Arc Root Motion in an Argon-Hydrogen DC Plasma Torch

Arc root motion on the anode surface of a DC nontransferred plasma torch was observed. Adding hydrogen changes the arc root attachment from a diffused type to a constricted type, and the arc root of Ar-H
₂
plasma suddenly jumps from one spot to another irregularly. Images of the arc root motions taken by a high-speed video camera are presented.