Publications

2022

• Erratum: Electric field measurements in plasmas: how focusing strongly distorts the E-FISH signal (2020 Plasma Sources Sci. Technol. 29 125002)
  
  • Chng Tat Loon
  • Starikovskaia Svetlana
  • Schanne-Klein Marie-Claire
  Plasma Sources Science and Technology, IOP Publishing, 2022, 31 (5), pp.059601. (10.1088/1361-6595/ac601d)
  DOI : 10.1088/1361-6595/ac601d
• The Magnetopause: an almost tangential interface between the magnetosphere and the magnetosheath
  
  • Ballerini Giulio
  • Rezeau Laurence
  • Belmont Gérard
  • Califano Francesco
  , 2022.
• Turbulence-driven magnetic reconnection and the magnetic correlation length in collisionless plasma turbulence
  
  • Stawarz Julia
  • Eastwood Jonathan
  • Phan Tai
  • Gingell Imogen
  • Pyakurel Prayash
  • Shay Michael
  • Robertson Sadie
  • Russell Christopher
  • Le Contel Olivier
  , 2022. <p><span>Observations of Earth’s magnetosheath from the Magnetospheric Multiscale (MMS) mission have provided an unprecedented opportunity to examine the detailed structure of the multitude of thin current sheets that are generated by plasma turbulence, revealing that a novel form of magnetic reconnection, which has come to be known as electron-only reconnection, can occur within magnetosheath turbulence. These electron-only reconnection events occur at thin electron-scale current sheets and have super-Alfvénic electron jets that can approach the electron Alfvén speed; however, they do not appear to have signatures of ion jets. It is thought that electron-only reconnection can occur when the length of the reconnecting current sheets along the outflow direction is short enough that the ions cannot fully couple to the newly reconnected magnetic field lines before they fully relax. In this work, we examine how the correlation length of the magnetic fluctuations in a turbulent plasma, which constrains the length of the current sheets that can be formed by the turbulence, impacts the nature of turbulence-driven magnetic reconnection. Using observations from MMS, we systematically examine 60 intervals of magnetosheath turbulence – identifying 256 small-scale reconnection events, both with and without ion jets. We demonstrate that the properties of the reconnection events transition to become more consistent with electron-only reconnection when the magnetic correlation length of the turbulence is below ~20 ion inertial lengths. We further discuss the implications of the results in the context of other turbulent plasmas by considering observations of turbulent fluctuations in the solar wind. <br></span></p> (10.5194/egusphere-egu22-11524)
  DOI : 10.5194/egusphere-egu22-11524
• Multiscale analysis of a current sheet crossing associated with a fast earthward flow during a substorm event detected by MMS
  
  • Le Contel Olivier
  • Retino Alessandro
  • Alexandrova Alexandra
  • Nakamura Rumi
  • Alqeeq Soboh
  • Baraka Mohammed
  • Chust Thomas
  • Mirioni Laurent
  • Catapano Filomena
  • Jacquey Christian
  • Toledo-Redondo Sergio
  • Stawarz Julia
  • Goodrich Katherine
  • Gershman Daniel
  • Fuselier Stephen
  • Mukherjee Joey
  • Ahmadi Narges
  • Graham Daniel
  • Argall Matthew
  • Fischer David
  , 2022. <p><span>In July 2017, the MMS constellation was evolving in the magnetotail with an apogee of 25 Earth radii and an average inter-satellite distance of 10 km (i.e. at electron scales). On 23</span><sup><span>rd</span></sup><span> of July around 16:19 UT, MMS was located at the edge of the current sheet which was in a quasi-static state. Then, MMS suddenly entered in the central plasma sheet and detected the local onset of a small substorm as indicated by the AE index (~400 nT). Fast plasma flows towards the Earth were measured for about 1 hour starting with a period of quasi-steady flow and followed by a series of saw-tooth plasma jets (“bursty bulk flows”). In the present study, we focus on a short sequence related to the crossing of an ion scale current sheet embedded in a fast earthward flow. The current sheet appears to be corrugated and with a significant guide field (BL/BM~0.5). Tailward propagating electrostatic solitary waves are detected just after the magnetic equator crossing and at the edge of the current sheet. We also analyze in detail an electron vortex magnetic hole also detected at the edge of this current sheet and discuss the Ohm’s law and energy conversion processes. We find that the energy dissipation associated with the electron vortex is three times greater (0.15nW/m3) than at the current sheet crossing (0.05nW/m3). Based on estimated statistical weight of these vortices we discuss possible consequences for the energy dissipation associated with fast earthward plasma flows.</span></p> (10.5194/egusphere-egu22-9481)
  DOI : 10.5194/egusphere-egu22-9481
• Study of a dayside magnetopause reconnection event detected by MMS and related to a large-scale solar wind perturbation.
  
