Roles of ion and electron dynamics in the onset of magnetic reconnection due to current sheet instabilities

Abstract

Roles of ion and electron kinetic effects in the trigger mechanism of magnetic reconnection due to current sheet instabilities are investigated by means of (2+1∕2)D explicit particle simulation. The simulation is performed for the Harris equilibrium without guide fields in the plane perpendicular to the antiparallel magnetic fields. The instabilities excited in the vicinity of the neutral sheet are classified into two modes, i.e., one is a longer wavelength kink mode and the other is a shorter wavelength kink mode. The growth of the longer kink mode depends only on the ion mass, while the growth of the shorter one depends only on the electron mass. Before the growth of these kink modes, the lower hybrid drift instability leads to two types of plasma diffusion: diffusion at the periphery controlled by ions and diffusion in the vicinity of the neutral sheet controlled by electrons. The diffusion at the periphery affects the ion distribution function at the neutral sheet through the ion meandering motion, and the ion-ion kink mode is destabilized as the electron-independent longer kink mode. The generation of the reconnection electric field at the neutral sheet due to the longer wavelength kink mode is characterized only by the ion dynamics and can take place commonly in ion-scale current sheets observed in the magnetosphere and laboratories.

Fast magnetic reconnection in a kinked current sheet

“…12,19 Especially, it is known that the kink mode is driven by the cross-field ion flow and gives rise to the magnetic dissipation through anomalous resistivity due to wave-particle interactions. [20][21][22][23] The kink mode has been recognized as the drift kink instability ͑DKI͒ for low mass ratio ͑m i / m e Շ 25͒. 20,21 Although this instability results in a significant decrease in the growth rate for high mass ratio ͑m i / m e Ͼ 100͒, 24 the kink mode still persists as the ion-ion kink instability for the realistic mass ratio with m i / m e = 1836 and the linear properties are proved identical essentially to the DKI.…”

Influence of a Guide Field on Collisionless Driven Reconnection

“…For complete understanding of collisionless reconnection, another important subject to be investigated is the role of anomalous resistivity associated with plasma instabilities in the presence of a strong guide field. Previous numerical simulation studies in the case of no guide field [4,7,8,20] have demonstrated that anomalous resistivity is generated through the excitation of a drift kink instability [3] in the ion-scale current sheet after nonlinear modification of the current sheet by a lower hybrid drift instability [2]. However, it is easily expected that the anomalous resistivity associated with plasma instabilities is largely altered by a strong guide field.…”

“…A series of particle-in-cell (PIC) simulation studies has disclosed that that there are two microscopic mechanisms, which break a frozen-in condition and excite magnetic reconnection in a collisionless plasma without any guide field: one is due to anomalous resistivity associated with plasma instabilities [2][3][4][5][6][7][8] and the other is due to the effect of a nongyrotropic particle motion, called "meandering motion", in the vicinity of a reconnection point [9][10][11][12][13].…”

Development of multi-hierarchy simulation model with non-uniform space grids for collisionless driven reconnection

“…Its generation mechanism cannot be described in the MHD framework. On the other hand, PIC simulations 3,4,[7][8][9][10][11] have demonstrated the microscopic process of magnetic reconnection from the first principle, thus, the generation mechanism of electrical resistivity can be treated self-consistently. However, computer resources required for PIC simulations are too huge to execute large-scale and long-time simulations such as the entire geomagnetosphere.…”

“…Some microscopic processes generating electrical resistivity, for instance, wave-particle interaction, [1][2][3][4] are needed as a trigger of magnetic reconnection. On the other hand, field topology changes on a macroscopic scale and global plasma transport occurs as a result of magnetic reconnection.…”