ENERGY DISSIPATION IN MAGNETIC NULL POINTS AT KINETIC SCALES
ENERGY DISSIPATION IN MAGNETIC NULL POINTS AT KINETIC SCALES
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DOI：
10.1088/0004-637x/807/2/155
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发表时间：
2015-07
期刊：
影响因子：
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通讯作者：
V. Olshevsky;A. Divin;E. Eriksson;S. Markidis;G. Lapenta
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作者：
V. Olshevsky;A. Divin;E. Eriksson;S. Markidis;G. Lapenta
我们使用动力学粒子在细胞和MHD模拟的观测数据集的支持下，调查在空间等离子体中的零点集群的磁重联。研究中的磁位形是由快速绝热磁通绳压缩驱动的，它消耗了几乎一半的初始磁场能量。在这个阶段，强大的电流被激发产生二次不稳定性，系统被带入一个“间歇性湍流”的状态在几个离子陀螺周期。重连事件分布在整个模拟域和能量耗散是相当体积填充。许多螺旋零点通过它们的脊柱互连形成嵌入磁通绳的零线;零点对证明了扭转脊柱重联的签名。然而，能量耗散主要发生在相邻磁通绳与相反方向的电流形成的剪切层。在这些区域中，径向零对自发地出现和消失，与电子流和小尺度电流片有关。根据星团对地球磁鞘的观测，模拟中的螺旋零值数量比径向零值数量多5-10倍。具有嵌入螺旋零点的扭曲磁场可能指示未来空间飞行任务（如磁层多尺度使命）的主要能量耗散区域。
We use kinetic particle-in-cell and MHD simulations supported by an observational data set to investigate magnetic reconnection in clusters of null points in space plasma. The magnetic configuration under investigation is driven by fast adiabatic flux rope compression that dissipates almost half of the initial magnetic field energy. In this phase powerful currents are excited producing secondary instabilities, and the system is brought into a state of “intermittent turbulence” within a few ion gyro-periods. Reconnection events are distributed all over the simulation domain and energy dissipation is rather volume-filling. Numerous spiral null points interconnected via their spines form null lines embedded into magnetic flux ropes; null point pairs demonstrate the signatures of torsional spine reconnection. However, energy dissipation mainly happens in the shear layers formed by adjacent flux ropes with oppositely directed currents. In these regions radial null pairs are spontaneously emerging and vanishing, associated with electron streams and small-scale current sheets. The number of spiral nulls in the simulation outweighs the number of radial nulls by a factor of 5–10, in accordance with Cluster observations in the Earth's magnetosheath. Twisted magnetic fields with embedded spiral null points might indicate the regions of major energy dissipation for future space missions such as the Magnetospheric Multiscale Mission.