  • Baraka Mohammed
  • Le Contel Olivier
  • Canu Patrick
  • Alqeeq Soboh
  • Akhavan-Tafti Mojtaba
  • Retino Alessandro
  • Chust Thomas
  • Alexandrova Alexandra
  • Fontaine Dominique
  , 2022. <p>Magnetic reconnection is a fundamental process that is ubiquitous in the universe and allows the conversion of the magnetic field energy into heating and acceleration of plasma. It’s also very important as it is responsible for the dominant transport of plasma, momentum, and energy across the magnetopause from the solar wind into the Earth magnetosphere. Coronal Mass Ejections (CMEs) and Corotating Interaction Regions (CIRs) are the primary large-scale propagating structures and important drivers of unusual space weather disturbances causing magnetospheric activity. The present study reports on a magnetic reconnection event detected by the Magnetospheric Multiscale mission (MMS) on 21 October 2015 around 04:40 UT and related to a large-scale solar wind (SW) perturbation impacting the Earth’s magnetopause. Based on OMNI data, the event impacting the Earth’s magnetosphere is ahead of weak CIR (SW beta=~7 and Alfvénic Mach number~15) where the density of solar wind is about ~20 cm <sup>-3 </sup>(compared with average SW density ~3-10 cm <sup>-3</sup>). Furthermore, the magnetosheath (MSH) density measured by MMS just after the crossing of the magnetopause is about ~95 cm <sup>-3</sup> (compared with average MSH density ~20 cm <sup>-3</sup>). Reconnection signatures such as ion and electron jets, Hall field, and energy conversion are compared with a “classical” reconnection event observed during quiet solar wind conditions.</p> (10.5194/egusphere-egu22-9556)
  DOI : 10.5194/egusphere-egu22-9556
• A statistical study of dipolarization fronts observed by MMS
  
  • Alqeeq Soboh
  • Le Contel Olivier
  • Canu Patrick
  • Retinò Alessandro
  • Breuillard Hugo
  • Chust Thomas
  • Alexandrova Alexandra
  • Mirioni Laurent
  • Khotyaintsev Yuri
  • Nakamura Rumi
  • Wilder Frederick
  • Wei Hanying
  • Fischer David
  • Gershman Daniel
  • Burch James
  • Torbert Roy
  • Giles Barbara
  • Fuselier Stephen
  • Ergun Robert
  • Lindqvist Per Arne
  , 2022. <p>In the present work, we consider 49 dipolarization fronts (DF) detected by the Magnetospheric Multiscale (MMS) mission on 2017, near the Earth’s magnetotail equator (Bx<5nT). Criteria for selecting DF using an AIDApy routine are based on difference of maximum and minimum values computed with a 306 s sliding window. They request a Bz increase, an ion velocity increase and a density decrease. This first automatic selection is then ajusted manually with the following criteria : Bz increase larger than 5 nT, ion velocity larger than 150 km/s, density decrease and both ion and electron temperature increases. All these events belong to the most common category (A) defined by Schmid et al., 2015 in term of density decrease and temperature increase at the DF. However, based on a superposed epoch analysis of DF basic properties (magnetic field, density, velocity, ...) we distinguish two subcategories of events depending on the shape of the DF. The first subcategory (55.1%) corresponds to a slow decrease of the magnetic field after the DF and is associated with smaller ion velocity and hotter plasma. The second subcategory (44.9%) has the same time scale for the rising and the falling of the magnetic field (a bump) associated with a decrease of ion and electron pressures and faster velocity as shown in Alqeeq et al. 2021. For both categories 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. We also analyzed the energy conversion process. For the first subcategory we found that the energy in the spacecraft frame is transferred from the electromagnetic field to the plasma (J·E>0) ahead or at the DF. For the second subcategory, we found the same behavior ahead or at the DF whereas it is the opposite (J·E<0) behind the front. In the fluid frame, we found that the energy is mostly transferred from the plasma to the electromagnetic field (J·E ′ <0) ahead or at the DF for both subcategories but energy dissipation (J·E ′ >0) only occurs behind the front for the second subcategory. The possible origin of these two subcategories is discussed.</p> (10.5194/egusphere-egu22-9532)
  DOI : 10.5194/egusphere-egu22-9532
• 3D Hybrid Simulations of the Interaction between Self-Consistently Generated Extreme Solar Events and the Terrestrial Geo-Environment
  
