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带电粒子在磁重联电流片中的加速
Alternative TitleCharged Particle Accelerations in Magnetic
李燕
Subtype博士
Thesis Advisor林隽
2012-06-04
Degree Grantor中国科学院研究生院(云南天文台)
Place of Conferral北京
Degree Discipline天体物理
Keyword太阳耀斑 磁重联 电流片 高能粒子
Abstract太阳是巨大的高能粒子加速器,能产生高达数GeV的离子和数MeV的电子。耀斑是太阳大气中剧烈的能量释放过程,巨大的能量在几分至几十分钟的时间内释放,大于20keV的电子和大于1MeV的离子包含了其中10%-50%的能量,这意味着加速和能量释放过程是密切相关的。所以,粒子加速就成为太阳耀斑研究最有吸引力的一个方向。 磁重联电流片中直流电场加速是太阳耀斑中粒子加速的主要机制之一。用试验粒子模拟直流电场中电子和质子加速对研究粒子和耀斑物理都具有重要意 义。本文内容安排如下: 第一章主要介绍太阳耀斑相关的物理背景,包括太阳耀斑的硬X-射线和射电观测、磁重联的基本概念和耀斑的理论模型。 第二章介绍了三种不同的加速机制, 包括由MHD湍动引起的随机加速、漂移激波和扩散激波加速、重联电流片中的电场加速。 第三章研究了带电粒子在有引导磁场存在的单X-点形电流片中的加速特征。使用试验粒子的方法计算了粒子的运动轨迹。研究了粒子最终能量和初始位置的关系。我们发现引导场的存在不仅使电子和质子分离,也使电场有选择的对不同初始位置的粒子进行加速。粒子的能谱是典型幂律谱。谱指数依赖于引导场、背景磁场及初始粒子分布。 第四章研究了带电粒子在对称和不对称多X-点和O-点电流片中的运动特征。粒子可以在很短的时间内被加速到很高的能量。电子和质子的能谱都呈现双或多幂律分布。被加速的粒子或者被磁岛束缚获得更多能量,或者跃过数个磁岛离开加速区。引导场的存在导致电子和质子运动方向的分离。 最后,在总结本文的同时,对今后的工作进行了展望。
Other AbstractThe sun is the most energetic particle accelerator in the solar system, producing ions of up to GeV and electrons of up to several MeV. Large solar flares are the most powerful explosions in the solar system. The accelerated above 20 keV electrons and the greater than 1 MeV ions appear to contain 10%-50% of this energy, indicating that the particle acceleration and energy release processes are intimately linked. Hence, one of the most fascinating aspects of solar flares is how the particles are accelerating to high energies. Particle acceleration by direct current (DC) electric field in a reconnecting current sheet is considered as one of the popular mechanisms of the acceleration of energetic particles during solar flares. Numerical simulations of electrons and protons acceleration through the test approach and studying on the energy spectrum and the trajectories of these energetic particles are very important to understand the process of particle acceleration and flare physics. This thesis is organized as follows: In Chapter 1, We first present a brief introduction to solar flares, including hard X ray (HXR) and radio observations of flares, some basic concepts and models of magnetic reconnection, and the standard model for solar flares, all of which are relevant to this thesis. In Chapter 2,we summarized the basic knowledge to three particle acceleration mechanism, These involve the stochastic acceleration by MHD turbulence generated in fast plasma reconnection outflows; shock-drift acceleration and diffusive-shock acceleration; and super-Dreicer acceleration in a reconnecting current sheet. In Chapter 3,Kinematic characteristics of electrons and protons in the magnetic reconnecting current sheet in the presence of a guide field are investigated. Particle trajectories are calculated for different values of the guide field by a test-particle calculation. The relationship between the final energy and the initial position has also been studied. We found that the addition of a guide field not only allows particles to get more energy and not only results in the separation of electrons and protons, but also causes the reconnecting electric field to selectively accelerate electrons and protons for different initial positions. The energy spectrum eventually obtained is the common power-law spectrum. The spectrum index depend on the guide field, the background magnetic field, and the initial distribution. In Chapter 4,kinematic characteristics of the accelerated particles in the current sheet including multiple X-points and O-points were investigated. The energy spectra for both particle species have a double or multiple power-law shape. Accelerated particles are either trapped within magnetic island regions, or escape the current sheet mainly along the open magnetic field. Also, protons and electrons are ejected from the current sheet in different directions. In the last chapter, we summarize this thesis and give prospects of further studies.
Subject Area天文学
Pages95
Language中文
Document Type学位论文
Identifierhttp://ir.ynao.ac.cn/handle/114a53/6619
Collection太阳物理研究组
Recommended Citation
GB/T 7714
李燕. 带电粒子在磁重联电流片中的加速[D]. 北京. 中国科学院研究生院(云南天文台),2012.
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