earth-like exoplanets. Methods. We used the hybrid particle-in-cell code MENURA to conduct 3D simulations of the turbulent solar wind and its interaction with an Earth-like magnetized planet through global numerical simulations of the magnetosphere and its surroundings. MENURA runs in parallel on graphics processing units, enabling efficient and self-consistent modeling of turbulence. Results. By comparison with a case in which the solar wind is laminar, we show that solar-wind turbulence globally influences the shape and dynamics of the bow shock, the magnetosheath structures, and the ion foreshock dynamics. Also, a turbulent solar wind disrupts the coherence of foreshock fluctuations, induces large fluctuations on the quasi-perpendicular surface of the bow shock, facilitates the formation of bubble-like structures near the nose of the bow shock, and modifies the properties of the magnetosheath region. Conclusions. The turbulent nature of the solar wind impacts the 3D shape and dynamics of the bow shock, magnetosheath, and ion foreshock region. This influence should be taken into account when studying solar-wind-planet interactions in both observations and simulations. We discuss the relevance of our findings for current and future missions launched into the heliosphere. (10.1051/0004-6361/202451520)
  DOI : 10.1051/0004-6361/202451520
• On the importance of flux-driven turbulence regime to address tokamak plasma edge dynamics
  
  • Panico Olivier
  • Sarazin Y
  • Hennequin P
  • Gürcan Ö D
  • Bigué R
  • Dif-Pradalier G
  • Garbet X
  • Ghendrih P
  • Varennes R
  • Vermare L
  Journal of Plasma Physics, Cambridge University Press (CUP), 2024, 91 (1). Turbulence self-organization is studied in the flux driven regime by means of the reduced model Tokam1D. Derived in the electrostatic and isothermal limit but keeping finite electron and ion temperatures, it features two instabilities that are suspected to dominate turbulent transport at the edge of L-mode tokamak plasmas: interchange (a reduced version of the resistive ballooning modes) and collisional drift waves, governed respectively by an effective gravity parameter g and the adiabaticity parameter C. The usual properties of these two instabilities are recovered in the linear regime. The nonlinear study focuses on the self-organization of collisional drift wave turbulence at g = 0. It is found that the energy stored in zonal flows (ZFs) decreases smoothly at small C due to the reduction of both electric and diamagnetic stresses. Conversely to gradient driven simulations, no sharp collapse is observed due to the self-consistent evolution of the equilibrium density profile. ZFs are found to structure into staircases at small and large C. These structures exhibit a rich variety of dynamics but are found robust to large perturbations. Their nucleation is found to be critically governed by the phase dynamics. Last, staircase structures are lost in the gradient driven regime, when the system is prevented to store turbulent energy into the equilibrium density (pressure) profile. (10.1017/S0022377824001624)
  DOI : 10.1017/S0022377824001624
• Analytical model of a Hall thruster
  
  • Lafleur Trevor
  • Chabert Pascal
  Physics of Plasmas, American Institute of Physics, 2024, 31 (9), pp.093507. Hall thrusters are one of the most successful and prevalent electric propulsion systems for spacecraft in use today. However, they are also complex devices and their unique E×B configuration makes modeling of the underlying plasma discharge challenging. In this work, a steady-state model of a Hall thruster is developed and a complete analytical solution presented that is shown to be in reasonable agreement with experimental measurements. A characterization of the discharge shows that the peak plasma density and ionization rate nearly coincide and both occur upstream of the peak electric field. The peak locations also shift as the thruster operating conditions are varied. Three key similarity parameters emerge that govern the plasma discharge and which are connected via a thruster current–voltage relation: a normalized discharge current, a normalized discharge voltage, and an amalgamated parameter, α¯, that contains all system geometric and magnetic field information. For a given normalized discharge voltage, the similarity parameter α¯ must lie within a certain range to enable high thruster performance. When applied to a krypton thruster, the model shows that both the propellant mass flow rate and the magnetic field strength must be simultaneously adjusted to achieve similar efficiency to a xenon thruster (for the same thruster geometry, discharge voltage, and power level). (10.1063/5.0220130)
  DOI : 10.1063/5.0220130
• Machine learning-based prediction of the electron energy distribution function and electron density of argon plasma from the optical emission spectra
  
