Publications

2025

• Shell models on recurrent sequences: Fibonacci, Padovan, and other series
  
  • Manfredini Lorenzo
  • Gürcan Özgür D.
  Physical Review E, American Physical Society (APS), 2025, 111 (2), pp.025103. A new class of shell models is proposed, where the shell variables are defined on a recurrent sequence of integer wave-numbers such as the Fibonacci or the Padovan series, or their variations including a sequence made of square roots of Fibonacci numbers rounded to the nearest integer. Considering the simplest model, which involves only local interactions, the interaction coefficients can be generalized in such a way that the inviscid invariants, such as energy and helicity, can be conserved even though there is no exact self-similarity. It is shown that these models basically have identical features with standard shell models, and produce the same power law spectra, similar spectral fluxes and analogous deviation from self-similar scaling of the structure functions implying comparable levels of turbulent intermittency. Such a formulation potentially opens up the possibility of using shell models, or their generalizations along with discretized regular grids, such as those found in direct numerical simulations, either as diagnostic tools, or subgrid models. It also allows to develop models where the wave-number shells can be interpreted as sparsely decimated sets of wave-numbers over an initially regular grid. In addition to conventional shell models with local interactions that result in forward cascade, a particular helical shell model with long range interactions is considered on a similarly recurrent sequence of wave numbers, corresponding to the Fibonacci series, and found to result in the usual inverse cascade. (10.1103/PhysRevE.111.025103)
  DOI : 10.1103/PhysRevE.111.025103
• Asymmetric dual cascade in gravitational wave turbulence
  
  • Gay Benoît
  • Galtier Sébastien
  , 2025. We numerically simulate, in both the forced and decay regimes, a fourth-order nonlinear diffusion equation derived from the kinetic equation of gravitational wave turbulence in the limit of strongly local quartic interactions. When a forcing is applied to an intermediate wavenumber $k_i$, we observe a dual cascade of energy and wave action. In the stationary state, the associated flux ratio is proportional to $k_i$, and the Kolmogorov-Zakharov spectra are recovered. In decaying turbulence, the study reveals that the wave action spectrum can extend to wavenumbers greater than the initial excitation $k_i$ with constant negative flux, while the energy flux is positive with a power law dependence in $k$. This leads to an unexpected result: a single inertial range with a Kolmogorov-Zakharov wave action spectrum extending progressively to wavenumbers larger than $k_i$. We also observe a wave action decay in time in $t^{-1/3}$ while the front of the energy spectrum progresses according to a $t^{1/3}$ law. These properties can be understood with simple theoretical arguments.
• Study of Dayside Magnetic Reconnection in the Presence of Cold Ions and Guide Field : A Focus on the Magnetospheric Separatrix
  
  • Baraka Mohammed
  , 2025. Depending on the orientation of the interplanetary magnetic field (IMF) transported by the solar wind, the magnetic field lines of the Earth's magnetic field can reconnect with those of the IMF at the dayside magnetopause, the boundary between the solar wind and the Earth's magnetic field. As the plasma conditions on each side of the magnetopause are different, the magnetic reconnection is called asymmetric. The reconnection process starts in a diffusion region at electron scales and generates fast diverging electron and ion jets. The boundaries separating the plasma flowing into the reconnection region from the outflow plasma are called the separatrices. This PhD thesis investigates in detail the structure of the magnetospheric separatrix far from the diffusion region in the presence of magnetospheric cold ions, a high density gradient and a moderate guide field. Using in-situ measurements of the NASA Magnetospheric Multiscale(MMS) mission and fully kinetic 2D Particle-In-Cell (PIC) simulations obtained from the open source SMILEI code, the current densities, electric and magnetic signatures as well as energy conversion processes are investigated. From in-situ measurements at the separatrix, the current density is found dominated by the ion diamagnetic current and the normal electric field sustained by the drift of the cold ions in agreement with the simulations. The energy conversion in the fluid frame is ensured by the parallel current and the electric field produced by the parallel electron pressure term. The partitioning of the energy between ions and electrons is discussed based on the pressure strain calculations. From the kinetic simulations performed with and without cold ions, and with and without guide field, it is found that with a guide field, the presence of cold ions reinforces the electron pressure gradient reducing the normal electric field and increasing the motion of the reconnection region. All these effects modify the energy and plasma exchanges between the solar wind and the Earth's magnetosphere.
• Numerical model of the PEGASES spacecraft thruster
  
