MRI: Development of a Plasma Dynamo Facility for Experimental Investigations of Fundamental Processes in Plasma Astrophysics

MRI：开发等离子体发电机设施，用于等离子体天体物理学基本过程的实验研究

• 批准号: 0923258
• 负责人: Cary Forest
• 金额: $ 175.72万
• 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: 2009
• 资助国家: 美国
• 起止时间: 2009-09-01 至 2013-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0923258&HistoricalAwards=false
• 关键词: MRI; Development; Plasma; Dynamo; Facility

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). With this award, a Plasma Dynamo Facility for investigating self-generation of magnetic fields and related processes in a large, weakly magnetized, fast flowing, and hot (conducting) plasma will be built . When completed, a major new, flexible plasma device and associated infrastructure will become available for a new generation of graduate students and postdoctoral researchers to carry out experiments in a previously uninvestigated plasma regime, a regime asymptotically similar to many astrophysical plasmas. Such laboratory plasmas have never before been studied (most hot, fast flowing plasma experiments have been magnetized), but recent advances in permanent magnet technology, plasma source development and new scheme for driving flow now make it possible. The device at the core of the facility will be a 3 meter diameter spherical vacuum vessel that uses an array of powerful permanent magnets on the vessel wall to provide plasma confinement. The magnets will be arranged in a multipole configuration that has a magnetic field localized to the plasma edge and provides a spherical, 1.3 m radius, field-free plasma volume. Recently developed large area Lanthanum Hexaboride plasma sources (provided by UCLA) will used for ionizing and heating the plasma; this will generate a steady-state, hot (10-30 eV) plasma. To stir the plasma, electrostatic electrodes, together with the permanent magnet array will be used to impart torque on the plasma in the magnetized edge region and viscously couple momentum from the edge plasma to the unmagnetized core. Numerical modeling has been used to show that such stirring can provide a variety of laminar and turbulent flows necessary for generating magnetohydrodynamic turbulence and for producing self-exciting dynamos. As part of this development proposal, the plasma control, data acquisition, and a core set of diagnostics will be developed. Finally, advanced plasma diagnostics will be applied, for the first time, to dynamo studies. The concept proposed here builds upon excitement in recent years of using liquid metals to study dynamos; un-magnetized liquid metals have been mechanically stirred and magnetic fields spontaneously created and observed. A plasma experiment has the potential to extend these studies to more astrophysically relevant parameters. The use of plasma, rather than liquid metals to study magnetic field generation will allow the magnetic Reynolds number (the dimensionless product of size x conductivity x speed that governs self-excitation of magnetic fields) to be more than a factor of 10 larger than in liquid metal experiments. It will also allow the viscosity to be varied independently of the conductivity: the magnetic Prandtl number (the ratio of the magnetic Reynolds number to the hydrodynamic Reynolds number) can be varied from the liquid metal regime (1) to the regime Pm 1 thought to be a critical parameter that governs the nature of many astrophysical situations since it governs the onset and nature of the turbulence.The device will be located in the Physics Department at the University of Wisconsin, and will be operated as a multi-investigator, multi-institutional facility. In addition to the large impact on the UW physics program, experimental investigations in this facility are likely to have strong national impact through connections to new astrophysics initiatives such as the Square Kilometer Array, where cosmic magnetism is one of four key science issues. The facility will be a major scientific infrastructure investment at the "intermediate scale" as has recently been recommended by the National Research Council's report Plasma 2010: Advancing Knowledge in the National Interest.

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。有了这个奖项，将建立一个等离子体发电机设施，用于研究大型、弱磁化、快速流动和热（导电）等离子体中磁场的自生和相关过程。完成后，一个新的、灵活的等离子体设备和相关的基础设施将为新一代的研究生和博士后研究人员提供，他们可以在以前未研究过的等离子体状态下进行实验，这一状态与许多天体物理等离子体渐近相似。这样的实验室等离子体以前从未被研究过（大多数热的、快速流动的等离子体实验都被磁化了），但最近永磁技术的进步、等离子体源的发展和驱动流动的新方案使它成为可能。该设施的核心装置将是一个直径3米的球形真空容器，在容器壁上使用一组强大的永磁体来提供等离子体约束。磁体将以多极结构排列，磁场定位于等离子体边缘，并提供球形，半径1.3 m，无场等离子体体积。最近开发的大面积六硼化镧等离子体源（UCLA提供）将用于电离和加热等离子体；这将产生一个稳定的，热的（10-30 eV）等离子体。为了搅拌等离子体，静电电极将与永磁阵列一起在磁化边缘区域对等离子体施加扭矩，并将动量从边缘等离子体粘耦合到未磁化的核心。数值模拟表明，这种搅拌可以提供产生磁流体动力学湍流和产生自激发电机所必需的各种层流和湍流。作为该开发计划的一部分，将开发等离子体控制、数据采集和一套核心诊断方法。最后，先进的等离子体诊断将首次应用于发电机研究。这里提出的概念是基于近年来使用液态金属研究发电机的兴奋；未磁化的液态金属被机械搅拌，磁场自发产生并被观察到。等离子体实验有可能将这些研究扩展到更多与天体物理相关的参数。使用等离子体而不是液态金属来研究磁场的产生将允许磁雷诺数（尺寸x电导率x控制磁场自激的速度的无量纲积）比液态金属实验大10倍以上。它还允许粘度的变化独立于电导率：磁普朗特数（磁雷诺数与流体动力雷诺数之比）可以从液态金属状态(1)变化到状态Pm 1， Pm 1被认为是一个关键参数，它控制着许多天体物理情况的性质，因为它控制着湍流的开始和性质。该装置将位于威斯康星大学物理系，并将作为一个多研究者、多机构的设施来运作。除了对华盛顿大学物理项目的巨大影响外，该设施的实验调查可能会通过与新的天体物理学计划（如平方公里阵列）的联系产生强大的国家影响，其中宇宙磁学是四个关键科学问题之一。正如美国国家研究委员会最近发布的报告《等离子体2010：促进国家利益的知识发展》所建议的那样，该设施将是一项“中等规模”的重大科学基础设施投资。