On the Electrical Characteristic of Atmospheric Pressure Air/He/ ${\rm O}_{2}/{\rm N}_{2}$ /Ar Plasma Needle

The electrical characteristics of an air plasma needle are investigated. The discharge is driven by pulsed direct current voltages. A series of discharge pulses appear for one applied voltage pulse. The interval between nearby discharge current is tens of nanoseconds, which corresponds to a frequency of tens of MHz. This is much higher than that of the Trichel pulse (tens of kHz). The frequency of the discharge current pulses increases with the applied voltage but decreases with the gas gap distance. The series current pulses are found not only existing in electronegative gases (air, pure O₂), but also in Ar and N₂. On the other hand, when He is used, there always appears only one discharge current pulse; by adding small percentage of O₂ to He, multiple discharges appear again.