Publications

2016

• Filamentary nanosecond surface dielectric barrier discharge at elevated pressures. Streamer-to-filamentary transition and application for plasma assisted combustion.
  
  • Shcherbanev Sergey
  , 2016. Non–equilibrium plasma is one of the most attractive and promising tool for many plasma–assisted applications. Production of active species (excited species, radicals, high energetic photons covering UV and IR spectral range) is important for gas pollution control, surface treatment, plasma actuators for aerodynamics application, biomedical applications and more recently the field of plasma medicine. For atmospheric and elevated gas densities the mainstream of the non–thermal plasma applications is the ignition of combustible mixtures or so–called Plasma–Assisted Ignition (PAI). Surface dielectric barrier discharges (SDBD), widely used for aerodynamic flow control, were recently suggested as distributed initiators of combustion in different systems. A principal possibility of using the SDBD ignitors at as high pressure as tens of bars has been demonstrated during the last 4-5 years. At the moment of the beginning of the thesis, the set of experimental data on the discharge and of ignition of fuels with SDBD was quite poor and insufficient for detailed analysis. Therefore, the experimental study of the surface DBD at atmospheric and elevated gas densities and the study of flame initiation with nanosecond SDBD were the object of the presented thesis. The results in the Thesis are presented in three parts. In the first part the nSDBD in a single shot regime at atmospheric air is investigated. The analysis of energy deposition, discharge current, intensity distribution and consequent energy release is performed. The positive and negative polarity pulses are used to produce surface discharge. The physics of anode and cathode–directed streamers is discussed. For both polarities of the applied pulses the electron density and reduced electric field are estimated and compared with calculations and/or 2D modeling results. The second part is devoted to the study of nSDBD at elevated pressures, up to 12 bar, in different gas mixtures ( N2, air, N2:CH4, N2:H2, Ar:O2, etc.). Two morphologically different forms of the nSDBD are considered: a “classical” streamer DBD at relatively low pressures and voltages, and a filamentary DBD at high pressures and/or voltages. The emission spectroscopy is used to obtain quantitative data about the discharge at high pressures (1-12 bar). The possible nature of the discharge filamentation is described. Finally, the third part describes the experiments of plasma–assisted ignition with nanosecond SDBD at elevated pressures. The discharge morphology in lean combustible ( H2:air) mixtures and following ignition of the mixtures are studied. The comparison of ignition by filamentary and streamer discharge at the pressures 1-6 bar is performed. Kinetic modeling of plasma assisted ignition for the electric fields typical for nSDBD, E/N = 100 − 200 Td is used for analysis of experimental data. Complex study of the discharges at atmospheric pressure, discharge at high pressures and ignition allow detailed description of the high-pressure distributed in space ignition by non--equilibrium plasma.
• Observations of wave-particle interactions in the flux pile-up region of asymmetric reconnection.
  
  • Argall M. R.
  • Paulson K. W.
  • Ahmadi N.
  • Matsui H.
  • Torbert R. B.
  • Alm L.
  • Le Contel Olivier
  • Fischer D.
  • Strangeway R. J.
  • Magnes W.
  • Russell C. T.
  • Giles B. L.
  • Khotyaintsev Y. V.
  • Ergun R.
  • Lindqvist P. A.
  , 2016, 31. Recent observations have shown electron energization to >100keV with simultaneous whistler wave activity in the vicinity of the dayside reconnection site. We investigate one possible mechanism for producing these energetic particles. The Electron Drift Instrument on MMS is capable of detecting wave-particle interactions up to 512 Hz. Whistler waves in this frequency range are generated in the flux pile-up region of reconnection. We find that the growing magnetic field gradient due to flux pile-up is responsible for electron bounce motion and betatron acceleration that increase the temperature anisotropy required for whistler wave growth. The whistler waves then energize and scatter electrons, freeing them to be further accelerated by other processes.
• Evolution of Collision Between the Counterstreaming Reconnection Jets During Multiple Reconnection.
  
  • Retinò Alessandro
  • Alexandrova Alexandra
  • Nakamura R.
  • Panov E. V.
  • Sasunov Y.
  • Nakamura T.
  • Vörös Z.
  • Semenov V. S.
  , 2016, 21, pp.SM21A-2440. Magnetic reconnection may proceed via multiple reconnection sites which implies the collision between the counterstreaming reconnection jets. We present the magnetotail observations of two reconnection X lines and the region of the reconnection jets collision in between. Using favorable location of two Cluster spacecraft probes, we analyzed the evolution of collision process. Under strengthened collision, the ion-scale current sheet-like structure formed between the colliding jets, becomes compressed. The strong emission of whistler waves is observed in the center of the compressed structure. Such observations might be helpful in understanding the multiple reconnection dynamics at the magnetopause where the colliding reconnection jets in the core of the flux rope have been recently observed by MMS.
• Cold ion demagnetization near the X-line of magnetic reconnection
  
