Plasma turbulence at scales of the order of the ion inertial length is mediated by several mechanisms, including linear wave damping, magnetic reconnection, the formation and dissipation of thin current sheets, and stochastic heating. It is now understood that the presence of localized coherent structures enhances the dissipation channels and the kinetic features of the plasma. However, no formal way of quantifying the relationship between scale-to-scale energy transfer and the presence of spatial structures has been presented so far. In the Letter we quantify such a relationship analyzing the results of a two-dimensional high-resolution Hall magnetohydrodynamic simulation. In particular, we employ the technique of space filtering to derive a spectral energy flux term which defines, in any point of the computational domain, the signed flux of spectral energy across a given wave number. The characterization of coherent structures is performed by means of a traditional two-dimensional wavelet transformation. By studying the correlation between the spectral energy flux and the wavelet amplitude, we demonstrate the strong relationship between scale-to-scale transfer and coherent structures. Furthermore, by conditioning one quantity with respect to the other, we are able for the first time to quantify the inhomogeneity of the turbulence cascade induced by topological structures in the magnetic field. Taking into account the low space-filling factor of coherent structures (i.e., they cover a small portion of space), it emerges that 80% of the spectral energy transfer (both in the direct and inverse cascade directions) is localized in about 50% of space, and 50% of the energy transfer is localized in only 25% of space.

中文翻译：

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湍流等离子体中的相干结构和光谱能量转移：一种空间滤波方法

离子惯性量级尺度上的等离子体湍流是由几种机制介导的，包括线性波阻尼，磁重连，薄电流片的形成和耗散以及随机加热。现在可以理解，局部相干结构的存在增强了等离子体的耗散通道和动力学特性。但是，到目前为止，还没有正式的方法可以量化尺度到尺度的能量转移与空间结构的存在之间的关系。在信中，我们通过分析二维高分辨率霍尔磁流体动力学模拟的结果来量化这种关系。特别是，我们采用空间滤波技术来得出频谱能量通量项，该项在计算域的任何点上都定义为：在给定波数上的频谱能量的有符号通量。相干结构的表征是通过传统的二维小波变换进行的。通过研究频谱能量通量与小波幅度之间的相关性，我们证明了标度到标度的传递与相干结构之间的紧密关系。此外，通过调节一个相对于另一个的数量，我们首次能够量化由磁场中的拓扑结构引起的湍流级联的不均匀性。考虑到相干结构的低空间填充因子（即，它们覆盖一小部分空间），可以发现80％的光谱能量传输（在正向和反向级联方向上）都局限在大约50％空间