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

TL;DR

This study investigates helium metastable atom distributions in atmospheric pressure micro-plasma jets, combining experimental laser absorption spectroscopy with 2D simulations to understand plasma excitation and sheath dynamics.

Contribution

It provides the first detailed spatial profiles of helium metastables in micro-plasma jets and links these profiles to plasma excitation mechanisms through combined experimental and simulation approaches.

Findings

Metastable density profiles reveal sheath structures and excitation distribution.

Transition observed from glow plasma to sheath discharge with gap variation.

Simulation confirms correlation between metastable profiles and excitation mechanisms.

Abstract

Space resolved concentrations of helium He 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 alpha-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/N2/O2 chemistry model the correlation between the metastable profiles and the underlying excitation mechanisms was obtained.