Appreciation of a collisional-radiative model for the description of an inductively coupled argon plasma

The collisional-radiative model has been applied to the argon ICP discharge in order to elucidate the excitation mechanism in the plasma. The population density distributions of 25 argon energy levels were calculated under a steady-state approximation by using the literature values of electron number density, 5 × 10 ¹⁴cm^?3 and electron temperature, 9000 K. In the case of an optically thin plasma, in which the induced absorption can be neglected, the calculated population densities showed an overpopulation for low lying states, and were very close to LTE values for the upper levels. These results suggest the following excitation mechanisms in the argon ICP; corona model for lower levels and ladder-like excitation and ionization by electron impact for upper levels. According to the present calculation, the non-overpopulation of argon metastable can be interpreted by the interconversion between metastable and radiative states. It has been found that the induced absorption of resonance lines in an optically thick plasma and the motion of species in an inhomogeneous plasma have significant effects on the population densities. The non-linear processes by collision between heavy particles were not predominant compared to electron impact processes.