Discharge Images of a Dielectric-Barrier-Free Atmospheric-Pressure Microplasma Controlled by an External Ballast Capacitor

A direct-current pulse-driven dielectric-free atmospheric-pressure microplasma controlled by an external capacitor is developed. Discharge images show that the electrical energy stored in the ballast capacitor controls effectively the discharge energy per pulse in air, He, and Ar gas flows. The effect of the ballast capacitance on the discharge from 22 pF to 10 nF is presented. This configuration provides a wide and stable microplasma operational regime, i.e., from a glow to a near-arc discharge.