Publications

2026

• Formation of gradients of atomic oxygen in nanosecond plasma for plasma-assisted detonation: experimental and numerical study
  
  • Lafaurie Victor
  • Shu Zhan
  • Zhang B
  • Terentjeviene M
  • Billeau Jean-Baptiste
  • Orel Inna
  • Hoyos Aristizabal Samuel
  • Vidal Pierre
  • Starikovskaia Svetlana
  Plasma Sources Science and Technology, IOP Publishing, 2026, 35 (2), pp.025022. This work aims at producing a gradient of atomic oxygen on a scale of 10 cm in a plane-to-plane nanosecond discharge in 150 mbar of air with a varying gap size for applications in combustion and ignition of detonation waves. Local measurements of atomic oxygen density along the discharge span, at varying heights between high-voltage and grounded electrode, are performed with Xe calibrated O-TALIF and validated by 2D numerical modelling. They both show existence of a gradient of atomic density of oxygen along the span. Reduced electric field is measured with two experimental techniques: optical emission spectroscopy by a spectral band intensity ratio of the first negative system and the second positive system of nitrogen, and E-FISH. It is also compared with numerical modelling. All techniques show existence of a gradient of reduced electric field along the span. This distribution of reduced electric field, in combination with the non-uniform energy deposition in the plasma, is shown to explain the measured gradient of density of atomic oxygen. (10.1088/1361-6595/ae3f53)
  DOI : 10.1088/1361-6595/ae3f53
• Spectral Properties and Energy Injection in Mercury's Magnetotail Current Sheet
  
  • Li Xinmin
  • Dong Chuanfei
  • Wang Liang
  • Aizawa Sae
  • Hadid L. Z.
  • Zhang Chi
  • Zhou Hongyang
  • Slavin James
  • Gao Jiawei
  • Stumpo Mirko
  • Zhang Wei
  Geophysical Research Letters, American Geophysical Union, 2026, 53 (4). Abstract Mercury's magnetotail hosts a thin and highly dynamic current sheet (CS), where magnetic reconnection and strong fluctuations frequently occur. Here, we statistically analyze magnetic field power spectra across 370 magnetotail CSs observed by MESSENGER. About 20% of the events are quasi‐laminar, showing single power‐law spectra, whereas ∼80% are turbulent, exhibiting a spectral break separating inertial and kinetic ranges. A dawn–dusk asymmetry is identified: inertial‐range slopes are systematically shallower on the dawnside, whereas kinetic‐range slopes are steeper, indicating more developed turbulence there, consistent with the higher occurrence of reconnection‐related processes on the dawnside. Component analysis shows that the transverse components, orthogonal to the tail‐aligned principal field ( B X ), display shallow slopes near −1 in the inertial range, suggesting energy injection at ion scales rather than a classical inertial range. These results demonstrate that Mercury's unique plasma environment fundamentally reshapes the initiation of turbulence and the redistribution of energy in the magnetotail. (10.1029/2025GL120144)
  DOI : 10.1029/2025GL120144
• Benchmark for two-dimensional large scale coherent structures in partially magnetized E × B plasmas—community collaboration & lessons learned
  
  • Powis Andrew T
  • Ahedo Eduardo
  • Álvarez Laguna Alejandro
  • Barléon Nicolas
  • Bello-Benítez Enrique
  • Beving Lucas
  • Boeuf Jean-Pierre
  • Bogopolsky Guillaume
  • Bourdon Anne
  • Cichocki Filippo
  • Cuenot Bénédicte
  • Denig Andrew
  • Donkó Zoltán
  • Elias Paul-Quentin
  • Encinar Miguel
  • Eremin Denis
  • Fajardo Pablo
  • Faraji Farbod
  • Fubiani Gwenael
  • Garrigues Laurent
  • Hara Kentaro
  • Hartmann Peter
  • Hopkins Matthew
  • Kaganovich Igor D
  • Knoll Aaron
  • Lapenta Giovanni
  • Magin Thierry
  • Marín-Cebrián Alberto
  • Merino Mario
  • Minelli Pierpaolo
  • Papahn Zadeh Mina
  • Parodi Pietro
  • Petronio Federico
  • Reza Maryam
  • Smolyakov Andrei I
  • Sydorenko Dmytro
  • Taccogna Francesco
  • Turner Miles M
  • Vermorel Olivier
  • Villafana Willca
  • Xu Liang
  Plasma Sources Science and Technology, IOP Publishing, 2026, 35 (2), pp.025002. Abstract Low-temperature plasmas (LTPs) are essential to both fundamental scientific research and critical industrial applications. As in many areas of science, numerical simulations have become a vital tool for uncovering new physical phenomena and guiding technological development. Code benchmarking remains crucial for verifying implementations and evaluating performance. This work continues the Landmark benchmark initiative, a series specifically designed to support the verification of LTP codes. In this study, seventeen simulation codes from a collaborative community of nineteen international institutions modeled a partially magnetized E × B Penning discharge. The emergence of large scale coherent structures, or rotating plasma spokes, endows this configuration with an enormous range of time scales, making it particularly challenging to simulate. The codes showed excellent agreement on the rotation frequency of the spoke as well as key plasma properties, including time-averaged ion density, plasma potential, and electron temperature profiles. Achieving this level of agreement came with challenges, and we share lessons learned on how to conduct future benchmarking campaigns. Comparing code implementations, computational hardware, and simulation runtimes also revealed interesting trends, which are summarized with the aim of guiding future plasma simulation software development. (10.1088/1361-6595/ae3985)
  DOI : 10.1088/1361-6595/ae3985
• Evidence of an Extended Alfvén Wing System at Enceladus: Cassini's Multi‐Instrument Observations
  
