Effect of the ponderomotive force on the development of beam-plasma instability

Abstract

The amplitude of the wave generated in a plasma during the development of beam-plasma instability is nonuniform in the longitudinal direction. The ponderomotive force associated with this nonuniformity leads to a redistribution of the plasma density; as a result, the wave amplitude and its spatial distribution change. As the beam current grows, the ponderomotive force plays an increasingly important role and radically changes the mechanism by which the beam-plasma instability saturates. Ion acoustic waves generated by the ponderomotive force propagate in the direction opposite to the propagation direction of the beam, thereby ensuring distributed feedback and giving rise to a strong low-frequency self-modulation of the wave amplitude and phase. Results are presented from experimental investigations of the self-modulation regime of the beam-plasma instability in a magnetized plasma waveguide. Theoretical estimates of the parameters of the low-frequency self-modulation agree well with the experimental data.