Abstract
The problem of thermal electron density fluctuations in a weakly ionized gas is considered from the point of view of particle diffusion in single particle phase space (μ space). When ion-neutral and electron-neutral two-body collisions constitute the only important force on the charged particles apart from an electrostatic self-consistent field, it is shown how the fluctuation theory may be developed from a transition probability describing the random walk of a single charged particle in the absence of the interaction field. Specific calculations of thermally excited low frequency electron density fluctuation spectra are carried out on the assumption that the random walk may be described in terms of classical Brownian motion or in terms of a combination of free flight and classical Brownian motion. The latter model is shown to be a first approximation to a more exact solution which may be obtained by solving an integral equation for the transition probability. First-order calculations are carried out for the case where the ion-neutral collisions may be treated as hard sphere elastic ones. The computational results are compared with those of earlier theories of fluctuations in a weakly ionized gas.