论文标题
湍流的小型发电机中的种子磁场
Seed magnetic fields in turbulent small-scale dynamos
论文作者
论文摘要
星系和星系簇中的磁场从非常弱的种子值扩增到观察到的$μ{\ rm g} $通过湍流发电机的强度。种子磁场可以具有原始或天体物理的起源。在星系或星系簇尺度上，种子场的强度和结构可能会大不相同，具体取决于种子场的产生机制。种子场首先遇到小规模的发电机，因此我们研究了种子场强度和结构对小规模发电机的影响。使用驱动湍流的数值模拟并考虑三种不同的种子场构型：1）均匀场，2）具有幂律光谱的随机场，以及3）具有抛物线光谱的随机场，我们表明，动力学生成的磁场的强度和统计特性独立于种子场的细节。我们证明，即使小规模的迪纳摩没有活性，由于大规模磁场的缠结，也可以线性地生成小规模的磁场。在存在小规模的发电机作用的情况下，我们发现丢失了非线性小规模发电机生成的磁场的种子场的任何记忆，因此，不可能在湍流介质中从进化的磁场中追踪后种子场信息。
Magnetic fields in galaxies and galaxy clusters are amplified from a very weak seed value to the observed $μ{\rm G}$ strengths by the turbulent dynamo. The seed magnetic field can be of primordial or astrophysical origin. The strength and structure of the seed field, on the galaxy or galaxy cluster scale, can be very different, depending on the seed-field generation mechanism. The seed field first encounters the small-scale dynamo, thus we investigate the effects of the strength and structure of the seed field on the small-scale dynamo action. Using numerical simulations of driven turbulence and considering three different seed-field configurations: 1) uniform field, 2) random field with a power-law spectrum, and 3) random field with a parabolic spectrum, we show that the strength and statistical properties of the dynamo-generated magnetic fields are independent of the details of the seed field. We demonstrate that, even when the small-scale dynamo is not active, small-scale magnetic fields can be generated and amplified linearly due to the tangling of the large-scale field. In the presence of the small-scale dynamo action, we find that any memory of the seed field for the non-linear small-scale dynamo generated magnetic fields is lost and thus, it is not possible to trace back seed-field information from the evolved magnetic fields in a turbulent medium.
