Modeling of direct current micro-plasma discharges in atmospheric pressure hydrogen

Numerical simulations and experimental studies were conducted to characterize direct current (dc) hydrogen discharge for a pin plate electrode configuration having an inter-electrode separation distance of 400 mu m. A self-consistent two-dimensional hybrid model was developed to simulate the atmospheric pressure dc hydrogen micro-discharges. The discharge simulation model considered consists of momentum and energy conservation equations for a multi-component gas mixture, conservation equations for each component of the mixture (electrons, ions, excited species and neutrals) and state relations. The model uses a drift-diffusion approximation for the electron and the ion fluxes. The species considered include H, H-2, H+, H-2(+), H-3(+), H*(2p) H-2(*) (C-1 Pi(u)2p pi), H-2v=1 and the electrons. The electric field is obtained from the solution of Poisson's equation. Numerical simulations and experimental measurements indicated some of the key features of a normal glow discharge: flat voltage-current characteristics and constant cathode current density. Basic plasma properties such as electron number density, gas temperature, electric field and electron temperature were studied. The model predicted a constant current density of similar to 22 A cm(-2) in the normal glow regime. The normal current density was found to be a temperature scaled value of a low pressure normal current density. The ion Joule heating and Frank-Condon heating were found to be the dominant gas heating mechanisms. The peak gas temperature of similar to 500 K indicated the discharge to be a non-thermal non-equilibrium discharge. Predictions from the model compares favorably well with the experimental measurements.