Papadopoulos Aristeides D, Anderson Johan, Kim Eun-Jin, Mavridis Michail, Isliker Heinz
School of Electrical and Computer Engineering, National Technical University of Athens, 157 80 Athens, Greece.
Department of Space, Earth and Environment, Chalmers University of Technology, SE-412 96 Göteborg, Sweden.
Entropy (Basel). 2023 Jun 15;25(6):942. doi: 10.3390/e25060942.
A geometrical method for assessing stochastic processes in plasma turbulence is investigated in this study. The thermodynamic length methodology allows using a Riemannian metric on the phase space; thus, distances between thermodynamic states can be computed. It constitutes a geometric methodology to understand stochastic processes involved in, e.g., order-disorder transitions, where a sudden increase in distance is expected. We consider gyrokinetic simulations of ion-temperature-gradient (ITG)-mode-driven turbulence in the core region of the stellarator W7-X with realistic quasi-isodynamic topologies. In gyrokinetic plasma turbulence simulations, avalanches, e.g., of heat and particles, are often found, and in this work, a novel method for detection is investigated. This new method combines the singular spectrum analysis algorithm with a hierarchical clustering method such that the time series is decomposed into two parts: useful physical information and noise. The informative component of the time series is used for the calculation of the Hurst exponent, the information length, and the dynamic time. Based on these measures, the physical properties of the time series are revealed.
本研究探讨了一种评估等离子体湍流中随机过程的几何方法。热力学长度方法允许在相空间上使用黎曼度量；因此，可以计算热力学状态之间的距离。它构成了一种几何方法，用于理解例如有序-无序转变中涉及的随机过程，在这种转变中预计距离会突然增加。我们考虑了具有实际准等动力学拓扑结构的仿星器W7-X核心区域中离子温度梯度（ITG）模式驱动湍流的回旋动理学模拟。在回旋动理学等离子体湍流模拟中，经常会发现例如热量和粒子的雪崩现象，在这项工作中，研究了一种新的检测方法。这种新方法将奇异谱分析算法与层次聚类方法相结合，从而将时间序列分解为两部分：有用的物理信息和噪声。时间序列的信息成分用于计算赫斯特指数、信息长度和动态时间。基于这些度量，揭示了时间序列的物理特性。
