Publications

2026

• Towards Gravitational Wave Turbulence within the Hadad-Zakharov metric
  
  • Gay Benoît
  • Babichev Eugeny
  • Galtier Sébastien
  • Noui Karim
  , 2026. 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.
• Low‐Pressure Microwave Air Plasma Decontamination of Black Pepper ( Piper nigrum ): From Microbial Efficacy to Quality Preservation
  
  • Soulier Manon
  • Kais Abderrahmane
  • Maho Thomas
  • Guillot Philippe
  • Muja Cristina
  Plasma Processes and Polymers, Wiley-VCH Verlag, 2026, 23 (4). ABSTRACT This study investigates low‐pressure microwave air plasma as a non‐thermal decontamination approach for spices, using black peppercorns as a model matrix. At 20 Pa and 80 W, the discharge exhibits electron densities of 10 9 –10 10 cm −3 , effective electron temperatures of 0.7 eV, while keeping the substrate temperature below 60°C. Under these conditions 1.2‐log reduction of native aerobic mesophilic and thermophilic flora is achieved after 60 min. Bacillus subtilis spores on peppercorns show a similar 1.2‐log reduction, versus > 6‐log on flat glass carriers, revealing a strong surface shielding effect. UV radiation drives early spore inactivation, while long‐lived reactive species contribute during prolonged exposures. These antimicrobial effects are achieved without significant compromise of the key quality attributes of black pepper. (10.1002/ppap.70165)
  DOI : 10.1002/ppap.70165
• White paper on the relevance of the European Solar Telescope (EST) for the French heliophysics community
  
  • Pariat Etienne
  • Noraz Quentin
  • Perri Barbara
  • Poirier Nicolas
  • Froment C.
  • Bigot Lionel
  • Aulanier Guillaume
  • Gelly Bernard
  • Aboudarham Jean
  • Aizawa Sae
  • Alexandrova Olga
  • Alqeeq Soboh
  • Amari Tahar
  • Auchère Frédéric
  • Bernoux Guillerme
  • Berthomier Matthieu
  • Bommier Veronique
  • Bonnin Xavier
  • Brun Allan Sacha
  • Bualé Isabelle
  • Buchlin Éric
  • Canou Aurélien
  • Canu Patrick
  • Corbard Thierry
  • Cornu Florence
  • Coustillet Camille
  • Cozzani Giulia
  • D’herbomez Léa
  • Diaz Castillo Saida
  • Dudok de Wit Thierry
  • Faurobert Marianne
  • Finley Adam
  • Fontaine Dominique
  • Garcia Rafael A.
  • Grappin Roland
  • Hadid Lina
  • Henadhira Arachchige Kalpa Harindra Perera
  • Janvier Miho
  • Jouve Laurène
  • Kieokaew Rungployphan
  • Kirkwood Hannah
  • Lavraud Benoit
  • Le Breton Jean-Pierre
  • Le Contel Olivier
  • Le Nestour Nicolas
  • Leblanc François
  • Masson Sophie
  • Meyer-Vernet Nicole
  • Parenti Susanna
  • Pitout Frédéric
  • Rieutord Michel
  • Romero Castañeda Jorge
  • Rouillard Alexis
  • Ruiz de Galarreta Claudia
  • Sahraoui Fouad
  • Schmieder Brigitte
  • Simon Pauline
  • Strugarek Antoine
  • Tallon Michel
  • Thepthong Panisara
  • Touresse Jade
  • Vial Jean-Claude
  • Vilmer Nicole
  • Zaslavsky Arnaud
  , 2026. The project of the European Solar Telescope aims to provide a state-of-the art infrastructure to study the Sun and its interactions with Earth and the heliosphere. This 4.2m aperture telescope will be equipped with multi conjugate adaptive optics, light-polarisation analyser, imaging spectrograph and integral field unit spectrographs. It will provide unprecedented observations of the solar photosphere and chromosphere and of the dynamical events and features that pertains to the low solar atmosphere. The EST project is presently in a phase of crystallisation, aiming at the creation of an European Research Infrastructure Consortium. While the French community has continuously been associated with the development of the EST project, some specific scientific aspects are more particularly relevant for the French astrophysics and heliophysics communities. The present review highlights the scientific research axes of high interest from the French community that shall strongly benefit from EST. The later will not only advance numerous topics of solar physics, as well as solar adaptive optics developments, but will also provide unrivaled datasets of high interest in the framework of space weather. This review also aims to highlight the space weather use that can be done with future EST observations, that will be particularly relevant for French heliophysicists.
• Comparative physicochemical study of dielectric barrier discharge and post-discharge plasmas to treat non-small cell lung carcinoma in murine models
  
  • Soulier Manon
  • Marmier Solenne
  • Decauchy Henri
  • Cremer Isabelle
  • Dufour Thierry
  Journal of Physics D: Applied Physics, IOP Publishing, 2026, 59 (9), pp.095202. While cold atmospheric plasmas (CAPs) are increasingly explored for cancer therapy, it remains unclear how distinct device configurations translate into differences in tissue coupling, safety, and therapeutic efficacy. To address this gap, a comparative evaluation of the two following CAP sources has been conducted: the ORJET (atmospheric pressure plasma jet in outer ring electrode configuration) and the PoDBD (post-discharge delivered by a dielectric barrier device with a grounded-mesh electrode). Electrical behavior is quantified on an equivalent electrical human body model, while optical emission spectroscopy and surface-oxidation assays are achieved on transdermal membranes and polyethylene substrates to characterize the nature and diffusion of plasma-generated reactive species. Thermal safety is examined in mice through real-time temperature monitoring and histological analysis while antitumor efficacy is determined in a syngeneic model of non-small cell lung cancer (NSCLC) treated five times. The two devices display fundamentally different modes of tissue coupling: ORJET delivers localized interfacial electric field while PoDBD exposes tissue solely to reactive oxygen and nitrogen species-rich post-discharge. Despite these differences, both generate similar reactive-species signatures, preserve tissue integrity when operated within safe thermal limits, and significantly slow tumor progression compared with controls, with no difference between devices. These findings indicate that therapeutic activity arises predominantly from reactive-species chemistry rather than electrical coupling, supporting the applicability of diverse CAP technologies for oncological treatment. (10.1088/1361-6463/ae46ac)
  DOI : 10.1088/1361-6463/ae46ac
• A study of the magnetic effects of the Equatorial Electrojet (EEJ) along the East Asian and West African sectors
  
