Publications

2020

• Measurements of electric field and dissociated species in nanosecond discharges for kinetic and biological applications
  
  • Orel Inna
  , 2020. The present thesis combines work on absolute and time resolved measurements of O and N atom densities and electric field as a function of specific deposited energy in nanosecond pulsed discharges at high reduced electric fields (above 100 Td) that develop in form of fast ionization wave (FIW). Ground state O-atom number density, [O], in capillary discharge in 28 mbar air with specific deposited energy of 0.5-1 eV/molecule was measured by optical actinometry technique with Ar as an actinometric admixture. Ar actinometric signal was corrected for N2 first positive system’s background emission. The experiment was highly supported by modelling of kinetic processes in plasma. It has been revealed that in conditions of both high reduced electric field and high specific deposited energy, reactions between charged and/or excited species become important. In particular, the 3-body recombination of O+ and Ar+ ions with electron as a third body become dominant in the early afterglow. The peak measured [O], 7.5x10^(16) cm^(-3), corresponds to 23% dissociation fraction. Longitudinal electric field was measured by electric field induced second harmonic generation (E-FISH) technique with picosecond laser in tube discharge in 20-100 mbar pure N2 with low specific deposited energy at the level of 10^(-3)-10^(-2) eV/molecule during the propagation of FIW and quasi-steady-state discharge. Despite ns-scale laser jitter, temporal resolution as high as 200 ps was attained with help of developed shot-by-shot data treatment procedure that also performed statistical analysis. The electric field in FIW was shown to have a pressure-independent peak value of about 10 kV/cm and 1-3 ns FWHM that increases with pressure. The peak reduced electric field reaches the value of 2 kTd at 20 mbar. It has been concluded that the second harmonic signal originates from the quartz of the discharge tube which disables the possibility of Laplacian field calibration. The calibration against electric field measured by back current shunt and capacitive probe was applied instead. Ground state N-atom number density, [N], in capillary and tube discharges was measured by two photon absorbed laser induced fluorescence (TALIF) technique. For 1 eV/molecule at capillary discharge, [N] reaches the peak value of 1.3x10^(17) cm^(-3) at about 1 us after the initiation of the discharge. [N] stays at the peak value up to 1 ms and then decreases exponentially until reaches the detection limit at 20 ms. The [N] peak value corresponds to 10% dissociation fraction and to effective N-atom production energy cost of almost 10 atoms/100 eV. Such high efficiency is governed by additional population process between charged and excited species, namely, electron impact dissociation of N2(A,B,C) triplet states. For 10^(-3)-10^(-2) eV/molecule at tube discharge, [N] shows rather constant 5.5x10^(12) cm^(-3) value for up to 80 us and further decreases. The thesis also discusses the interest of ns discharges in biological applications on the example of plasma-assisted regenerative medicine. Cold atmospheric plasma (CAP) device was developed for treatment of dental pulp derived mesenchymal stem cells. CAP effect on cells was assessed by morphological cell analysis, viability test, cytotoxicity test, proliferative test, labelled flow cytometry for measurements of intracellular ROS accumulation and fluorescence microscopy for cytoskeleton and nuclei imaging that had led to establishment of non-toxic protocol of cell treatment by CAP.
• Electric field measurements in plasmas: how focusing strongly distorts the E-FISH signal
  
  • Chng Tat Loon
  • Starikovskaia Svetlana
  • Schanne-Klein Marie-Claire
  Plasma Sources Science and Technology, IOP Publishing, 2020, 29 (12), pp.125002. (10.1088/1361-6595/abbf93)
  DOI : 10.1088/1361-6595/abbf93
• Compressible Turbulence in the Interstellar Medium: New Insights from a High-resolution Supersonic Turbulence Simulation
  
  • Ferrand R.
  • Galtier S.
  • Sahraoui F.
  • Federrath C.
  The Astrophysical Journal, American Astronomical Society, 2020, 904 (2), pp.160. (10.3847/1538-4357/abb76e)
  DOI : 10.3847/1538-4357/abb76e
• Automatic Classification of Plasma Regions in Near-Earth Space with Supervised Machine Learning: Application to Magnetospheric Multi Scale 2016-2019 Observations
  
