arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 1902.02733physics.plasm-ph
收藏

等离子体动熵的位置和速度空间分解及其在粒子模拟中的应用

Decomposition of Plasma Kinetic Entropy into Position and Velocity Space and the Use of Kinetic Entropy in Particle-in-Cell Simulations

Haoming Liang, Paul A. Cassak, Sergio Servidio, Michael A. Shay, James F. Drake, Marc Swisdak, Matt R. Argall, John C. Dorelli, Earl E. Scime, William H. Mattha… 展开作者

Haoming Liang, Paul A. Cassak, Sergio Servidio, Michael A. Shay, James F. Drake, Marc Swisdak, Matt R. Argall, John C. Dorelli, Earl E. Scime, William H. Matthaeus, Vadim Roytershteyn, Gian Luca Delzanno

摘要:

我们描述了一个系统的发展动力学熵的诊断完全动力学粒子在细胞(PIC)模拟和使用它来解释等离子体物理过程中的日光层,行星和天体物理系统。首先,我们以两种形式计算动力学熵--与每个宏观态的微观态数的对数相关的“组合”形式和与$f \ln f$相关的“连续”形式,其中$f$是粒子分布函数。我们讨论了各自的优缺点,并讨论了在PIC代码中实现它们的微妙之处。使用位置空间中的二维和速度空间中的三维的无碰撞PIC模拟,我们验证了动力学熵诊断的实施,并讨论如何优化数值参数以确保准确的结果。在反平行磁重联的优化模拟中,我们发现总的动力学熵守恒到3%。动力学熵可以分解为一个位置空间熵和一个速度空间熵之和,我们用它来研究无碰撞重联过程中动力学熵输运的性质。我们发现在磁重联过程中,由于等离子体的加热,电子和离子的速度空间熵随时间增加,而位置空间熵则由于等离子体的压缩而减小。该项目使用无碰撞模拟,因此它不能解决物理耗散机制;尽管如此,这里开发的基础设施应该对碰撞或弱碰撞日光层,行星和天体物理系统的研究有用。除了重联,诊断预计将适用于等离子体湍流和无碰撞冲击。

英文摘要:

We describe a systematic development of kinetic entropy as a diagnostic in fully kinetic particle-in-cell (PIC) simulations and use it to interpret plasma physics processes in heliospheric, planetary, and astrophysical systems. First, we calculate kinetic entropy in two forms -- the ``combinatorial'' form related to the logarithm of the number of microstates per macrostate and the ``continuous'' form related to $f \ln f$, where $f$ is the particle distribution function. We discuss the advantages and disadvantages of each and discuss subtleties about implementing them in PIC codes. Using collisionless PIC simulations that are two-dimensional in position space and three-dimensional in velocity space, we verify the implementation of the kinetic entropy diagnostics and discuss how to optimize numerical parameters to ensure accurate results. We show the total kinetic entropy is conserved to three percent in an optimized simulation of anti-parallel magnetic reconnection. Kinetic entropy can be decomposed into a sum of a position space entropy and a velocity space entropy, and we use this to investigate the nature of kinetic entropy transport during collisionless reconnection. We find the velocity space entropy of both electrons and ions increases in time due to plasma heating during magnetic reconnection, while the position space entropy decreases due to plasma compression. This project uses collisionless simulations, so it cannot address physical dissipation mechanisms; nonetheless, the infrastructure developed here should be useful for studies of collisional or weakly collisional heliospheric, planetary, and astrophysical systems. Beyond reconnection, the diagnostic is expected to be applicable to plasma turbulence and 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。

↑