MAGNETOHYDRODYNAMIC SIMULATIONS OF RECONNECTION AND PARTICLE ACCELERATION: THREE-DIMENSIONAL EFFECTS
MAGNETOHYDRODYNAMIC SIMULATIONS OF RECONNECTION AND PARTICLE ACCELERATION: THREE-DIMENSIONAL EFFECTS
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DOI：
10.1088/0004-637x/735/2/102
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发表时间：
2011-03
期刊：
影响因子：
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通讯作者：
G. Kowal;E. M. de Gouveia Dal Pino;A. Lazarian
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文献类型：
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作者：
G. Kowal;E. M. de Gouveia Dal Pino;A. Lazarian
磁场可以通过一个被称为磁重联的过程改变其拓扑结构。这一过程不仅对理解大尺度磁场的起源和演化很重要，而且被认为是一种可能有效的粒子加速器，主要通过一阶费米过程产生宇宙射线。在这项工作中，我们研究的粒子加速插入重联区的属性，并表明，平行于磁场的测试粒子插入磁流体动力学（MHD）域的重联不包括动力学效应，如压力各向异性，霍尔项，或异常的影响，速度分量呈指数增长。此外，垂直分量的加速度在这种模型中总是可能的。我们发现，在收缩的磁岛或电流片的粒子加速主要通过一阶费米过程，如前所述，而外部的电流片和岛屿的粒子主要经历漂移加速由于磁场梯度。考虑无导场的二维MHD模型，我们发现平行加速在某一水平停止。然而，这种饱和效应在存在平面外引导场或三维模型的情况下被去除。因此，我们强调的重要性，指导领域和完全三维的研究，一个完整的理解过程中的粒子加速在天体物理重联环境。
Magnetic fields can change their topology through a process known as magnetic reconnection. This process in not only important for understanding the origin and evolution of the large-scale magnetic field, but is seen as a possibly efficient particle accelerator producing cosmic rays mainly through the first-order Fermi process. In this work we study the properties of particle acceleration inserted in reconnection zones and show that the velocity component parallel to the magnetic field of test particles inserted in magnetohydrodynamic (MHD) domains of reconnection without including kinetic effects, such as pressure anisotropy, the Hall term, or anomalous effects, increases exponentially. Also, the acceleration of the perpendicular component is always possible in such models. We find that within contracting magnetic islands or current sheets the particles accelerate predominantly through the first-order Fermi process, as previously described, while outside the current sheets and islands the particles experience mostly drift acceleration due to magnetic field gradients. Considering two-dimensional MHD models without a guide field, we find that the parallel acceleration stops at some level. This saturation effect is, however, removed in the presence of an out-of-plane guide field or in three-dimensional models. Therefore, we stress the importance of the guide field and fully three-dimensional studies for a complete understanding of the process of particle acceleration in astrophysical reconnection environments.