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An experiment was performed to determine the temperature distribution within a stationary plasma in atmospheric air produced by a continuously operating CO2 laser. A peak temperature of 17000 °K (±5%) was found to exist at a point 1.1 cm ahead of the focal point. The radiation surrounding the hot plasma core was found to consist primarily of the first negative system of nitrogen.

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A two-dimensional laser-sustained plasma model, which is based on the laminar, Navier-Stokes equations for the flow and geometric ray tracing for the laser beam, has been evaluated and compared with existing experimental results for a wide range of forced convective argon flows. The influence of gas inlet velocity, gas pressure, laser power, and focusing geometry on the structure of the plasma was examined. The model agreed well with the existing experimental data in both global structure and detailed temperature distribution, particularly for static pressures greater than 2 atm. It was found that the diffusion approximation for the optically thick portion of the thermal radiation was not adequate for low-pressure (less than 2 atm) plasmas and that the radiationinduced thermal conductivity had to be adjusted in order to obtain agreement between the model calculations and experimental results. The present model calculations were also compared with a recently published semitwo-dimensional model and the results indicate that the existing one-dimensional and semi-two-dimensional models do not provide adequate solutions for the laser-sustained plasma. Nomenclature c p = specific heat at constant pressure, J/kg-K h = specific enthalpy, J/kg / = laser intensity, W/m 2 k = intrinsic thermal conductivity, W/m-K & eff = effective thermal conductivity, W/m-K rad = radiation-induced thermal conductivity, W/m-K <7rad -radiation heat loss, J/m 3 -s r = radius, m s = distance along the laser ray, m u -axial velocity, m/s v = radial velocity, m/s x = axial distance, m y -radial distance, m a.= absorption coefficient at 10.6 />tm wavelength, 1/m ju = viscosity, kg/m-s p = density, kg/m 3

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