Towards a Unified Model of the Low-Current Glow Discharge with a Liquid-Phase Anode

A self-consistent model describing a glow discharge in argon with a liquid-phase (distilled water) anode is presented. The model is based on an extended hydrodynamic description of plasma and takes into account the heating of the metal cathode and liquid-phase anode, as well as the equilibrium evaporation of water molecules into the discharge gap and the kinetics of elementary processes involving them. A numerical study is performed for two key cases: the discharge initiation in a pure argon atmosphere and that with the initial presence of water molecules at a concentration corresponding to the saturated vapor pressure at an initial liquid-phase anode temperature of 293 K. For the first case, it is shown that a change in the plasma-forming ion from $${\text{Ar}}_{2}^{ + }$$ to the hydrated cluster $${{{\text{H}}}_{9}}{\text{O}}_{4}^{ + }$$ ion and also a change in the dominant negatively charged particle from the electron to the OH– ion are observed during the evaporation of water molecules. For the second case, it is shown that $${{{\text{H}}}_{9}}{\text{O}}_{4}^{ + }$$ is the dominant positive ion over the entire time interval. The competition between electrons and OH– ions on times up to ~0.01 s was detected for negatively charged particles. The OH– ion becomes the dominant negatively charged particle at times larger than 1 s but the electron density remains comparable by the order of magnitude, which is critical for maintaining plasma conductivity.