Secondary decay of an ion-acoustic wave is shown to provide an efficient saturation mechanism for stimulated Brillouin scattering in underdense plasma (n<0.5ncr). Phase effects and linear damping of ion waves are included in the analysis. In the weak damping regime, secondary decay dominates linear damping providing efficient saturation of Brillouin scattering. Heavy linear damping of ion waves increases the threshold for secondary decay considerably and very small densities are required to obtain saturation.
PHYSICAL REVIEW LETTERS 9AUGUST1982vortex pairs. The solid lines in Fig. 4(b) are drawn with slope f. Over a wide range of 6, the data agree with the lines, indicating that over that angular range the % mode indeed corresponds to m =1. There it has a wavelength equal to f the circumference, and it moves at the same speed as the m = 3 mode. For 0.6 < 0/2?r^O.7, the mode develops a phase anomaly and "drops back" by half a wavelength so as to be able to continue periodically around the annulus. At slightly different axial positions on the same vortex pair, we have observed the transition taking place in the range 0.5^ 6/2n% 0.8 by "jumping ahead" by half a wavelength. This transition region is stationary in the laboratory frame, possibly because of pinning by slight geometric imperfections.We are grateful to R.
A kinetic model for stable, underdense plasma in the presence of a strong electromagnetic pump wave is presented. Ion dynamics are properly treated to account for enhancement in electrostatic fluctuations. Such fluctuations are important even for pump strength below threshold for the oscillating two-stream and parametric decay instabilities in the underdense region. Thresholds of these instabilities are numerically determined. The results of calculations for the static form factor S(k) electron collision terms, and the absorption coefficient are presented for stable, homogeneous plasmas. For moderate pump values (below instability threshold) enhanced fluctuation levels and increased absorption are found, which have relevance to a variety of experimental situations involving high-intensity laser, microwave, or radio wave interaction with plasmas.
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