Design of a microwave-induced atmospheric-pressure plasma source based on cylindrical resonant cavity TM₀₁₀ mode

Abstract A microwave-induced low-temperature atmospheric-pressure source based on cylindrical resonant cavity TM 010 mode was designed. The microwave power was fed into the cavity from a rectangular waveguide on top of it through a coupling hole. A metal pin with adjustable insertion depth was added to the cavity to tune its resonant frequency. The fed waveguide was connected by a sliding short. By tuning the sliding short, the energy transfer efficiency from the waveguide to the cavity was changed. Experiments showed that it could induce an argon discharge in the resonant cavity at atmospheric pressure with as low as 30 W incident wave power without any extra trigger. The plasma length reached 50 mm when the incident wave power was 200 W. By exciting the argon with an extra ignitor in the feeding waveguide, the length of the plasma plume could be extended to 260 mm when the incident wave power was 800 W. The plasma generated by this device was filamentous for both cases. The emission spectrum proved the uniformity of the plasma along its length. This work will be helpful in providing a new alternative microwave plasma device for waste gas treatment or chemical reactions that require plasma catalysis.