Investigating the CO₂ conversion in high-power microwave plasmas using imaging techniques

Plasmas are an attractive option to create CO from CO₂, since they can be powered by green electricity, and switched on short timescales. The energy efficiency and conversion efficiency are crucial, and microwave plasmas are currently the best performing in terms of these two parameters. In a microwave plasma reactor, the power is deposited in a small volume that is centered in the reactor tube by a swirling flow pattern. Thermal processes are dominant in the plasma volume. A thermal CO₂ plasma can still be up to 70% efficient when the quench is superideal, which means that during cooling not only the CO is conserved, but also the oxygen radicals react selectively with CO₂ molecules. Mixing of gas from the hot core with the cooler periphery helps to minimize CO losses and to optimize the utilization of the oxygen radicals. The research project focuses on exploring a new region of the parameter space at high power, thanks to a newly built 10 kW microwave reactor. The plasma behavior is studied with an imaging diagnostic, which makes it possible to analyze the discharge shape and the emission intensity profile in the radial and axial directions as well. The reactor performance is studied for different pressures, flows, and microwave powers to see whether the conversion efficiency can be improved by boosting the treated fraction of the gas.