Publications

2023

• Nanosecond Surface Dielectric Barrier Discharge: Experimental investigation of streamer to filament transition in high-pressure gases
  
  • Lafaurie V
  • Starikovskaia S
  , 2023. In high-pressure nanosecond surface dielectric barrier discharges (nSDBD) it is common to observe two different type of streamer development: a diffuse mode and a filamentary mode [1-2]. The transition between these modes was defined as the apparition of 2 to 5 filaments with varying applied voltage. In this study, the effects of photoionisation and electronegativity of the gas mixture on the transition voltage were compared for a wide range of pressures and concentrations. In the positive polarity, it was found that photoionisation played a stabilising role on the diffusive discharge for all studied pressures, while electronegativity appeared to reduce the threshold for transition at lower pressures. In the negative polarity, the photoionisation effect was no longer observable while the filament threshold was lowered for more electronegative mixtures. Fundemental understanding of these processes is of great importance in many applications, most of all in plasma-assisted combustion [3-4].
• Cold plasma therapy applied to non-small cell lung cancer: deciphering the relevant plasma parameters to induce antitumor effects
  
  • Geraud Korentin
  • Marmier Solenne
  • Soulier Manon
  • Decauchy Henri
  • Cremer Isabelle
  • Dufour Thierry
  , 2023.
• Investigating the performances of cold plasma endoscopy for cholangiocarcinoma local treatment
  
  • Soulier Manon
  • Pavy Allan
  • Decauchy Henri
  • Geraud Korentin
  • Lekbaby Bouchra
  • Aoudjehane Lynda
  • Camus Marine
  • Fouassier Laura
  • Dufour Thierry
  , 2023.
• Benchmark of particle-in-cell simulations of a Penning-type discharge: Preliminary results
  
  • Garrigues Laurent
  • Fubiani G.
  • Boeuf Jean-Pierre
  • Powis A T
  • Villafana W
  • Kaganovich I
  • Raitses Y
  • Petronio F
  • Alvarez-Laguna A
  • Bourdon A
  • Chabert P
  • Bogopolsky G
  • Cuenot B
  • Vermorel O
  • Sydorenko D
  • Papahn Zadeh M
  • Smolyakov A
  • Cichocki F
  • Minelli P
  • Taccogna F
  • Eremin D
  • Xu L
  • Denig A
  • Hara K
  • Elias P Q
  • Bello Benitez E
  • Marin A
  • Ahedo E
  • Merino M
  • Fajardo P
  • Donko Z
  • Hartmann P
  • Turner M
  • Reza M
  • Faraji F
  • Knoll A
  • Parodi P
  • Magin T
  , 2023.
• W-band tunable, multi-channel, frequency comb Doppler backscattering diagnostic in the ASDEX-Upgrade tokamak
  
  • Molina Cabrera P.
  • Kasparek W.
  • Happel T.
  • Eixenberger H.
  • Kammerloher L.
  • Hennequin P.
  • Höfler K.
  • Honoré C.
  Review of Scientific Instruments, American Institute of Physics, 2023, 94 (8). This article presents the design, implementation, and first data of a uniquely flexible, multi-channel, frequency comb Doppler backscattering diagnostic recently made operational in the ASDEX-Upgrade tokamak 1. It uses a double sideband signal fed into a x6 frequency multiplier to produce a multiple-frequency output spectrum. Seven of these frequencies are simultaneously measured in the receiver via a two-step frequency down-conversion and traditional I/Q demodulation. The frequency comb spectrum is fully tunable to sit anywhere in the W-band. The inter-frequency separation is also uniquely tunable remotely between 0.1 and 6 GHz without any hardware changes. The diagnostic can be operated in both O and X-mode polarizations and at both oblique and normal incidence to the cutoff layer. The time evolution of backscattered signals, in excess of 30 dB, from 7 distinct frequencies sampled simultaneously are presented across an L to H-mode confinement regime transition. (10.1063/5.0151271)
  DOI : 10.1063/5.0151271
• Transport and zonal flows dynamics in flux-driven interchange & drift waves turbulence
  
  • Panico Olivier
  • Sarazin Yanick
  • Hennequin Pascale
  • Gürcan Özgür D.
  , 2023. Cross-field transport, that controls the energy confinement time in tokamaks, is mainly driven by turbulence. In L-mode edge plasmas, the interchange and drift waves instabilities are expected to be dominant. The first one is linked to the magnetic curvature while the second derives from the parallel conductivity [1]. It is observed that the resulting ion-scale turbulence can self-organize into zonal flows (ZFs) that participate efficiently to its saturation [2, 3]. More recently, it has been observed that ZFs can structure into staircases [4], hence producing a set of micro-barriers that can efficiently mitigate avalanche transport. In this work, the issues of ZFs generation and impact on transport are addressed by means of a reduced flux-driven nonlinear model that features both interchange and drift waves instabilities [5, 6]. The linear properties of both instabilities are controlled by two plasma parameters, the mean curvature g of the magnetic field, and the adiabaticity parameter C that scales like the square of the parallel wave vector divided by the electron-ion collision frequency. It is shown here that albeit the interchange parameter is controlling the structuration into staircases, the adiabaticity parameter controls the turbulent energy that gets stored in the flows. Moreover, the confinement time normalized to a mixing length estimate exhibits the same dependencies as the energy balance between turbulent modes and zonal flows, attesting the efficiency of nonlinearly generated flows to mitigate turbulent transport.
• Kinetic processes in fast collisionless plasma flows
  
