Publications

2019

• Measuring the magnetic structure velocity for the 11 July 2017 magnetotail reconnection event
  
  • Denton R. E.
  • Hasegawa H.
  • Torbert R. B.
  • Manuzzo Roberto
  • Sonnerup B. U. Ö.
  • Genestreti K. J.
  • Dors I.
  • Belmont Gérard
  • Rezeau Laurence
  • Califano F.
  , 2019. Velocities in magnetic reconnection events, such as those of particles, are best understood in the frame of reference of the magnetic structure that is ultimately responsible for the reconnection process. We discuss four different methods for evaluating the velocity of the magnetic structure, and use those methods to find the magnetic structure velocity for the 11 July 2017 magnetotail reconnection event studied by Torbert et al. (Science, 2018). The four methods are timing analysis, the SpatioTemporal Difference (STD) method of Shi et al. (JGR, 2006), Electron Magnetohydrodynamic (EMHD) reconstruction (Sonnerup et al., JGR, 2016), and polynomial reconstruction of the magnetic field in the vicinity of the spacecraft using the magnetic field and particle current density as input to the model. The relative merits of the different techniques will be discussed, and the different results compared.
• Nonlinear Diffusion Models for Gravitational Wave Turbulence
  
  • Galtier Sébastien
  • Nazarenko Sergey V.
  • Buchlin Éric
  • Thalabard Simon
  Physica D: Nonlinear Phenomena, Elsevier, 2019, 390, pp.84-88. A fourth-order and a second-order nonlinear diffusion model in spectral space are proposed to describe gravitational wave turbulence in the approximation of strongly local interactions. We show analytically that the model equations satisfy the conservation of energy and wave action, and reproduce the power law solutions previously derived from the kinetic equations with a direct cascade of energy and an explosive inverse cascade of wave action. In the latter case, we show numerically by computing the second-order diffusion model that the non-stationary regime exhibits an anomalous scaling which is understood as a self-similar solution of the second kind with a front propagation following the law kf∼(t∗−t)3.296 , with t<t∗ . These results are relevant to better understand the dynamics of the primordial universe where potent sources of gravitational waves may produce space–time turbulence. (10.1016/j.physd.2019.01.007)
  DOI : 10.1016/j.physd.2019.01.007
• Experimental study of pulsed microwave discharges at pressures ranging over five orders of magnitude
  
  • Shcherbanev S.A.
  • Ali Cherif Mhedine
  • Starikovskaia Svetlana
  • Ikeda Yuji
  Plasma Sources Science and Technology, IOP Publishing, 2019, 28, pp.045009 (10pp). Microwave discharge igniter (MDI) is a discharge system developed to initiate combustion in automotive engines. The MDI uses a sequence of N = 700 microwave (2.45 GHz) pulses 100 ns in duration separated by 1 &#956;s. The initial breakdown is provided by the &#64257;rst microwave pulse, 5 &#956;s in duration. The aim of pulsing the microwave signal is to keep an optimal combination of parameters when, even at elevated pressures, (i) the discharge propagates over the largest possible volume; (ii) the plasma is non-equilibrium. Properties of plasma produced by MDI igniter in non-combustible gas mixtures at ambient gas temperature and gas pressure in the range between 0.2 mbar and 8 bar were studied experimentally. Discharge spatial structure was analyzed with the help of time-resolved ICCD imaging. Near-UV optical emission spectra taken in different pulses provided the information about rotational and vibrational temperatures. The electric &#64257;eld was estimated on the basis of ratio of emission of the second positive and the &#64257;rst negative systems of molecular nitrogen. (10.1088/1361-6595/aae765)
  DOI : 10.1088/1361-6595/aae765
• Nonlinear interaction of whistler waves in a magnetized plasma with density ducts
  
  • Zaboronkova T. M.
  • Krafft Catherine
  • Yashina N. F.
  Physics of Plasmas, American Institute of Physics, 2019, 26, pp.102104. The nonlinear resonant interactions between whistler waves guided bydensity ducts surrounded by a uniform magnetized plasma are studied. Itis shown that, under specific conditions that are determined, a time-harmonic external electromagnetic field can drive the parametricinstability of guided whistlers. Both cases of cylindrical and planarducts are considered, of either decreased or increased plasma density.The frequency interval where the magnetized plasma may be resonant isanalyzed. The growth rate and the threshold of the parametricinstability are determined. Numerical calculations are presented forparameters typical of "space plasmas and" modeling laboratoryexperiments where guided whistler propagation was observed. (10.1063/1.5110958)
  DOI : 10.1063/1.5110958
• Filamentary nanosecond surface dielectric barrier discharge. Experimental comparison of the streamer-to-filament transition for positive and negative polarities.
  