  • Lequette Nicolas
  , 2025. The electric spacecraft propulsion industry is actively transitioning to new propellants.Until recently, the favoured propellant was xenon. It is the heaviest stable noble gas, characteristics that enhance the thrust-to-power ratio of electric thrusters. However, the limited supply cannot satisfy the growing demand as space industrializes.New propulsion systems are designed around lighter noble gases, trading efficiency for affordability.Others make use of molecular propellants, namely iodine. Despite being reactive, this element, a neighbour of xenon in the periodic table, can offer similar performances with the benefit of a higher storage density.The development of the next propulsion systems requires design and simulation tools adapted to alternative propellants. In this work, we propose using a 1D Particle-In-Cell code coupled with a fluid model as a fast way to simulate the low-pressure discharges found in electric thrusters.We implemented an analytical model to emulate the particle transport in the unsimulated directions.This method allows the simulation of simple geometries with a 1D model. In addition, the vacuum permittivity scaling technique allows to speed up whole device simulations.To ensure the accuracy of our model, we extensively validated it using the diagnostic data measured on the PEGASES thruster. This validation process covered a range of noble gases and iodine ICP discharges, including argon, krypton, xenon.Noble gas validation showed that the code could reproduce the trends in the electron parameters as the pressure and power evolved. However, its reduced dimensionality and the fluid model hinder its predictive power at low pressure and high power. In iodine, the low-pressure simulations are in good agreement with the experimental data. However, the model struggles to maintain the delicate balance between the numerous species at high pressure.
• Ionospheric Plasma Irregularities During Intense geomagnetic storms of Solar Cycle 25
  
  • Imtiaz Nadia
  • Calabia Andres
  • Anoruo Chukwuma
  • Zahid Aqsa
  • Amory Christine
  • Adhikari Binod
  Annales Geophysicae, European Geosciences Union, 2025. Abstract. This study aims to characterize several key aspects of the ionosphere during intense geomagnetic storms that occurred on March 23–25, 2023, April 23–25, 2023, November 4–7, 2023 and May 10–13, 2024 during the ascending phase of Solar Cycle 25 (SC25). We are especially interested to study the role of asymmetric Joule Heating (JH) in the structuring of the Equatorial Ionization Anomaly (EIA), such as double crest, single crest, or merged, which may lead to the formation or suppression of post-sunset ionospheric plasma irregularities. For this purpose, we use the Weimer 2005 Model simulations to analyze the JH patterns during the four strong geomagnetic storms, and Madrigal TEC maps are used to observe changes in the intensity, location, and symmetry of the EIA during these disruptive times. Equatorial/low-latitude ionospheric plasma irregularities at different longitudes under geomagnetically disturbed conditions are studied using the Rate of Change TEC Index (ROTI), which is calculated from GPS receiver measurements. A strong JH is observed during the May 2024 storm (also known as the Mother's Day storm) during its main phase, which occurs after sunset between 18:00 and 00:00 UT. The other storms have the JH strength in the following order from strong to weak: March 2023, April 2023, and November 2023. Besides inter-hemispheric asymmetry, all the storms show stronger variation in the JH patterns. We conclude that the resulting change in the thermospheric winds and electric fields due to storm conditions alter the EIA structures. It has been found that the generation of ionospheric plasma irregularities and their geographical distribution strongly depend on EIA's density gradients and general structure. For instance, it is noticed that the double crest EIA structures with strong plasma density gradients play important role to the generation of post sunset ionospheric plasma irregularities during the main phases of these geomagnetic storms. On the other hand, the single crest or merged EIA structure comprise of a diffuse region of high electron density centered directly over the equator, without a pronounced trough, as observed during the storm of November 2023. The single crest EIA exhibit nearly uniform plasma density distribution do not favor the generation of ionospheric plasma irregularities. The role of storm-time penetrating electric field in the structuring and seeding of ionospheric plasma irregularities has been investigated. The research will contribute to our understanding of the basic physics of the ionosphere, especially the mechanisms governing the development and evolution of the EIA and ionospheric plasma irregularities under various magnetically disturbed conditions. (10.5194/egusphere-2025-86)
  DOI : 10.5194/egusphere-2025-86
• Impact of pressure anisotropy on the cascade rate of Hall magnetohydrodynamic turbulence with biadiabatic ions
  
  • Simon Pauline A
  • Sahraoui Fouad
  • Galtier Sébastien
  • Laveder Dimitri
  • Passot Thierry
  • Sulem Pierre-Louis
  Physical Review E, American Physical Society (APS), 2025, 111 (1), pp.015210. The impact of ion pressure anisotropy on the energy cascade rate of Hall-MHD turbulence with biadiabatic ions and isothermal electrons is evaluated in three-dimensional direct numerical simulations, using the exact (or third-order) law derived by Simon and Sahraoui in 2022. It is shown that pressure anisotropy can enhance or reduce the cascade rate, depending on the scales, in comparison with the prediction of the exact law with isotropic pressure, by an amount that correlates well with pressure anisotropy, $a_p = p_⊥ / p_∥ ≠ 1$, that develops in simulations initialized with an isotropic pressure ($a_{p0} = 1$). A simulation with initial pressure anisotropy $a_{p0} = 4$ confirms this trend, exhibiting a stronger impact on the cascade rate, both in the inertial range and at larger scales, close to the forcing scales. Furthermore, a Fourier-based numerical method, to compute exact laws in numerical simulations in the full ($ℓ_⊥ , ℓ_∥$) increment plane, is presented. (10.1103/PhysRevE.111.015210)
  DOI : 10.1103/PhysRevE.111.015210
• Derivation of a 4-moment model for electron transport in Hall thrusters from a gyrokinetic model
  