  • Le Contel O.
  • Retinò A.
  • Alqeeq S.
  • Chust T.
  • Khotyaintsev Y.
  • Nakamura R.
  • Lindqvist P.-A.
  • Gershman D. J.
  • Burch J. L.
  • Torbert R. B.
  • Ergun R. E.
  • Giles B. L.
  • Fuselier S. A.
  • Russell C. T.
  • Saito Y.
  • Génot V.
  • Lavraud B.
  • Turner D. L.
  • Cohen I. J.
  , 2023. The collisionless plasma of the Earth’s magnetotail hosts non stationary plasma transport caused by fast and transient flows moving towards the Earth with speeds larger than hundreds of km/s. These flows generate sharp increases of the northward component of the magnetic field called dipolarisation fronts. These kinetic scale structures of a few ion inertial lengths along the direction of propagation are associated with an intense wave activity such as lower-hybrid waves, whistler mode waves and electromagnetic phase-space holes. Furthermore, these dipolarisation fronts move with their own dynamic current circuit and drive important energy conversion processes contributing to the energy global cycle of the magnetospheric system. I propose to discuss recent results obtained by analysing data from the Multiscale Magnetospheric mission consisting of four satellites evolving in a tetrahedral configurationand separated at the electron scale. Finally, I will stress the need to go further by implementing new space missions capable of measuring the kinetic and fluid scales simultaneously.
• Operando time and space-resolved liquid-phase diagnostics reveal the plasma selective synthesis of nanographenes
  
  • Kurniawan Darwin
  • Caielli Francesca
  • Thyagajaran Karthik
  • Ostrikov Kostya
  • Chiang Wei-Hung
  • Pai David Z
  Nanoscale, Royal Society of Chemistry, 2023, 16 (32), pp.15104-15112. Coupling atmospheric-pressure low-temperature plasmas to electrochemical reactors enables the generation of highly reactive species at plasma–liquid interfaces. This type of plasma electrochemical reactor (PEC) has been used to synthesize fluorescent nitrogen-doped graphene quantum dots (NGQDs), which are usable for multifunctional applications in a facile, simple, and sustainable way. However, the synthesis mechanism remains poorly understood, as well as the location of synthesis. To research these issues, we present an in situ diagnostics study on liquid phase chemistry during the PEC synthesis of NGQDs from chitosan. Monitoring of the photoluminescence and UV-VIS absorption at different depths in the reaction medium during plasma treatment reveals that the NGQD production initiates at the plasma–liquid interface but its completion and/or accumulation occurs at a few millimetres depth below the interface, where the liquid ceases to flow convectively, as determined by particle image velocimetry. Our study provides insights into the plasma synthesis of fluorescent GQDs/NGQDs from carbon precursors that may prove useful for achieving the scalability of PEC processes up to continuous-flow or array reactors. (10.1039/D4NR01280A)
  DOI : 10.1039/D4NR01280A
• Space weather investigation Frontier (SWIFT)
  
  • Akhavan-Tafti M.
  • Johnson L.
  • Sood R.
  • Slavin J.
  • Pulkkinen T.
  • Lepri S.
  • Kilpua E.
  • Fontaine D.
  • Szabo A.
  • Wilson L.
  • Le G.
  • Atilaw T.
  • Ala-Lahti M.
  • Soni S.
  • Biesecker D.
  • Jian L.
  • Lario D.
  Frontiers in Astronomy and Space Sciences, Frontiers Media, 2023, 10. The Space Weather Investigation Frontier (SWIFT) mission will aim at making major discoveries on the three-dimensional structure and dynamics of heliospheric structures that drive space weather. The focus will be on Interplanetary Coronal Mass Ejections (ICMEs) that originate from massive expulsions of plasma and magnetic flux from the solar corona. They cause the largest geomagnetic storms and solar energetic particle events, threatening to endanger life and disrupt technology on Earth and in space. A big current problem, both regarding fundamental solar-terrestrial physics and space weather, is that we do not yet understand spatial characteristics and temporal evolution of ICMEs and that the existing remote-sensing and in-situ observatories are not suited for resolving multi-layered and evolutionary structures in these massive storm drivers. Here, we propose a groundbreaking mission concept study using solar sail technology that, for the first time, will make continuous, in-situ multi-point observations along the Sun-Earth line beyond the Lagrange point L1 (sub-L1). This unique position, in combination with L1 assets, will allow distinguishing between local and global processes, spatial characteristics, temporal evolution, and particle energization mechanisms related to ICMEs. In addition, measurements of the magnetic field in earthbound ICMEs and their sub-structures from the SWIFT location will double the current forecasting lead-times from L1. This concept also paves the way for missions with increasingly longer forecasting lead-times, addressing NASA and NOAA’s space weather goals, as set forth by the Decadal Survey. The objective of this communication is to inform the community of the ongoing effort, including plans to further develop the mission concept, supported by the Heliophysics Flight Opportunities Studies (HFOS) program under NASA’s Research Opportunities in Space and Earth Sciences (ROSES). (10.3389/fspas.2023.1185603)
  DOI : 10.3389/fspas.2023.1185603
• Structure Dominated Two-Dimensional Turbulence : Formation, Dynamics and Interactions of Dipole Vortices
  