  • Cazzola Emanuele
  • Fontaine Dominique
  • Savoini Philippe
  , 2022. In this work we present some results from 3D hybrid simulations of the interaction between extreme solar events, such as Coronal Mass Ejections (CMEs) or Co-rotating Interaction Regions (CIRs), and a 3D Earth-like geo-environment. The events are generated and let evolve self-consistently in order to represent their typical realistic Earth-hitting characteristics as described by the averaged profiles obtained from decades of observations at 1 AU. Both shock-less and shock-driven configurations are considered to highlight the differences between the two scenarios in terms of their kinetic dynamics, as well as in terms of the effects on the Bow-Shock / Magnetosheath / Magnetosphere system.</p> (10.5194/egusphere-egu22-2755)
  DOI : 10.5194/egusphere-egu22-2755
• Physics of plasma jets and interaction with surfaces: review on modelling and experiments
  
  • Viegas Pedro
  • Slikboer Elmar
  • Bonaventura Zdenek
  • Guaitella Olivier
  • Sobota Ana
  • Bourdon Anne
  Plasma Sources Science and Technology, IOP Publishing, 2022, 31 (5), pp.053001. Abstract Plasma jets are sources of repetitive and stable ionization waves, meant for applications where they interact with surfaces of different characteristics. As such, plasma jets provide an ideal testbed for the study of transient reproducible streamer discharge dynamics, particularly in inhomogeneous gaseous mixtures, and of plasma–surface interactions. This topical review addresses the physics of plasma jets and their interactions with surfaces through a pedagogical approach. The state-of-the-art of numerical models and diagnostic techniques to describe helium jets is presented, along with the benchmarking of different experimental measurements in literature and recent efforts for direct comparisons between simulations and measurements. This exposure is focussed on the most fundamental physical quantities determining discharge dynamics, such as the electric field, the mean electron energy and the electron number density, as well as the charging of targets. The physics of plasma jets is described for jet systems of increasing complexity, showing the effect of the different components (tube, electrodes, gas mixing in the plume, target) of the jet system on discharge dynamics. Focussing on coaxial helium kHz plasma jets powered by rectangular pulses of applied voltage, physical phenomena imposed by different targets on the discharge, such as discharge acceleration, surface spreading, the return stroke and the charge relaxation event, are explained and reviewed. Finally, open questions and perspectives for the physics of plasma jets and interactions with surfaces are outlined. (10.1088/1361-6595/ac61a9)
  DOI : 10.1088/1361-6595/ac61a9
• Investigation of DC and RF biased gridded ion thruster plume phenomena
  
  • Calvoso Habl Lui Txai
  , 2022. In recent years, two promising technologies emerged to improve the performance and decrease the cost of ion thrusters; RF biasing of ion acceleration grids and the use of iodine as a propellant.These techniques may represent a significant technological step forward; however, when using either of them, the physical processes in the plasma generation and especially on the downstream plasma plume are intricate, having significant implications on the device's performance.The main goal of this work was to elucidate the physics of the plasma plume when using these technologies through a numerical and experimental approach.A dedicated numerical model of the plume was developed to study RF grid biasing, which allowed a determination of the behavior of several phenomena and the expansion of previous numerical work.A prototype using RF grid biasing was also investigated experimentally, which was operated at the highest values of acceleration energy and frequency to date, demonstrating that it can generate a well-neutralized plume with acceptable performance and provide initial benchmark data available for this type of thruster.The experiments also showed an excellent agreement with the numerical and theoretical predictions, which confirmed both the correctness of the model developed here, and previous works, and being an important advancement towards developing a flight prototype.For iodine, the characteristics of the plume and the thruster performance were measured and compared to xenon, showing unique and, in several cases, better characteristics.A new automated instrument to determine the ion beam profile was developed, and to improve the quality of experiments and increase the knowledge base on iodine plasmas, the secondary electron emission yield of iodine ions was measured for the first time.During this work, the thruster tested was launched onboard a space mission, which permitted a comparison of ground and flight results with excellent agreement obtained.
• The Magnetopause: an almost tangential interface between the magnetosphere and the magnetosheath
  
