A Novel microwave plasma source based on rectangular resonator

Summary form only given. This paper introduces a novel microwave plasma source, which is comprised of a WR430 waveguide, an inductive waveguide coupling window, a rectangular microwave resonator, a closed rectangular quartz cavity and a sliding short-circuit plunger. And this quartz cavity can be removed to generate open microwave plasma. The WR430 waveguide connects the coupling window and the standard microwave device (three-screw tuner). The microwave energy is coupled into the resonator and quartz cavity through the coupling window. The short-circuit plunger is freely adjusted in the range from zero to 90 mm. The structure of this microwave plasma source is optimized by using CST and the optimal result indicates: the width, height and thickness of the coupling window are separately 35.5 mm, 54.6 mm and 2 mm; the width and height of the resonator is 113.2 mm and 77 mm, respectively; the outer dimensions and wall thickness of the quartz cavity are separately 240 mm, 112 mm, 76 mm and 8 mm. The microwave energy stores in the form of standing wave in the resonator and several large strong-electric-field regions periodically distributes inside it. The maximum electric intensity of the standing wave within the quartz cavity is about 3400 V / m for per watt of microwave power at best resonator length (named the resonator resonant length) for the microwave frequency f = 2.45 GHz. After removing the quartz cavity, an open microwave plasma is produced in the resonator. The air plasma stays a little far from the coupling window and its root is located at the middle of the resonator wide face. After introducing the quartz cavity, an atmospheric air microwave plasma is generated in the cavity by the procedure: firstly producing a low-pressure air plasma and then making the plasma open to the atmosphere. These two kinds of atmospheric air plasmas are both comparatively stable and their volumes both approach to 100 cm³. With the quartz cavity or not, the microwave - eflectance of the microwave plasma source increases with the increase of the microwave power when the atmospheric air plasma is produced. For lower powers, the reflectance with the plasma is even smaller than that without the plasma. The smaller microwave reflectance indicates that the impedance of the microwave plasma source is more approaching to the equivalent impedance of the microwave generation and transmission system. It can be found that the rotational temperatures of previous two-case atmospheric air plasmas both roughly have nothing to do with the microwave power by comparing normalized NO_γ (A-X) and OH (A-X) rotational lines¹ at different microwave powers.