Helicity and dynamo action in magnetized stellar radiation zones
Helicity and dynamo action in magnetized stellar radiation zones
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磁化恒星辐射区的螺旋度和发电机作用
DOI：
10.1111/j.1365-2966.2012.21569.x
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发表时间：
2012
影响因子：
4.8
通讯作者：
Elstner
中科院分区：
文献类型：
--
作者：
Rüdiger;Kitchatinov;Elstner
计算了恒星辐射区环形磁场的非轴对称泰勒不稳定性驱动的螺旋度和α效应。在线性近似中，一个纯的环向场总是激发成对的模式具有相同的增长率，但相反的螺旋度，使净螺旋度消失。如果磁场背景场具有额外（弱）极向分量的螺旋结构，则其中一种模式占主导地位，产生与背景场当前螺旋度相关的净动力学螺旋度。计算了平均电动势，结果表明，最快增长模的α效应与背景场的电流螺旋度同号。发现α效应太小，不能驱动α 2发电机，但在弱极向场时，αΩ发电机的激励条件可以满足。此外，如果发电机通过磁不稳定性产生它自己的α效应，那么它的符号就不会出现问题。然而，在所有情况下，α效应都表现出极强的集中，因此可能的αΩ发电机可能只在极区工作。因此，我们的线性理论的结果导致了一个新的拓扑问题的存在的大规模发电机在恒星辐射区的电流驱动的不稳定性的基础上。
The helicity and α effect driven by the non-axisymmetric Tayler instability of toroidal magnetic fields in stellar radiation zones are computed. In the linear approximation, a purely toroidal field always excites pairs of modes with identical growth rates but with opposite helicity so that the net helicity vanishes. If the magnetic background field has a helical structure by an extra (weak) poloidal component then one of the modes dominates, producing a net kinetic helicity anticorrelated with the current helicity of the background field. The mean electromotive force is computed with the result that the α effect by the most rapidly growing mode has the same sign as the current helicity of the background field. The α effect is found to be too small to drive an α2dynamo, but the excitation conditions for an αΩ dynamo can be fulfilled for weak poloidal fields. Moreover, if the dynamo produces its own α effect by the magnetic instability, then problems with its sign do not arise. For all cases, however, the α effect shows an extremely strong concentration to the poles so that a possible αΩ dynamo might only work at the polar regions. Hence, the results of our linear theory lead to a new topological problem for the existence of large-scale dynamos in stellar radiation zones on the basis of the current-driven instability of toroidal fields.