Unexpected Plasma Plume Shapes Produced by a Microsecond Plasma Gun Discharge

The plasma plume shapes produced at the outlet of a 1 mm inner diameter plasma gun capillary are investigated over an extended range of both neon flow rates and pulse repetition rate (prr). Various complex, but stable, plume shapes are observed. It appears first that for a given flow rate, the plume shape can be modulated with prr sweeping, revealing fascinating multidart shape when discharge is triggered at a fundamental frequency and up to the sixth harmonic. Second, reproducible similar plume patterns, either multidarts or conical shaped, can be obtained for given appropriate flow rate/prr parameter couples. These phenomena tend to show the effect of the force exchange between the neutral gas flow and the discharge species resulting in plume patterning.