Electrostatic plasma resonances

Abstract

It is shown that the resonances observed in microwave scattering from a positive column depend on the existence of a radial electron density gradient. Deductions are made about the boundary conditions governing the space charge distribution associated with the resonant scattering. A comparison with electrostatic probe measurements shows that subsidiary resonances exist, their position being a function of number density and probing frequency. The principal resonance, on the other hand, depends also on the external geometry. It is a feature of measurements made in this way that the principal resonance occurs at a frequency somewhat less than the mean plasma frequency.