磁流体动力学Turbulence中磁场的特征线
Characteristic Lengths of Magnetic Field in Magnetohydrodynamic Turbulence
摘要：
在湍流发电机的框架中，流体运动通过场线的拉伸来放大弱种子磁场。虽然放大过程一直是一个活跃的研究课题，很少有人关注的长度尺度的磁场。本文对磁流体动力学湍流中磁场的特征长度进行了数值研究。我们考虑了平均磁场很弱或为零的情况，这种情况适用于星系际空间的湍流。我们的调查结果如下。(1)在饱和时，磁场谱的峰值出现在$\sim L_0/2$处，其中$L_0$是能量注入尺度，而最含能量的尺度是$\sim L_0/5$。投影的二维场的谱的峰值尺度是$\sim L_0$。(2)在磁场放大阶段，$\sim t^{1.5}$的能量均分尺度呈幂律增长，而积分和曲率尺度呈线性增长。均分、积分和曲率尺度分别在$\sim L_0$、$\sim 0.3L_0$和$\sim 0.15L_0$处饱和。(3)由星系际磁场（IGMF）引起的法拉第旋转测度（RM）中定义的磁场的相干长度与积分尺度有关。我们提出了一个公式，表示RM的标准偏差，$σ_{RM}$，在积分尺度和均方根强度的IGMF，并估计$σ_{RM}$将是$\sim 100$和$\sim$几拉德m $^{-2}$的集群和细丝，分别。
英文摘要：
In the framework of turbulence dynamo, flow motions amplify a weak seed magnetic field through the stretching of field lines. Although the amplification process has been a topic of active research, less attention has been paid to the length scales of magnetic field. In this paper, we described a numerical study on characteristic lengths of magnetic field in magnetohydrodynamic turbulence. We considered the case of very weak or zero mean magnetic field, which is applicable to the turbulence in the intergalactic space. Our findings are as follows. (1) At saturation, the peak of magnetic field spectrum occurs at $\sim L_0/2$, where $L_0$ is the energy injection scale, while the most energy containing scale is $\sim L_0/5$. The peak scale of spectrum of projected, two-dimensional field is $\sim L_0$. (2) During the stage of magnetic field amplification, the energy equipartition scale shows a power-law increase of $\sim t^{1.5}$, while the integral and curvature scales show a linear increase. The equipartition, integral, and curvature scales saturate at $\sim L_0$, $\sim 0.3L_0$, and $\sim 0.15L_0$, respectively. (3) The coherence length of magnetic field defined in the Faraday rotation measure (RM) due to the intergalactic magnetic field (IGMF) is related to the integral scale. We presented a formula that expresses the standard deviation of RM, $σ_{RM}$, in terms of the integral scale and rms strength of the IGMF, and estimated that $σ_{RM}$ would be $\sim 100$ and $\sim$ a few rad m$^{-2}$ for clusters and filaments, respectively.
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