  • Tazakkati Zoubaïr
  • Laguna Alejandro Alvarez
  • Massot Marc
  • Pichard Teddy
  , 2025. <div><p>We model the motion of a population of electrons in a strong electromagnetic field undergoing elastic electron/electron collisions. This regime is derived from a dimensional analysis of the electron confinement in Hall-effect thrusters. The electrons exhibit a very high cyclotron frequency and a E × B-drift, modelled by stiff PDEs at the mesoscopic scale. We obtain a gyrokinetic model in which the fastest oscillations of the system are filtered out by averaging the rotation of the electrons around the magnetic field lines. The model is derived in the strong electromagnetic field limit. Based on this gyrokinetic model, we then develop a 10-moment model. The averaging operation performed at the kinetic scale leads to symmetry properties that allow to reduce the 10-moment model to a 4-moment model.</p></div>
• Step-by-step verification of particle-in-cell Monte Carlo collision codes
  
  • Parodi Pietro
  • Petronio Federico
  Physics of Plasmas, American Institute of Physics, 2025, 32 (1). The particle-in-cell (PIC) method with Monte Carlo collisions (MCC) is widely used in the simulation of non-equilibrium plasmas for electric propulsion and laboratory applications. Due to the simplicity of the basic PIC algorithm and the specific modeling needs of the different research groups, many codes have been independently developed. Verification of these codes, i.e., ensuring that the computational code correctly implements the intended mathematical models and algorithms, is of fundamental importance. Different benchmark cases, such as one from Turner et al. [Phys. Plasmas 20, 013507 (2013)], Charoy et al. [Plasma Sources Sci. Technol. 28, 105010 (2019)], and Villafana et al. [Plasma Sources Sci. Technol. 30, 075002 (2021)], have been published in recent years. These have consisted of a complex physical setup, in which many computation modules interact to yield the final result. Although this approach has the advantage of testing the code in a realistic case, it may hide some implementation errors. Moreover, in the case of disagreement, the previous works do not provide an easy way to identify the faulty code modules. In this work, we propose a step-by-step approach for the verification of PIC-MCC codes in a 2D-3V electrostatic setup. The criteria for the test cases are (i) they should highlight possible implementation errors by testing the modules separately, whenever possible (ii) they should be free from physical instabilities to avoid chaotic behavior, and (iii) the numerical result should be accompanied by analytical calculations, for confirmation purposes. The seven test cases identified all show excellent agreement between the authors' codes. (10.1063/5.0241527)
  DOI : 10.1063/5.0241527
• Spatio-temporal features of ionospheric disturbances resulting from March 2023 geomagnetic storm: Comparisons with March 2015 St. Patrick’s Day storm
  
  • Younas Waqar
  • Khan Majid
  • Amory-Mazaudier C.
  • Nishimura Yukitoshi
  • Kamran M.
  Advances in Space Research, Elsevier, 2025, 75 (2), pp.2433-2448. This study explores the ionospheric disturbances induced by the March 2023 geomagnetic storm, offering insights into the complex interplay between space weather events and the Earth’s upper atmosphere. In this regard, data from ionospheric maps (global and regional electron contents) and topside plasma density (provided by the Swarm satellites) have been used. Furthermore, the findings are compared with those of the March 2015 St. Patrick’s Day storm of solar cycle 24, which exhibited notably similar onset conditions. The Global Electron Content (GEC) displays substantial positive surges in the African, Pacific, and American sectors, with a notable enhancement in the American sector on March 24, 2023. During the recovery phase (March-23 storm), negative storm effects are observed across all longitudinal sectors, with greater intensity at low-latitudes compared to mid-latitudes. Moreover, the study highlights discrepancies in positive storm effects when compared to the St. Patrick’s Day storm. During the March-2023, there was no positive storm effect observed in the pacific mid-latitude regions. This longitudinal difference in occurrence of positive storm may be attributed to potential influences from variations in the z-component of the interplanetary magnetic field and energy inputs into the magnetosphere. A super fountain effect is observed exclusively in the American sectors during both storms, exhibiting a noticeable hemispheric asymmetry. The non-uniform planetary distribution of disturbed thermospheric winds likely played a major role in the ionospheric asymmetry in the American region during the 2023 event. (10.1016/j.asr.2024.10.042)
  DOI : 10.1016/j.asr.2024.10.042
• Spatiotemporal dynamics of nanosecond pulsed discharge in the form of a fast ionization wave: self-consistent two-dimensional modeling and comparison with experiments under negative and positive polarity
  
