磁声波对辐射带高能电子加速机制的研究

Electrons acceleration and scattering by magnetospheric magnetosonic (MS) wave have recently become the focus of renewed interest in radiation belt dynamics. MS waves have been observed in a wide range of L and MLT both inside and outside the plasmasphere, and shown to occur with a high probability with most intense wave intensity. The interaction between MS waves and energetic electrons is now considered as an important mechanism for the origin of killer electrons. This project will construct an approaching-real MS wave model based on observational data from THEMIS and RBSP with spatial and frequency distribution and geomagnetic environment dependence. Test particle simulation method will be developed and applied to study of MS-electron interactions. Based on our preliminary works, we will calculate energy and pitch angle diffusion rate, as well as the cross-intersection diffusion rate of electron by MS waves. These results will be compared to those obtained based on quasi-linear theory to inspect the validity of the quasi-linear approximation. Moreover, an advanced test particle simulation algorithm, which has the property of non-dissipation over long time calculations, will be applied to show the full image of electron acceleration process by MS wave, as well as the non-linear effects. Furthermore, we will explore the possibility and efficiency of near-equatorial mirroring electrons accelerated and scattered by MS wave, which could potentially lead to new findings.

磁层磁声波加速高能电子的研究，是辐射带动力学领域内相对较新的一个研究课题。磁层磁声波由于具有分布区域广、覆盖整个磁地方时以及波的强度较大的观测事实，它对电子的加速可能提供辐射带杀手电子起源和波-粒子作用的一个重要的新机制。本项目将结合THEMIS星座以及最新的Van Allen 探测器(RBSP) 数据，建立接近真实的磁声波空间、频率、时间分布模型；在此模型基础上，发展和运用精确和有效的试验粒子计算方法，计算磁声波对电子能量扩散系数、投掷角扩散系数以及交叉扩散系数；与准线性理论得到的结果进行比较，确定磁声波-电子相互作用准线性近似的有效程度；发展能有效地进行长时间无损耗运算的试验粒子计算方法和程序，揭示磁声波加速辐射带高能电子的完整过程和非线性效应；计算近90度投掷角粒子在波动场中的运动，研究其潜在的与多波模连续共振而被快速加速的可能性。

改进并发展了电磁波对辐射带电子共振作用的试验粒子模拟算法。改进后的算法可有效地模拟磁声波对电子的加速和散射过程。利用准线性理论与试验粒子模拟两种方法研究磁声波对辐射带电子作用的机制。建立了具有多次谐波精细结构与传播方向分布的磁声波模型，及其在全球磁地方时的分布。结合试验粒子模拟与福克-普郎克扩散模拟，揭示了磁声波可通过朗道共振的平行加速，将近90度投掷角的高能电子散射至两边的投掷角上，从而形成蝴蝶状角向分布。同时，联合范阿伦卫星观测及数值模拟，首次指出磁声波是形成内辐射带与槽区、以及外辐射带的高能电子蝴蝶状角向分布的关键因素，并可潜在地对超相对论电子形成蝴蝶状角向分布。由于磁声波的存在，辐射带高能电子不再集中在磁赤道附近，而大量分布在中高纬，从而使中高纬空间也充满辐射。

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