Control of cathode arc root behavior in a reverse polarity hollow electrode plasma torch using an exit nozzle

In this study, a hollow electrode plasma torch with a cylindrical exit nozzle was proposed and tested to control the behavior of cathode arc roots in the reverse polarity electrical connection for the non-transferred mode operation. The test results revealed that in the absence of an exit nozzle, cathode arc roots cause arcing on the electrically floated torch housing, producing an unstable plasma jet. However, in the presence of an exit nozzle, when injecting the secondary gas with a swirl through a gap between the exit nozzle and front electrode, it was confirmed that cathode arc roots can be controlled to form only on the surface of the front electrode, producing a stable plasma jet without arcing on the torch housing. Additionally, the presence of an exit nozzle was observed to have little influence on the voltage–current characteristics of a reverse polarity hollow electrode plasma torch. Instead, heat loss to the coolant was reduced compared to that in the absence of an exit nozzle, thereby improving thermal efficiency.