  • Toledo-Redondo Sergio
  • Andre M.
  • Khotyaintsev Y. V.
  • Vaivads A.
  • Walsh A. P.
  • Li W.
  • Graham D. B.
  • Lavraud B.
  • Masson A.
  • Aunai N.
  • Divin A. V.
  • Dargent Jérémy
  • Fuselier S. A.
  • Gershman D. J.
  • Dorelli J. C.
  • Giles B. L.
  • Avanov L. A.
  • Pollock C. J.
  • Saito Y.
  • Moore T. E.
  • Coffey V. N.
  • Chandler Michael O.
  • Lindqvist P. A.
  • Torbert R. B.
  • Russell C. T.
  , 2016, 21, pp.SM21A-2451. We report observatios of the Ion Diffusion Region (IDR) of magnetic reconnection by MMS at the dayside magnetopause. Cold plasma (tens of eV) of ionospheric origin was present inside the IDR the 22 October 2015 and its behavior differed from the hot plasma (several keV). In particular, cold ions remained magnetized and followed E x B inside most of the IDR. We identify a sub-region and name it the cold IDR of the size of the cold ion gyroradius ( 15 km) where cold ions are demagnetized and accelerated parallel to E. Using multi-spacecraft measurements we identify a sharp cold ion density gradient separating the two regions.
• Differential kinetic behavior of protons and alpha particles in turbulent solar wind: hybrid Vlasov simulations
  
  • Perrone D.
  • Valentini F.
  • Stabile S.
  • Pezzi O.
  • Servidio S.
  • Veltri P.
  • de Marco R.
  • Bruno Roberto
  • Lavraud B.
  • de Keyser J.
  • Consolini G.
  • Brienza D.
  • Marcucci M. F.
  • Sorriso-Valvo L.
  • Retinò Alessandro
  • Vaivads A.
  • Salatti M.
  , 2016, 21, pp.SH21C-2541. The general picture of turbulence in plasmas becomes more complicated in the solar wind because of its multi-component nature. In fact, although the solar wind is predominantly constituted of protons, is also made up of a finite amount of alpha particles, together with a few percent of heavier ions. `In situ' observations have shown that heavy ions (alpha particles in particular) seem to be preferentially heated and accelerated with respect to protons. However, due to very scarce measurements of heavy ions at time resolutions comparable with their kinetic scales, energy partition between species in turbulent plasma dissipation is basically unexplored. THOR measurements of ions at high temporal resolution, together with high energy and angular resolutions, could allow solving this key issue. For the moment, most of the information comes from numerical simulations and a crucial support is given by self-consistent, fully nonlinear Vlasov models. Here, hybrid Vlasov-Maxwell simulations are used to investigate the role of kinetic effects in a two-dimensional turbulent multi-ion plasma, composed of protons, alpha particles, and fluid electrons. In particular, the differential kinetic dynamics of ions are analyzed in terms of anisotropy e non-gyrotropy of the ion distribution functions. The stronger deviations of the ion velocity distributions from the thermodynamic equilibrium (Maxwellian configuration) appear localized near the peaks of the current density, associates also to a significant increase of the ion temperature. This behavior is found to be more important for alpha particles than for protons.
• MMS observations of magnetic reconnection in small-scale current sheets in magnetosheath turbulence.
  
  • Chasapis A.
  • Matthaeus W. H.
  • Parashar T.
  • Le Contel Olivier
  • Retinò Alessandro
  • Breuillard Hugo
  • Khotyaintsev Y. V.
  • Vaivads A.
  • Lavraud B.
  • Moore T. E.
  • Burch J. L.
  • Torbert R. B.
  • Lindqvist P. A.
  • Ergun R.
  • Marklund G. T.
  • Goodrich K. A.
  • Wilder F. D.
  • Chutter M.
  • Needell J.
  • Rau D.
  • Dors I.
  • Russell C.
  • Le G.
  • Magnes W.
  • Strangeway R. J.
  • Bromund K. R.
  • Leinweber H. K.
  • Plaschke F.
  • Fischer D.
  • Anderson B. J.
  • Pollock C.
  • Giles B. L.
  • Paterson W. R.
  • Dorelli J. C.
  • Gershman D. J.
  • Avanov L. A.
  • Saito Y.
  , 2016, 21, pp.SM21A-2438. Magnetic reconnection occurs in thin current sheets that form in turbulent plasmas. It leads to particle heating and acceleration and is thought to play an important role for the turbulent dissipation at kinetic scales, energy. However, in situ observations are scarce and the extent of its contribution to turbulent dissipation has yet to be determined. The MMS mission allows us to closely study kinetic-scale intermittent structures that form in turbulent plasma as well as to detect thin reconnecting current sheets and examine their properties. We present the results of MMS observations in the turbulence of the Earth's magnetosheath. We performed a statistical study of small-scale intermittent structures and their role in heating and accelerating electrons. We examined one current sheet in detail which shows evidence of reconnection, focusing on the mechanisms that drive the observed heating and acceleration within it and the role of wave-particle interactions.
• MMS Observations of Ion-scale Magnetic Island in the Magnetosheath Turbulent Plasma
  
