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arXiv 2602.22653physics.plasm-ph
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非线性熵转移通过各向同性湍流在回旋湍流中

Nonlinear entropy transfer via zonal flows in gyrokinetic plasma turbulence

The Graduate University for Advanced Studies(高级研究大学院大学);Faculty of Arts and Sciences, Komazawa University(驹泽大学文理学部);National Institute for Fusion Science(核聚变科学研究所)

Motoki Nakata, Tomo-Hiko Watanabe, Hideo Sugama

AI总结:

研究了回旋湍流中非线性熵转移过程,揭示各向同性流对输运调节的作用及不同湍流类型间的熵转移差异。

摘要:

基于回旋熵平衡关系,研究了在托卡马克离子温度梯度(ITG)和电子温度梯度(ETG)驱动湍流中的非线性熵转移过程,这些关系适用于各向同性模式和非各向同性模式,并通过熵转移函数耦合,该函数被视为因雷诺应力而扩展的各向同性流产生。对引入的“三元”熵转移函数进行频谱分析,揭示了各向同性模式和非各向同性模式之间的非线性相互作用及其对湍流输运水平的影响。发现不同类型的熵转移过程发生在ITG和ETG湍流之间:在ITG不稳定性饱和阶段,从非各向同性模式到各向同性模式的熵转移是显著的,而一旦强各向同性流生成,稳态湍流状态下向各向同性模式的熵转移变得相当弱。相反,各向同性流通过三元相互作用,调节从低径向波数(对热流有贡献)的非各向同性模式到高径向波数(但对热流贡献较少)的非各向同性模式的熵转移。连续的熵转移过程到更高径向波数模式与稳态湍流状态中的输运调节相关。相比之下,在ETG湍流的不稳定性饱和和稳态阶段,低波数非各向同性模式之间的熵转移过程占主导地位,而非通过各向同性模式的转移。

英文摘要:

Nonlinear entropy transfer processes in toroidal ion temperature gradient (ITG) and electron temperature gradient (ETG) driven turbulence are investigated based on the gyrokinetic entropy balance relations for zonal and non-zonal modes, which are coupled through the entropy transfer function regarded as a kinetic extension of the zonal-flow production due to the Reynolds stress. Spectral analyses of the "triad" entropy transfer function introduced in this study reveal not only the nonlinear interactions among the zonal and non-zonal modes, but also their effects on the turbulent transport level. Different types of the entropy transfer processes between the ITG and ETG turbulence are found: The entropy transfer from non-zonal to zonal modes is substantial in the saturation phase of the ITG instability, while, once the strong zonal flow is generated, the entropy transfer to the zonal modes becomes quite weak in the steady turbulence state. Instead, the zonal flows mediate the entropy transfer from non-zonal modes with low radial-wavenumbers (with contribution to the heat flux) to the other non-zonal modes with higher radial-wavenumbers (but with less contribution to the heat flux) through the triad interaction. The successive entropy transfer processes to the higher radial-wavenumber modes are associated with transport regulation in the steady turbulence state. In contrast, in both the instability-saturation and steady phases of the ETG turbulence, the entropy transfer processes among low-wavenumber non-zonal modes are dominant rather than the transfer via zonal modes.

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