  • Ding Chenyang
  • Khomenko A.Yu.
  • Shcherbanev S.A.
  • Starikovskaia Svetlana
  Plasma Sources Science and Technology, IOP Publishing, 2019, 28 (8), pp.085005. Streamer-to-filament transition is a general feature of high pressure high voltage nanosecond surface dielectric barrier discharges (nSDBDs) for mixtures containing molecular gases. The transition is observed at high pressures and voltages in a single-shot experiment a few nanoseconds after the start of the discharge. A set of experimental results comparing streamer-to-filament transition and properties of plasma in the filaments for the identical high voltage pulses of negative and positive polarity is presented. The transition curves in voltage-pressure coordinates are obtained for N 2 :O 2 mixtures with different content of molecular oxygen, from 0 to 20%, at the pressure range 1-12 bar. Continuous optical spectra are compared for both polarities in 6 bar synthetic air. Electron density is calculated from Stark broadening of H α line at λ = 656.5 nm in the discharge and in early afterglow, 40 nanoseconds after the end of the high voltage pulse. Hydrodynamic perturbations are measured using schlieren imaging in 1-6 bar air for streamer and filamentary mode for both polarities. The review of common and distinctive features of the filamentary single-shot nSDBD for two polarities of the applied pulse is provided. (10.1088/1361-6595/ab2d7a)
  DOI : 10.1088/1361-6595/ab2d7a
• Electric field induced second harmonic (E-FISH) generation for characterization of fast ionization wave discharges at moderate and low pressures
  
  • Chng Tat Loon
  • Orel Inna
  • Starikovskaia Svetlana
  • Adamovich I.V.
  Plasma Sources Science and Technology, IOP Publishing, 2019, 28 (4), pp.045004 (8pp). The electric &#64257;eld in an ionization wave discharge in nitrogen at 20100 mbar, initiated by positive polarity, high-voltage, ns duration pulses, is measured by ps second harmonic generation. The axial electric &#64257;eld component is determined both during the propagation of the ionization wave along the discharge tube, and after the wave reaches the grounded electrode, spanning the entire discharge gap. The temporal resolution of the present measurements is 200 ps, with the spatial resolution in the axial direction of approximately 0.5 mm. The second harmonic signal exhibits a quadratic dependence on the Laplacian electric &#64257;eld but indicates that in this pressure range most of the signal is generated within the wall of the tube. Absolute calibration of the signal is obtained from the current shunt data, after the ionization wave has reached the grounded electrode. Comparison of the data taken at different pressures shows that the peak value of the axial electric &#64257;eld in the wave front, 811 kV cm&#8722;1, has a fairly weak dependence on pressure, with the peak reduced electric &#64257;eld reaching &#8776;2000 Td at 20 mbar. Reducing the pressure from 100 to 20 mbar, while keeping the discharge pulse voltage waveform the same, steepens the ionization wave front considerably, from 3.0 to 1.0 ns full width at half maximum. The results demonstrate that ps second harmonic generation may be employed for electric &#64257;eld measurements in low-pressure discharges, discharges sustained in small diameter capillary tubes, and discharges sustained in gas mixtures with low nonlinear susceptibility, at the conditions when the detection of the signal generated directly in the plasma is challenging. High temporal resolution of the present measurements indicates a possibility of detection of non-local electron kinetics effects induced by a rapidly va (10.1088/1361-6595/ab0b22)
  DOI : 10.1088/1361-6595/ab0b22
• Four-Spacecraft Measurements of the Shape and Dimensionality of Magnetic Structures in the Near-Earth Plasma Environment
  
