Publications

2025

• Distributed Quantum Advantage for Local Problems
  
  • Balliu Alkida
  • Brandt Sebastian
  • Coiteux-Roy Xavier
  • d'Amore Francesco
  • Equi Massimo
  • Le Gall François
  • Lievonen Henrik
  • Modanese Augusto
  • Olivetti Dennis
  • Renou Marc-Olivier
  • Suomela Jukka
  • Tendick Lucas
  • Veeren Isadora
  , 2025, pp.451-462. We present the first local problem that shows a super-constant separation between the classical randomized LOCAL model of distributed computing and its quantum counterpart. By prior work, such a separation was known only for an artificial graph problem with an inherently global definition [Le Gall et al. 2019]. We present a problem that we call iterated GHZ, which is defined using only local constraints. Formally, it is a family of locally checkable labeling problems [Naor and Stockmeyer 1995]; in particular, solutions can be verified with a constant-round distributed algorithm. We show that in graphs of maximum degree $\Delta$, any classical (deterministic or randomized) LOCAL model algorithm will require $\Omega(\Delta)$ rounds to solve the iterated GHZ problem, while the problem can be solved in $1$ round in quantum-LOCAL. We use the round elimination technique to prove that the iterated GHZ problem requires $\Omega(\Delta)$ rounds for classical algorithms. This is the first work that shows that round elimination is indeed able to separate the two models, and this also demonstrates that round elimination cannot be used to prove lower bounds for quantum-LOCAL. To apply round elimination, we introduce a new technique that allows us to discover appropriate problem relaxations in a mechanical way; it turns out that this new technique extends beyond the scope of the iterated GHZ problem and can be used to e.g. reproduce prior results on maximal matchings [FOCS 2019, PODC 2020] in a systematic manner. (10.1145/3717823.3718233)
  DOI : 10.1145/3717823.3718233
• Fiber-based high-energy 1550 nm laser for generating high-order harmonics
  
  • Mikhneva Anastasiia
  • Boukhaoui Djamila
  • Idlahcen Saïd
  • Houard Jonathan
  • Blum Ivan
  • Godin Thomas
  • Guiramand Leo
  • Amrani Foued
  • Gérôme Frédéric
  • Benabid Fetah
  • Gauthier David
  • Merdji Hamed
  • Boutu Willem
  • Vella Angela
  • Hideur Ammar
  , 2025, pp.CG-4.4. The demand for precise, high-energy Extreme Ultraviolet (EUV) sources is growing across scientific and industrial fields. Studies have demonstrated that bulk crystals driven by mid-infrared laser pulses can generate high-order harmonics with enhanced intensities, extended cut-off energies, and improved damage thresholds [1]. While high-energy OPCPA and OPA systems have been successfully utilized to achieve these results, their complexity highlights the need for simpler, more compact solutions [1, 2, 3]. Ultrafast mid-IR fiber lasers have emerged as a promising alternative for high-harmonic generation (HHG). However, their pulse energies are limited to the nanojoule range [4]. Here, we report the first demonstration of high-order harmonics generated in bulk crystals using a high-energy fiber laser operating near 1550 nm. Our laser system integrates an erbium-doped fiber amplifier with a gas-filled hollow-core photonic crystal fiber (HC-PCF) for post-compression, delivering few-cycle pulses with durations under 50 fs, microjoule-level pulse energies, and a repetition rate of 660 kHz (fig. 1) [5].
• Petri nets and higher-dimensional automata
  
