Plasma fluctuation spectra as a diagnostic tool for sub-micron dust

It is shown that the measurements of density fluctuation spectra in dusty plasmas can constitute a basis for in situ diagnostic of invisible submicron dust. The self-consistent kinetic theory that includes the charging processes and the natural density fluctuations of the dust particles predicts modifications of the spectra due to the presence of dust. A laboratory experiment was carried out where submicron dust was produced in a gas phase and diagnosed by surface analysis of samples and by measurements of its influence on the plasma density fluctuation spectra. Quantitative comparison of the latter with the theory yields information on dust density, size, and distribution in agreement with the results of the surface analysis. The method can be applied to various plasma environments in laboratory and space.