  • Fadanelli S
  • Lavraud B.
  • Califano F.
  • Jacquey C.
  • Kacem I.
  • Vernisse Y.
  • Penou E.
  • Gershman D J
  • Dorelli J
  • Pollock C.
  • Giles B L
  • Avanov L.
  • Burch J.
  • Chandler M. O.
  • Coffey V N
  • Eastwood J P
  • Ergun R
  • Farrugia C J
  • Fuselier S A
  • Genot V N
  • Grigorenko E
  • Hasegawa H
  • Khotyaintsev Y
  • Le Contel Olivier
  • Marchaudon Aurélie
  • Moore T E
  • Nakamura R
  • Paterson W R
  • Phan T
  • Rager A. C.
  • Russell C T
  • Saito Y
  • Sauvaud J.-A
  • Schiff C
  • Smith S E
  • Toledo Redondo S
  • Torbert R B
  • Wang S
  • Yokota S
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2019, 124 (8), pp.6850-6868. We present a new method for determining the main relevant features of the local magnetic field configuration, based entirely on the knowledge of the magnetic field gradient four-spacecraft measurements. The method, named "magnetic configuration analysis" (MCA), estimates the spatial scales on which the magnetic field varies locally. While it directly derives from the well-known magnetic directional derivative and magnetic rotational analysis procedures (Shi et al., 2005, htpps://doi.org/10.1029/ 2005GL022454; Shen et al., 2007, https://doi.org/10.1029/2005JA011584), MCA was specifically designed to address the actual magnetic field geometry. By applying MCA to multispacecraft data from the Magnetospheric Multiscale (MMS) satellites, we perform both case and statistical analyses of local magnetic field shape and dimensionality at very high cadence and small scales. We apply this technique to different near-Earth environments and define a classification scheme for the type of configuration observed. While our case studies allow us to benchmark the method with those used in past works, our statistical analysis unveils the typical shape of magnetic configurations and their statistical distributions. We show that small-scale magnetic configurations are generally elongated, displaying forms of cigar and blade shapes, but occasionally being planar in shape like thin pancakes (mostly inside current sheets). Magnetic configurations, however, rarely show isotropy in their magnetic variance. The planar nature of magnetic configurations and, most importantly, their scale lengths strongly depend on the plasma β parameter. Finally, the most invariant direction is statistically aligned with the electric current, reminiscent of the importance of electromagnetic forces in shaping the local magnetic configuration. (10.1029/2019JA026747)
  DOI : 10.1029/2019JA026747
• The RPW/Search Coil Magnetometer onboard Solar Orbiter
  
  • Kretzschmar Matthieu
  • Krasnoselskikh V.
  • Jannet G.
  • Jean-Yves B.
  • Fergeau P.
  • Timofeeva M.
  • Dudok de Wit Thierry
  • Maksimovic M.
  • Chust Thomas
  • Le Contel O.
  • Soucek J.
  , 2019, 2019. Measuring the fluctuating magnetic fields associated to various phenomena such as waves, shocks, and turbulence is essential for the Solar Orbiter mission. These measurements rely on a tri-axial Search Coil Magnetometer (SCM) built at the Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E) in Orléans, France. Two antennas of SCM covers the 10Hz-50kHz frequency range, while the third antenna is a dual-band one that covers also the 1kHz-1MHz frequency range. The highest sensitivity is reached respectively at 3kHz and 10kHz for the low and high frequency channels, with a level of 10^-5 nT/sqrt(Hz). The SCM is allocated on the boom of the spacecraft and the LFR, TDS, and HFR analyzers of the RPW experiment will register and process its signal on-board. <P />Extensive calibrations have been performed at RPW system level with both SCM and the analyzers ; the final calibration procedure depends on temperature, RPW configuration, and takes into account the signal received by all three magnetic antennas simultaneously.
• The Radio and Plasma Waves (RPW) Instrument on Solar Orbiter : Capabilities and Performance
  