  • Amrane Amazigh
  • Bazille Hugo
  • Fahrenberg Uli
  • Hélouët Loïc
  • Schlehuber-Caissier Philipp
  , 2025, 15714, pp.18-40. Unlabelled - Coronal dimmings associated with coronal mass ejections (CMEs) from the Sun have gained much attention since the late 1990s when they were first observed in high-cadence imagery of the SOHO/EIT and Yohkoh/SXT instruments. They appear as localized sudden decreases of the coronal emission at extreme ultraviolet (EUV) and soft X-ray (SXR) wavelengths, that evolve impulsively during the lift-off and early expansion phase of a CME. Coronal dimmings have been interpreted as "footprints" of the erupting flux rope and also as indicators of the coronal mass loss by CMEs. However, these are only some aspects of coronal dimmings and how they relate to the overall CME/flare process. The goal of this review is to summarize our current understanding and observational findings on coronal dimmings, how they relate to CME simulations, and to discuss how they can be used to provide us with a deeper insight and diagnostics of the triggering of CMEs, the magnetic connectivities and coronal reconfigurations due to the CME as well as the replenishment of the corona after an eruption. In addition, we go beyond a pure review by introducing a new, physics-driven categorization of coronal dimmings based on the magnetic flux systems involved in the eruption process. Finally, we discuss the recent progress in studying coronal dimmings on solar-like and late-type stars, and how to use them as a diagnostics for stellar coronal mass ejections and their properties. Supplementary information - The online version contains supplementary material available at 10.1007/s41116-025-00041-4. (10.1007/978-3-031-94634-9_2)
  DOI : 10.1007/978-3-031-94634-9_2
• Categorical semantics of compositional reinforcement learning
  
  • Bakirtzis Georgios
  • Savvas Michail
  • Topcu Ufuk
  Journal of Machine Learning Research, Microtome Publishing, 2025, 26 (130), pp.1-37. Compositional knowledge representations in reinforcement learning (RL) facilitate modular, interpretable, and safe task specifications. However, generating compositional models requires the characterization of minimal assumptions for the robustness of the compositionality feature, especially in the case of functional decompositions. Using a categorical point of view, we develop a knowledge representation framework for a compositional theory of RL. Our approach relies on the theoretical study of the category MDP, whose objects are Markov decision processes (MDPs) acting as models of tasks. The categorical semantics models the compositionality of tasks through the application of pushout operations akin to combining puzzle pieces. As a practical application of these pushout operations, we introduce zig-zag diagrams that rely on the compositional guarantees engendered by the category MDP. We further prove that properties of the category MDP unify concepts, such as enforcing safety requirements and exploiting symmetries, generalizing previous abstraction theories for RL.
• Navigating the sociotechnical labyrinth: Dynamic certification for responsible embodied AI
  
  • Bakirtzis Georgios
  • Aler Tubella Andrea
  • Theodorou Andreas
  • Danks David
  • Topcu Ufuk
  , 2025. Sociotechnical requirements shape the governance of artificially intelligent (AI) systems. In an era where embodied AI technologies are rapidly reshaping various facets of contemporary society, their inherent dynamic adaptability presents a unique blend of opportunities and challenges. Traditional regulatory mechanisms, often designed for static---or slower-paced---technologies, find themselves at a crossroads when faced with the fluid and evolving nature of AI systems. Moreover, typical problems in AI, for example, the frequent opacity and unpredictability of the behaviour of the systems, add additional sociotechnical challenges. To address these interconnected issues, we introduce the concept of dynamic certification, an adaptive regulatory framework specifically crafted to keep pace with the continuous evolution of AI systems. The complexity of these challenges requires common progress in multiple domains: technical, socio-governmental, and regulatory. Our proposed transdisciplinary approach is designed to ensure the safe, ethical, and practical deployment of AI systems, aligning them bidirectionally with the real-world contexts in which they operate. By doing so, we aim to bridge the gap between rapid technological advancement and effective regulatory oversight, ensuring that AI systems not only achieve their intended goals but also adhere to ethical standards and societal values. (10.1016/B978-0-44-340553-2.00019-8)
  DOI : 10.1016/B978-0-44-340553-2.00019-8
• Improved monocular depth prediction using distance transform over pre-semantic contours with self-supervised neural networks
  
