Anode attachment stability and anode heat fluxes for high intensity arcs, with argon, nitrogen and helium gas flow parallel to the anode

Summary form only given. The arc - anode attachment and anode heat fluxes play an important role for anode erosion characteristics and anode lifetime. A better knowledge of these phenomena is required to optimize the anode performance. In this study we have addressed the question of the interaction of the arc with an anode when there is a cold gas flow parallel to the anode surface forming a cold boundary layer and leading to a constant motion of the anode attachment with a corresponding fluctuation in plasma power. This situation is encountered in many applications of non-transferred plasma torches such as plasma spraying where the fluctuation in plasma jet power can have a detrimental influence on the quality of the produced coating. A constricted attachment mode appears at low lateral gas flows of nitrogen, because of the high thermal conductivity of nitrogen. A lateral gas flow of helium results in little deflection, indicating that the arc attachment mode depends on the lateral gas momentum flux. The total anode heat transfer is reduced for increasing lateral gas flow rates probably primarily due to a convective heat loss from the arc to the argon atmosphere and chamber walls.