  • Maksimovic M.
  • Soucek J.
  • Bale S. D.
  • Bonnin X.
  • Chust Thomas
  • Khotyaintsev Y.
  • Kretzschmar Matthieu
  • Plettemeier D.
  • Steller M.
  • Štverák S.
  , 2019, 2019, pp.15 pp.. We will review the instrumental capabilities of the Radio and Plasma Waves (RPW) Instrument on Solar Orbiter. This instrument is designed to measure in-situ magnetic and electric fields and waves from 'DC' to a few hundreds of kHz. RPW will also observe solar radio emissions up to 16 MHz. The RPW instrument is of primary importance to the Solar Orbiter mission and science requirements, since it is essential to answer three of the four mission overarching science objectives. In addition, RPW will exchange on-board data with the other in-situ instruments, in order to process algorithms for interplanetary shocks and type III Langmuir waves detections.
• Introduction to plasma physics
  
  • Belmont Gérard
  • Rezeau Laurence
  • Riconda C.
  • Zaslavsky A.
  , 2019.
• Experimental investigation of the tilt angle of turbulent structures in the core of fusion plasmas
  
  • Pinzon Javier
  • Happel T.
  • Hennequin Pascale
  • Angioni Clemente
  • Estrada Teresa
  • Lebschy Alexander
  • Stroth Ulrich
  • Asdex Upgrade Team The
  Nuclear Fusion, IOP Publishing, 2019, 59, pp.074002. The tilt angle of turbulent structures stands for the anisotropy of turbulence which is essential for understanding the dynamics of magnetized plasmas. It is a quantity predicted by theory and simulations, that provides information on the interplay between turbulence, micro-instabilities and plasma flows. A new method for measuring the tilt angle of turbulent structures in the core region of fusion plasmas using Doppler reflectometry is presented. First measurements of this type on the ASDEX Upgrade tokamak have shown a significant difference of tilt angle for different plasma conditions. The dominance of sheared flows in determining the structure tilt is experimentally demonstrated for different turbulence regimes. (10.1088/1741-4326/ab227e)
  DOI : 10.1088/1741-4326/ab227e
• Non-Isothermal Sheath Model for Low Pressure Plasmas
  
  • Tavant Antoine
  • Lucken Romain
  • Bourdon Anne
  • Chabert Pascal
  Plasma Sources Science and Technology, IOP Publishing, 2019, 28 (7), pp.075007. The evolution of the electron mean energy in the pre-sheath and the sheath of a low pressure plasma bounded by two planes is investigated with 1D particle in cell simulations. We observed that the electron mean energy is not constant in the sheath, but instead decreases significantly from the bulk towards the wall. From the simulations, a polytropic state law is proposed, allowing us to close the fluid equations for the electrons without the isothermal hypothesis. A comparison between the fluid model and the simulations show that the non-isothermal sheath model is more accurate than the isothermal model. The impact of the electron mean energy variation on the potential sheath drop and the electron particle and heat flux is evaluated. (10.1088/1361-6595/ab279b)
  DOI : 10.1088/1361-6595/ab279b
• High-Frequency Wave Generation in Magnetotail Reconnection: Linear Dispersion Analysis
  
  • Burch J. L.
  • Dokgo K.
  • Hwang K.-J.
  • Torbert R. B.
  • Graham D. B.
  • Webster J. M.
  • Ergun R. E.
  • Giles B. L.
  • Allen R. C.
  • Chen L.-J.
  • Wang S.
  • Genestreti K. J.
  • Russell C. T.
  • Strangeway R. J.
  • Le Contel Olivier
  Geophysical Research Letters, American Geophysical Union, 2019, 46 (8), pp.4089-4097. Plasma and wave measurements from the NASA Magnetospheric Multiscale mission are presented for magnetotail reconnection events on 3 July and 11 July 2017. Linear dispersion analyses were performed using distribution functions comprising up to six drifting bi-Maxwellian distributions. In both events electron crescent-shaped distributions are shown to be responsible for upper hybrid waves near the X-line. In an adjacent location within the 3 July event a monodirectional field-aligned electron beam drove parallel-propagating beam-mode waves. In the 11 July event an electron distribution consisting of a drifting core and two crescents was shown to generate upper-hybrid and beam-mode waves at three different frequencies, explaining the observed broadband waves. Multiple harmonics of the upper hybrid waves were observed but cannot be explained by the linear dispersion analysis since they result from nonlinear beam interactions. (10.1029/2019GL082471)
  DOI : 10.1029/2019GL082471
• Turbulent Heating in the Accelerating Region Using a Multishell Model
  
