Student Excellence Award Finalist: Insight into chemistry and transport in CO₂ microwave discharges through comparisons between simulations and experiments

In the past few years, a lot of attention has been devoted to the study of CO₂ dissociation by means of microwave (MW) discharges. Nevertheless, mechanisms underlying this kind of discharge are not well understood and only a synergy between experiments and models can help to shed a light on them. A fully native 1-D radial fluid model has been developed to simulate a CO₂ MW discharge operated at DIFFER. The model is coupled to a Monte Carlo Flux code for electron kinetics. Model results are validated against spatially-resolved measurements of the main neutral species and electron number density, gas and electron temperature, obtained by advanced laser scattering diagnostics at DIFFER. It is found that (i) radial mass and heat transport are fundamental to predict values of product formation (CO and O), (ii) detailed charged particles kinetics provides a better understanding of the contraction phenomenon in CO₂ plasmas, and (iii) a non-Boltzmann electron energy distribution function explains counter-intuitive electron temperature measurements by Thomson scattering. The excellent agreement between experiments and simulations allows one to clarify the role of different transport and chemical processes in determining plasma composition and electron properties.