Effect of collisions on the plasma line of the electron density fluctuation spectrum

Abstract

The Klimontovich-Dupree formalism is used to investigate the effect of electron-neutral collisions on the plasma line of the electron density fluctuation spectrum. The Fourier transform of the fluctuation electron number density is calculated by integrating along electron trajectories consisting of straight-line segments joined at electron-neutral scattering sites. It is shown that the scattering process itself results in the excitation of plasma oscillations and contributes to the plasma line intensity. The electron density autocorrelation is calculated by ensemble averaging over the initial positions and velocities of all the electrons in the system and averaging over a transition probability describing the electron-neutral collisions. The transition probability is expanded as a power series in the collision frequency. The plasma line spectrum is calculated in the limit that the electron travels many wavelengths between collisions. The principal result of this is that collisions enhance the intensity of the plasma line by as much as a factor of six when the collision frequency exceeds the Landau damping decrement. This result is of most interest in attempts to observe the electron plasma line with the incoherent-scatter radar in the E-region of the ionosphere when the electron density is enhanced by auroral bombardment.