EPIC理论模型和程序研发及其在磁重联研究中的应用

发布时间：2018-07-16 18:34

【摘要】：随着等离子体实验诊断和空间卫星观测技术的发展、特别是国家重大科技基础设施《空间环境地面模拟装置》空间等离子体环境模拟与研究系统(SPERF)的建设和“磁层多尺度过程”(MMS)国际卫星探测计划的启动,对电子惯性尺度内电子动力学行为的研究吸引了物理学家和空间科学家们的广泛关注。然而作为研究等离子体的重要手段之一,针对电子动力学行为研究的数值模拟方法的发展还不完善:只有流体近似的电子磁流体(EMHD)模型程序,没有研究动理学效应的模拟程序。因此,发展针对于电子动力学行为研究的粒子模拟模型并开发相应的程序编码迫在眉捷。为了更好的研究时空尺度在电子惯性尺度的小空间范围和快时间尺度的物理过程,我们提出发展EPIC(Electron Particle-in-Cell)模型。EPIC模型是将电子视为粒子,利用在PIC(Particle-in-Cell)程序处理,而对离子采用流体描述,可以在考虑离子的大尺度流体运动的同时有效的对电子动力学行为进行深入的动理学模拟研究。本文详细介绍了EPIC模型的物理基础,从EPIC模型基本假设出发、建立了EPIC模型方程组;在快尺度近似下对EPIC模型方程进行简化处理,得到程序编写所使用的模型方程。然后,我们在EPIC模型的理论框架下进一步构建了EPIC数值模拟方法的基本流程,并在流程图的指导下分别构建了坐标系、YEE网格,权重处理的程序实现方法。同时根据EPIC模型自身特点设计了二维YEE网格图,对电磁场方程进行了离散化处理。而后给出了电磁场由半网格量转化成整点网格量的方法,最后讨论了程序的计算稳定性条件和电子在边界上的处理方法。最终完成EPIC模型的数值程序代码的编写。利用编写的EPIC程序,我们对空间等离子体磁重联过程进行模拟,完成了程序的验证,并进一步取得了初步研究成果。在介绍了磁重联相关的基本理论以及常见的磁重联模型的基础上,分析了磁重联过程中Hall四极场的形成。随后利用EPIC数值模拟程序对地球磁尾的磁重联现象进行了模拟,得到了已知的磁重联现象的基本物理特征,验证了程序的正确性。进而利用EPIC模型程序对驱动磁重联过程进行了研究,取得了初步成果:发现外部驱动流的大小对Hall四极场和重联率有显著影响,驱动流的增大可以明显增强Hall四极场结构并提高了磁重联的重联率;同时也分析了驱动流分布对重联率的影响,发现随着驱动流空间分布宽度的增大,重联率在整体上呈上升趋势。这些工作为利用EPIC开展电子惯性尺度上各种物理过程的研究奠定了基础。
[Abstract]:With the development of plasma experimental diagnosis and space satellite observation technology, In particular, the construction of the Space Plasma Environment Simulation and Research system (SPERF) and the launch of the "Magnetospheric Multiscale process" (MMS) International Satellite Exploration Program, The study of electron dynamics in electron inertial scale has attracted the attention of physicists and space scientists. However, as one of the most important methods to study plasma, the numerical simulation method for the study of electron dynamic behavior is not perfect: only the fluid approximate electron magnetic fluid (EMHD) model program, and no simulation program to study the kinetic effect are available. Therefore, the particle simulation model for the study of electron dynamics behavior is developed and the corresponding program codes are developed. In order to better study the physical process of space-time scale in the small space range of electronic inertial scale and fast time scale, we propose to develop epic (Electron Particle-in-Cell) model. Epic model is to treat electrons as particles and process them in PIC (Particle-in-Cell) program. When the ion is described by fluid, it can be used to simulate the electronic dynamic behavior effectively while considering the large scale fluid motion of ions. In this paper, the physical foundation of epic model is introduced in detail. Based on the basic hypothesis of epic model, the epic model equations are established, and the epic model equations are simplified under the fast scale approximation, and the model equations used in programming are obtained. Then, under the theoretical framework of epic model, we further construct the basic flow chart of epic numerical simulation method, and under the guidance of flow chart, construct the program realization method of coordinate system Yee grid and weight processing separately. At the same time, according to the characteristics of epic model, the two-dimensional Yee grid diagram is designed, and the electromagnetic field equation is discretized. Then the method of converting electromagnetic field from semi-grid to full-point grid is given. Finally, the computational stability condition of the program and the method of dealing with the electron on the boundary are discussed. The final completion of epic model of the numerical program code. By using the epic program, we simulated the magnetic reconnection process of space plasma, completed the verification of the program, and obtained the preliminary research results. Based on the introduction of the basic theory of magnetic reconnection correlation and the common magnetic reconnection model, the formation of Hall quadrupole field in magnetic reconnection process is analyzed. Then the magnetic reconnection phenomenon of the earth's magnetic tail is simulated by using epic numerical simulation program. The basic physical characteristics of the known magnetic reconnection phenomenon are obtained and the correctness of the program is verified. Furthermore, the process of driving magnetic reconnection is studied by epic model program. The results show that the size of external driving flow has a significant influence on the Hall quadrupole field and reconnection rate. The increase of driving flow can obviously enhance the Hall quadrupole structure and increase the reconnection rate of magnetic reconnection, at the same time, the influence of driving flow distribution on reconnection rate is analyzed. It is found that with the increase of driving flow spatial distribution width, The reconnection rate showed an upward trend on the whole. These work have laid a foundation for the study of various physical processes on the electronic inertial scale using epic.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：V419.2

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