Control of the arc motion in DC plasma spray torch with a cascaded anode

Two common concerns in DC plasma torches are the stability of plasma jet and anode erosion. The first can be addressed by using a cascaded anode; the second by controlling the residence time of the arc attachment on the anode wall, by injecting the plasma gas with a strong vortex and/or using an external axial magnetic field.

In this study, we consider the SinplexPro™ plasma torch (Oerlikon Metco) that uses an inter-electrode insert and a vortex gas injection. Previous calculations and experimental observations have shown that the anode arc attachment is restrained along a line on the anode wall; and that vortex injection is generally not very effective in the operating window of the torch. The idea is then to apply a magnetic field to the anode segment so as to limit the residence time of the arc in any point. A 3-D, time-dependent MHD model that couples the gas phase and electrodes is used to determine the intensity of the magnetic field that makes it possible to control the motion of the arc without affecting too much the stability of the plasma jet issuing from the torch.