Experimental Investigation of Reconnection in a Line-tied Plasma

线结等离子体中重联的实验研究

• 批准号: 0903900
• 负责人: Cary Forest
• 金额: $ 52.38万
• 依托单位: University of Wisconsin-Madison
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-08-01 至 2013-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0903900&HistoricalAwards=false
• 关键词: Experimental; Investigation; Reconnection; Line; tied

In this work, magnetic reconnection phenomena will be investigated in a line-tied pinch experiment. There is a long history of experimental studies in periodic, toroidal configurations which has built up an understanding of reconnection based on the existence of mode rational (or mode-resonant)surfaces where the parallel wave number k_|| vanishes. However, it is common in astrophysics to observe or infer reconnection in bounded systems with line-tying in which a vanishing k_ll is absent. Thus, there remain major, mostly uncharted questions of how reconnection occurs, how it differs from periodic reconnection, and what concepts will replace the k_ll identification with reconnection. It is a topic arguably of comparable scope to periodic reconnection, yet research in this area has been scarce.In this work, a diagnostic will be constructed for observing the large,localized current and resulting reconnection predicted to exist in the saturated phase of the line-tied kink instability. This will be carried out in two different magnetic equilibria. The first is a simple linear pinch in which instability has already been experimentally observed. The second will be in a zero net current equilibrium, one similar to the line-tied equilibria of flux tubes emerging from the solar corona and twisted by vortical motion of the flux tube footpoints. The experiments will be carried out in the Rotating Wall Machine (which also has a fusion science mission, supported by the DoE). The experiment is a linear screw pinch and uses electrostatic plasma guns for producing a current carrying column. Its primary mission is to investigate the stabilization of the resistive wall mode by moving metal walls. An internal kink instability has been observed to grow and saturate in the the experiment. Detailed measurements showed that an ideal,line-tied kink mode begins growing when the effective safety factor (which measures the field line twist) drops below 1 inside the plasma; the saturated state corresponds to a rotating helical equilibrium. In addition to the ideal mode, reconnection events were observed to periodically flatten the current profile and change the magnetic topology. The reconnection events strongly resemble the reconnection phenomena described in numerical simulations of a nearly identical geometry. Numerical simulations predict the existence of a large, localized current which gives rise to reconnection. These current sheets differ significantly from the current sheets predicted in toroidal experiments: their eigenfunctions have structure in the axial direction as well as in the radial direction. We propose to install a 2D array of magnetic probes on a 6 x 6 grid at the axial midpoint of the plasma column to discover whether this current sheet exists or not. We also propose to modify the plasma gun geometry such that the central gun injects current in the opposite direction to the surrounding 7 guns. This geometry more closely resembles the type of current profiles expected in the flux tubes emerging from the surface of the sun. The results will be compared to analytical theory and to a numerical model of the experiment implemented in the NIMROD code.This proposal was submitted to the NSF-DoE Partnership in Plasma Science and Engineering joint solicitation 08-589. This award is being funded jointly by the Divisions of Physics and Astronomical Sciences of the Mathematical and Physical Sciences Directorate.

在这项工作中，将在线条夹紧实验中研究磁重新连接现象。 在周期性的，环形配置中，实验研究的历史悠久，它基于模式有理（或模式共振）表面的存在建立了对重新连接的理解，其中并行波数k_ ||消失。然而，在天体物理学中，在没有线条键的界限系统中观察或推断重新连接，其中不存在消失的k_ll。因此，仍然存在重大的，主要是未知的问题，即重新连接的发生方式，与周期性重新连接的差异以及哪些概念将替换为重新连接的k_ll识别。 这可以说是一个与周期性重新连接相当的范围的话题，但是在这项工作中，该领域的研究却很少。在这项工作中，将构建一个诊断，用于观察大型的，局部的电流和结果的重新连接，预计将存在于线条绑定的截然纽带不稳定的饱和阶段。这将在两个不同的磁平衡中进行。第一个是简单的线性捏，其中已经观察到了不稳定。 第二个将处于零净电流平衡状态，一种类似于太阳能电晕出现的通量管的线平衡，并因通量管脚点的涡流运动而扭曲。 实验将在旋转壁机中进行（该实验也具有DOE支持的融合科学任务）。该实验是线性螺丝夹，并使用静电等离子体枪生产电流载体柱。它的主要任务是通过移动金属壁研究电阻壁模式的稳定。在实验中，已经观察到内部扭结不稳定能力生长和饱和。 详细的测量结果表明，当有效的安全系数（测量场线扭转）在等离子体内部1以下时，理想的线条绑定模式开始增长。饱和状态对应于旋转的螺旋平衡。 除了理想模式外，还观察到重新连接事件可以定期扁平当前轮廓并更改磁拓扑。 重新连接事件非常类似于在几乎相同几何形状的数值模拟中描述的重新连接现象。数值模拟预测了大型局部电流的存在，从而引起重新连接。 这些电流板与环形实验中预测的当前板有显着差异：它们的本征函数在轴向方向以及径向方向上具有结构。我们建议在等离子体柱的轴向中点的6 x 6网格上安装2D磁盘阵列，以发现此电流是否存在。我们还建议修改等离子枪的几何形状，以使中央枪将电流注入与周围7支枪相反的方向。这种几何形状更类似于从太阳表面出现的通量管中预期的电流轮廓的类型。结果将与分析理论进行比较，并将其在Nimrod代码中实现的实验的数值模型进行比较。该提案已提交给NSF-DOE合作伙伴关系等离子体科学与工程联合邀请08-589。该奖项由数学和物理科学局的物理学和天文科学的划分共同资助。