  • Ballerini Giulio
  • Rezeau Laurence
  • Belmont Gérard
  • Califano Francesco
  , 2022.
• BibHelioTech
  
  • Génot Vincent
  • Dablanc Axel
  • Cabanac Guillaume
  • de Salabert Camille
  • Barreaux Sabine
  • Cuxac Pascal
  • Dufourg Nicolas
  • Aunai Nicolas
  • Exbrayat Williams
  , 2022. A partir d’un corpus d’articles scientifiques du domaine héliophysique utilisant des données de missions spatiales, nous réaliserons une détection textuelle automatisée sur les événements observés, les satellites/instruments utilisés, les régions spatiales et les processus physiques concernés, afin de relier ces entités avec les publications dont elles sont extraites, dans des catalogues exploitables par les outils d’analyse de données de la discipline. Ce lien fort et systématisé entre données et publications, inexistant à ce jour, augmentera l’expérience d’analyse de données en immergeant le chercheur dans le contexte bibliographique de son cas d’étude, améliorera significativement la reproductibilité des résultats publiés, et facilitera la réutilisation de ces catalogues dans de nouvelles études statistiques et comparatives.
• Magnetohydrodynamics
  
  • Pariat Etienne
  , 2022, pp.1-2. Hydromagnetics; Magneto-fluid dynamics Acronyms MHD Magnetohydrodynamics Definition Magnetohydrodynamics (MHD) is a physical paradigm pertinent to describe the dynamics of electrically conducting fluids, such as plasmas, electrolytes, and liquid metals. MHD couples fluids dynamics with electromagnetism. (10.1007/978-3-642-27833-4_2706-2)
  DOI : 10.1007/978-3-642-27833-4_2706-2
• Re-analysis of the Cassini RPWS/LP data in Titan's ionosphere: electron density and temperature of cold electron populations
  
  • Chatain Audrey
  • Wahlund Jan-Erik
  • Shebanits Oleg
  • Hadid Lina
  • Morooka Michiko
  • Edberg Niklas J. T.
  • Carrasco Nathalie
  • Guaitella Olivier
  , 2022. The Cassini Langmuir Probe (LP) data acquired in the ionosphere of Titan are re-analysed to finelystudy the electron behaviour in the birthplace of Titan’s aerosols (900-1200 km) [Waite et al 2007].The detailed analysis of the complete Cassini LP dataset below 1200 km (57 flybys) shows the systematic detection of 2 to 4 electron populations (further named P1, P2, P3, P4), with reproducible characteristics depending on altitude and solar illumination. Populations P1 and P2 are always present, contrarily to P3 and P4. Due to their low density and low potential, P1 electrons are suspected to be photo-electrons [Wahlund et al 2009] or secondary electrons emitted on the probe stick.The electron populations densities and temperatures are deduced from the Orbital Motion Limited theory and the Sheath Limited theory [Wahlund et al 2009, Whipple 1965]. We observe that electron temperatures do not vary much with altitude between 1200 and 950 km, except for P4. Statistical correlations with other quantities measured by Cassini are investigated. In particular, we observe that P3 and P4 densities are correlated with the extreme UV flux.From our results we suggest possible origins for the three populations P2, P3 and P4, coming from the plasma surrounding the probe:-P2 is detected in all cases, at rather low density (~500 cm-3) and temperature (~0.04 eV). These are possibly induced by particle precipitation.-P3 electrons are denser with stronger solar illumination and higher pressure (up to 3000 cm-3). Therefore, they are likely to be related to photo-ionization. They are hotter than P2 electrons (~0.06-0.07 eV).-P4 electrons are only observed on dayside and below 1200 km, in the place where heavy negative ions and aerosols are present. They are then plausibly linked to dusty plasma effects. We suggest two possible formation processes: (1) the photo-emission of electrons from grains could be triggered by photons of a few eV due to the negative charge born by the aerosols [Shebanits et al 2016; Tigrine et al 2018] ; (2) electrons could also be thermo-emitted from the grains, as a result Powered by TCPDF (www.tcpdf.org)of their heating by diverse processes such as heterogeneous chemistry, sticking of electrons or recombination of radicals [Woodard et al 2020]. (10.5194/egusphere-egu22-8878)
  DOI : 10.5194/egusphere-egu22-8878
• The incompressible energy cascade rate in anisotropic solar wind turbulence
  
