质子尺度下具有精确动理学平衡的开尔文-亥姆霍兹不稳定性
Kelvin-Helmholtz instability at proton scales with an exact kinetic equilibrium
AI总结：
本文利用Hybrid Vlasov-Maxwell模拟研究质子尺度下开尔文-亥姆霍兹不稳定性的动理学效应，揭示精确初始平衡态对能量向短尺度传递和粒子速度分布偏离热平衡的关键作用，并支持MMS任务的空间观测结果。
摘要：
开尔文-亥姆霍兹不稳定性是普通流体和等离子体中普遍存在的物理过程，在空间环境中也经常被观测到。本文通过Hybrid Vlasov-Maxwell模拟，研究了磁化无碰撞等离子体中开尔文-亥姆霍兹不稳定性在非线性和湍流阶段质子尺度上的动理学效应。这项工作的主要目标是揭示这种不稳定性演化所引发的粒子反作用，因为能量沿湍流级联到达动理学尺度。有趣的是，当开尔文-亥姆霍兹不稳定性在一个并非精确平衡态的初始状态上发展时，湍流会受到抑制。另一方面，当考虑初始平衡条件时，能量可以有效地向短尺度传递，达到典型的质子波长并驱动粒子动力学。由于粒子与湍流涨落场的相互作用，质子速度分布显著偏离局域热力学平衡，偏离程度随系统中湍流水平的增加而增大，并且位于强磁应力区域附近。这些数值结果支持了近期来自Magnetospheric MultiScale任务的空间观测，即地球磁鞘中由湍流动力学驱动的离子动理学效应（Perri et al., 2020, JPlPh, 86, 905860108），以及地球磁层中由开尔文-亥姆霍兹不稳定性驱动的效应（Sorriso-Valvo et al., 2019, PhRvL, 122, 035102）。
英文摘要：
The Kelvin-Helmholtz instability is a ubiquitous physical process in ordinary fluids and plasmas, frequently observed also in space environments. In this paper, kinetic effects at proton scales in the nonlinear and turbulent stage of the Kelvin-Helmholtz instability have been studied in magnetized collisionless plasmas by means of Hybrid Vlasov-Maxwell simulations. The main goal of this work is to point out the back reaction on particles triggered by the evolution of such instability, as energy reaches kinetic scales along the turbulent cascade. Interestingly, turbulence is inhibited when Kelvin-Helmholtz instability develops over an initial state which is not an exact equilibrium state. On the other hand, when an initial equilibrium condition is considered, energy can be efficiently transferred towards short scales, reaches the typical proton wavelengths and drives the dynamics of particles. As a consequence of the interaction of particles with the turbulent fluctuating fields, the proton velocity distribution deviates significantly from the local thermodynamic equilibrium, the degree of deviation increasing with the level of turbulence in the system and being located near regions of strong magnetic stresses. These numerical results support recent space observations from the Magnetospheric MultiScale mission of ion kinetic effects driven by the turbulent dynamics at the Earth's magnetosheath (Perri et al., 2020, JPlPh, 86, 905860108) and by the Kelvin-Helmholtz instability in the Earth's magnetosphere (Sorriso-Valvo et al., 2019, PhRvL, 122, 035102).
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