  • Arellano Fatima Jenina
  • Kusaba Minoru
  • Wu Stephen
  • Yoshida Ryo
  • Donkó Zoltán
  • Hartmann Peter
  • Tsankov Tsanko V
  • Hamaguchi Satoshi
  Journal of Vacuum Science & Technology A, American Vacuum Society, 2024, 42 (5), pp.053001. Optical emission spectroscopy (OES) is a highly valuable tool for plasma characterization due to its non-intrusive and versatile nature. The intensities of the emission lines contain information about the parameters of the underlying plasma -electron density n e and temperature or more generally the electron energy distribution function (EEDF). This study aims to obtain the EEDF and ne from the OES data of argon plasma with machine learning (ML) techniques. Two different models, i.e., the Kernel Regression for Functional Data (KRFD) and an artificial neural network (ANN), are used to predict the normalized EEDF and Random Forest (RF) regression is used to predict n e . The ML models are trained with computed plasma data obtained from Particle-in-Cell/Monte Carlo Collision simulations coupled with a collisional-radiative model. All three ML models developed in this study are found to predict with high accuracy what they are trained to predict when the simulated test OES data are used as the input data. When the experimentally measured OES data are used as the input data, the ANN-based model predicts the normalized EEDF with reasonable accuracy under the discharge conditions where the simulation data are known to agree well with the corresponding experimental data. However, the capabilities of the KRFD and RF models to predict the EEDF and ne from experimental OES data are found to be rather limited, reflecting the need for further improvement of the robustness of these models. (10.1116/6.0003731)
  DOI : 10.1116/6.0003731
• 3D cylindrical BGK model of electron phase-space holes with finite velocity and polarization drift
  
  • Gauthier Gaëtan
  • Chust Thomas
  • Le Contel Olivier
  • Savoini Philippe
  Physics of Plasmas, American Institute of Physics, 2024, 31 (3), pp.032306. Nonlinear kinetic structures, called electron phase-space holes (EHs), are regularly observed in space and experimental magnetized plasmas. The existence of EHs is conditioned and varies according to the ambient magnetic field and the parameters of the electron beam(s) that may generate them. The objective of this paper is to extend the 3D Bernstein–Greene–Kruskal model with cylindrical geometry developed by L.-J. Chen et al. [“Bernstein–Greene–Kruskal solitary waves in three-dimensional magnetized plasma,” Phys. Rev. E 69, 055401 (2004)] and L.-J. Chen et al., [“On the width-amplitude inequality of electron phase space holes,” J. Geophys. Res. 110, A09211 (2005)] to include simultaneously finite effects due to (i) the strength of the ambient magnetic field B0, by modifying the Poisson equation with a term derived from the electron polarization current, and (ii) the drift velocity ue of the background plasma electrons with respect to the EH, by considering velocity-shifted Maxwellian distributions for the boundary conditions. This allows us to more realistically determine the distributions of trapped and passing particles forming the EHs, as well as the width-amplitude relationships for their existence. (10.1063/5.0181180)
  DOI : 10.1063/5.0181180
• Poloidal localization of the explosive onset of edge localized modes
  
  • Trier E.
  • Hennequin P.
  • Maraschek M.
  • Giannone L.
  • Vanovac B.
  Nuclear Fusion, IOP Publishing, 2024, 64 (2), pp.026004. In ASDEX Upgrade lower single null H-mode plasmas, the onset of the explosive phase of Edge Localized Modes (ELMs) is poloidally localized in the X-point/outer strike point (X/OSP) region. From this location, ELMs develop on average towards the low-field and high-field sides in typically 100 μ s . An associated magnetic activity localized in the X/OSP region is also observed in-between ELMs, at a lower level than at the ELM onset, and interpreted as being due to perturbed currents connected to the divertor target-s. Its broadband spectra typically extend up to 100 k H z –due to short-lived events of variable frequencies–and are dominated by n = 1 toroidal mode numbers rotating in the counter-current direction. (10.1088/1741-4326/ad13ae)
  DOI : 10.1088/1741-4326/ad13ae
• Multi-Instrument Observation of the Ionospheric Irregularities and Disturbances during the 23–24 March 2023 Geomagnetic Storm
  
  • Tahir Afnan
  • Wu Falin
  • Shah Munawar
  • Amory-Mazaudier Christine
  • Jamjareegulgarn Punyawi
  • Verhulst Tobias G W
  • Ameen Muhammad Ayyaz
  Remote Sensing, MDPI, 2024, 16 (9), pp.1594. This work investigates the ionospheric response to the March 2023 geomagnetic storm over American and Asian sectors from total electron content (TEC), rate of TEC index, ionospheric heights, Swarm plasma density, radio occultation profiles of Formosat-7/Cosmic-2 (F7/C2), Fabry-Perot interferometer driven neutral winds, and E region electric field. During the storm’s main phase, post-sunset equatorial plasma bubbles (EPBs) extend to higher latitudes in the western American longitudes, showing significant longitudinal differences in the American sector. Over the Indian longitudes, suppression of post-sunset irregularities is observed, attributed to the westward prompt penetration electric field (PPEF). At the early recovery phase, the presence of post-midnight/near-sunrise EPBs till post-sunrise hours in the American sector is associated with the disturbance of dynamo-electric fields (DDEF). Additionally, a strong consistency between F7/C2 derived amplitude scintillation (S4) ≥ 0.5 and EPB occurrences is observed. Furthermore, a strong eastward electric field induced an increase in daytime TEC beyond the equatorial ionization anomaly crest in the American region, which occurred during the storm’s main phase. Both the Asian and American sectors exhibit negative ionospheric storms and inhibition of ionospheric irregularities at the recovery phase, which is dominated by the disturbance dynamo effect due to equatorward neutral winds. A slight increase in TEC in the Asian sector during the recovery phase could be explained by the combined effect of DDEF and thermospheric composition change. Overall, storm-time ionospheric variations are controlled by the combined effects of PPEF and DDEF. This study may further contribute to understanding the ionospheric responses under the influence of storm-phase and LT-dependent electric fields. (10.3390/rs16091594)
  DOI : 10.3390/rs16091594
• Realization of a gas puff imaging system on the Wendelstein 7-X stellarator
  
