LIF investigations on NO, O and N in a supersonic N2/O2/NO RF plasma jet

Abstract

Laser induced fluorescence (LIF) has been employed to study NO, O, N, Fe species present in the expanded stream of N2/NO and O2/NO plasma jets. The gas is excited in a coaxial RF capacitive discharge and expands through a de Laval nozzle, with a pressure ratio P1/P2 in the range 20–40, into a vessel at P2 in the range 0.1–0.5 Torr. Supersonic multiple expansion–compression waves are observed. NO from gas mixture, and Fe produced by sputtering of the RF electrode, have been examined as possible tracers of the plasma jet expansion flow fields. The NO rotational temperature and density have been measured by LIF. NO and Fe are reliable tracers, but the NO dissociation limits its use to only low power plasma jets. The absolute density of O and N atoms achieved by TALIF is about 20% and 1.5% for 500 W O2 and N2 plasma jets, respectively. The TALIF calibration is carried out in situ. The procedures for O and N atoms are discussed.