  • Hariat Marwane
  • Manzanera Antoine
  • Filliat David
  , 2025, pp.21868-21879. Monocular depth estimation (MDE) with self-supervised training approaches struggles in low-texture areas, where photometric losses may lead to ambiguous depth predictions. To address this, we propose a novel technique that enhances spatial information by applying a distance transform over pre-semantic contours, augmenting discriminative power in low texture regions. Our approach jointly estimates pre-semantic contours, depth and ego-motion. The pre-semantic contours are leveraged to produce new input images, with variance augmented by the distance transform in uniform areas. This approach results in more effective loss functions, enhancing the training process for depth and ego-motion. We demonstrate theoretically that the distance transform is the optimal variance-augmenting technique in this context. Through extensive experiments on KITTI, Cityscapes, Waymo, NYUv2 and ScanNet our model demonstrates robust performance, surpassing competing self-supervised methods in MDE. (10.1109/CVPR52734.2025.02037)
  DOI : 10.1109/CVPR52734.2025.02037
• Toughening effects of out-of-crack-path architected zones
  
  • Triclot Julie
  • Corre Thomas
  • Lazarus Véronique
  • Gravouil Anthony
  , 2024. The increasing use of architected materials has broadened the possibilities of mechanical behaviour. In this article, we aim to explore these new possibilities in terms of in-service behaviour, especially in terms of crack propagation by performing an in-depth study in the framework of Linear Elastic Fracture Mechanics (LEFM). The specific configuration studied here is the case where the architected zones are symmetrically positioned adjacently to the crack path and no propagation occurs within the zone. This problem is addressed both numerically and experimentally. Numerically, an path-following algorithm is used to simulate the crack propagation. Different toughening aspects of the addition of architected zones are identified. First, a temporary increase in crack propagation resistance is shown. It comes from a temporary increase of stored elastic energy in the architected zones, thus acting as mechanical springs. Second, a snap-back instability appears, linked to the release of the previously stored energy. It leads to a higher energy dissipated by the crack propagation process. Experimentally, we evidence the possibility to reproduce the theoretical results using 3D printing. A good quantitative comparison is obtained between numerical and experimental approaches. This study shows that it is possible to improve crack propagation resistance while lightening the component by addition of architected zones outside the crack path. This opens up the way to tune finely, through the use of optimization tools, the crack propagation response.
• Path-following methods for quasi-static crack propagation simulated by variational phase field approach
  
  • Loiseau Flavien
  • Lazarus Veronique
  , 2025.
• Correct-by-construction requirement decomposition
  
  • Sun Minghui
  • Bakirtzis Georgios
  • Jafarzadeh Hassan
  • Fleming Cody
  Software and Systems Modeling, Springer Verlag, 2025, pp.1-16. In systems engineering, accurately decomposing requirements is crucial for creating well-defined and manageable system components, particularly in safety-critical domains. Despite the critical need, rigorous, top-down methodologies for effectively breaking down complex requirements into precise, actionable sub-requirements are scarce, especially compared to the wealth of bottom-up verification techniques. Addressing this gap, we introduce a formal decomposition for contract-based design that guarantees the correctness of decomposed requirements if specific conditions are met. Our (semi-)automated methodology augments contract-based design with reachability analysis and constraint programming to systematically identify, verify, and validate sub-requirements representable by continuous bounded sets---continuous relations between real-valued inputs and outputs. We demonstrate the efficacy and practicality of a correct-by-construction approach through a comprehensive case study on a cruise control system, highlighting how our methodology improves the interpretability, tractability, and verifiability of system requirements. (10.1007/s10270-025-01291-4)
  DOI : 10.1007/s10270-025-01291-4
• Caractérisation expérimentale du bruit d’un drone en vol stationnaire en environnements réel et contrôlé
  
