Laboratory Studies of the Magneto-Rotational Instability in Plasma

这个令人兴奋的项目将导致有史以来第一次对一种从理论和数值上研究已久的效应进行实验演示，这种效应对于理解天体物理系统至关重要，该系统由物质通过复杂的扁平结构流向中心致密物体。通过旋转圆盘的吸积涉及从遥远的类星体到附近的恒星系统的许多天文现象。这一新颖和创新的实验也将提供许多教育机会。该项目将是有史以来第一次在等离子体实验中研究磁致旋转不稳定性(MRI)。尽管核磁共振是当前吸积解释的主要组成部分，但到目前为止，研究都是理论的、数值的，而且只有一套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)，它使用了一种新的方法，在合适的条件下限制和搅拌热的、快速流动的等离子体来观察核磁共振，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。来自磁盘外部某处的弱磁场会导致快速增长的磁不稳定性，而磁不稳定性本身又会导致湍流，从而增强有效粘度。数值模拟显示了所需类型的影响，最近用液态金属进行的实验研究了起效条件。然而，与液态金属相比，等离子体实验有几个关键的优点：(1)等离子体是组成最自然形成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导电性而变化，模拟大多数盘外部区域和中心附近的条件。PCX现在正在升级为更强大的约束磁铁、更高的输入功率和更大的等离子体体积。这些改善应该更有效地显示MRI的开始，甚至是多模式MRI的湍流。该奖项将支持(1)寻找不稳定迹象及其与数值模拟的比较；(2)测量有效动量传输以与理论预测相比较；以及(3)识别特定于等离子体并超出标准模型的物理效应。在外展活动中，将在本科生物理顶峰实验室课程中增加一个基本的等离子体实验。广受欢迎的《宇宙异域等离子体》交易卡片将更新，等离子体天体物理学主题将成为该大学《物理奇观》节目的一部分。

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.