Transmission measurements of electrostatic plasma waves in the GHz frequency range

In the positive column of an argon low-pressure gas discharge, waves in the GHz range were transmitted parallel and perpendicularly to the tube axis between two probes. These waves were identified as electrostatic waves by means of their dispersion relation. The observed dispersion is described better by the equation: ω/ω p = 1 + 2 KT . k 2 / m ω p 2 ) which is an approximation of the lowest damped Landau pole in the range 1 < ω/ω p ≲ 1.5 (Pavkovich and other authors), than by the Bohm and Gross formula: ω 2 = ω p 2 + 3 KT . k 2 / m (ω = wave frequency, ω p = plasma frequency, K = Boltzmann constant, T,m = electron temperature and electron mass respectively, k = wavenumber).