  • Gürcan Ö
  Journal of Physics A: Mathematical and Theoretical, IOP Publishing, 2023, 56 (28), pp.285701. Two dimensional turbulence in geophysical fluids and plasma physics tends to be spotty, intermittent and rich in large scale structures such as coherent vortices or zonal flows, due to various mechanisms of self organization. Nonlinear solutions that rely on the vanishing of nonlinearity, especially the dipole vortex solution, stand out as key aspects of this structure dominated turbulence state. Using numerical simulations, it is demonstrated that an initial condition with a small number of high intensity turbulent patches, evolves towards a state dominated by coherent structures, and in particular dipole vortices, as each patch is organized into a finite number of dipole vortices that are ejected from this initially active region. In order to study the details of this process, an initial condition of two Gaussian peaks of the stream function is considered, and it was shown to result in a Chaplygin-Lamb dipole if the peaks have the same amplitude, or a Flierl-Stern-Whitehead dipole that rotates in the direction implied by the excess of vorticity if they do not. Analytical estimates for the velocity, the radius and the radius of curvature of the resulting dipole vortex is given in terms of the peaks and widths of the initial conditions. These are then verified by a detailed comparison of the analytical form of the vorticity of the dipole vortex and its numerical realization. It is argued that since these coherent structures are spared from the strong shear forces normally exerted by the nonlinearities, and can coexist with other localized solutions, or large scale flow patterns, they provide the backbone of the structure dominated or "sporadic" turbulent state in two dimensions, on top of which other structures, waves and instabilities can develop. In order to elucidate these, a number of collision scenarios are considered. It is also shown that a simple two point vortex approximation to a dipole vortex seems to be appropriate for describing their evolution far from each-other, or for computing head on collisions between two or more dipole vortices, but not in the case of close or grazing collisions or their interaction with a nontrivial large scale flow. (10.1088/1751-8121/acdc6b)
  DOI : 10.1088/1751-8121/acdc6b
• The introduction of a virtual radial direction in axial-azimuthal PIC simulations of Hall Thrusters
  
  • Petronio Federico
  • Bourdon Anne
  • Alvarez Laguna Alejandro
  • Chabert Pascal
  , 2023. Hall Thrusters (HTs) are well-settled space propulsion systems that are nowadays largely used in space missions. In recent years, the need of designing new thrusters has met the great boost in computing capacities: several codes have been developed to guide the development of future thrusters. Among them, particle-in-cell (PIC) codes adopt a kinetic description of the plasma and efficiently describe the evolution of the discharge in an HT. In the present work, we use a bi-dimensional PIC code to simulate the axial-azimuthal plane of such device. Starting from the design of current thrusters, we coupled the PIC code with a model for a RLC filter that damps the large Breathing Mode oscillations. We also introduced a simplified model of the radial dimension, referred to as fake-r, in the 2D axial-azimuthal simulation: at each timestep we remove from the simulation a number of particles corresponding to the Bohm flux at the walls. Several fake-r thicknesses have been tested and their effect on some important plasma parameters are discussed. We also verified that the chosen value for the azimuthal length in PIC simulations has a significant impact on the discharge current evolution.
• In-situ optical diagnostics of plasma electrochemical reactors
  