  • Huang S. Y.
  • Sahraoui Fouad
  • Retinò Alessandro
  • Le Contel Olivier
  • Yuan Z.
  • Chasapis A.
  • Aunai N.
  • Breuillard Hugo
  • Deng X.
  • Zhou M.
  • Fu H.
  • Pang Y.
  • Wang D.
  • Torbert R. B.
  • Goodrich K. A.
  • Ergun R.
  • Khotyaintsev Y. V.
  • Lindqvist P. A.
  • Russell C. T.
  • Pollock C.
  • Giles B. L.
  • Moore T. E.
  • Magnes W.
  • Strangeway R. J.
  • Bromund K. R.
  • Leinweber H. K.
  • Plaschke F.
  • Anderson B. J.
  • Burch J. L.
  , 2016, 21, pp.SM21A-2437. In this letter, first observations of ion-scale magnetic island from the Magnetospheric Multiscale (MMS) mission in the magnetosheath turbulent plasma are presented. The magnetic island is characterized by bipolar variation of magnetic fields with magnetic field compression, strong core field, density depletion and strong currents dominated by the parallel component to the local magnetic field. The estimated size of magnetic island is about 8di, where di is the ion inertial length. Distinct particle behaviors and wave activities inside and at the edges of the magnetic island are observed: parallel electron beam accompanied with electrostatic solitary waves and strong electromagnetic lower hybrid drift waves inside the magnetic island; bidirectional electron beams, whistler waves, weak electromagnetic lower hybrid drift waves and strong broadband electrostatic noise at the edges of the magnetic island. Our observations demonstrate that highly dynamical, strong wave activities and electron-scale physics occur within ion-scale magnetic islands in the magnetosheath turbulent plasma.
• Optimal Weighting of Multi-Spacecraft Data to Estimate Gradients of Physical Fields
  
  • Chanteur Gérard
  • Le Contel Olivier
  • Sahraoui Fouad
  • Retinò Alessandro
  • Mirioni Laurent
  , 2016, 21, pp.SM21A-2448. Multi-spacecraft missions like the ESA mission CLUSTER and the NASA mission MMS are essential to improve our understanding of physical processes in space plasmas. Several methods were designed in the 90's during the preparation phase of the CLUSTER mission to estimate gradients of physical fields from simultaneous multi-points measurements [1, 2]. Both CLUSTER and MMS involve four spacecraft with identical full scientific payloads including various sensors of electromagnetic fields and different type of particle detectors. In the standard methods described in [1, 2], which are presently in use, data from the four spacecraft have identical weights and the estimated gradients are most reliable when the tetrahedron formed by the four spacecraft is regular. There are three types of errors affecting the estimated gradients (see chapter 14 in [1]) : i) truncature errors are due to local non-linearity of spatial variations, ii) physical errors are due to instruments, and iii) geometrical errors are due to uncertainties on the positions of the spacecraft. An assessment of truncature errors for a given observation requires a theoretical model of the measured field. Instrumental errors can easily be taken into account for a given geometry of the cluster but are usually less than the geometrical errors which diverge quite fast when the tetrahedron flattens, a circumstance occurring twice per orbit of the cluster. Hence reliable gradients can be estimated only on part of the orbit. Reciprocal vectors of the tetrahedron were presented in chapter 4 of [1], they have the advantage over other methods to treat the four spacecraft symmetrically and to allow a theoretical analysis of the errors (see chapters 4 of [1] and 4 of [2]). We will present Generalized Reciprocal Vectors for weighted data and an optimization procedure to improve the reliability of the estimated gradients when the tetrahedron is not regular. A brief example using CLUSTER or MMS data will be given. This approach also operates for any number of spacecraft. References [1] Analysis Methods for Multi-Spacecraft Data, ISSI Scientific Report, SR-001, Eds. G. Paschmann and P.W. Daly, ISSI, Bern, Switzerland, 1998. [2] Multi-Spacecraft Analysis Methods Revisited, ISSI Scientific Report, SR-008, Eds. G. Paschmann and P.W. Daly, ISSI, Bern, Switzerland, 2008.
• MMS Observations of Parallel Electric Fields During a Quasi-Perpendicular Bow Shock Crossing
  
  • Goodrich K. A.
  • Schwartz S. J.
  • Ergun R.
  • Wilder F. D.
  • Holmes J.
  • Burch J. L.
  • Gershman D. J.
  • Giles B. L.
  • Khotyaintsev Y. V.
  • Le Contel Olivier
  • Lindqvist P. A.
  • Strangeway R. J.
  • Russell C.
  • Torbert R. B.
  , 2016, 22. Previous observations of the terrestrial bow shock have frequently shown large-amplitude fluctuations in the parallel electric field. These parallel electric fields are seen as both nonlinear solitary structures, such as double layers and electron phase-space holes, and short-wavelength waves, which can reach amplitudes greater than 100 mV/m. The Magnetospheric Multi-Scale (MMS) Mission has crossed the Earth's bow shock more than 200 times. The parallel electric field signatures observed in these crossings are seen in very discrete packets and evolve over time scales of less than a second, indicating the presence of a wealth of kinetic-scale activity. The high time resolution of the Fast Particle Instrument (FPI) available on MMS offers greater detail of the kinetic-scale physics that occur at bow shocks than ever before, allowing greater insight into the overall effect of these observed electric fields. We present a characterization of these parallel electric fields found in a single bow shock event and how it reflects the kinetic-scale activity that can occur at the terrestrial bow shock.
• Examination of Energetic Electron Acceleration in the Vicinity of Earth's Dayside Magnetopause with MMS
  