  • Terry J L
  • von Stechow A.
  • Baek S G
  • Ballinger S B
  • Grulke O.
  • von Sehren C.
  • Laube R.
  • Killer C.
  • Scharmer F.
  • Brunner K J
  • Knauer J.
  • Bois S.
  Review of Scientific Instruments, American Institute of Physics, 2024, 95 (9), pp.093517. A system for studying the spatiotemporal dynamics of fluctuations in the boundary of the W7-X plasma using the “Gas-Puff Imaging” (GPI) technique has been designed, constructed, installed, and operated. This GPI system addresses a number of challenges specific to long-pulse superconducting devices, such as W7-X, including the long distance between the plasma and the vacuum vessel wall, the long distance between the plasma and diagnostic ports, the range of last closed flux surface (LCFS) locations for different magnetic configurations in W7-X, and management of heat loads on the system’s plasma-facing components. The system features a pair of “converging–diverging” nozzles for partially collimating the gas puffed locally ≈135 mm radially outboard of the plasma boundary, a pop-up turning mirror for viewing the gas puff emission from the side (which also acts as a shutter for the re-entrant vacuum window), and a high-throughput optical system that collects visible emission resulting from the interaction between the puffed gas and the plasma and directs it along a water-cooled re-entrant tube directly onto the 8 × 16 pixel detector array of the fast camera. The DEGAS 2 neutral code was used to simulate the Hα (656 nm) and HeI (587 nm) line emission expected from well-characterized gas-puffs of H2 and He and excited within typical edge plasma profiles in W7-X, thereby predicting line brightnesses used to reduce the risks associated with system sensitivity and placement of the field of view. Operation of GPI on W7-X shows excellent signal-to-noise ratios (>100 at 2 Mframes/s) over the field of view for minimally perturbing gas puffs. The GPI system provides detailed measurements of the two-dimensional (radial and poloidal) dynamics of plasma fluctuations in the W7-X edge and scrape-off layer and in and around the magnetic islands outside the LCFS that make up the island divertor configuration employed on W7-X. (10.1063/5.0219336)
  DOI : 10.1063/5.0219336
• Interplay of the magnetic and current density field topologies in axisymmetric devices for magnetic confinement fusion
  
  • Firpo Marie-Christine
  Journal of Plasma Physics, Cambridge University Press (CUP), 2024. In magnetic confinement fusion devices close to axisymmetry, such as tokamaks, a key element is the winding profile of the magnetic field lines, or its inverse, the safety profile $q=q_{\mathbf{B}}$. A corresponding profile, $q_{\mathbf{J}}$, can be defined for the current density field lines. Amp\`{e}re's law relates any mode of current perturbation $\delta \mathbf{J}_{m,n}$ with a mode of magnetic perturbation $\delta \mathbf{B}_{m,n}$. It is shown that the knowledge of the pair $(q_{\mathbf{B}},q_{\mathbf{J}})$ allows then to characterize the resonant, or non-resonant, nature of the modes for both the magnetic and current density field lines. The expression of $q_{\mathbf{J}}$ in flux coordinate is derived. Including this calculation in the real-time Grad-Shafranov equilibrium reconstruction codes would yield a comprehensive view of the magnetics. The monitoring of the pair $(q_{\mathbf{B}},q_{\mathbf{J}})$ would then allow investigating the role played by the resonant modes for the current density, that are current filamentary modes, in the plasma small-scale turbulence. By driving the magnetic and current density profiles apart so that the images of $q_{\mathbf{B}}$ and $q_{\mathbf{J}}$ are disjoint, these filamentary modes would not impact the magnetic field topology, being not associated to magnetic islands but to non-resonant magnetic modes. It remains to be explored to which extent such a configuration, where the spectrum of tiny current density filaments produces a spectrum of magnetic modes that has practically no effect on heat transport, is beneficial. (10.1017/S002237782400103X)
  DOI : 10.1017/S002237782400103X
• Statistical analysis of high-frequency whistler waves at Earth's bow shock: Further support for stochastic shock drift acceleration
  
