Dynamic behavior of hydrogen and nitrogen radicals in pulse modulated induction thermal plasmas

Influence of pulse modulation of the coil current sustaining a high-power Ar-N2-H2 induction thermal plasma was experimentally studied on the time-averaged particle composition of the thermal plasma. Optical emission spectroscopy measurement was carried out to obtain the time evolution in the relative radiation intensities of excited atoms and molecules flowing into the reaction chamber. The radiation intensities of atomic species like N and H changed faster than those of molecular species N2 and NH. It was also found that, the time-averaged radiation intensities of N and H atomic lines increase by pulse modulation of the coil current, while those of N2 and NH decrease by the pulse modulation under the same time-averaged input power condition. In addition to spectroscopy measurements, the surface temperature of a Ti specimen irradiated by the Ar-N2-H2 induction thermal plasma was also measured and was found to decrease by the pulse-modulation. This implies that pulse modulation of the coil current produces more atomic species without increasing heat flux onto the specimen surface.