Publications

2025

• 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
• 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
• 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
• 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
• 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
• 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
• Hybrid simulations of Mercury’s global dynamics and the interplanetary ions’ precipitation fluxes under different interplanetary conditions
  
  • Cazzola E.
  • Fontaine D.
  • Modolo R.
  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
• 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
• Survey of the edge radial electric field in L-mode TCV plasmas using Doppler backscattering
  
  • Rienäcker S
  • Hennequin P
  • Vermare L
  • Honoré C
  • Coda S
  • Labit B
  • Vincent Benjamin
  • Wang Y
  • Frassinetti L
  • Panico O
  Plasma Physics and Controlled Fusion, IOP Publishing, 2025, 67 (6), pp.065003. A Doppler backscattering (DBS) diagnostic has recently been installed on the Tokamak à Configuration Variable (TCV) to facilitate the study of edge turbulence and flow shear in a versatile experimental environment. The dual channel V-band DBS system is coupled to TCV’s quasi-optical diagnostic launcher, providing access to the upper low-field side region of the plasma cross-section. Verifications of the DBS measurements are presented. The DBS equilibrium v ⊥ profiles are found to compare favorably with gas puff imaging (GPI) measurements and to the E r inferred from the radial force balance of the carbon impurity. The radial structure of the edge E r × B equilibrium flow and its dependencies are investigated across a representative set of L-mode TCV discharges, by varying density, auxiliary heating and magnetic configuration. (10.1088/1361-6587/add0e0)
  DOI : 10.1088/1361-6587/add0e0
• Phase transition from turbulence to zonal flows in the Hasegawa–Wakatani system
  
  • Guillon P L
  • Gürcan Ö D
  Physics of Plasmas, American Institute of Physics, 2025, 32 (1). The transition between two-dimensional hydrodynamic turbulence and quasi-one-dimensional zonostrophic turbulence is examined in the modified Hasegawa–Wakatani system, which is considered as a minimal model of β-plane-like drift-wave turbulence with an intrinsic instability. Extensive parameter scans were performed across a wide range of values for the adiabaticity parameter C describing the strength of coupling between the two equations. A sharp transition from 2D isotropic turbulence to a quasi-1D system, dominated by zonal flows, is observed using the fraction of the kinetic energy of the zonal modes as the order parameter, at C≈0.1. It is shown that this transition exhibits a hysteresis loop around the transition point, where the adiabaticity parameter plays the role of the control parameter of its nonlinear self-organization. It was also observed that the radial particle flux scales with the adiabaticity parameter following two different power law dependencies in the two regimes. A simple quasi-linear saturation rule which accounts for the presence of zonal flows is proposed, and is shown to agree very well with the observed nonlinear fluxes. Motivated by the phenomenon of quasi-one dimensionalisation of the system at high C, a number of reduction schemes based on a limited number of modes were investigated and the results were compared to direct numerical simulations. In particular, it was observed that a minimal reduced model consisting of 2 poloidal and 2 radial modes was able to replicate the phase transition behavior, while any further reduction failed to capture it. (10.1063/5.0242282)
  DOI : 10.1063/5.0242282
• Characterization of the solar wind context during the third Mercury flyby of BepiColombo
  
  • Rojo M.
  • Réville V.
  • Aizawa S.
  • Varsani A.
  • Schmid D.
  • Jarry M.
  • Rodríguez-García L.
  • Persson M.
  • Rouillard A.
  • Heyner D.
  • Milillo A.
  • André N.
  • Saito Y.
  • Murakami G.
  • Kasper J. C.
  • Bale S. D.
  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