无碰撞磁重联中的电场结构和静电波动

Magnetic reconnection provides a physical mechanism for fast energy conversion from magnetic energy to plasma bulk kinetic energy and thermal energy, and it is used to explain many eruptive phenomena in space plasma, such as substorm, solar flare etc. However, in magnetic reconnection, electric field plays an critical role not only in the dissipation from magnetic energy to plasma bulk kinetic energy and thermal energy, but also in the acceleration of charged particles. Furthermore, there exist several kinds of electrostatic waves in magnetic reconnection, such as lower hybrid waves and electrostatic solitary structures. These waves are closely associated with electron dynamics in magnetic reconnection, and may trigger the onset of magnetic reconnection. We will implement particle-in-cell simulations as well as data analysis to study the generation and growth of the electron motion term and electron pressure tensor term, which support the inductive electric field perpendicular to the reconnection plane, and identify their role in the dissipation of magnetic energy and acceleration of charged particles. Then, we will discuss the generation mechanism of the Hall electric field in the reconnection plane. We will also study the region and generation mechanism of electrostatic waves in magnetic reconnection, and their relation with the electron dynamics in magnetic reconnection. Based on these, we will identify their role in the onset of magnetic reconnection.

磁重联提供了一种快速将磁场能量转化为等离子体动能和热能的物理机制，它和空间等离子体中的许多爆发现象，如磁层亚暴、太阳耀斑等，密切相关。但是在磁重联中，电场无论是在将磁场能量耗散成等离子体动能和热能，还是带电粒子的加速过程中，都起着关键性的作用。另外，在无碰撞磁重联的扩散区还存在着各种静电波动，如低混杂波和静电孤立结构等，它们和重联中的电子动力学行为密切相关，并可能导致了磁重联的触发。本项目拟采用粒子模拟方法，并结合卫星观测资料，研究无碰撞磁场重联中垂直于重联面的引导电场中电子运动项和压力张量项的产生和增长机制，揭示它们在将磁场能量耗散成等离子体动能和热能以及带电粒子加速过程中的作用，并在此基础上讨论重联平面内Hall电场的产生机制。此外，静电波动在无碰撞磁重联中产生的物理机制，以及它们和电子动力学行为之间的关系也是本项目的研究重点，我们还将进一步揭示它们和磁重联触发之间的关系。

磁重联提供了一种快速将磁场能量转化为等离子体动能和热能的物理机制，它和空间等离子体中的许多爆发现象，如磁层亚暴、太阳耀斑等，密切相关。但是在磁重联中，电场无论是在将磁场能量耗散成等离子体动能和热能，还是带电粒子的加速过程中，都起着关键性的作用。我们通过粒子模拟方法，研究了无碰撞重联中重联电场的快速增长机制，提出了一种自增长的理论模型来解释重联点附近的电子压力梯度项和远离重联点处的电子运动项的快速增长，并发现上述两项在重联过程中呈指数增长，并且后者的增长率是前者的两倍；在分离线区域的静电孤立结构是由于bump-on-tail不稳定性产生的，这种不稳定性首先激发准单色的静电波，这些静电波快速增长进入非线性演化阶段，相互合并，最后形成静电孤立结构。通过卫星观测资料，在重联扩散区的磁通量管的边缘和中心都发现了低混杂波，并且中心的低混杂波可能是边缘激发后传进去的，表明低混杂波确有可能提供了触发磁重联的物理机制。