About the in fluence of gas-flow and power on the formation of specific atomic oxygen distributions in a plasma needle operated in high power-mode

摘要

We report on the creation of atomic oxygen in the euent of a plasma needle in front of a dielectric substrate operated with helium at ambient air. Two-photon absorption laserinduced fluorescence spectroscopy, combined with gas flow simulation, has been employed to obtain spatially-resolved ground state atomic oxygen densities. There is clear evidence that ground state atomic oxygen shows two different distribution patterns near the surface, directly dependent on the input parameter power and gas-flow. When the feed gas flow rate is low, the radial density peaks along the axis of the needle. At high flow rate, a ring-shaped density distribution appears. The peak density is on the order of 10~(21) m~(-3) in both cases. The results are consistent with a previous report of the flow-dependent bacterial killing pattern observed under similar conditions [1]. Further observations show a comparable influence of the applied generator power on the oxygen distribution. With increasing power the oxygen distribution changes from a single, on-axis peak to a ring-shaped structure.