Phase space scales of free energy dissipation in gradient-driven gyrokinetic turbulence
Phase space scales of free energy dissipation in gradient-driven gyrokinetic turbulence
复制标题
梯度驱动回旋湍流中自由能耗散的相空间尺度
DOI：
10.1017/s0022377814000154
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发表时间：
2014
影响因子：
2.5
通讯作者：
A. Navarro
中科院分区：
文献类型：
--
作者：
D. Hatch;F. Jenko;Vasil Bratanov;A. Navarro
采用简化的四维（垂直速度积分）平板离子温度梯度驱动湍流的陀螺动力学模型，研究了大范围背景梯度和碰撞频率下湍流动力学系统中自由能量耗散的相空间尺度。平行速度以埃尔米特多项式表示，允许在四维相空间上详细研究自由能动力学的尺度。一个全光谱代码- DNA代码-解决了这个系统被描述。埃尔米特自由能谱明显比预期的线性更陡峭，导致碰撞耗散在速度空间的大尺度上达到峰值，即使是任意小的碰撞。陡峭的埃尔米特谱的一个关键原因是一个临界平衡-平行流时间和非线性相关时间的平衡-延伸到高埃尔米特数n。尽管耗散总是在所有相空间维度的大尺度上达到峰值，但当碰撞足够低和/或非线性能量传递足够强时，小尺度耗散在综合意义上变得重要。利用基因代码进行环面全陀螺动力学仿真，验证了简化模型的结果。在当前实验中发现的典型碰撞频率对应于稍微有利于大尺度耗散的湍流状态，而像ITER和空间和天体物理等离子体这样的低碰撞系统中的湍流预计将越来越依赖于小尺度耗散机制。这项工作有望为回旋动力学简化建模工作提供信息，如大涡模拟和回旋流体技术。
A reduced four-dimensional (integrated over perpendicular velocity) gyrokinetic model of slab ion temperature gradient-driven turbulence is used to study the phase-space scales of free energy dissipation in a turbulent kinetic system over a broad range of background gradients and collision frequencies. Parallel velocity is expressed in terms of Hermite polynomials, allowing for a detailed study of the scales of free energy dynamics over the four-dimensional phase space. A fully spectral code – the DNA code – that solves this system is described. Hermite free energy spectra are significantly steeper than would be expected linearly, causing collisional dissipation to peak at large scales in velocity space even for arbitrarily small collisionality. A key cause of the steep Hermite spectra is a critical balance – an equilibration of the parallel streaming time and the nonlinear correlation time – that extends to high Hermite number n. Although dissipation always peaks at large scales in all phase space dimensions, small-scale dissipation becomes important in an integrated sense when collisionality is low enough and/or nonlinear energy transfer is strong enough. Toroidal full-gyrokinetic simulations using the Gene code are used to verify results from the reduced model. Collision frequencies typically found in present-day experiments correspond to turbulence regimes slightly favoring large-scale dissipation, while turbulence in low-collisionality systems like ITER and space and astrophysical plasmas is expected to rely increasingly on small-scale dissipation mechanisms. This work is expected to inform gyrokinetic reduced modeling efforts like Large Eddy Simulation and gyrofluid techniques.
影响因子：
8.6
作者：
Barnes, M.;Parra, F. I.;Schekochihin, A. A.
通讯作者：
Schekochihin, A. A.