One-Dimensional Simulation of Microwave Discharge in a Gas Bubble in Water

Abstract

This work is devoted to simulating a microwave discharge in water and studying kinetic processes in a gaseous mixture of water decomposition products. Calculations have been performed for atmospheric and low pressure and a constant gas temperature. A one-dimensional model has been developed on the basis of the joint solution of the balance equation for neutral and charged plasma components, the Boltzmann equation, the equation for the stationary distribution of the microwave field in the plasma-filled volume, and the Poisson equation. Using the zero-dimensional model, an abridged kinetic reaction scheme for water vapor plasma was obtained, which was employed in the one-dimensional model. The calculations have been carried out for preset values of the microwave field. It has been shown that the modes of transition from electronegative to electropositive plasma obtained using the zero-dimensional model at E/N values above 350 Td are not observed in the case of the one-dimensional model of microwave discharge. In a wide range of microwave field values specified on the antenna, the microwave plasma in water is electronegative. The concentration of electrons is low in comparison with the concentration of positive ions H₃O⁺, ${{{\text{H}}}_{5}}{\text{O}}_{2}^{ + }$, and H₃O⁺(H₂O)₃, quasi-neutrality is maintained by the negative ion OH⁻, and the degree of dissociation of water does not exceed 20–25%.