磁通量管的多尺度动力学与反向磁能传递
Multi-scale dynamics of magnetic flux tubes and inverse magnetic energy transfer
摘要：
我们报告的分析和数值研究的三维阵列相同的磁通量管的动力学在减少磁流体动力学描述的等离子体。我们建议，这个系统的长期演变是由磁通管合并，这种合并是动态约束的有关（理想）不变，{ \it即}的守恒。每个管的磁势和轴向通量。我们还建议，在垂直于合并平面的方向上，通量管演变临界平衡的方式。这些概念使我们能够构建一个分析模型，以了解磁能和含能尺度等量如何作为时间的函数演化。特别重要的是，它的二维对应的结论是，这个系统表现出一个反向转移的磁能，终止仅在系统规模。我们进行直接的数值模拟，证实了这些预测，并揭示了系统的演变的其他有趣的方面。我们发现，例如，早期的时间演化的特点是急剧衰减的初始磁能，我们归因于无处不在的电流片的形成。我们还表明，当初始条件是一个随机的，小规模的磁种子场时，观察到一个定量类似的反向转移的磁能。
英文摘要：
We report on an analytical and numerical study of the dynamics of a three-dimensional array of identical magnetic flux tubes in the reduced-magnetohydrodynamic description of the plasma. We propose that the long-time evolution of this system is dictated by flux-tube mergers and that such mergers are dynamically constrained by the conservation of the pertinent (ideal) invariants, {\it viz.} the magnetic potential and axial fluxes of each tube. We also propose that in the direction perpendicular to the merging plane, flux tubes evolve in critically-balanced fashion. These notions allow us to construct an analytical model for how quantities such as the magnetic energy and the energy-containing scale evolve as functions of time. Of particular importance is the conclusion that, like its two-dimensional counterpart, this system exhibits an inverse transfer of magnetic energy that terminates only at the system scale. We perform direct numerical simulations that confirm these predictions and reveal other interesting aspects of the evolution of the system. We find, for example, that the early time evolution is characterized by a sharp decay of the initial magnetic energy, which we attribute to the ubiquitous formation of current sheets. We also show that a quantitatively similar inverse transfer of magnetic energy is observed when the initial condition is a random, small-scale magnetic seed field.
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