  • Cotté Benjamin
  • Simião Pitta Vinícius
  • Hoareau Damien
  • Beausse Yoann
  • Toralba Thibault
  • Doaré Olivier
  • Chapoutot Alexandre
  , 2025. La mesure du bruit des drones dans un environnement réaliste est importante afin d’évaluer leur impact sur les riverains, mais aussi pour comprendre les sources de bruit dominantes en fonction des opérations de vol et ainsi améliorer les outils de modélisation et de simulation du bruit. Cette caractérisation expérimentale est une tâche difficile à cause de la variabilité des conditions météorologiques en milieu extérieur, du bruit de fond, et du bruit du drone. En effet, les différentes hélices du drone voient leur vitesse de rotation varier indépendamment pour assurer la stabilité en vol. C’est pourquoi des mesures en environnement contrôlé comme des chambres anéchoïques sont également réalisées afin de diminuer la variabilité du bruit, même si la taille limitée de ces installations limitent les opérations de vol réalisables. L’objectif de cette étude est de comparer les mesures de bruit en chambre anéchoique et en environnement extérieur pour un drone quadricoptère de petite taille en vol stationnaire, afin de déterminer les similitudes et différences entre les deux types de mesures. Les mesures en chambre anéchoïque ont été réalisées sur une structure fixe, ce qui permet de caractériser les hélices soit de façon isolée, soit par paire soit pour l’ensemble des quatre hélices. Pour les mesures en milieu extérieur, six microphones placés sur des plate-formes rigides ont été utilisées, et des mesures en vol stationnaire à trois hauteurs ont été réalisées. Même si les signaux acoustiques mesurés en extérieur présentent une plus grande complexité, les mêmes composantes spectrales sont retrouvées dans les deux types d’environnement. En particulier, une forte émergence du bruit des moteurs à environ 18 fois la fréquence de passage des pales est observée.
• Observation of a Multimode Displaced Squeezed State in High-Harmonic Generation
  
  • Theidel David
  • Cotte Viviane
  • Heinzel Philip
  • Griguer Houssna
  • Weis Mateusz
  • Sondenheimer René
  • Merdji Hamed
  , 2024. High harmonic generation is a resource of extremely broad frequency combs of ultrashort light pulses. The non-classical nature of this new quantum source has been recently evidenced in semiconductors by showing that high harmonic generation generates multimode squeezed states of light. Applications in quantum information science require the knowledge of the mode structure of the created states, defining how the quantum properties distribute over the spectral modes. To achieve that, an effective Schmidt decomposition of the reduced photonic state is performed on a tripartite harmonic set by simultaneously measuring the second- and third-order intensity correlation function. The Schmidt number is estimated which indicates an almost single-mode structure for each harmonic, a useful resource in quantum technology. By modelling our data with a displaced squeezed state, we retrieve the dependencies of the measured correlation as a function of the high harmonic driving laser intensity. The effective high-harmonic mode distribution is retrieved, and the strength of the contributing squeezing modes is estimated. Additionally, we demonstrate a significant violation of a Cauchy-Schwarz-type inequality for three biseparable partitions by multiple standard deviations. Our results confirm non-classicality of the high-harmonic generation process in semiconductors. The source operates at room temperature with compact lasers, and it could become a useful resource for future applications in quantum technologies. (10.48550/arXiv.2411.02311)
  DOI : 10.48550/arXiv.2411.02311
• Les spécialisations industrielles des PECO membres de l’Union européenne sur la période 1992-2018 : Une lecture structurale
  
  • Anedda Raffaele
  • Lebert Didier
  Economie appliquée, Classiques Garnier, 2025 (6), pp.119-147. L’histoire de la transformation des systèmes productifs des pays anciennement socialistes ayant rejoint l’Union européenne durant les années 2000 est aujourd’hui établie. Après une période de transition marquée par de fortes perturbations macro- et méso-économiques débordant pour certains d’entre eux leurs dates d’entrée dans l’Union, ces pays ont stabilisé ces systèmes quelquefois caractérisés désormais par des spécialisations industrielles high tech prononcées. L’objectif de l’article consiste à proposer une architecture empirique fondée sur la théorie de la dominance économique pour représenter cette transformation à l’échelle de chacun des onze pays concernés. Une typologie des trajectoires constatées est ensuite établie. (10.48611/isbn.978-2-406-18063-0.p.0119)
  DOI : 10.48611/isbn.978-2-406-18063-0.p.0119
• Les inégalités d’intégration au sein de l’espace économique méditerranéen au tournant du xxie siècle
  
