The influence of oxygen concentration on the hollow cathode discharge in He/O2 mixed gas

Hollow cathode discharge in He/O2 mixed gas is simulated using a two-dimensional fluid model for the first time. The model contains 15 particles and 66 reactions. The evolutions of discharge current, electric field, charged and reactive particles with different oxygen concentrations are obtained. The primary mechanisms of generation and loss for particles under different oxygen concentrations are discussed. The results show that the added O2 in helium has both positive and negative effects on the discharge. The discharge does not monotonically change with the increasing oxygen concentration. When the oxygen concentration is low, oxygen admixture could enhance the discharge, that is, the discharge current, radial electric field, electron density, O2+ density, O density, and the O(1D) density increase with the increase of oxygen concentration. When the oxygen concentration is high, it will weaken discharge, that is, the discharge current, radial electric field, electron density, O2+ density, O density, and the O(1D) density decrease with the increase of oxygen concentration. The main reactive particles in discharge are O and O(1D). These densities are much higher than the density of charged particles. The optimal oxygen concentration for O and O(1D) is 0.5% and 0.4%, and the corresponding maximum density is 4.34 × 1013 cm−3 and 1.50 × 1013 cm−3. The generation and loss rates for these particles at different oxygen concentrations are calculated, which contributes to the change in particle densities.