  • Andrés N.
  • Sahraoui Fouad
  • Huang S.
  • Hadid L. Z.
  • Galtier S.
  Astronomy & Astrophysics - A&A, EDP Sciences, 2022, 661, pp.A116. Context. The presence of a magnetic guide field induces several types of anisotropy in solar wind turbulence. The energy cascade rate between scales in the inertial range depends strongly on the direction of this magnetic guide field, splitting the energy cascade according to the parallel and perpendicular directions with respect to magnetic guide field. Aims. Using more than two years of Parker Solar Probe (PSP) observations, the isotropy and anisotropy energy cascade rates are investigated. The variance and normalized fluctuation ratios, the kinetic and magnetic energies, and the normalized cross-helicity and residual energy are studied. The connection between the heliocentric distance, the local temperature of the plasma, and the energy cascade components is made. Methods. Using exact relations for fully developed incompressible magnetohydrodynamic (MHD) turbulence, the incompressible energy cascade rate is computed. In particular, using the isotropy and 2D and slab assumptions, the isotropic, perpendicular, and parallel energy cascade rate components are estimated. Results. The variance anisotropy ratios, for both velocity and magnetic fields, do not exhibit a dependence with respect to the heliocentric distance r between 0.2 and 0.8 au. While the velocity normalized fluctuation ratio shows a dependence with r , the magnetic normalized fluctuation ratio does not. A strong correlation between the isotropic and anisotropic energy cascade rates and the temperature is found. A clear dominance of the perpendicular cascades over the parallel cascades as PSP approaches the Sun is observed. A dominant 2D cascade and/or geometry over the slab component in slow solar wind turbulence in the largest MHD scales is observed. (10.1051/0004-6361/202142994)
  DOI : 10.1051/0004-6361/202142994
• Direct observations of anomalous resistivity and diffusion in collisionless plasma
  
  • Graham D.
  • Khotyaintsev Yu.
  • André M.
  • Vaivads A.
  • Divin A.
  • Drake J.
  • Norgren C.
  • Le Contel O.
  • Lindqvist P.-A.
  • Rager A.
  • Gershman D.
  • Russell C.
  • Burch J.
  • Hwang K.-J.
  • Dokgo K.
  Nature Communications, Nature Publishing Group, 2022, 13 (1), pp.2954. Abstract Coulomb collisions provide plasma resistivity and diffusion but in many low-density astrophysical plasmas such collisions between particles are extremely rare. Scattering of particles by electromagnetic waves can lower the plasma conductivity. Such anomalous resistivity due to wave-particle interactions could be crucial to many processes, including magnetic reconnection. It has been suggested that waves provide both diffusion and resistivity, which can support the reconnection electric field, but this requires direct observation to confirm. Here, we directly quantify anomalous resistivity, viscosity, and cross-field electron diffusion associated with lower hybrid waves using measurements from the four Magnetospheric Multiscale (MMS) spacecraft. We show that anomalous resistivity is approximately balanced by anomalous viscosity, and thus the waves do not contribute to the reconnection electric field. However, the waves do produce an anomalous electron drift and diffusion across the current layer associated with magnetic reconnection. This leads to relaxation of density gradients at timescales of order the ion cyclotron period, and hence modifies the reconnection process. (10.1038/s41467-022-30561-8)
  DOI : 10.1038/s41467-022-30561-8
• Lower‐Hybrid Wave Structures and Interactions With Electrons Observed in Magnetotail Reconnection Diffusion Regions
  
