Modeling of low-temperature argon plasma in capacitively-coupled glow discharges with a collisional-radiative model*

A detailed collisional-radiative (CR) model is implemented and coupled with a one-dimensional two-temperature fluid model to investigate capacitively coupled radio-frequency argon discharges at low pressures. The fluid model is based on the drift-diffusion approximation. The CR model, comprising a state-to-state approach, describes atomic processes such as electron impact excitation, electron impact ionization, radiation emission, heavy-particle collision excitation/ionization, and radiative recombination in a comprehensive manner and predicts the number densities of all individual excited states for the 4s, 4p, 3d, and 5s manifolds (excited states up to 14.304 eV). Non-Maxwellian electron energy distribution functions (EEDF) obtained with Bolsig+ are employed in the model, while fine-structure collisional cross-sections are acquired from the LXCat database.  A detailed comparison of the numerical predictions with experimental data for the 4s states, the 4p states, and the electron number densities at different operating conditions is presented, and possible reasons for discrepancies are discussed. We also explore the sensitivity of the model to input parameters, such as collision cross-sections and transport coefficients, and investigate the importance of high-lying excited states (higher than the 4p states).

Keywords: capacitively-coupled plasma (CCP), collisional-radiative model, Argon plasma kinetics, non-equilibrium kinetics, validation