  • Hadid Lina Z.
  • Chust Thomas
  • Wahlund Jan-Erik
  • Morooka Michiko W
  • Roussos Elias
  • Witasse Olivier
  • Rabia Jonas
  • Pisa David
  • Kim Konstantin
  • Edberg Niklas J T
  • Rymer Abigail M
  • Lamy Laurent
  • Kotsiaros Stavros
  • Aizawa Sae
  • Jeandet Alexis
  • Modolo Ronan
  • André Nicolas
  • Canu Patrick
  • Bowers Charles F
  • Jia Xianzhe
  • Coates Andrew J
  • Jones Geraint H
  • Parsec‐wallis Anna
  • Agiwal Omakshi
  • Holmberg Mika K G
  • Nénon Quentin
  • Cao Hao
  • Kurth William S
  • Dougherty Michele K
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2026, 131 (2). We report in situ evidence for Enceladus' Alfvén wing system and its coupling with Saturn's ionosphere, based on multi-instrument observations from the Cassini spacecraft. Analysis of 36 events, including 13 from non-flyby paths, confirms the existence of a Main Alfvén Wing (MAW) current system generated at Enceladus, and associated Reflected Alfvén Wings (RAWs) occurring both at Saturn's ionosphere and on the density gradient of Enceladus' plasma torus, extending longitudinally to at least ∼ 120°(∼2,000 moon radii) downstream of the moon. Additionally, the observations reveal the systematic existence of a filamentation process of these large-scale Alfvénic perturbations (MAW and RAWs) during their propagation at any distance from their source. These findings demonstrate a more extensive electrodynamic coupling than previously reported for Enceladus and more generally for any moon-magnetosphere interaction. Moreover, the observation of energetic electron depletions and water-group ion signatures at longitudes even further from the moon supports the interpretation of an extended and persistent interaction region. These results highlight Enceladus' role in shaping Saturn's magnetospheric environment and underscore the importance of future missions to exhaustively analyze this type of complex interaction between a moon and a planet. Plain Language Summary Saturn's small icy moon Enceladus interacts with the planet's magnetic field, generating intermittent aurora in Saturn's upper atmosphere and electromagnetic waves that travel along invisible magnetic connections between them. During its 13-year mission, the Cassini spacecraft repeatedly crossed these magnetic field lines linked to Enceladus. We used data from several Cassini instruments to study how energy and particles move between the moon and Saturn. We detected wave activity characteristic of Alfvén waves (similar to vibrations on a string), forming as Saturn's magnetic field flows past Enceladus. Due to a complex system of reflection at both Saturn's ionosphere and the boundary of Enceladus' torus, these waves were found not only near the moon but also trailing far behind it, extending more than 504,000 km (over 2,000 times the moon's radius) behind it. This is the first time that Alfvén waves have been observed to be directly linked to the charged particles associated with Enceladus. This shows that Enceladus plays a much bigger role in shaping Saturn's space environment than previously thought, and reveals how moons can influence their host planet across vast distances. (10.1029/2025ja034657)
  DOI : 10.1029/2025ja034657
• High-order moment closure for nonmagnetized electrons in partially ionized plasmas
  
  • Alvarez Laguna A.
  • Hara K.
  Physical Review E, American Physical Society (APS), 2026, 113 (2), pp.025207. Linearized moment equations are often used to derive closure models for the hydrodynamic equations of multi-component plasmas near thermodynamic equilibrium. However, the linearized transport equations lose their validity in rarefied conditions or in the presence of strong electric fields, when the velocity distribution functions (VDFs) of the different species are non-Maxwellian and the drift between the species, i.e., the Mach number of the relative motion, becomes large. In this paper, we develop a nonlinear, high-order moment model for nonmagnetized electrons in partially ionized plasmas. We present a fourteen-moment model using a Hermitian expansion of the VDF that considers density, momentum, anisotropic pressure tensor, contracted heat flux vector, and contracted scalar kurtosis. We consider the relevant collisional processes in partially ionized plasmas, such as elastic and inelastic electron-neutral, electron-impact ionization, electron-electron Coulomb, and electron-ion Coulomb collisions. The collisional terms in the electron moment equations are integrated analytically for finite Mach numbers and accounting for the nonlinear terms in the Boltzmann operator, which are often neglected in linearized closure models. The proposed closure presents novel cross-coupling effects between moments of different tensorial nature within the collisional terms. The present nonlinear fourteen-moment model is benchmarked against a Monte Carlo simulation under a spatially homogeneous configuration, showing good agreement for a wide range of reduced electric field (e.g., up to 1000 Td) before runaway electrons occur, improving the results of a linear fourteen-moment model. (10.1103/lm1z-bzt3)
  DOI : 10.1103/lm1z-bzt3
• Magnetic reversals in a geodynamo model with a stably–stratified layer
  
  • Müller Nicolás P
  • Gissinger Christophe
  • Pétrélis François
  Physics of the Earth and Planetary Interiors, Elsevier, 2026, 371, pp.107502. We study the process of magnetic reversals in the presence of a stably-stratified layer below the core-mantle boundary using direct numerical simulations of the incompressible magnetohydrodynamics equations under the Boussinesq approximation in a spherical shell. We show that the dipolar-multipolar transition shifts to larger Rayleigh numbers in the presence of a stably-stratified layer, and that the dipolar strength of the magnetic field at the core-mantle boundary increases due to the skin effect. By imposing an heterogeneous heat flux at the outer boundary, we break the equatorial symmetry of the flow, and show that different heat flux patterns can trigger different dynamo solutions, such as hemispheric dynamos and polarity reversals. Using kinematic dynamo simulations, we show that the stably-stratified layer leads to similar growth rates of the dipole and quadrupole components of the magnetic field, playing the role of a conducting boundary layer, favouring magnetic reversals, and a dynamics predicted by low-dimensional models. (10.1016/j.pepi.2026.107502)
  DOI : 10.1016/j.pepi.2026.107502
• Cold atmospheric plasma mediates antibiofilm activity and sensitization to further plasma and antibiotic challenges against Staphylococcus aureus
  
