外加剪切流下磁重联动力学过程的粒子模拟研究

Magnetic reconnection is a basic plasma process in which magnetic field energy is rapidly converted into kinetic energy, associated with the change of the topology of the magnetic field. While being thought to plays an important role in the dynamics of the magnetospheres, the solar corona, and laboratory experiments. In the previous researches ，it was found that the sub-Alfvenic shear flow in the incompressible 2D MHD will suppress the reconnection instability. But resent studies show that the sub-Alfvenic shear flow ,the thickness of which exceeds a critical value ,can accelerate the development of the reconnection instability, while the super-Alfvenic shear flow can suppress the development of the magnetic reconnection because of the Alfvenic resonant layers generated in the inflow region. When the plasma is compressible, the results are different. It is found that the shear flows form one or two pairs of slow shocks, which suppress the development of magnetic reconnection. With inclusion of Hall effects, it is found that whistler waves are generated in the downstream region of slow shocks. The whistler waves propagating toward the reconnection region drive a large bursty enhancement in magnetic reconnection during its decaying phase. Recently, we do some studies of dynamic processes of magnetic reconnection with external shear flows by using PIC simulation and the preliminary results indicate that dynamic processes of magnetic reconnection is very different . Therefore we propose to study the influences of shear flow on magnetic reconnection by using PIC simulation and hope that we can reveal the properties of magnetic reconnection under the external shear flow to help us to understand some observational phenomena.

磁场重联过程在空间和实验室等离子体中都有非常重要的应用。早期通过对不可压磁流体模型的研究认为，亚阿尔芬速度剪切流总是使撕裂模稳定，随后的研究发现而当剪切流的宽度大于某个临界值的时候，可以促进撕裂模的不稳定性，超阿尔芬速度剪切流会使入流区形成阿尔芬共振层，抑制重联。而当磁流体是可压缩的时候，剪切流会使入流区产生激波，抑制重联，但是当引入Hall效应的时候，激波的下游区会产生哨声波，使处于衰退期的重联过程发生爆发式的重联率增长。可见随着各种非理想效应的引入，存在剪切流的重联过程变的越来越复杂。粒子模拟（PIC）是第一性原理的模拟方法，它包含了所有的非理想效应。最近，我们通过使用PIC的方法对伴随有剪切流的磁场重联过程进行了初步研究，发现可以得到很多与MHD模拟不同的结果，所以希望通过此研究的开展深入的揭示剪切流对磁场重联过程的影响，以便更好的解释空间和实验室等离子体中的一些现象。