Basic Laboratory Experiments of Plasma Turbulence: Alfven Wave Collisions

磁化等离子体中湍流的动力学和演化是等离子体科学的一个基本问题。对这一基本等离子体物理过程的基本理解的提高将影响等离子体湍流发挥重要作用的许多研究领域和学科：在天体物理学中，从星系团到黑洞周围的吸积盘，再到银河系湍流星际介质中恒星的诞生地的等离子体；在空间等离子体，如日冕、太阳风和地球的磁层；在磁约束聚变项目的实验室等离子体中。因此，跨领域的研究可以提高我们对等离子体湍流的认识，有可能影响这一非常广泛的研究前沿。阿尔芬波在磁化等离子体湍流动力学中起着核心作用。理论研究表明，构成湍流的非线性相互作用只发生在沿磁场方向相反的阿尔芬波之间。因此，正是这些相互作用，通常被简单地称为反向传播的阿尔芬波之间的“碰撞”，构成了等离子体湍流的基本组成部分。今天关于各向异性磁化等离子体湍流的现代理论是基于这种反传播阿尔芬波碰撞的直观概念发展起来的。为了更好地理解这些阿尔芬波碰撞的非线性动力学，并测试支撑等离子体湍流现代理论模型的核心概念，对阿尔芬波碰撞的观测或实验测量是必不可少的。该项目旨在通过在加州大学洛杉矶分校的大型等离子体装置（LAPD）上进行实验室实验来测量Alfven波碰撞的非线性演化，并使用天体物理回旋动力学代码AstroGK对Alfven波碰撞的非线性动力学模拟提供理论指导，从而提高我们对等离子体湍流基本组成部分的理解。

The dynamics and evolution of turbulence in a magnetized plasma is a fundamental issue in plasma science. An improved basic understanding of this fundamental plasma physics process will impact many research areas and disciplines in which plasma turbulence plays an important role: in astrophysical plasmas from clusters of galaxies to accretion disks around black holes to the birthplace of stars in the turbulent interstellar medium of our Galaxy; in space plasmas such as the solar corona, solar wind, and Earth's magnetosphere; and in the laboratory plasmas of the magnetic confinement fusion program. Cross-cutting studies to advance our knowledge of plasma turbulence, therefore, have the potential to impact this very wide range of research frontiers.Alfven waves play a central role in the dynamics of magnetized plasma turbulence. Theoretical studies suggest that the nonlinear interactions that constitute the turbulence occur only between Alfven waves traveling in opposite directions along the magnetic field. Therefore it is these interactions, often referred to simply as "collisions" between counter-propagating Alfven waves, that form the fundamental building blocks of plasma turbulence. Today's modern theories of anisotropic magnetized plasma turbulence have been developed based on this intuitive concept of counter-propagating Alfven wave collisions. To better understand the nonlinear dynamics of these Alfven wave collisions---and to test this central concept underpinning modern theoretical models of plasma turbulence---observational or experimental measurements of Alfven wave collisions are essential. This project seeks to improve our understanding of the fundamental building blocks of plasma turbulence by performing laboratory experiments on the Large Plasma Device (LAPD) at UCLA to measure the nonlinear evolution of Alfven wave collisions, with theoretical guidance provided by nonlinear kinetic simulations of Alfven wave collisions using the Astrophysical Gyrokinetics code, AstroGK.