Kinetic Physics of Homogeneous Turbulence in Collisionless Plasmas

这是美国国家科学基金会和美国能源部共同资助的一个项目，湍流的多尺度特性给动力学模拟带来了严峻的计算挑战。该项目将积极推动等离子体湍流的全粒子模拟的极限。 最近开发的并行，隐式，全粒子动力学模拟代码将被用来执行模拟，将显示如何长波长模式非线性级联到较短的波长。该项目的重点是对湍流的最不了解和最有争议的方面，即长波长湍流向短动力学尺度的过渡，以及波长短于这种过渡的湍流特性。目标是解决太阳风中长波长模式如何从惯性范围级联到短波长范围的物理问题。惯性范围是相当好的描述单流体，磁流体动力学（MHD）模型，这已被证明是一个非常有效的方法来描述长波长的波动在太阳风。观测结果表明，在光谱中断处的波数，惯性范围结束，对应于离子的惯性长度。离子惯性长度标志着单流体理论的崩溃，动力学效应在这一区域中占主导地位。因此，短波长区域仍然是太阳风湍流中了解最少的组成部分，许多基本问题，如控制断点的物理学，都没有完全了解。正确对待所谓的？耗散范围？湍流在等离子体中无处不在，发生在各种环境中，如星际介质，吸积盘，行星磁层和太阳风。主要的理论焦点一直在长波长的湍流，其中MHD是一个很好的近似。该项目将使用一系列波湍流理论和最先进的全粒子动力学模拟，利用无与伦比的计算资源，研究湍流从惯性范围到以哨声波为特征的短波长范围的演变。 拟议的活动将加强研究基础设施。该项目将使用包括基于细胞的技术在内的尖端模拟技术，以推动完全粒子模拟（PIC）的极限。这些进展将为等离子体物理学界过渡到使用基于细胞的计算机进行模拟的新技术铺平道路。这些代码将通过免费的GNU通用公共许可证（v2）通过Google Code项目提供。该网站将不仅包括代码和示例输入文件，而且还包括（i）代码及其方法的简要说明，（ii）关于如何使用代码的维基百科风格手册，其中详细说明了如何设置问题并运行它，以及（iii）用于读取和绘制结果的示例图形文件。

The is a jointly funded project between the National Science Foundation and the Department of Energy.The multi-scale nature of turbulence poses a severe computational challenge for kinetic simulations. This project will aggressively push the limits of full particle simulations of turbulence in plasmas. A recently developed parallel, implicit, full particle kinetic simulation code will be used to perform simulations that will show how long wavelength modes non-linearly cascade to shorter wavelengths. The focus of this project is on the least understood and most controversial aspect of turbulence, namely the transition of long wavelength turbulence to short, kinetic scales and the properties of turbulence at wavelengths shorter than this transition. The goal is to address the physics of how the long wavelength modes cascade from the inertial range to the short wavelength range in the solar wind. The inertial range is fairly well described by single-fluid, magnetohydrodynamic (MHD) models, which have proved to be a very effective approach to describing long-wavelength fluctuations in the solar wind. Observations have shown that the wavenumber at the spectral break, where the inertial range ends, corresponds to the ion inertial length. The ion inertial length marks the breakdown of single fluid theory and kinetic effects become dominant in this regime. As a result, the short wavelength regime has remained the least understood component of solar wind turbulence and many basic questions such as the physics controlling the breakpoint are not completely understood. The proper treatment of the so-called ?dissipation range? requires a fully kinetic treatment.Turbulence is ubiquitous in plasmas, occurring in a variety of settings such as interstellar medium, accretion disks, planetary magnetospheres, and the solar wind. The main theoretical focus has been on long wavelength turbulence where MHD is a good approximation. This project will use a tandem of wave turbulence theory and state-of-the-art full particle kinetic simulations with unmatched computational resources to investigate the evolution of turbulence from the inertial range down to the short wavelength regime characterized by whistler waves. The proposed activity will enhance the infrastructure for research. The project will use cutting edge simulations including cell-based technology to push the limits of full particle-in-cell (PIC) simulations. These advances will pave the way for the plasma physics community to transition to new techniques for simulations using cell-based computers. The codes will be made available through a free GNU General Public License (v2), via the Google Code project. The web site will include not only the code and sample input files, but it also include (i) a brief description of the code and its methods, (ii) a wikipedia-style manual on how to use the code with an extensive description on how to set up a problem and run it, and (iii) sample graphics files to read and plot the results.