磁场重联中离子轨道的混合模拟研究

HYBRID SIMULATION OF PARTICLE ACCELERATION CAUSED BY MAGNETIC RECONNECTION

在使用 2 .5维混合模拟方法研究了Petschek模型稳态驱动磁场重联演化的基础上 ,本文考察了计算域内各典型区域中粒子分布函数的变化 ,描绘了重联区不同位置几种类型的非Maxwell分布函数 .结果表明 ,磁场重联会将重联区少部分粒子加速到很高的能量 ,不同加速程度的粒子将形成球壳状的速度分布 .粒子的轨道特征表明 ,在重联区中出流的粒子 ,有一部分被磁镜捕获 ,其回旋半径大于重联区宽度 ,并构成整个流体速度的低速部分 .另外 ,在X中性点附近进入重联区的粒子沿磁力线向出流区以三种形式漂移 ,分别为 :沿磁力线逃逸、捕获在磁镜中随流体运动、横越磁力线漂移 ,其比例分别约为 70 % ,2 0 %和 10 % .

Applying a 2.5-D hybrid simulation, we have studied the particles acceleration caused by magnetic reconnection. The results show that the reconnection process will not only heat all the particles, but also accelerate a few particles to comparatively high velocities (about 2.0v A). Such selective accelerating makes the velocity distribution of all particles change from the Maxwellian distribution to a shell or quasi-shell distribution. In addition, this shape varies with the change of particle positions. In order to study the accelerating process occurring near the X-type neutral point, we have observed the time-variation of velocities and positions of selected particles. Among the particles are flowed out inside the reconnection region, some are trapped in the magnetic mirror, with a convolution radius that outsteps the width of the reconnection region. These particles can thus construct the low speed part of the fluid near the boundary of out flow regions. On the other hand, there are three kinds of drifting trajectory of particles entering the reconnection region beside the X-type neutral point: flee along the field lines, be trapped in the magnetic mirrors, and traverse the local field lines. The ratios of particles undergoing the three kinds of trajectory are about 70%, 20%,10%, respectively.