Parametric instability of a linearly polarized monochromaticAlfven wave:Perpendicular decay in low beta plasma

【摘要】：Two-dimensional hybrid simulations are performed to investigate the parametric decay of a monochromatic Alfven wave with a linear polarization in low beta plasma.We find that the parametric decay is actually a two-dimentional process.Initially,the parametric decay takes place along the propagating direction of the pump wave,and then the decay occurs in the perpendicular direction.With the increase of the amplitude of the pump wave,both the linear growth rate and the saturated amplitude of the parametric decay increase,and the spectral range of the excited waves becomes broad in the perpendicular direction.While the linear growth rate of the parametric decay decreases with the increase of the plasma beta,the effects of the plasma beta on the saturated amplitude and the spectral range of the excited waves in the perpendicular direction are neglected.The parametric decay of an obliquely propagating pump wave is also studied in this paper.Similarly,the decay initially takes place along the propagating direction of the pump wave,and then it occurs in the perpendicular direction.The spectral range of the excited waves broadens in the perpendicular direction with the increase of the propagating angle of the pump wave(the angle between the propagating direction of the pump wave and the ambient magnetic field).