On the detection of both the ionisation waves and so-called echo phenomenon by Langmuir and capacitive probes

Both Langmuir and capacitive probes detect two signals, corresponding to the usual ionisation wave and a so-called echo phenomenon, which is almost an oscillation of the entire positive column occurring when the wavefront reaches the anode region. The amplitude of these signals behaves differently according to the bias of the Langmuir probe. The origin of internal feedback might be explained by this echo phenomenon.