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arXiv 1707.05907physics.plasm-phastro-ph.SRphysics.space-ph
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无碰撞等离子体中磁重联对Alfvénic turbulence的破坏

Disruption of Alfvénic turbulence by magnetic reconnection in a collisionless plasma

A. Mallet, A. A. Schekochihin, B. D. G. Chandran

备注：
21 pages, 1 figure, accepted for publication in JPP
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摘要：

我们计算的破坏尺度$λ_{\rm D}$在动态对齐Alfvénic湍流的片状结构被破坏的磁重联在低$β$碰撞等离子体的发病。$λ_{\rm D}$的缩放取决于所考虑的统计的顺序，在更大的尺度上更密集的结构被破坏。主导能谱的结构的破坏尺度是$λ_{\rm D}\sim L_\perp^{1/9}(d_eρ_s)^{4/9}$，其中$d_e$是电子惯性尺度，$ρ_s$是离子声音尺度，而$L_\perp$是湍流的外部尺度。当$β_e$和$ρ_s/L_\perp$足够小时，尺度$λ_{\rm D}$大于$ρ_s$，并且在$λ_{\rm D}$而不是在$ρ_s$处的能谱中存在中断。我们提出，由破坏产生的波动是循环的通量绳，这可能已经在太阳风中观察到。我们预测这些结构的振幅和半径之间的关系，并量化的重要性的中断过程中的级联的未中断的结构的填充分数和分数减少的能量包含在它们中的离子声标度$ρ_s$。这两种组分都强烈依赖于$β_e$，在较低的$β_e$下，破坏的结构变得更加重要。最后，我们预测，$λ_{\rm D}$和$ρ_s$之间的能谱是陡峭的比$k_\perp^{-3}$，当这个范围存在。这种陡峭的“过渡范围”有时会在太阳风湍流的短时间间隔内观察到。因此，无碰撞磁重联的发生可能会显著影响离子陀螺仪周围等离子体湍流的性质。

英文摘要：

We calculate the disruption scale $λ_{\rm D}$ at which sheet-like structures in dynamically aligned Alfvénic turbulence are destroyed by the onset of magnetic reconnection in a low-$β$ collisionless plasma. The scaling of $λ_{\rm D}$ depends on the order of the statistics being considered, with more intense structures being disrupted at larger scales. The disruption scale for the structures that dominate the energy spectrum is $λ_{\rm D}\sim L_\perp^{1/9}(d_eρ_s)^{4/9}$, where $d_e$ is the electron inertial scale, $ρ_s$ is the ion sound scale, and $L_\perp$ is the outer scale of the turbulence. When $β_e$ and $ρ_s/L_\perp$ are sufficiently small, the scale $λ_{\rm D}$ is larger than $ρ_s$ and there is a break in the energy spectrum at $λ_{\rm D}$, rather than at $ρ_s$. We propose that the fluctuations produced by the disruption are circularised flux ropes, which may have already been observed in the solar wind. We predict the relationship between the amplitude and radius of these structures and quantify the importance of the disruption process to the cascade in terms of the filling fraction of undisrupted structures and the fractional reduction of the energy contained in them at the ion sound scale $ρ_s$. Both of these fractions depend strongly on $β_e$, with the disrupted structures becoming more important at lower $β_e$. Finally, we predict that the energy spectrum between $λ_{\rm D}$ and $ρ_s$ is steeper than $k_\perp^{-3}$, when this range exists. Such a steep "transition range" is sometimes observed in short intervals of solar-wind turbulence. The onset of collisionless magnetic reconnection may therefore significantly affect the nature of plasma turbulence around the ion gyroscale.

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