11:00 〜 11:15
[PEM10-07] Macroscopic description of the anomalous dissipation to drive magnetic reconnection
キーワード：磁気再結合、粒子シミュレーション、乱流、オームの法則、異常散逸
Magnetic reconnection is an important process in magnetospheric dynamics, enabling energy and momentum transports from the solar wind to the magnetosphere and triggering a fast energy release stored in the magnetotail magnetic field to cause substorms. The reconnection process is driven by the kinetic (microscopic) processes that take place at the x-line to dissipate the magnetic field. Meanwhile, the global dynamics has been described in the magnetohydrodynaics (MHD) framework where the kinetic effects are not explicitly treated. Magnetic reconnection in MHD is in most cases driven through the ad-hoc anomalous resistivity under an assumption that the non-ideal electric field should be proportional to the current density. However, the kinetic origin of the resistivity remains unrevealed and, furthermore, there is no guarantee that the non-ideal terms in the Ohm’s law can be really proportional to the current density in collisionless plasma.
To address these issues, we have carried out large-scale 3D particle-in-cell simulations of magntic reconnection with no guide-field. The simulation results show that the flow shear instabilities drive intense electromagnetic turbulence in the thin current layer formed around the reconnection x-line. It is found that the turbulence gives rise to the magnetic dissipation and electron heating in the diffusion region (Fujimoto & Sydora, 2021). It is interesting to notice that the ions hardly react to the turbulence, indicating that the turbulence does not cause siginificant momentum exchange between electrons and ions resulting in the resistivity. It is demonstrated instead that the dissipation is mainly caused by the viscosity associated with electron momentum transport across the current layer. In other words, the electric field raised from the turbulence is proportional to the Laplacian of the current density rather than the current density itself. The present results suggest a fundamental modification of the MHD framework based on the anomalous resistivity to generate the dissipation. In this talk, we will present the generation mechanism of the turbulence at the x-line and the macroscopic description of the resultant anomalus dissipation to drive reconnection.
Ref. Fujimoto, K., & Sydora, R. D. 2021, ApJL, 909, L15
To address these issues, we have carried out large-scale 3D particle-in-cell simulations of magntic reconnection with no guide-field. The simulation results show that the flow shear instabilities drive intense electromagnetic turbulence in the thin current layer formed around the reconnection x-line. It is found that the turbulence gives rise to the magnetic dissipation and electron heating in the diffusion region (Fujimoto & Sydora, 2021). It is interesting to notice that the ions hardly react to the turbulence, indicating that the turbulence does not cause siginificant momentum exchange between electrons and ions resulting in the resistivity. It is demonstrated instead that the dissipation is mainly caused by the viscosity associated with electron momentum transport across the current layer. In other words, the electric field raised from the turbulence is proportional to the Laplacian of the current density rather than the current density itself. The present results suggest a fundamental modification of the MHD framework based on the anomalous resistivity to generate the dissipation. In this talk, we will present the generation mechanism of the turbulence at the x-line and the macroscopic description of the resultant anomalus dissipation to drive reconnection.
Ref. Fujimoto, K., & Sydora, R. D. 2021, ApJL, 909, L15