  • Amano Takanobu
  • Masuda Miki
  • Oka Mitsuo
  • Kitamura Naritoshi
  • Le Contel Olivier
  • Gershman Daniel J
  Physics of Plasmas, American Institute of Physics, 2024, 31 (4), pp.042903. We statistically investigate high-frequency whistler waves (with frequencies higher than ∼10% of the local electron cyclotron frequency) at Earth's bow shock using magnetospheric multi-scale (MMS) spacecraft observations. We focus specifically on the wave power within the shock transition layer, where we expect electron acceleration via stochastic shock drift acceleration (SSDA) to occur associated with efficient pitch-angle scattering by whistler waves. We find that the wave power is positively correlated with both the Alfvén Mach number in the normal incidence frame MA and in the de Hoffmann–Teller frame MA/cos θBn⁠. The empirical relation with MA/cos θBn is compared with the theory of SSDA that predicts a threshold wave power proportional to (MA/cos θBn)−2⁠. The result suggests that the wave power exceeds the theoretical threshold for MA/cos θBn≳30–60⁠, beyond which efficient electron acceleration is expected. This aligns very well with previous statistical analysis of electron acceleration at Earth's bow shock [Oka et al., Geophys. Res. Lett. 33, 5–6 (2006)]. Therefore, we consider that this study provides further support for SSDA as the mechanism of electron acceleration at Earth's bow shock. At higher-Mach-number astrophysical shocks, SSDA will be able to inject electrons into the diffusive shock acceleration process for subsequent acceleration to cosmic-ray energies. (10.1063/5.0196502)
  DOI : 10.1063/5.0196502
• Longitudinal features of day- and night-time ionospheric annual variations during the solar cycles 23 and 24
  
  • Younas Waqar
  • Khan Majid
  • Amory-Mazaudier C.
  Advances in Space Research, Elsevier, 2024, 73 (9), pp.4426-4438. We present a study concerning the ionospheric annual variations (IAV) using the global ionospheric maps (GIMs). In this regard, the corresponding regional electron content (REC) is computed in four longitudinal sectors, namely Asia, Africa, America and Pacific. The features of day-and night-time IAV are investigated using (i) band-pass filters and (ii) summer to winter (SW) ratio of REC. The results indicate that IAV are stronger in the southern hemisphere as compared to its northern counterpart. The asymmetry in the amplitude of IAV is maximum for the Pacific region, followed by America, Africa and Asia. The IAV in southern hemisphere are regular ionospheric variations (RIAV) with positive and negative peaks occurring in the months of December and June, respectively. The northern hemisphere and latitudinal regions exhibit a day-time anomalous ionospheric annual variations (AIAV), during the peak years of the considered solar cycles, in which maxima (minima) occurs in local winter (summer). In this regard, the phase of AIAV is found to vary with solar activity. The night-time IAV show anomalous behavior in the northern hemisphere during the solar minimum. The SW ratio of day-time REC is less than unity at northern hemisphere during the peak of a solar cycle. However, the said ratio is always greater than one in southern counterpart. The fitting curve for day-time SW ratio has a strong negative slope in the northern hemisphere. The threshold of SSN (sunspot number) indicating the presence of the daytime winter anomaly at low-latitudes is found to be 25, 80, and 115 in the Africa, Asia-Pacific, and American regions, respectively. Additionally, this anomaly becomes observable in the mid-latitudes region of America and the Pacific region for SSN values exceeding 100 and 150, respectively. On the other hand, the correlation and fitting analysis demonstrate that night-time SW ratio enhances with increase in the solar activity. This result predicts that night-time winter anomaly can only be present during the periods of minimum and low solar activity. However, our analysis revealed that the night-time winter anomaly is observable only in the African low-latitude region for SSN<85. (10.1016/j.asr.2024.01.033)
  DOI : 10.1016/j.asr.2024.01.033
• Validation of short-pulse reflectometry turbulence measurements with a synthetic diagnostic
  
  • Krutkin O.
  • Kumar U.
  • Mazzi S.
  • Brunner S.
  • Coda S.
  • Rienäcker S.
  • van Rossem M.
  Nuclear Fusion, IOP Publishing, 2024, 64 (2), pp.026010. Experimental measurements of the turbulence amplitude utilizing a short pulse reflectometry method are presented. Two discharges with shaped plasma possessing opposite signs of triangularity are considered and a higher turbulence amplitude is found in the positive triangularity case. To confirm this result, a synthetic short pulse reflectometry diagnostic is developed. Local gyrokinetic modeling with the GENE code is carried out to produce turbulence relevant to the experimental conditions. This turbulence is then used as an input for the full-wave CUWA code to produce synthetic short pulse reflectometry signals. By matching synthetic and experimental reflectometry data, the difference between turbulence amplitudes in the two cases is confirmed. Additionally, the capability of the diagnostic to also measure the frequency spectrum of the turbulence is demonstrated. (10.1088/1741-4326/ad15b1)
  DOI : 10.1088/1741-4326/ad15b1
• Mechanisms of Fundamental Electromagnetic Wave Radiation in the Solar Wind
  