  • Capuzzo Elena
  • Mas Fiol Guillem
  • Cayet Nadège
  • Varet Hugo
  • Pizarro-Cerda Javier
  • Frescaline Nadira
  • Rousseau Antoine
  • Dussurget Olivier
  FEMS Microbes, Oxford University Press, 2026, 7, pp.xtag039. Staphylococcus aureus biofilms pose significant challenges in clinical settings due to their growing resistance to conventional antibiotics. While cold atmospheric plasma (CAP) is known for its bactericidal effects, its impact on biofilm architecture and physiology, and subsequent antimicrobial susceptibility remains poorly understood. This study investigates the effects of CAP treatment on S. aureus biofilms. We demonstrate that CAP not only reduces biofilm but also disrupts biofilm architecture and alters bacterial cell morphology. Transcriptomic analysis reveals distinct gene expression profiles following treatments with CAP and hydrogen peroxide, one of its active components, highlighting unique stress responses. We further show that CAP treatment of S. aureus grown on agar plates sensitizes bacteria to additional CAP exposure and induces genomic alterations involved in cell envelope integrity, defence mechanisms and DNA replication, recombination, and repair. Importantly, CAP treatment enhances bacterial susceptibility to the topical antibiotic for wound care mupirocin. These findings provide novel insights into the mechanisms underlying CAP-mediated biofilm control and offer a promising strategy to potentiate existing antimicrobial therapies. (10.1093/femsmc/xtag039)
  DOI : 10.1093/femsmc/xtag039
• Anisotropic truncation for turbulent transport and zonal flows in the Hasegawa–Wakatani system
  
  • Guillon P
  • Angles R
  • Sarazin Yanick
  • Gürcan Ö
  Plasma Physics and Controlled Fusion, IOP Publishing, 2026, 68 (8), pp.085022. Reduced models based on an anisotropic truncation of the Fourier space, retaining only a few poloidal wave-numbers while keeping the full radial resolution, are developed and first applied to the Hasegawa–Wakatani system. The impact of the truncation is studied first by considering the fixed-gradient formulation, and by comparing to direct numerical simulations (DNSs). The turbulent particle flux, and the transition from quasi-two dimensional turbulence to the zonal flow (ZF) dominated state, are used as the main criteria for validation. It is found that at least 4 poloidal modes, distributed around the most unstable mode, are needed to observe a sharp transition, and that about 10 modes are needed to reproduce each transport regime. Then, similar reduced models are developed in a flux-driven formulation and compared to the DNS, focusing on two cases far from the nonlinear threshold of the transition from turbulence to zonal dominated states of the fixed gradient formulation. In that case, using 10 modes allows to match the probability distribution function of the particle flux of the DNS approximately. Considering the role played by different poloidal scales in the turbulent cascade, it is observed that in the turbulent state, an inverse energy cascade in radial wave-numbers takes place at large poloidal scales, while a forward enstrophy cascade in radial wave-numbers is observed to occur at smaller poloidal scales. Moreover, when they form, ZFs feed on poloidal scales that are around and slightly smaller than the injection scale, while giving their energy to the larger poloidal scales. In that case, there is an anisotropic inverse energy transfer, akin to inverse cascade, from the energy injection to the large poloidal scales through ZFs, while the forward enstrophy cascade seems to stay isotropic. (10.1088/1361-6587/ae92b2)
  DOI : 10.1088/1361-6587/ae92b2
• Plasma plume symmetrization by electron rotation and ion detachment properties in a diverging magnetic nozzle
  
  • Pioch Romain
  • Chabert Pascal
  • Désangles Victor
  Physical Review E, American Physical Society (APS), 2026, 113 (3), pp.035209. The ion flux direction in a rapidly diverging magnetic field and the role of Earth's magnetic field in plasma dynamics are investigated experimentally using a low power electron cyclotron resonance thruster. The comparison between ion trajectories measured with a directional Faraday cup and the magnetic field geometry allows us to assess some of the ion flow properties. The results show that the ion trajectories follow the magnetic field lines in the center part of the plasma plume but not on its edges, defining the detachment location. Once detached, ions follow straight line trajectories, and their detachment has a divergent nature. The effect of the thruster operating condition on these properties is explored. Plasma potential measurements carried out with an emissive probe reveal the presence of a large radial electric field, pointing outward at the detachment point, that explains the divergent nature of the ion detachment. The amplitude of the induced E × B drift rotation of the electrons in the nozzle damps the disymmetrizing influence of Earth's magnetic field on the electron dynamics and leads to an axisymmetric plasma plume. This mechanism is demonstrated using single particle simulations. (10.1103/3twz-bcvk)
  DOI : 10.1103/3twz-bcvk
• Equatorial ionospheric plasma bubbles during intense geomagnetic storms of Solar Cycle 25
  
  • Imtiaz Nadia
  • Calabia Andres
  • Anoruo Chukwuma
  • Zahid Aqsa
  • Amory-Mazaudier Christine
  • Adhikari Binod
  Annales Geophysicae, European Geosciences Union, 2026, 44 (1), pp.489-509. This study examines the low-latitude ionospheric response to four intense geomagnetic storms during Solar Cycle 25 (March, April, November 2023, and May 2024), focusing on Equatorial Ionization Anomaly (EIA) variations and post-sunset plasma irregularities. We used the Weimer (2005) model for Joule Heating (JH), Madrigal total electron content (TEC) maps, and GNSS-derived ROTI to analyze storm-time changes in EIA structure and equatorial plasma bubbles (EPBs). The May 2024 storm exhibited the strongest post-sunset JH, particularly near the June solstice, while March and April storms showed moderate JH and November the lowest. Equinox storms produced nearly symmetric JH patterns, while solstice storms revealed interhemispheric asymmetries. Following JH thresholds are used for the classification of storms: weak (20–30 mW m−2, November), moderate (30–50 mW m−2, March/April) and strong (>50 mW m−2, May). JH, together with storm-time electric fields and equatorial meridional winds, influence the location, strength, hemispheric asymmetry, and the generation or suppression of plasma irregularities of the EIA crest. The generation of ionospheric plasma irregularities and their geographical distribution strongly depend on EIA's density gradients and general structure. Well-developed double-crest EIAs with steep density gradients favor post-sunset irregularities, while single-crest or merged EIAs are less favorable. Fluctuations in the IMF Bz drive east-west prompt penetration electric fields that dynamically modulate the F region, altering the plasma fountain effect, the EIA structure, and the distribution of plasma bubbles after sunset. These results suggest that during geomagnetic storms, the combined effects of storm-driven electrodynamics and neutral winds modulate low-latitude ionospheric variability, influencing EIA dynamics and the formation of plasma irregularities. (10.5194/angeo-44-489-2026)
  DOI : 10.5194/angeo-44-489-2026
• Towards Gravitational Wave Turbulence within the Hadad-Zakharov metric
  