  • Verdini Andrea
  • Grappin Roland
  • Montagud-Camps Victor
  Solar Physics, Springer Verlag, 2019, 294. Recent studies of turbulence-driven solar winds indicate that fast winds are obtained only at the price of unrealistic bottom boundary conditions: too large wave amplitudes and small frequencies. In this work, the incompressible turbulent dissipation is modeled with a large-scale von Karman-Howarth-Kolmogorov-like phenomenological expression (Q_K41<SUP>0</SUP>). An evaluation of the phenomenology is thus necessary to understand if unrealistic boundary conditions result from physical or model limitations. To assess the validity of the Kolmogorov-like expression, Q_K41<SUP>0</SUP>, one needs to compare it to exact heating, which requires describing the cascade in detail. This has been done in the case of homogeneous MHD turbulence, including expansion, but not in the critical accelerating region. To assess the standard incompressible turbulent heating in the accelerating region, we use a reduced MHD model (multishell model) in which the perpendicular turbulent cascade is described by a shell model, allowing to reach a Reynolds number of 10<SUP>6</SUP>. We first consider the homogeneous and expanding cases, and find that primitive MHD and multishell equations give remarkably similar results. We thus feel free to use the multishell model in the accelerating region. The results indicate that the large-scale phenomenology is inaccurate and it overestimates the heating by a factor at least 20, thus invalidating earlier studies of winds driven by incompressible turbulence. We conclude that realistic 1D wind models cannot be based solely on incompressible turbulence, but probably need an addition of compressible turbulence and shocks to increase the wave reflection and thus the heating. (10.1007/s11207-019-1458-y)
  DOI : 10.1007/s11207-019-1458-y
• Energy Conversion and Electron Acceleration in the Magnetopause Reconnection Diffusion Region
  
  • Pritchard K. R.
  • Burch J. L.
  • Fuselier S. A.
  • Webster J. M.
  • Torbert R. B.
  • Argall M. R.
  • Broll J.
  • Genestreti K. J.
  • Giles B. L.
  • Le Contel Olivier
  • Mukherjee J.
  • Phan T. D.
  • Rager A. C.
  • Russell C. T.
  • Strangeway R. J.
  Geophysical Research Letters, American Geophysical Union, 2019, 46 (17-18), pp.10274-10282. Data are analyzed from a Magnetospheric Multiscale encounter with a dayside magnetopause reconnection region on 29 December 2016. The uniqueness of the event stems from the small ( 7 km) average spacecraft separation and the sequential sampling of an electron diffusion region with electron crescent distributions. We quantitatively investigate the earthward acceleration of magnetosheath electrons through the in-plane null by the polarization electric field EN that points radially outward from the magnetopause. The results compare favorably with previous plasma simulations with one important difference that the reconnection electric field (EM) extends throughout the region of strong EN so that both fields energize electrons in the same region. This acceleration is quantified here for the first time. As the spacecraft penetrate deeper into the region of enhanced EN, the magnetic reflection of lower-energy electrons produces a thinner crescent. (10.1029/2019GL084636)
  DOI : 10.1029/2019GL084636
• Training on GNSS and Space Weather in Africa in the framework of the North-South scientific network GIRGEA
  
  • Amory-Mazaudier Christine
  • Fleury Rolland
  • Masson F.
  • Gadimova S.
  • Anas Emran
  Sun and Geosphere, BBC SWS Regional Network, 2019, 1 (141), pp.71-79. This paper presents the successful setting up of a research and teaching network for space weather in developed and fragile countries. This development took nearly a quarter of a century with the help of international cooperation. Numerous studies have been developed in different domains of Space Weather concerning the impact of solar events on the ionosphere and the Earth's magnetic field, ionospheric electric currents and the induced currents in the ground (GIC) Other studies have also been conducted on climate change, lightning and the movement of tectonic plates. We underline the importance of Global Navigation Satellite Systems [GNSS] for the development of space weather research and capacity building during the last decades (10.31401/SunGeo.2019.01.10)
  DOI : 10.31401/SunGeo.2019.01.10
• Experimental and numerical investigation of the transient charging of a dielectric surface exposed to a plasma jet
  
