Publications

2024

• Stability analysis of WEST L-mode discharges with improved confinement from boron powder injection
  
  • Bodner Grant
  • Bourdelle Clarisse
  • Manas Pierre
  • Gallo Alberto
  • Afonin Kirill
  • Diallo Ahmed
  • Lunsford Robert
  • Moreau Philippe
  • Nagy Alexander
  • Clairet Frederic
  • Gil Christophe
  • Tsitrone Emmanuelle
  • Vermare L
  Plasma Physics and Controlled Fusion, IOP Publishing, 2024. WEST L-mode plasmas with dominant electron heating and no core torque source have observed improvements in confinement during boron (B) powder injection. These results are reminiscent of previous powder injection experiments on other devices and gaseous impurity seeding experiments on WEST. During powder injection, the stored energy increased up to 25% due to enhanced ion and electron heat and particle confinement. The improvements in confinement were not indicative of an L-H transition. To identify the dominant mechanisms and the causality chain behind these improvements in confinement, we employ interpretative modelling using METIS, predictive integrated modelling using a high-fidelity plasma simulator (HFPS), and stand-alone gyrokinetic simulations using QuaLiKiz. Interpretative modelling with METIS allowed for the estimation of missing data while maintaining good overall consistency with experiment. These results provided the initial conditions for fully predictive flux driven simulations using the HFPS. From these simulations, quasi-linear gyrokinetic analysis was performed at ρ=0.5 and ρ=0.65. Collisionality was found to be a strong candidate for turbulence suppression at ρ=0.5, while a combination of collisionality and the $T_e$ /$T_i$ ratio was found to be the likely mechanism at ρ=0.65. The results additionally suggested that increased $Z_{eff}$ (through main ion dilution) could play a role in the improved confinement, but this could not be confirmed due to a lack of experimental measurements. The modelling framework established here can now be used to evaluate and exploit a variety of future powder injection experiments. (10.1088/1361-6587/ad2c29)
  DOI : 10.1088/1361-6587/ad2c29
• Absolute calibration of the ratio of Xe/O two-photon absorption cross-sections for O-TALIF applications
  
  • Shu Z
  • Popov N
  • Starikovskaia S
  Plasma Sources Science and Technology, IOP Publishing, 2024, 33 (2), pp.025019. Abstract The paper presents a calibration of the ratio of two-photon absorption cross-sections, σ X e ( 2 ) / σ O ( 2 ) , necessary for the absolute O-atom density measurements by two-photon absorption laser-induced fluorescence (TALIF) technique. To calibrate the ratio of the cross-sections, a special discharge with 100% dissociation of molecular oxygen, and so with a known ‘reference’ density of O-atom [O] r e f = 2 ⋅ [O 2 ] was suggested. This is a nanosecond capillary discharge in N 2 :O 2 mixtures with a few percent of oxygen at a reduced electric field of a few hundred of Townsend and specific deposited energy of about 1 eV mol −1 . Voltage at the electrodes, electrical current in the plasma, longitudinal electric field and energy delivered to the gas were measured with 0.2 ns synchronisation. Additionally, radial distribution of emission of excited nitrogen molecules and gas temperature in the discharge and afterglow were obtained experimentally. Detailed 1D kinetic modeling was suggested to confirm complete O 2 dissociation and to analyse the main reactions. By comparing the data measured by TALIF technique with the ‘reference’ density of oxygen atoms [O] r e f , the ratio of the two-photon absorption cross-sections σ X e ( 2 ) / σ O ( 2 ) was determined. (10.1088/1361-6595/ad270f)
  DOI : 10.1088/1361-6595/ad270f
• Study of the breathing mode development in Hall thrusters using hybrid simulations
  
  • Petronio Federico
  • Alvarez Laguna Alejandro
  • Bourdon Anne
  • Chabert Pascal
  Journal of Applied Physics, American Institute of Physics, 2024, 135 (7). We use a 2.5D hybrid simulation to study the breathing mode (BM) dynamics in Hall thrusters (HTs). This involves a 1D Euler fluid simulation for neutral dynamics in the axial direction, coupled with a 2D axial–azimuthal Particle-in-Cell (PIC) simulation for charged species. The simulation also includes an out-of-plane virtual dimension for wall losses. This setup allows us to replicate the BM’s macroscopic features observed in experiments. A comprehensive analysis of plasma parameters in BM’s phases divides it into two growth and two decay sub-phases. Examining 1D axial profiles of electron temperature, gas and plasma densities, and particle creation rate shows that an increase in electron temperature alone cannot sustain ionization. Ionization seems to be influenced by the spatial correlation between electron and gas densities and the ionization rate coefficient. Investigating ion back-flow reveals its impact on modulating neutral flux entering the ionization region. The hybrid simulation’s outcomes let us assess the usual 0D predator–prey model’s validity and identify its limitations. The ionization and ion convection term approximations hold, but the gas convective term approximation does not. Introducing an alternative gas convective term approximation involving constant density ejection from the ionization region constructs an unstable BM model consistent with simulation results. In addition, this paper explores how varying the imposed voltage and mass flow rate impacts the BM. The BM frequency increases with imposed voltage, aligning with theoretical predictions. The mass flow rate variation has a limited effect on BM frequency, following the theoretical model’s trend. (10.1063/5.0188859)
  DOI : 10.1063/5.0188859
• Transport and staircase formation in competing flux-driven interchange & drift waves turbulence
  
