Large avalanche buildup in low-pressure SF6 under nonuniform-field conditions

Waveforms exhibiting a double-peak structure were observed under a geometrically decreasing field and in presence of a large amount of photo-released electrons at the cathode. The characteristics of these structures were found to vary with the intensity of the applied DC field and upon the degree of the UV beam focus. The second peak was seen to occur right after the first transit time and its magnitude could exceed that of the first peak. A theoretical model was developed in order to study this experimental observation. It was found that the field depression towards the anode and a source of secondary electrons at the cathode needed to be incorporated to reproduce the double-peak feature