  • Gay Benoît
  • Babichev Eugeny
  • Galtier Sébastien
  • Noui Karim
  Phys.Rev.D, 2026, 113 (12), pp.124074. The theory of gravitational wave turbulence describes the long-term statistical behaviour of a set of weakly nonlinear interacting waves. In this paper, we aim to study aspects of gravitational turbulence within the framework of general relativity using the Hadad-Zakharov (HZ) metric. The latter is parameterised by four functions (the coefficients of a diagonal metric) that must satisfy seven non-trivial Einstein equations, six of which are independent. The issue of their mutual compatibility is therefore essential, yet it has so far been overlooked. In this work, we argue that these equations can be compatible in the weakly nonlinear regime under specific conditions. Our analytical investigation is complemented by direct numerical simulations performed with a new GPU-based code, TIGER. A comparative analysis of the evolution of the Ricci and Kretschmann scalars indicates that gravitational wave turbulence corresponds to the propagation of a genuine physical degree of freedom. These numerical findings, however, must be interpreted with caution, given the difficulty of satisfying all seven Einstein equations simultaneously with sufficient accuracy. On the other hand, our simulations reproduce well the expected properties of the wave turbulence regime, with the emergence of a dual cascade of energy and wave action, and for the latter the observation of the Kolmogorov-Zakharov spectrum. In addition, our analysis reveals that the canonical variables of the problem evolve towards a nearly Gaussian statistical distribution punctuated by intermittent coherent (spatially localised and long-living) structures. In contrast to the canonical variables, the structure functions of the gauge-invariant metric components exhibit monofractal behaviour, which is a classical property of wave turbulence. (10.1103/vc5p-c3w8)
  DOI : 10.1103/vc5p-c3w8
• Mercury’s Low‐Latitude Boundary Layer: Identification of Distinct Proton Populations Using MESSENGER Spacecraft Data
  
  • Wang X.
  • Hadid L. Z.
  • Aizawa S.
  • Sahraoui F.
  • Raines J M
  • Lavraud B.
  Journal of Geophysical Research. Planets, Wiley-Blackwell, 2026, 131 (5), pp.e2025JE009617. We have performed a comprehensive analysis of Mercury's Low-Latitude Boundary Layer (LLBL) using data from the MErcury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) spacecraft during its orbital phase. Using combined magnetic field and ion measurements, we identified 202 LLBL events and categorized them into three distinct types based on proton energy distributions: single-population, double-population, and energy-shifted LLBLs. While the first two types have been observed at Earth, the third is reported here for the first time in a planetary magnetosphere. Each type exhibits unique ion characteristics and distinct local time distribution: (a) single-population LLBLs show magnetosheath-like energy spectra; (b) double-population LLBLs contain two coexisting components with energy similar to that of the magnetosheath and magnetosphere; and (c) energy-shifted LLBLs exhibit a smooth energy increase from the magnetosheath level to the magnetospheric level. These types are clearly separated in local time, with singlepopulation LLBLs near the subsolar region, double-population LLBLs extending to dusk, and energy-shifted LLBLs on the dawnside, reflecting distinct plasma transport and energization processes. Energy-shifted LLBLs exhibit significant perpendicular energization in the dawn region, where magnetosheath ions entering the magnetosphere drift dawnward and are further energized by cross-field potential drops. Mercury's smaller geometric radius and magnetic field curvature, which lead to stronger ion drift, likely make this drift-driven energization more pronounced than at Earth. These results offer new insight into plasma transport across Mercury's magnetopause and lay the foundation for future BepiColombo investigations, which will provide higher temporal and energy resolution multi-point observations of Mercury's magnetospheric dynamics.</p><p>Plain Language Summary Mercury, the smallest and closest planet to the Sun in our Solar System, has a magnetic field that interacts with the solar wind, a fast stream of charged particles from the Sun. At this interaction region, a boundary layer forms that affects how solar wind particles enter the magnetosphere. Understanding the formation of this boundary helps us learn how Mercury's space environment works and how it differs from Earth's. Using observations from NASA's MESSENGER spacecraft, we examined more than 200 events in this boundary region at low latitudes. We found that the energy distribution of particles falls into three categories, each showing different energy patterns and occurring at different local times around the planet. One category, where particle energies gradually increase as they move inward, has never been reported at any planet before. These findings offer new clues to how particles and energy are transported in Mercury's magnetic environment and will help interpret upcoming measurements from the BepiColombo mission (10.1029/2025je009617)
  DOI : 10.1029/2025je009617
• Climatology of Plasma Irregularities Using ROTI Index From 2008 to 2023 in East West Asia
  
