Gyrokinetic Simulation and Theory of Non-diffusive Transport and Chaotic Flows in Non-Equilibrium Magnetized Plasmas

非平衡磁化等离子体中非扩散输运和混沌流的回旋运动模拟与理论

• 批准号: RGPIN-2014-06521
• 负责人: Sydora, Richard
• 金额: $ 1.82万
• 依托单位: University of Alberta
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2017
• 资助国家: 加拿大
• 起止时间: 2017-01-01 至 2018-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=633187
• 关键词: Gyrokinetic; Simulation; Theory; Non; diffusive

The turbulent transport of heat, particles and momentum has an impact on a wide range of plasma phenomena ranging from laboratory magnetic and inertial confinement systems for fusion energy applications, to space weather and plasma astrophysics. A large number of advances in understanding plasma turbulence and transport have been made using analytic theory and numerical simulation, such as nonlinear mode interaction, energy cascades, secondary instabilities, turbulence spreading and the role of sheared flows. Another feature of transport in these systems that are driven from equilibrium, are large fluctuations that exhibit complex spatio-temporal patterns and coherent structures which induce large relative displacements. It is these displacements, and their temporal dependence, that cause departures from the classical, diffusive fluxes commonly described by a local Fick’s law. Instead the non-equilibrated systems evolve according to spatially non-local processes that can exhibit temporal memory and partial coherency. It is phenomena of this type, so-called non-diffusive transport, that is addressed in this proposal within the context of magnetized plasmas containing cross-field pressure and/or current density gradients. Recent theoretical work has suggested that non-diffusive transport properties are connected with chaotic dynamics and that fractional diffusion models are an appropriate theoretical description. Experimental evidence for non-diffusive transport has been documented in controlled temperature gradient experiments in a large linear plasma device (Large Plasma Device (LAPD), Gekelman et al., Rev. Sci. Instrum. 62, 2875 (1991)) and underlying microscopic structures have been found to have universal features related to deterministic chaos. New transport models based on these experimental findings have been formulated based on the fractional Fokker-Planck equation and chaotic advection. One of the main purposes of this investigation is to apply fully nonlinear kinetic simulations to resolve the major question as to whether the underlying microscopic dynamics is indeed chaotic or stochastic in nature and to compare with predictions based on fractional diffusion and chaotic advection. The approach taken is based on 3D gyrokinetic particle simulation in cylindrical geometry including electromagnetic effects applied to thermal transport in magnetized temperature filament experiments and related high current density channels that form magnetic structures know as flux ropes. These non-equilibrium plasma conditions (temperature filaments or current channels) can also form during antenna-launch of large amplitude low frequency plasma normal modes called shear Alfven waves. In all cases the nonlinear evolution of the self-consistent electromagnetic fields as well as the diffusion of charged particles and heat in the LAPD-type plasmas will be analyzed and compared with experiment and theoretical models. The global gyrokinetic simulations use realistic plasma parameters and can follow the evolution on transport time scales. Spatially localized synthetic probes will be developed to generate time series that can be compared to laboratory measurements and individual tagging of particles will allow us to explore microscopic diffusivity in detail. Numerical simulations such as these are key to development of a predictive capability for turbulent transport in a variety of plasma environments. The research experience for trainees, at the leading edge between theory/modeling and experiment, will provide valuable skills and preparation for work in both academic and industrial settings.

热、粒子和动量的湍流传输对从聚变能应用的实验室磁和惯性约束系统到空间天气和等离子体天体物理学等一系列广泛的等离子体现象产生影响。利用解析理论和数值模拟在理解等离子体湍流和输运方面取得了大量进展，如非线性模相互作用、能量级联、二次不稳定性、湍流扩展和剪切流的作用。在这些系统中，从平衡驱动的另一个特点是大的波动，表现出复杂的时空模式和相干结构，引起大的相对位移。正是这些位移，以及它们的时间依赖性，导致偏离经典的，扩散通量通常由当地菲克定律描述。相反，非平衡系统的演变，根据空间非本地的过程，可以表现出时间记忆和部分相干性。这是这种类型的现象，所谓的非扩散传输，这是解决在本提案的磁化等离子体的上下文中包含交叉场的压力和/或电流密度梯度。最近的理论工作表明，非扩散输运性质与混沌动力学和分数扩散模型是一个适当的理论描述。在大型线性等离子体装置（Large Plasma Device（LAPD），Gekelman等人，Rev. Sci.仪器。62，2875（1991））和潜在的微观结构已经被发现具有与确定性混沌相关的普遍特征。新的传输模型的基础上，这些实验结果已制定的分数福克-普朗克方程和混沌平流的基础上。这项调查的主要目的之一是应用完全非线性动力学模拟来解决的主要问题，是否根本的微观动力学确实是混沌或随机的性质，并与预测的基础上分数扩散和混沌平流比较。所采取的方法是基于三维回旋粒子模拟的圆柱形几何形状，包括电磁效应应用于热传输磁化温度灯丝实验和相关的高电流密度通道，形成磁结构称为通量绳。这些非平衡等离子体条件（温度细丝或电流通道）也可以在称为剪切阿尔芬波的大振幅低频等离子体正常模式的天线发射期间形成。在所有情况下，自洽电磁场的非线性演化以及带电粒子和热在LAPD型等离子体中的扩散将进行分析，并与实验和理论模型进行比较。全球gyrokinetic模拟使用现实的等离子体参数，可以遵循运输时间尺度上的演变。将开发空间定位的合成探针，以生成可以与实验室测量结果进行比较的时间序列，并对颗粒进行单独标记，使我们能够详细探索微观扩散率。诸如此类的数值模拟是发展各种等离子体环境中湍流输运预测能力的关键。学员的研究经验，在理论/建模和实验之间的前沿，将提供宝贵的技能和准备工作在学术和工业环境。