This research has the ultimate goal of enhancing our understanding of the arc-anode attachment, particularly in the regions of unstable operation in order to establish guidelines for design of arcing devices with longer life and greater reliability. Shorter term objectives are: (1) the development of methods to predict arc-anode attachment movement for nozzle anodes as a function of arc current, gas type, flow rate, and channel diameter; these parameters determine velocity and temperature distributions in the boundary layer and therefore the characteristics of the current transfer from the arc to the anode; and (2) determination of conditions for which a transition occurs form a diffuse arc-anode attachment to a constricted one in terms that are independent of the specific arcing configuration. To accomplish this, a combination of modeling and experiments are performed for two different configurations: with the axis of the arc parallel to the anode and with the axis of the arc perpendicular to the anode. Specific tasks include modeling of the arc-anode attachment instability for nozzle flow arcs with a three-dimensional dynamic model; experimental investigation of the arc-anode attachment movement in nozzle anodes to obtain the relationship between attachment velocity and the cold gas boundary layer thickness; and experimental investigation of the change in arc-anode attachment with an arc axis perpendicular to the anode as a function of plasma flow velocity and other factors.
Improved understanding of arc-electrode effects is essential for improving performance and lifetime in a variety of plasma devices such as discharge lamps, circuit breakers, arcjet thrusters, plasma spray torches, and arc heaters for metallurgical processing.
