Influence of nozzle diameter on electric arc dynamics in a cascaded-anode plasma torch

Conventional plasma torches are widely used in plasma spraying. They comprise a rod-shaped doped-tungsten cathode with a conical tip and a concentric water-cooled copper anode. However, this design leads to electric arc instabilities, resulting in plasma jet fluctuations. Theses instabilities have an effect on the enthalpy of the plasma jet and on its mixing with the cold surrounding gaz. In order to improve the plasma jet stability, new designs of plasma torch were developed with a cascaded anode, consisting of a stack of copper rings insulated from each other. This configuration allows an extend of the arc length which permits to increase the enthalpy of the plasma jet and to reduce its fluctuations. An example of such torches is the SinplexProTM from Oerlikon Metco which uses a single cathode and a cascaded anode. This work focuses on SinplexProTM plasma torch diagnostics with the study of electric arc dynamics. Influence of plasma forming gas composition on anodic arc attachment and voltage signal is studied.