Effects of cathode spot dynamics on Trichel pulses

Negative corona discharge has been investigated in air in the point-to-plane electrode configuration in Trichel pulse regime. Average discharge current was measured and oscillography of discharge current with simultaneous frontal and side video observation of cathode spot were performed. Observations showed that fixation of cathode spot in certain position on the cathode surface was always accompanied by Trichel pulse train with constant amplitude and pulse time separation. When Trichel pulses are irregular the irregularity of cathode spot position is also observed. It is found that the smaller the curvature of the surface region on which the spot is localized the higher the pulse amplitude is realized. Generalized amplitude-pulse separation time characteristics of Trichel pulses were measured as function of discharge gap, voltage, pressure and cathode diameter for tungsten, copper, graphite and aluminum cathodes. Such diagrams let demonstrate separately effects of cathode spot dynamics and effects of gap conditions on Trichel pulses. These results let predict Trichel pulse parameters and spread in values for given in advance point-plane electrode system and hence may be useful for corona applications.