Numerical simulation for the generating conditions of a laser-sustained argon plasma jet

Abstract

The temperature map of a laser-sustained argon plasma is calculated in the gas flow field upstream of a sonic nozzle orifice. The discretized equation of energy conservation is solved with a finite difference method. A forced parallel gas flow field is introduced in order to simulate the gas flow through the nozzle. Such a parallel flow does not account for the pre-cooling effect at the nozzle throat, so that the isentropic laws must be applied at the end of each iteration (outlet) for re-introducing the corresponding gas flux into the inlet conditions of the next iteration. In this way, the gas flux calculation is self-consistent and convergence is obtained after about 200 iterations. The results are compared with experimental data. The agreement is rather satisfactory except that the theoretical laser power threshold is about one order of magnitude higher than the experimental measurement. This is due to the parallel gas flow scheme, which overestimates the gas flux in the plasma core. This effect can be corrected by taking a gas flux value to account for the convergence of the stream tubes toward the nozzle.