Laboratory Studies of the Magneto-Rotational Instability in a Plasma

本项目首次开始研究等离子体实验中的磁致旋转不稳定性(MRI)。核磁共振在等离子体天体物理学中具有潜在的非常重要的作用，但它作为等离子体的替代品仅在理论上、数值上和在液态金属实验中进行了有限的研究。计划在这里进行的核磁共振研究将在等离子体库埃特实验(PCX)中进行，这是一种既限制又搅拌热等离子体的新型实验，具有观察核磁共振所需的参数。吸积是天体物理学中的一个基本过程，星际气体和等离子体在中心的点状吸积物体周围塌缩成旋转的圆盘。一定存在一种机制，使盘状物质失去轨道能量，向外输送角动量，并落入中心物体。根据理论和数值模拟，核磁共振成像是这一机制的主要候选者。这项研究建立在最近液态金属实验引起的兴奋的基础上，以调查磁共振成像的起始条件。与液态金属实验相比，等离子体实验有几个优点，包括最自然形成的吸积盘是由等离子体组成的，它允许更大和更真实的磁雷诺数，它允许独立调整粘度和电导率。PCX最近展示了高速、MRI稳定的Couette流，这项工作将1)寻找MHD不稳定的迹象，2)将结果与数值模拟进行比较，3)测量饱和不稳定的有效动量传输，4)确定特定于等离子体的、超出标准磁流体模型的物理效应。PCX实验将对所有流动驱动的MHD问题产生广泛的影响，并将继续促进实验室等离子体物理学家和天体物理之间的强大联系，由国家科学基金会磁自组织中心在实验室和天体物理等离子体。该奖项支持一名研究生进行提议的实验，部分支持技术人员和学生监督。

AST-1211937ForestThis project begins the first ever study of the magnetorotational instability (MRI) in a plasma experiment. The MRI is potentially very important in plasma astrophysics, but it has only been studied theoretically, numerically, and in a limited fashion in liquid metal experiments as a substitute for plasma. The MRI studies planned here will be carried out in the Plasma Couette Experiment (PCX), a novel experiment that both confines and stirs a hot plasma, with the parameters necessary for observing the MRI. Accretion is a fundamental process in astrophysics whereby interstellar gas and plasma collapse into rotating disks around a central, point-like accreting object. There must be a mechanism that causes disk matter to lose orbital energy, transport angular momentum outward, and fall into the central object. The MRI is a leading candidate for this mechanism, based on theory and numerical simulations. This study builds on the recent excitement caused by liquid metal experiments to investigate the onset conditions for the MRI. A plasma experiment has several advantages over a liquid metal experiment, including that most naturally occurring accretion disks are made up of plasmas, that it allows larger and more realistic magnetic Reynolds numbers, and that it permits independent adjustment of the viscosity and the conductivity. The PCX has recently demonstrated high speed, MRI-stable Couette flows, and this work will 1) search for signs of the MHD instability, 2) compare results with numerical simulations; 3) measure the effective momentum transport of the saturated instability; and 4) identify physical effects which are plasma specific and beyond the standard magnetohydrodynamics model.The PCX experiments will have broad impact on all flow-driven MHD problems and will continue a strong connection between laboratory plasma physicists and astrophysics facilitated by the NSF Center for Magnetic Self-Organization in Laboratory and Astrophysical Plasmas. This award supports a single graduate student to carry out the proposed experiments, with partial support for technical staff and student supervision.