Experimental investigation on improving the efficiency of power coupling from the incident microwave to the discharge in a plasma torch
Wencong Zhang, Li Wu, Zhuang Liu, Junwu Tao, Kama Huang
Abstract
A high efficiency of power coupling from the incident microwave to the discharge is a general demand for large-scale and high-power applications of microwave plasma torches. This paper aims to experimentally explore the possibility of improving the power coupling efficiency by choosing a proper glass tube in a microwave plasma torch with a metallic enclosure, rather than using additional tuning measures such as a movable short-circuited ending plunger or a three-stub tuner. The power coupling efficiencies for the glass tubes with different wall thicknesses were experimentally measured under different incident microwave powers and different pressures. The results showed that the power coupling efficiency was improved with the increase in the glass tube wall thickness in a wide range of operating conditions for the microwave plasma torch with specific dimensions. An efficiency higher than 85% can be achieved once the wall thickness of the glass tube is in a particular range. This indicates that external tuning measures can be reduced for the microwave plasma torch with a proper glass tube, which helps to save the cost of tuning devices and enhance the flexibility in different working environments.