  • Kourtzanidis Konstantinos
  • Starikovskaia Svetlana M
  Journal of Physics D: Applied Physics, IOP Publishing, 2025, 58 (19), pp.195202. Nanosecond discharges are characterized by a shift in energy branching toward the excitation of electronic levels and dissociation, making them particularly attractive for plasma chemistry. Understanding the spatio-temporal structure of these discharges is especially important. This paper presents a detailed 2D-axisymmetric numerical analysis of a nanosecond discharge propagating in a long tube and in pure nitrogen. The modeling is conducted using a self-consistent plasma fluid solver under the local mean energy approximation, including photoionization. The discharge develops at moderate pressures, 1–10 Torr, in the form of a fast ionization wave (FIW). Simulations are performed for both negative and positive polarities of the voltage pulse applied to the high-voltage electrode. The computational results are validated against available experimental data, including FIW velocity within the studied pressure range, electron density, longitudinal electric field, and the radial distribution of N₂(C³Π<i>_u</i>) emission on a nanosecond timescale. (10.1088/1361-6463/adcace)
  DOI : 10.1088/1361-6463/adcace
• Kinetic theory and moment models of electrons in a reactive weakly-ionized non-equilibrium plasma
  
  • Laguna Alejandro Alvarez
  • Pichard Teddy
  Kinetic and Related Models, AIMS, 2025. <div><p>We study the electrons in a multi-component weakly-ionized plasma with an external electric field under conditions that are far from thermodynamic equilibrium, representative of a gas discharge plasma. Our starting point is the generalized Boltzmann equation with elastic, inelastic and reactive collisions. We perform a dimensional analysis of the equation and an asymptotic analysis of the collision operators for small electron-to-atom mass ratios and small ionization levels. The dimensional analysis leads to a diffusive scaling for the electron transport. We perform a Hilbert expansion of the electron distribution function that, in the asymptotic limit, results in a reduced model characterized by a spherically symmetric distribution function in the velocity space with a small anisotropic perturbation. We show that the spherical-harmonics expansion model, widely used in low-temperature plasmas, is a particular case of our approach. We approximate the solution of our kinetic model with a truncated moment hierarchy. Finally, we study the moment problem for a particular case: a Langevin collision (equivalent to Maxwell molecules) for the electron-gas elastic collisions. The resulting Stieltjes moment problem leads to an advection-diffusion-reaction system of equations that is approximated with two different closures: the quadrature method of moments and a Hermitian moment closure. A special focus is given along the derivations and approximations to the notion of entropy dissipation.</p></div> (10.3934/krm.2025007)
  DOI : 10.3934/krm.2025007
• Ion-rich acceleration during an eruptive flux rope event in a multiple null-point configuration
  
  • Pesce-Rollins Melissa
  • Mackinnon Alexander
  • Klein Karl-Ludwig
  • Russell Alexander
  • Hudson Hugh
  • Warmuth Alexander
  • Wiegelmann Thomas
  • Masson Sophie
  • Parnell Clare
  • Nitta Nariaki V
  • Omodei Nicola
  The Astrophysical Journal, American Astronomical Society, 2025, 989 (2), pp.148. We report on the $γ$-ray emission above 100~MeV from the GOES M3.3 flare SOL2012-06-03. The hard X-ray (HXR) and microwave emissions have typical time profiles with a fast rise to a well-defined peak followed by a slower decay. The $&gt;$100~MeV emission during the prompt phase displayed a double-peaked temporal structure with the first peak following the HXR and microwaves, and the second one, about three times stronger, occurring $17 \pm 2$ seconds later. The time profiles seem to indicate two separate acceleration mechanisms at work, where the second $γ$-ray peak reveals a potentially pure or at least largely dominant ion acceleration. The Atmospheric Imaging Assembly imaging shows a bright elliptical ribbon and a transient brightening in the north-western (NW) region. Nonlinear force-free extrapolations at the time of the impulsive peaks show closed field lines connecting the NW region to the south-eastern part of the ribbon and the magnetic topology revealed clusters of nulls. These observations suggest a spine-and-fan geometry, and based on these observations we interpret the second $γ$-ray peak as being due to the predominant acceleration of ions in a region with multiple null points. The $&gt;$100 MeV emission from this flare also exhibits a delayed phase with an exponential decay of roughly 350 seconds. We find that the delayed emission is consistent with ions being trapped in a closed flux tube with gradual escape via their loss cone to the chromosphere. (10.3847/1538-4357/adeb7f)
  DOI : 10.3847/1538-4357/adeb7f
• Quantum Offset of Velocity Imaging-Based Electron Spectrometry and the Electron Affinity of Arsenic
  
  • Blondel Christophe
  • Drag Cyril
  Physical Review Letters, American Physical Society, 2025, 134 (4), pp.043001. Electron imaging has been routinely used for electron spectrometry. It has been ignored, however, that the maximum-intensity circles that surround electric field-produced electron spots do not materialize envelopes of trajectories, but the first interior fringes of a caustic. Neglecting the gap between the fringe and the parent envelope has resulted in spectrometric errors, notably on some reference values of electron affinities. Evidence for the effect is given by photodetachment microscopy of O- and a measurement of the electron affinity of ⁷⁵As, which is found to be 0.804486(3) eV. (10.1103/PhysRevLett.134.043001)
  DOI : 10.1103/PhysRevLett.134.043001
• Steady-state plasma model of an iodine-fueled Hall thruster
  
