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

Laser-induced fluorescence (LIF) measurements of seeded nitric oxide and na turally occurring species in a diamond-depositing de arcjet of hydrogen/arg on/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 demons trate the importance of gas recirculation on the chemical composition of th e arcjet plume. The gas flow in the arcjet plume is supersonic, with a maxi mum axial speed of 2.6 km/s at the center of the nozzle exit. This axial ve locity decreases with radius with a parabolic distribution in the plume. Th ere 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 m aximum temperature at the plume center is 2400 R and varies less than 15% w ith 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 stagna tion point becomes significant, and a maximum radial velocity of 1300 m/s i s determined. (C) 2000 Optical Society of America.