Rp. Drake et al., LINEAR RAY-OPTICS THEORY OF THE RADIATION-DRIVEN ION-ACOUSTIC DECAY INSTABILITY IN FLOWING, INHOMOGENEOUS PLASMAS, Physics of plasmas, 1(8), 1994, pp. 2448-2459
The linear Wentzel-Kramers-Brillouin (WKB) or ray-optics theory of the
ion-acoustic decay instability is developed for flowing inhomogeneous
, fluid plasmas of arbitrary ionic charge, as is needed in the plannin
g and analysis of experiments. Equations are developed for the instabi
lity threshold in a homogeneous plasma and for the amplification in pl
asmas that may be inhomogeneous in more than one spatial direction and
/or in time. These equations are formulated so that prior WKB theory o
f three-wave parametric instabilities may be directly applied to this
problem. The results are compared with prior work on this instability,
and are applied to several circumstances of practical interest. One f
inds that, for typical conditions, large amplification is possible ove
r a wide range of angles. In addition, the flow properties of the plas
ma are found to be crucial in determining the angular distribution of
the amplification produced by the instability. In particular, the magn
itude of the plasma flow, when the flow is subsonic, directly controls
the angle of maximum WKB amplification.