相对论静磁平衡最低阶不稳定模的动力学模拟
Kinetic simulations of the lowest-order unstable mode of relativistic magnetostatic equilibria
摘要：
我们提出的粒子在细胞数值对等离子体模拟的相对论二维静磁平衡称为“ABC”领域的结果。特别是，我们专注于最低阶不稳定的配置组成的两个最小值和两个最大值的磁矢势。初始对称性的破坏导致电能的指数增长和两个电流层的形成，这与Syrovatskii首次描述的“X点崩溃”的图像是一致的。层内的磁重联将一部分粒子加热到非常高的能量。在线性不稳定性饱和后，电流层被破坏，系统混沌地演化，在随机的二阶费米过程中扩散粒子能量，导致形成幂律能量分布。随着平均磁化强度的增加，幂律斜率变硬，但它们明显比从哈里斯型层开始的模拟中产生的更软。最大粒子能量与平均磁化强度成正比，这部分归因于有效电场的增加，部分归因于加速时间尺度的增加。我们详细描述了动态电流层的演变结构，并报告磁螺旋守恒。这些结果可以应用于高度磁化的天体物理环境，理想的等离子体不稳定性触发快速的磁耗散与有效的粒子加速和耀斑的高能辐射。
英文摘要：
We present the results of particle-in-cell numerical pair plasma simulations of relativistic 2D magnetostatic equilibria known as the 'ABC' fields. In particular, we focus on the lowest-order unstable configuration consisting of two minima and two maxima of the magnetic vector potential. Breaking of the initial symmetry leads to exponential growth of the electric energy and to the formation of two current layers, which is consistent with the picture of 'X-point collapse' first described by Syrovatskii. Magnetic reconnection within the layers heats a fraction of particles to very high energies. After the saturation of the linear instability, the current layers are disrupted and the system evolves chaotically, diffusing the particle energies in a stochastic second-order Fermi process leading to the formation of power-law energy distributions. The power-law slopes harden with the increasing mean magnetization, but they are significantly softer than those produced in simulations initiated from Harris-type layers. The maximum particle energy is proportional to the mean magnetization, which is attributed partly to the increase of the effective electric field and partly to the increase of the acceleration time scale. We describe in detail the evolving structure of the dynamical current layers, and report on the conservation of magnetic helicity. These results can be applied to highly magnetized astrophysical environments, where ideal plasma instabilities trigger rapid magnetic dissipation with efficient particle acceleration and flares of high-energy radiation.
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