  • Chabert Pascal
  • Bourdon Anne
  • Esteves Benjamin
  • Lafleur Trevor
  Journal of Applied Physics, American Institute of Physics, 2025, 138 (4), pp.043303. A time-independent, one-dimensional plasma model is proposed and used to investigate the characteristics and performance of iodine-fueled Hall thrusters. The model accounts for radial plasma-wall losses and includes major iodine collisional reaction processes such as molecular dissociation. Thruster performance is found to be comparable to that obtained with xenon, although iodine allows extension of the operating range to lower mass flow rates and discharge voltages. The model predicts an appreciable fraction of molecular ions (I2+) within the thruster plume that depends on the discharge voltage and propellant mass flow rate and that contributes significantly to the thrust. In contrast to xenon, electron impact dissociation of iodine leads to the unique formation of two distinct ionization zones within the thruster: a region closer to the anode associated with the ionization of molecular iodine and a downstream region associated with the ionization of atomic iodine. (10.1063/5.0263183)
  DOI : 10.1063/5.0263183
• Positive and negative DC glow discharges: A comparative study to characterize self-organized patterns on water surface
  
  • Dufour Thierry
  • Ogden Elliot
  Physics of Plasmas, American Institute of Physics, 2025, 32 (4), pp.043502. Self-organized patterns (SOPs) in plasma discharges arise from the complex interplay of electric field, reactive species, and charged particles, driven by non-linear plasma dynamics. While studies have explored SOP formation in various configurations, no systematic comparison of positive and negative DC glow discharges (NGD) has been conducted to explain why SOPs form exclusively when polarization is negative. This study aims to analyze SOP formation mechanisms by comparing the electrical, optical, and spectral properties of positive and negative DC glow discharges interacting with a grounded water surface. Key differences in gas temperature, electric field, and reactive species distribution are hence identified. For positive DC glow discharges, the gas temperature remains in the 350–370 K range, while the reduced electric field remains below 100 Td across the gap. The plasma is dominated by OH• and N2* species, whose excitation results from direct electron impact and energy transfer in a low-field environment. The absence of strong ionization and electric field gradients leads to a spatially homogeneous emission layer on the liquid surface, resulting in a circular uniform plasma pattern without self-organization. In contrast, SOP emerges exclusively under NGD at currents above 15 mA. These discharges are characterized by a non-linear reduced electric field, peaking at 485 Td at 1 mm from the cathode pin, dropping below 100 Td in the central gap and rising to 460 Td near the water surface. There, the plasma layer still contains not only OH• and N2* species but also N2+ ions, the latter being critical for SOP formation. SOP morphology evolves with gap size: at 7 mm, patterns transition from specks to filaments, with pattern diameters and thickness as high as 5.5 mm and 210 μm, respectively. Lowering water surface tension with surfactants reduces SOP size and modifies pattern morphology. Our results deepen understanding of plasma self-organization mechanisms, particularly the role of polarity and liquid surface dynamics. (10.1063/5.0251603)
  DOI : 10.1063/5.0251603
• Bridging multifluid and drift-diffusion models for bounded plasmas
  
  • Gangemi G M
  • Alvarez Laguna Alejandro
  • Massot M.
  • Hillewaert K.
  • Magin T.
  Physics of Plasmas, American Institute of Physics, 2025, 32 (2), pp.023502. Fluid models represent a valid alternative to kinetic approaches in simulating low-temperature discharges: a well-designed strategy must be able to combine the ability to predict a smooth transition from the quasineutral bulk to the sheath, where a space charge is built at a reasonable computational cost. These approaches belong to two families: multifluid models, where momenta of each species are modeled separately, and drift-diffusion models, where the dynamics of particles is dependent only on the gradient of particle concentration and on the electric force. It is shown that an equivalence between the two models exists and that it corresponds to a threshold Knudsen number, in the order of the square root of the electron-to-ion mass ratio; for an argon isothermal discharge, this value is given by a neutral background pressure Pn≳1000 Pa. This equivalence allows us to derive two analytical formulas for a priori estimation of the sheath width: the first one does not need any additional hypothesis but relies only on the natural transition from the quasineutral bulk to the sheath; the second approach improves the prediction by imposing a threshold value for the charge separation. The new analytical expressions provide better estimations of the floating sheath dimension in collisions-dominated regimes when tested against two models from the literature. (10.1063/5.0240640)
  DOI : 10.1063/5.0240640
• Identifying the Growth Phase of Magnetic Reconnection using Pressure-Strain Interaction
  
  • Barbhuiya M. Hasan
  • Cassak Paul
  • Chasapis Alex
  • Shay Michael
  • Cozzani Giulia
  • Retinò Alessandro
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2025, 130 (3), pp.e2024JA033446. Magnetic reconnection often initiates abruptly and then rapidly progresses to a nonlinear quasi-steady state. While satellites frequently detect reconnection events, ascertaining whether the system has achieved steady-state or is still evolving in time remains challenging. Here, we propose that the relatively rapid opening of the reconnection separatrices within the electron diffusion region serves as an indicator of the growth phase of reconnection. The opening of the separatrices is produced by electron flows diverging away from the neutral line downstream of the X-line and flowing around a dipolarization front. This flow pattern leads to characteristic spatial structures in the electron pressure-strain interaction that could be a useful indicator for the growth phase of a reconnection event. We employ two-dimensional particle-in-cell numerical simulations of anti-parallel magnetic reconnection to validate this prediction. We find that the signature discussed here, alongside traditional reconnection indicators, can serve as a marker of the growth phase. This signature is potentially accessible using multi-spacecraft single-point measurements, such as with NASA's Magnetospheric Multiscale satellites in Earth's magnetotail. Applications to other settings where reconnection occurs are also discussed. (10.1029/2024JA033446)
  DOI : 10.1029/2024JA033446
• Characterization of the solar wind context during the third Mercury flyby of BepiColombo
  
