论文标题

MHD湍流:有偏见的评论

MHD Turbulence: A Biased Review

论文作者

Schekochihin, Alexander A.

论文摘要

这篇综述将过去几年的发展置于规范时线的背景下(Kolmogorov到Iroshnikov-Kraichnan到Goldreich-Sridhar到Boldyrev)。有人认为,贝雷斯尼亚克的反对意见是,如果将后者理解为间歇性效应,那么Boldyrev的一致性理论违反了RMHD恢复对称性。因此,在这种解释中恢复了Boldyrev的量表,是湍流系统中间歇性物理理论的一个例子。对齐结构的出现带来了重新连接物理,因此MHD湍流理论与撕裂和当前地面破坏的物理学交织在一起。 Loureiro,Mallet等人的最新工作。经过审查,有人认为,我们终于对MHD级联的构图一直始终保持到耗散量表。这张照片似乎与BoldyRev的Aligned Cascade调和了Beresnyak的Kolmogorov缩放量的Kolmogorov缩放。这些想法还可以在理解饱和的MHD发电机方面取得一些进展,该动力被认为是通过重新连接控制的,并以小尺度的含量与撕裂的介导的级联反应相似,类似于其强度均值。在此核心叙述的边缘,标准的弱-MHD扰动理论被认为需要调整 - 并提出了一种方案 - 考虑了以下部分,即自发出现的2D冷凝水在中介Alfven波级联反应时发挥作用。这在大尺度上完成了MHD级联的图片。对MHD湍流的剩余能量,剩余和衰减的状态(在其中重新连接再次出现),对MHD湍流不平衡(为此提出了新理论)进行了许多未成年问题的调查。最后,有人认为,研究的自然方向现在远离MHD并进入动力学领域。

This review puts the developments of the last few years in the context of the canonical time line (Kolmogorov to Iroshnikov-Kraichnan to Goldreich-Sridhar to Boldyrev). It is argued that Beresnyak's objection that Boldyrev's alignment theory violates the RMHD rescaling symmetry can be reconciled with alignment if the latter is understood as an intermittency effect. Boldyrev's scalings, recovered in this interpretation, are thus an example of a physical theory of intermittency in a turbulent system. Emergence of aligned structures brings in reconnection physics, so the theory of MHD turbulence intertwines with the physics of tearing and current-sheet disruption. Recent work on this by Loureiro, Mallet et al. is reviewed and it is argued that we finally have a reasonably complete picture of MHD cascade all the way to the dissipation scale. This picture appears to reconcile Beresnyak's Kolmogorov scaling of the dissipation cutoff with Boldyrev's aligned cascade. These ideas also enable some progress in understanding saturated MHD dynamo, argued to be controlled by reconnection and to contain, at small scales, a tearing-mediated cascade similar to its strong-mean-field counterpart. On the margins of this core narrative, standard weak-MHD-turbulence theory is argued to require adjustment - and a scheme for it is proposed - to take account of the part that a spontaneously emergent 2D condensate plays in mediating the Alfven-wave cascade. This completes the picture of the MHD cascade at large scales. A number of outstanding issues are surveyed, concerning imbalanced MHD turbulence (for which a new theory is proposed), residual energy, subviscous and decaying regimes of MHD turbulence (where reconnection again features prominently). Finally, it is argued that the natural direction of research is now away from MHD and into kinetic territory.

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