  • Leonard T. W.
  • Jaynes A. N.
  • Baker D. N.
  • Zhao H.
  • Blake J. B.
  • Burch J. L.
  • Cohen I.
  • Ergun R.
  • Fennell J. F.
  • Gershman D. J.
  • Giles B. L.
  • Le Contel Olivier
  • Mauk B.
  • Russell C. T.
  • Strangeway R. J.
  • Torbert R. B.
  • Turner D. L.
  • Wilder F. D.
  , 2016, 32. The Magnetospheic Multiscale Fly's Eye Energetic Particle Spectrometer instrument has made the first observations of energetic particle acceleration near a low-latitude dayside magnetic reconnection region at the Earth's magnetopause. The study by Jaynes et al. (2016) observed particle energization at the magnetospheric edge of a reconnection jet, concurrently with whistler-mode and broadband electrostatic waves during an event on 19 September 2015. Investigating the spatial regions and occurrence rate of these hundreds of keV electrons may provide insight into the generation of the relativistic radiation belt population. In this investigation we build a dataset of these energetic particle acceleration events in order to characterize the observations by determining the occurrence rate, production region, and associated wave activity. Additionally, we show a few events in microscopic detail and examine the intricate plasma and wave parameters to uncover the cause of such prompt and intense electron acceleration.
• Observation and Simulation of Chorus Waves Generation at the Gradients of Magnetic Holes
  
  • Ahmadi N.
  • Argall M. R.
  • Paulson K. W.
  • Ergun R.
  • Wilder F. D.
  • Germaschewski K.
  • Khotyaintsev Y. V.
  • Torbert R. B.
  • Russell C. T.
  • Strangeway R. J.
  • Magnes W.
  • Le Contel Olivier
  • Giles B. L.
  , 2016, 31, pp.SM31C-07. The Magnetospheric Multiscale (MMS) mission observed chorus waves at the gradients of magnetic holes on the dayside magnetosheath. The magnetic holes are nonlinear mirror structures which are anticorrelated with particle density. We used expanding box Particle-in-cell simulations and produced the mirror instability magnetic holes. We show that chorus waves are generated at the gradients of magnetic holes in our simulations which is in agreement with MMS observations. We investigate the possible mechanism for enhancing the electron temperature anisotropy at the magnetic field gradients. We analyze the electron pitch angle distributions and electron distribution functions in our simulations and compare it with MMS observations. We also measure the Poynting flux to investigate how much energy is carried away by the fields via chorus waves.
• The Non-linear Evolution of Whistler-mode Waves at the Dayside Magnetopause and Its Relation to Magnetic Reconnection and Particle Acceleration
  
  • Wilder F. D.
  • Ergun R.
  • Goodrich K. A.
  • Newman D. L.
  • Goldman M. V.
  • Schwartz S. J.
  • Jaynes A. N.
  • Holmes J.
  • Sturner A. P.
  • Eriksson S.
  • Burch J. L.
  • Torbert R. B.
  • Phan T.
  • Argall M. R.
  • Le Contel Olivier
  • Khotyaintsev Y. V.
  • Lindqvist P. A.
  • Giles B. L.
  • Gershman D. J.
  • Strangeway R. J.
  • Russell C. T.
  • Leonard T. W.
  , 2016, 31. Whistler-mode waves have been observed at the subsolar magnetopause in association with magnetic reconnection, including near the electron diffusion region (EDR) and near the separatrices. Observations by the Magnetospheric Multiscale (MMS) mission have shown oblique whistler-mode waves at the electron edge of the reconnection layer that are coincident with time-domain structures such as double layers and electrostatic solitary waves, as well as intense Langmuir oscillations. Additionally, large amplitude non-linear parallel oscillations often coincide with these waves, and may be the result of interactions between the whistler-mode waves and electron-acoustic waves, similar to what has been observed in the radiation belts. We present results of an investigation by MMS into the non-linear evolution of these whistlers and their effects on the local plasma population. Preliminary results suggest that the waves are less common near EDR candidates than on the separatrices and that, via non-linear parallel electric fields, they contribute to direct acceleration of electrons.
• Cold Electrons as the Drivers of Parallel, Electrostatic Waves in Asymmetric Reconnection
  
