Numerical profile correction of microwave cavity resonance spectroscopy measurements of the electron density in low-pressure discharges.

Low-temperature plasmas are widely studied in laboratory environments and form the backbone of many industrial processes. Highly energized electrons enable processes such as ionization, dissociation, and plasma chemical reactions, while the heavy species, such as neutral gas atoms and molecules, remain near room temperature. Hence, understanding the electron dynamics is crucial to the control and optimization of plasmas and their applications. In this contribution, we investigated the impact of electron density profile correction on microwave cavity resonance spectroscopy (MCRS) as a diagnostic tool for low-pressure discharges. Following standard practice, we first obtained a volume-averaged electron density by assuming a uniform plasma in the interpretation of the MCRS diagnostic technique. Second, we compare the experiments with a numerical model solved using PLASIMO software to evaluate the predictive capabilities. Third, we obtained profile-corrected electron densities by means of incorporating the numerically obtained distribution of the electron density and the numerical solution for the resonant microwave electric field in the interpretation of the experimental data using MCRS. Although the volume-averaged data agree closely with the electron density found from the numerical model, it is shown that implementing the spatial distribution of the electron density and the microwave electric field leads to a significant correction to the experimental data. The developed strategy could easily be implemented in other situations deploying MCRS as a non-invasive technique for measuring the electron density.