A Novel Self-Excited Atmospheric Pressure Microwave Plasma Jet Using Rectangular Coaxial Line

A novel self-excited atmospheric pressure microwave plasma jet (APMPJ) based on a coaxial line is successfully proposed for the medical treatment. The finite-element method (FEM) is applied to obtain the optimal size of the APMPJ. The plasma parameters, such as electron density and electron temperature, are calculated within 0.1 ms. When the plasma reaches a stable state, the electron density is closed to 1022 m−3, and the electron temperature is calculated to be 1.3 eV. According to the experimental results, the argon plasma jet can be self-excited at an incident power of 20 W, and the gas temperature of the plasma jet is closed to 318 K at an incident power of 15 W. In addition, the air plasma jet can be self-excited at an incident power of 110 W. Finally, the change in the density ratio of hydroxyl (OH) radical to other particles when water vapor is added to the APMPJ at different flow rates is analyzed. It is found that a small amount of water vapor can greatly increase the relative content of OH which is tested by spectrometer.