  • Holmes J.
  • Ergun R.
  • Newman D. L.
  • Wilder F. D.
  • Schwartz S. J.
  • Goodrich K. A.
  • Eriksson S.
  • Torbert R. B.
  • Russell C. T.
  • Lindqvist P. A.
  • Giles B. L.
  • Pollock C. J.
  • Le Contel Olivier
  • Strangeway R. J.
  • Burch J. L.
  , 2016, 21. The Magnetospheric MultiScale mission (MMS) has observed several instances of asymmetric reconnection at Earth's magnetopause, where plasma from the magnetosheath encounters that of the magnetosphere. On Earth's dayside, the magnetosphere is often made up of a two-component distribution of cold (<< 10 eV) and hot ( 1 keV) plasma, sometimes including the cold ion plume. Magnetosheath plasma is primarily warm ( 100 eV) post-shock solar wind. Where they meet, magnetopause reconnection alters the magnetic topology such that these two populations are left cohabiting a field line and rapidly mix. There have been several events observed by MMS where the Fast Plasma Instrument (FPI) clearly shows cold ions near the diffusion region impinging upon the warm magnetosheath population. In many of these, we also see patches of strong electrostatic waves parallel to the magnetic field - a smoking gun for rapid mixing via nonlinear processes. Cold ions alone are too slow to create the same waves; solving for roots of a simplified dispersion relation shows the electron population damps out the ion modes. From this, we infer the presence of cold electrons; in one notable case found by Wilder et al. 2016 (in review), they have been observed directly by FPI. Vlasov simulations of plasma mixing for a number of these events closely reproduce the observed electric field signatures. We conclude from numerical analysis and direct MMS observations that cold plasma mixing, including cold electrons, is the primary driver of parallel electrostatic waves observed near the electron diffusion region in asymmetric magnetic reconnection.
• Response of quasi-adiabatic ions to magnetotail reconfigurations
  
  • Delcourt Dominique
  • Malova H. V.
  • Zelenyi L. M.
  , 2016, 43, pp.SM43A-2470. Particles traveling in sharp field reversals like in the Earth's magnetotail may not conserve their magnetic moment (first adiabatic invariant) due to significant variation of the magnetic field on the length scale of their Larmor radius. Although their motion is non-adiabatic per say and differs from a regular helical one, some particles may experience negligible net change of magnetic moment, a behavior that is referred to as quasi-adiabatic [Büchner and Zelenyi, 1989] like in the well-known Speiser orbit [Speiser, 1965]. Such a behavior is more pronounced at specific values of the adiabaticity parameter kappa (square root of the minimum curvature radius to maximum Larmor radius ratio) due to resonance between the slow gyromotion in the tail midplane and the fast oscillation in the direction perpendicular to it. On the other hand, during rapid reconfigurations of the magnetotail as observed during substorms, the impulsive electric field induced by the time-varying magnetic field may lead to non-adiabatic behaviors as well, with large variations of the magnetic moment for particles that have cyclotron periods comparable to the field variation time scale. In this case, the kappa parameter that is used to characterize spatial non-adiabaticity cannot be used since magnetic field lines are rapidly evolving in time. We examine the response of quasi-adiabatic ions in the presence of such short-lived reconfigurations of the magnetic field lines using single particle calculations. We demonstrate that quasi-adiabatic ions may remain quasi-adiabatic while experiencing an impulsive energization under the effect of the induced electric field ; hence, their faster oscillations about the tail midplane and their higher resonance order. Systematic acceleration up to about 3VE (where VE is the peak ExB drift speed during field line reconfiguration) is found for the lowest energy particles. We show that, altogether, impulsive transport and energization may be responsible for short-lived earthward injections of ions and for the Time-of-Flight dispersed ion structures that are observed at low altitudes in the plasma sheet boundary layer.
• Classifying Large-Amplitude Parallel Electric Fields Along the Magnetopause and Their Effect on Magnetic Reconnection
  
  • Goodrich K. A.
  • Ergun R.
  • Wilder F. D.
  • Holmes J.
  • Khotyaintsev Y. V.
  • Lindqvist P. A.
  • Burch J. L.
  • Gershman D. J.
  • Giles B. L.
  • Le Contel Olivier
  • Strangeway R. J.
  • Russell C. T.
  • Torbert R. B.
  , 2016, 31. During the first year of the Magnetospheric Multiscale Mission (MMS) there have been multiple observations of large amplitude parallel electric fields, as high as 100 mV/m, associated with magnetic reconnection along the terrestrial magnetopause. These electric fields have been observed as a variety of different wave phenomena and plasma structures. One distinct and rare type of plasma structures are unipolar, high amplitude, parallel electric field pulses which are observed directly adjacent to the electron diffusion region and are thought to represent secondary reconnection. Intense parallel plasma waves are interpreted to be ion acoustic waves, electron acoustic waves or beam mode, indicative of cold plasma mixing. Nonlinear structures commonly associated with Alfvénic turbulence on the magnetospheric side of the magnetopause are also reported. We present examples of these three parallel electric field signatures and examine their possible implications on magnetic reconnection.
• Exact Scaling Laws for Helical Three-dimensional Two-fluid Turbulent Plasmas
  
