DETERMINATION OF GAS-TEMPERATURE AND VELOCITY PROFILES IN AN ARGON THERMAL-PLASMA JET BY LASER-LIGHT SCATTERING

Gas-temperature and velocity profiles at the exit plane of a thermal a rgon plasma torch have been determined directly from a high-resolution Doppler-shifted line-shape analysis of laser light scattered by the p lasma. Peak temperature and velocity values observed were 13 350 K+/-7 % and 1100 m s-1+/-3%. Velocities as low as 45 m s-1+/-45% were measur ed in the fringe of the jet. An injection-seeded pulsed neodymium-dope d yttrium aluminum garnet laser was used as the laser source and the s cattered laser light was analyzed with a scanning tandem Fabry-Perot i nterferometer. Temperature data obtained from laser scattering are com pared with values obtained from emission spectroscopy and show a sever e departure from local thermodynamic equilibrium (LTE) in the outer re gions of the jet. Gas temperatures were observed to increase as the to rch operating current increased from 300 to 500 A, but remained consta nt as the operating current increased to 900 A. However, electron temp eratures and densities continued to increase with operating current. T his suggests that increasing the electrical power drives the plasma aw ay from LTE. Measured temperature and velocity profiles were found to be nearly parabolic.