Topic/Type: 1.6 Plasma-based devices, Poster

### Numerical analysis and optimization of power coupling efficiency in waveguide-based microwave plasma source

H. Nowakowska1, M. Jasinski1, J. Mizeraczyk1, 2

1 The Szewalski Institute of Fluid-Flow Machinery, PAS, Gdansk, Poland
2 Dept. of Marine Electronics, Gdynia Maritime University, Gdynia, Poland

Atmospheric pressure microwave plasma sources (MPS) operating at power levels above 1 kW are usually fed from a rectangular waveguide. One of the vital issues of designing an efficiently working MPS is a proper matching of its impedance to the feeding line; otherwise an incident electromagnetic wave cannot sustain the plasma because it reflects from the MPS. The ratio of reflected wave power flux $\small P_R$ to incident wave power flux $\small P_I$ depends on geometry and dimensions of the MPS as well as plasma dimensions and parameters. In general, it is possible to use a set of microwave tuners to obtain situation that for a particular plasma no wave is reflected from the MPS. However, to meet industrial requirements it is desired to have an MPS with a simple method of tuning and such that the reflected wave power is close to zero (i.e. power coupling efficiency is close to 100%) for a wide range of plasma parameters; the latter is essential for a stable operation of the MPS. Experimental optimization of the MPS to increase its power coupling efficiency and stability of operation is as a rule material and time consuming, while numerical simulations make it possible to obtain a solution faster and more efficiently.

We have performed simulations of 3D electromagnetic field distributions in a standard-waveguide-based MPS with a reduced-height section, through which a discharge tube penetrates, and a movable plunger as the only tuning means. The simulations were done for the electromagnetic field frequency 2.45 GHz, different dimensions of the reduced-height section and wide ranges of plasma electron concentration and electron-neutral collision frequency. For each case, we have determined electric field distributions inside the MPS and in the plasma region. Additionally, we have calculated so called tuning characteristics, i.e. ratio $\small P_R/P_I$ as a function the movable plunger position. From the tuning characteristics, we have determined such dimensions that assure power coupling efficiency higher than 95% and stable operation for the waveguide-based microwave plasma source. The numerically obtained tuning characteristics have been compared with experimental ones and good agreement between them has been found. Simulations were performed using commercial Comsol Multiphysic software.