Shi Xiaofei, Artemyev Anton, Angelopoulos Vassilis, Liu Terry, Wilson Iii Lynn B
Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, California, USA.
NASA Goddard Space Flight Center, Heliophysics Science Division, Greenbelt, MD, USA.
Nat Commun. 2025 Jan 2;16(1):77. doi: 10.1038/s41467-024-55464-8.
Shock waves, the interface of supersonic and subsonic plasma flows, are the primary region for charged particle acceleration in multiple space plasma systems, including Earth's bow shock, which is readily accessible for in-situ measurements. Spacecraft frequently observe relativistic electron populations within this region, characterized by energy levels surpassing those of solar wind electrons by a factor of 10,000 or more. However, mechanisms of such strong acceleration remain elusive. Here we use observations of electrons with energies up to 200 kiloelectron volts and a data-constrained model to reproduce the observed power-law electron spectrum and demonstrate that the acceleration by more than 4 orders of magnitude is a compound process including a complex, multi-step interaction between more commonly known mechanisms and resonant scattering by several distinct plasma wave modes. The proposed model of electron acceleration addresses a decades-long issue of the generation of energetic (and relativistic) electrons at planetary plasma shocks. This work may further guide numerical simulations of even more effective electron acceleration in astrophysical shocks.
激波作为超音速和亚音速等离子体流的界面，是包括地球弓形激波在内的多个空间等离子体系统中带电粒子加速的主要区域，地球弓形激波便于进行原位测量。航天器经常在该区域观测到相对论电子群体，其能量水平比太阳风电子高出10000倍或更多。然而，这种强加速的机制仍然难以捉摸。在这里，我们利用对能量高达200千电子伏特的电子的观测以及一个数据约束模型来重现观测到的幂律电子谱，并证明超过4个数量级的加速是一个复合过程，包括更常见机制之间复杂的多步相互作用以及几种不同等离子体波模式的共振散射。所提出的电子加速模型解决了行星等离子体激波处高能（和相对论）电子产生这一长达数十年的问题。这项工作可能进一步指导天体物理激波中更有效电子加速的数值模拟。
