Secondary electron emission in the course of the first Trichel-like pulse development in N/sub 2/+SF/sub 6/ mixtures

Waveforms of the first negative corona current pulses in 70% N/sub 2/+30% SF/sub 6/ mixture at a pressure of 13.33 kPa were investigated as a function of applied gap voltage. Based on the observed changes of the pulse shape, the role of different emission processes in the course of the discharge development was elucidated. At corona threshold, the pulse took the form of a simple hump, consistent with secondary electron emission due to positive-ion impact. A small increase in gap voltage resulted in the formation of a double-peaked pulse form which can be explained in terms of independent photoemission and secondary emission due to positive-ion bombardment. At higher voltage values (1.5 to two times higher than the corona threshold voltage), a peculiar form of the current pulse leading edge was observed and tentatively has been attributed to a field emission.