  • Panico Olivier
  • Sarazin Y
  • Hennequin P
  • Gürcan Ö D
  , 2024.
• PHARE: Parallel hybrid particle-in-cell code with patch-based adaptive mesh refinement
  
  • Aunai Nicolas
  • Smets Roch
  • Ciardi Andrea
  • Deegan Philip
  • Jeandet Alexis
  • Payet Thibault
  • Guyot Nathan
  • Darrieumerlou Loic
  Computer Physics Communications, Elsevier, 2024, 295, pp.108966. Modeling multi-scale collisionless magnetized processes constitutes an important numerical challenge. By treating electrons as a fluid and ions kinetically, the so-called hybrid Particle-In-Cell (PIC) codes represent a promising intermediary between fully kinetic codes, limited to model small scales and short durations, and magnetohydrodynamic codes used large scale. However, simulating processes at scales significantly larger than typical ion particle dynamics while resolving sub-ion dissipative current sheets remain extremely difficult. This paper presents a new hybrid PIC code with patch-based adaptive mesh refinement. Here, hybrid PIC equations are solved on a hierarchy of an arbitrary number of Cartesian meshes of incrementally finer resolution dynamically mapping regions of interest, and with a refined time stepping. This paper presents how the hybrid PIC algorithm is adapted to evolve such mesh hierarchy and the validation of the code on a uniform mesh, fixed refined mesh and dynamically refined mesh. (10.1016/j.cpc.2023.108966)
  DOI : 10.1016/j.cpc.2023.108966
• Skewness and kurtosis of solar wind proton distribution functions: The normal inverse-Gaussian model and its implications
  
  • Louarn P.
  • Fedorov A.
  • Prech L.
  • Owen C J
  • D’amicis R.
  • Bruno R.
  • Livi S.
  • Lavraud B.
  • Rouillard A P
  • Génot V.
  • André N.
  • Fruit G.
  • Réville Victor
  • Kieokaew R.
  • Plotnikov I.
  • Penou E.
  • Barthe A.
  • Lewis G.
  • Berthomier M.
  • Allegrini F.
  • Alterman B L
  • Lepri S T
  • Raines J M
  • Verscharen D.
  • Mele G.
  • Fargette N.
  • Horbury T S
  • Maksimovic M.
  • Kasper J C
  • Bale S D
  Astronomy & Astrophysics - A&A, EDP Sciences, 2024, 682, pp.A44. Context. In the solar wind (SW), the particle distribution functions are generally not Gaussian. They present nonthermal features that are related to underlying acceleration and heating processes. These processes are critical in the overall dynamics of this expanding astrophysical fluid. Aims. The Proton Alpha Sensor (PAS) on board Solar Orbiter commonly observes skewed proton distributions, with a more populated high-energy side in the magnetic field direction than the Gaussian distribution. Our objectives are: (1) to identify a theoretical statistical function that adequately models the observed distributions and (2) to use its statistical interpretation to constrain the acceleration and heating processes. Methods. We analyzed the 3D velocity distribution functions (VDFs) measured by PAS and compared them to model statistical functions. Results. We show that the normal inverse Gaussian (NIG), a type of hyperbolic statistical distribution, provides excellent fits of skewed and leptokurtic proton distributions. NIG can model both the core distribution and the beam, if present. We propose an interpretation that is inspired by the mathematical formulation of the NIG. It assumes that the acceleration or heating mechanism can be modeled as a drifting diffusion process in velocity space, controlled (or subordinated) by the time of interaction of the particles with “accelerating structures”. The probability function of the interaction time is an inverse Gaussian (IG), obtained by considering a random drift across structures of a given size. The control of the diffusion by interaction times that follow an IG probability function formally defines the NIG distribution. Following this model, we show that skewness and kurtosis can be used to estimate the kinetic and thermal energy gains provided by the interaction with structures. For example, in the case studies presented here, the analyzed populations would have gained kinetic energy representing approximately two to four times their thermal energy, with an increase in velocity – due to acceleration – of from one-tenth to one-third of the observed flow velocity. We also show that the model constrains the initial temperature of the populations. Conclusions. Overall, the NIG model offers excellent fits of the observed proton distributions. Combining the skewness and the kurtosis, it also leads to constraints in the part of acceleration and heating due to the interactions with structures in the formation of the proton populations. We suggest that these effects add to the classical thermal evolution of the bulk velocity and temperature resulting from SW expansion. (10.1051/0004-6361/202347874)
  DOI : 10.1051/0004-6361/202347874
• Kinetic effects in thin layers: effects on jump conditions and discontinuity properties
  
