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高空核爆过程会向内磁层注入大量相对论性电子，形成人工辐射带，这些高能电子可能对航天器造成显著影响。本文利用Comprehensive Inner Magnetosphere-Ionosphere Model (CIMI模型)模拟研究了核爆注入的电子由局地集中分布向环向均匀分布演化的过程，揭示了人工辐射带形成过程中电子团表现出的螺旋包围、环向膨胀与扩散均匀的行为特征。对初始时刻集中在L=1.1 ∼2.2、环向覆盖1个时区左右的核爆电子进行的数值模拟表明，核爆注入电子主要通过螺旋包围过程演化至环向均匀分布，扩散作用的贡献相对较小。电子注入后，在地球磁场的约束下做自西向东环绕地球的漂移运动。外侧电子漂移速度更快，因此注入电子团会在环向上剪切拉伸，以螺旋线结构包围地球。此外，研究还发现螺旋结构的形成过程伴随有电子的环向膨胀，主要由漂移过程中能量色散和投掷角色散机制驱动。不同能量和投掷角的电子漂移速度不同，因此逐渐环向分离，造成环向分布范围扩展，填充螺旋结构的间隙。在通过形成螺旋结构与环向膨胀包围地球后，核爆注入的高能电子进一步通过扩散作用演变为环向均匀分布的结构，形成相对稳定的人工辐射带。
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关键词:
- 高空核爆 /
- 人工辐射带 /
- Fokker-Planck方程 /
- 电子扩散
High-altitude nuclear explosions can inject significant amounts of relativistic electrons into the inner magnetosphere, resulting in the formation of artificial radiation belts. These high-energy electrons pose a potential threat to spacecraft due to their long-term stability and impact on space weather. The investigation of the formation and evolution of artificial radiation belts is of great significance for the safety of spacecraft and human space activities. In this study, the Comprehensive Inner Magnetosphere-Ionosphere Model (CIMI model) is employed to simulate the transition of electrons from a locally concentrated distribution to an azimuthally uniform distribution, revealing the spiral encircling, azimuthal expansion, and diffusion behaviors exhibited by the electron cloud during the formation of artificial radiation belts. The CIMI model is a 4D model based on the Fokker-Planck equation. It simulates the evolution of particles across four degrees of freedom: radial, azimuthal, energy, and equatorial pitch angle. Unlike previous studies, which have mainly focused on the long-term evolution of artificial radiation belts that have already reached azimuthal uniformity, this work specifically addresses the azimuthal evolution process of the injected electrons and how they form the artificial radiation belts. Numerical simulations were conducted on the captured nuclear explosion electrons initially concentrated at L = 1.1 ~ 2.2 and covering approximately one time zone azimuthally. The results show that the injected electrons primarily evolve into an azimuthally uniform distribution through a spiral encircling process, with diffusion playing a smaller role. During this process, the electrons undergo eastward drift, with those at higher altitudes exhibiting faster drift velocities. The velocity shear leads to the formation of a helical structure around the Earth. Additionally, the formation of this spiral structure is accompanied by azimuthal expansion, driven mainly by energy and pitch angle dispersion during the drift. Electrons with different energies and equatorial pitch angles exhibit varying drift speeds, contributing to the azimuthal expansion of electron clusters during the drift. The expansion process can fill the gaps in the helical structure. Ultimately, the electron distribution achieves azimuthal uniformity through energy-pitch angle diffusion.-
Keywords:
- high-altitude nuclear explosions /
- artificial radiation belt /
- Fokker-Planck equations /
- electrons diffusion
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