Two- and three-dimensional simulation analysis of microwave excited plasma for deposition applications: operation with argon at atmospheric pressure

The present work is concerned with the simulation analysis of a microwave plasma torch suitable for deposition applications prior to the admixture of any precursor. The self-consistent numerical model describes the electromagnetic field of the microwaves entering an R26 waveguide, the plasma generation, the gas flow through a tube crossing the waveguide, and the heat transfer in the gas. The plasma description avoids the assumption of quasi-neutrality and provides, therefore, a solution including the near-wall regions. The multiphysics model is applied to the source operated in argon at atmospheric pressure. Quasi-stationary solutions are obtained in a 2D Cartesian geometry and in a 3D geometry employing increasing degrees of complexity with respect to the physics, the reaction kinetics and the boundary conditions. The distribution of the electromagnetic field and the plasma parameters resulting from 2D fully coupled one- and two-ion models is analyzed for an incoming microwave power of 1 kW and a gas flow rate of 18 slm. The 2D model is capable of predicting the plasma parameters at a reasonable computational cost. The application of a 3D plasma-microwave model shows that the spatial distribution of the electromagnetic field and the plasma parameters is not, in general, axially symmetric. In the plane corresponding to the 2D work plane, the results of 3D one-ion plasma model show agreement with the 2D results, however, at significant computational costs. The 2D simulation analysis carried out allows us to draw up a decision-making with regard to the setup performance.