Scattering of Microwaves from Plasma Waves Excited in an Electron Beam-Plasma Interaction

摘要

The process of incoherent scattering of microwaves from plasma waves is used to investigate the spatial development of the unstable longitudinal fluctuation spectrum of plasma electrons excited by an electron beam in a plasma in the absence of an external magnetic field. The most unstable plasma waves propagating at any angle to the beam direction are found to have a phase velocity approximately equal to the projection of the beam velocity in that direction and are thus directly excited by the beam. The effect of a finite beam radius on the instability is experimentally determined, and, it is found that this effect is modified as the instability develops. Microwave scattering from the harmonic of the plasma wave is observed and the dispersion behavior of the harmonic wave measured. Experiments comparing the radiation emitted by the plasma waves to the microwaves scattered from the plasma waves are in agreement with a theory by Ichimaru and Starr. (Author)