Transport Properties, Pattern Dynamics and Self-Organized States in Magnetized Plasmas

磁化等离子体存在于各种空间和天体物理环境中，在用于核聚变的磁约束装置以及其他技术上重要的装置中发挥着重要作用。等离子体在密度、温度和电流等方面的空间不均匀性会驱动小尺度的不稳定波，这些波将非线性饱和并导致涉及多个自由度的准平稳湍流状态。这些湍流起伏可以诱导粒子、能量和动量输运，通常称为“异常输运”，以区别于等离子体带电粒子之间的经典库仑碰撞产生的碰撞输运。在异常输运中，输运过程涉及不同的机制，从扩散到平流以及湍流或混沌运动下的混合。近年来，G. Haller提出了一个研究复杂流体输运过程的新概念，称为拉格朗日相干结构（Lagrangian Coherent structure， LCS），它自然地构成了输运动力学的框架。LCS可以将流域划分为宏观区域，在宏观区域内会发生快速混合现象。在LCS的有限时间跨度内，宏观区域不交换流体元素，因此可能充当运输障碍。LCS概念具有广泛的适用性，已开发的分析技术已用于海洋表面的污染物输送，浮游生物繁殖，血液流动，太阳光球流动和大气数据集分析。它直到最近才被引入等离子体物理学，该提案的主要目标之一是充分表征磁化等离子体中的LCS，其中输运是由带电粒子在交叉电场和磁场以及沿规则或随机限制磁场的组合漂移引起的。在这项工作中，我们提出了研究拉格朗日相干结构在两个磁化等离子体系统在三维圆柱形几何。第一个由几个相互作用的磁通绳组成，第二个是一个有多个磁化热丝靠近的结构。这些系统将首先使用具有适当边界条件的回旋动力学细胞内粒子模拟进行建模，以便与线性等离子体装置中的测量结果进行比较。LCS的分析工具将应用于模拟数据，并与大型线性等离子体装置的实验结果进行比较。该项目的一个主要成果将是首次详细描述磁化等离子体中的LCS，其中输运源于ExB漂移和磁场的随机化。

Magnetized plasmas are present in a variety of space and astrophysical environments and play an important role in magnetic confinement devices for fusion as well as other technologically important devices. Plasmas are generally far from equilibrium and spatial inhomogeneities in the density, temperature and current can drive small-scale unstable waves that will saturate nonlinearly and lead to a quasi-stationary turbulent state involving many degrees of freedom. These turbulent fluctuations can induce particle, energy and momentum transport which is generally termed "anomalous transport" to distinguish it from collisional transport that arises from classical Coulombic collisions among the plasma charged particle species. In anomalous transport there are different mechanisms involved in the transport processes ranging from diffusion to advection and mixing in the case of turbulent or chaotic motions. Recently a new concept in the study of transport processes in complex fluid flows has been introduced by G. Haller, termed Lagrangian Coherent Structures (LCS) and naturally form a skeleton of the transport dynamics. The LCS can separate the flow domain into macro-regions inside which fast mixing phenomena will take place. Over the finite time span of the LCS macro-regions do not exchange fluid elements and thus may act as transport barriers. The LCS concept has wide applicability and the analysis techniques that have been developed were used in pollutant transport on ocean surfaces, spreading of plankton blooms, blood flow, solar photospheric flows and atmospheric dataset analysis. It has only recently been introduced into plasma physics and one of the main objectives of the proposal is to fully characterize the LCS in magnetized plasmas where transport arises from a combination of charged particle drifts in crossed electric and magnetic fields and along confining magnetic field which are regular or stochastic. In this work we propose to investigate Lagrangian Coherent Structures in two magnetized plasma systems in 3D cylindrical geometry. The first consists of several mutually interacting magnetic flux ropes and the second is a configuration with multiple magnetized thermal filaments in close proximity. These systems will be first be modeled using gyrokinetic particle-in-cell simulations with proper boundary conditions so that they can be compared with measurements in a linear plasma device. The tools for analysis of LCS will be applied to the simulation data and compared to results from experiments in a large linear plasma device. A major outcome of this project will be the first detailed characterization of the LCS in magnetized plasma where transport arises from ExB drifts and stochastization of the magnetic field.