Student Excellence Award Finalist:Reconsidering the importance of vibrations and translations:a new perspective on efficient plasma activation of CO$_{\mathrm{2}}$

Vibrational non-equilibrium conditions are frequently put forward as a prerequisite for energy-efficient chemical conversion of CO$_{\mathrm{2\thinspace }}$in moderate to high-pressure plasma sources. The merits and mechanisms of non-equilibrium plasma reactivity are, however, still subject to debate as key literature results remain to be reproduced experimentally. Furthermore, the consequences of pressure-related discharge contraction and gas-dynamic transport are often disregarded, despite being essential in a comprehensive interpretation of plasma-chemical experiments. In this contribution, plasma contraction and transport are consolidated for the first time using 2D thermal chemical kinetics modeling of the flow reactor. By incorporating experimentally obtained non-uniform power deposition profiles, gas temperatures, and approximations for axial and radial transport, a holistic but straightforward description of the CO$_{\mathrm{2\thinspace }}$microwave plasma emerges: we find that the reactor performance is adequately described by plasma-induced thermal chemistry. However, the predominance of turbulent transport of plasma species towards colder regions may induce strong (vibrational) non-equilibrium conditions in the plasma periphery, irrespective of the quasi-thermal nature of the plasma itself. Leveraging the reactivity of O radicals with CO$_{\mathrm{2}}$ in a non-equilibrium plasma periphery may make possible energy efficiencies of over 70{\%}, warranting further investigation into post-discharge kinetics and transport.