  • Wang Shan
  • Chen Li‐jen
  • Bessho Naoki
  • Ng Jonathan
  • Hesse Michael
  • Graham Daniel
  • Le Contel Olivia
  • Gershman Daniel
  • Giles Barbara
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2022, 127 (5). (10.1029/2021JA030109)
  DOI : 10.1029/2021JA030109
• Analysis of a curved shock front microstructures and associated electron/ion foreshock for a subcritical shock regime
  
  • Savoini Philippe
  • Lembège Bertrand
  , 2022. Previous numerical works on electron/ion foreshocks observed upstream of a curved shock have been already performed within a self-consistent approach based on 2D PIC simulation (Savoini et Lembege, 2010, 2013, 2015), but are restricted to a supercritical regime only. Present two dimensional PIC (Particle in cell) simulations are used in order to analyze the features of a curved shock and associated foreshocks in a subcritical regime. In order to investigate the dynamic of each electron and ion backstreaming populations, we used test-particles in a pre-computed electromagnetic field (issued from 2D PIC simulations) which allows us to define precisely the characteristic of each population in terms of initial velocity and/or their upstream position to the θ_Bn angle (angle between the local shock normal and the interplanetary magnetic field IMF). Then, results allow to clarify the following questions: what is the impact of the subcritical regime (i) on the persistence of each electron/ion foreshock respectively ?, (ii) in the case the persistence is confirmed how the location (along the curved front) and the angular direction of each foreshock edge are affected ?, and (iii) how the mapping of upstream local distribution functions are impacted ? Preliminary results will be presented and compared with those already obtained for a supercritical shock. (10.5194/egusphere-egu22-3631)
  DOI : 10.5194/egusphere-egu22-3631
• Exact law for compressible pressure-anisotropic magnetohydrodynamic turbulence: Toward linking energy cascade and instabilities
  
  • Simon P.
  • Sahraoui Fouad
  Physical Review E, American Physical Society (APS), 2022, 105 (5), pp.055111. (10.1103/PhysRevE.105.055111)
  DOI : 10.1103/PhysRevE.105.055111
• Phase and amplitude evolution in the network of triadic interactions of the Hasegawa–Wakatani system
  
  • Gürcan Ö.
  • Anderson J.
  • Moradi S.
  • Biancalani A.
  • Morel P.
  Physics of Plasmas, American Institute of Physics, 2022, 29 (5), pp.052306. The Hasegawa–Wakatani system, commonly used as a toy model of dissipative drift waves in fusion devices, is revisited with considerations of phase and amplitude dynamics of its triadic interactions. It is observed that a single resonant triad can saturate via three way phase locking, where the phase differences between dominant modes converge to constant values as individual phases increase in time. This allows the system to have approximately constant amplitude solutions. Non-resonant triads show similar behavior only when one of its legs is a zonal wave number. However, when an additional triad, which is a reflection of the original one with respect to the y axis is included, the behavior of the resulting triad pair is shown to be more complex. In particular, it is found that triads involving small radial wave numbers (large scale zonal flows) end up transferring their energy to the subdominant mode which keeps growing exponentially, while those involving larger radial wave numbers (small scale zonal flows) tend to find steady chaotic or limit cycle states (or decay to zero). In order to study the dynamics in a connected network of triads, a network formulation is considered, including a pump mode, and a number of zonal and non-zonal subdominant modes as a dynamical system. It was observed that the zonal modes become clearly dominant only when a large number of triads are connected. When the zonal flow becomes dominant as a “collective mean field,” individual interactions between modes become less important, which is consistent with the inhomogeneous wave-kinetic picture. Finally, the results of direct numerical simulation are discussed for the same parameters, and various forms of the order parameter are computed. It is observed that nonlinear phase dynamics results in a flattening of the large scale phase velocity as a function of scale in direct numerical simulations. (10.1063/5.0089073)
  DOI : 10.1063/5.0089073
• Fine structure of streamer-to-filament transition in high-pressure nanosecond surface dielectric barrier discharge
  
