Magnetic reconnection at 3D null points: effect of magnetic field asymmetry
Magnetic reconnection at 3D null points: effect of magnetic field asymmetry
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DOI：
10.1051/0004-6361/200913002
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发表时间：
2010-03-01
影响因子：
6.5
通讯作者：
Pontin, D. I.
中科院分区：
文献类型：
--
作者：
Al-Hachami, A. K.;Pontin, D. I.
上下文许多天体物理等离子体中的磁场，例如日冕中的磁场，已知具有高度复杂且清晰的三维结构。在磁场线被锚定的高β区域（如太阳内部）中，湍流等离子体运动可以在磁场中储存大量能量。这种能量只有在磁重联发生时才能释放。重联可能只会发生在磁场梯度很大的地方，而这样的位置的一个候选者是磁零点，例如在太阳大气中就有很多。重联导致磁场拓扑结构的变化，能量以热量、动能和粒子加速度的形式释放。因此，重联是许多动力学过程的原因，例如耀斑和喷流。本文的目的是研究磁场重联在三维零点的性质，相对于它们的依赖于周围的磁场的对称性的零。特别是，我们研究的磁通量重联率在零点，以及如何形成的电流片及其属性。我们使用数学建模和有限差分电阻MHD模拟。据发现，考虑的磁场重联模式的基本结构是不受影响的变化的磁场对称性，即，等离子体流被发现交叉的脊柱和风扇的零。然而，电流片的峰值强度和尺寸取决于场线的对称性/不对称性。结果表明，磁场的不对称性对重联率有很强的依赖性。在磁零点附近的磁场的对称性/不对称性可以对任何相关重联区域的几何形状以及重联过程进行的速率产生深远的影响。
Context. The magnetic field in many astrophysical plasmas, for example in the solar corona, is known to have a highly complex and clearly three-dimensional structure. Turbulent plasma motions in high-beta regions where field lines are anchored, such as the solar interior, can store large amounts of energy in the magnetic field. This energy can only be released when magnetic reconnection occurs. Reconnection may only occur in locations where huge gradients of the magnetic field develop, and one candidate for such locations are magnetic null points, known to be abundant for example in the solar atmosphere. Reconnection leads to changes in the topology of the magnetic field, and energy being released as heat, kinetic energy and acceleration of particles. Thus reconnection is responsible for many dynamic processes, for instance flares and jets.Aims. The aim of this paper is to investigate the properties of magnetic reconnection at a 3D null point, with respect to their dependence on the symmetry of the magnetic field around the null. In particular we examine the rate of reconnection of magnetic flux at the null point, as well as how the current sheet forms and its properties.Methods. We use mathematical modelling and finite difference resistive MHD simulations.Results. It is found that the basic structure of the mode of magnetic reconnection considered is unaffected by varying the magnetic field symmetry, that is, the plasma flow is found to cross both the spine and fan of the null. However, the peak intensity and dimensions of the current sheet are dependent on the symmetry/asymmetry of the field lines. As a result, the reconnection rate is also found to be strongly dependent on the field asymmetry.Conclusions. The symmetry/asymmetry of the magnetic field in the vicinity of a magnetic null can have a profound effect on the geometry of any associated reconnection region, and the rate at which the reconnection process proceeds.