  • Rojo M.
  • Réville V.
  • Aizawa Sae
  • Varsani A.
  • Schmid D.
  • Jarry M.
  • Rodríguez-García L.
  • Persson M.
  • Rouillard Alexis P
  • Heyner D.
  • Milillo A.
  • André N.
  • Saito Y.
  • Murakami G.
  • Kasper J.
  • Bale S.
  Astronomy & Astrophysics - A&A, EDP Sciences, 2025, 698, pp.A221. Context: The interaction of the solar wind (SW) with the coupled magnetosphere-exosphere-surface of Mercury is complex. Charged particles released by the SW can precipitate along planetary magnetic field lines on specific areas of the surface of the planet. The processes responsible for the particle precipitation strongly depend on the orientation of the interplanetary magnetic field (IMF) upstream of Mercury. Aims: During the third Mercury flyby (MFB3) by BepiColombo, the properties of the SW inferred from BepiColombo observations of a highly compressed magnetosphere corresponded to those of a very dense plasma embedded in a slow SW. The Mercury Electron Analyzer (MEA) measured continuous high-energy electron fluxes in the nightside dawn sector of the compressed magnetosphere. In order to constrain further studies related to the origin of these populations, we aim to firmly confirm the initial inferences and detail the SW properties throughout MFB3. Methods: We took advantage of a close radial alignment between Parker Solar Probe (PSP) and Mercury. We monitored the activity of the Sun using SOHO coronagraphs and we used a potential field source surface model to estimate the location of the magnetic footpoints of PSP and BepiColombo on the photosphere of the Sun. We propagated the plasma parameters and the IMF measured by PSP at BepiColombo, to check if the plasma impacted Mercury. Results: We show that during MFB3, PSP and BepiColombo connected magnetically to the same region at the solar surface. The slow SW perturbation first measured at PSP propagated to Mercury and BepiColombo, as was confirmed by similarly elevated plasma densities measured at PSP and BepiColombo. The IMF orientation stayed southward during the whole MFB3. Conclusions: Our results provide strong constraints for future studies of the magnetospheric structure and dynamics during MFB3, including tail reconnection, electron and ion energization, and subsequent plasma precipitation onto the surface of Mercury. (10.1051/0004-6361/202553870)
  DOI : 10.1051/0004-6361/202553870
• Risk Assessment of the Ground Magnetic Response to the March and April 2023 Geomagnetic Storms Using Geomagnetically Induced Currents Indices
  
  • Amaechi Paul O
  • Messanga Honore
  • Grodji Frank O
  • Akala Andrew
  • Despirak Irina
  • Ngwira Chigomezyo M
  • Oyeyemi Elijah
  • Amory-Mazaudier Christine
  Space Weather: The International Journal of Research and Applications, American Geophysical Union (AGU), 2025, 23 (4), pp.e2024SW004324. We analyzed the solar origin and ground response during the severe geomagnetic storms (GSs) of 23–24 March (GS1) and 23–24 April 2023 (GS2) using Geomagnetically Induced Currents Indices (GIC indices) computed from geomagnetic field data. The GSs were initiated by erupting filaments and associated slow (fast) halo coronal mass ejections on 20 March (21 April) 2023. GS1 was also influenced by coronal hole high speed streams (CR HSSs) while substorm onsets drove the most intense GIC X (GIC Y ) of 86 (70) in Abisko, Sweden. GS2 was marked by strong negative Bz in a sheath and magnetic cloud with larger GIC indices of 84 (69) driven by magnetic pulsations, as evident at Abisko. This posed a moderate risk to power networks in Sweden. The threat however, reached only a low/moderate risk level in Boulder during the Sudden Impulse (SI)/main phase of GS1. For GS2, a low risk level was attained in Vernadsky and Eyrewell. As expected, at low latitude, GIC indices constituted a very low risk to ground infrastructures during both storms. The results also revealed longitudinal features with larger GIC indices in Boulder (Vernadsky) during the GS1 (GS2), and a North South Asymmetry characterized by a higher risk level in the northern (southern) hemisphere at the American longitude. Additionally, this study provides evidence that the equatorial electrojet can enhance GIC indices at the magnetic equator in the presence of sufficiently strong dH/dt. Finally, we relate GIC indices at high latitudes to the CR HSS on 23 March, and a magnetic cloud during the recovery phase on 24 April 2023. (10.1029/2024SW004324)
  DOI : 10.1029/2024SW004324
• On the use of pulsed DC bias for etching high aspect ratio features
  