  • Ding Ch
  • Jean A
  • Popov N A
  • Starikovskaia S M
  Plasma Sources Science and Technology, IOP Publishing, 2022, 31 (4), pp.045013. The fine structure of a streamer-to-filament transition in a single-shot high-voltage nanosecond surface dielectric barrier discharge in molecular nitrogen at pressure P = 6 bar was studied with the help of ICCD microimaging. An intermediate discharge structure, existing for only a few nanoseconds, was observed in the time interval between two discharge modes: streamer discharge, with a typical electron density of n_e ∼ 10^{15} cm^{−3} , and filamentary discharge, with n_e ∼ 10^{19} cm^{−3} . The structure was observed for both polarities of the high-voltage electrode. The structure can be briefly described as a stochastic appearance of thin channels propagating a bit faster than the main ionization front of merged surface streamers, transforming in a few nanoseconds in a bi-directional ionization wave. One wave, which we associate with a feather-like structure in optical emission, propagates further away from the high-voltage electrode, and another, a backward wave of emission, propagates back towards the edge of the high-voltage electrode. When the backward wave of emission almost reaches the high-voltage electrode, the filament appears. Plasma properties of the observed structure were studied to better understand the nature of a streamer-to-filament transition. Theoretical analysis suggests that the instability of a flat front of ionization wave (Laplacian instability) triggers the streamer-to-filament transition, and that a surface stem (a tiny region with enhanced electron density) should be in the origin of the bi-directional ionization wave. (10.1088/1361-6595/ac5c5f)
  DOI : 10.1088/1361-6595/ac5c5f
• Nanosecond plasmas for detonability enhancement
  
  • Cherif Ali
  • Lafaurie Victor
  • Starikovskaia Svetlana
  • Vidal Pierre
  , 2022.
• Evidence for Whistler Waves Propagating Into the Electron Diffusion Region of Collisionless Magnetic Reconnection
  
  • Zhong Z.
  • Zhou M.
  • Graham D.
  • Khotyaintsev Yu.
  • Wu Y.
  • Le Contel O.
  • Li H.
  • Tao X.
  • Tang R.
  • Deng X.
  Geophysical Research Letters, American Geophysical Union, 2022, 49 (7). (10.1029/2021GL097387)
  DOI : 10.1029/2021GL097387
• Nighttime morphology of vertical plasma drifts over Vietnam during different seasons and phases of sunspot cycles
  
  • Pham Thi Thu Hong
  • Amory-Mazaudier Christine
  • Le Huy Minh
  • Saito Susumu
  • Hozumi Kornyanat
  • Nguyen Thanh Dung
  • Luong Thi Ngoc
  Advances in Space Research, Elsevier, 2022. This study is the first to provide the nighttime morphology of vertical plasma drifts over Vietnam at the equatorial trough and the northern tropical crest of ionization anomaly in the Asian sector. We use the h’F data in Vietnam from Bac Lieu observatory (9.28°N, 105.73°E, dip: 1.73°N) during the 2006–2019 period and Phu Thuy observatory (21.03°N, 105.96°E, dip: 14.49°N) for the 1964–2011 period, to calculate the vertical plasma drift velocity (Vd) and analyze the annual, seasonal, sunspot cycle, and sunspot cycle (SC) phase evolutions. For Bac Lieu, the PRE and minimum reversal peaks evolve according to the sunspot cycles. The seasonal average of the drift pattern shows that the PRE peak appears earlier one hour in summer (1800 LT) than in equinoxes and winter (1900 LT) and the minimum reversal peak occurred about 2100–2200 LT, except in summer, in which this peak identifies around 0100 LT. This drift pattern exhibits a semiannual asymmetry during PRE/minimum reversal periods with peaks in March and September/October. The evening-time pre-reversal enhancement (PRE) at Bac Lieu is dependent on the phase of the sunspot cycle. For Phu Thuy, the mean annual peak magnitudes of Vd during the PRE and minimum reversal periods exhibit a poor correlation with the sunspot number (Rz). For the SC seasonal variation, the lowest PRE peak magnitude in autumn appeared one hour later compared with winter, one hour earlier than summer, and the same time as spring, while the minimum reversal peak is larger in summer for SCs 20–23 and in autumn for SCs 20, 23, and 24 at around 0200–0300 LT than in another season at about 2000, 2200, and 2300 LT. The morphology of the seasonal average variations of Vd is rather similar for all SCs except SC 24 at Phu Thuy. The PRE peak during the high solar activity years (2000 LT) appears earlier about 4 h than that during the low solar years (at 2300 LT/0000 LT). The monthly average of plasma drift also exhibits semiannual asymmetry during PRE events for cycles 22, 24, and minimum reversal period for cycle 24 with peaks in March and September. In addition, it shows an annual variation for the remaining cycles during PRE/minimum reversal periods with peaks in the summer months. The pre-sunrise enhancement characteristic (0500 LT) was observed during all seasons and phases (ascending, descending, minimum) at Bac Lieu, summer for all SCs, equinoxes for SC 24, the ascending and minimum phases for the SC 24, and the descending phase for the SC 23 at Phu Thuy. (10.1016/j.asr.2022.04.010)
  DOI : 10.1016/j.asr.2022.04.010
• Anisotropy of Magnetic Field Spectra at Kinetic Scales of Solar Wind Turbulence as Revealed by the Parker Solar Probe in the Inner Heliosphere
  
