Numerical model of a laser-sustained argon plasma

A steady state axi-symmetric model was developed to predict the size, shape and temperature of a laser-sustained plasma in flowing argon. The power of the carbon dioxide (CO2) laser and the free stream gas velocity were inputs to the model. An algorithm, which is an alternative to the ray tracing method, was used to calculate the laser power absorbed by the plasma. Temperature dependent thermal conductivity, specific heat, and viscosity values taken from the literature were used. The finite volume method, along with the SIMPLE algorithm was used to discretize and solve the three governing equations: conservation of mass, momentum, and energy. The effects of the flow velocity, laser power, and the beam mode on the laser sustained plasma were studied and agree well with published experimental data in the literature for argon flow velocities in the range of 4–10 m/s and with experiments conducted using a flow velocity of 5.5 m/s. At low flow velocities (<2 m/s), the model over-predicts absorption of the laser beam. This can be attributed to the absence of refraction in the model, which becomes significant as the LSP moves further upstream, toward the laser. The simulations indicated that the laser beam mode had a significant effect on the size, shape, and absorption of the plasma.