  • Shi Xingyi
  • Sadighi Samaneh
  • Rauf Shahid
  • Luo Han
  • Wang Jun-Chieh
  • Kenney Jason
  • Booth Jean-Paul
  • Marinov Daniil
  • Foucher Mickaël
  • Sirse Nishant
  Journal of Vacuum Science & Technology A, American Vacuum Society, 2025, 43 (1). Inductively coupled plasmas (ICPs) containing Cl2 are widely used for plasma etching in the semiconductor industry. One common issue during plasma etching is aspect ratio dependent etching (ARDE), which is generally attributed to variation in the flux of etchant species to the bottom of features with different dimensions. Insufficient fluxes of neutral etchants to the bottom of high aspect ratio features can also result in sputtering, which tends to distort the feature profile. This article addresses two issues relevant to Cl2 ICP and plasma etching in these plasmas. First, a comprehensive set of diagnostics is used to validate a model for Cl2 ICP for gas pressure between 3 and 90 mTorr. The plasma diagnostics include microwave resonant hairpin probe-based measurements of electron density, photolysis-calibrated two-photon laser induced fluorescence measurement of Cl density, photo-detachment-based measurement of Cl− density, and laser diode absorption spectroscopy of argon metastable species to measure the gas temperature. Consistent with the experiments, the model shows that the electron density peaks near the center of the chamber at low gas pressure due to rapid diffusion. The electron density peak moves under the coils at higher pressures. Using the validated Cl2 model, we investigate ICPs with rectangular pulsed DC voltage for bias. It is shown that the Cl flux at the bottom of a trench decreases significantly with increasing aspect ratio of the trench. Neutral to ion flux ratio is therefore low at the bottom of higher aspect ratio trenches. The duty cycle of the pulsed bias waveform is found to be an effective means of increasing the neutral to energetic ion flux ratio, which should help with ARDE and sputter reduction. (10.1116/6.0003943)
  DOI : 10.1116/6.0003943
• Hybrid simulations of Mercury’s global dynamics and the interplanetary ions’ precipitation fluxes under different interplanetary conditions
  
  • Cazzola E.
  • Fontaine D.
  • Modolo Ronan
  Astronomy & Astrophysics - A&A, EDP Sciences, 2025, 701, pp.A209. Aims. We aim to quantify the impact of different interplanetary conditions met by Mercury along its orbit between its aphelion (~0.47 AU) and perihelion (~0.31 AU) on the Hermean environment, including the rate of solar-wind ion precipitation onto the surface.Methods. We performed a set of 3D global hybrid simulations (kinetic ions and fluid electrons) with interplanetary conditions taken from recent statistics from observations on board the Parker Solar Probe and MESSENGER missions in such a way as to represent an average scenario at both the aphelion and perihelion positions, and in the cases of a slow (250 km/s) and fast (450 km/s) solar wind.Results. The results are in general agreement with empirical models. However, we have found that the subsolar stand-off distances of magnetopause and bow shock, respectively, in the range of 1.0–1.4 RM and 1.3–2.0 RM, are relatively shorter than global statistical averages of, respectively, 1.45 and 1.96 RM. We also observe a local time (LT) asymmetry in the cusp’s location, with the northern cusp located in the post-noon sector centred around 13–14.3 LT and the southern cusp located in the pre-noon sector centred around 9–10.7 LT. Noticeably, the southern cusp region takes the shape of a parallelogram extended from southern middle latitudes in the pre-noon sector to equatorial latitudes in the post-noon sector. We suggest that these effects could result from the orientation of the interplanetary magnetic field along the Parker spiral, which is characterised by an almost radial orientation with a small duskward component. (10.1051/0004-6361/202553953)
  DOI : 10.1051/0004-6361/202553953
• Breaking seed dormancy in Mediterranean Brassica rapa wild populations: is cold plasma treatment efficient?
  
  • Wagner Marie-Hélène
  • Dufour Thierry
  • Geraci Anna
  • Oddo Elisabetta
  • Tarantino G.R.
  • Scafidi F.
  • Bailly C.
  • Hadj Arab H.
  • Boucenna B.
  • Tiret Mathieu
  • Falentin Cyril
  • Dupont A.
  • Ducournau S.
  • Chèvre Anne-Marie
  Seed Science and Technology, International Seed Testing Association Ista, 2025, 53 (3), pp.369-389. Turnip (Brassica rapa) is a native species of the Mediterranean area, spread from northwest France to south Algeria. In this study, dormancy and germination traits were assessed for 61 wild Brassica rapa populations collected across the Mediterranean region. Seed dormancy is a key factor influencing germination and seedling establishment. Three dormancy-breaking methods were compared: gibberellic acid, scarification and cold plasma. The efficiency and selectivity were evaluated through germination ability, time to 10% germination (T10), mean germination time and greenhouse emergence. Five days after imbibition, germination was only 18% for the untreated seeds but 60% for the plasma-treated seeds. Germination also began 24 hours earlier and mean germination time was reduced across most populations. However, there was a limited effect on seedling emergence, which remained around 55% for both untreated and treated samples. Comparative analysis indicates that cold plasma was more effective in alleviating embryo dormancy. In addition, histological and scanning electron microscopy showed that the seed coat differed according to the geographical origin of the populations, with a deeper dormancy in seeds from Sicilian populations. (10.15258/sst.2025.53.3.03)
  DOI : 10.15258/sst.2025.53.3.03
• Investigation of Filamentary and Diffuse DBD in CO₂ by Means of InSitu FTIR Absorption Spectroscopy
  
