Enhanced ozone production in a pulsed dielectric barrier discharge plasma jet with addition of argon to a He-O$_2$ flow gas

Ozone production in a plasma jet DBD driven with a 20-ns risetime unipolar pulsed voltage can be significantly enhanced using helium as the primary flow gas with an O$_2$ coflow. The overvolted discharge can be sustained with up to a 5\% O$_2$ coflow at $<$20 kHz pulse repetition frequency at 13 kV applied voltage. Ozone production scales with the pulse repetition frequency up to a ``turnover frequency'' that depends on the O$_2$ concentration, total gas flow rate, and applied voltage. For example, peak ozone densities $>$10$^{16}$ cm$^{-3}$ were measured with 3\% O$_2$ admixture and $<$3 W input power at a 12 kHz turnover frequency. A further increase in the repetition frequency results in increased discharge current and 777 nm O($^5P$) emission, but decreased ozone production and is followed by a transition to a filamentary discharge mode. The addition of argon at concentrations $\geq$5\% reduces the channel conductivity and shifts the turnover frequency to higher frequencies. This results in increased ozone production for a given applied voltage and gas flow rate. Time-resolved Ar(1$s_5$) and He(2$^3S_1$) metastable densities were acquired along with discharge current and ozone density measurements to gain insight into the mechanisms of optimum ozone production.