Behavior of a Microwave Cavity Discharge over a Wide Range of Pressures and Flow Rates

Experiments are conducted over a wide range of pressures, flow rates, and power levels to demonstrate the versatility of a microwave cavity discharge. The experimental results are justified using a linear, cold plasma theory that accounts for the electron-neutral particle collisional losses in the plasma. The resonant coupling of E. M. energy to a surface wave and the resulting formation of a long, large volume plasma column is demonstrated. The absorbed power characteristics of the microwave cavity discharge are examined for gas pressures up to 500 torr and flow rates up to 2500 cm3/min in the TE011 and TE*111 mode operation of the plasma cavity system. The experimental results show that the absorbed power variation as a function of pressure of this discharge is uniform. The power absorbed by the flowing plasma is shown to increase directly as a function of the flow rate initially and reach a saturation at high flow rates. By simultaneously optimizing the cavity length, discharge pressure, and the gas flow, it is possible to couple as much as 90% of the incident power to the plasma.