Squire J, Bhattacharjee A
Max Planck and Princeton Center for Plasma Physics, Department of Astrophysical Sciences and Princeton Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543, USA.
TAPIR, Mailcode 350-17, California Institute of Technology, Pasadena, California 91125, USA.
Phys Rev Lett. 2015 Oct 23;115(17):175003. doi: 10.1103/PhysRevLett.115.175003. Epub 2015 Oct 20.
We propose a new mechanism for a turbulent mean-field dynamo in which the magnetic fluctuations resulting from a small-scale dynamo drive the generation of large-scale magnetic fields. This is in stark contrast to the common idea that small-scale magnetic fields should be harmful to large-scale dynamo action. These dynamos occur in the presence of a large-scale velocity shear and do not require net helicity, resulting from off-diagonal components of the turbulent resistivity tensor as the magnetic analogue of the "shear-current" effect. Given the inevitable existence of nonhelical small-scale magnetic fields in turbulent plasmas, as well as the generic nature of velocity shear, the suggested mechanism may help explain the generation of large-scale magnetic fields across a wide range of astrophysical objects.
我们提出了一种新的湍流平均场发电机机制，其中由小尺度发电机产生的磁涨落驱动大尺度磁场的产生。这与通常认为小尺度磁场对大尺度发电机作用有害的观点形成鲜明对比。这些发电机出现在存在大尺度速度剪切的情况下，并且不需要净螺旋度，这是由湍流电阻率张量的非对角分量产生的，作为“剪切电流”效应的磁类似物。考虑到湍流等离子体中不可避免地存在非螺旋小尺度磁场，以及速度剪切的普遍性质，所提出的机制可能有助于解释广泛的天体物理对象中大尺度磁场的产生。
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