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Ion Acceleration by Foreshock Bubbles
Journal of Geophysical Research: Space Physics ( IF 2.8 ) Pub Date : 2021-04-14 , DOI: 10.1029/2020ja028924
N. Omidi 1 , S. H. Lee 2 , D. G. Sibeck 2
Affiliation  

Foreshock bubbles (FBs) form as a result of the interaction between solar wind discontinuities and backstreaming ion beams in the foreshock. They are carried by the solar wind in the anti‐sunward direction and are associated with high energy ions. We employ electromagnetic hybrid (kinetic ions, fluid electrons) simulations and test particle calculations to investigate ion acceleration by FBs. Simulation results show that the maximum energies which the ions attain are not sensitive to the topology of the FBs, which varies from spherical to planar limits. However, the solar wind velocity does control the maximum energies reached by FB acceleration. Test particle calculations show that ion energization takes place through reflection of sunward moving ions from FBs through one or more collisions consistent with second‐order Fermi acceleration. The results also indicate that energy gain does not reach that expected for elastic reflections. Examination of ion energy spectra within different FBs shows a self‐similar pattern consisting of distribution peaked at the solar wind ram energy Esw with a distribution tail that reaches energies of ∼5.6 Esw. This behavior is consistent with second‐order Fermi acceleration and the inherent limitations on energy gain in this process. We also discuss the role of nonlinear structures called foreshock cavitons in the acceleration process.

中文翻译:

通过前震气泡加速离子

由于太阳风的不连续性与前兆中的离子束逆流之间的相互作用,形成了前兆气泡(FBs)。它们由太阳风沿反太阳方向运载,并与高能离子相关。我们采用电磁混合(动力学离子,流体电子)模拟和测试粒子计算来研究FBs对离子的加速作用。仿真结果表明,离子获得的最大能量对FB的拓扑结构不敏感,而FBs的拓扑结构从球形到平面都变化。但是,太阳风速确实控制着FB加速所达到的最大能量。测试粒子的计算表明,通过与二阶费米加速度一致的一次或多次碰撞,来自FB的朝上移动的离子的反射发生了离子加电。结果还表明,能量增益未达到弹性反射的期望值。对不同FB中离子能谱的检查显示出一种自相似的模式,该模式由在太阳风夯能量处达到峰值的分布组成E sw,分布尾巴的能量达到〜5.6 E sw。此行为与二阶费米加速度和此过程中能量获取的固有限制是一致的。我们还将讨论称为前兆空洞的非线性结构在加速过程中的作用。
更新日期:2021-05-06
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