  • Slikboer Elmar
  • Viegas Pedro
  • Bonaventura Z.
  • Garcia-Caurel Enric
  • Sobota Ana
  • Bourdon Anne
  • Guaitella Olivier
  Plasma Sources Science and Technology, IOP Publishing, 2019, 28 (9), pp.095016. This work investigates the dynamical charging of a surface under exposure of a non-equilibrium plasma jet at atmospheric pressure through a quantitative comparison between modeling and experiments. We show using mono-polar pulses with variable pulse duration and amplitude that the charging time (i.e. the time from impact of the ionization wave till the fall of the high voltage pulse) is a crucial element determining the plasma-surface interaction. This is done through direct measurements of the electric field induced inside the target using the optical diagnostic technique called Mueller polarimetry and comparison with the electric field calculated using a 2D fluid model of the plasma jet interaction with the target in the same conditions as in the experiments. When the charging time is kept relatively short (less than 100 ns), the surface spreading of the discharge and consequent surface charge deposition are limited. When it is relatively long (up to microseconds), the increased surface spreading and charge deposition significantly change the electric field to which the target is exposed during the charging time and when the applied voltage returns to zero. (10.1088/1361-6595/ab3c27)
  DOI : 10.1088/1361-6595/ab3c27
• Non-thermal DBD plasma array on seed germination of different plant species
  
  • Liu Bo
  • Honnorat Bruno
  • Yang Hang
  • Arancibia Monreal J.
  • Rajjou Loic
  • Rousseau Antoine
  Journal of Physics D: Applied Physics, IOP Publishing, 2019, 52 (2), pp.025401. A dielectric barrier discharge (DBD) reactor producing cold plasma at atmospheric pressure has been used to treat seeds of eight different species and investigate their responses in term of germination. The device is made of nine cylindrical DBDs organized in a array and partially immersed in water. O2, N2, and air were flown in the device; the cold plasma from such gas is formed in the bubbles and touch liquid surface. Seeds were either located inside the water during plasma treatment process (direct treatment) or were watered by the water exposed to cold plasma beforehand (indirect treatment). Such plasma activated water contains reactive oxygen species and reactive nitrogen species. The statistical analysis shows that the probability of germinating of treated mung bean, mustard and radish is significantly higher than in control groups (p&#8201;&#8201;<&#8201;&#8201;0.05) for indirect treatments. A comparison of different treatment modalities (direct versus indirect treatment and gas composition) on germination boost has been completed on mung bean seeds. It is shown that direct plasma treatment using different gas (O2, N2, and air) give a strong enhancement of the mung bean germination probability compared to the control group; in the case of indirect treatment, only plasma air-treated water lead to a significant germination boost compared to the control group; this effect is still smaller than the one obtained using a direct treatment. (10.1088/1361-6463/aae771)
  DOI : 10.1088/1361-6463/aae771
• Dependence on plasma shape and plasma fueling for small edge-localized mode regimes in TCV and ASDEX Upgrade
  
  • Labit B.
  • Eich T.
  • Harrer G.F.
  • Wolfrum E.
  • Bernert M.
  • Dunne M.G.
  • Frassinetti L.
  • Hennequin Pascale
  • Maurizio R.
  • Merle A.
  • Meyer H.
  • Saarelma S.
  • Sheikh U.
  • Eurofusion Mst1 Team The
  Nuclear Fusion, IOP Publishing, 2019, 59 (8), pp.086020. Within the EUROfusion MST1 work package, a series of experiments has been conducted on AUG and TCV devices to disentangle the role of plasma fueling and plasma shape for the onset of small ELM regimes. On both devices, small ELM regimes with high confinement are achieved if and only if two conditions are fulfilled at the same time. Firstly, the plasma density at the separatrix must be large enough (), leading to a pressure profile flattening at the separatrix, which stabilizes type-I ELMs. Secondly, the magnetic configuration has to be close to a double null (DN), leading to a reduction of the magnetic shear in the extreme vicinity of the separatrix. As a consequence, its stabilizing effect on ballooning modes is weakened. (10.1088/1741-4326/ab2211)
  DOI : 10.1088/1741-4326/ab2211
• Comparison between ad-hoc and instability-induced electron anomalous transport in a 1D fluid simulation of Hall-effect thruster
  
