Particle-in-Cell Experiments Examine Electron Diffusion by Whistler-Mode Waves: 2. Quasi-Linear and Nonlinear Dynamics
Particle-in-Cell Experiments Examine Electron Diffusion by Whistler-Mode Waves: 2. Quasi-Linear and Nonlinear Dynamics
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细胞内粒子实验通过惠斯勒模式波检查电子扩散：2. 准线性和非线性动力学
DOI：
10.1029/2020ja027949
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发表时间：
2020
期刊：
影响因子：
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通讯作者：
Allanson O
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文献类型：
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作者：
Allanson O
测试粒子代码表明，由于与低振幅非相干哨声模波的相互作用而引起的电子动力学可以通过准线性理论充分描述。然而，有重要证据表明，较高振幅的波会导致电子动力学无法使用准线性理论充分描述。使用Allanson等人介绍的方法。(2019，https：//doi.org/10.1029/2019JA027088），我们跟踪了电子由于与非相干哨声模式波的相互作用而在所有能量和俯仰角空间中的动态响应。我们进行了五个实验，每个实验具有不同的电磁波振幅值。我们发现，在1,000个陀螺周期量级的时间尺度T上，电子动力学与低振幅非相干波的准线性理论扩散系数（Bw，rms/B 0）2 <$3.7·10−10）吻合得很好。然而，共振相互作用与更高的振幅波造成显着的非扩散动力学以及扩散动力学。当电子动力学提取和分析的时间尺度短于T，我们能够隔离扩散和非扩散（平流）动力学。有趣的是，当在这些适当较短的时间尺度（数百或数十个回转周期的量级）上考虑时，动力学的扩散分量与准线性理论的预测非常一致，即使波振幅高达（Bw，rms/B 0）2≈5.8·10 - 6。准线性理论是基于基本的扩散动力学，但本文提出的证据也表明存在一个明显的平流分量。因此，对具有更高振幅哨声模式波的波粒相互作用的电子动力学的正确描述可能需要包含扩散和平流项的福克-普朗克方程。
Test particle codes indicate that electron dynamics due to interactions with low amplitude incoherent whistler mode‐waves can be adequately described by quasi‐linear theory. However there is significant evidence indicating that higher amplitude waves cause electron dynamics not adequately described using quasi‐linear theory. Using the method that was introduced in Allanson et al. (2019, https://doi.org/10.1029/2019JA027088), we track the dynamical response of electrons due to interactions with incoherent whistler‐mode waves, across all energy and pitch angle space. We conduct five experiments each with different values of the electromagnetic wave amplitude. We find that the electron dynamics agree well with the quasi‐linear theory diffusion coefficients for low amplitude incoherent waves with (Bw,rms/B0)2≈3.7·10−10, over a time scaleTof the order of 1,000 gyroperiods. However, the resonant interactions with higher amplitude waves cause significant nondiffusive dynamics as well as diffusive dynamics. When electron dynamics are extracted and analyzed over time scales shorter thanT, we are able to isolate both the diffusive and nondiffusive (advective) dynamics. Interestingly, when considered over these appropriately shorter time scales (of the order of hundreds or tens of gyroperiods), the diffusive component of the dynamics agrees well with the predictions of quasi‐linear theory, even for wave amplitudes up to (Bw,rms/B0)2≈5.8·10−6. Quasi‐linear theory is based on fundamentally diffusive dynamics, but the evidence presented herein also indicates the existence of a distinct advective component. Therefore, the proper description of electron dynamics in response to wave‐particle interactions with higher amplitude whistler‐mode waves may require Fokker‐Planck equations that incorporate diffusive and advective terms.