Low-Frequency Waves in SF6 Positive Columns Diluted with N2 Gas

Backward waves with frequencies around 1 kHz were observed in SF6 positive columns which contain N2 gas in concentrations of 10% or more at the total pressures of 0.7 and 1.0 Torr. The wave amplitude decreases as the mixing ratio of N2 gas increases. This decrease results in the depression of the generation of negative ions due to N2 gas.