  • Pai David Z.
  • Chiang Wei-Hung
  • Kurniawan Darwin
  • Caielli Francesca
  • Thyagarajan Karthik
  • Bellet Romain
  • Khereddine Hanane
  • Polprasarn Kasidapa
  • Orrière Thomas
  , 2023. Many methods for synthesizing nanomaterials are complex and can require high temperature, acids, bases, or reducing agents. The plasma electrochemical reactor (PEC), composed of an atmospheric-pressure low-temperature plasma in contact with an aqueous electrode, may provide unique physico-chemical conditions that sidestep these disadvantages because non-equilibrium electrochemistry and nucleation are initiated in solution without additional heating or strong/toxic reagents. Indeed, PECs have successfully synthesized graphene quantum dots (GQD) [1,2]. The precise mechanism of GQD growth is likely to be complex, involving non-equilibrium plasma chemistry and interactions near the plasma-liquid interface. Up to now, investigations of the liquid-phase chemistry have relied principally on ex situ measurements with little or no spatially-resolved information. In addition, conventional experimental techniques can suffer from a lack of selectivity and/or degradation of dyes, chemical probes, or spin traps introduced into the liquid. To extend the scope of diagnostics, we employ an in situ approach using multiple diagnostic techniques to study a wide range of physical and chemical properties at the plasma-water interface. The centrepiece of this platform is in situ spontaneous Raman microspectroscopy, which is advantageous because of its non-intrusiveness, selectivity, versatility, and straightforward calibration. Shaping the laser beam into a light sheet enables probing of the interfacial region with micron-scale spatial resolution. To observe the effect of the plasma on the solvent, we tracked the Raman spectrum of water. Analysis of the –OH stretch band reveals that the plasma weakens the hydrogen bonding network of water. This effect becomes especially pronounced near the interface, at a depth of a few tens of microns. Likewise, at a similar depth, the concentrations of aqueous H2O2 and NO3- both exceed those of the bulk liquid [3]. Similar interfacial layers have been modeled in past studies for radical species such as OH but not for long-lived species such as NO3-. Concerning GQDs, we tracked their production via in situ photoluminescence (PL) and UV-VIS absorption spectroscopies. Both the PL and absorption intensities reached a maximum not at the interface but rather at a depth of a few millimeters. This observation corroborates with liquid flow field measurements by particle image velocimetry, which revealed a low-velocity zone at this depth. Under certain conditions, we could observe the consumption of the carbon precursor over the course of plasma treatment using in situ Raman spectroscopy. Finally, we characterized plasma properties near the interface, such as the electron number density, using optical emission spectroscopy. Together, these results provide the fullest description to date of the reaction environment during GQD synthesis. Acknowledgments Financial support: ANR grants ANR-15-CE06-0007-01 and ANR-11-LABX-0017-01, PHC Orchid 40938YL, CNRS-IEA “GRAFMET”, Fédération Plas@Par, EUR PLASMAScience, Poitou-Charentes region (CPER program) References [1] Orrière, T., Kurniawan, D., Chang, Y. C., Pai, D. Z., & Chiang, W. H. (2020). Nanotechnology 31 (485001). [2] Yang, J. S., Pai, D. Z., & Chiang, W. H. (2019). Carbon 153, 315-319. [3] Pai, D. Z. (2021) J. Phys. D. : Appl. Phys. 54, 355201
• Dynamics of Two-dimensional Type III Electron Beams in Randomly Inhomogeneous Solar Wind Plasmas
  
  • Krafft C.
  • Savoini P.
  The Astrophysical Journal, American Astronomical Society, 2023, 949 (1), pp.24. Abstract The dynamics of a type III electron beam generating Langmuir wave turbulence and subsequent electromagnetic emissions is studied owing to two-dimensional Particle-In-Cell simulations performed in both homogeneous and randomly inhomogeneous solar wind plasmas. Important differences in the beam dynamics are highlighted between both cases, due to Langmuir waves’ transformations on the density fluctuations. This paper studies the dynamics of a weak beam interacting with Langmuir wave turbulence scattered by initially applied plasma density fluctuations, in terms of particle acceleration, non-Gaussian suprathermal electron tails, broadening and relaxation of velocity distributions, beam density localization, and electron diffusion or trapping in a turbulent plasma. Density fluctuations are the cause of beam acceleration during its relaxation stage; after Langmuir wave saturation, it gains up to half the energy lost during deceleration while wave turbulence is damping, exhibiting asymptotically a suprathermal tail of electrons carrying around 30% of its initial kinetic energy. Some important features observed for one-dimensional beams exciting Langmuir wave turbulence in randomly inhomogeneous plasmas can be recovered. (10.3847/1538-4357/acc1e4)
  DOI : 10.3847/1538-4357/acc1e4
• Subion-Scale Turbulence Driven by Magnetic Reconnection
  
  • Manzini D.
  • Sahraoui F.
  • Califano F.
  Physical Review Letters, American Physical Society, 2023, 130 (20), pp.205201. (10.1103/PhysRevLett.130.205201)
  DOI : 10.1103/PhysRevLett.130.205201
• Validation of non-equilibrium kinetics in CO 2 –N 2 plasmas
  
