Damping-Growth Transition for Ion-Acoustic Waves in a Density Gradient

A damping-growth transition for ion-acoustic waves propagating in a nonuniform plasma ($e$-folding length for the density $l_n$) is observed at a wavelength $\lambda \sim 2\pi l_n$. This result supports calculations performed in connection with the problem of heating of the solar corona by ion-acoustic waves generated in the solar photosphere.