A Simple and Stable Atmospheric Pressure Electrodeless Water Vapor Microwave Plasma Torch

An atmospheric pressure microwave plasma source operating on water vapor has many potential applications. To avoid the corrosion of metal electrodes in a traditional water vapor microwave plasma system, we propose a simple water vapor electrodeless microwave plasma device. By introducing a ceramic tube, the device can work directly with liquid water without complex evaporation equipment. This study examined the relationship between microwave power and water vapor torch plasma duration. When the microwave power is greater than 800 W, the plasma torch can be excited permanently and stably without the loss of ceramic. The excitation of the oxygen atom, hydroxyl radical, and hydrogen atom was found using optical spectroscopy, confirming the water vapor’s decomposition. In addition, it was also found that the crystallinity of the ceramic was improved after microwave discharge. This work enriches the microwave plasma techniques for water vapor for various applications, such as electric propulsion, hydrogen production, and surface treatment.