Parametric instabilities of circularly polarized Alfvén waves in plasmas with beam protons
Parametric instabilities of circularly polarized Alfvén waves in plasmas with beam protons
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DOI：
10.1029/2009ja014178
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发表时间：
2009-07
影响因子：
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通讯作者：
Y. Nariyuki;T. Hada;K. Tsubouchi
中科院分区：
文献类型：
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作者：
Y. Nariyuki;T. Hada;K. Tsubouchi
在太阳风中观测到的质子速度分布函数（vdf）经常显示束分量。本文采用一维混合模拟的方法，讨论了核心质子-电子束质子等离子体中圆极化Alfven波的参数不稳定性。数值计算结果表明，核心质子-电子束质子等离子体中参数不稳定性的非线性演化不同于核心质子-电子等离子体。此外，线性色散关系的数值解表明质子动力学效应的重要性，这与以往的研究结果一致。在光束稳定的情况下，根据参数不稳定性对宽带Alfven波的激发，质子在速度空间中扩散，导致光束分量的散射和展宽。质子vdf的这种时间演化改变了波色散关系，影响了参数不稳定性的性质，与以往的理论研究一致。因此，即使衰减不稳定性在线性阶段占主导地位，母波也主要被非线性阶段的调制不稳定性耗散。相位相干湍流的产生与调制不稳定性的发生相对应。在具有不稳定光束的等离子体中也观察到参数不稳定性。当左极化（LH-） Alfven波初始给定时，后向传播的右极化（RH-）和左极化（LH-） Alfven波都被我们运行中的衰减不稳定性所激发。随着时间的推移，相位相干湍流是由调制不稳定性产生的，就像稳定光束的情况一样。一些质子束通过回旋加速器与主波的共振而垂直加速。
[1] The proton velocity distribution functions (VDFs) observed in the solar wind often show beam components. In this study, by means of one-dimensional hybrid simulation, parametric instabilities of circularly polarized Alfven waves in core proton-electron-beam proton plasmas are discussed. Numerical results show that nonlinear evolution of parametric instabilities in core proton-electron-beam proton plasmas are different from those in core proton-electron plasmas. Furthermore, numerical solutions of the linear dispersion relations suggest the importance of the proton kinetic effects, which agrees with the past studies. In the case that the beams are stable, according to the excitation of the broadband Alfven waves by the parametric instabilities, protons are diffused in the velocity space, resulting in the scattering and broadening of the beam components. Such time evolution of the proton VDFs changes the wave dispersion relation and affects the properties of the parametric instabilities, in agreement with the past theoretical studies. As a result, even if a decay instability is dominant at the linear stage, the parent wave can mainly be dissipated by the modulational instability at the nonlinear stage. Phase coherent turbulence is generated corresponding to the occurrence of the modulational instability. Parametric instabilities are also observed in plasmas with unstable beams. When left-hand polarized (LH-) Alfven wave is initially given, both backward propagating right-hand polarized (RH-) and LH- Alfven waves are excited by the decay instabilities in our runs. As time elapses, phase coherent turbulence is generated by the modulational instabilities, as in the case of stable beams. Some of the beam protons are perpendicularly accelerated by cyclotron resonance with the primary wave.