  • Retino A.
  • Breuillard H.
  • Dupuis R.
  • Le Contel O.
  • Amaya J.
  • Lapenta G.
  , 2020, 00. The proper classification of plasma regions in near-Earth space is crucial to perform unambiguous statistical studies of fundamental plasma processes such as shocks, magnetic reconnection, waves and turbulence, jets and their combinations. The majority of available studies have been performed by using human-driven methods, such as visual data selection or the application of predefined thresholds to different observable plasma quantities. While human-driven methods have allowed performing many statistical studies, these methods are often time-consuming and can introduce important biases. On the other hand, the recent availability of large, high-quality spacecraft databases, together with major advances in machine-learning algorithms, can now allow meaningful applications of machine learning to in situ plasma data. In this study, we apply the multi-layer perceptron (MLP) and the fully convolutional neural network (FCN) deep machine-leaning algorithms to the recent Magnetospheric Multi Scale (MMS) mission data in order to classify eight key plasma regions in near-Earth space for the period 2016-2019. For this purpose, we use available intervals of time series for each such plasma region, which were labeled by using human-driven selective downlink applied to MMS burst data. We discuss several quantitative parameters to assess the accuracy of both methods. Our results indicate that, while both methods are reliable to classify labeled time series data, the FCN method seems to be more accurate since it takes into account the dynamical features of each region. We also show good accuracy of the FCN method when applied to unlabeled MMS data. Finally, we show how this method used on MMS data can be extended to similar data from the Cluster mission, indicating that such method can be successfully applied to any in situ spacecraft plasma database.
• Magnetohydrodynamic and kinetic scale turbulence in the near-Earth space plasmas: a (short) biased review
  
  • Sahraoui Fouad
  • Hadid Lina
  • Huang Shiyong
  Reviews of Modern Plasma Physics, Springer Singapore, 2020, 4 (1). The near-Earth space is a unique laboratory to explore turbulence and energy dissipation processes in magnetized plasmas thanks to the availability of high quality data from various orbiting spacecraft, such Wind, Stereo, Cluster, Themis, and the more recent one, the NASA Magnetospheric MultiScale (MMS) mission. In comparison with the solar wind, plasma turbulence in the magnetosheath remains far less explored, possibly because of the complexity of the magnetosheath dynamics that challenges any "realistic" theoretical modeling of turbulence in it. This complexity is due to different reasons such as the confinement of the magnetosheath plasma between two dynamical boundaries, namely the bow shock and the magnetopause; the high variability of the SW pressure that "shakes" and compresses continuously the magnetosheath plasma; and the presence of large density fluctuations and temperature anisotropies that generate various instabilities and plasma modes. In this paper we will review some results that we have obtained in recent years on plasma turbulence in the SW and the magnetosheath, both at the Magneto-HydroDynamics (MHD) and the sub-ion (kinetic) scales, using the state of the art theoretical models and in-situ spacecraft observations. We will focus on three major features of the plasma turbulence, namely its nature and scaling laws, the role of small scale coherent structures in plasma heating, and the role of density fluctuations in enhancing the turbulent energy cascade rate. The latter is estimated using (analytical) exact laws derived for compressible MHD theories applied to in-situ observations from the Cluster and Themis spacecraft. Finally, we will discuss some current trends in space plasmas turbulence research and future space missions dedicated to this topic that are currently being prepared within the community. (10.1007/s41614-020-0040-2)
  DOI : 10.1007/s41614-020-0040-2
• Physics of E × B discharges relevant to plasma propulsion and similar technologies
  
