Ion acoustic waves at a plasma sheath

The propagation of ion acoustic waves toward a plasma sheath is considered, using a fluid model which allows charge separation. It is assumed that wavelengths are sufficiently short to apply the WKB approximation and that amplitudes remain sufficiently small to use the linear approximation. Under these approximations, ion acoustic waves are not reflected from a plasma sheath, and in general are somewhat damped, although they may undergo weak growth deep in the sheath.