3.9 Feedback Experiments on Multimode Ionization Waves

The influence of feedback and external driving signals on growth and saturation of ionization waves in a finite length positive column discharge has been investigated. Inserting a frequency‐swept driving signal the ionization wave response exhibits eigenmodes which are equally spaced on the wavenumber axis. In the absence of any external perturbation only one mode is spontaneously excited. By external feedback the dominant ionization wave can be caused to mode jump. It is observed that with external electrodes, the mode changes occurred from the cathode, and propagated with a finite velocity (approximately that of the group velocity of the waves). Measurements of the spatial gain and its saturation for different discharge currents (or gain) are compared with the Landau saturation formula to give gain and saturation coefficients.