  • Grodji F.O.
  • Yao H.F.M.
  • Amaechi P.O.
  • Amory-Mazaudier C.
  • Doumbia V.
  • Kouassi N.
  • Kassamba A.A.
  • Tuo Z.
  Advances in Space Research, Elsevier, 2026. This paper presents a comparative analysis of the Equatorial Electrojet (EEJ) effects along the East Asian (140° E) and West African (5° W) sectors using geomagnetic field data recorded in 1993. The data were obtained within the frameworks of the International Equatorial Electrojet Year (IEEY) campaign for West Africa and the Solar-Terrestrial Energy Program (STEP) project for the Asian sector. The analysis was conducted under quiet magnetic conditions (Am < 20 nT) to facilitate the investigation of regular daily variations () induced by the EEJ. Key electrodynamic parameters of the EEJ such as ribbon width, center position, and maximum current intensity were estimated using latitudinal profiles of the H and Z components of the geomagnetic field. The results reveal significant latitudinal and longitudinal variations characterized by a wider EEJ ribbon in Asia (∼714 km) compared to West Africa (∼601 km), and a higher peak current intensity in West Africa (214.3 ± 30.9 A/km) relative to Asia (142.4 ± 31.9 A/km). Also, in 1993, the EEJ centre was located north of the magnetic equator in West Africa and south of it in Asia, indicating a pronounced hemispheric asymmetry. Seasonal variations show higher EEJ intensities during the equinoxes than during the solstices in both longitude sectors. Throughout 1993, the EEJ peak intensity over West Africa consistently surpassed that over East Asia, irrespective of the magnetic season. Furthermore, the frequency of occurrence of the counter-electrojet (CEJ) was higher in West Africa, especially during the morning hours. This study shows that EEJ morphology and strength are modulated by longitude-dependent factors, including ionospheric conductivity, neutral winds, atmospheric tides, and the geomagnetic field. (10.1016/j.asr.2026.03.039)
  DOI : 10.1016/j.asr.2026.03.039
• 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
• Benchmark for two-dimensional large scale coherent structures in partially magnetized E × B plasmas—community collaboration &amp; 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
• 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
• Benchmark for two-dimensional large scale coherent structures in partially magnetized E×B plasmas -Community collaboration &amp; lessons learned
  
  • Powis Andrew T
  • Ahedo Eduardo
  • Alvarez Laguna A.
  • 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 P
  • 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 E
  • 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
  , 2025. <div><p>Low-temperature plasmas 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 low-temperature plasma 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.</p></div>
• Properties of Magnetic Switchbacks in the Near-Sun Solar Wind
  
  • Badman Samuel T.
  • Fargette Naïs
  • Matteini Lorenzo
  • Agapitov Oleksiy V.
  • Akhavan-Tafti Mojtaba
  • Bale Stuart D.
  • Bharati Das Srijan
  • Bizien Nina
  • Bowen Trevor A.
  • Dudok de Wit Thierry
  • Froment Clara
  • Horbury Timothy
  • Huang Jia
  • Jagarlamudi Vamsee Krishna
  • Larosa Andrea
  • Madjarska Maria S.
  • Panasenco Olga
  • Pariat Etienne
  • Raouafi Nour E.
  • Rouillard Alexis P.
  • Ruffolo David
  • Sioulas Nikos
  • Soni Shirsh Lata
  • Sorriso-Valvo Luca
  • Suen Gabriel Ho Hin
  • Velli Marco
  • Verniero Jaye
  Space Science Reviews, Springer Verlag, 2026, 222. Magnetic switchbacks are fluctuations in the solar wind in which the interplanetary magnetic field sharply deflects away from its background direction so as to create folds in magnetic field lines while remaining of roughly constant magnitude. The magnetic field and velocity fluctuations are extremely well correlated in a way corresponding to Alfvénic fluctuations propagating away from the Sun. For a background field which is nearly radial this causes an outwardly propagating jet to form. Switchbacks and their characteristic velocity jets have recently been observed to be nearly ubiquitous by Parker Solar Probe with in situ measurements in the inner heliosphere within 0.3 AU. Their prevalence, substantial energy content, and potentially fundamental role in the dynamics of the outer corona and solar wind motivate the significant research efforts into their understanding. Here we review the in situ measurements of these structures (primarily by Parker Solar Probe). We discuss how they are identified and measured, and present an overview of the primary observational properties of these structures, both in terms of individual switchbacks and their collective arrangement into "patches". We identify both properties for which there is a strong consensus and those that have limited or qualified support and require further investigation. We identify and collate several open questions and recommendations for future studies. (10.1007/s11214-026-01267-w)
  DOI : 10.1007/s11214-026-01267-w
• 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
• 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
• 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
• 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
• 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
• 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
• 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