Dynamics of hollow cathode discharge using fluid models with and without metastable atom involvement in helium

Abstract

The characteristics of hollow cathode discharge are simulated by two types of fluid models in helium, one with metastable atom involvement and another without. Discharge current, particle density, and ionization rate are simulated. Results show that metastable atoms exert an important influence on the steady state discharge and the temporal characteristics of this discharge. Discharge is maintained at a lower sustain voltage in the model with metastable atoms than in that without metastable atoms. At the same low sustain voltage, marked differences in quantitative and qualitative characteristics are observed between the two models. With increasing sustain voltage, the discharge parameters simulated by the two models become qualitatively similar, but their quantitative differences increase. The discharge current and electron density in the model with metastable atoms are significantly higher than that in the model without metastable atom involvement at the same sustain voltage. Furthermore, the discharge current and electron density gap simulated by the two models increase as the sustain voltage increases. The difference in characteristics between the two models originate from variation of the contribution of different ionization types to the generation of new electrons at different sustain voltages. With increasing sustain voltage, stepwise ionization originating from metastable atoms becomes increasingly crucial to the discharge. Results further show that the temporal characteristics of the two models are similar when the metastable atom density is low. However, in the model with metastable atoms, discharge current and particle density continue to rise until a steady discharge is obtained after a quasi-steady stage. The different temporal characteristics observed between the models appear to originate from the influence of metastable atoms. The percentage of stepwise ionization relative to the total ionization increases with time.