  • Krafft C.
  • Savoini P.
  • Polanco-Rodríguez F J
  The Astrophysical Journal Letters, Bristol : IOP Publishing, 2024, 967 (2), pp.L20. Large-scale and long-term two-dimensional particle-in-cell simulations performed for parameters relevant to type III solar radio bursts have provided new results on the generation mechanisms of fundamental electromagnetic waves radiated at the plasma frequency ω_p . The paper first considers the nonlinear wave interaction process of electromagnetic decay (EMD) in a homogeneous solar wind plasma with an electron-to-ion temperature ratio <i>T_e/T_i</i> &gt; 1. The dynamics of ion-acoustic waves (dispersion, spectra, growth/damping) is studied, and signatures confirming the three-wave interactions (cross-bicoherence, correlations between waves' phases and between waves' growths, resonance conditions) are provided. The decisive role played in EMD by the backscattered Langmuir waves coming from the electrostatic decay (ESD) is demonstrated. EMD can be triggered by ion acoustic waves coming from the two cascades of the faster and more intense ESD. The same study is then performed in a solar wind plasma with random density fluctuations. In this case, EMD is not suppressed but develops only within plasma regions of reduced or quasi-uniform density. It coexists with linear mode conversion (LMC) of Langmuir waves into electromagnetic radiation, which is the fastest and most prominent process, as well as with ESD. LMC can lead to enhanced occurrence of EMD in the early stage. Moreover, the impact of <i>T_e/T_i</i> on electromagnetic energy growth and saturation is shown to be rather weak. Ion-acoustic waves are heavily damped at <i>T_e</i> ∼ <i>T_i</i>, so that EMD is overcome by nonlinear induced scattering on thermal ions. In actual solar wind plasmas, EMD should be more easily observed in plasma regions weakly perturbed by the background density turbulence and where ion temperature is decreased. (10.3847/2041-8213/ad47b5)
  DOI : 10.3847/2041-8213/ad47b5
• Advanced Methods for Analyzing in-Situ Observations of Magnetic Reconnection
  
  • Hasegawa H.
  • Argall M. R.
  • Aunai N.
  • Bandyopadhyay R.
  • Bessho N.
  • Cohen I. J.
  • Denton R. E.
  • Dorelli J. C.
  • Egedal J.
  • Fuselier S. A.
  • Garnier P.
  • Génot V.
  • Graham D. B.
  • Hwang K. J.
  • Khotyaintsev Y. V.
  • Korovinskiy D. B.
  • Lavraud B.
  • Lenouvel Q.
  • Li T. C.
  • Liu Y. -H.
  • Michotte de Welle B.
  • Nakamura T. K. M.
  • Payne D. S.
  • Petrinec S. M.
  • Qi Y.
  • Rager A. C.
  • Reiff P. H.
  • Schroeder J. M.
  • Shuster J. R.
  • Sitnov M. I.
  • Stephens G. K.
  • Swisdak M.
  • Tian A. M.
  • Torbert R. B.
  • Trattner K. J.
  • Zenitani S.
  Space Science Reviews, Springer Verlag, 2024, 220. There is ample evidence for magnetic reconnection in the solar system, but it is a nontrivial task to visualize, to determine the proper approaches and frames to study, and in turn to elucidate the physical processes at work in reconnection regions from in-situ measurements of plasma particles and electromagnetic fields. Here an overview is given of a variety of single- and multi-spacecraft data analysis techniques that are key to revealing the context of in-situ observations of magnetic reconnection in space and for detecting and analyzing the diffusion regions where ions and/or electrons are demagnetized. We focus on recent advances in the era of the Magnetospheric Multiscale mission, which has made electron-scale, multi-point measurements of magnetic reconnection in and around Earth's magnetosphere. (10.1007/s11214-024-01095-w)
  DOI : 10.1007/s11214-024-01095-w
• Temporally Resolved Type III Solar Radio Bursts in the Frequency Range 3–13 MHz
  
  • Vecchio Antonio
  • Maksimovic Milan
  • Chrysaphi Nicolina
  • Kontar Eduard P.
  • Krupar Vratislav
  The Astrophysical Journal Letters, Bristol : IOP Publishing, 2024, 974. Radio observations from space allow to characterize solar radio bursts below the ionospheric cutoff, which are otherwise inaccessible, but suffer from low, insufficient temporal resolution. In this Letter we present novel, high-temporal resolution observations of type III solar radio bursts in the range 3–13 MHz. A dedicated configuration of the Radio and Plasma Waves (RPW) High Frequency Receiver (HFR) on the Solar Orbiter mission, allowing for a temporal resolution as high as ∼0.07 s (up to 2 orders of magnitude better than any other spacecraft measurements), provides for the very first time resolved measurements of the typical decay time values in this frequency range. The comparison of data with different time resolutions and acquired at different radial distances indicates that discrepancies with decay time values provided in previous studies are only due to the insufficient time resolution not allowing to accurately characterize decay times in this frequency range. The statistical analysis on a large sample of ∼500 type III radio bursts shows a power low decay time trend with a spectral index of ‑0.75 ± 0.03 when the median values for each frequency are considered. When these results are combined with previous observations, referring to frequencies outside the considered range, a spectral index of ‑1.00 ± 0.01 is found in the range ∼0.05–300 MHz, compatible with the presence of radio-wave scattering between 1 and 100 R _☉. (10.3847/2041-8213/ad7bbb)
  DOI : 10.3847/2041-8213/ad7bbb
• Interplay between the non-resonant streaming instability and self-generated pressure anisotropies
  
