Linear signatures in nonlinear gyrokinetics: interpreting turbulence with pseudospectra
Linear signatures in nonlinear gyrokinetics: interpreting turbulence with pseudospectra
复制标题
非线性回旋运动学中的线性特征：用伪谱解释湍流
DOI：
10.1088/1367-2630/18/7/075018
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发表时间：
2016
影响因子：
3.3
通讯作者：
M. Pueschel
中科院分区：
文献类型：
--
作者：
D. Hatch;F. Jenko;A. Navarro;V. Bratanov;P. Terry;M. Pueschel
等离子体湍流的一个显著特征是，它倾向于在强烈湍流状态下保留基本线性本征模的特征--这一特性可以用来仅使用线性信息来预测湍流的各个方面。在这一背景下，这项工作通过三个透镜--线性本征值谱、伪谱和奇异值分解(SVD)来研究梯度驱动的陀螺动力学等离子体湍流。我们研究了一个简化的陀螺动力学模型，它的线性本征值谱包括离子温度梯度驱动模、稳定漂移波和表示朗道阻尼的动力学模。我们的目标是表征这些熟悉的成分在非线性湍流状态中表现出来的方式(如果有的话)。这一追求得到了伪谱的帮助，伪谱通过表征线性算子对扰动的反应，提供了对线性算子更细微的看法。我们介绍了一种新的技术，利用伪谱的概念将奇异值分解提取的非线性演化相空间结构与线性算子联系起来。利用这一技术，我们识别出不仅与最不稳定本征模有关的非线性结构，而且还与非线性激发的次优势模有关。出现的总体图景是这样一个系统，在该系统中，线性物理的特征在湍流中持续存在，尽管以线性本征值方法无法完全解释的方式；非模式处理对于理解湍流的关键特征是必要的。
A notable feature of plasma turbulence is its propensity to retain features of the underlying linear eigenmodes in a strongly turbulent state—a property that can be exploited to predict various aspects of the turbulence using only linear information. In this context, this work examines gradient-driven gyrokinetic plasma turbulence through three lenses—linear eigenvalue spectra, pseudospectra, and singular value decomposition (SVD). We study a reduced gyrokinetic model whose linear eigenvalue spectra include ion temperature gradient driven modes, stable drift waves, and kinetic modes representing Landau damping. The goal is to characterize in which ways, if any, these familiar ingredients are manifest in the nonlinear turbulent state. This pursuit is aided by the use of pseudospectra, which provide a more nuanced view of the linear operator by characterizing its response to perturbations. We introduce a new technique whereby the nonlinearly evolved phase space structures extracted with SVD are linked to the linear operator using concepts motivated by pseudospectra. Using this technique, we identify nonlinear structures that have connections to not only the most unstable eigenmode but also subdominant modes that are nonlinearly excited. The general picture that emerges is a system in which signatures of the linear physics persist in the turbulence, albeit in ways that cannot be fully explained by the linear eigenvalue approach; a non-modal treatment is necessary to understand key features of the turbulence.
影响因子：
8.6
作者：
Barnes, M.;Parra, F. I.;Schekochihin, A. A.
通讯作者：
Schekochihin, A. A.