Factors affecting the Cl atom density in a chlorine discharge

A mathematical model was developed for the bulk plasma of an electrodeless chlorine discharge sustained in a tubular reactor. The model was used to investigate the factors affecting the Cl atom density in the plasma. Rate coefficients for electron-particle reactions in the Cl2/Cl mixture were obtained by solving the Boltzmann transport equation for the electron-energy distribution function. These rate coefficients were then used in a plasma model to calculate the self-sustaining electric field, electron density, and atomic chlorine density in the plasma. The effect of frequency, power, gas flow rate, neutral density, tube radius, and wall recombination coefficient was examined. For otherwise identical conditions, nearly the same atom density was obtained in 13.56 MHz and 2.45 GHz discharges. It was found that very high degrees of molecular dissociation are possible with only a few W/cm3 in the plasma. Despite the fact that the atom density decreased with increasing feed gas flow rate, the atom flux increased with flow rate. In the parameter range investigated, lower pressures and larger tube radii favored higher atom density in the plasma. The model is useful for optimizing source efficiency and for use as a ‘‘module’’ in multidimensional radical transport and reaction models of remote plasma processing reactors.