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Benchmarked and Upgraded Particle-in-Cell Simulations Treating Excited State Atoms as a Fluid in Argon Discharge

Particle-in-cell Monte Carlo collision (PIC/MCC) simulations are important for understanding low pressure low-temperature discharge dynamics, since no assumptions are needed to determine the electron energy distribution function. Benchmark work is needed to build a solid base in the correctness of PIC/MCC codes. In this work, the basic object-oriented plasma device PIC/MCC code (oopd1-v1) is strictly benchmarked against the well-established xpdp1 code over a wide range of pressures (0.03 - 15 Torr), and varying size of the blocking capacitor in the external circuit (5 – 10 5 nF). An excellent agreement between codes is obtained. By upgrading oopd1-v1, incorporating excited argon atoms, metastable and radiative Ar m , Ar r , and Ar(4p), their role in rf capacitive discharges, especially in the collisional regime, was explored. It is found that the presence of the metastable atoms Ar m enhances the plasma density by a factor of 3 - 5 at 1.6 Torr and even higher at pressure up to 5 Torr. The proportion of metastable pooling ionization and step-wise ionization as an ionization source increases with increasing pressure and becomes more important than direct electronneutral ionization at 5 – 15 Torr. Also. as the pressure is increased the ionization occurs near the plasma-sheath interfaces, with little ionization within the plasma bulk region.