  • Belmont G
  • Ballerini G
  • Rezeau L
  • Califano F
  , 2024. In plasmas as in neutral fluids, there are a few types of well-established kinds of discontinuities: shocks, rotational discontinuities, etc., whose properties are based on the so-called "Rankine-Hugoniot" jump relations. In the classic theory, these relations are based only on universal conservation laws so that they are independent of the physics occurring inside the layer and of the theory used for describing it, fluid or kinetic. We will highlight what are the underlying assumptions behind the classic theory and show its limits. We will first make explicit the role of the pressure anisotropy, which is ubiquitous in magnetized plasmas. It makes in particular "evolutionary" the rotational discontinuity, so justifying its existence through wave steepening. Furthermore, we will show that the Finite Larmor radius (FLR) effects, implying non-gyrotropic pressure tensors, are of primary importance for the plasma equilibrium at thin layers, and that they can determine their stationary widths. Taking FLR effects into account results in discontinuity properties that are notably different from the classic ones in the quasi-tangential limit and can explain the observations at the terrestrial magnetopause. We show that the change concerning the rotational discontinuity is comparable to the change of the MHD Alfvén wave into a Kinetic Alfvén wave for the linear modes.
• Experimental evidence of the role of non-gyrotropy in magnetopause equilibrium
  
  • Ballerini Giulio
  • Rezeau Laurence
  • Belmont Gérard
  • Califano Francesco
  , 2024.
• Identifying footpoints of pre-eruptive and coronal mass ejection flux ropes with sunspot scars
  
  • Xing Chen
  • Aulanier Guillaume
  • Schmieder Brigitte
  • Cheng Xin
  • Ding Mingde
  Astronomy & Astrophysics - A&A, EDP Sciences, 2024, 682, pp.A3. Context. The properties of pre-eruptive structures and coronal mass ejections (CMEs) are characterized by those of their footpoints, the latter of which attract a great deal of interest. However, the matter of how to identify the footpoints of pre-eruptive structures and how to do so with the use of ground-based instruments still remains elusive. Aims. In this work, we study an arc-shaped structure intruding in the sunspot umbra. It is located close to the (pre-)eruptive flux rope footpoint and it is expected to help identify the footpoint. Methods. We analyzed this arc-shaped structure, which we call a “sunspot scar”, in a CME event on July 12, 2012, and in two CME events from observationally inspired magnetohydrodynamic simulations performed by OHM and MPI-AMRVAC. Results. The sunspot scar displays a more inclined magnetic field with a weaker vertical component and a stronger horizontal component relative to that in the surrounding umbra and is manifested as a light bridge in the white light passband. The hot field lines anchored in the sunspot scar are spatially at the transition between the flux rope and the background coronal loops and temporally in the process of the slipping reconnection which builds up the flux rope. Conclusions. The sunspot scar and its related light bridge mark the edge of the CME flux rope footpoint and particularly indicate the edge of the pre-eruptive flux rope footpoint in the framework of “pre-eruptive structures being flux ropes”. Therefore, they provide a new perspective for the identification of pre-eruptive and CME flux rope footpoints, as well as new methods for studying the properties and evolution of pre-eruptive structures and CMEs with photospheric observations only. (10.1051/0004-6361/202347053)
  DOI : 10.1051/0004-6361/202347053
• Acceleration of an interplanetary shock through the magnetosheath: a global hybrid simulation
  
  • Moissard C.
  • Savoini P.
  • Fontaine D.
  • Modolo Ronan
  Frontiers in Astronomy and Space Sciences, Frontiers Media, 2024, 11, pp.1330397. According to most observations and simulations, interplanetary shocks slow down when they propagate through the magnetosheath. In this article, we present results from a self-consistent global hybrid PIC simulation of an interplanetary shock which, by contrast, accelerates as it propagates through the magnetosheath. In this simulation, the solar wind upstream of the interplanetary shock is set up with an Alfvén Mach number M A = 4.5 and the interplanetary magnetic field (IMF) is set up to be almost parallel to the y direction in GSE coordinate system. The ‘planet’ is modelled as a magnetic dipole with no tilt: the dipole is in the GSE’s z direction. In the ecliptic plane (Oxy), which contains the interplanetary magnetic field (IMF), the magnetic field lines are piling up against the magnetopause, and the velocity of the interplanetary shock decreases from 779 ± 48 km/s in the solar wind down to 607 ± 48 km/s in the magnetosheath. By contrast, in the noon-meridian plane (Oxz), which is perpendicular to the IMF, the velocity of the interplanetary shock in the magnetosheath can reach values up to 904 ± 48 km/s. This study suggests that interplanetary shocks can accelerate as they propagate through the magnetosheath. This finding, reported here for the first time, could have important implications for space weather, as it corresponds to the case where an interplanetary shock catches up with a low Alfvén Mach number solar transient such as an interplanetary coronal mass ejection. (10.3389/fspas.2024.1330397)
  DOI : 10.3389/fspas.2024.1330397
• Measurement of the main neutral species densities and temperatures in iodine plasmas using optical absorption techniques
  
