A new actinometry approach, helium state enhanced actinometry (SEA), is presented. This diagnostics uses the emission of the atomic states O(3p3P) (λ=844.6 nm), Ar(2p1) (λ=750.4 nm) and He(33S) (λ=706.5 nm) and allows the atomic oxygen density and the mean electron energy to be determined simultaneously from the spectral line intensity ratios. Here, the atomic states are selected in a way that they cover a wide range of the electron energy distribution function (EEDF). The method is compared to the classical actinometry approach and energy resolved actinometry (ERA) based on measurements on the COST microplasma jet. In addition, a benchmark against two-photon absorption laser induced fluorescence (TALIF) measurements is performed. Both atomic oxygen densities and mean electron energies are in good agreement with the literature. Furthermore, SEA offers a number of advantages over known approaches. Firstly, the experimental complexity is significantly reduced by using time-integrated spectra instead of phase-resolved measurements, as used in the original ERA approach. Secondly, the precision of the energy measurement can be significantly improved by the use of the helium state. In addition, known uncertainties e.g. due to excitation of oxygen excited levels via metastable oxygen states can be reduced.
Micro cavity plasma arrays have numerous applications, such as the treatment of volatile organic compounds (VOCs) or the generation of new species. In recent years, the focus has also shifted to plasma catalysis, in which catalytic surfaces are combined with plasmas. The key to all of these applications is the generation of reactive species such as atomic oxygen within the plasma. Typically, atomic oxygen densities can be measured by laser spectroscopic methods. In the case of a micro plasma array, which consists of thousands of cavities with a diameter between 50-200 µm, optical access is limited. For this reason, an optical emission spectroscopy (OES) approach, helium state enhanced actinometry (SEA), is used. 2D resolved narrow bandwidth measurements are performed by using an ICCD camera in combination with a tunable bandpass filter (550-1000 nm). The discharge is operated in helium with an oxygen admixture of 0.1%. An argon admixture of 0.05% is used as actinometer gas. The triangular excitation voltage is varied between amplitudes of 400 and 800 V at a frequency of 15 kHz. Very high dissociation degrees up to nearly complete dissociation are observed. Time resolved measurements show significant differences in oxygen density between the increasing and the decreasing potential phase.
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