Parametric instabilities of circularly polarized large-amplitude dispersive Alfvén waves: excitation of parallel-propagating electromagnetic daughter waves
Parametric instabilities of circularly polarized large-amplitude dispersive Alfvén waves: excitation of parallel-propagating electromagnetic daughter waves
复制标题
圆偏振大振幅色散阿尔文波的参数不稳定性：平行传播电磁子波的激励
DOI：
10.1017/s0022377800015981
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发表时间：
1991
影响因子：
2.5
通讯作者：
M. Goldstein
中科院分区：
文献类型：
--
作者：
A. Viñas;M. Goldstein
研究了大振幅圆偏振色散阿尔文波的参量衰减和调制不稳定性。我们的治疗是更一般的比以前的推导的基础上，我们允许在任意角度的背景磁场的不稳定的子波的传播的双流体方程，虽然我们在本文中主要关注的是探索新的方面的传播平行于直流磁场。除了众所周知的耦合泵波静电子波，我们发现了一个新的参数通道，泵波耦合直接电磁子波。电磁不稳定性的激发只发生在调制（k/k 0 ≤ 1）而不是衰减（k/k 0 < 1）时。与静电耦合激发的调制不稳定性相反，左旋（K > 0）和右旋（K < 0）极化都存在电磁调制不稳定性。对于大的k/k 0，电磁通道占主导地位，而在较低的值，静电通道具有较大的增长率，对于适度的色散值，泵浦波振幅和等离子体β。与静电调制不稳定性不同，电磁不稳定性的增长率随着泵浦波振幅的增加而单调增加。这种分析证实，对于衰变，主要过程是耦合到静电子波，至少对于平行传播。对于调制，与电磁子波的耦合通常占主导地位，这表明参量调制不稳定性实际上是一种电磁现象。
We investigate the parametric decay and modulational instabilities of a large-amplitude circularly polarized dispersive Alfvén wave. Our treatment is more general than that of previous derivations based on the two-fluid equations in that we allow for propagation of the unstable daughter waves at arbitrary angles to the background magnetic field, although our main concern in this paper is the exploration of new aspects of propagation parallel to the DC magnetic field. In addition to the well-known coupling of pump waves to electrostatic daughter waves, we find a new parametric channel where the pump wave couples directly to electromagnetic daughter waves. Excitation of the electromagnetic instability occurs only for modulation (k/k0 ≤ 1) and not for decay (k/k0 < 1). In contrast with the modulational instability excited by the electrostatic coupling, the electromagnetic modulational instability exists for both left-hand (K > 0) and right-hand (K < 0) polarization. For large k/k0, the electromagnetic channel dominates, while at lower values the electrostatic channel has a larger growth rate for modest values of dispersion, pump-wave amplitude and plasma β. Unlike the electrostatic modulational instability, the growth rate of the electromagnetic instability increases monotonically with increasing pump wave amplitude. This analysis confirms that, for decay, the dominant process is coupling to electrostatic daughter waves, at least for parallel propagation. For modulation, the coupling to electromagnetic daughter waves usually dominates, suggesting that the parametric modulational instability is really an electromagnetic phenomenon.