  • Esteves Benjamin
  • Blondel Christophe
  • Chabert Pascal
  • Michel Tanguy
  • Drag Cyril
  Plasma Sources Science and Technology, IOP Publishing, 2024, 33, pp.1. Iodine is a promising propellant for future plasma thrusters used in space propulsion. It is therefore important to understand the basic physics and chemistry of low-pressure iodine plasmas. In the present work, optical absorption methods are used to measure the densities of iodine molecules, I2 , and iodine atoms, I, the translational temperature of the atoms and the dissociation fraction. The plasma is generated in a long quartz tube by a capacitively coupled RF discharge, and the pressure is varied between a few Pa and a few tens of Pa. The translational temperature of the atom vapour increases both with RF power and with pressure and reaches 1000 K at 50 watts and 25 Pa. The molecules appear to be efficiently dissociated, with a dissociation fraction found above 65 %, on average along the line-of-sight, at 120 watts and 5 Pa. The population of the upper, 2P1/2 , fine-structure level of the atomic ground term is found to be negligible, which confirms the existence of a high quenching rate, due to collisions with molecules and/or atoms. These measurements can be helpful for chemistry models of iodine plasmas. (10.1088/1361-6595/ad169d)
  DOI : 10.1088/1361-6595/ad169d
• The radial localization of the transition from low to high confinement mode in the ASDEX Upgrade tokamak
  
  • Cavedon M
  • Happel T
  • Hennequin P.
  • Dux R
  • Höfler K
  • Plank U
  • Pütterich T
  • Stroth U
  • Viezzer E
  • Wolfrum E
  Plasma Physics and Controlled Fusion, IOP Publishing, 2024, 66 (2), pp.025011. Abstract A novel experimental method is applied to localize the initial suppression of turbulence, in the form of density fluctuations, at the transition from the low (L-) to the high (H-) confinement mode in toroidal magnetic fusion plasmas. The high radial and temporal resolution, combined with the unprecedented statistical significance, provided the awaited information on a possible dominant E × B shear layer in L-H transition physics. We show, for the first time, that the H-mode turbulence suppression is initiated at the inner E × B shear layer in the ASDEX Upgrade tokamak possibly shedding light on the causality behind the L-H transition process. (10.1088/1361-6587/ad1ae3)
  DOI : 10.1088/1361-6587/ad1ae3
• Spacecraft Outgassing Observed by the BepiColombo Ion Spectrometers
  
  • Fränz M.
  • Rojo M.
  • Cornet T.
  • Hadid L.
  • Saito Y.
  • André N.
  • Varsani A.
  • Schmid D.
  • Krüger H.
  • Krupp N.
  • Delcourt D.
  • Katra B.
  • Harada Y.
  • Yokota S.
  • Verdeil C.
  • Aizawa S.
  • Millilo A.
  • Orsini S.
  • Mangano V.
  • Fiethe B.
  • Benkhoff J.
  • Murakami G.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2024, 129 (1). Abstract During the first flyby of the BepiColombo composite spacecraft at Mercury in October 2021 ion spectrometers observed two intense spectral lines with energies between 10 and 70 eV. The spectral lines persisted also at larger distances from Mercury and were observed again at lower intensity during cruise phase in March 2022 and at the second and third Mercury flyby as a single band. The ion composition indicates that water is the dominant gas source. The outgassing causes the composite spacecraft to charge up to a negative potential of up to −50 V. The distribution and intensity of the lower energy signal depends on the intensity of low energy electron fluxes around the spacecraft which again depend on the magnetic field orientation. We interpret the observation as being caused by water outgassing from different source locations on the spacecraft being ionized in two different regions of the surrounding potential. The interpretation is confirmed by two dimensional particle‐in‐cell simulations. (10.1029/2023JA032044)
  DOI : 10.1029/2023JA032044
• New insights into the consequences of different interplanetary conditions on the near-Hermean environment
  