  • Marret Alexis
  • Ciardi Andrea
  • Smets Roch
  Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP): Policy P - Oxford Open Option A, 2024, 532 (4), pp.4082-4088. The non-thermal particles escaping from collision-less shocks into the surrounding medium can trigger a non-resonant streaming instability that converts parts of their drift kinetic energy into large amplitude magnetic field perturbations, and promote the confinement and acceleration of high energy cosmic rays. We present simulations of the instability using an hybrid-Particle-in-Cell approach including Monte Carlo collisions, and demonstrate that the development of the non-resonant mode is associated with important ion pressure anisotropies in the background plasma. Depending on the initial conditions, the anisotropies may act on the instability by lowering its growth and trigger secondary micro-instabilities. Introducing collisions with neutrals yield a strong reduction of the magnetic field amplification as predicted by linear fluid theory. In contrast, Coulomb collisions in fully ionized plasmas are found to mitigate the self-generated pressure anisotropies and promote the growth of the magnetic field. (10.1093/mnras/stae1773)
  DOI : 10.1093/mnras/stae1773
• Self-consistent calculation of the optical emission spectrum of an argon capacitively coupled plasma based on the coupling of particle simulation with a collisional-radiative model
  
  • Donkó Zoltán
  • Tsankov Tsanko V
  • Hartmann Peter
  • Jenina Arellano Fatima
  • Czarnetzki Uwe
  • Hamaguchi Satoshi
  Journal of Physics D: Applied Physics, IOP Publishing, 2024, 57 (37), pp.375209. We report the development of a computational framework for the calculation of the optical emission spectrum of a low-pressure argon capacitively coupled plasma (CCP), which is based on the coupling of a particle-in-cell/Monte Carlo collision simulation code with a diffusion-reaction-radiation code for Ar I excited levels. In this framework, the particle simulation provides the rates of the direct and stepwise electron-impact excitation and electron-impact de-excitation for 30 excited levels, as well as the rates of electron-impact direct and stepwise ionization. These rates are used in the solutions of the diffusion equations of the excited species in the second code, along with the radiative rates for a high number of Ar-I transitions. The calculations also consider pooling ionization, quenching reactions, and radial diffusion losses. The electron energy distribution function and the population densities of the 30 excited atomic levels are computed self-consistently. The calculations then provide the emission intensities that reproduce reasonably well the experimentally measured optical emission spectrum of a symmetric CCP source operated at 13.56 MHz with 300 V peak-to-peak voltage, in the 2-100 Pa pressure range. The accuracy of the approach appears to be limited by the one-dimensional nature of the model, the treatment of the radiation trapping through the use of escape factors, and the effects of radiative cascades from higher excited levels not taken into account in the model. (10.1088/1361-6463/ad4e42)
  DOI : 10.1088/1361-6463/ad4e42
• Structure and dynamics of the Hermean magnetosphere revealed by electron observations from the Mercury electron analyzer after the first three Mercury flybys of BepiColombo
  
  • Rojo M.
  • André N.
  • Aizawa Sae
  • Sauvaud Jean‐andré
  • Saito Y.
  • Harada Y.
  • Fedorov A.
  • Penou E.
  • Barthe A.
  • Persson M.
  • Yokota S.
  • Mazelle C.
  • Hadid L.
  • Delcourt D.
  • Fontaine D.
  • Fränz M.
  • Katra B.
  • Krupp N.
  • Murakami G.
  Astronomy & Astrophysics - A&A, EDP Sciences, 2024, 687, pp.A243. Context: The Mercury electron analyzer (MEA) obtained new electron observations during the first three Mercury flybys by BepiColombo on October 1, 2021 (MFB1), June 23 , 2022 (MFB2), and June 19, 2023 (MFB3). BepiColombo entered the dusk side magnetotail from the flank magnetosheath in the northern hemisphere, crossed the Mercury solar orbital equator around midnight in the magnetotail, traveled from midnight to dawn in the southern hemisphere near the closest approach, and exited from the post-dawn magnetosphere into the dayside magnetosheath. Aims: We aim to identify the magnetospheric boundaries and describe the structure and dynamics of the electron populations observed in the various regions explored along the flyby trajectories. Methods: We derive 4s time resolution electron densities and temperatures from MEA observations. We compare and contrast our new BepiColombo electron observations with those obtained from the Mariner 10 scanning electron spectrometer (SES) 49 yr ago. Results: A comparison to the averaged magnetospheric boundary crossings of MESSENGER indicates that the magnetosphere of Mercury was compressed during MFB1, close to its average state during MFB2, and highly compressed during MFB3. Our new MEA observations reveal the presence of a wake effect very close behind Mercury when BepiColombo entered the shadow region, a significant dusk-dawn asymmetry in electron fluxes in the nightside magnetosphere, and strongly fluctuating electrons with energies above 100s eV in the dawnside magnetosphere. Magnetospheric electron densities and temperatures are in the range of 10–30 cm −3 and above a few 100s eV in the pre-midnight-sector, and in the range of 1–100 cm −3 and well below 100 eV in the post-midnight sector, respectively. Conclusions: The MEA electron observations of different solar wind properties encountered during the first three Mercury flybys reveal the highly dynamic response and variability of the solar wind-magnetosphere interactions at Mercury. A good match is found between the electron plasma parameters derived by MEA in the various regions of the Hermean environment and similar ones derived in a few cases from other instruments on board BepiColombo. (10.1051/0004-6361/202449450)
  DOI : 10.1051/0004-6361/202449450
• Global Environmental Constraints on Magnetic Reconnection at the Magnetopause From In Situ Measurements
  
