MOTION OF ANODE ATTACHMENT AND FLUCTUATIONS OF PLASMA JET IN DC ARC PLASMA TORCH

Abstract

The anode attachment region of a dc arc in the plasma torch with water stabilization was studied using high speed photography and time resolved measurement of light radiation intensity. The motion of anode attachment on the electrode surface in the restrike mode was investigated. The downstream motion of the anode attachment proceeds in the small scale jumps related to the small scale restrikes. The velocity of the motion is affected by the arc current and by position of the anode relative to the arc column. The velocity varies during the downstream motion of the spot in correlation with the variations of plasma flow velocity. The anode jet is created on the surface of the electrode and its interaction with the main jet causes instability of the main jet. The experimental results well correspond to the assumption that diffusion electron currents flowing between the arc plasma and the anode surface are principal cause of formation of new arc attachment and that the energy balance on the anode surface and in the adjacent gap of partially ionized gas is decisive rather than electric breakdown of the gap.