Studies of the anode region of a high-intensity argon arc

Abstract

This paper is concerned with experimental and analytical/numerical studies of the anode region of an atmospheric pressure argon arc in a current range from 100 to 300 A. The arc arrangement allows unobstructed viewing of the entire anode region, including the anode itself, and it is also suitable for simulating short as well as long arcs. Depending on the flow situation in the anode region, two different types of stable arc roots are observed. The diffuse anode arc root, characterized by a strong flow impinging on the anode surface, is well known from free-burning, short arcs. The second type reveals a more or less vevere constriction in front of the anode, caused by the entrainment of gas into the arc, resulting in an anode jet. Measurements of the induced flow at the cathode of such an arc show a linear increase of the induced mass flow rate with increasing current. This correlation can be confirmed by a simple analysis. A fast-scanning, computer-controlled system has been used for spectrometric measurements of the temperature distribution for both modes of anode arc roots, assuming local thermodynamic equilibrium (LTE) in the arc. The maximum temperatures in the arc core compare favorably with calculated temperature distributions of the constricted mode. The calculated isotherms, however, show a substantial shift which is probably due to the chosen boundary conditions at the end of the constrictor tube.