Zhang Qile, Guo Fan, Daughton William, Li Hui, Li Xiaocan
Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
Dartmouth College, Hanover, New Hampshire 03755, USA.
Phys Rev Lett. 2021 Oct 29;127(18):185101. doi: 10.1103/PhysRevLett.127.185101.
The relaxation of field-line tension during magnetic reconnection gives rise to a universal Fermi acceleration process involving the curvature drift of particles. However, the efficiency of this mechanism is limited by the trapping of energetic particles within flux ropes. Using 3D fully kinetic simulations, we demonstrate that the flux-rope kink instability leads to strong field-line chaos in weak-guide-field regimes where the Fermi mechanism is most efficient, thus allowing particles to transport out of flux ropes and undergo further acceleration. As a consequence, both ions and electrons develop clear power-law energy spectra that contain a significant fraction of the released energy. The low-energy bounds are determined by the injection physics, while the high-energy cutoffs are limited only by the system size. These results have strong relevance to observations of nonthermal particle acceleration in space and astrophysics.
磁重联过程中场线张力的松弛引发了一个涉及粒子曲率漂移的普适费米加速过程。然而，该机制的效率受到通量绳内高能粒子捕获的限制。通过三维全动理学模拟，我们证明在费米机制最有效的弱引导场区域，通量绳扭结不稳定性会导致强烈的场线混沌，从而使粒子能够从通量绳中输运出来并经历进一步加速。结果，离子和电子都形成了清晰的幂律能谱，其中包含相当一部分释放的能量。低能边界由注入物理过程决定，而高能截止仅受系统大小限制。这些结果与空间和天体物理学中非热粒子加速的观测密切相关。
