LASER-INDUCED FLUORESCENCE DIAGNOSTIC FOR TEMPERATURE AND VELOCITY-MEASUREMENTS IN A HYDROGEN ARCJET PLUME

A diagnostic has been developed to measure velocity and translational temperature in the plume of a 1-kW-class arcjet thruster operating on hydrogen. Laser-induced fluorescence with a narrow-band cw laser is us ed to probe the Balmer alpha transition of excited atomic hydrogen. Th e velocity is determined from the Doppler shift of the fluorescence ex citation spectrum, whereas the temperature is inferred from the linesh ape. Analysis shows that although Doppler broadening is the only signi ficant broadening mechanism, the fine structure of the transition must be taken into account. Near the exit plane, axial velocities vary fro m 4 to 14 km/s, radial velocities vary from 0 to 4 km/s, and swirl vel ocities are shown to be relatively small. Temperatures from 1000 to 50 00 K indicate high dissociation fractions.