Benchmarked and upgraded particle-in-cell simulations of a capacitive argon discharge at intermediate pressure: the role of metastable atoms

Abstract

The capacitive argon discharge operated in the intermediate pressure regime is studied by performing one-dimensional particle-in-cell Monte Carlo collision simulations. First, the basic object-oriented plasma device code (oopd1-v1) is strictly benchmarked against the well-established xpdp1 code over a wide range of pressure (0.05–15 Torr) and varying blocking capacitor of the external circuit (5–105 nF), and excellent agreement is obtained. The oopd1-v1 is upgraded to oopd1-v2 and oopd1-v3, by adding excited atoms modeled as time- and space-evolving fluid species. The metastable Arm, the radiative Arr, and the Ar(4p) manifold, and their roles in discharge equilibrium are explored. It is found that the presence of the metastable Arm enhances the plasma density by a factor of 3 at 1.6 Torr and even higher at pressures up to 5 Torr. At low pressure (0.05 Torr), electron impact ionization from the ground state atom dominates the ionization over the whole discharge region, while metastable pooling and step-wise ionization has small contribution. The proportion of metastable pooling ionization and step-wise ionization increases with increasing pressure and becomes the dominant ionization source at 5–15 Torr.