The Role of Parametric Instabilities in Turbulence Generation and Proton Heating: Hybrid Simulations of Parallel-propagating Alfvén Waves
The Role of Parametric Instabilities in Turbulence Generation and Proton Heating: Hybrid Simulations of Parallel-propagating Alfvén Waves
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DOI：
10.3847/1538-4357/abbccd
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发表时间：
2020-06
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影响因子：
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通讯作者：
C. González;A. Tenerani;M. Velli;P. Hellinger
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文献类型：
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作者：
C. González;A. Tenerani;M. Velli;P. Hellinger
大振幅阿尔文波往往是不稳定的参数不稳定性，导致在一个衰减过程中的初始波到不同的子波取决于振幅的波动和等离子体β。相对于子波的平均磁场的传播角在确定衰变类型中起着重要作用。在本文中，我们重新审视这个问题的多维混合模拟。特别是，我们研究的衰减和随后的非线性演化的大振幅阿尔文波通过调查的饱和机制的不稳定性和其最终的非线性状态达到不同的波振幅和等离子体β条件。相对于一维模拟的衰减不稳定性被抑制的等离子体β值的增加，我们发现，在多维的衰减过程中持续通过的压缩/磁声衰减不稳定性在大的等离子体β值。在一般情况下，衰减过程作为一个触发器，以开发一个垂直的湍流级联，并提高平均场对齐的波粒相互作用。我们确实发现，饱和状态的特征在于湍流等离子体显示出在阿尔芬速度和温度升高，我们归因于朗道共振和俯仰角散射在相空间中的场对齐的光束。
Large-amplitude Alfvén waves tend to be unstable to parametric instabilities that result in a decay process of the initial wave into different daughter waves depending upon the amplitude of the fluctuations and the plasma beta. The propagation angle with respect to the mean magnetic field of the daughter waves plays an important role in determining the type of decay. In this paper, we revisit this problem by means of multidimensional hybrid simulations. In particular, we study the decay and the subsequent nonlinear evolution of large-amplitude Alfvén waves by investigating the saturation mechanism of the instability and its final nonlinear state reached for different wave amplitudes and plasma beta conditions. As opposed to one-dimensional simulations where the Decay instability is suppressed for increasing plasma beta values, we find that the decay process in multidimensions persists at large values of the plasma beta via the filamentation/magnetosonic decay instabilities. In general, the decay process acts as a trigger both to develop a perpendicular turbulent cascade and to enhance mean field-aligned wave–particle interactions. We find indeed that the saturated state is characterized by a turbulent plasma displaying a field-aligned beam at the Alfvén speed and increased temperatures that we ascribe to the Landau resonance and pitch-angle scattering in phase space.