Relaxation, Intermittency and Dissipation in a Collisionless Plasma

这个项目的目的是提高对等离子体中湍流的基础科学的理解。湍流是流体或气体的复杂动力学，由跨越空间和时间的广泛尺度的非线性作用力产生。湍流产生了许多重要的影响，例如热量和能量的混合和快速传输；这影响了地球上的流体以及空间和太阳上的导电气体或等离子体。湍流在空间中通常是不均匀的--它往往会迅速自组织成形状不规则的“细胞”。在这些细胞内，胞浆通常是静止的，但细胞之间的薄边界非常活跃，有时会产生爆炸性的结果。在这个项目中，研究了导致这种自组织和细胞边界形成的过程。这项工作将支持一名博士后研究人员，并增进对许多观测到的空间等离子体现象的理解，包括太阳耀斑和太阳风中湍流的变异性，从而促进空间气象的科学基础。松弛过程、湍流级联和耗散机制都是等离子体物理及其应用的重要研究领域。然而，这些通常是单独研究的。这个项目提出的基本假设是，间歇性级联的性质和它所导致的耗散，强烈地受到起源于包含能量的尺度的特定松弛过程的影响。尤其是局域弛豫导致了空间胞化，与之相关的空间不均匀控制了相干结构的形成，而相干结构的耗散有望大大增强。这一点已经在磁流体力学等流体等离子体模型中进行了研究，尽管还不完全，但在本项目中要考虑的全动力学等离子体模型中却知之甚少。建立这样的基本联系，即参数随着松弛模式的不同而变化，将促进对基本等离子体物理的理解。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The purpose of this project is to improve understanding of the basic science of turbulence in a plasma. Turbulence is the complex dynamics of a fluid or gas resulting from nonlinear forces that span a wide range of scales in space and time. Many important effects emerge from turbulence, such as mixing and rapid transport of heat and energy; this influences terrestrial fluids as well as electrically conducting gases, or plasmas, in space and on the sun. Turbulence is usually not uniform in space – it tends to quickly self-organize into irregularly shaped "cells." Inside these cells the plasma is typically quiescent, but the thin boundaries between cells are highly active with sometimes explosive results. Processes causing this self-organization and formation of the cell boundaries are studied in this project. This effort will support a post-doctoral researcher and advance understanding of many observed space plasma phenomena, including solar flares and variability of turbulence in the solar wind, thus contributing to the science underlying space weather.Relaxation processes, turbulence cascade and dissipation mechanisms are each an important area of study in plasma physics and its applications. However these are most frequently studied separately. The fundamental hypothesis advanced in this project is that the nature of the intermittent cascade, and the dissipation that it leads to, are strongly influenced by specific relaxation processes that originate at the energy containing scales. In particular, local relaxation leads to spatial cellularization, and the associated spatial nonuniformity controls the formation of coherent structures, where dissipation is expected to be greatly enhanced. This has been studied, although incompletely, in fluid plasma models such as magnetohydrodynamics, but is poorly understood in fully kinetic plasma models to be considered within this project. Establishing such fundamental connections as parameters are changed to vary among modes of relaxation will advance understanding of fundamental plasma physics.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.