Numerical model of an Ar/NH3 atmospheric pressure direct current discharge in parallel plate geometry

Abstract

A one dimensional fluid model is used to investigate the role of ammonia added to an argon DC discharge at atmospheric pressure. The equations solved are the particle balances, assuming a drift-diffusion approximation for the fluxes, and the electron energy balance equation. The self-consistent electric field is obtained from the simultaneous solution of Poisson’s equation. The electron-neutral collision rates are expressed as a function of the average electron energy. The model is comprised of 40 species (neutrals, radicals, ions, and electrons). In total, 75 electron-neutral, 43 electron-ion, 167 neutral-neutral, 129 ion-neutral, 28 ion-ion, and 90 3-body reactions are used in the model. The effects of gas mixing ratio on the densities of plasma species are systematically investigated. The calculated densities of the main plasma species are presented. It is found that in an Ar/NH3 plasma, the main neutrals (Ar*, Ar**, NH3*, NH, H2, NH2, H, and N2) are present at high densities. The Ar2+ and Ar+ ions are the dominant ions in the plasma. Furthermore, the NH3+ ions have a relatively higher density than other ammonia ions, whereas the density of other ions is negligible. Finally, a comparison is made between a pure Ar discharge and dielectric barrier discharge in a mixture of Ar/NH3. It is demonstrated that gas mixing ratio has a significant effect on the densities of plasma species, besides ammonia radical molecules and ammonia ions, and it also affects their ratio. Once the mixing ratio of Ar/NH3 is close to 1:1 at atmospheric pressure, the densities of NH, NH2+ and NH4+ reach to the maximum. The maximum of the different positive ammonia ions corresponds to the different ammonia mixing ratio.