  • Kaganovich Igor
  • Smolyakov Andrei
  • Raitses Yevgeny
  • Ahedo Eduardo
  • Mikellides Ioannis
  • Jorns Benjamin
  • Taccogna Francesco
  • Gueroult R
  • Tsikata Sedina
  • Bourdon Anne
  • Boeuf Jean-Pierre
  • Keidar Michael
  • Powis Andrew Tasman
  • Merino Mario
  • Cappelli Mark
  • Hara Kentaro
  • Carlsson Johan
  • Fisch Nathaniel
  • Chabert Pascal
  • Schweigert Irina
  • Lafleur Trevor
  • Matyash Konstantin
  • Khrabrov Alexander
  • Boswell Rod
  • Fruchtman Amnon
  Physics of Plasmas, American Institute of Physics, 2020, 27 (12), pp.120601. This paper provides perspectives on recent progress in understanding the physics of devices in which the external magnetic field is applied perpendicular to the discharge current. This configuration generates a strong electric field that acts to accelerate ions. The many applications of this set up include generation of thrust for spacecraft propulsion and separation of species in plasma mass separation devices. These “E × B” plasmas are subject to plasma–wall interaction effects and to various micro- and macroinstabilities. In many devices we also observe the emergence of anomalous transport. This perspective presents the current understanding of the physics of these phenomena and state-of-the-art computational results, identifies critical questions, and suggests directions for future research. (10.1063/5.0010135)
  DOI : 10.1063/5.0010135
• Automatic Plasma Processes Detection with Supervised Machine Learning: Application to Plasma Jet Dipolarization Fronts in Near-Earth Space using MMS Data
  
  • Retino A.
  • Breuillard H.
  • Dupuis R.
  • Le Contel O.
  • Amaya J.
  • Lapenta G.
  , 2020, 04. The detection of plasma processes in near-Earth space is crucial to perform unambiguous statistical studies of fundamental plasma processes such as shocks, magnetic reconnection, waves and turbulence, jets and their combinations. The majority of available studies have been performed by using human-driven methods, such as visual data selection or the application of predefined thresholds to different observable plasma quantities. While human-driven methods have allowed performing many statistical studies, these methods are often time-consuming and can introduce important biases. On the other hand, the recent availability of large, high-quality spacecraft databases, together with major advances in machine-learning algorithms, now allow meaningful applications of machine learning to in situ plasma data. In this study, we apply a fully convolutional neural network (FCN) deep machine-leaning algorithm to the recent Magnetospheric Multi Scale (MMS) mission data in order to classify dipolarization fronts in the Earth's magnetotail. For this purpose, we use available intervals of time series which were labeled as such by using human-driven selective downlink applied to MMS data. We discuss the data selection and the chosen model and its parameters. Our results show that the FCN method employed is reliable to identify dipolarization fronts in the time series data since it takes into account the dynamical features of the plasma. We also show that the model is able to detect dipolarization fronts in time series not labeled as such, indicating that such method can be potentially applied to other in situ spacecraft plasma process.
• The effect of the exposed electrode oxidation on the filamentation thresholds of a nanosecond DBD
  
  • Selivonin Igor
  • Ding Chenyang
  • Starikovskaia Svetlana
  • Moralev Ivan
  Journal of Physics: Conference Series, IOP Science, 2020, 1698, pp.012028. (10.1088/1742-6596/1698/1/012028)
  DOI : 10.1088/1742-6596/1698/1/012028
• Propagation of VLF waves guided by plane density trough in the magnetosphere
  
  • Zaboronkova Tatyana
  • Yashina Natalia
  • Krafft Catherine
  , 2020, pp.116-120. (10.1109/DD49902.2020.9274595)
  DOI : 10.1109/DD49902.2020.9274595
• Scaling of pulsed nanosecond capillary plasmas at different specific energy deposition
  
  • Zhu Yifei
  • Starikovskaia Svetlana
  • Babaeva Natalia Yu
  • Kushner Mark J
  Plasma Sources Science and Technology, IOP Publishing, 2020, 29 (12), pp.125006. Nano-second, capillary discharges (nCDs) are unique plasma sources in their ability to sustain high specific energy deposition ωdep approaching 10 eV/molecule in molecular gases. This high energy loading on short timescales produces both high plasma densities and high densities of molecular exited states. These high densities of electrons and excited states interact with each other during the early afterglow through electron collision quenching and associative ionization. In this paper we discuss results from a 2-dimensional computational investigation of a nCD sustained in air at a pressure of 28.5 mbar and with a voltage amplitude 20 kV. Discharges were investigated for two circuit configurations-a floating low voltage electrode and with the low voltage electrode connected to ground through a ballast resistor. The first configuration produced a single ionization wave from the high to low voltage electrode. The second produced converging ionization waves beginning at both electrodes. With a decrease of the tube radius, the velocity of the ionization fronts decreased while the shape of the ionization wave changed from the electron density being distributed smoothly in the radial direction, to being hollow shaped where there is a higher electron density near the tube wall. For sufficiently small tubes, the near-wall maxima merge to have the higher density on the axis of the capillary tube. In the early afterglow, the temporal and radial behavior of the N2(C 3 Πu) density is a sensitive function of ωdep due to electron collision quenching. These trends indicate that starting from ωdep ≥0.3 eV/molecule, it is necessary to take into account interactions of electrons with electronically excited species during the discharge and early afterglow. (10.1088/1361-6595/abc413)
  DOI : 10.1088/1361-6595/abc413
• Fast quenching of metastable O2 (a 1Δg ) and O2 (b 1Σg+ ) molecules by O( 3P) atoms at high temperature
  
