Arc Root Attachment on the Anode Surface of Arc Plasma TorchObserved with a Novel Method

Abstract

The arc-root attachment on the anode surface of a dcnon-transferred arc plasma torch has been successfully observed using anovel approach. A specially designed copper mirror with a boron nitridefilm coated on its surface central-region is employed to avoid theeffect of intensive light emitted from the arc column upon theobservation of weakly luminous arc root. It is found that the arc-rootattachment is diffusive on the anode surface of the argon plasma torch,while constricted arc roots often occur when hydrogen or nitrogen isadded into argon as the plasma-forming gas.