Parametric instability of a large-amplitude nonmonochromatic Alfvén wave
Parametric instability of a large-amplitude nonmonochromatic Alfvén wave
复制标题
大振幅非单色阿尔文波的参数不稳定性
DOI：
--
复制
发表时间：
1996
期刊：
影响因子：
--
通讯作者：
M. Velli
中科院分区：
文献类型：
--
作者：
F. Malara;M. Velli
在一维几何中研究了有限振幅Alfven波的参数不稳定性。泵浦波是非线性磁流体动力学(MHD)方程的精确解，即磁场扰动具有均匀的强度，并在垂直于传播方向的平面上旋转，但其傅立叶谱包含多个波长。首次用解析方法研究了弱非单色区。结果表明，不稳定的增长率随一个衡量偏离单色情况的参数而呈二次曲线减小。通过数值求解不稳定性方程，研究了当泵浦光波的相位函数具有幂函数谱时的完全非单色情况。虽然在单色情况下增长速度最大，但对于宽光谱泵浦波，增长速度也保持在相同的数量级。对于准单色波，对生长率的修正仅取决于位相函数的谱指数。
The parametric instability of a finite‐amplitude Alfven wave is studied in a one‐dimensional geometry. The pump wave is an exact solution of the nonlinear magnetohydrodynamic (MHD) equations, i.e., the magnetic field perturbation has a uniform intensity and rotates in the plane perpendicular to the propagation direction, but its Fourier spectrum contains several wavelengths. The weakly nonmonochromatic regime is first studied by an analytical approach. It is shown that the growth rate of the instability decreases quadratically with a parameter that measures the departure from the monochromatic case. The fully nonmonochromatic case is studied by numerically solving the instability equations, when the phase function of the pump wave has a power‐law spectrum. Though the growth rate is maximum in the monochromatic case, it remains of the same order of magnitude also for wide spectrum pump waves. For quasimonochromatic waves the correction to the growth rate depends only on the spectral index of the phase func...