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The purpose of the paper is to describe the decoupling processes of electron and ion dynamics in the reconnection layer (current sheet and separatrix regions) and how the in-plane electrostatic electric field and the parallel electric field are produced. During driven magnetic reconnection of oppositely directed magnetic field lines, both ions and electrons drift together with the merging field lines toward the neutral sheet where the magnetic field lines reconnect. Because the electron outflow velocity is much larger than the ion outflow velocity, a pair of currents flow inward toward the magnetic reconnection region and produce the quadrupole out-of-plane magnetic field concentrated around the separatrix regions. The parallel electric field is produced by the driving electric field and the quadrupole magnetic field and points toward the downstream direction. The parallel electric field accelerates electrons toward the reconnection region direction but ions move slowly across the separatrix field lines, which causes decoupling of the electron and ion flow dynamics around the separatrix regions to generate charge separation and produce electrostatic electric field pointing across the separatrix field lines toward the mid-plane direction. Around the magnetic reconnection region where the magnetic fields become weakened and reversed, the particle orbits perpendicular to the field lines become meandering. Because the ion meandering region width is much larger than the electron meandering region width, charge separation is produced inside the ion meandering region and produces a pair of strong bipolar in-plane electrostatic electric fields pointing toward the mid-plane direction. With the production of quadrupole magnetic field, the parallel electric field and the electrostatic electric field, particle dynamics and acceleration/heating can be understood., source:https://doi.org/10.1585/pfr.11.1401081, identifier:0000-0001-6618-7806

In the last three years, magnetic reconnection research in the MAST spherical tokamak achieved major progress by the use of new 32 chord ion Doppler tomography and 130 channel YAG and 300 channel Ruby Thomson scattering diagnostics. In addition to the previously achieved high power plasma heating during merging, detailed full temperature profile measurements including the diffusion region have been achieved for the first time. 2D imaging measurements of ion and electron temperature profiles have revealed that magnetic reconnection mostly heats ions globally in the downstream region of outflow jet and electrons locally around the X-point. The toroidal field in MAST “over 0.3T” strongly inhibits cross-field thermal transport, and the characteristic peaked electron temperature profile around the X-point is sustained on a millisecond time scale. In contrast, ions are mostly heated in the downstream region of outflow acceleration and around the stagnation point formed by reconnected flux mostly by viscosity dissipation and shock-like compressional damping of the outflow jet. Toroidal confinement also contributes to the characteristic ion temperature profile, forming a ring structure aligned with the closed flux surface. There is an effective confinement of the downstream thermal energy due to a thick layer of reconnected flux. The characteristic structure is sustained for longer than an ion-electron energy relaxation time ( 4 ms), and the energy exchange between ions and electrons contributes to the bulk electron heating in the downstream region. The toroidal guide field mostly contributes to the formation of a localized electron heating structure around the X-point but not to bulk ion heating downstream.

Accepted: 2003-05-27

The Energization and Radiation in Geospace (ERG) project for solar cycle 24 will explore how relativistic electrons in the radiation belts are generated during space storms. This geospace exploration project consists of three research teams: the ERG satellite observation team, the ground-based network observation team, and the integrated data analysis/simulation team. Satellite observation will provide in situ measurements of features such as the plasma distribution function, electric and magnetic fields, and plasma waves, whereas remote sensing by ground-based observations using, for example, HF radars, magnetometers, optical instruments, and radio wave receivers will provide the global state of the geospace. Various kinds of data will be integrated and compared with numerical simulations for quantitative understanding. Such a synergetic approach is essential for comprehensive understanding of relativistic electron generation/loss processes through crossenergy and cross-regional coupling in which different plasma populations and regions are dynamically coupled with each other. In addition, the ERG satellite will utilize a new and innovative measurement technique for wave-particle interactions that can directly measure the energy exchange process between particles and plasma waves. In this paper, we briefly review some of the profound problems regarding relativistic electron accelerations and losses that will be solved by the ERG project, and we provide an overview of the project., QC 20150306

Large-amplitude magnetic pulsations on ion inertial length scales are often observed in space plasmas, but their theoretical explanation is still controversial. We discuss a possible mechanism, different from ideas based on the classical plasma instabilities, for the generation of these pulsations. It is demonstrated that a competition between dispersion and wave steepening processes can lead to the transformation of a large-scale magnetosonic structure into trains of solitons. This kind of longitudinal filamentation is possible for both slow and fast magnetosonic perturbations. Results of numerical simulations are compared with Cluster spacecraft measurements and show that the steepening filamentation mechanism can explain the emergence of a certain class of solitary waves observed in space plasmas.