  • Huang S.
  • Xu S.
  • Zhang J.
  • Sahraoui Fouad
  • Andrés N.
  • He J.
  • Yuan Z.
  • Deng X.
  • Jiang K.
  • Wei Y.
  • Xiong Q.
  • Wang Z.
  • Yu L.
  • Lin R.
  The Astrophysical Journal Letters, Bristol : IOP Publishing, 2022, 929 (1), pp.L6. Abstract Using the Parker Solar Probe data taken in the inner heliosphere, we investigate the power and spatial anisotropy of magnetic field spectra at kinetic scales (i.e., around sub-ion scales) in solar wind turbulence in the inner heliosphere. We find that strong anisotropy of the magnetic spectra occurs at kinetic scales with the strongest power in the perpendicular direction with respect to the local magnetic field (forming an angle θ B with the mean flow velocity). The spectral index of the magnetic spectra varies from −3.2 to −5.8 when the angle θ B changes from 90° to 180° (or 0°), indicating that strong anisotropy of the spectral indices occurs at kinetic scales in the solar wind turbulence. Using a diagnosis based on the magnetic helicity, we show that the anisotropy of the spectral indices can be explained by the nature of the plasma modes that carry the cascade at kinetic scales. We discuss our findings in light of existing theories and current development in the field. (10.3847/2041-8213/ac5f02)
  DOI : 10.3847/2041-8213/ac5f02
• Comprehensive experimental turbulence measurements for scale-resolved multichannel gyrokinetic code validation
  
  • Höfler K.
  • Görler T
  • Happel T.
  • Hennequin P.
  • C. Lechte
  • P. A. Molina Cabrera
  • R. S. Bielajew
  • G. D. Conway
  • F. Jenko
  • R. M. Mcdermott
  • P. A. Schneider
  • A. E. White
  • Stroth U.
  , 2022. Turbulence is the main driver of heat and particle transport which deteriorates the performance of fusion plasmas. To design turbulence optimised devices, simulation codes need to be validated by experiments. Validation work has already been done for a single or a small number of turbulence observables. A comprehensive set of experimental turbulence data is measured on ASDEX Upgrade for two different plasma scenarios where the electron gradient length is changed by means of ECRH. It includes wavenumber spectra, density and temperature fluctuation amplitudes and radial correlation lengths, the poloidal dependence of the velocity perpendicular to the magnetic field as well as the cross-phase between density and temperature fluctuations. These quantities are measured by Doppler reflectometers in both X-mode and O-mode polarization and an electron cyclotron emission radiometer. They are compared to gyrokinetic turbulence simulations from the GENE code. For this purpose synthetic diagnostic modeling is applied to account for diagnostic effects on measurements. The work shows the encouraging example of code validation where a remarkable number of measured physics quantities is successfully reproduced by the code. We highlight the simultaneous agreement between experiment and simulation of all investigated turbulence quantities. This study provides a sound scientific justification for using codes such as GENE in the design of future fusion reactors.