  • Volynets Andrey Vladimirovich
  • Lopaev Dmitry
  • Rakhimova T
  • Proshina O
  • Chukalovsky Alexander
  • Booth Jean-Paul
  Plasma Sources Science and Technology, IOP Publishing, 2020. (10.1088/1361-6595/abbf92)
  DOI : 10.1088/1361-6595/abbf92
• In situ evidence of firehose instability in multiple reconnection
  
  • Alexandrova Alexandra
  • Retino Alessandro
  • Divin Andrey
  • Matteini Lorenzo
  • Le Contel Olivier
  • Breuillard Hugo
  • Catapano Filomena
  • Cozzani Giulia
  • Zaitsev Ivan
  • Deca Jan
  , 2020. Energy conversion via reconnecting current sheets is common in space and astrophysical plasmas. Frequently, current sheets disrupt at multiple reconnection sites, leading to the formation of plasmoid structures between sites, which might affect energy conversion. We present in situ evidence of the firehose instability in multiple reconnection in the Earth's magnetotail. The observed proton beams accelerated in the direction parallel to magnetic field and ion-scale fluctuations of whistler type imply the development of firehose instability between two active reconnection sites. The linear wave dispersion relation, estimated for the measured plasma parameters, indicates a positive growth rate of firehose-related electromagnetic fluctuations. Simulations of temporal evolution of the observed multiple reconnection by using a 2.5D implicit particle-in-cell code show that, as the plasmoid formed between two reconnection sites evolves, the plasma at its edge becomes anisotropic and overcomes the firehose marginal stability threshold, leading to the generation of magnetic field fluctuations. The combined results of observations and simulations suggest that the firehose instability, operating between reconnection sites, converts plasma kinetic energy into energy of magnetic field fluctuations, counteracting the conversion of magnetic energy into plasma energy occurring at reconnection sites. This suggests that magnetic energy conversion in multiple reconnection can be less efficient than in the case of the single-site reconnection.
• Joint Europa Mission (JEM) a multi-scale study of Europa to characterize its habitability and search for extant life
  
  • Blanc Michel
  • André Nicolas
  • Prieto-Ballesteros Olga
  • Gómez-Elvira Javier
  • Jones Geraint D.
  • Sterken Veerle
  • Desprats William
  • Gurvits Leonid
  • Khurana Krishan
  • Balmino Georges
  • Blöcker Aljona
  • Broquet Renaud
  • Bunce Emma
  • Cavel Cyril
  • Choblet Gael
  • Colins Geoffrey
  • Coradini Marcello
  • Cooper John
  • Dirkx Dominic
  • Fontaine Dominique
  • Garnier Philippe
  • Gaudin David
  • Hartogh Paul
  • Iess Luciano
  • Jäggi Adrian
  • Kempf Sascha
  • Krupp Norbert
  • Lara Luisa M.
  • Lasue Jérémie
  • Lainey Valéry
  • Leblanc François
  • Lebreton Jean-Pierre
  • Longobardo Andrea
  • Lorenz Ralph
  • Martins Philippe
  • Martins Zita
  • Marty Jean-Charles
  • Masters Adam
  • Mimoun David
  • Palumba Ernesto
  • Regnier Pascal
  • Saur Joachim
  • Schutte Adriaan
  • Sittler Edward
  • Spohn Tilman
  • Stephan Katrin
  • Szegő Károly
  • Tosi Federico
  • Vance Steve
  • Wagner Roland
  • van Hoolst Tim
  • Volwerk Martin
  • Westall Frances
  Planetary and Space Science, Elsevier, 2020, 193, pp.104960. Europa is the closest and probably the most promising target to search for extant life in the Solar System, based on complementary evidence that it may fulfil the key criteria for habitability: the Galileo discovery of a sub-surface ocean; the many indications that the ice shell is active and may be partly permeable to transfer of chemical species, biomolecules and elementary forms of life; the identification of candidate thermal and chemical energy sources necessary to drive a metabolic activity near the ocean floor.In this article we are proposing that ESA collaborates with NASA to design and fly jointly an ambitious and exciting planetary mission, which we call the Joint Europa Mission (JEM), to reach two objectives: perform a full characterization of Europa's habitability with the capabilities of a Europa orbiter, and search for bio-signatures in the environment of Europa (surface, subsurface and exosphere) by the combination of an orbiter and a lander. JEM can build on the advanced understanding of this system which the missions preceding JEM will provide: Juno, JUICE and Europa Clipper, and on the Europa lander concept currently designed by NASA (Maize, report to OPAG, 2019). (10.1016/j.pss.2020.104960)
  DOI : 10.1016/j.pss.2020.104960
• Determination of absolute O(3P) and O2(a1Δg) densities and kinetics in fully modulated O2 dc glow discharges from the O2(X3Σg-) afterglow recovery dynamics
  
