Flow characterization of a diamond-depositing dc arcjet by laser-induced fluorescence

Laser-induced fluorescence (LIF) measurements of seeded nitric oxide and naturally occurring species in a diamond-depositing de arcjet of hydrogen/argon/methane (0.8:1.0:0.005) at 25 Torr are used to determine the temperature and velocity fields in a gas jet. LIF measurements are also used to demonstrate the importance of gas recirculation on the chemical composition of the arcjet plume. The gas flow in the arcjet plume is supersonic, with a maximum axial speed of 2.6 km/s at the center of the nozzle exit. This axial velocity decreases with radius with a parabolic distribution in the plume. There is no measurable radial velocity in the free stream of the arcjet plume, and the radial expansion of the plume is consistent with diffusion. The maximum temperature at the plume center is 2400 R and varies less than 15% with chamber pressures of 10-50 Torr. The substrate is placed in the arcjet plume normally to the directed velocity, producing a stagnation point. The gas temperature above this stagnation point is observed to rise abruptly as a consequence of the supersonic shock. The radial velocity near the stagnation point becomes significant, and a maximum radial velocity of 1300 m/s is determined. (C) 2000 Optical Society of America.