在日地環境中的許多現象，帶電粒子束不穩定性在其生成機制中都扮演著重要的角色。舉例來說，在普遍接受的第三型太陽電波爆發兩步生成機制中，第一步即是由帶電粒子束不穩定性激發高頻靜電波，進而透過非線性波與波的交互作用產生電漿放射。此外，在地球前震波周圍所觀測到的低頻電磁波擾動，也被認定是由高能粒子束透過帶電粒子束不穩定性所激發。在過去關於帶電粒子束不穩定性的研究中，不論是數值模式或是理論模式，大多採用連續、均勻、且帶有完美馬克士威速度分布的帶電粒子束。然而，在真實的太空環境中，帶電粒子束並不常以上述理想假設存在。因此，非理想型之帶電粒子束於電漿不穩定性發展過程中的影響，也就成為了太空環境實際應用時的關鍵。基於上述背景，本計畫將針對高頻太陽電波爆發問題，研究非理想型帶電粒子束在非線性演化過程中，對於電漿不穩定性發展以及電漿放射所造成的影響。此外，本計畫也將研究由帶電粒子束不穩定性激發之低頻電磁波。在帶電粒子束不穩定性的演化過程中，靜電波往往會先被激發並造成系統中的粒子呈現非均向性之動量分布，進而引起隨後的低頻電磁波擾動。本研究將針對此問題，觀察不穩定性發展過程中之能量轉換與粒子散射行為，比較帶電粒子束不穩定性與壓力非均向不穩定性之異同。 ;The application of beam-plasma instabilities have been overwhelmingly present in the study of Sun-Earth environment. For instance, in the core mechanism of type III solar radio bursts, the electrostatic streaming instability is generally adopted in the well-known two-step process with the accompanying nonlinear wave-wave interaction. Meanwhile, the low-frequency electromagnetic wave excitation led by an energetic particle stream is also reported in the Earth's foreshock. In the past studies of beam-plasma instability, a uniform and continuous beam with prefer Maxwellian momentum distribution is generally adopted in the theoretical and numerical models. However, it is not realistic to expect the electron/ion beam generated in the space environment would be tallied with above ideal characteristics. Thus the investigation of realistic beam effects is critical for the application in the Sun-Earth environment. In this study, for the high-frequency solar radio bursts problem, the non-ideal type beam will be imported in the numerical system to observe its effects on the beam-plasma interaction and accompanying plasma emission. In addition, this studies will also involve the low-frequency electromagnetic wave excitation problems. Particularly, pressure anisotropy will develop in the early stage of nonlinear evolution processes and may lead the later significant magnetic field perturbations. By examining the energy transformation and particle scattering in the nonlinear evolution processes, the issue of whether the electromagnetic streaming instabilities can be also interpreted as the pressure anisotropy instabilities will be also addressed in this study.