  • Fromentin C
  • Silva T
  • Dias T
  • Baratte E
  • Guaitella O
  • Guerra V
  Plasma Sources Science and Technology, IOP Publishing, 2023, 32 (5), pp.054004. This work explores the effect of N 2 addition on CO 2 dissociation and on the vibrational kinetics of CO 2 and CO under various non-equilibrium plasma conditions. A self-consistent kinetic model, previously validated for pure CO 2 and CO 2 –O 2 discharges, is further extended by adding the kinetics of N 2 . The vibrational kinetics considered include levels up to v = 10 for CO, v = 59 for N 2 and up to v 1 = 2 and v 2 = v 3 = 5, respectively for the symmetric stretch, bending and asymmetric stretch modes of CO 2 , and account for electron-impact excitation and de-excitation (e–V), vibration-to-translation (V–T) and vibration-to-vibration energy exchange (V–V) processes. The kinetic scheme is validated by comparing the model predictions with recent experimental data measured in a DC glow discharge operating in pure CO 2 and in CO 2 –N 2 mixtures, at pressures in the range 0.6–4 Torr (80.00–533.33 Pa) and a current of 50 mA. The experimental results show a higher vibrational temperature of the different modes of CO 2 and CO and an increased dissociation fraction of CO 2 , that can reach values as high as 70%, when N 2 is added to the plasma. On the one hand, the simulations suggest that the former effect is the result of the CO 2 –N 2 and CO–N 2 V–V transfers and the reduction of quenching due to the decrease of atomic oxygen concentration; on the other hand, the dilution of CO 2 and dissociation products, CO and O 2 , reduces the importance of back reactions and contributes to the higher CO 2 dissociation fraction with increased N 2 content in the mixture, while the N 2 (B 3 Π g ) electronically excited state further enhances the CO 2 dissociation. (10.1088/1361-6595/acce64)
  DOI : 10.1088/1361-6595/acce64
• Mueller polarimetric imaging as a tool for detecting the effect of non-thermal plasma treatment on the skin
  
  • Yang Hang
  • Liu Bo
  • Park Junha
  • Blaise Océane
  • Duchesne Constance
  • Honnorat Bruno
  • Vizet Jérémy
  • Rousseau Antoine
  • Pierangelo Angelo
  Biomedical optics express, Optical Society of America - OSA Publishing, 2023, 14 (6), pp.2736. Non-thermal plasma (NTP) is a promising technique studied for several medical applications such as wound healing or tumor reduction. The detection of microstructural variations in the skin is currently performed by histological methods, which are time-consuming and invasive. This study aims to show that full-field Mueller polarimetric imaging is suitable for fast and without-contact detection of skin microstructure modifications induced by plasma treatment. Defrosted pig skin is treated by NTP and analyzed by MPI within 30 minutes. NTP is shown to modify the linear phase retardance and the total depolarization. The tissue modifications are inhomogeneous and present distinct features at the center and the fringes of the plasma-treated area. According to control groups, tissue alterations are primarily caused by the local heating concomitant to plasma-skin interaction. (10.1364/BOE.482753)
  DOI : 10.1364/BOE.482753
• Quiet Sun flux rope formation via incomplete Taylor relaxation
  
  • Robinson Rebecca
  • Aulanier Guillaume
  • Carlsson Mats
  Astronomy & Astrophysics - A&A, EDP Sciences, 2023, 673, pp.A79. Context. Low-altitude nanoflares are among the candidates for atmospheric heating in the quiet Sun’s corona. Low-altitude twisted magnetic fields may be involved in such events, as they are in larger flares. But for nanoflares, the exact role, topology, and formation mechanisms of these twisted fields remain to be studied. Aims. In this paper, we investigate the formation and evolution of a preflare flux rope in a fully stratified, 3D magnetohydrodynamics simulation of the quiet Sun using the Bifrost code. This study focuses on the time period before the rope eventually reconnects with an overlying field, resulting in a nanoflare-scale energy on the order of 10 17 J. One puzzle is that this modeled flux rope does not form by any of the mechanisms usually at work in larger flares, such as flux emergence, flux cancellation, or tether-cutting reconnection. Methods. Using Lagrangian markers to trace representative field lines, we follow the spatiotemporal evolution of the flux rope. By focusing on current volumes (which we call current sheets) between these lines, we identify flux bundles and associated reconnecting field line pairs. We also analyze the time-varying distribution function for the force-free parameter as the flux rope relaxes. Lastly, we compare different seeding methods for tracing magnetic field lines, and discuss their relevance to the analysis. Results. We show that the modeled flux rope is gradually built from the coalescence of numerous current-carrying flux tubes. This occurs through a series of component reconnections that are continuously driven by the complex flows in the underlying convection zone. These reconnections lead to an inverse cascade of helicity from small scales to larger scales. We also find that the system attempts to relax toward a linear force-free field, but that the convective drivers and the nanoflare event prevent full Taylor relaxation. Conclusions. Using a self-consistently driven simulation of a nanoflare event, we show for the first time an inverse helicity cascade tending toward a Taylor relaxation in the Sun’s corona, resulting in a well-ordered flux rope that later reconnects with surrounding fields. This provides context clues toward understanding the buildup of nanoflare events in the quiet Sun through incomplete Taylor relaxations, when no relevant flux emergence or cancellation is observed. (10.1051/0004-6361/202346065)
  DOI : 10.1051/0004-6361/202346065
• Cinquième edition de l’école IMAO en Côte d’Ivoire
  
  • Komenan Zaka
  • Obrou Olivier
  • Amory-Mazaudier Christine
  , 2023 (121), pp.18-19.
• On the 3D global dynamics of terrestrial bow-shock rippling in a quasi-perpendicular interaction with steady solar wind
  
