Spatial dynamics of helium metastables in sheath or bulk dominated rf micro-plasma jets

Abstract

Abstract. Space resolved concentrations of helium He ( 3 S 1 ) metastable atoms in an atmospheric pressure radio-frequency micro-plasma jet were measured using tunable diode laser absorption spectroscopy. The spatial profile of metastable atoms in the volume between the electrodes was deduced for various electrode gap distances. Density profiles reveal the sheath structure and reflect the plasma excitation distribution, as well as the dominance of the α-mode discharge. Gap width variations show the transition from a normal glow plasma to a pure sheath discharge. In order to analyze and verify the experimentally observed profiles of the metastable atoms a 2-dimensional simulation model was set up. Applying an appropriate He/N 2 /O 2 chemistry model the correlation between the metastable profiles and the underlying excitation mechanisms was obtained.

Methods of gas purification and effect on the ion composition in an RF atmospheric pressure plasma jet investigated by mass spectrometry

“…The micro atmospheric pressure plasma jet (μ-APPJ) has been in the focus of many studies in the past and is described in great detail in [4,[26][27][28][29][30]. Here, a short description of the recent design will be given together with the operating procedure.…”

“…Two reasons are suggested for this observation: (1) In the chain of charge transfer reactions among primary ions with neutral gas species the charge is generally transferred to the species with the lowest ionization energy. (2) Penning ionization through helium metastables plays an important role in the creation of ions in atmospheric pressure plasmas [27]. The He(2 3 S) state carries an energy of 19.8 eV which allows it to readily ionize any other atomic or molecular species (except neon) with their typical ionization energies that are between 10 eV and 15 eV [32] within the bulk plasma of the jet.…”

Gas breakdown mechanism in pulse-modulated asymmetric ratio frequency dielectric barrier discharges

“…The similar phenomenon of the two separated regions of high density metastables merging to one in the central region as the reduction of the gap width was observed experimentally in the rf microplasma jet in mixed He/N 2 /O 2 gases by Niermann. 13 In order to see the relative importance of atomic and molecular metastables, we present the spatiotemporal density contour maps of the He* and He 2 * for the cases DG ¼ 0.8 mm (r 2 /r 1 ¼ 1.11) in Figs. 10(a) and 10(b) and the maps for the case DG ¼ 0.4 mm (r 2 /r 1 ¼ 1.05) in Figs.…”

“…12 Spatial dynamics of helium He ( 3 S 1 ) metastable atoms in sheath or bulk dominated rf micro-plasma jet were described by a numerical model in Ref. 13. Wang and Wang 14 found in the ac-driven discharges that the atomic metastables were mainly produced in the active phase and their density distribution had two peaks near both the cathode and anode without consideration for the molecular metastables.…”

Modeling of a Non‐Thermal RF Plasma Jet at Atmospheric Pressure

“…The applied two‐dimensional fluid model was able to describe the to transition as known from low pressure RF discharges. Several jets with plane‐parallel electrodes have been used which are convenient to compare experimental investigations with results of phase‐resolved one‐dimensional or extended (partly two‐dimensional) fluid models …”