Experimental and theoretical investigation of oxygen glow discharge structure at low pressures

An experimental and theoretical investigation of the oxygen glow discharge structure at low pressures has been performed. Radial dependencies of the e lectron energy distribution function, the ambipolar plasma potential, and t he negative ion concentration, as well as the axial electric field and the concentrations of atomic and singlet oxygen were measured. A new approach t o the application of laser photodetachment method has been used to measure the negative ion concentration. It allows one to obtain information about f ast processes after the photodetachment at low frequencies (similar to 100- 200 Hz) by using the simplest modulation technique. A self-consistent model involving the electrodynamics and kinetics of the discharge was developed. The observed variations of the negative ion densities with current density and oxygen pressure were explained in the model frame by a dependence of t he detachment rate constant of the O- + O --> e + O-2 process on the effect ive ion temperature (k = 1.9 . 10(-10) root 1100/T-i(eff)). It was shown th at the feature of oxygen de discharge at low pressures is a possibility to change the basic type of negative ions from the O- to the O-2(-). This effe ct become more pronounced with decreasing current density.