  • Martorelli Roberto
  • Lafleur Trevor
  • Bourdon Anne
  • Chabert Pascal
  Physics of Plasmas, American Institute of Physics, 2019, 26 (8), pp.083502. Anomalous electron transport is a long-standing problem in the understanding of Hall-effect thrusters. Recent results have suggested as a possible cause a kinetic instability, but few attempts have succeeded in implementing such phenomena in a fluid simulation of the thruster. The common approach in this case relies on including an ad-hoc model of the anomalous transport and so to fit experimental results. We propose here a comparison between the friction force and the anomalous heating arising from the ad-hoc model, with the corresponding effects coming from the use of the instability-induced transport. The results are obtained through a one-dimensional fluid simulation of the Hall-effect thruster with ad-hoc anomalous transport. The comparison shows good agreement between the two approaches, suggesting indeed that the instability-induced anomalous transport is the good candidate for reproducing the ad-hoc simulations and paving the way for a full self-consistent implementation of the phenomena in a fluid simulation. (10.1063/1.5089008)
  DOI : 10.1063/1.5089008
• Inverse cascade of hybrid helicity in B&#937;-MHD turbulence
  
  • Menu Mélissa
  • Galtier Sébastien
  • Petitdemange Ludovic
  Physical Review Fluids, American Physical Society, 2019, 4, pp.073701. We investigate the impact of a solid-body rotation &#937;0 on the large-scale dynamics of an incompressible magnetohydrodynamic turbulent flow in presence of a background magnetic field B0 and at low Rossby number. Three-dimensional direct numerical simulations are performed in a periodic box, at unit magnetic Prandtl number and with a forcing at intermediate wave number kf=20. When &#937;0 is aligned with B0 (i.e., &#952;&#8801;(&#937;0,B0)=0), inverse transfer is found for the magnetic spectrum at k<kf. This transfer is stronger when the forcing excites preferentially right-handed (rather than left-handed) fluctuations; it is smaller when &#952;>0 and becomes weak when &#952;&#8805;35&#8728;. These properties are understood as the consequence of an inverse cascade of hybrid helicity which is an inviscid/ideal invariant of this system when &#952;=0. Hybrid helicity emerges, therefore, as a key element for understanding rotating dynamos. Implication of these findings on the origin of the alignment of the magnetic dipole with the rotation axis in planets and stars is discussed. (10.1103/PhysRevFluids.4.073701)
  DOI : 10.1103/PhysRevFluids.4.073701
• Crossing of Plasma Structures by spacecraft: a path calculator
  
  • Manuzzo Roberto
  • Belmont Gérard
  • Rezeau Laurence
  • Califano F.
  • Denton R E
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2019, 124 (12), pp.10119-10140. When spacecraft (s/c) missions probe plasma structures (PSs) the relative location of the s/c with respect to the PS is unknown. This information is, however, needed to measure the geometrical features of the PS (orientation and thickness) and to understand the physical processes underlying the PS dynamics. Methods to determine the s/c location exist, but they need strong assumptions to be satisfied (stationarity and special spatial dependencies). The number of cases for which these assumptions are likely to be valid for the entire PS seems to be limited, and even weak departures from these hypotheses may affect the results. For a quasi‐1‐D geometry in particular, the determination of the velocity component along the two quasi‐invariant directions is very inaccurate and the assumption of strict stationarity may lead these quantities to diverge. In this paper we present new methods to compute the s/c trajectory through a PS, without a priori assumption on its spatial geometry, and able to work even in the presence of weak nonstationarities. The methods are tested both on artificial and real data, the latter provided by the Magnetospheric Multiscale mission probing the Earth's magnetopause. The 1‐D and 2‐D trajectories of the Magnetospheric Multiscale are found that can be used as an initial step for future reconstruction studies. Advanced minimization procedures to optimize the results are discussed. (10.1029/2019JA026632)
  DOI : 10.1029/2019JA026632
• ViDA: a Vlasov-DArwin solver for plasma physics at electron scales
  