  • Lebert Didier
  Economie appliquée, Classiques Garnier, 2025 (6), pp.11-35. Nous proposons un nouvel indicateur mesurant les inégalités d’intégration des pays au sein d’un espace d’échanges commerciaux. Cet indicateur associe une approche globale à une autre révélant la contribution spécifique de chaque pays à sa valeur. Nous l’appliquons à l’espace économique méditerranéen (EEM) sur la période 1980-2004, période précédant une intense dynamique institutionnelle visant à intégrer davantage le Nord et le Sud de la Méditerranée. Avant ces transformations institutionnelles, l’EEM reste une zone globalement peu intégrée, et cette faible intégration est entretenue par les principaux pays d’Europe qui en sont membres. (10.48611/isbn.978-2-406-18063-0.p.0011)
  DOI : 10.48611/isbn.978-2-406-18063-0.p.0011
• POLSAR2POLSAR: A SEMI-SUPERVISED DESPECKLING ALGORITHM FOR POLARIMETRIC SAR IMAGES
  
  • Mendes Cristiano Ulondu
  • Dalsasso Emanuele
  • Zhang Yi
  • Denis Loïc
  • Tupin Florence
  ISPRS Journal of Photogrammetry and Remote Sensing, Elsevier, 2025, 220 (0924-2716), pp.783-798. <div><p>Polarimetric Synthetic Aperture Radar (PolSAR) imagery is a valuable tool for Earth observation. This imaging technique finds wide application in various fields, including agriculture, forestry, geology, and disaster monitoring. However, due to the inherent presence of speckle noise, filtering is often necessary to improve the interpretability and reliability of PolSAR data. The effectiveness of a speckle filter is measured by its ability to attenuate fluctuations without introducing artifacts or degrading spatial and polarimetric information. Recent advancements in this domain leverage the power of deep learning. These approaches adopt a supervised learning strategy, which requires a large amount of speckle-free images that are costly to produce. In contrast, this paper presents PolSAR2PolSAR, a semi-supervised learning strategy that only requires, from the sensor under consideration, pairs of noisy images of the same location and acquired in the same configuration (same incidence angle and mode as during the revisit of the satellite on its orbit). Our approach applies to a wide range of sensors. Experiments on Radarsat-2 and RCM data demonstrate the capacity of the proposed method to effectively reduce speckle noise and retrieve fine details. The code of the trained models is made freely available at https://gitlab.telecom-paris.fr/ring/polsar2polsar. The repository additionally contains a model fine-tuned on SLC PolSAR images from NASA's UAVSAR sensor.</p></div>
• Small-scale interface dynamic modelling based on the geometric method of moments for a two-scale two-phase flow model with a disperse small scale
  
  • Loison Arthur
  • Pichard Teddy
  • Kokh Samuel
  • Massot Marc
  Journal of Fluid Mechanics, Cambridge University Press (CUP), 2025, 1003 (A27), pp.1--42. In this contribution, we develop a versatile formalism to derive unified two-phase models describing both the separated and disperse regimes as introduced by Loison et al. (2024). It relies on the stationary action principle and interface geometric variables. This contribution provides a novel method to derive small-scale models for the dynamics of the interface geometry. They are introduced here on a simplified case where all the scales and phases have the same velocity and that does not take into account large-scale capillary forces. The derivation tools yield a proper mathematical framework through hyperbolicity and signed entropy evolution. The formalism encompasses a hierarchy of small-scale reduced-order models based on a statistical description at a mesoscopic kinetic level and is naturally able to include the description of a disperse phase with polydispersity in size. This hierarchy includes both a cloud of spherical droplets and non-spherical droplets experiencing a dynamical behaviour through incompressible oscillations. The associated small-scale variables are moments of a number density function resulting from the geometric method of moments (GeoMOM). This method selects moments as small-scale geometric variables compatible with the structure and dynamics of the interface; they are defined independently of the flow topology and, therefore, this model allows the coupling of the two-scale flow with an inter-scale transfer. It is shown in particular that the resulting dynamics provides partial closures for the interface area density equation obtained from the averaging approach. (10.1017/jfm.2024.1200)
  DOI : 10.1017/jfm.2024.1200
• High-harmonic generation in solids from a high-energy fiber laser system
  
