磁旋转驱动Turbulence中的磁螺旋度和发电机Action
Magnetic Helicities and Dynamo Action in Magneto-rotationally Driven Turbulence
摘要：
我们研究之间的关系磁通量代，作为一个指标的大型发电机行动，和磁螺旋度，计算作为一个整体的发电机体积，在一个简单的发电机。我们认为发电机的行动驱动的磁旋转湍流（MRT）的剪切盒近似。我们考虑磁开放的边界条件，允许通量的螺旋度或计算域。我们规避了缺乏规范不变性的问题，在开放的领域，通过选择一个特定的规范-缠绕规范-提供了一个自然的解释，在成对场线的平均缠绕数。我们使用这个规范精确地定义和测量螺旋度和螺旋度通量的发电机行动的几个实现。我们发现，在这些情况下，系统作为一个整体不打破反射对称性和总螺旋度仍然很小，即使在大量的磁通量产生的情况下。我们没有发现产生的磁通量和螺旋度或通过边界的螺旋度通量之间的特殊联系。我们认为，这一结果可能是由于MRT发电机过程的本质上是非线性的。
英文摘要：
We examine the relationship between magnetic flux generation, taken as an indicator of large-scale dynamo action, and magnetic helicity, computed as an integral over the dynamo volume, in a simple dynamo. We consider dynamo action driven by Magneto-Rotational Turbulence (MRT) within the shearing-box approximation. We consider magnetically open boundary conditions that allow a flux of helicity in or out of the computational domain. We circumvent the problem of the lack of gauge invariance in open domains by choosing a particular gauge -- the winding gauge -- that provides a natural interpretation in terms of average winding number of pairwise field lines. We use this gauge precisely to define and measure the helicity and helicity flux for several realizations of dynamo action. We find in these cases, that the system as a whole does not break reflectional symmetry and the total helicity remains small even in cases when substantial magnetic flux is generated. We find no particular connection between the generation of magnetic flux and the helicity or the helicity flux through the boundaries. We suggest that this result may be due to the essentially nonlinear nature of the dynamo processes in MRT.
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