Self-consistent computation of the optical emission spectrum of low-pressure argon CCPs

The talk reports the coupling of a particle-in-cell / Monte Carlo collision (PIC/MCC) simulation code for a low-pressure argon capacitively coupled plasma with a collisional radiative model (CRM) to predict the optical emission spectrum of the discharge self-consistently in the 2-100 Pa pressure range. The simulation is based on the classical PIC/MCC method, which is, however, upgraded by including (i) computation of the spatial density distribution of 30 excited levelsof Ar, (ii) electron impact excitation and de-excitation collisions between these levels, (iii) radiative transitions between the excited levels as well as between the excited levels and the ground state, (iv) quenching reactions of the excited levels, (v) stepwise ionization from the 1s and 2p excited levels, (vi) pooling ionization involving the 1s levels. The presence of the excited level populations is found to affect considerably the electron energy distribution function and the plasma density above ~20 Pa. Therefore, in this domain, only a self-consistent coupling of the PIC/MCC and the CRM can be expected to provide reasonably accurate results. The radiation transport is modelled by adopting an escape factor that accounts for the partial imprisonment of the radiation, which plays a role not only in the case of resonant transitions.