  • Michotte de Welle B.
  • Aunai N.
  • Lavraud B.
  • Génot V.
  • Nguyen G.
  • Ghisalberti A.
  • Smets R.
  • Jeandet A.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2024, 129 (8), pp.e2023JA032098. Progress in locating the X‐line on the magnetopause beyond the atypical due south interplanetary magnetic field (IMF) condition is hampered by the fact that the global plasma and field spatial distributions constraining where reconnection could develop on the magnetopause are poorly known. This work presents global maps of the magnetic shear, current density and reconnection rate, on the global dayside magnetopause, reconstructed from two decades of measurements from Cluster, Double Star, THEMIS and MMS missions. These maps, generated for various IMF and dipole tilt angles, offer a unique comparison point for models and observations. The magnetic shear obtained from vacuum magnetostatic draping is shown to be inconsistent with observed shear maps for IMF cone angles in 12.5° ± 2.5° ≤ | θ co | ≤ 45° ± 5°. Modeled maximum magnetic shear lines fail to incline toward the equator as the IMF clock angle increases, in contrast to those from observations and MHD models. Reconnection rate and current density maps are closer together than they are from the shear maps, but this similarity vanishes for increasingly radial IMF orientations. The X‐lines maximizing the magnetic shear are the only ones to sharply turns toward and follow the anti‐parallel ridge at high latitude. We show the behavior of X‐lines with varying IMF clock and dipole tilt angles to be different as the IMF cone angle varies. Finally, we discuss a fundamental disagreement between X‐lines maximizing a given quantity on the magnetopause and predictions of local X‐line orientations. (10.1029/2023JA032098)
  DOI : 10.1029/2023JA032098
• Magnetospheric Venus Space Explorers (MVSE) mission: A proposal for understanding the dynamics of induced magnetospheres
  
  • Albers Roland
  • Andrews Henrik
  • Boccacci Gabriele
  • Pires Vasco D C
  • Laddha Sunny
  • Lundén Ville
  • Maraqten Nadim
  • Matias João
  • Krämer Eva
  • Schulz Leonard
  • Palanca Ines Terraza
  • Teubenbacher Daniel
  • Baskevitch Claire
  • Covella Francesca
  • Cressa Luca
  • Moreno Juan Garrido
  • Gillmayr Jana
  • Hollowood Joshua
  • Huber Kilian
  • Kutnohorsky Viktoria
  • Lennerstrand Sofia
  • Malatinszky Adel
  • Manzini Davide
  • Maurer Manuel
  • Nidelea Daiana Maria Alessandra
  • Rigon Luca
  • Sinjan Jonas
  • Suarez Crisel
  • Viviano Mirko
  • Knutsen Elise Wright
  Acta Astronautica, Elsevier, 2024, 221, pp.194-205. Induced magnetospheres form around planetary bodies with atmospheres through the interaction of the solar wind with their ionosphere. Induced magnetospheres are highly dependent on the so- lar wind conditions and have only been studied with single spacecraft missions in the past. This gap in knowledge could be addressed by a multi-spacecraft plasma mission, optimized for study- ing global spatial and temporal variations in the magnetospheric system around Venus, which hosts the most prominent example of an induced magnetosphere in our solar system. The MVSE mission comprises four satellites, of which three are identical scientific spacecraft, carrying the same suite of instruments probing different regions of the induced magnetosphere and the solar wind simultaneously. The fourth spacecraft is the transfer vehicle which acts as a relay satellite for communications at Venus. In this way, changes in the solar wind conditions and extreme solar events can be observed, and their effects can be quantified as they propagate through the Venusian induced magnetosphere. Additionally, energy transfer in the Venusian induced mag- netosphere can be investigated. The scientific payload includes instrumentation to measure the magnetic field, electric field, and ion-electron velocity distributions. This study presents the scientific motivation for the mission as well as requirements and the resulting mission design. Concretely, a mission timeline along with a complete spacecraft design, including mass, power, communication, propulsion and thermal budgets are given. This mission was initially conceived at the Alpbach Summer School 2022 and refined during a week-long study at ESA’s Concurrent Design Facility in Redu, Belgium (10.1016/j.actaastro.2024.05.017)
  DOI : 10.1016/j.actaastro.2024.05.017
• Mercury's plasma environment after BepiColombo's third flyby
  
