Diagnostics and modeling in a pure argon plasma: Energy balance study

A self-consistent pseudo-one-dimensional (zero-dimensional with diffusion) plasma model and optical emission spectroscopy are used in tandem to investigate the power coupling efficiency for a pure argon microwave plasma. The self-consistent model is developed by simultaneously solving the Boltzmann equation (for the non-Maxwellian electron energy distribution function), electron number density balance equation, energy balance equation, and the excited state rate equations in a collisional-radiative model. The absolute line emission intensity is utilized to obtain number densities of three argon excited states [$4p$ (7147 Å), $5p$ (4300 Å), and $5d$ (6043 Å)] in a 5 Torr, 680 W input power argon discharge. The absolute continuum emission from the plasma was utilized to determine the maximum electron number density. A comparison of the numerical and experimental data indicates that only 2%–5% (10–35 W) of the input power is deposited in the plasma. A control volume heat transfer analysis validates this claim. The experimentally determined energy balance shows that the remaining input power (645–670 W) bypasses the plasma and is dissipated in the reactor cooling systems.