  • Booth Jean-Paul
  • Chatterjee Abhyuday
  • Guaitella Olivier
  • Sousa João Santos
  • Lopaev Dmitry
  • Zyryanov S
  • Rakhimova T
  • Voloshin D
  • Mankelevich Yu
  • de Oliveira Nelson
  • Nahon Laurent
  Plasma Sources Science and Technology, IOP Publishing, 2020, 29, pp.115009. A method is presented for the determination of the absolute densities of O(3P) atoms and O2(a1Δg) molecules in an O2 electrical discharge, which does not depend on any calibration procedure or knowledge of optical transition strengths. It is based on observing the recovery dynamics of the O2(X3Σg -) density in the afterglow of a fully-modulated discharge, and is demonstrated in a dc glow discharge in pure О2 at pressures of 0.2-4 Torr. The time-resolved O2(X3Σg -) density was measured by VUV absorption spectroscopy using the monochromator branch of the VUV DESIRS beamline at Synchrotron SOLEIL, but this methodology could be used with another density measurement technique. During the active discharge, the O2(X3Σg -) density is depleted by a combination of О2 dissociation, excitation into metastable states (principally (a1Δg) ) and gas heating/dilation. After discharge extinction, the O2(X3Σg -) density progressively recovers to its initial (before discharge) value, with three distinct time-constants due to: i) gas cooling (fast), ii) O(3P) atom recombination (intermediate), and iii)O2(a1Δg) quenching (slow). The O(3P) and O2(a1Δg) dynamics can be separated easily, allowing the O(3P) and O2(a1Δg) afterglow loss kinetics to be determined, as well as their mole fractions in the steady-state discharge. Both the O(3P) and (a1Δg) mole-fractions increase with current (up to the highest current studied, 40 mA) and pass through maxima with pressure at 1 Torr, reaching 16.5% and 8%, respectively. O(3P) atoms are principally lost by recombination at the borosilicate tube surface, with a loss probability in the afterglow of ~8x10-4, nearly independent of gas pressure and discharge current (in contrast to previous observations in the active discharge [1] . The (a1Δg) dynamics were also measured by IR emission spectroscopy. In the late afterglow this agrees well with the O2(X3Σg -) recovery dynamics, corresponding to an (a1Δg) surface loss probability of ~2.2x10-4. The initial (a1Δg) loss is faster than in the later afterglow, indicating that it is also quenched by O atoms. (10.1088/1361-6595/abb5e7)
  DOI : 10.1088/1361-6595/abb5e7
• An asymptotic preserving well-balanced scheme for the isothermal fluid equations in low-temperature plasma applications
  