  • Bajon Corentin
  • Baratte Edmond
  • Sadi Dihya
  • Guaitella O.
  • Belinger A.
  • Dap Simon
  • Hoder T.
  • Naudé N.
  Journal of Physical Chemistry C, American Chemical Society, 2025, 129 (38), pp.16967-16976. This work investigates CO₂ dielectric barrier discharges (DBDs) at atmospheric pressure in the filamentary and diffuse regimes for the first time using in situ FTIR absorption measurements. The conversion factor of CO₂ is determined and is consistent with the results obtained for DBDs in the literature, following a power law with respect to the specific energy input in both regimes. Vibrational temperatures for CO₂ and CO molecules as well as rotational temperature are also determined within the discharge. A noticeably high vibrational temperature of CO is observed for low specific energy input (SEI). It drops abruptly when increasing the SEI which is attributed to strong vibrationalto-translational energy transfers by O atoms coming from CO₂ dissociation. Except that, the ordering of the different temperatures is similar to the results reported for other CO₂ discharges generated at lower pressures: the vibrational temperature of CO is higher than those of the different vibrational modes of CO₂. The latter are slightly higher than the rotational temperature of the gas for the diffuse mode, whereas they are almost the same for the filamentary mode. The evolution of the measured parameters as a function of the specific energy input is then discussed and a detailed comparison of the two different regimes is carried out. These data together with the knowledge of the reduced electric field in the diffuse regime, which is included in the range 120-140 Td for all conditions, can be of significant importance for further studies exploring the fundamentals of CO₂ plasma chemistry at atmospheric pressure, serving as reference for kinetic models. (10.1021/acs.jpcc.5c02224)
  DOI : 10.1021/acs.jpcc.5c02224
• Fast gas heating and peculiarities of temperature measurements by optical emission spectroscopy in nanosecond surface dielectric barrier discharge
  
  • Zhang Bin
  • Kreyder Geoffrey
  • Popov Nikolay
  • Shcherbanev Sergey
  • Starikovskaia Svetlana
  Plasma Sources Science and Technology, IOP Publishing, 2025, 34 (9), pp.095010. The aim of this work is the experimental and theoretical study of nanosecond Surface dielectric barrier discharge (SDBD) parameters in atmospheric pressure air. Measurements of electric current and delivered energy, ICCD images of the discharge at all stages of its evolution, and gas heating in the discharge and near afterglow are performed. The paper presents the results of 2D numerical modeling of the nanosecond SDBD. The results of the calculations are compared with measured data on the dynamics of current, energy input and gas heating. Special attention is paid to the study of the spatial structure of the discharge, in particular, to the distribution of gas temperature and the second positive system emission intensity in the direction perpendicular to the surface of the dielectric. It is shown that the results of temperature measurements in SDBD using optical emission spectroscopy technique are severely influenced by this spatial structure. The parameters of a probe discharge of smaller amplitude, which is formed by a reflected pulse 500 ns after the main discharge, are also calculated. The possibility of using the second diagnostic pulse to measure the gas temperature in the afterglow discharge is discussed. (10.1088/1361-6595/ae00ef)
  DOI : 10.1088/1361-6595/ae00ef
• Refining the modeling strategy for anomalous electron transport in fluid simulations of Hall thrusters via insights from PIC simulations
  
  • Petronio Federico
  • Alvarez Laguna Alejandro
  • Guillon Martin Jacques
  • Bourdon Anne
  • Chabert Pascal
  Physics of Plasmas, American Institute of Physics, 2025, 32 (7), pp.073513. Modeling anomalous transport in fluid simulations is a fundamental challenge for developing efficient and robust fluid simulation tools for Hall thrusters. This paper investigates optimal strategies for modeling anomalous transport in such simulations. Using the particle-in-cell (PIC) benchmark (BM) setup of Charoy et al., we demonstrate that various terms in the electron momentum equation can be readily identified. In particular, we show that the assumption of expressing the rate of change of the electron momentum due to instability as proportional to the momentum itself does not hold under these simulation conditions. Subsequently, we present two fluid simulations that replicate the conditions of the PIC BM setup. The first employs the conventional empirical anomalous collision frequency approach. While this model provides generally satisfactory results, it fails to capture specific plasma characteristics. The second fluid model adopts a data-driven approach to represent the anomalous force terms in the momentum equation. This approach furnishes significantly improved results, suggesting that although the anomalous collisionality framework provides meaningful outcomes, it can be effectively replaced by more advanced techniques. (10.1063/5.0274535)
  DOI : 10.1063/5.0274535