arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2005.13539physics.plasm-phastro-ph.SRcs.NAmath.NAphysics.comp-ph
收藏

深入研究分布函数：用连续介质Vlasov-Maxwell模拟理解相空间动力学

A Deep Dive into the Distribution Function: Understanding Phase Space Dynamics with Continuum Vlasov-Maxwell Simulations

James Juno

阅读 PDF
arXiv 页面 ↗HTML 原文 ↗

摘要：

在无碰撞和弱碰撞等离子体中，粒子分布函数是一幅丰富的基础物理挂毯。然而，实际上利用粒子分布函数来理解弱碰撞等离子体的动力学是具有挑战性的。相关的方程系统，即Vlasov-Maxwell-Fokker-Planck（VM-FP）方程系统，难以数值积分，并且传统方法如粒子网格法将计数噪声引入分布函数。在这篇论文中，我们提出了一个新的算法来离散VM-FP方程组，以研究动力学区域中的等离子体。采用间断Galerkin（DG）有限元方法进行空间离散，采用三阶强稳定性Runge-Kutta方法进行时间离散，得到了等离子体时空分布函数的精确解。我们都证明了数值方法保留了VM-FP系统的关键物理特性，如能量守恒和热力学第二定律，并以数值方式证明了这些特性。这些结果的背景下，在历史上的DG方法。我们讨论了算法的重要性是别名的自由，一个必要条件，推导出稳定的DG计划的动力学方程，以保持隐式的守恒关系嵌入在粒子分布函数，和计算有利的实施方式，使用一个模式，正交基础比较传统的DG方法应用于计算流体动力学。最后，我们演示了如何高保真表示的分布函数，结合新的诊断，允许详细分析的基本等离子体过程，如无碰撞冲击中的碰撞机制。

英文摘要：

In collisionless and weakly collisional plasmas, the particle distribution function is a rich tapestry of the underlying physics. However, actually leveraging the particle distribution function to understand the dynamics of a weakly collisional plasma is challenging. The equation system of relevance, the Vlasov-Maxwell-Fokker-Planck (VM-FP) system of equations, is difficult to numerically integrate, and traditional methods such as the particle-in-cell method introduce counting noise into the distribution function. In this thesis, we present a new algorithm for the discretization of VM-FP system of equations for the study of plasmas in the kinetic regime. Using the discontinuous Galerkin (DG) finite element method for the spatial discretization and a third order strong-stability preserving Runge-Kutta for the time discretization, we obtain an accurate solution for the plasma's distribution function in space and time. We both prove the numerical method retains key physical properties of the VM-FP system, such as the conservation of energy and the second law of thermodynamics, and demonstrate these properties numerically. These results are contextualized in the history of the DG method. We discuss the importance of the algorithm being alias-free, a necessary condition for deriving stable DG schemes of kinetic equations so as to retain the implicit conservation relations embedded in the particle distribution function, and the computational favorable implementation using a modal, orthonormal basis in comparison to traditional DG methods applied in computational fluid dynamics. Finally, we demonstrate how the high fidelity representation of the distribution function, combined with novel diagnostics, permits detailed analysis of the energization mechanisms in fundamental plasma processes such as collisionless shocks.

机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。

↑