Discharge characteristics and reactive species dynamics in Ar/O2 micro-hollow cathode discharges

The discharge characteristics and generation/consumption mechanisms of different species in argon–oxygen micro-hollow cathode discharge are investigated through simulations and experiments. Micro-hollow cathode discharge efficiently produces multiple reactive oxygen species with high density, exhibiting the following density order: O > O(1D) > O2(a1Δg) > O(1S) > O(5S) > O(5P) >O3. Simulation results reveal a complex coupling process among these species, where each reaction simultaneously generates and consumes different particles, ultimately establishing dynamic equilibrium in particle densities. The primary mechanism for electron production is direct ionization (e + Ar → 2e + Ar+), and electron depletion is dominated by three-body recombination [2e + Ar+ → Ar(4s) + e]. Atomic oxygen (O) is primarily generated through collisional quenching [O(1D) + O2 → O + O2], and its depletion is governed by electron-impact excitation [e + O → O(1D) + e]. The excited oxygen atom [O(1D)] originates mainly from two reactions: the collision reaction between electrons and O2 molecules [e + O2 → O + O(1D) + e] and the excitation reaction between electrons and O atoms [e + O → O(1D) + e]. The collision excitation reaction [e + O2 → e + O2(a1Δg)] is the primary pathway for O2(a1Δg) formation. Notably, O2(a1Δg) is generated at a high rate outside the cavity, leading to its peak density being located outside the cavity.