Kinetic model for low-density non-stationary gas discharge in water vapour

Abstract

A capacitive discharge in water vapour in the pressure range 133–150 Pa was studied. The discharge is an effective ecologically pure source of OH* hydroxyl emission in the VUV and UV spectral range (A 2Σ+ → X 2Π transition). The time profiles of densities of plasma species at different values of reduced electric field (E/N) were calculated using a kinetic model of the discharge. It is shown that E/N ∼ 190–200 Td is a breaking field for water vapour plasma, and with an increase in E/N a transition from electronegative to electropositive plasma takes place. The primary positive ions in the water vapour plasma are H3O+ ions, and the primary negative ions are OH− ions.