Parameters of a glow discharge in CF4

Measurements are presented of the reduced electric field Ez/N (where Ez is the longitudinal electric field strength and N is the neutral particle number density) in the positive column of a constant-current discharge in carbon tetrafluoride CF4 in the pressure range p = 0.2-2.3 torr and discharge current range I = 10-90 mA (corresponding to a current density j = 3.9-35 mA/cm2). The measured values of the reduced electric field are described within experimental error by a single function Ez/N of r0N, where r0 = 0.9 cm is the discharge tube radius. It is concluded that in the positive column of a constant-current discharge in CF4 direct ionization of CF4 molecules by electron impact dominates other possible ionization mechanisms, e.g., ionization of CF4 discharge using different models of the positive column; here the agreement between the calculated and experimental dependence of Ez/N on r0N serves as a criterion for evaluating the description of the discharge by the various models. The calculations reveal that in order to describe the positive column of a glow discharge in CF4 accurately it is necessary first to correctly take into account the effect of negative ions on the charged-particle balance (including the effect of striation in the positive column on regions with markedly different ion densities); secondly, it is shown that the nonlocal spatial behavior of the electron rate coefficients must be taken into account by solving the Boltzmann equation for the electron energy distribution function in the spatially nonuniform case. 8 refs., 5 figs