基于粒子云方法研究地磁场对运动电子束的时空分布影响

空间电荷效应是空间带电粒子分布直接产生的相关效应，对于理解空间辐射环境有着重要意义。为研究地球磁场对空间电荷效应的影响，文章通过数值求解Poisson方程和相对论粒子运动方程，建立粒子云（particle-in-cell, PIC）自洽模型，并构建地球偶极子磁场模型作为内磁层背景磁场（空间分布L值为3～7）。在模型基础上，给出内磁层典型电子束结构（能量0.1～100 keV）的两种初始分布（Uniform和Gaussian分布），模拟电子束在地磁场影响下的动力学过程。结果表明:电子束结构受地磁场影响出现纵向的整体偏转，并由于自场效应产生了纵向的拉伸和横向的发散；电子束整体的偏转角主要受地磁场强弱以及电子束运动与磁场夹角影响，而拉伸和发散效应则主要受电子束能量等参数所影响。

Particle-in-cell simulations of space-time evolution of moving electron beams modulated by geomagnetic field

The space-time evolution of moving electron beams is influenced directly by the distribution of the space charged particles, and the space radiation environment is an important issue. To simulate the space-time evolution of moving electron beams modulated by the Earth’s magnetic field, a self-consistent particle-in-cell (PIC) model is established by numerically solving the Poisson equation and the relativistic particle motion equation, along with the dipolar magnetic field model to represent the background field of the Earth’s inner magnetosphere (3≤L≤7). Based on these models, the kinetic process of the electron beams (0.1 keV≤E_k≤100 keV) travelling through the Earth’s magnetic field is simulated, for two different initial distributions (Uniform and Gaussian ones). It is shown that the electron beam structure can be longitudinally deflected by the geomagnetic field, and longitudinally elongated and transversely spread by the self-field effect. The deflection angle is mainly related to the strength of the magnetic field and the angle between the magnetic field and the beam longitudinal direction, while the elongation and the spread are mainly affected by the energy of the beam structure.