Laboratory Studies of the Magneto-Rotational Instability in a Plasma

AST-0808095 Forest该项目将研究磁旋转不稳定性（MRI），使用新构造的等离子体库埃特流装置进行首次实验，该装置使用新颖的几何形状来限制和搅拌热等离子体。 吸积是几乎所有天体形成的基本过程，但很长一段时间都不清楚是什么导致盘物质失去轨道能量，是什么向外传输角动量并使盘物质落在中心物体上。 目前的工作假设是，弱磁场导致快速增长的磁不稳定性，使磁盘湍流和极大地增加有效粘度，这是由数值模拟支持。 最近令人兴奋的实验使用液体金属来研究磁共振成像，但等离子体实验允许更大的磁雷诺数和粘度的变化独立于电导率，使用最有可能发生在自然吸积的物质状态，调查从弱到强磁化的过渡，只有适度的场强，并使用等离子体物理学中发展良好的测量技术。 这样的实验从来没有进行过，但从现有的多偶极子约束实验的简单外推表明，这是可行的。 这项工作将表征具有静电搅拌的环形尖点等离子体的参数，寻找MRI的迹象以与理论进行比较，并确定超出标准磁流体动力学模型的等离子体特定效应。研究的中心部分包括对本科生和研究生的培训和指导，他们参与了该项目的各个方面，并将定期被派往科学会议上介绍他们的成果。 外联活动将包括公开讲座和新闻稿。

AST-0808095ForestThis project will study the MagnetoRotational Instability (MRI), carrying out the first-ever experiments with a newly constructed plasma couette flow device which uses a novel geometry to confine and stir a hot plasma. Accretion is a fundamental process by which virtually all astrophysical bodies form, but for a long time it was unclear what causes the disk matter to lose orbital energy, what it is that transports angular momentum outward and makes the disk material fall onto the central object. The current working hypothesis is that a weak magnetic field leads to a quickly growing magnetic instability, rendering the disk turbulent and tremendously increasing the effective viscosity, and this is supported by numerical simulation. Recent exciting experiments use liquid metals to study the MRI, but a plasma experiment allows larger magnetic Reynolds number and the variation of viscosity independent of conductivity, uses the state of matter most likely to occur in natural accretion, investigates the transition from weakly to strongly magnetized with only modest field strengths, and uses measurement techniques well-developed in plasma physics. Such an experiment has never been performed, but simple extrapolations from existing multi-dipole confinement experiments show it is feasible. This work will characterize the parameters of the ring cusp plasma with electrostatic stirring, search for signs of the MRI to compare to theory, and identify plasma-specific effects beyond the standard magneto-hydro-dynamical model.A central part of research includes the training and mentoring of undergraduate and graduate students, who are involved in all aspects of the project and will be sent regularly to scientific meetings to present their results. Outreach activities will include public lectures and press releases.