  • Cazzola Emanuele
  • Fontaine D.
  • Savoini P.
  Journal of Atmospheric and Solar-Terrestrial Physics, Elsevier, 2023, 246, pp.106053. The phenomenon of bow-shock surface rippling has been studied throughout multidimensional simulations of ad hoc planar shock fronts. However, the investigation of global bow-shock behaviour with a 3D curved scenario has been poorly addressed thus far. In this work, we present an analysis of this scenario occurring during a low-β quasiperpendicular interaction with the interplanetary magnetic field by means of kinetic 3D computer simulations. The analysis was carried out with 3D hybrid simulations properly set to reproduce the interaction between solar wind and a realistic near-Earth environment. We have found that the ripples behave as IMFperpendicular elongated structures extending along the bow-shock meridian plane and propagating parallel to the IMF orientation from the nose towards the flanks with a constant velocity (in the case studied here ∼ 8 times the upstream Alfvén speed). We have also confirmed that these ripples feature a broad range of wavelengths along the entire travel path, as locally observed with past simulations and observations (in this case ≥ 8 d i). Moreover, from a kinetic analysis of the velocity distribution across the bow-shock nose, we have observed global signatures of the occurrence of shock-front reformation. We suggest that, among other kinetic mechanisms, shock-front reformation in the nose region can play an important role in the perturbation of the bow-shock surface, leading to the generation of modulations ultimately propagating along the bow-shock surface as MHD waves. (10.1016/j.jastp.2023.106053)
  DOI : 10.1016/j.jastp.2023.106053
• Fundamental study of plasma-catalytic surface interactions for CO2 conversion andapplication of fluidized bed reactors
  
  • Garcia Soto Carolina
  , 2023. The increase in global temperature is attributed to the greenhouse gas effect especially from carbon dioxide (CO2) emissions. Several strategies are explored to close the carbon cycle either by transforming CO2 into platform molecules or synthetic fuels. Non-thermal plasmas can provide an environment out of equilibrium allowing CO2 conversion with low energy cost but they are poorly selective. Coupling the plasma with a catalytic material could offer a significant advantage by improving the conversion performance and selectivity. Fluidized bed (FB) reactors are an innovative way to combine plasma and catalysts for CO2 conversion. FB increase the surface contact area with the gas/plasma phase and improve the heat transfer. This work consists on studying plasma/catalyst interaction from a fundamental point of view and understanding the specific mechanisms that intervene in a FB plasma reactor in order to improve its performance. To understand the complexity of this mutual interaction dedicated experiments at low pressure for time resolved measurements of adsorbed and gas phase species were performed before analyzing the performances of atmospheric pressure reactors. DC glow discharges at low pressure (1-6 mbar) were used due to the homogeneity of the plasma and previous plasma kinetic studies done in similar configuration. The plasma-catalytic surface reactions were studied in detail on CeO2 surface during CO2 and CO2-CH4 plasma by in situ FTIR transmission experiments. Carbonates species were identified upon exposure to CO2 gas. During CO2 plasma exposure, the phenomenon "plasma-assisted desorption" was further clarified by identifying 3 main contributions: increase in temperature, variations in partial pressures but also effect of short live excited species. Same studies under CO2-CH4 plasma highlight the formation of formates by reaction between carbonates and hydroxyls. This same mechanism is suggested by ex situ experiments carried out at the University of Bucharest using a Dielectric Barrier Discharge (DBD) reactor at atmospheric pressure and DRIFTS for surface analysis. These results lay the groundwork for identifying the type of reaction mechanism that would improve catalysts suitable for CO2 conversion. The study of CO2 plasma interacting with a fluidizing catalytic material has been done in a DC glow discharge - FB reactor before looking at the performance of FB-DBD at atmospheric pressure. FB-glow discharge was investigated with and without Al2O3 particles with aid of Optical Emission Spectroscopy. The interaction of an inert material in the discharge zone has a special interest to highlight the influence of the particles on the plasma properties. The results indicate a decay in Oxygen atom density through the fluidization of Al2O3 probably to an increase in the available surface where O recombine into O2 potentially preventing the reverse reaction. Simultaneously, CO concentration increases which is confirmed by FTIR spectroscopy analysis of the downstream gas. The rotational temperature was calculated by CO Angstrom system. The temperature does not increase significantly although the presence of Al2O3 particles seems to constrain the plasma spatially. This increase in performance is observed in DBD at atmospheric pressure comparing fluidized bed to a packed bed configuration under the same conditions. Without catalytic activity, Al2O3 has a physical effect modifying the chemistry and therefore, improving CO2 conversion. The specificities of the plasma/catalyst coupling and the advantages they can bring for an efficient conversion of CO2 could thus be identified to allow future optimization of fluidized bed plasma reactors, which are proving very promising.
• Plasma instabilities in Hall Thrusters : a theoretical and numerical study
  