  • Andrés Nahuel
  • Galtier Sébastien
  • Sahraoui Fouad
  , 2016, 41, pp.SH41A-2508. We derive exact scaling laws for a three-dimensional incompressible helical two-fluid plasma, without the assumption of isotropy. For each ideal invariant of the two-fluid model, i.e. the total energy, the electron helicity and the proton helicity, we derive simple scaling laws in terms of two-point increments correlation functions as a function of the velocity field of each species and the magnetic field. These variables are appropriate for comparison with in-situ measurements in the solar wind at different spatial ranges and data from numerical simulations. Finally, with the exact scaling laws and dimensional analysis we predict the magnetic energy and electron helicity spectra for different ranges of scales.
• Formation of Accelerated Backstreaming Particles within the Quasi-perpendicular Ion Terrestrial Foreshock: 2D Full-Particle and Test-particles simulations
  
  • Savoini Philippe
  • Lembège Bertrand
  , 2016, 22, pp.SH22A-07. Backstreaming ion populations are observed upstream of the Terrestrial bow shock and form the ion foreshock. Two distinct populations have been firmly identified by spacecrafts within the quasi-perpendicular shock region (i.e. for 45° <= ThetaBn <= 90°, where ThetaBn is the angle between the shock normal and the upstream magnetostatic field): so called (i) field-aligned ion beams (« FAB ») characterized by a gyrotropic distribution, and (ii) gyro-phase bunched ions («GPB »), characterized by a NON gyrotropic distribution.The origin of these backstreaming ions is still an important unresolved question which can be partially analyzed with the help of 2D PIC simulation of a curved shock, where full curvature effects, time of flight effects and both electrons and ions dynamics are fully included by a self consistent approach. Our previous analysis (Savoini et Lembege, 2015) has evidenced that these two populations can be generated directly by the macroscopic fields at the shock front itself. Present results based on ion trajectories analysis confirm: (i) the importance of the interaction time DeltaTinter spent by ions within the shock front. "GPB" population is characterized by a very short interaction time (DeltaTinter = 1 to 2 tci) in comparison to the "FAB" population (DeltaTinter = 2 tci to 10 tci), where tci is the upstream ion gyroperiod. (ii) the key role of the injection angle (i.e. defined between the normal of the shock front and the gyration velocity at the time incoming ions hit the shock front) which strongly differs between FAB and GPB ions. (iii) that "FAB" ions drift along the shock front and « scan » a large ThetaBn range (up to 20°) which explains the loss of their initial gyro-phase, before being re-injected into the upstream region. Moreover, our test-particule simulations evidence the importance of the shock wave profile for both the « FAB » and « GPB » populations. Such results show that the reflection process is not continuous in time and in space, but strongly depends of the local shock front profile met by incoming ions at their hitting time. The same simulations also emphasize the slight decrease of backstreaming ions density when the electric field space charge effect present within the shock front is artificially canceled. A comparison between self-consistent and test-particles results will be presented in more details.
• Physics of the diffusion region in the Magnetospheric Multiscale era
  
  • Chen L. J.
  • Hesse Michael
  • Wang S.
  • Ergun R.
  • Bessho N.
  • Burch J. L.
  • Giles B. L.
  • Torbert R. B.
  • Gershman D. J.
  • Wilson Iii L. B.
  • Dorelli J. C.
  • Pollock C. J.
  • Moore T. E.
  • Lavraud B.
  • Strangeway R. J.
  • Russell C. T.
  • Khotyaintsev Y. V.
  • Le Contel Olivier
  • Avanov L. A.
  , 2016, 13. Encounters of reconnection diffusion regions by the Magnetospheric Multiscale (MMS) mission during its first magnetopause scan are studied in combination with theories and simulations. The goal is to understand by first-principles how stored magnetic energy is converted into plasma thermal and bulk flow energies via particle energization, mixing and interaction with waves. The magnetosheath population having much higher density than the magnetospheric plasma is an outstanding narrator for and participant in the magnetospheric part of the diffusion region. For reconnection with negligible guide fields, the accelerated magnetosheath population (for both electrons and ions) is cyclotron turned by the reconnected magnetic field to form outflow jets, and then gyrotropized downstream. Wave fluctuations are reduced in the central electron diffusion region (EDR) and do not dominate the energy conversion there. For an event with a significant guide field to magnetize the electrons, wave fluctuations at the lower hybrid frequency dominate the energy conversion in the EDR, and the fastest electron outflow is established dominantly by a strong perpendicular electric field via the ExB flow in one exhaust and by time-of-flight effects along with parallel electric field acceleration in the other. Whether the above features are common threads to magnetopause reconnection diffusion regions is a question to be further examined.
• Magnetospheric Multiscale Observations of Flux-Rope Interactions in the Turbulent Terrestrial Magnetosheath
  
