—This issue includes articles devoted to the results of the work of the section “Experimental laboratory astrophysics and geophysics” of the National Center for Physics and Mathematics.
This paper deals with acceleration processes in the magnetotail and the processes that enhance particle precipitation from the tail into the ionosphere through electric fields in the auroral ...acceleration region, generating or intensifying discrete auroral arcs. Particle acceleration in the magnetotail is closely related to substorms and the occurrence, and consequences, of magnetic reconnection. We discuss major advances in the understanding of relevant acceleration processes on the basis of simple analytical models, magnetohydrodynamic and test particle simulations, as well as full electromagnetic particle-in-cell simulations. The auroral acceleration mechanisms are not fully understood, although several, sometimes competing, theories and models received experimental support during the last decades. We review recent advances that emphasize the role of parallel electric fields produced by quasi-stationary or Alfvénic processes.
•We reviewed the resonant wave-particle interaction in various Sapace Plasma systems.•We presented a general theory of trapping (capture) into resoance and scattering on resonance of charged ...particles by electrostatic or electromagnetic waves in the presence of a background magnetic field.
In the present review we survey space plasma systems where the nonlinear resonant interaction between charged particles and electromagnetic waves plays an important role. We focus on particle acceleration by strong electromagnetic waves. We start with presenting a general description of nonlinear resonant interaction based on the theory of slow-fast Hamiltonian systems with resonances. Then we turn to several manifestations of the resonance effects in various space plasma systems. We describe a universal approach for evaluating main characteristics of the resonant particle dynamics: probability of trapping into resonance, energy change due to scattering and trapping. Then we demonstrate how effects of nonlinear resonant trapping and scattering can be combined in a generalized kinetic equation. We also discuss the stability of trapped motion and evolution of particle ensemble in systems with trapping. The main objective of this review is to provide a general approach for characterizing plasma systems with nonlinear resonant interactions.
Knowledge of the ion composition in the near-Earth’s magnetosphere and plasma sheet is essential for the understanding of magnetospheric processes and instabilities. The presence of heavy ions of ...ionospheric origin in the magnetosphere, in particular oxygen (O
+
), influences the plasma sheet bulk properties, current sheet (CS) thickness and its structure. It affects reconnection rates and the formation of Kelvin-Helmholtz instabilities. This has profound consequences for the global magnetospheric dynamics, including geomagnetic storms and substorm-like events. The formation and demise of the ring current and the radiation belts are also dependent on the presence of heavy ions. In this review we cover recent advances in observations and models of the circulation of heavy ions in the magnetosphere, considering sources, transport, acceleration, bulk properties, and the influence on the magnetospheric dynamics. We identify important open questions and promising avenues for future research.
Abstract
Boundary current sheets (CSs) can be formed in collisionless space plasmas in the environment of exoplanets and cold stars. Usually they represent curved surfaces carrying the electric ...current analogous to the well-known planetary ionospheres, magnetopauses, or stellar coronas surrounding celestial bodies. At smaller local scales, some of them can be imagined as planar current layers of a finite scale located parallel to the surface of a celestial object and, correspondingly, perpendicular to the direction of the gravitational force. In some cases, this force crossed with magnetic field can influence the dynamics of charged particles in CSs and substantially change the structure of both the current layer and the magnetic field. We have generalized our prior model, taking into account a multi-ion plasma composition and a magnetic field configuration with a shear. It is shown that, due to the drift motion of plasma particles in the crossed gravitational and magnetic fields, the structure of CSs becomes more complex, accruing asymmetric and shifted profiles of the current and plasma densities that depend on dominating current carriers and the characteristics of the magnetic shear. We discuss possible applications of the results to the interpretation of observations of boundary layers in different space plasmas.
Current sheets (CSs) play a crucial role in the storage and conversion of magnetic energy in planetary magnetotails. Using high‐resolution magnetic field data from MAVEN spacecraft, we report the ...existence of super thin current sheets (STCSs) in the Martian magnetotail. The typical half‐thickness of the STCSs is ~5 km, and it is much less than the gyroradius of thermal protons (ρp). The STCSs are embedded into a thicker sheet with L ≥ ρp forming a multiscale current configuration. The formation of STCS does not depend on ion composition, but it is controlled by the small value of the normal component of the magnetic field at the neutral plane (BN). A number of the observed multiscale CSs are located in the parametric map close to the tearing‐unstable domain, and thus, the inner STCS can provide an additional free energy to excite ion tearing mode in the Martian magnetotail.
The intense electron‐scale current structures (ECSs) with the current density J ≥ 30 nA/m2 are often observed in the Plasma Sheet (PS) during high‐speed bulk flows. Using MMS observations we have ...analyzed 41 earthward and 37 tailward flow intervals and found 452 and 754 ECSs distributed over the PS region, respectively. Almost all ECSs are generated by high‐speed electron beams. The duration of ECSs is ≤1 s, and many of them have a half‐thickness L ≤ a few ρe (ρe is the gyroradius of thermal electrons). In such thin ECSs electrons become demagnetized and experience the dynamics like that observed in the electron diffusion region. Strong nonideal electric fields (E’) associated with violation of frozen‐in condition for electrons are observed in the ECSs. This results in the intense energy conversion with J·E’ up to hundreds pW/m3. The major part of the dissipating energy is transferred to electron heating and acceleration. We suggest that the ECSs are manifestations of kinetic‐scale turbulence driven by the high‐speed ion bulk flows. The inductive electric fields generated by the growing magnetic fluctuations accelerate electron beams which, in turn, generate the ECSs. The ECSs thinning during their evolution, probably, stops for L ≤ a few ρe. Further thinning leads to development of kinetic instability causing the current disruption and strong electric field generation. The last accelerates new electron beams which generate new ECSs in other locations. Thus, the life cycles of the ECSs contribute to energy cascade in turbulent plasma at electron kinetic scales.