  • Alvarez-Laguna Alejandro
  • Pichard Teddy
  • Magin Thierry
  • Chabert Pascal
  • Bourdon Anne
  • Massot Marc
  Journal of Computational Physics, Elsevier, 2020, 419, pp.109634. We present a novel numerical scheme for the efficient and accurate solution of the isothermal two-fluid (electron + ion) equations coupled to Poisson's equation for low-temperature plasmas. The model considers electrons and ions as separate fluids, comprising the electron inertia and charge separation. The discretization of this system with standard explicit schemes is constrained by very restrictive time steps and cell sizes related to the resolution of the Debye length, electron plasma frequency, and electron sound waves. Both sheath and electron inertia are fundamental to fully explain the physics in low-pressure and low-temperature plasmas. However, most of the phenomena of interest for fluid models occur at speeds much slower than the electron thermal speed and are quasi-neutral, except in small charged regions. A numerical method that is able to simulate efficiently and accurately all these regimes is a challenge due to the multiscale character of the problem. In this work, we present a scheme based on the Lagrange-projection operator splitting that preserves the asymptotic regime where the plasma is quasi-neutral with massless electrons. As a result, the quasi-neutral regime is treated without the need of an implicit solver nor the resolution of the Debye length and electron plasma frequency. Additionally, the scheme proves to accurately represent the dynamics of the electrons both at low speeds and when the electron speed is comparable to the thermal speed. In addition, a well-balanced treatment of the ion source terms is proposed in order to tackle problems where the ion temperature is very low compared to the electron temperature. The scheme significantly improves the accuracy both in the quasi-neutral limit and in the presence of plasma sheaths when the Debye length is resolved. In order to assess the performance of the scheme in low-temperature plasmas conditions, we propose two specifically designed test-cases: a quasi-neutral two-stream periodic perturbation with analytical solution and a low-temperature discharge that includes sheaths. The numerical strategy, its accuracy, and computational efficiency are assessed on these two discriminating configurations. (10.1016/j.jcp.2020.109634)
  DOI : 10.1016/j.jcp.2020.109634
• Experimental characterization of helium plasma jets
  
  • Hofmans Marlous
  , 2020. This thesis studies an atmospheric pressure helium plasma jet that is powered by positive, unipolar pulses at a kHz frequency. Experiments are performed that focus on the propagation dynamics, flow structure and temperature in a freely expanding jet, as well as the influence of a metallic target on the plasma.Stark polarization spectroscopy yields an axial electric field of around 10 kV/cm in the capillary of the jet and an increase up to 20 kV/cm in the plume, which is constant for different amplitudes and durations of the applied voltage pulse. Thomson and rotational Raman scattering are used to determine the electron density and electron temperature, at different axial and radial positions, as well as the gas temperature and the density of N2 and O2 that are mixed into the helium from the surrounding air.Quantitative comparison of these experimental results with results from a 2D fluid model show a good agreement and allow for a better understanding of the obtained results, namely that the electric field in the ionization front depends linearly on the flow composition at that location. Schlieren imaging shows the onset of turbulent structures at high applied flow rates and at the application of the voltage pulses. The gas temperature, as measured by a temperature probe, is found to increase by around 12 C when the plasma is ignited and by around 25 C when a metallic target is placed in front of the jet.
• Editorial conclusions to the special issue on electrical discharges for aerospace applications
  
  • Leonov Sergey B
  • Starikovskaia Svetlana
  • Ombrello Timothy
  • Cappelli Mark A
  Journal of Physics D: Applied Physics, IOP Publishing, 2020, 53 (41), pp.410201. This Special Issue, dedicated to the fundamentals and applications of electrical discharges for active control of gas flows and combustion, space propulsion, diagnostics and simulations, has 17 new manuscripts representing research performed in 8 countries. This success reflects a broad interest of the plasma physics and aerospace communities in the integration of plasma technology into aerospace applications. (10.1088/1361-6463/ab9d9a)
  DOI : 10.1088/1361-6463/ab9d9a
• Oscillation analysis in Hall thrusters with 2D (axial-azimuthal) Particle-In-Cell simulations
  
  • Charoy Thomas
  • Lafleur Trevor
  • Bourdon Anne
  • Chabert Pascal
  , 2020.
• Tailoring OH and O production in an atmospheric-pressure plasma in Helium with O2 and H2O admixtures
  
