於行星磁層中，高能中性粒子(ENAs)藉由高能質子與中性氣體的電荷交換碰撞而產生。卡西尼(Cassini)太空船之酬載-帶電與中性粒子成像儀器(MIMI/INCA, Ion and Neutral CAmera)提供了土星磁層中能量範圍由10千電子伏特至220千電子伏特之氫與氧ENA成像，分布約由土衛二(Enceladus)軌道至土衛一(Titan)軌道範圍。ENA影像顯示其強度常在土星磁層夜側與晨側加強，應是發生於夜側的高能電漿入射所導致。 本研究模擬了夜側之高能入射質子雲在進入土星磁場後隨著時間的演化，在共轉磁場之運動，質子雲與土衛二噴發與逸散的水氣所造成之中性雲的電荷交換作用而生成ENA。帶電粒子於磁場中的運動、與中性氣體之電荷交換率，接取決於帶電粒子所含之能量。為了理解影響ENA生成的時間與分布之機制，本研究考量了多種變因，如土星磁場、電場模型。最後，將比較模擬結果與儀器之ENA成像，並且嘗試歸納其改變要素。;In a planetary magnetosphere, Energetic Neutral Atoms (ENAs) are generated by charge exchange collisions between energetic ions and neutral gas. The INCA (Ion and Neutral CAmera) instrument onboard the MIMI experiment of the Cassini spacecraft provides ENA images for hydrogen and oxygen for energies between 10 keV and 220 keV depending on the mode. An important discovery of INCA concerns the appearance of source regions of hydrogen ENAs rotating around Saturn outside the orbit of Enceladus. The intensity of the ENA flux tends to brighten up in the midnight to dawn sector, which might be associated with the higher occurrence of energetic charged particles injection events in this region. In this study, we examine the time evolution of a cloud of energetic ions in drift motion relative to the rotating magnetosphere. Besides the dispersal of the energetic ions as a function of their energies, the charge exchange interaction with the neutral cloud created by Enceladus has been simulated. To figure out the possible processes that affect the temporal and spatial variations of ENAs, we examined the effects of an extra noon to mid-night electric field, partial corotation of the plasma and a magnetic field deduced from MAG magnetic field measurements, respectively. A comparison with observational results will be presented.