  • Cazzola Emanuele
  • Fontaine D.
  • Modolo Ronan
  , 2024. In this work we investigate the effects of different interplanetary conditions on the near-Mercury’s dynamics by means of hybrid simulations. In fact, along its orbit Mercury experiences significantly different environments in terms of interplanetary magnetic field (IMF) intensity and direction, as well as solar wind density and velocity. In particular, we show the variations occurring in the bow-shock / magnetosheath / magnetopause system under a Parker’s spiral IMF configuration as the orbit passes from the Aphelion position at 0.47 AU to the Perihelion position at 0.30 AU, as well as the effects of solar winds at different velocities. We observe these boundaries being significantly compressed towards the planetary surface as result of the interaction with high dynamic pressure and/or high Alfenic Mach number conditions. Moreover, a quasi-radial IMF configuration leads to the formation of an intense foreshock region concurring to further affect the boundaries characteristics. Finally, one of the main consequences of such a variable near-planet magnetic dynamics is the different rate, intensity and energy distribution of the interplanetary particles capable of precipitating onto the planetary surface. These particles are thought to be one of the main source of the neutrals seen in the exosphere. We observe that the precipitation mainly occurs along the open-lines magnetic cusps regions. Unlike what found from some past simulations, these regions show a significant longitudinal displacement from the north-south meridian line probably due to the quasi-radial configuration, as well as a latitudinal displacement towards the equatorial plane as the incoming solar wind compression increases. Additionally, the presence of a compressed magnetosphere / bow-shock scenario concurs to increase the precipitation rate in the equatorial regions.
• Modeling of mutual impedance experiments and quasi-thermal noise spectroscopy in magnetized plasma
  
  • Dazzi Pietro
  • Henri Pierre
  • Issautier Karine
  • Bucciantini Luca
  • Lavorenti Federico
  • Califano Francesco
  • Wattieaux Gaëtan
  , 2024, pp.500229. Mutual impedance experiments and quasi-thermal noise spectroscopy are two in situ plasma diagnostic techniques. They both rely on electric antennas in contact with the plasma, and both measure electron properties, notably electron density and temperature. They differ in that mutual impedance is an active technique, while quasi-thermal noise is a passive technique. Mutual impedance experiments measure the mutual impedance spectrum between two antennas. This measurement is performed by generating an electric perturbation within the plasma using one antenna, while another antenna simultaneously measures the electric field. Quasi-thermal noise spectroscopy uses one dipolar antenna, connected to a sensitive radio receiver, that measures the electric field fluctuations produced by the thermal motion of the ambient particles of the plasma. Both techniques are included in the scientific payload of past, current, and future NASA, ESA, and JAXA space missions, such as Rosetta, Parker Solar Probe, BepiColombo, JUICE, and Comet Interceptor. Instrumental models for both techniques are needed to interpret the instrumental output and derive measurements of the electron properties. They take into account both the electron plasma dispersion function and the geometry of the instrument. The modelling current state-of-the-art is largely focused on the limit of an unmagnetized plasma, that in this context identifies a plasma where the ratio of plasma to electron cyclotron frequency is much larger than one. We highlight here that the magnetized plasma regime will be of interest for future planetary space missions, including BepiColombo and JUICE, and to prepare future mission in the Earth's magnetosphere. In this context, we provide for the first time a complete diagnostic, in magnetized plasmas, of the plasma electron density and temperature, and the magnetic field magnitude and direction, based on mutual impedance experiments and quasi-thermal noise spectroscopy. For this purpose, we developed numerical models for both mutual impedance experiments and quasi-thermal noise spectroscopy in a magnetized plasma. A diagnostic is derived for the plasma density, the electron temperature, and the magnetic field. We validated these instrumental models against both laboratory and space measurements. The dependency of this diagnostic on the antenna shape and size is investigated, as well as the expected precision of these techniques as plasma diagnostic.
• The Magnetopause: an almost tangential interface between the magnetosphere and the magnetosheath
  
  • Ballerini Giulio
  • Rezeau Laurence
  • Belmont Gérard
  • Califano Francesco
  , 2024.
• SPODIFY: Space Plasma Object Detection Inspired From Yolo
  
  • Nguyen Gautier
  • Bernoux Guillerme
  • Aunai Nicolas
  , 2024.
• Reconnection Inside a Dipolarization Front of a Diverging Earthward Fast Flow
  
