Müller Wolf-Christian, Malapaka Shiva Kumar, Busse Angela
Max-Planck-Institut für Plasmaphysik, 85748 Garching, Germany.
Phys Rev E Stat Nonlin Soft Matter Phys. 2012 Jan;85(1 Pt 2):015302. doi: 10.1103/PhysRevE.85.015302. Epub 2012 Jan 17.
The nonlinear dynamics of magnetic helicity HM, which is responsible for large-scale magnetic structure formation in electrically conducting turbulent media, is investigated in forced and decaying three-dimensional magnetohydrodynamic turbulence. This is done with the help of high-resolution direct numerical simulations and statistical closure theory. The numerically observed spectral scaling of HM is at variance with earlier work using a statistical closure model [Pouquet et al., J. Fluid Mech. 77, 321 (1976)]. By revisiting this theory, a universal dynamical balance relation is found that includes the effects of kinetic helicity as well as kinetic and magnetic energies on the inverse cascade of HM and explains the above-mentioned discrepancy. Consideration of the result in the context of mean-field dynamo theory suggests a nonlinear modification of the α-dynamo effect, which is important in the context of magnetic-field excitation in turbulent plasmas.
在受迫和衰减的三维磁流体动力学湍流中，研究了磁螺旋度(H_M)的非线性动力学，它负责在导电湍流介质中形成大规模磁结构。这借助于高分辨率直接数值模拟和统计闭合理论来完成。数值观测到的(H_M)的谱标度与早期使用统计闭合模型的工作[Pouquet等人，《流体力学杂志》77, 321 (1976)]不同。通过重新审视该理论，发现了一个通用的动力学平衡关系，其中包括动能螺旋度以及动能和磁能对(H_M)反向级联的影响，并解释了上述差异。在平均场发电机理论的背景下考虑该结果，表明对α发电机效应有非线性修正，这在湍流等离子体中的磁场激发背景下很重要。
