AGS-PRF: Instability of Sheetlike Structures in Alfvenic Turbulence

AGS-PRF：阿尔芬湍流中片状结构的不稳定性

• 批准号: 1624501
• 负责人: Alfred Mallet
• 金额: $ 8.6万
• 依托单位: Mallet Alfred
• 依托单位国家: 美国
• 项目类别: Fellowship Award
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-12-01 至 2018-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1624501&HistoricalAwards=false
• 关键词: AGS; PRF; Instability; Sheetlike; Structures

The solar wind provides the background of the space environment in which our planet exists. It is analogous, in some ways, to the jet streams in Earth's atmosphere, with flows that vary in speed and direction. This solar wind is the background on which space weather events occur. To correctly and accurately model space weather events and their impact on Earth, it is crucial to appropriately model the solar wind. The solar wind is turbulent in nature and this project aims to understand the intermittency of turbulence and certain instabilities that are expected to arise in the turbulent space plasmas such as those at the magnetopause and as a result of solar flares. Turbulent plasma is ubiquitous in astrophysics, so understanding plasma turbulence is important more generally, and not just in the setting of the solar wind - for example, in accretion disks, galaxy clusters, or in fusion devices on earth. This work is a unique combination of theoretical work to predict when the instabilities set in and numerical experiments to verify the prediction. This work is very timely and will form a basis for predictions for NASAs upcoming mission Solar Probe Plus. The PI of this Postdoctoral Research Fellowship plans to incorporate student participation through a research class at the University of New Hampshire as well as through the organization of a session at the Solar and Heliospheric INterplanetary Environment (SHINE) meeting. Typically, 25% of the attendees of this meeting are students. The project seeks to investigate the impacts of Kelvin-Helmoltz and plasmoid instabilities on Alfevnic turbulence. These instabilities become important once coherent structures in the turbulent plasma, the Elsasser sheets, reach a critical aspect ratio. The growth rates of these instabilities will be predicted and then confirmed with Reduced Magnetohydrodynamics simulations. The updated turbulence model will predict the local anisotropy of the turbulence, how the outer scale properties of the turbulence in the solar wind affect the statistical properties at small scales, and the type of intermittent structures that are produced. The dissipation in plasmas is observed to be closely linked to intermittent structures. This is an important current topic of interest to the community. The intermittent structures formed in the Alfvenic turbulence investigated here are strongly affected by the presence of the instabilities, and so this project is important for the understanding of the dissipation of turbulent energy.

太阳风提供了我们星球所处的空间环境的背景。在某些方面，它类似于地球大气层中的急流，其流动速度和方向各不相同。这种太阳风是空间天气事件发生的背景。为了正确和准确地模拟空间天气事件及其对地球的影响，对太阳风进行适当的模拟至关重要。太阳风本质上是湍流的，这个项目的目的是了解湍流的间歇性和预计将在湍流空间等离子体中出现的某些不稳定性，例如磁层顶等离子体和太阳耀斑的结果。湍流等离子体在天体物理学中无处不在，因此对等离子体湍流的理解更加重要，而不仅仅是在太阳风的背景下--例如，在吸积盘、星系团或地球上的聚变设备中。这项工作是一项独特的理论工作，用来预测何时出现不稳定性，并用数值实验来验证预测。这项工作非常及时，将为美国宇航局即将执行的太阳探测器Plus任务奠定基础。这一博士后研究奖学金的PI计划通过新汉普郡大学的一个研究班以及通过在太阳和日球层星际环境(SIRE)会议上组织一次会议来纳入学生的参与。通常，25%的与会者是学生。该项目旨在研究开尔文-赫尔莫茨不稳定性和等离子体不稳定对阿尔芬尼湍流的影响。一旦湍流等离子体中的相干结构，即Elsasser薄片达到临界纵横比，这些不稳定性就变得重要起来。这些不稳定性的增长速度将被预测，然后用简化的磁流体力学模拟来证实。更新的湍流模式将预测湍流的局部各向异性，太阳风中湍流的外部尺度特性如何影响小尺度上的统计特性，以及产生的间歇结构的类型。观察到等离子体中的耗散与间歇结构密切相关。这是当前社会感兴趣的一个重要话题。本文所研究的Alfvenic湍流中形成的间歇结构受不稳定的影响很大，因此这一项目对于理解湍流能量的耗散是很重要的。