The group "Allgemeine Elektrotechnik und Plasmatechnik" at the faculty for engineering and information science.

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Atomic oxygen generation in atmospheric pressure RF plasma jets driven by tailored voltage waveforms in mixtures of He and O2

Absolute atomic oxygen densities measured space resolved in the active plasma volume of a COST microplasma reference jet operated in He/O2 and driven by tailored voltage waveforms are presented. The measurements are performed for different shapes of the driving voltage waveform, oxygen admixture concentrations, and peak-to-peak voltages. Peaks- and valleys-waveforms constructed based on different numbers of consecutive harmonics, N, of the fundamental frequency f0 = 13.56 MHz their relative phases and amplitudes are used. The results show that the density of atomic oxygen can be controlled and optimized by voltage waveform tailoring (VWT). It is significantly enhanced by increasing the number of consecutive driving harmonics at fixed peak-to-peak voltage. The shape of the measured density profiles in the direction perpendicular to the electrodes can be controlled by VWT as well. For N > 1 and peaks-/valleys-waveforms, it exhibits a strong spatial asymmetry with a maximum at one of the electrodes due to the spatially asymmetric electron power absorption dynamics. Thus, the atomic oxygen flux can be directed primarily towards one of the electrodes. The generation of atomic oxygen can be further optimized by changing the reactive gas admixture and by tuning the peak-to-peak voltage amplitude. The obtained results are understood based on a detailed analysis of the spatio-temporal dynamics of energetic electrons revealed by phase resolved optical emission spectroscopy (PROES).

Release Date
Permanent Identifier (URI)
Is supplementing
Plasma Source Name
Plasma Source Application
Plasma Source Specification
Plasma Source Properties
COST-jet, consists of two identical and co-planar parallel electrodes made of stainless steel. The electrode gap is 1 mm. The electrodes are enclosed by two quartz plates confining the plasma volume to 1×1×30 mm^3, the frequency and gas flow vary.
Plasma Medium Name
Plasma Medium Properties
The discharge is operated in helium (5.0 purity) with oxygen (5.0 purity) admixture. This flow rate range of O2 corresponds to reactive gas concentrations between 0.05% and 1% in the He buffer gas. The gas pressure inside the jet is estimated to be 1.02(±0.02)×105 Pa. The temperature is roughly room temperature.
Plasma Medium Procedure
The flow rate of helium is fixed at 1000 sccm while the oxygen flow rate is varied from 0.5 to 10 sccm.
English (United States)
Public Access Level
Funding Agency
Contact Name
Ihor Korolov
Contact Email

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