Instability of self-sustained gas discharges at corona onset for various experimental conditions

The DC discharge phenomenology at corona onset was further examined. The pulse characteristics observed for the investigated N₂ mixtures with a low content of SF₆ were found to differ greatly from those observed in the case of pure SF₆, air or air-SF₆ mixtures. For negative-corona conditions, dilution of SF₆ in N₂ has resulted into the disappearance of pulse sequences. In particular, if we consider data relative to the case where the SF₆ content was 1%, the effect of increasing the non-uniformity of the geometrical field was obvious: It quenched the discharge activity. Streaks of large pulses followed by an ionic contribution disappeared to the profit of single discharge events consisting of a single pulse over the 1-ms frame.