Magnetohydrodynamic Turbulence in the Plasmoid-mediated Regime
Magnetohydrodynamic Turbulence in the Plasmoid-mediated Regime
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DOI：
10.3847/1538-4357/aaac83
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发表时间：
2018-02-20
影响因子：
4.9
通讯作者：
Bhattacharjee, A.
中科院分区：
文献类型：
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作者：
Comisso, L.;Huang, Y. -M.;Bhattacharjee, A.
磁流体动力学湍流和磁场重联是天体物理环境中普遍存在的现象。在大多数情况下，这些过程不是孤立发生的，而是相互作用的。这使得这些过程的综合理论极具挑战性。在这里，我们提出了一个理论的磁流体动力学湍流驱动在一个大的规模，自洽帐户的相互作用与磁重联发生在较小的尺度。磁场重联产生等离子体团（通量绳），这些等离子体团从磁场产生的噪音中生长出来，最终破坏它们诞生的片状结构。这些结构的破坏导致的湍流能量级联的修改，这反过来又施加了反馈效应的等离子体团形成通过湍流产生的噪声。在这种等离子体团介导的范围内的能谱相对于标准惯性范围变陡，并且不遵循简单的幂律。由于湍流和重连之间的复杂的相互作用，我们还发现，长度尺度，标志着开始的等离子体团介导的范围和耗散长度尺度不服从真正的幂律。过渡磁雷诺数相当温和，高于该雷诺数，等离子体团的形成在统计上变得足够显着，足以影响湍流级联，这意味着等离子体团预计会改变许多天体物理系统中的湍流消散路径。
Magnetohydrodynamic turbulence and magnetic reconnection are ubiquitous in astrophysical environments. In most situations these processes do not occur in isolation but interact with each other. This renders a comprehensive theory of these processes highly challenging. Here we propose a theory of magnetohydrodynamic turbulence driven at a large scale that self-consistently accounts for the mutual interplay with magnetic reconnection occurring at smaller scales. Magnetic reconnection produces plasmoids (flux ropes) that grow from turbulence-generated noise and eventually disrupt the sheet-like structures in which they are born. The disruption of these structures leads to a modification of the turbulent energy cascade, which in turn exerts a feedback effect on the plasmoid formation via the turbulence-generated noise. The energy spectrum in this plasmoid-mediated range steepens relative to the standard inertial range and does not follow a simple power law. As a result of the complex interplay between turbulence and reconnection, we also find that the length scale that marks the beginning of the plasmoid-mediated range and the dissipation length scale do not obey true power laws. The transitional magnetic Reynolds number above which the plasmoid formation becomes statistically significant enough to affect the turbulent cascade is fairly modest, implying that plasmoids are expected to modify the turbulent path to dissipation in many astrophysical systems.