Experimental study on the characteristics of low power microwave plasma jet within local vacuum environment

A microwave plasma jet based on a coaxial cavity can be generated in atmosphere and vacuum environments. It is shown that with argon gas and a power range of $53–60W$⁠, cavity efficiency ranges from 54% to 68%. The electron density distribution and the microwave return loss of the confined plasma jet adjacent to a metal object and their dependency on argon mass flow rate and power have been studied by applying emission/Langmuir probe and spatial reflected wave diagnostic equipments in a low scatter vacuum environment. The results show that the electron density ranges from $8.8×1014to7.53×1016∕m3$⁠, and the electron density on the centerline of the jet decreases exponentially from the nozzle exit plane, but its distribution off the centerline is in an upheaved curve. Increasing mass flow rate at constant power and increasing power at constant mass flow rate increase electron density mildly. From typical measurements of microwave return loss, it is noted that the plasma jet attenuates microwaves in a $6to8GHz$ range.