Effect of a high-frequency field on the reflection of ion acoustic waves from the sheath at a grid

Abstract

Experiments are described which show that the reflection coefficient for ion acoustic waves (IAW) from the sheath at a grid is affected by an HF electric field with a frequency f/sub HF/<or approximately=5f/sub pi/(f/sub pi/=ion plasma frequency). For peak-to-peak amplitudes of the HF voltage drop across the sheath Phi /sub 0/<or approximately=k/sub B/T/sub e//e and f/sub HF/>f/sub pi/, the energy distribution of the ions passing through the grid develops a hot tail and the reflected wave suffers enhanced Landau damping. If Phi /sub 0/>or approximately=k/sub B/T/sub e//e and f/sub HF/<f/sub pi/, a large-amplitude IAW is excited at the grid; a well-defined ion beam is formed; and local growth of the reflected wave is observed. Test waves launched from the grid show the same propagation characteristics as the reflected waves.<<ETX>>