CAREER: Laboratory studies of large amplitude Alfven waves

阿尔芬波是磁化等离子体的基本低频正常模式。阿尔芬波在实验室等离子体（如托卡马克）和近地空间等离子体（如太阳风和地球磁层）中无处不在。阿尔芬波的非线性物理在许多自然过程中起着中心作用。从弱湍流的观点来看，阿尔芬波之间的相互作用是磁湍流中能量级联的基础。磁层中的场向结构（如密度空腔）被认为是由非线性阿尔芬波引起的重力动势或加热产生的。由大振幅阿尔芬波引起的电子加速被认为在空间等离子体中是重要的，并且可以解释极光电子加速。虽然这些波的线性特性已经被详细探讨，但与大振幅阿尔芬波相关的非线性效应尚未在实验室实验中得到阐明。在这个职业规划中提出的研究将集中在实验室实验中与大振幅阿尔芬波传播相关的现象。这些现象包括：(1)电子加热和加速；(2)场向密度结构的形成；(3)Alfven波与自生丝状结构的相互作用；(4)剪切Alfven波之间的热波相互作用，包括受激参数衰变。在加州大学洛杉矶分校的大型等离子体装置（LAPD）中，利用谐振腔或简单的环形天线产生了大振幅剪切Alfven波。在最大振幅处，观察到强烈的电子加热，定位于与波相关的电流通道。此外，电子加速的证据在朗缪尔探针测量中被观察到。将研究这种加热和粒子加速的性质，重点是对波频率的依赖(!/！C,i)，垂直结构，和背景等离子体参数。随着加热，密度变化在朗缪尔探针和干涉仪测量中都被观察到。将研究产生密度变化的质动势、加热或其他现象（如电离）的作用。本文还将探讨Alfven波与自生场向温度和密度结构之间的相互作用。先前对LAPD中大振幅Alfven波的研究主要集中在热波相互作用上，特别是共传播调制相互作用。这些热波研究将得到扩展，重点是反传播相互作用，包括剪切阿尔芬波到离子声波的受激参数衰减。拟议的职业规划的教育发展方面集中在两个主要任务上：(1)针对洛杉矶一些最弱势高中的教师和学生的高中推广计划；(2)对加州大学洛杉矶分校用于教学实验室等离子体物理的设施进行重大升级。高中外展计划将包括每年为两名教师举办的夏季研讨会，旨在为发展基于探究的物理学习方法提供资源和帮助。等离子实验课程的设施和课程将会升级，寻求课程的现代化，并通过吸引对物理学和其他学科的许多子领域感兴趣的学生来扩大课程的影响。

The Alfven wave is the fundamental low frequency normal mode of a magnetized plasma. Alfven waves are ubiquitous in laboratory plasmas such as the tokamak and near-earth space plasmas such as the solar wind and the earths magnetosphere. The nonlinear physics of Alfven waves plays a central role in many natural processes. From a weak turbulence point of view, interactions between Alfven waves are fundamental to the cascade of energy in magnetic turbulence. Field-aligned structures (e.g. density cavities) in the magnetosphere are thought to be created by ponderomotive forces or heating due to nonlinear Alfven waves. Electron acceleration by large amplitude Alfven waves is thought to be important in space plasmas, and may explain auroral electron acceleration. While the linear characteristics of these waves have been explored in detail, nonlinear effects associated with large amplitude Alfven waves have not been elucidated in laboratory experiments. The research proposed in this career plan will focus on phenomena associated with the propagation of large amplitude Alfven waves in a laboratory experiment. These phenomena include: (1) electron heating and acceleration, (2) formation of field-aligned density structure, (3) interactionof Alfven waves with self-generated filamentary structures and (4) beat-wave interactions between shear Alfven waves, including stimulated parametric decay.Large amplitude shear Alfven waves have been generated in the Large Plasma Device(LAPD) at UCLA using either a resonant cavity or simple loop antennas. At the largest amplitudes, strong electron heating is observed, localized to current channels associated with the wave. In addition, evidence for electron acceleration is observed in Langmuir probe measurements. The nature of this heating and particle acceleration will be studied, focusing on dependence on the wave frequency (!/!c,i), perpendicular structure, and background plasma parameters. Along with heating, density modifications are observed both in Langmuir probe and interferometer measurements. The role of ponderomotive forces, heating or other phenomena (e.g. ionization) in creating the density modifications will be investigated. The interaction between the Alfven waves and the self-generated field-aligned temperature and density structures will also be explored. Previous studies of large amplitude Alfven waves in LAPD have focused on beat-wave interactions, in particular a co-propagating modulational interaction. These beat-wave studies will be extended, focusing on counter-propagating interactions including stimulated parametric decay of shear Alfven waves into ion acoustic waves.The educational development aspects of the proposed career plan are focused on two primary tasks: (1) a high school outreach program targeted at teachers and students at some of the most disadvantaged high schools in Los Angeles and (2) a significant upgrade of the facilities used for teaching laboratory plasma physics at UCLA. The high school outreach program will include a summer workshop for two teachers a year, targeted at providing resources for and assistance in developing inquiry-based approaches to learning physics. The plasma laboratory course facilities and curriculum will be upgraded, seeking to modernize the course and broaden the impact of the course by attracting students interested in many subfields of physics and other disciplines.