Absorption of Electrostatic Waves by Plasma Electrons

Experimental observations with supporting theory are described of the energy exchange between a plasma column and an externally applied rf electric field that was nearly longitudinal. When electron collisions may be neglected and the wave-particle interaction can be considered weak, the frequency-dependent power absorption, as predicted by solution of the linearized Boltzmann equation, is a resonant process involving electrons having velocities near the phase velocity of the applied field. Similarities between absorption of rf energy in this experiment and collisionless absorption of electron plasma waves are evident, and the experimental results support the ideas of Landau damping. Application of “strong” rf fields to a drifting electron plasma produces a nonlinear deformation of the time-averaged distribution. Measurements of this deformation compare favorably with a quasilinear calculation for weak nonlinear behavior.