Microwave Scattering Due to Acoustic-Ion-Plasma-Wave Instability

Abstract

An analysis is presented of an experimental study of microwave scattering from nonequilibrium plasmas in which the electrons had a large steady drift velocity $v_d$ with respect to the ions. According to theory, such plasmas must support "relatively undamped" acoustic-ion-plasma waves due to a two-stream instability type of mechanism. Measurements of the frequency-power spectrum of the scattered signal show agreement with theory. In particular, as predicted, the measured scattering cross sections were large in comparison with the Thomson cross section. The effects of collisions predicted by theory did not show up in the experimental results. As expected from theoretical considerations of nonlinear effects (such as the nonlinear coupling between the plasma modes of different wave numbers), the relative drift velocity and the electron-ion temperature ratio tend toward a saturation value as the plasma current is increased. The experimental results indicate that the nonlinear effects are relatively weak.