  • Hadid Lina Z.
  • Delcourt Dominique
  • Harada Yuki
  • Rojo Mathias
  • Aizawa Sae
  • Saito Yoshifumi
  • André Nicolas
  • Glass Austin N.
  • Raines Jim M.
  • Yokota Shoichiro
  • Fränz Markus
  • Katra Bruno
  • Verdeil Christophe
  • Fiethe Björn
  • Leblanc François
  • Modolo Ronan
  • Fontaine Dominique
  • Krupp Norbert
  • Krüger Harald
  • Leblanc Frédéric
  • Fischer Henning
  • Berthelier Jean-Jacques
  • Sauvaud Jean-André
  • Murakami Go
  • Matsuda Shoya
  Communications Physics, Nature Research, 2024, 7, pp.316. Understanding Mercury's magnetosphere is crucial for advancing our comprehension of how the solar wind interacts with the planetary magnetospheres. Despite previous missions, several gaps remain in our knowledge of Mercury's plasma environment. Here, we present findings from BepiColombo's third flyby, offering a synoptic view of the large scale structure and composition of Mercury's magnetosphere. The Mass Spectrum Analyzer (MSA), Mass Ion Analyzer (MIA), and Mass Electron Analyzer (MEA) on the magnetospheric orbiter reveal insights, including the identification of trapped energetic hydrogen (H⁺) with energies around 20 keV e^‑1 evidencing a ring current, and a cold ion plasma with energies below 50 eV e^‑1. Additionally, we observe a Low-Latitude Boundary Layer (LLBL), which is a region of turbulent plasma at the edge of the magnetosphere, characterized by bursty ion enhancements, indicating an ongoing injection process in the duskside magnetosphere flank. These observations during cruise phase provide a tantalizing glimpse of future discoveries expected from the Mercury Plasma Particle Experiment (MPPE) instruments after orbit insertion, promising broader impacts on our understanding of planetary magnetospheres. (10.1038/s42005-024-01766-8)
  DOI : 10.1038/s42005-024-01766-8
• Occurrence rate of equatorial Spread F and GPS ROTI in the ionospheric anomaly region over Vietnam
  
  • Pham Thi Thu Hong
  • Christine Amory Mazaudier
  • Le Huy Minh
  • Saito Susumu
  • Nguyen Thanh Dung
  • Luong Thi Ngoc
  • Luu Viet Hung
  • Nguyen Chien Thang
  • Nguyen Ha Thanh
  • Michi Nishioka
  • Septi Perwitasari
  Vietnam Journal of Earth Sciences, Vietnam Academy of Science and Technology (VAST), 2024, 46 (4), pp.553-569. This paper presents the first observations of the occurrence rates of Spread F and GPS total electron content (TEC) index (ROTI) over Vietnam at the equatorial trough and the northern tropical crest of ionization anomaly in the Asian sector. The data have been examined for the monthly and nighttime variations in the occurrence of these two data at Bac Lieu (9.28°N, 105.73°E, dip: 1.73°N) and Phu Thuy (21.03°N, 105.95°E, dip: 14.49°N) during 2023. For Bac Lieu, the monthly variation in the occurrence of the range Spread F (RSF) has the maxima in the February, May, and September months, while the mixed Spread-F (MSF) and ROTI occurrences exhibit a semiannual asymmetry with peaks in March/April and October. For the nighttime variation, occurrence peaks at 1915-1930 LT for RSF, at about 1945-2100 LT for MSF, and between 2030-2330 LT for ROTI. Regarding the frequency Spread F (FSF) occurrence, the maximum values in the monthly variation are in April, and the nighttime variation peaks at about 2115-2315 LT. For Phu Thuy, the monthly variation of RSF, MSF, and ROTI occurrences also exhibit a semiannual asymmetry with peaks in March/April and October. These peak magnitudes are largest for ROTI, moderate for MSF, and smallest for RSF. The nighttime variation of RSF, MSF, and ROTI occurrence peaks show intense season changes from winter to autumn at pre-midnight, spring at post-midnight, and summer at postmidnight. The FSF occurrences are more significant in summer than in other seasons, mainly after midnight. The time order appearance of the Spread F types at Bac Lieu and Phu Thuy is first of RSF, then MSF, and finally FSF. This could reflect that the formation mechanisms of Spread F types are different and require further research. Our observations also showed that the post-midnight occurrence of Spread F is much larger than ROTI at Bac Lieu and Phu Thuy. The monthly variations in occurrence rates of Spread F and ROTI at Bac Lieu and Phu Thuy are similar, but these occurrence rates at Bac Lieu are usually larger than at Phu Thuy. (10.15625/2615-9783/21368)
  DOI : 10.15625/2615-9783/21368