Comparative Observation of Ar,Ar-H2 and Ar-N2 DC Arc Plasma Jets and Their Arc Root Behaviour at Reduced Pressure

Results observed experimentally are presented,about the DC arc plasma jets andtheir arc-root behaviour generated at reduced gas pressure without or with an applied magneticfield.Pure argon,argon-hydrogen or argon-nitrogen mixture was used as the plasma-forming gas.A specially designed copper mirror was used for a better observation of the arc-root behaviouron the anode surface of the DC non-transferred arc plasma torch.It was found that in thecases without an applied magnetic field,the laminar plasma jets were stable and approximatelyaxisymmetrical.The arc-root attachment on the anode surface was completely diffusive whenargon was used as the plasma-forming gas,while the arc-root attachment often became constrictivewhen hydrogen or nitrogen was added into the argon.As an external magnetic field was applied,the arc root tended to rotate along the anode surface of the non-transferred arc plasma torch.