Effect of Charged Particle-Neutral Collisions on Collective Thomson Scattering

Abstract

The effect of charged particle-neutral collisions on the spectrum of electromagnetic radiation scattered by the free electrons in plasmas is investigated. The calculations are restricted to the regime where λe ≫ k−1 > λD, where λe is the mean free path for electron, k is the magnitude of the scattering k vector, and λD is the Debye length. The spectral density of the electron density fluctuations is computed from the Vlasov equation with the aid of a relaxational collision model. The results thus obtained correspond to Salpeter's expressions with a finite damping constant. The effect of collisions with neutrals on the central ion peak is found to be small in most laser scattering experiments. The effect of collisions on the electron wings, however, is much stronger. Approximate analytical estimates and more accurate numerical evaluation of the scattering cross section suggest that electron-neutral collisions may enhance the scattering from the longitudinal electron waves.