Université Grenoble Alpes, ISTerre, F-38000 Grenoble, France and CNRS, ISTerre, F-38000 Grenoble, France.
Phys Rev Lett. 2014 Oct 31;113(18):184501. doi: 10.1103/PhysRevLett.113.184501. Epub 2014 Oct 28.
The contribution of small scale turbulent fluctuations to the induction of a mean magnetic field is investigated in our liquid sodium spherical Couette experiment with an imposed magnetic field. An inversion technique is applied to a large number of measurements at Rm≈100 to obtain radial profiles of the α and β effects and maps of the mean flow. It appears that the small scale turbulent fluctuations can be modeled as a strong contribution to the magnetic diffusivity that is negative in the interior region and positive close to the outer shell. Direct numerical simulations of our experiment support these results. The lowering of the effective magnetic diffusivity by small scale fluctuations implies that turbulence can actually help to achieve self-generation of large scale magnetic fields.
我们在带有外加磁场的液态钠球型对流传导实验中研究了小尺度湍动涨落对平均磁场产生的贡献。采用反演技术对 Rm≈100 时的大量测量数据进行处理，得到了α效应和β效应的径向分布以及平均流的图谱。结果表明，小尺度湍动涨落可以用一种强贡献模型来模拟磁扩散系数，在内部区域为负，在外壳附近为正。我们实验的直接数值模拟支持这些结果。小尺度涨落降低有效磁扩散系数意味着湍流实际上有助于实现大尺度磁场的自生成。