  • Drabindra Pandit
  • Rolland Fleury
  • Christine Amory‐mazaudier
  Space Weather: The International Journal of Research and Applications, American Geophysical Union (AGU), 2026, 24 (4), pp.e2025SW004759. This study investigates characteristics of ionospheric irregularities over the East–West Asian equatorial region using the Rate of TEC Index (ROTI) derived from Global Navigation Satellite System (GNSS) measurements. Data from four stations (GUAM, PIMO, CUSV, and IISC) were analyzed for 2008–2023, covering solar cycle (SC) 24 and the ascending phase of SC 25. While our findings are generally aligned with previous research, this work presents new insights into the complex behavior of ionospheric scintillation in this sector. A key finding is the significant spatial variability in irregularity occurrence, with stations at similar magnetic dip (11–13°) exhibiting varying activity levels. Notable longitudinal asymmetries were also identified, particularly at GUAM, which shows reduced autumnal activity, likely due to local differences in Pre‐Reversal Enhancement (PRE) and magnetic declination. Our study shows a clear daily pattern: scintillation begins after sunset (18:00–19:00 LT), peaks in the late evening (20:00–21:30 LT), and declines by early morning. A slight increase in ROTI is consistently observed just before sunrise at all locations. Temporally, results show dependence on the 11‐year SC and a distinct seasonal pattern, with activity concentrated in equinoctial months. The spring maximum is generally stronger than the autumn one across stations. Finally, although the long‐term trend follows the SC, the relationship is non‐linear. Outliers, such as anomalous activity in 2019, demonstrate that while the Sunspot Number (SSN) is a primary long‐term driver, scintillation is also modulated by short‐term geophysical phenomena. (10.1029/2025SW004759)
  DOI : 10.1029/2025SW004759
• Electron temperatures in the ionosphere of Venus from Solar Orbiter/Radio and Plasma Waves instrument
  
  • Vecchio A.
  • Maksimovic M.
  • Galand M. I. F.
  • Bonnin X.
  • Astier P.-L.
  • Edberg N. J. T.
  • Píša D.
  • Boldú J. J.
  • Matteini L.
  • Chust T.
  • Hadid L. Z.
  • Kretzschmar Matthieu
  • Khotyaintsev Yu. V.
  • Souček J.
  • Horbury T.
  • Bale S. D.
  Astronomy & Astrophysics - A&A, EDP Sciences, 2026, 709. Context. On February 18, 2025, Solar Orbiter (SO) completed its fourth gravity assist maneuver of Venus (VGAM4) and reached an unprecedented proximity coming within 378 km of the planet. This flyby was necessary to steer the spacecraft into an orbit outside the plane of the ecliptic. Near the closest approach, only the Radio and Plasma Wave (RPW) and Magnetometer (MAG) instruments were operational; this enabled high-cadence measurements to be taken to investigate the plasma properties of the Venusian ionosphere. Aims. The main goal of this study is to derive the electron density and temperature in the ionosphere of Venus using electric potential measurements from RPW, and to characterize them. Methods. During approximately five minutes around the closest approach, the High Frequency Receiver of RPW detected radio emissions of a type naturally generated by planetary ionospheres whose frequency can be related to the electron density. Using quasithermal noise spectroscopy, we inferred the electron temperature at discrete altitudes and solar zenith angles. Results. Solar Orbiter measured an average density and electron temperature in the ionosphere of Venus of 12 385 ± 148 cm⁻³ and 0.43 ± 0.05 eV, respectively. These values are in agreement with in-situ measurements by Pioneer Venus Orbiter (PVO) obtained at the solar maximum. Binned magnetic fields and temperatures are anticorrelated, which suggests that the magnetic flux ropes, observed in the Venus ionosphere, are more likely non-force-free structures. Conclusions. The findings presented in this paper, together with the measurement from the Parker Solar Probe (PSP) during the third gravity assist, support the conclusion that the plasma density in the Venusian ionosphere above 350 km varies with solar activity, whereas the electron temperature shows a much weaker dependence. Notably, the electron temperature remains consistent across the three missions (SO, PSP, and PVO), despite varying levels of solar activity. This suggests that, over the altitude and solar zenith regions probed, the thermal structure of the Venusian ionosphere is not driven by solar extreme ultraviolet (EUV) heating alone, but is also shaped by external heat sources near the ionopause. Processes such as the damping of whistler mode waves, solar wind ion heating, and thermal conduction from the hot ionosheath appear to play a major role. (10.1051/0004-6361/202557868)
  DOI : 10.1051/0004-6361/202557868
• Mutual impedance experiments in a laboratory plasma: Experimental validation of numerical modeling
  
  • Dazzi P.
  • Henri P.
  • Bucciantini L.
  • Briaud E.
  • Brochot J. Y.
  • de Keyser J.
  • Edberg N. J. T.
  • Issautier K.
  • Kretzschmar Matthieu
  • Lecas T.
  • Revillet C.
  • Souffi H.
  • Vengeons G.
  • Wattieaux G.
  Astronomy & Astrophysics - A&A, EDP Sciences, 2026, 707. Context. In situ measurements of space plasma are necessary to explore heliospheric and planetary ionized environments. Mutual impedance experiments are an active plasma diagnostic technique used to measure the properties of space plasmas, including the plasma density and the electron temperature. Although various models have been developed for unmagnetized space plasmas, they fail to describe the instrument behavior in magnetized plasmas, such as the ionosphere and magnetosphere of magnetized planets and moons. A quantitative instrument model of the mutual impedance experiment is required, however, for current and future space missions, including ESA/JAXA BepiColombo and ESA JUICE, which will both conduct mutual impedance experiments (PWI/AM2P and RPWI/MIME, respectively). Aims. We develop an instrument model for exploring and quantitatively characterizing mutual impedance experiment measurements performed in planetary plasmas, with the goal of providing in situ diagnostics of the plasma density and electron temperature. Methods. To reach this goal, we combined numerical investigation and laboratory experiments. We investigated the experimental regime of high magnetization for the first time, where the electron gyrofrequency is higher than the plasma frequency, both experimentally and numerically. On the experimental side, we built a setup composed of a plasma chamber, a mutual impedance experiment, and a Langmuir probe. With this, we achieved a controlled plasma environment representative of magnetized space plasmas, which we diagnosed with two independent plasma instruments. On the numerical side, we developed a model for magnetized mutual impedance experiments that took the geometry of the mutual impedance antennas and the plasma chamber into account and that employed a kinetic linear description of the plasma electrons. Results. First, we characterized the plasma environment generated in the plasma chamber: the achievable plasma parameters, the stability, and the repeatability of the plasma conditions. Second, we validated the instrument model by comparing the numerical model predictions to the measurements obtained in the plasma chamber. Third, we extracted the plasma density and temperature from in situ mutual impedance measurements using our new numerical instrument model, and we validated them using the independent in situ measurements from the Langmuir probe. Conclusions. This work (i) proves that mutual impedance experiments are able to provide robust plasma diagnostics in a magnetized space plasma environment, and (ii) develops a methodological framework that will be used for the planetary space missions BepiColombo and JUICE to perform both the in-flight calibration and the exploitation of the measurements from PWI/AM2P and RPWI/MIME, respectively, in the magnetospheres of Mercury, Jupiter, and Ganymede. (10.1051/0004-6361/202554409)
  DOI : 10.1051/0004-6361/202554409
• Global plasma modeling of an air-breathing gridded-ion thruster for very low Earth orbit applications
  
