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 electron energy distribution function, the ambipolar plasma potential, and the negative ion concentration, as well as the axial electric field and the concentrations of atomic and singlet oxygen were measured. A new approach to the application of laser photodetachment method has been used to measure the negative ion concentration. It allows one to obtain information about fast processes after the photodetachment at low frequencies (~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 the detachment rate constant of the O^-+O→e+O₂ process on the effective ion temperature (k=1.9·10^-10-√1100/T_i^eff). It was shown that the feature of oxygen dc discharge at low pressures is a possibility to change the basic type of negative ions from the O^- to the O₂^-. This effect become more pronounced with decreasing current density