  • Petronio Federico
  , 2023. Hall thrusters (HTs) are electric propulsion systems widely used in space applications since their invention in the 1960s. Their ExB configuration allows for ionizing a propellant gas, usually xenon, and accelerating outwards the ions to create thrust.Hall thrusters are used for an increasing diversity of space missions, including telecommunications, Earth observation, scientific exploration, and deep space missions.However, the physics of low-temperature low-pressure magnetized plasmas, typical of these thrusters, is complex; several plasma processes that have direct relevance to the thruster performance and lifetime are still poorly understood. Therefore, currently, long and expensive life tests are required to design and develop new thrusters.It is necessary to develop in the coming years a new experimental/numerical methodology to propose innovative designs, capable of meeting the issues and challenges of the space industry. Towards this objective, this thesis presents theoretical and simulation results on the physics of low-temperature low-pressure magnetized plasmas in the radial-azimuthal and axial-azimuthal planes of a HT. A 2D Particle-In-Cell (PIC) code, LPPic, has been enriched by adding the effects of the third dimension (i.e. the one not considered in the simulation) and an external electrical circuit, to get closer to real thrusters.Moreover, a spectral reconstruction technique to locally calculate the power spectral density, the Two-Points Power Spectral Density (PSD2P), has been implemented to analyze the simulation results.Plasma instabilities have a direct impact on discharge physics and thruster performance, as they strongly influence the anomalous electron transport in the axial direction. In this work, we present a theoretical study on the development of instabilities by deriving a 3D dispersion relation. The 3D dispersion was simplified to recover the best-known 1D and 2D dispersions for this type of plasma and theoretical results were compared with the results of PIC simulations. The radial-azimuthal simulations made it possible to formalize a criterion for the growth of the Modified Two-Stream Instability (MTSI) and to evaluate its contribution to the anomalous transport. For their part, the axial-azimuthal simulations allowed us for characterizing the Ion Transit-Time Instability (ITTI), better understanding its growth and its effect on the population of low-energy ions in the plasma plume. In addition, these simulations have explained the propagation of the ion acoustic wave (IAW) in the discharge: this instability starts in the central part of the thruster channel and propagates toward the cathode and anode.Eventually, LPPic has been used to study the influence of different input parameters (cathode electron temperature, anode voltage, mass flow rate, magnetic field shape, propellant gas) on the discharge characteristics and on the thruster performance. The stability of the LPPic code with respect to large variations in input values suggests that a 2D PIC code could be used in an experimental/numerical methodology to design new devices selecting interesting configurations/operating conditions before running 3D PIC simulations.
• Evolution of atomic oxygen density in the early afterglow of a nanosecond CO 2 discharge
  
  • Shu Z
  • Pokrovskiy G V
  • Starikovskaia S M
  , 2023. In low temperature nonequilibrium plasmas, the dominating channel of CO 2 conversion is usually the dissociation of mixture molecules by electron impact under high electric field and high deposited energy, which can be provided by nanosecond discharges. It is important to apply time-resolved measurements of major species like atomic oxygen in the CO 2 discharges to better understand the dynamic processes. The nanosecond discharge was initiated in the capillary tube with 2.0 mm of internal diameter and 52.89 mm of inter-electrode distance. High-voltage pulses (9 kV of amplitude, 30 ns of FWHM and 10 Hz of repetitive frequency) were delivered via the coaxial cable. CO 2 under 19.5 mbar flowed at the rate of 10 sccm so that each discharge was initiated in the new gas portion. Two-photon absorption laser-induced fluorescence (TALIF) was used to measure the absolute density of atomic oxygen in the afterglow. The ground-state O atoms were excited by a 225.7 nm focused laser pulse, and 845 nm fluorescence signal was detected by a photomultiplier (PMT). An optical pulse slicer was used to narrow the bandwidth of the laser pulse to determine the effective decay rates of the excited O atoms. Calibration was taken by Xe-TALIF under the pressure of 2 mbar. The measured electrical parameters of the CO 2 discharge show that the reduced electric field reaches 700 Td and the specific deposited energy is almost 1 eV/particle immediately after the first nanosecond pulse. The TALIF measurements indicate a temporal profile of O(3p 3P 0,1,2) effective decay rates between 0.3 to 0.9 ns-1 and ground-state O-atom absolute density between 10 16 to 10 17 cm -3, which gives the dissociation rate up to 20 % in a single pulse. Acknowledgements The work was partially done in the framework of activity of E4C Interdisciplinary Center of IPP. References [1] G.V. Pokrovskiy, PhD Thesis, l’Institut Polytechnique de Paris (2021) [2] G.V. Pokrovskiy, N.A. Popov and S.M. Starikovskaia, Plasma Sources Sci. Techn., 31(3), 035010 (2022).
• Plasma turbulence within cometary plasma environments
  