  • Carer Charlélie
  • Verdier Solène
  • Flack Léo
  • Scemama Adrien
  • Petronio Federico
  Physics of Plasmas, American Institute of Physics, 2026, 33 (8). A volume-averaged (zero-dimensional) global model of an atmospheric nitrogen–oxygen mixture is proposed. This model is used to predict the performance of an air-breathing electric gridded-ion thruster. Based on particle and energy balance equations, it computes the densities and temperatures of the different species in the discharge chamber and evaluates the thrust generated by ions extracted from the plasma and accelerated between two grids. Simulation results over a range of input radio frequency (RF) powers and altitudes are used to assess the feasible operating regimes and to identify the main limiting mechanisms. Coupling the global model with a simplified drag analysis indicates that satellite operation should be feasible at altitudes between 200 and 250 km, for RF power levels ranging from 1.5 to 3 kW. However, certain limitations associated with the gas compression system and drag estimation deserve further investigation. (10.1063/5.0327675)
  DOI : 10.1063/5.0327675
• Plasma Dynamics and Structure of Titan's Induced Magnetosphere From Wave, Magnetic Field, and Plasma Measurements
  
  • Kim K.
  • Modolo Ronan
  • Edberg N J T
  • Morooka M.
  • Romanelli N.
  • Moissard C.
  • Holmberg M K G
  • Bertucci C.
  • Berthelier Jean-Jacques
  • Canu P.
  • Piberne R.
  • Coates A J
  • Dubinin E.
  • Regoli L.
  • Kurth W S
  • Wahlund J.‐e.
  • Waite J H
  • Dougherty M K
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2026, 131 (4). In this study, we combine Cassini fields and particle observations to investigate Titan's induced magnetosphere from the TA to T82 flybys, including flybys from the Cassini prime, equinox, and part of the solstice mission, to investigate the average location and the shape of Titan's induced magnetosphere. Although earlier studies have provided valuable information on Titan's induced magnetosphere, they were largely based on separate analyses of fields and particle data. We provide an integrated map of electron density and temperature in Titan's near plasma environment to outline the external boundary of the induced magnetosphere. We identify a dense ionospheric region and an extended plasma wake with electron densities ranging between 10^-2 and 10³ cm^-3. In addition, we systematize the spatial distribution of pick-up ions at Titan with respect to the background convective electric field. We indicate that pickup ions are found in the positive hemisphere of the Kronian plasma convective electric field. The mass of the observed pickup corresponds to methane group ions, N$_2^+$ ions as well as protons and molecular hydrogen ions. The Kronian background electric field progressively accelerates these ions, and we estimate its intensity by reconstructing the radial energy gain of this population in response to the convective electric field. We find the estimated from the pickup ions electric field values within 0.05 mV m^-1 and 1.92 mV m^-1 range, which is consistent with an estimate of 0.61 mV m^-1 deduced from |v_corot x B| computation. (10.1029/2025JA034830)
  DOI : 10.1029/2025JA034830
• Hall thruster modeling with multiple simulation techniques: Model benchmarking, fluid–kinetic consistency, and experimental validation
  
  • Petronio Federico
  • Alvarez Laguna Alejandro
  • Bourdon Anne
  • Lafleur Trevor
  • Chabert Pascal
  Journal of Applied Physics, American Institute of Physics, 2026, 139 (9), pp.093303. Numerical plasma models are critical tools for aiding the design and understanding of electric propulsion systems, such as Hall thrusters, particularly when considering challenges associated with diagnostic access and reliable internal measurements. For complex plasma systems, such as Hall thrusters, theoretical verification solutions are often missing, and therefore, benchmarking represents an important element in assessing the correctness and consistency of the underlying mathematical model, and the computational performance of the numerical implementation. In this work, we benchmark three different numerical codes by simulating an SPT-100 Hall thruster under identical operating conditions. The codes include one-dimensional stationary and non-stationary fluid models describing the axial thruster direction, as well as a two-dimensional axial–azimuthal Particle-In-Cell/Monte Carlo Collision (PIC/MCC) model. A partial validation is performed with available experimental measurements of the discharge current, thrust, and anode specific impulse, showing good agreement. Overall, the fluid and PIC/MCC models compare favorably with each other, and several fluid approximations are found to be acceptable. For example, axial electron energy transport is relatively minor such that the electron temperature is reasonably determined by a local energy balance. Other approximations, however, require a more careful examination: particularly the assumption of Maxwellian electrons and the neglect of electron–wall collisions in the electron momentum balance equations. (10.1063/5.0305019)
  DOI : 10.1063/5.0305019
• Relativistic Feedback Discharges in Dielectric Solids
  
