Experimental and numerical investigations of line-shaped microwave argon plasma source

In the following, numerical and experimental results for a line-shaped argon plasma source over a wide range of gas pressure (2–50 Torr) and microwave power (200–800 W) are presented. The line-shaped plasmas have been generated in a rectangular Pyrex tube, 15mm in height and 5mm inner width placed-in a linear slot made in the upper wide wall of a custom-made narrow rectangular waveguide. The microwave power is coupled to the discharge gas via the slot. The effects of the waveguide width, power level (electron density, and discharge tube insertion depth on the excited axial (along x) electric field profile and hence the uniformity of the produced plasmas are investigated numerically using commercial software CST Microwave Studio®, and charge coupled device (CCD) camera. Results showed that, a uniform line-shaped plasma is generated as waveguide width decreased to 58 mm, plasma density value ≪ n_res = 3.7×10¹¹ cm⁻³, and discharge tube insertion depth = 0mm. An optical emission spectroscopy study was also realized to deduce the relative density of argon species and electron excitation temperature T_exc. In general, argon spectral lines intensity was increased enhanced markedly when microwave power increased, while the different lines showed different behavior as argon pressure increased. The electron excitation temperature T_exc decreases with increasing argon pressure, but almost constant overall the whole plasma length.