  • Vörös Z.
  • Yordanova E.
  • Varsani A.
  • Graham D. B.
  • Norgren C.
  • Nakamura R.
  • Narita Y.
  • Magnes W.
  • Baumjohann W.
  • Fischer D.
  • Plaschke F.
  • Khotyaintsev Y. V.
  • Vaivads A.
  • Erkisson E.
  • Lindqvist P. A.
  • Marklund G. T.
  • Ergun R.
  • Leubner M. P.
  • Russell C. T.
  • Strangeway R. J.
  • Le Contel Olivier
  • Pollock C. J.
  • Giles B. L.
  • Torbert R. B.
  • Burch J. L.
  • Avanov L. A.
  • Dorelli J. C.
  • Gershman D. J.
  • Paterson W. R.
  • Lavraud B.
  • Saito Y.
  , 2016, 13. Recent global hybrid and fully kinetic simulations of the terrestrial magnetosphere have shown that the turbulent quasi-parallel (QP) magnetosheath contains multi-scale interacting structures such as jets, flux ropes, waves, vortices, reconnecting current sheets, over the fluid, ion and electron scales. Multi-scale flux-rope interactions in magnetosheath plasma turbulence downstream of a QP shock are investigated on the basis of particle, plasma and field measurements from the Magnetospheric Multiscale (MMS) mission satellites. It is demonstrated that magnetic flux rope interactions are associated with magnetic flux pileup, density depletion and with formation of proton scale current sheets, electron scale spiky structures and particle heating. This study also demonstrates how patchy dissipation and plasma heating can occur in collisionless turbulent plasmas.
• Cold plasma and magnetic reconnection at the magnetopause boundary layer
  
  • Toledo-Redondo Sergio
  • Andre M.
  • Khotyaintsev Y. V.
  • Li W.
  • Graham D. B.
  • Walsh A. P.
  • Arnaud M.
  • Lavraud B.
  • Vaivads A.
  • Divin A. V.
  • Dargent Jérémy
  • Aunai N.
  • Fuselier S. A.
  • Gershman D. J.
  • Dorelli J. C.
  • Giles B. L.
  • Avanov L. A.
  • Pollock C. J.
  • Saito Y.
  • Moore T. E.
  • Coffey V. N.
  • Chandler Michael O.
  • Lindqvist P. A.
  • Torbert R. B.
  • Russell C. T.
  , 2016, 12, pp.SM12A-02. Magnetic reconnection is a fundamental plasma process that permits the exchange of energy and mass between colliding plasmas, e.g., between the Solar Wind and the Earth's magnetosphere. Several studies have reported the presence of cold plasma of ionospheric origin at the magnetospheric side of the magnetopause. As a result, the particle distribution functions involved in reconnection are far from equilibrium, exhibiting a cold plasma beam in addition to the typical hot plasmas from the magnetosheath and the magnetosphere. Cold ions possess a much smaller gyroradius and therefore introduce a new length-scale into the system. This situation leads to structures of the size of the cold ion gyroradius and allows for the existence of new instabilities. In addition, the energization of cold plasma by reconnection is governed by different processes than for the hot plasma.
• Fast and Slow Solar Wind: Energy Transfer Rate in Compressible MHD Turbulence
  
  • Hadid L. Z.
  • Sahraoui Fouad
  • Galtier Sébastien
  • Banerjee Supratik
  , 2016, 51, pp.SH51B-2582. The role of compressible fluctuations in the energy cascade in the fast and slow solar wind is investigated. A focus is put on comparing the energy cascade rates estimated using the exact laws derived for incompressible MHD turbulence [Politano and Pouquet, 1998] (PP98) and for compressible isothermal turbulence recently derived by Galtier and Banerjee, 2013 (BG13). New features are evidenced using the BG13 model in comparison with the PP98 model: i) broader inertial range (more than two decades of scales); ii) higher energy cascade rate (up to 4 times); iii) less anisotropic cascade rates (along and perpendicular to the local mean field). Furthermore, a term-by-term analysis of the compressible model emphasized the relative importance of the new flux term in the BG13 model, and provided new insight into the role played by the compressible fluctuations in the solar wind.
• THOR contribution to space weather science
  
  • Vaivads A.
  • Opgenoorth H. J.
  • Retinò Alessandro
  • Khotyaintsev Y. V.
  • Soucek J.
  • Valentini F.
  • Escoubet C. Philippe
  • Chen C. H. K.
  • Vainio Rami O.
  • Fazakerley A.
  • Lavraud B.
  • Narita Y.
  • Marcucci M. F.
  • Kucharek H.
  • Bale S. D.
  • Moore T. E.
  • Kistler L. M.
  • Samara M.
  , 2016, 11, pp.SH11C-2275. Turbulence Heating ObserveR - THOR is a mission proposal to study energy dissipation and particle acceleration in turbulent space plasma. THOR will focus on turbulent plasma in pristine solar wind, bow shock and magnetosheath. The orbit of THOR is tuned to spend long times in those regions allowing THOR to obtain high resolution data sets that can be used also for space weather science. Here we will discuss the space weather science questions that can be addressed and significantly advanced using THOR. Link to THOR: http://thor.irfu.se.
• Compressible MHD Turbulence in the Slow Solar Wind: Energy Transfer Rate
  
