地基高频加热激励ELF/VLF波对辐射带高能电子的准线性散射

Quasi-linear diffusion of the radiation belt energetic electrons by ground-based HF heater-induced ELF/VLF emissions

地球内、外辐射带电子通量的变化对于空间飞行器,尤其是中低轨卫星的防护有着非常重要的影响.基于回旋共振波粒相互作用的准线性理论,使用地基高频发射器发射电波调制低电离层背景电流可以人工激励ELF/VLF波,这些波能使辐射带相对论电子发生抛射角散射沉降进入大气层从而降低其生存期.为了定量地分析人工激励ELF/VLF波散射辐射带高能粒子的可行性,针对内、外辐射带,本文选取了两个典型区域:L=4.6和L=1.5.数值计算结果表明,在内、外辐射带由于ELF/VLF波的人工注入而造成的高能电子损失时间尺度很大程度上取决于冷等离子体参量α*(∝B2/N0,这里B是背景磁场,N0是电子数密度)、电波频谱特性和功率,以及与波发生回旋共振的电子能量.一般来讲,在外辐射带人工ELF/VLF哨声波散射相对论电子使之沉降到大气层要容易得多;低能量的高能电子(200 keV)要比高能量的相对论电子(500 keV)更有效地通过抛射角散射进入大气层.考虑到高频电波加热电离层激励的ELF/VLF波可能会被捕获在磁层空腔中,来回反射从而得到增强,因此在适当的条件下,地基高频加热装置发射足够的电波功率进入电离层诱导大幅度ELF/VLF波注入到内磁层,能够在1至3天的时间尺度内快速散射外辐射带相对论电子使之沉降,也能够在10天量级的时间尺度里散射生存周期一般为100天甚至更长的内辐射带相对论电子.

The dynamics of energetic electron fluxes in both the inner and the outer radiation belts is very important with respect to satellite protection, in particular for low and middle-orbit satellites. Based on the quasi-linear theory of gyroresonant waveparticle interaction, we compute the diffusion coefficients and loss timescales for radiation belt energetic electrons due to cyclotron resonance with artificial ELF/VLF emissions that are radiated through modulating the currents in the lower ionosphere by groundbased powerful high-frequency （HF） transmitter. We test the electron pitch-angle scattering in the outer zone, typically at L = 4.6 （where the HAARP facility is located） and in the inner zone, typically at L = 1.5. The results indicate that the electron loss timescales due to artificial injection of ELF/VLF waves in the inner and the outer radiation belts depend largely on the value of the cold-plasma parameter α^＊ （ ∝ B^2/No, where B is the ambient magnetic field and No the electron number density）, the properties of wave frequency spectrum, the wave power and the electron energy in resonance with the waves. Generally, relativistic electrons in the outer zone are much easier to be precipitated into the atmosphere by artificial ELF/VLF whistler waves and lower-energy electrons （≤200 keV） can undergo pitch-angle scattering more efficiently than higher-energy electrons （≥1500 keV）. Since ELF/VLF waves can experience in situ amplification due to multiple magnetospherie reflections within the magnetospherie cavity, it can be reasonably expected that, under suitable situations, ground-based HF transmitters can provide feasible radiation power into the ionosphere to induce the injection of ELF/VLF waves into the inner magnetosphere, and consequently account for potential rapid removal of outer belt relativistic electrons in a timeseale of from I to 3 days and of inner belt relativistic electrons that generally have a lifetime of 100 days or more in a timescale of the order of 10 days.