Key Points
Electron‐scale current structures (ECSs) with a few L/ρe thickness are observed in the plasma sheet during fast ion bulk flows
The ECSs are mostly generated by demagnetized electrons experiencing the dynamics similar to that observed in electron diffusion region
In the ECSs J·E’ reaches the values typical for EDR, thus, they significantly contribute to the turbulent energy cascade at electron scales
Thin current sheets (TCSs) are the key structures in space and laboratory plasmas responsible for the accumulation and subsequent release of the stored magnetic energy. Spacecraft measurements in the ...near Earth's space revealed the complicated multilayer TCSs structure consisting from extremely thin and strong electron current embedded inside the thicker ion current layer. In this paper we present for the first time the analytical self‐consistent model of 1D super thin electron current sheet (STCS) supported by magnetized electrons within a much wider (but still very thin) proton structure carried by nonmagnetized (quasi‐adiabatic) particles. We take into account the dependence of electron STCS on anisotropy of electron distribution and magnetic field shear often existing in realistic TCS configurations. It is shown that the structure of the embedded STCS can be described by the simple nonlinear equation, which allows to estimate the scaling of STCS thickness due to coupling of electron and ion domains, although electron dynamics described by guiding center drift approximation is scale free. The theoretical results are in a good agreement with MMS spacecraft observations in the Earth's magnetotail.
Key Points
The model of extremely thin current layer is constructed and investigated
The thickness of embedded electron current layer is estimated in a wide range of parameters of the model
Comparison of MMS observational data with theoretical results revealed a good agreement
We analyze the structure of the Earth magnetotail current sheet (CS) in middle, X∈−50,−20 RE, and distant, X∈−100,−80 RE, regions using data set of 573 CS crossings by Geotail in 1994–1995. For a ...subset of 213 CSs we determine the CS thickness L, average current density j0, and velocity vD=j0/en0 (n0 is the ion number density). We find similar dawn‐dusk distributions of CS parameters for middle and distant tail: L is about 3000 km at the dusk flank and grows up to 12,000 km toward the dawn flank; j0 grows toward the dusk flank by a factor of 2–3; and the most intense CSs (with higher vD) are observed near midnight. We show that ion‐scale CSs with the thickness of several ion thermal gyroradii (say less than seven) are observed in middle and distant tail in more than 50% of crossings. For observed CSs electrons likely provide the dominant contribution to the current density. We divide the subset into intense and weak CSs (using parameter vD). Weak CSs have thickness of about 20 ion thermal gyroradii and Bz of about 1.5 nT. Intense CSs have thickness of about 3–7 thermal gyroradii and much smaller Bz implying more stretched field line configuration. Intense CSs are accompanied by fast ion flows: vD is larger for larger amplitudes of ion bulk velocity vx that is likely due to larger contribution of Speiser ions. The properties of the CS in middle and distant tail are compared with those found for the near‐Earth tail.
Key Points
We collected data set of current sheets near and beyond the lunar orbit with determined thickness
Ion‐scale current sheets are frequently observed near and beyond the lunar orbit
The most intense current sheets are observed in the presence of fast earthward/tailward plasma flows
Numerous studies of the current sheets (CS) in the Earth's magnetotail showed that quasi‐adiabatic ion dynamics plays an important role in the formation of complicated multilayered current ...structures. In order to check whether the similar mechanisms operate in the Martian magnetotail, we analyzed 80 CS crossings using MAVEN measurements on the nightside of Mars at radial distances ~1.0–2.8RM. We found that CS structures experience similar dependence on the value of the normal component of the magnetic field at the neutral plane (BN) and on the ratio of the ion drift velocity outside the CS to the thermal velocity (VT/VD) as it was observed for the CSs in the Earth's magnetotail. For the small values of BN, a thin and intense CS embedded in a thicker one is observed. The half‐thickness L of this layer is ~30–100 km ≤ ρH+ (ρH+ is a gyroradius of thermal protons outside the CS). With the increase of BN, the L also increases up to several hundred kilometers (~ρO+, ρO2+), the current density decreases, and the embedding feature disappears. Our statistical analysis showed a good agreement between L values observed by MAVEN and the CS scaling obtained from the quasi‐adiabatic model, if the plasma characteristics in Martian CSs are used as input parameters. Thus, we may conclude that in spite of the differences in magnetic topology, ion composition, and plasma thermal characteristics observed in the Earth's and Martian magnetotails, similar quasi‐adiabatic mechanisms contribute to the formation of the CSs in the magnetotails of both planets.
Key Points
Thin and intense current layers with a half‐thickness L of ~30–100 km ≤ ρH+ embedded in a thicker CSs are observed in the Martian magnetotail
The embedded current layers can be explained by quasi‐adiabatic dynamics of multicomponent ion population
The CS thickness depends on BN/B0 and on VT/VD of the dominant ion component in agreement with the quasi‐adiabatic scaling law
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