Due to elevated pressure, cold atmospheric pressure plasmas generate excimer species, which can emit highly energetic photons, thus transferring energy inside the discharge and to treated substrates. However, they are difficult to assess, as they are absorbed by air or window material. Here, we present a method to measure vacuum ultraviolet photons using a monochromator with an aerodynamic window. The emission spectra of a radiofrequency‐excited atmospheric plasma jet were analyzed for typical gas mixtures. The data indicate that helium excimers contribute notably to the excitation of molecular and atomic species. The emission intensities do not follow densities of ground‐state species, underlining the variety of excitation channels and the change of the electron energy distribution function under changing gas composition.
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 [Formula: see text]-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 [Formula: see text]-mode. We performed a set of measurements on the capillary-jet in the [Formula: see text]- and [Formula: see text]-mode and compared the [Formula: see text]-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.
The energy balance of a plasma holds fundamental information not only about basic plasma physics, but it is also important for tailoring plasmas to specific applications. Especially RF-driven atmospheric pressure plasma jets (APPJs) operated in helium with oxygen admixture have high application potential in industry and medicine. Many types of plasma jets have been studied up to now, leading to the challenge how to compare results from various sources. We have developed a method for measuring the power deposited in the plasma as the parameter to compare different sources and gas mixtures with each other. Furthermore, we studied energy transport as a function of this input power and molecular gas admixture in a newly developed APPJ based on the COST-reference jet with a capillary as a dielectric in between the electrodes. The gas temperature, atomic oxygen density, ozone density and absolute emission intensity in the visible wavelength range have been determined. Combining the results gave an energy balance with most of the energy deposited into gas heating. Production of final chemical products made up a small amount of the deposited power while radiation was negligible for all combinations of external parameters studied.
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