  • Boukhaoui D.
  • Mikhneva A.
  • Idlahcen S.
  • Houard Jonathan
  • Godin T.
  • Guiramand L.
  • Blum Ivan
  • Amrani F.
  • Gérôme F.
  • Benabid F.
  • Gauthier D.
  • Boutu W.
  • Merdji H.
  • Vella Angela
  • Hideur A.
  APL Photonics, AIP Publishing LLC, 2025, 10 (2), pp.026106. We demonstrate high-harmonic generation (HHG) in solids using a high-energy fiber laser system operating at 1550 nm. The driving few-cycle source consists of an erbium-doped fiber chirped pulse amplifier combined with a postcompression stage featuring a gas-filled hollow-core photonic crystal fiber (HC-PCF). The nonlinear self-compression process in the HC-PCF enables the generation of ultrashort pulses with sub-50 fs durations and µJ-levels energies at a 660 kHz repetition rate. Perturbative and non-perturbative harmonics were subsequently generated when focusing the few-cycle pulses into zinc oxide (ZnO) and magnesium oxide (MgO) bulk samples. In the latter, in particular, we observed the generation of EUV harmonics up to H29 (below 55 nm), highlighting the remarkable potential of such a platform for the development of compact HHG sources. (10.1063/5.0244415)
  DOI : 10.1063/5.0244415
• 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>
• High-Harmonic Generation in an Optical Fiber Functionalized with Zinc Oxide Thin Films
  
  • Tiliouine Idris
  • Leventoux Yann
  • Orlianges Jean-Christophe
  • Crunteanu Aurelian
  • Froidevaux Marie
  • Merdji Hamed
  • Février Sébastien
  Photonics, MDPI, 2025, 12 (1), pp.82. High-order harmonic generation (HHG) in semiconductor thin films from ultrashort mid-infrared laser drivers holds the potential for the realization of integrated sources of extreme ultraviolet light. Here, we demonstrate solid-state HHG in zinc oxide thin films synthesized by the radiofrequency reactive magnetron sputtering process directly on the cleaved facets of optical fibers. Harmonics 3 to 13 of the radiation from a fiber-based laser system delivering 500 kW, 96 fs pulses at 3130 nm are produced in the thin film and guided along the fiber. A proper choice of the laser wavelength and fiber material allows for filtering out the mid-IR pump laser and achieving the HHG mode selection. The possibility to nanostructure the fiber exit by, e.g., focused ion beam milling paves the way to an increased control over the HHG spatial mode. (10.3390/photonics12010082)
  DOI : 10.3390/photonics12010082
• 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
• 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
• Incoherent Diffraction Imaging with a Pseudo-Thermal Light Source
  
  • Claveria Pablo San Miguel
  • Antunes Sesbastião
  • Biesterfeld Peer
  • Fernandes Matilde
  • Garcia Matilde
  • Nunes Matilde
  • Fernandez Lucas Ansia
  • Williams Gareth
  • Froehlich Sven
  • Theidel David
  • Mosel Philip
  • Fsaifes Ihsan
  • Trabattoni Andrea
  • Piccardo Marco
  • Chanteloup Jean-Christophe
  • Kovacev Milutin
  • Merdji Hamed
  • Fajardo Marta
  Optica Open, 2025. Incoherent Diffraction Imaging - IDI - is a diffraction-based imaging technique that has been recently proposed to exploit the partial coherence of incoherently scattered light to retrieve structural information from the scattering centers. Similar to the stellar intensity interferometry of Hanbury Brown and Twiss, the signal builds up on the second-order spatial correlations of the emitted light. The complex spatial distribution of the target is thereby encoded in the spatial intensity fluctuations of the scattered light. The first experimental realisations of this imaging technique have been realised using the fluorescence excited by an ultra-short X-ray pulse at Free Electron Laser (FEL) facilities. Here, we propose an alternative set-up based on a table-top Pseudo-Thermal Light Source. This set-up allows us to explore IDI under a wide range of physically relevant conditions as well as to benchmark numerical and analytical models currently used to determine the imaging capabilities of this technique. (10.48550/arXiv.2501.05417)
  DOI : 10.48550/arXiv.2501.05417
• Modeling polycyclic aromatic hydrocarbons (PAH) and liquid organic hydrogen carriers (LOHC) with the SAFT-γ Mie group-contribution equation of state
  
  • Velásquez Sarmiento Edgar
  • Paricaud Patrice
  , 2025.
• 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
• 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