  • Pasko Victor P
  • Celestin Sebastien
  • Bourdon Anne
  Physical Review Letters, American Physical Society, 2026, 136 (9), pp.095301. The photoelectric feedback processes leading to growth of relativistic runaway electron avalanches are believed to be responsible for extreme uxes of gamma rays produced from very compact regions of space with dimensions on the order of hundred meters in association with lightning activity in the Earths natural environment (Pasko et al., 2025, https://doi.org/10.1029/2025JD043897). Here we demonstrate for the rst time that the same photoelectric feedback discharges can be realized on centimeter scales in common solid state dielectric materials, like quartz, acrylic and bismuth germanate. These discharge can serve as new sources of high energy X-ray radiation. (10.1103/4p6l-rzck)
  DOI : 10.1103/4p6l-rzck
• Interhemispheric and Latitudinal Variability of Ionospheric Disturbances During the 19-20 December 2015 Geomagnetic Storm: Insights from the South American Sector
  
  • Afolabi Oladayo O
  • Candido Claudia M.N.
  • Becker-Guedes F.
  • Amory-Mazaudier Christine
  • Fleury Rolland
  Advances in Space Research, Elsevier, 2026. This study investigates the response of the South American ionosphere to the December 19-20, 2015, geomagnetic storm using multi-instrument satellite and ground-based data. An interplanetary shock triggered prompt penetration electric fields (PPEFs) during the storm's initial phase, initiating rapid DP2 currents and significant equatorial electrojet (EEJ) fluctuations, particularly in Jicamarca, Peru. Our analysis shows that dayside field-aligned currents (FACs) are the primary drivers of the observed DP2 fluctuations. The South Atlantic Magnetic Anomaly (SAMA) also induced a westward geomagnetic gradient-induced current at the equatorward boundary, which suppressed the EEJ current at São Luiz during the magnetically quiet period. During the storm's main phase, eastward PPEFs enhanced ionospheric irregularities at several Global Positioning Satellite (GPS) stations: Sao Luiz (14.8%), Cuiaba (11.4%), and Jatai (15.5%) in Brazil; Tucuma (33.6%) and Rio Grande (33.2%) in Argentina; and all Peruvian GPS stations (5.8 -57.6%), with Arequipa showing the highest percentage. Conversely, irregularities were inhibited at Eusebio (-31.5%), São José dos Campos (-11.8%), and Campo Grande (-4.8%) in Brazil, and Rosario (-9.4%) and Villegas (-0.8%) in Argentina, relative to a magnetically quiet day, which was attributed to the interplay between westward disturbance dynamo electric fields (DDEF) and PPEF. Joule heating, peaking at 14:35 UT on 20 December drove equatorward disturbance winds that generated the DDEF and modulated irregularities during the recovery phase. Westward DDEF suppressed post-sunset irregularities across most Brazilian and Argentine stations (-50.2% to -10.1%), but slightly enhanced post-midnight ionospheric irregularities at Cuiabá (+4.3%) and Tucuma (+21.1%). All Peruvian stations recorded post-midnight enhancements (+14.8% to +136.7%), with Arequipa showing the highest increase. We quantified the delayed magnetic response of the disturbance dynamo (Ddyn) relative to Joule heating, revealing propagation delays of approximately 6, 8.5, and 8.2 h in Brazil, Argentina, and Peru, respectively. Ddyn exhibited strong spatiotemporal variability, including spatial anomalies associated with the SAMA. The Peruvian sector dominated the Ddyn power (59.0%), followed by Brazil (35.1%) and Argentina (5.9%). Evidence of interhemispheric FAC asymmetry, attributed to seasonal variability, was also observed. These findings significantly advance our understanding of storm-time lowlatitude electrodynamics and their regional variability. (10.1016/j.asr.2025.09.026)
  DOI : 10.1016/j.asr.2025.09.026
• Future trajectories of the BepiColombo MPO and Mio spacecraft: a quantitative tool for magnetospheric region prediction
  
  • Hollman Daragh M
  • Jackman Caitríona M
  • Domijan Katarina
  • Bowers Charles F
  • Hadid Lina Z
  • Heyner Daniel
  Earth Planets and Space, Springer / Terra Scientific Publishing Company, 2026, 78 (1), pp.188. Mercury possesses one of the most dynamic magnetospheres in our solar system, with strong driving by the solar wind, and significant motion of the magnetospheric boundaries in response. The BepiColombo mission will provide the first dual-spacecraft view of this system. In order to maximise the scientific output from BepiColombo, we need quantitative predictions of which magnetospheric region each spacecraft will be sampling at any given time. This is important for the planning of spacecraft operations, where the coordination and collaboration of many instruments across two spacecraft is vitally important, not only for science, but also due to telemetry and power limitations. In this work, we outline a new method using MESSENGER observations to make quantified predictions, with uncertainties, of the probability of observing solar wind, magnetosheath, and magnetosphere for a given position in Mercury’s magnetospheric environment. We apply this technique to five of the six completed BepiColombo Mercury flybys, and additionally forecast magnetospheric region sampling during a representative 10-hour interval of the nominal science mission. We aim to make this approach as accessible as possible, and include in a software repository simple worked examples to aid users in applying these predictions in their own research. (10.1186/s40623-026-02515-7)
  DOI : 10.1186/s40623-026-02515-7
• First in Situ Detection of the Magnetic Component of a Solar Type III Radio Wave
  
  • Kretzschmar Matthieu
  • Vecchio Antonio
  • Krasnoselskikh Vladimir
  • Maksimovic Milan
  • Soucek Jan
  • Pisa David
  • Gasque Claire
  • Bale Stuart D.
  • Dudok de Wit Thierry
  • Pulupa Marc
  • Khotyaintsev Yuri V.
  • Chust Thomas
  • Jannet Guillaume
  • Brochot Jean-Yves
  • Revillet Claire
  • Fergeau Patrice
  • Bonnin Xavier
  • Goetz Keith
  The Astrophysical Journal Letters, Bristol : IOP Publishing, 2026, 1001. Solar radio bursts, and astrophysical radio emissions in general, are observed either in space or on the ground by measuring their fluctuating electric field. Here, we report the first measurement of the magnetic component of a solar radio wave, observed simultaneously by the Solar Orbiter and Parker Solar Probe missions. The observations were made during the type III radio burst on 2021 October 28. The analysis of the wave polarization and magnetic and electric field amplitudes allows us to estimate the refractive index and put constraints on the direction of the wave. The wave is found to be consistent with an ordinary-mode wave and with a source near the southeast limb of the Sun. These results pave the way for future observations and analyses of the magnetic field of radio waves, in particular, for solar radio bursts. (10.3847/2041-8213/ae5893)
  DOI : 10.3847/2041-8213/ae5893
• Self-consistent stabilization of large-scale linear magnetic holes via ion trapping
  