  • Hosner M.
  • Nakamura R.
  • Schmid D.
  • Nakamura T.
  • Panov E.
  • Volwerk M.
  • Vörös Z.
  • Roberts O.
  • Blasl K.
  • Settino A.
  • Korovinskiy D.
  • Marshall A.
  • Denton R.
  • Burch J.
  • Giles B.
  • Torbert R.
  • Le Contel O.
  • Escoubet C.
  • Dandouras I.
  • Carr C.
  • Fazakerley A.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2024, 129 (1). Abstract We examine a Dipolarization Front (DF) event with an embedded electron diffusion region (EDR), observed by the Magnetospheric Multiscale (MMS) spacecraft on 08 September 2018 at 14:51:30 UT in the Earth's magnetotail by applying multi‐scale multipoint analysis methods. In order to study the large‐scale context of this DF, we use conjunction observations of the Cluster spacecraft together with MMS. A polynomial magnetic field reconstruction technique is applied to MMS data to characterize the embedded electron current sheet including its velocity and the X‐line exhaust opening angle. Our results show that the MMS and Cluster spacecraft were located in two counter‐rotating vortex flows, and such flows may distort a flux tube in a way that the local magnetic shear angle is increased and localized magnetic reconnection may be triggered. Using multi‐point data from MMS we further show that the local normalized reconnection rate is in the range of R ∼ 0.16 to 0.18. We find a highly asymmetric electron in‐ and outflow structure, consistent with previous simulations on strong guide‐field reconnection events. This study shows that magnetic reconnection may not only take place at large‐scale stable magnetopause or magnetotail current sheets but also in transient localized current sheets, produced as a consequence of the interaction between the fast Earthward flows and the Earth's dipole field. (10.1029/2023JA031976)
  DOI : 10.1029/2023JA031976
• Impact of solar-wind turbulence on a planetary bow shock: A global 3D simulation
  
  • Behar E.
  • Pucci F.
  • Simon Wedlund C.
  • Henri P.
  • Ballerini G.
  • Preisser L.
  • Califano F.
  Astronomy & Astrophysics - A&A, EDP Sciences, 2024, 692. Context. The interaction of the solar-wind plasma with a magnetized planet generates a bow-shaped shock ahead of the wind. Over recent decades, near-Earth spacecraft observations have provided insights into the physics of the bow shock, and the findings suggest that solar-wind intrinsic turbulence influences the bow shock dynamics. On the other hand, theoretical studies, primarily based on global numerical simulations, have not yet investigated the global three-dimensional (3D) interaction between a turbulent solar wind and a planetary magnetosphere. This paper addresses this gap for the first time by presenting an investigation of the global dynamics of this interaction that provides new perspectives on the underlying physical processes. Aims. We use the newly developed numerical code MENURA to examine how the turbulent nature of the solar wind influences the 3D structure and dynamics of magnetized planetary environments, such as those of Mercury, Earth, and magnetized Earth-like exoplanets. Methods. We used the hybrid particle-in-cell code MENURA to conduct 3D simulations of the turbulent solar wind and its interaction with an Earth-like magnetized planet through global numerical simulations of the magnetosphere and its surroundings. MENURA runs in parallel on graphics processing units, enabling efficient and self-consistent modeling of turbulence. Results. By comparison with a case in which the solar wind is laminar, we show that solar-wind turbulence globally influences the shape and dynamics of the bow shock, the magnetosheath structures, and the ion foreshock dynamics. Also, a turbulent solar wind disrupts the coherence of foreshock fluctuations, induces large fluctuations on the quasi-perpendicular surface of the bow shock, facilitates the formation of bubble-like structures near the nose of the bow shock, and modifies the properties of the magnetosheath region. Conclusions. The turbulent nature of the solar wind impacts the 3D shape and dynamics of the bow shock, magnetosheath, and ion foreshock region. This influence should be taken into account when studying solar-wind-planet interactions in both observations and simulations. We discuss the relevance of our findings for current and future missions launched into the heliosphere. (10.1051/0004-6361/202451520)
  DOI : 10.1051/0004-6361/202451520
• 3D cylindrical BGK model of electron phase-space holes with finite velocity and polarization drift
  
  • Gauthier Gaëtan
  • Chust Thomas
  • Le Contel Olivier
  • Savoini Philippe
  Physics of Plasmas, American Institute of Physics, 2024, 31 (3), pp.032306. Nonlinear kinetic structures, called electron phase-space holes (EHs), are regularly observed in space and experimental magnetized plasmas. The existence of EHs is conditioned and varies according to the ambient magnetic field and the parameters of the electron beam(s) that may generate them. The objective of this paper is to extend the 3D Bernstein–Greene–Kruskal model with cylindrical geometry developed by L.-J. Chen et al. [“Bernstein–Greene–Kruskal solitary waves in three-dimensional magnetized plasma,” Phys. Rev. E 69, 055401 (2004)] and L.-J. Chen et al., [“On the width-amplitude inequality of electron phase space holes,” J. Geophys. Res. 110, A09211 (2005)] to include simultaneously finite effects due to (i) the strength of the ambient magnetic field B0, by modifying the Poisson equation with a term derived from the electron polarization current, and (ii) the drift velocity ue of the background plasma electrons with respect to the EH, by considering velocity-shifted Maxwellian distributions for the boundary conditions. This allows us to more realistically determine the distributions of trapped and passing particles forming the EHs, as well as the width-amplitude relationships for their existence. (10.1063/5.0181180)
  DOI : 10.1063/5.0181180
• Connecting Solar Wind Velocity Spikes Measured by Solar Orbiter and Coronal Brightenings Observed by SDO
  
