混合模拟中非线性朗道阻尼的研究
Investigating Nonlinear Landau Damping in Hybrid Simulations
AI总结：
本研究通过混合模拟评估非线性朗道阻尼，发现其阻尼率依赖大尺度磁场功率，且逆级联产生大尺度磁场，大尺度阿尔文湍流可抑制流不稳定性，影响宇宙射线自约束。
摘要：
宇宙射线自约束的现象学研究通常依赖于线性理论，用以描述流不稳定性增长率以及所产生的磁模的阻尼率。目前存在多种不同的表达式，特别是对于非线性朗道阻尼的速率，该机制通常被认为是暖电离等离子体中最主要的阻尼机制。利用共振流不稳定性机制下的混合粒子（hybrid-PIC）模拟，我们对非线性朗道阻尼进行了全面评估，并表明在给定尺度上的阻尼率取决于更大尺度上磁场中的功率。此外，我们发现存在逆级联过程，该过程在大于共振尺度的尺度上产生磁场。在此，我们将先前针对单能非热粒子分布获得的结果扩展到更广泛的宇宙射线分布情形，作为发展现象学模型的第一步。在大尺度上预先存在的阿尔文性质湍流严重影响低能宇宙射线产生的波的阻尼；取决于其振幅，此类湍流可能抑制流不稳定性的增长，从而使得宇宙射线要么在所有能量下都自约束，要么完全不受约束。
英文摘要：
Phenomenological studies of cosmic-ray self-confinement often hinge on the linear theory for the growth rate of the streaming instability and for the damping rate of the generated magnetic modes. Largely different expressions exist, especially for the rate of nonlinear Landau damping, which is often assumed to be the most important damping mechanism in warm ionized plasmas. Using hybrid-PIC simulations in the resonant streaming instability regime, we present a comprehensive assessment of nonlinear Landau damping and show that the damping rate at a given scale depends on the power in magnetic fields on larger scales. Furthermore, we find that an inverse cascade develops, which produces magnetic fields on scales larger than the resonant ones. Here we extend previous results obtained for a mono-energetic distribution of non-thermal particles to the case of broader CR distributions, as a first step towards developing phenomenological models. Pre-existing turbulence of Alfvénic nature at large scales severely affects the damping of waves produced by low-energy CRs; depending on its amplitude, such a turbulence may inhibit the growth of streaming instability so that CRs are either self-confined at all energies or not at all.
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