A large-volume microwave plasma source based on parallel rectangular waveguides at low pressures

Abstract

A large-volume microwave plasma with good stability, uniformity and high density is directly generated and sustained. A microwave cavity is assembled by upper and lower metal plates and two adjacently parallel rectangular waveguides with axial slots regularly positioned on their inner wide side. Microwave energy is coupled into the plasma chamber shaped by quartz glass to enclose the space of working gas at low pressures. The geometrical properties of the source and the existing modes of the electric field are determined and optimized by a numerical simulation without a plasma. The calculated field patterns are in agreement with the observed experimental results. Argon, helium, nitrogen and air are used to produce a plasma for pressures ranging from 1000 to 2000 Pa and microwave powers above 800 W. The electron density is measured with a Mach–Zehnder interferometer to be on the order of 1014 cm−3 and the electron temperature is obtained using atomic emission spectrometry to be in the range 2222–2264 K at a pressure of 2000 Pa at different microwave powers. It can be seen from the interferograms at different microwave powers that the distribution of the plasma electron density is stable and uniform.