Resonant impedance-matching slow-wave ring structure microwave applicator for plasmas

摘要

A microwave applicator has exactly six equal length parallel rods equally distributed in 60° angular intervals in a circle, and at circumferential intervals that are one half the wavelength of operation of a microwave power source. The circumference is therefore preferred to be three wavelengths. The top ends of every rod terminate in a top planar shorting ring. The bottom ends of every rod terminate in a bottom planar shorting ring which is perpendicular to each of the rods and which is parallel to the top planar shorting ring. Intermediate to the two planar shorting rings are an upper and lower planar feed ring that are each parallel to the outside planar shorting rings. The upper planar feed ring connects to odd numbered rods and the lower planar feed ring connects to even numbered rods. A ridged tapered waveguide is connected to the feed rings at a point intersected by any one of the rods. A quartz, ceramic, or sapphire plasma tube is passed through the central axis of the planar shorting rings and feed rings. The applicator is tuned by either internal or external means to match its resonant frequency to that of the microwave source such that impedance mismatch reflections are minimized and the energy transferred to the plasma generated within the plasma tube is maximized.