  • Hou Chuanpeng
  • Rouillard Alexis
  • He Jiansen
  • Gannouni Bahaeddine
  • Réville Victor
  • Louarn Philippe
  • Fedorov Andrey
  • Přech Lubomír
  • Owen Christopher
  • Verscharen Daniel
  • D’amicis Raffaella
  • Sorriso-Valvo Luca
  • Fargette Naïs
  • Coburn Jesse
  • Génot Vincent
  • Raines Jim
  • Bruno Roberto
  • Livi Stefano
  • Lavraud Benoit
  • André Nicolas
  • Fruit Gabriel
  • Kieokaew Rungployphan
  • Plotnikov Illya
  • Penou Emmanuel
  • Barthe Alain
  • Kataria Dhiren
  • Berthomier Matthieu
  • Allegrini Frederic
  • Fortunato Vito
  • Mele Gennaro
  • Horbury Timothy
  The Astrophysical Journal Letters, Bristol : IOP Publishing, 2024, 968 (2), pp.L28. The Parker Solar Probe's discovery that magnetic switchbacks and velocity spikes in the young solar wind are abundant has prompted intensive research into their origin(s) and formation mechanism(s) in the solar atmosphere. Recent studies, based on in situ measurements and numerical simulations, argue that velocity spikes are produced through interchange magnetic reconnection. Our work studies the relationship between interplanetary velocity spikes and coronal brightenings induced by changes in the photospheric magnetic field. Our analysis focuses on the characteristic periodicities of velocity spikes detected by the Proton Alpha Sensor on the Solar Orbiter during its fifth perihelion pass. Throughout the time period analyzed here, we estimate their origin along the boundary of a coronal hole. Around the boundary region, we identify periodic variations in coronal brightening activity observed by the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory. The spectral characteristics of the time series of in situ velocity spikes, remote coronal brightenings, and remote photospheric magnetic flux exhibit correspondence in their periodicities. Therefore, we suggest that the localized small-scale magnetic flux within coronal holes fuels a magnetic reconnection process that can be observed as slight brightness augmentations and outward fluctuations or jets. These dynamic elements may act as mediators, bonding magnetic reconnection with the genesis of velocity spikes and magnetic switchbacks. (10.3847/2041-8213/ad4eda)
  DOI : 10.3847/2041-8213/ad4eda
• Analytical model of a Hall thruster
  
  • Lafleur Trevor
  • Chabert Pascal
  Physics of Plasmas, American Institute of Physics, 2024, 31 (9), pp.093507. Hall thrusters are one of the most successful and prevalent electric propulsion systems for spacecraft in use today. However, they are also complex devices and their unique E×B configuration makes modeling of the underlying plasma discharge challenging. In this work, a steady-state model of a Hall thruster is developed and a complete analytical solution presented that is shown to be in reasonable agreement with experimental measurements. A characterization of the discharge shows that the peak plasma density and ionization rate nearly coincide and both occur upstream of the peak electric field. The peak locations also shift as the thruster operating conditions are varied. Three key similarity parameters emerge that govern the plasma discharge and which are connected via a thruster current–voltage relation: a normalized discharge current, a normalized discharge voltage, and an amalgamated parameter, α¯, that contains all system geometric and magnetic field information. For a given normalized discharge voltage, the similarity parameter α¯ must lie within a certain range to enable high thruster performance. When applied to a krypton thruster, the model shows that both the propellant mass flow rate and the magnetic field strength must be simultaneously adjusted to achieve similar efficiency to a xenon thruster (for the same thruster geometry, discharge voltage, and power level). (10.1063/5.0220130)
  DOI : 10.1063/5.0220130
• On the importance of flux-driven turbulence regime to address tokamak plasma edge dynamics
  
