导电介质随机流中初始磁能增长的有限记忆时间和各向异性效应
Finite memory time and anisotropy effects for initial magnetic energy growth in random flow of conducting media
摘要：
发电机机制是一个磁场在运动的导电流体中自激的过程。与天体物理系统有关的这一机制的最有趣的应用之一是等离子体随机运动的情况。对于该过程的第一阶段，控制发电机方程可以简化为一阶常微分方程组。在这种情况下，我们提出了一种计算磁能增长率的正规方法。在此基础上，我们计算了具有有限记忆时间和拉伸矩阵各向异性统计分布的随机流的增长率，并与各向同性情形和短相关近似下的相应结果进行了比较。我们发现，对于中等斯特劳哈尔数和中等各向异性的分析结果再现数值估计的增长率相当不错，而较大的管理参数的定量差异变得很大。特别是，分析近似适用于Strouhal数s<0.6，我们发现一些数值模型和观测的例子，这个区域可能是相关的。而出乎意料的是，我们发现，镜像不对称性并不有助于获得的增长率，虽然镜像不对称效应是已知的发电机行动的后期阶段是至关重要的。
英文摘要：
The dynamo mechanism is a process of magnetic field self-excitation in a moving electrically conducting fluid. One of the most interesting applications of this mechanism related to the astrophysical systems is the case of a random motion of plasma. For the very first stage of the process, the governing dynamo equation can be reduced to a system of first order ordinary differential equations. For this case we suggest a regular method to calculate the growth rate of magnetic energy. Based on this method we calculate the growth rate for random flow with finite memory time and anisotropic statistical distribution of the stretching matrix and compare the results with corresponding ones for isotropic case and for short-correlated approximation. We find that for moderate Strouhal numbers and moderate anisotropy the analytical results reproduce the numerically estimated growth rates reasonably well, while for larger governing parameters the quantitative difference becomes substantial. In particular, analytical approximation is applicable for the Strouhal numbers s<0.6 and we find some numerical models and observational examples for which this region might be relevant. Rather unexpectedly, we find that the mirror asymmetry does not contribute to the growth rates obtained, although the mirror asymmetry effects are known to be crucial for later stages of dynamo action.
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