DETERMINATION OF THE ARC-ROOT POSITION IN A DC PLASMA TORCH

The behavior of an arc operated in the nontransferred mode with a coni cal-shaped cathode and a nozzle-shaped anode is studied by applying ge neral two-dimensional conservation equations and auxiliary relations f or the simulation of arc channel flows. The position of the arc-root a ttachment at the anode surface is determined by using Steenbeck's mini mum principle, which postulates a minimum arc voltage for a given curr ent and certain given boundary conditions. The overall effects of the anode-arc root on the plasma flow are studied by comparing the results with those of the transferred mode of operation. Specific arc-channel diameters are chosen in the simulation in order to verify the numeric al model through comparisons with experimental results. The results sh ow that Steenbeck's minimum principle is useful for determining the po sition of the arc-root attachment at the anode surface. Application of this method for control of the arc-anode attachment may be valuable i n the design and operation of plasma spray torches to avoid jet instab ilities.