  • Ballerini Giulio
  • Arrò Giuseppe
  • Califano Francesco
  • Henri P.
  • Pucci Francesco
  • Simon Wedlund Cyril
  • Preisser Luis
  Physics of Plasmas, American Institute of Physics, 2026, 33. Magnetic holes (MHs) are localized depressions in the magnetic field commonly observed in space plasmas such as the solar wind, planetary magnetosheaths, and cometary environments. Despite the abundance of spacecraft observations, the mechanisms governing the generation of these structures are not fully understood. In this study, we investigate the stability of magnetic depressions in a controlled plasma environment via two-dimensional hybrid particle-in-cell simulations using the Menura code. Initializing the system with preexisting magnetic field depressions embedded in a mirror-stable plasma allows us to isolate the fundamental physical mechanisms responsible for stabilization and equilibrium. We analyze the roles of the initial depth, characteristic width, and magnetic field geometry of the depression. Our results demonstrate that narrow depressions (of the order of ion kinetic scales) are unstable, whereas broader structures can reach stable equilibria through ion trapping, resulting in localized density enhancements and temperature anisotropy consistent with in situ observations of large-scale MHs. The findings highlight the importance of ion trapping for stabilization and provide a controlled framework to investigate MH dynamics. (10.1063/5.0327618)
  DOI : 10.1063/5.0327618
• Nonlinear phase synchronization and the role of spacing in shell models
  
  • Manfredini L.
  • Gürcan Ö D
  Physical Review E, American Physical Society (APS), 2026, 113 (1), pp.015101. A shell model can be considered as a self-similar chain of interacting triads, where each triad can be interpreted as a nonlinear oscillator that can be mapped to a spinning top. Investigating the relation between phase dynamics and intermittency in such a chain of nonlinear oscillators, it is found that synchronization is linked to increased energy transfer. In particular, our results indicate that the observed systematic increase of intermittency, as the shell spacing is decreased, is associated with strong phase alignment among consecutive triadic phases, facilitating the energy cascade. It is shown that while the overall level of synchronization can be quantied using a Kuramoto order parameter for the global phase coherence in the inertial range, a local, weighted Kuramoto parameter can be used for the detection of burst-like events propagating across shells in the inertial range. This novel analysis reveals how locally phase-locked states are associated with the passage of extreme events of energy ux. Applying this method to helical shell models ( i.e. for a class of helical interactions that couple the two helicities in a non separable topology) reveals that a reduction in phase coherence correlates with suppression of intermittency. When inverse cascade scenarios are considered using two dierent shell models including a non local helical shell model, and a local standard shell model with a modied conservation law, it was shown that a particular phase organization is needed in order to sustain the inverse energy cascade. It was also observed that the PDFs of the triadic phases were peaked in accordance with the basic considerations of the form of the ux, which suggests that a triadic phase of π/2 and -π/2 maximizes the forward and the inverse energy cascades respectively. (10.1103/2vxp-1k2t)
  DOI : 10.1103/2vxp-1k2t
• Disturbed and quiet days ∑O/N₂ variations at low and mid-latitudes during solar cycles 23 and 24
  
  • Khan Jahan Zeb
  • Younas Waqar
  • Amory-Mazaudier Christine
  • Khan Majid
  Advances in Space Research, Elsevier, 2026, 77 (5), pp.6295-6314. We analyzed the column density ratio of thermospheric compositions (∑O/N₂) using data from the Global Ultraviolet Imager (GUVI) onboard the TIMED satellite from 2002 to 2020. Daily ∑O/N 2 values for the three most geomagnetically disturbed and quietest days each month were used to compute monthly means at low and mid-latitudes across both hemispheres. These variations were also examined across various longitudinal sectors, including Asia, Africa, and the Americas. The fluctuations in ∑O/N₂ were more pronounced at mid-latitudes than at low latitudes, with low latitude values in both hemispheres peaking near the equinoxes. At midlatitudes, the highest values occurred during local winter, with stronger peaks in the Northern Hemisphere (NH) than in the Southern Hemisphere (SH). The winter and equinoctial maxima are also observed in all longitudinal sectors. Besides this, the distinct longitudinal asymmetries over Asian, African, and American regions at mid-latitudes, influenced by geomagnetic field geometry, are also observed. The downwelling of ∑O/N₂ in local winter is stronger, while upwelling in local summer is weaker in the longitudinal sectors containing the magnetic pole. Annual (AV) and semiannual variations (SAV) were extracted using a bandpass filter. AV was stronger at mid-latitudes, peaking in local winter and highlighting the winter anomaly in both hemispheres. SAV were dominant at low latitudes, with positive peaks at equinoxes and negative dips at solstices, generally in phase across hemispheres and longitude sectors. The amplitudes of AV and SAV are stronger during solar maximum periods, justifying the solar cycle trend. Analysis also revealed that during geomagnetically disturbed periods, ∑O/N₂ typically decreased (≤ -10%) at mid-latitudes and increased (≥10%) at low latitudes compared to quiet periods. Although opposite trends-enhancement at mid-latitudes and depletion at low latitudes -were occasionally observed, they were less significant. This study aims to provide valuable insights into the dynamics of thermospheric composition, thereby contributing to the improved modeling of ionospheric behavior and space weather forecasting. (10.1016/j.asr.2025.12.115)
  DOI : 10.1016/j.asr.2025.12.115