  • Pezzi Oreste
  • Cozzani Giulia
  • Califano Francesco
  • Valentini Francesco
  • Guarrasi Massimiliano
  • Camporeale Enrico
  • Brunetti Gianfranco
  • Retinò Alessandro
  • Veltri Pierluigi
  Journal of Plasma Physics, Cambridge University Press (CUP), 2019, 85 (5), pp.905850506. We present a VlasovDArwin numerical code (ViDA) specifically designed to address plasma physics problems, where small-scale high accuracy is requested even during the nonlinear regime to guarantee a clean description of the plasma dynamics at fine spatial scales. The algorithm provides a low-noise description of proton and electron kinetic dynamics, by splitting in time the multi-advection Vlasov equation in phase space. Maxwell equations for the electric and magnetic fields are reorganized according to the Darwin approximation to remove light waves. Several numerical tests show that ViDA successfully reproduces the propagation of linear and nonlinear waves and captures the physics of magnetic reconnection. We also discuss preliminary tests of the parallelization algorithm efficiency, performed at CINECA on the Marconi-KNL cluster. ViDA will allow the running of Eulerian simulations of a non-relativistic fully kinetic collisionless plasma and it is expected to provide relevant insights into important problems of plasma astrophysics such as, for instance, the development of the turbulent cascade at electron scales and the structure and dynamics of electron-scale magnetic reconnection, such as the electron diffusion region. (10.1017/S0022377819000631)
  DOI : 10.1017/S0022377819000631
• Plasma gun for medical applications: engineering an equivalent electrical target of human body and deciphering relevant electrical parameters
  
  • Judée Florian
  • Dufour Thierry
  Journal of Physics D: Applied Physics, IOP Publishing, 2019, 52 (16), pp.16 - 18. Simulations and experimental works have been carried out in a complementary way to engineer a basic material target mimicking the same dielectric properties of the human body. It includes a resistor in parallel with a capacitor, whose values (Rh=1500 Ω and Ch=100 pF) are estimated in regard of parameters commonly utilized upon in vivo campaigns (frequency=30 kHz, gap=10 mm, high voltage electrode surface=12.6 mm 2). This equivalent electrical human body (EEHB) circuit can be used as a reference and realistic target to calibrate electrical properties of therapeutic plasma sources before their utilization on patients. In this letter, we consider a configuration where this EEHB target interacts with a plasma gun (PG). Plasma power measurements performed in such configuration clearly indicate two operating modes depending on the value of the supplied voltage. Hence, the plasma gun generates pulsed atmospheric plasma streams likely to present therapeutic interest for voltages comprised between 3.0 and 8.5 kV while for higher values, transient arcs of thermal plasma are generated and represent substantial risks for the patient. (10.1088/1361-6463/ab03b8)
  DOI : 10.1088/1361-6463/ab03b8
• Signatures of Cold Ions in a Kinetic Simulation of the Reconnecting Magnetopause
  
  • Dargent Jérémy
  • Aunai Nicolas
  • Lavraud B.
  • Toledo-Redondo Sergio
  • Califano F.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2019, 124 (4), pp.2497-2514. Abstract At the Earth's magnetopause, a low-energy ion population of ionospheric origin is commonly observed at the magnetospheric side. In this work we use a 2-D fully kinetic simulation to identify several original signatures related to the dynamics of cold ions involved in magnetic reconnection at the asymmetric dayside magnetopause. We identify several original signatures of the cold ions dynamics driven by the development of magnetic reconnection at the asymmetric dayside magnetopause. We find that cold ions tend to rarefy in the diffusion region, while their density is enhanced as a result of compression along magnetospheric separatrices. We also observe the formation of crescent-shaped cold ion distribution functions along the separatrices in the near-exhaust region, and we present an analytical model to explain this signature. Finally, we give evidence of a localized parallel heating of cold ions. These signatures should be detected with the magnetospheric multiscale mission high-resolution observations. (10.1029/2018JA026343)
  DOI : 10.1029/2018JA026343