Laboratory Studies of the Magneto-Rotational Instability in Plasma

等离子体磁旋转不稳定性的实验室研究

• 批准号: 1518115
• 负责人: Cary Forest
• 金额: $ 41.26万
• 依托单位: University of Wisconsin-Madison
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-09-01 至 2019-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1518115&HistoricalAwards=false
• 关键词: Laboratory; Studies; Magneto; Rotational; Instability

This exciting project will lead to the first ever experimental demonstration of an effect long studied theoretically and numerically, which is crucial for understanding astrophysical systems powered by material flowing through a complex flattened structure and onto a central compact object. Accretion through a swirling disk concerns many astronomical phenomena on scales from distant quasars to nearby star systems. This novel and innovative experiment will also provide many educational opportunities.This project will be the first ever study of the magnetorotational instability (MRI) in a plasma experiment. Although the MRI is a major component of current explanations of accretion, studies have so far been theoretical, numerical, and with a limited set of liquid metal experiments. This study will use the Plasma Couette Experiment (PCX), which uses a new way both to confine and to stir hot, fast-flowing plasmas under the right conditions to observe the MRI, which explains how matter in an accretion disk transports angular momentum outward, and thus falls into the central object. A weak magnetic field from somewhere outside the disk leads to a quickly growing magnetic instability that itself leads to turbulence, which enhances the effective viscosity. Numerical simulations have shown an effect of exactly the required sort, and recent experiments with liquid metals have studied the onset conditions. However, plasma experiments have several key advantages over liquid metals: (1) plasmas are the state of matter that makes up most naturally occurring accretion disks; (2) plasmas can be configured with more appropriate fluid parameters; and (3) plasma viscosity can be varied independently of the conductivity, mimicking conditions both in the outer regions of most disks, and in the regime near the center. The PCX is now being upgraded to stronger confining magnets, higher input power, and larger plasma volume. These improvements should more effectively show the onset of the MRI, and even multi-mode MRI turbulence. This award will support (1) a search for signs of the instability and its comparison with numerical simulations; (2) measurement of the effective momentum transport to compare with theoretical predictions; and (3) identification of physics effects which are plasma specific and beyond the standard model.Among the outreach activities, a basic plasma experiment will be added to the undergraduate physics capstone lab class. The popular "Exotic Plasmas of the Universe" trading cards will be updated, and plasma astrophysics themes will be part of the university's "Wonders of Physics" show.

这一激动人心的项目将首次对理论和数值上长期研究的效应进行实验证明，这对于理解由流过复杂扁平结构并流向中心致密物体的物质提供动力的天体物理系统至关重要。通过旋转盘的吸积涉及从遥远的类星体到附近恒星系统的许多天文现象。这个新颖创新的实验也将提供许多教育机会。该项目将是首次在等离子体实验中研究磁旋转不稳定性（MRI）。虽然核磁共振成像是当前吸积解释的主要组成部分，但迄今为止的研究都是理论性的，数值的，以及有限的液态金属实验。这项研究将使用等离子体库埃特实验（PCX），它使用一种新的方法来限制和搅拌热的，在适当条件下快速流动的等离子体来观察MRI，这解释了吸积盘中的物质如何向外传输角动量，从而落入中心物体。来自圆盘外某处的弱磁场会导致快速增长的磁不稳定性，而磁不稳定性本身会导致湍流，从而增强有效粘度。数值模拟显示了所需要的那种效应，最近用液态金属进行的实验研究了开始条件。然而，等离子体实验与液态金属相比有几个关键的优势：(1)等离子体是构成大多数自然发生的吸积盘的物质状态；(2)等离子体可以配置更合适的流体参数；(3)等离子体粘度可以独立于电导率而变化，模拟了大多数圆盘外部区域和靠近中心区域的情况。PCX现在正在升级为更强的限制磁铁，更高的输入功率和更大的等离子体体积。这些改进将更有效地显示MRI的开始，甚至多模MRI湍流。该奖项将支持(1)寻找不稳定性的迹象并与数值模拟进行比较；(2)测量有效动量输运，与理论预测进行比较；(3)识别等离子体特有的和超出标准模型的物理效应。在拓展活动中，将在本科物理顶点实验课中增加一门基础等离子体实验。流行的“宇宙的奇异等离子体”交易卡将被更新，等离子体天体物理学主题将成为该大学“物理奇观”展览的一部分。