  • Pucci Francesco
  • Behar Etienne
  • Henri P.
  • Wedlund Cyril Simon
  • Ballerini Giulio
  , 2023. We present a numerical work in which the interaction between a comet and the solar wind is studied in 2D in the plane perpendicular to the solar wind mean field direction. Our simulations are conducted with the hybrid Particle-in-Cell (PIC) code Menura that allows for the injection of a turbulent solar wind [1].First, we consider the case of laminar solar wind and we present a study on the equivalent Mach number of the two-ion-species (cometary and solar wind) plasma surrounding the comet. We develop an expression for the Mach number having suitable limits in the two asymptotic cases of infinite cometary and solar wind ion density; our expression is derived by extending previous studies on bi-ion plasma models [2]. Through numerical simulations in which the cometary activity is varied, we show how our Mach number is able to unambiguously describe the existence and location of the cometary shock.Second, we compare two runs, one with a laminar and one with a turbulent solar wind in the case of moderate cometary activity. We divide the simulation domain into the regions upstream and downstream the cometary shock. We analyze how plasma turbulence properties are affected by the passage through the shock in the case of a turbulent solar wind. Then, we divide the downstream region into three different regions identified by different solar wind-to-cometary ion density ratios. We study the downstream turbulence properties in the case of laminar and turbulent impinging solar wind and how they vary in those regions. [1] Behar, E., Fatemi, S., Henri, P., & Holmström, M. (2022, May). Menura: a code for simulating the interaction between a turbulent solar wind and solar system bodies. In Annales Geophysicae (Vol. 40, No. 3, pp. 281-297). Copernicus GmbH.[2] Dubinin, E. M., Sauer, K., McKenzie, J. F., & Chanteur, G. (2002). Nonlinear waves and solitons propagating perpendicular to the magnetic field in bi-ion plasma with finite plasma pressure. Nonlinear Processes in Geophysics, 9(2), 87-99. (10.5194/egusphere-egu23-9003)
  DOI : 10.5194/egusphere-egu23-9003
• Two classes of magnetotail Dipolarization Fronts observed by MagnetosphericMultiscale Mission: A statistical overview
  
  • Alqeeq Soboh
  • Le Contel Olivier
  • Canu Patrick
  • Retinò Alessandro
  • Chust Thomas
  • Mirioni Laurent
  • Chuvatin Alexandre
  • Nakamura Rumi
  • Ahmadi Narges
  • Wilder Frederick
  • Gershman Daniel
  • Khotyaintsev Yuri
  • Lindqvist Per Arne
  • Ergun Robert
  • Burch James
  • Torbert Roy
  • Fuselier Stephen
  • Russell Christopher
  • Wei Hanying
  • Strangeway Robert
  , 2023. We carried out a statistical study of 132 Dipolarization Fronts (DFs) events detected by the Magnetospheric Multiscale mission (MMS) during the full 2017 Earth’s magnetotail season. We found that two DF classes can be distinguished: class I (74.4%) corresponds to the standard DF properties and energy dissipation whereas a new class II (25.6%), which includes the six DF discussed in S. Alqeeq et al. 2022, corresponds to a bump of the magnetic field associated with a minimum of the ion and electron pressures and a reversal of the energy conversion process. For both classes we found that ions are mostly decoupled from the magnetic field by the Hall fields. The electron pressure gradient term is also contributing to the ion decoupling and likely responsible for an electron decoupling at DF. Both DF classes show that the energy conversion process in the spacecraft frame is driven by the diamagnetic current dominated by the ion pressure gradient. In the fluid frame, it is driven by the electron pressure gradient. In addition, we have shown that the energy conversion processes are not homogeneous at the electron scale mostly due to the variations of the electric fields for both DF classes. (10.5194/egusphere-egu23-7317)
  DOI : 10.5194/egusphere-egu23-7317
• On the Response of the near-Mercury Environment to Different Interplanetary Conditions from full-scale 3D Hybrid Simulations
  
  • Cazzola Emanuele
  • Fontaine Dominique
  • Modolo Ronan
  , 2023. While waiting for further insights from the upcoming data from the BepiColombo mission, this work presents some results from full-scale 3D hybrid (ions kinetic and electrons fluid) computer simulations of the near-Mercury environment under different interplanetary conditions. During its orbit Mercury passes from an high density high magnetic field intensity region (Perihelion) to a low density low magnetic field intensity region (Aphelion). Such environment change drastically influences the response of its magnetic environment, including the stand-off distance of both Bow-Shock and Magnetopause. Being these latter not distant from each other nor from the Hermean exosphere, such a dynamics may lead to important interactions between the planetary and interplanetary environments, as well as lead to unpredictable scenarios whenever the interplanetary conditions occasionally result more extreme than those average values curretly known.Here we aim to give more insights  into the near-Mercury environments under more significant interplanetary conditions by means of full-scale 3D multi-species hybrid simulations, including the Aphelion and Perihelion conditions known to date, as well as more extreme conditions, and compare these results with currently available in-situ observations and recent similar computer simulations.  (10.5194/egusphere-egu23-11568)
  DOI : 10.5194/egusphere-egu23-11568