2D spatial mapping of the electron temperature, electron number density, and argon molecular ion number density in a microwave argon plasma jet

Abstract

A detailed characterization of electron parameters, particularly temperature and number density, is essential to understand the physics driving non-equilibrium plasma jets sustained by microwave electromagnetic fields. These parameters are typically extracted from optical emission spectroscopy, a widely used and non-intrusive diagnostic method. Single point measurements or along a line-of-sight to extract a profile are the most applied techniques, while performing 2D spatially resolved measurement continues to be a challenge. Although filter-based imaging techniques offer spatial resolution, spectral information is limited to only a few emission lines. Conversely, acquiring full spectra across a 2D region requires sequential point-by-point scanning, making real-time 2D mapping complex. In this study, we address these limitations by coupling hyperspectral imaging with collisional-radiative modeling to simultaneously extract and map, with an exceptionally high spatial resolution, the electron temperature, electron number density, and argon molecular ion number density. The results are obtained in both contracted (100% Ar) and expanded (Ar + 0.35% Xe) microwave plasma jets expanding into ambient air. The electron temperature, electron density, and molecular ion density exhibit distinct and structured spatial distributions, with electron temperature peaking and molecular ions accumulating at the edges.