RF-driven atmospheric-pressure capillary plasma jet in a He/O2 gas mixture: Multi-diagnostic approach to energy transport

Abstract

Atmospheric-pressure plasma jets operated in noble gases with an oxygen admixture have high application potential in industry and medicine. In this paper, we report on an extension of the well-studied RF-driven plasma jet from the European Cooperation in Science and Technology (COST-Jet), which has shown to deliver stable and reproducible discharge conditions but is limited to the α-discharge mode at low input powers. The so-called capillary-jet features the same discharge geometry as the COST-Jet, but the plasma is ignited inside a capillary with a square cross section acting as a dielectric in front of the electrodes. This prevents a glow-to-arc-transition at high input powers and allows stable operation in the γ-mode. We performed a set of measurements on the capillary-jet in the α- and γ-mode and compared the α-mode results to data obtained for the COST-Jet showing that the discharges are indeed similar and that the capillary-jet extends the accessible parameter range to high input powers. The presented results include power characteristics, temperature measurements, atomic oxygen densities from helium state enhanced actinometry, and molecular beam mass spectrometry (MBMS) as well as ozone densities from MBMS as functions of input power and molecular oxygen admixture. The results are summarized into an energy balance with most of the power dissipated into heating of the plasma feed gas.