Comparison of point-to-plane discharges in air and SF6

In the first part (DC voltages) some experimental results, for predischarge regimes, in air under pressure and in SF 6 are discussed. A comparison of the results obtained indicate a similar behaviour in air and SF 6 if one allows for a shift in pressure. In the second part some image converter recordings obtained in air and SF 6 are presented (impulse work). They show details of the streamer-to-spark transition with positive impulses. The physical mechanism responsible for that transition are discussed. These studies were effected in point-to-plane geometry with small gaps (1-2 cm).