  • Sahraoui Fouad
  • Andrés Nahuel
  • Hadid L. Z.
  • Galtier Sébastien
  • Dmitruk P.
  • Mininni P. D.
  , 2016, 21, pp.SH21C-2538. The role of compressible fluctuations in the MHD turbulence is investigated using direct numerical simulations and in-situ spacecraft in the solar wind. A focus is put on verifying the exact third-order law derived for compressible isothermal turbulence by Banerjee and Galtier, 2013. The numerical simulations use a 3D compressible MHD code in the isothermal limit (&#61543; =1) with low sonic Mach numbers (Ms<1). The main goal is to evaluate the relative importance of the new flux and source terms involved in the derived law. Direct comparison with spacecraft observations from the Themis spacecraft in the fast and slow solar wind will be made.
• On Statistics of Electric Field Amplitudes in the Langmuir Turbulence
  
  • Krasnoselskikh V.
  • Voshchepynets A.
  • Volokitin A.
  • Krafft C.
  , 2016, 41, pp.SH41A-2513. We present a systematic study of the properties of the Langmuir wave turbulence generated by bump-on-tail instability in strongly non-homogeneous plasma. This type of turbulence occurs in numerous processes involving electrons beams in space plasmas. We analyse the synthetic data obtained in the numerical simulation based on two different approaches: the Hamiltonian model, and so-called probabilistic model. The Hamiltonian model describes in the self-consistent manner the wave-particle and wave-wave interactions in inhomogeneous magnetized plasmas. The model enables us to study the general properties of the distributions of the amplitudes of the Langmuir waves driven by the high-velocity electron beams in the fluctuating plasma. We pay special attention to the study of statistics of Languir waves under conditions when the decay instability, involving ion-sound waves, is developed. The probabilistic model, being modified version of the standard quasi-linear theory requires much less computational resources. Due to this it enables us to performed a detailed analysis of the statistics of the amplitudes of the Langmuir waves in the plasma with density fluctuations. To analyze data obtained in both numerical models, a Pearson technique was used to classify the probability distribution functions (PDF) of the logarithm of wave intensity. It was shown that core parts the PDF's belong to Pearson types I,IV and VI, depending on the spatial profiles of the density fluctuations, rather than to the normal distribution. The study also showed that the high-amplitude parts of the distributions follow power-low or exponential decay, depending on the type of core distribution.
• Currents and associated electron scattering and bouncing near the diffusion region at Earth's magnetopause
  
  • Lavraud B.
  • Zhang Y.
  • Vernisse Y.
  • Gershman D. J.
  • Dorelli J. C.
  • Cassak P.
  • Dargent Jérémy
  • Pollock C.
  • Giles B. L.
  • Aunai N.
  • Argall M. R.
  • Avanov L. A.
  • Barrie A.
  • Burch J. L.
  • Chandler Michael O.
  • Chen L. J.
  • Clark G. B.
  • Cohen I. J.
  • Coffey V. N.
  • Eastwood Jonathan P.
  • Egedal J.
  • Eriksson S.
  • Ergun R.
  • Farrugia C. J.
  • Fuselier S. A.
  • Genot V. N.
  • Graham D. B.
  • Grigorenko E. E.
  • Hasegawa H.
  • Jacquey C.
  • Kacem I.
  • Khotyaintsev Y. V.
  • Macdonald E.
  • Magnes W.
  • Marchaudon A.
  • Mauk B.
  • Moore T. E.
  • Mukai Toshifumi
  • Nakamura R.
  • Paterson W. R.
  • Penou E.
  • Phan T.
  • Rager A. C.
  • Retinò Alessandro
  • Rong Z. J.
  • Russell C. T.
  • Saito Y.
  • Sauvaud J.-A.
  • Schwartz S. J.
  • Shen C.
  • Smith S. E.
  • Strangeway R. J.
  • Toledo-Redondo Sergio
  • Torbert R. B.
  • Turner D. L.
  • Wang S.
  • Yokota S.
  , 2016, 21, pp.SM21A-2404. Based on high-resolution measurements from NASA's Magnetospheric Multiscale mission, we present the dynamics of electrons associated with current systems observed near the diffusion region of magnetic reconnection at Earth's magnetopause. Using pitch angle distributions (PAD) and magnetic curvature analysis we demonstrate the occurrence of electron scattering in the curved magnetic field of the diffusion region down to energies of 20 eV. We show that scattering occurs closer to the current sheet as the electron energy decreases. The scattering of inflowing electrons, associated with field-aligned electrostatic potentials and Hall currents, produces a new population of scattered electrons with broader PAD which bounce back and forth in the exhaust. Except at the center of the diffusion region the two populations are collocated and behave adiabatically: the PAD of inflowing electrons focuses inward (towards lower magnetic field), while the bouncing population gradually peaks at 90° away from the center (where it mirrors owing to higher magnetic field and probable field-aligned potentials).