  • Panico Olivier
  • Sarazin Y
  • Hennequin P
  • Gürcan Ö D
  • Bigué R
  • Dif-Pradalier G
  • Garbet X
  • Ghendrih P
  • Varennes R
  • Vermare L
  Journal of Plasma Physics, Cambridge University Press (CUP), 2024, 91 (1). Turbulence self-organization is studied in the flux driven regime by means of the reduced model Tokam1D. Derived in the electrostatic and isothermal limit but keeping finite electron and ion temperatures, it features two instabilities that are suspected to dominate turbulent transport at the edge of L-mode tokamak plasmas: interchange (a reduced version of the resistive ballooning modes) and collisional drift waves, governed respectively by an effective gravity parameter g and the adiabaticity parameter C. The usual properties of these two instabilities are recovered in the linear regime. The nonlinear study focuses on the self-organization of collisional drift wave turbulence at g = 0. It is found that the energy stored in zonal flows (ZFs) decreases smoothly at small C due to the reduction of both electric and diamagnetic stresses. Conversely to gradient driven simulations, no sharp collapse is observed due to the self-consistent evolution of the equilibrium density profile. ZFs are found to structure into staircases at small and large C. These structures exhibit a rich variety of dynamics but are found robust to large perturbations. Their nucleation is found to be critically governed by the phase dynamics. Last, staircase structures are lost in the gradient driven regime, when the system is prevented to store turbulent energy into the equilibrium density (pressure) profile. (10.1017/S0022377824001624)
  DOI : 10.1017/S0022377824001624
• Realization of a gas puff imaging system on the Wendelstein 7-X stellarator
  
  • Terry J L
  • von Stechow A.
  • Baek S G
  • Ballinger S B
  • Grulke O.
  • von Sehren C.
  • Laube R.
  • Killer C.
  • Scharmer F.
  • Brunner K J
  • Knauer J.
  • Bois S.
  Review of Scientific Instruments, American Institute of Physics, 2024, 95 (9), pp.093517. A system for studying the spatiotemporal dynamics of fluctuations in the boundary of the W7-X plasma using the “Gas-Puff Imaging” (GPI) technique has been designed, constructed, installed, and operated. This GPI system addresses a number of challenges specific to long-pulse superconducting devices, such as W7-X, including the long distance between the plasma and the vacuum vessel wall, the long distance between the plasma and diagnostic ports, the range of last closed flux surface (LCFS) locations for different magnetic configurations in W7-X, and management of heat loads on the system’s plasma-facing components. The system features a pair of “converging–diverging” nozzles for partially collimating the gas puffed locally ≈135 mm radially outboard of the plasma boundary, a pop-up turning mirror for viewing the gas puff emission from the side (which also acts as a shutter for the re-entrant vacuum window), and a high-throughput optical system that collects visible emission resulting from the interaction between the puffed gas and the plasma and directs it along a water-cooled re-entrant tube directly onto the 8 × 16 pixel detector array of the fast camera. The DEGAS 2 neutral code was used to simulate the Hα (656 nm) and HeI (587 nm) line emission expected from well-characterized gas-puffs of H2 and He and excited within typical edge plasma profiles in W7-X, thereby predicting line brightnesses used to reduce the risks associated with system sensitivity and placement of the field of view. Operation of GPI on W7-X shows excellent signal-to-noise ratios (>100 at 2 Mframes/s) over the field of view for minimally perturbing gas puffs. The GPI system provides detailed measurements of the two-dimensional (radial and poloidal) dynamics of plasma fluctuations in the W7-X edge and scrape-off layer and in and around the magnetic islands outside the LCFS that make up the island divertor configuration employed on W7-X. (10.1063/5.0219336)
  DOI : 10.1063/5.0219336
• Interplay of the magnetic and current density field topologies in axisymmetric devices for magnetic confinement fusion
  
  • Firpo Marie-Christine
  Journal of Plasma Physics, Cambridge University Press (CUP), 2024. In magnetic confinement fusion devices close to axisymmetry, such as tokamaks, a key element is the winding profile of the magnetic field lines, or its inverse, the safety profile $q=q_{\mathbf{B}}$. A corresponding profile, $q_{\mathbf{J}}$, can be defined for the current density field lines. Amp\`{e}re's law relates any mode of current perturbation $\delta \mathbf{J}_{m,n}$ with a mode of magnetic perturbation $\delta \mathbf{B}_{m,n}$. It is shown that the knowledge of the pair $(q_{\mathbf{B}},q_{\mathbf{J}})$ allows then to characterize the resonant, or non-resonant, nature of the modes for both the magnetic and current density field lines. The expression of $q_{\mathbf{J}}$ in flux coordinate is derived. Including this calculation in the real-time Grad-Shafranov equilibrium reconstruction codes would yield a comprehensive view of the magnetics. The monitoring of the pair $(q_{\mathbf{B}},q_{\mathbf{J}})$ would then allow investigating the role played by the resonant modes for the current density, that are current filamentary modes, in the plasma small-scale turbulence. By driving the magnetic and current density profiles apart so that the images of $q_{\mathbf{B}}$ and $q_{\mathbf{J}}$ are disjoint, these filamentary modes would not impact the magnetic field topology, being not associated to magnetic islands but to non-resonant magnetic modes. It remains to be explored to which extent such a configuration, where the spectrum of tiny current density filaments produces a spectrum of magnetic modes that has practically no effect on heat transport, is beneficial. (10.1017/S002237782400103X)
  DOI : 10.1017/S002237782400103X