Enhancement of plasma direct currents by intense alternating current fields

Instabilities in a plasma containing electrons drifting relative to the ions and subjected to an intense ac electric field of frequency ω are investigated. The beat disturbance produced by the interaction of the driving field and ion density fluctuations of wavenumber ki accelerates electrons of velocity ω/ki. If this is larger than the electron drift velocity, the acceleration enhances the current, while the recoil momentum imparted to the ion fluctuation can cause it to grow. The process has been simulated on a one-dimensional plasma model and it was found that the small amplitude growth is in agreement with a theory which is a minor modification of that for the anomalous high-frequency resistivity. Nonlinear effects ultimately saturate the growth of the instability and the current enhancement, and some discussion of these is given.