Numerical study of laser-sustained argon plasmas in a forced convective flow

A two-dimensional laser sustained plasma model, which uses laminar, incompressible 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 radiation-induced 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 semi-two-dimensional model, and our results indicate that the existing one-dimensional and semi-two-dimensional models do not provide adequate solutions for the laser sustained plasma.