Ar/O₂ gas pressure dependences of a pulsed zirconium arc and extracted ion characteristics

A pulsed dc zirconium arc discharge is generated in an argon diluted oxygen gas by separating a pin electrode as an anode from the cathode. The arc is transiently generated, and its life time is approximately 3 ms for a series resistance of 1 Ω and a dc output of 33 V. The life is prolonged and the plasma becomes stable with increasing the arc current. A target with a diameter of 100 mm is set at 150 mm from the arc source, and is immersed in the plasma. A pulse voltage is applied to the target to extract ions from the plasma. The ion current is not detected after approximately 8 ms since the plasma initiation. When the plasma is generated in oxygen without argon, the plasma generation time is scattered, and the plasma is unstable. An ion density is estimated from the temporal behavior of the target voltage in the recovery region after the pulse voltage. The ion density at the target is approximately 2.5 × 10¹⁵ m^{- 3} at a mixed gas pressure of 1.9 Pa, which corresponds to the plasma density of 1.1 × 10¹⁷ m^{- 3} under an assumption of electron temperature of 1 eV.