Electron acoustic waves in pure ion plasmas

Standing electron acoustic waves (EAWs) are observed in a pure ion plasma. EAWs are slow nonlinear plasma waves; at small amplitude their phase velocities (vph≃1.4v¯ for small kλD) and their frequencies are in agreement with theory. At moderate amplitude, EAW-type plasma waves can be excited over a broad range of frequencies. This frequency variability comes from the plasma adjusting its velocity distribution so as to make the plasma mode resonant with the drive frequency. Wave-coherent laser-induced fluorescence shows the intimate nature of the wave-particle interaction, and how the particle distribution function is modified by the wave driver until the plasma mode is resonant with the driver.