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研究生： 劉晉銘
Chin-Min Liu
論文名稱： 土星環鄰近地區之帶電塵埃粒子動力學
Dynamics of Charged Dust Grains in the Vicinity of the Saturnian Rings
指導教授： 葉永烜
Wing-Huen Ip
口試委員:
學位類別： 碩士
Master
系所名稱： 地球科學學院 - 太空科學研究所
Graduate Institute of Space Science
論文出版年： 2013
畢業學年度： 101
語文別： 英文
論文頁數： 131
中文關鍵詞： 土星 、土星環 、磁場 、帶電塵埃粒子 、倫吉-庫塔法 、蒙地卡羅法
外文關鍵詞： Saturn, Saturnian rings, magnetic field, charged dust grains, Runge-Kutta method, Monte Carlo method
相關次數： 點閱：11  下載：0 
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    • 我的論文研究主要目標在於探討及研究土星環鄰近地區之中帶著大範圍Q/m值的帶電塵埃粒子之運動軌道的演化及其物理意涵，並且藉由帶電塵埃粒子的軌道運動，其數量密度分佈亦可透過數值模擬得之。在此次的研究之中，我使用了4 階Runge-Kutta法來模擬帶電塵埃粒子之運動軌道以及使用上述之方法加上來自於Monte Carlo法的相關概念來模擬帶電塵埃粒子之數量密度分佈，並且在所有的運動軌道之中，帶電塵埃粒子的電荷值都固定不變，並且我也計算帶電塵埃粒子受到shadow effect影響之下的運動軌道及其數量密度分佈，因受到shadow effect的影響，帶電塵埃粒子之電性將會有所變化而非固定不變。根據模擬的結果顯示，當帶電塵埃粒子的Q/m≥10^-4 e/mP且出發點在穩定臨界半徑(rc=1.53 RS)內則他們將會透過虹吸式流動撞擊到土星的上層大氣，此外，土星赤道電離層減損效應也有可能是因為帶有Q/m=10^-6–10^-7 e/mP的帶電塵埃粒子入射到土星赤道上層大氣因而造成，其現象亦被Cassini太空船觀測到。假如帶電塵埃粒子受到shadow effect的影響，其運動軌道將會和單純只帶有正電荷或是負電荷之帶電塵埃粒子有很大的不同。從帶電塵埃粒子在Encke Gap內的運動軌道計算之中，我們可以瞭解到Q/m和角速度之間的關係，其可以提供軌道穩定性的相關資訊。然而，因為目前尚未有靠近土星環鄰近地區的現地量測，因此這份研究將可以提供在未來觀測時所需之模型基礎，並且亦可以解釋在土星上層大氣及土星環系統所觀測到的現象，此外，亦可解釋土星環和土星彼此之間的交互作用。

    The objective of my thesis research aims to study the evolution and physical implications of the orbital motion of charged dust grains with different charge-to-mass ratios (Q/m) in the vicinity of the Saturnian rings. By the way,
    the number density distributions of charged dust grains with different Q/m could also be acquired via numerical simulations. In this research, I used the Runge-Kutta 4th order method and which with some concepts from the Monte
    Carlo method to calculate the trajectories and number densities of the charged dust grains, respectively. The charge was fixed for all the orbital motion. However, I also tested the trajectories and number densities of charged dust
    grains affected by the shadow effect, and the charge properties of charged dust grains would be different instead of fixed. According to the results, when Q/m≥10^-4 e/mP, charged dust grains would precipitate into the upper atmosphere of Saturn via siphon flow if the injected positions of which were smaller than the stability critical radius (rc=1.53 RS). Besides, perhaps the ionosphere depletion of Saturnian equator was due to the injection of charged dust grains which with Q/m between 10^-6–10^-7 e/mP, and this phenomenon was observed via the Cassini radio occultation measurements. Furthermore, if charged dust grains did the orbital motion with the shadow effect, then something was different from purely positively or negatively charged dust grains did. The trajectories of charged dust
    grains within the Encke Gap could provide the information about the orbital stability via the relation between Q/m and angular velocity. However, there has not been in-situ observation near the ring plane until now, so this research work not only provides the cornerstone for the future observational model but also interprets some phenomena which happened to the upper atmosphere of Saturn, Saturnian ring system, and the interaction between Saturnian ring system and Saturn.

    摘要 i Abstract ii Acknowledgements iii Contents iv List of Figures vi List of Tables xvi Chapter 1 Introduction 1 1.1 Saturn and Its Ring System 1 1.1.1 Saturn 1 1.1.2 Saturnian Ring System 12 1.1.3 Charged Dust Grains in Saturnian Ring System 18 1.2 Research Goals 18 1.3 Cassini-Huygens Mission 20 1.3.1 Prime Mission 22 1.3.2 Extended Missions 23 1.3.3 The Instruments of Cassini Orbiter 24 Chapter 2 Equation of Motion and Description of the Programmes 26 2.1 Gravitational Force and Lorentz Force 26 2.1.1 Gravitational Force 26 2.1.2 Lorentz Force 27 2.2 Charged Dust Grains 30 2.2.1 The Charging of Dust Grains 30 2.2.2 The Size of Dust Grains 32 2.3 Description of the Programmes 34 2.3.1 Description of the Trajectories 34 2.3.2 Description of the Number Densities 35 2.3.3 Description of the Trajectories within the Encke Gap 41 Chapter 3 Results 43 3.1 Trajectories 43 3.1.1 Dipolar Magnetic Field 43 3.1.2 Measured Magnetic Field 47 3.1.3 Shadow Effect 52 3.2 Number Densities 63 3.2.1 Positively Charged Dust Grains 63 3.2.2 Negatively Charged Dust Grains 71 3.2.3 Shadow Effect 80 3.3 The Trajectories of Charged Dust Grains within the Encke Gap 93 Chapter 4 Discussion 98 Chapter 5 Future Work 101 Bibliography 104

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