  • Wagenaars Erik
  • Brisset Alexandra
  • Schröter Sandra
  • Niemi Kari
  • O'Connell Deborah
  • Booth Jean-Paul
  • Gibson Andrew
  , 2020. Reactive oxygen species (ROS), including OH and O, are key in many applications of atmospheric-pressure plasmas. Controlled delivery of known amounts of ROS is important for the efficiency and safety of plasma-based treatments. Adding molecular admixtures such as O2 and H2O to the plasma feed gas, rather than relying of ambient diffusion, enhances the control of ROS production. Here, we investigated the kinetics of OH and O in an RF atmospheric-pressure plasma in Helium with H2O+O2 admixtures. The density of OH was measured by UV absorption spectroscopy. A 0D plasma-chemical kinetics model was used to compare the experimental results and understand the reaction pathways. Densities of OH in the order of 1014 cm−3 were measured for increasing H2O content. The addition of O2 did not significantly increase the OH density, despite the fact that the OH production, mainly through O and O* species, increases by a factor of ten, because the destruction pathways also depend on O and O*, and increase accordingly by roughly the same factor. This means that admixtures of H2O+O2 allow the independent control of OH, through H2O content, and O, through O2 content, allowing more detailed control of ROS delivery in applications
• Experimental and numerical investigation of an iodine plasma
  
  • Marmuse Florian
  • Esteves Benjamin
  • Drag Cyril
  • Booth Jean-Paul
  • Bourdon Anne
  • Chabert Pascal
  , 2020.
• Comparison between multifluid and Particle-In-Cell (PIC) simulations of instabilities and boundary layers in low-temperature low pressure magnetized plasmas for electric pro- pulsion applications.
  
  • Reboul Louis
  • Alvarez-Laguna Alejandro
  • Magin Thierry E.
  • Chabert Pascal
  • Bourdon Anne
  • Massot Marc
  , 2020.
• 2D radial-azimuthal Particle-In- Cell benchmark for ExB discharges
  
  • Villafana Willca
  • Bourdon Anne
  • Chabert Pascal
  • Cuenot Benedicte
  • Hara Kentaro
  • Jimenez M
  • Petronio Federico
  • Smolyakov A
  • Taccogna Francesco
  • Tavant Antoine
  • Vermorel Olivier
  , 2020.
• Characterization of plasma jets interacting with dielectric and metallic targets: comparison between simulations and experiments
  
  • Bourdon Anne
  • Viegas Pedro
  • Slikboer Elmar
  • Hofmans Marlous
  • van Rooij Olivier
  • Obrusník Adam
  • Klarenaar Bart
  • Bonaventura Zdenek
  • Garcia-Caurel Enric
  • Guaitella Olivier
  • Sobota Ana
  , 2020.
• Sheath instabilities at large secon- dary electron emission in Hall thrusters
  
  • Chabert Pascal
  • Tavant Antoine
  • Charoy Thomas
  • Bourdon Anne
  , 2020.
• Magnetic effects on fields morphologies and reversals in geodynamo simulations
  
  • Menu Mélissa D
  • Petitdemange Ludovic
  • Galtier Sebastien
  Physics of the Earth and Planetary Interiors, Elsevier, 2020, 307, pp.106542. The dynamo eect is the most popular candidate to explain the non-primordial magnetic elds of astrophysical objects. Although many systematic studies of parameters have already been made to determine the dierent dynamical regimes explored by direct numerical geodynamo simulations, it is only recently that the regime corresponding to the outer core of the Earth characterized by a balance of forces between the Coriolis and Lorentz forces is accessible numerically. In most previous studies, the Lorentz force played a relatively minor role. For example, they have shown that a purely hydrodynamic parameter (the local Rossby number Ro) determines the stability domain of dynamos dominated by the axial dipole (dipolar dynamos). In this study, we show that this result cannot hold when the Lorentz force becomes dominant. We model turbulent geodynamo simulations with a strong Lorentz force by varying the important parameters over several orders of magnitude. This method enables us to question previous results and to argue on the applications of numerical dynamos in order to better understand the geodynamo problem. Strong dipolar elds considerably aect the kinetic energy distribution of convective motions which enables the maintenance of this eld conguration. The relative importance of each force depends on the spatial length scale, whereas Ro is a global output parameter which ignores the spatial dependency. We show that inertia does not induce a dipole collapse as long as the Lorentz and the Coriolis forces remain dominant at large length scales. (10.1016/j.pepi.2020.106542)
  DOI : 10.1016/j.pepi.2020.106542