Spectral analysis of subcritical microwave discharge in high pressure air

Recently, microwave discharge has caught more and more attentions due to its potential of industrial applications. It has such advantages as no electrodes, less pollution and easy to generate. Furthermore, high pressure microwave plasma becomes a hot spot of investigations because many industrial applications must be preceded at high pressure. Subcritical microwave discharge is considered to be a good way to generate high pressure microwave plasma. This paper introduces a microwave plasma source, which can excite subcritical microwave discharge at 1-5 bar in air by microwave pulse. A spectrum measuring system was used to acquire the emission spectra of air microwave plasma. The emission spectra of the plasma under different pressures and different incident microwave powers were analyzed. Band spectra and spectral lines of NO, N₂ and O are identified and some metallic spectral lines are also found.