Effect of Anode Attachment on Flow Structure in Plasma Jet Generated in DC Arc Torcha

Abstract

ABSTRACT: Effect of an arc anode attachment on stability of plasma jet was studied in a plasma torch with dc electric arc stabilized by water. The torch was equipped with an external anode and thus direct observation of interaction of the anode attachment with the plasma jet was possible. High speed photography of the anode region and the jet was synchronized with voltage measurements. Different modes of the anode attachment were distinguished and movement of the attachment along the anode surface was photographed. Formation of an anode jet was observed. An interaction of the anode jet with the main jet produce strong instability of plasma flow in the jet which rapidly develops into jet whipping and fluttering. It is shown that momentum flux in the anode jet is comparable with the one in the main jet and thus a formation of the anode jet is principal cause of a plasma jet instability. Results of spectroscopic diagnostics of the anode region indicate strong entrainment of ambient air into the anode jet.