HF discharges sustained in a resonance cavity or in a resonant plasma

The densities obtained in self-resonant HF discharges are perfectly explained using a linear theory to determine the position of the resonances; they can be created either on one of the plasma's own resonances or on a cavity resonance; densities exceeding the critical density (ω p > ω; ω is the excitation frequency and ωp is the plasma frequency) can be achieved. A theoretical model based on energy balance explains the experimental results. In a second part, a plasma column is obtained by exciting a plasma mode (either the axial symmetry mode or the dipole mode); initially, the plasma is created in the cavity and extends widely outside due to the force in ∇E2; this allows the wave to propagate over a greater distance and, by repeating this mechanism until the wave is attenuated, to obtain a plasma column; the speed of this mechanism has been measured. Densities a thousand times greater than the critical density have been achieved by exciting the axial symmetry mode.