The anode region of high intensity arcs with cold cross flow

Abstract

The anode region of an argon high intensity arc with a superimposed cold flow has been investigated experimentally. Three-dimensional electron temperature and electron density distributions have been obtained with a laser Thomson scattering system, and the flow fields have been observed with a high speed Schlieren system. The transition from a steady mode to a takeover mode and finally to a restrike mode has been clearly identified. During the transition, the flow field becomes turbulent and the electron temperature and the electron density values in the major anode attachments increase significantly. Starting from a takeover mode, extended anode boundary layers have been found, which have high electron temperatures and low electron densities, indicating their non-equilibrium nature. In a restrike mode, the restrike behaviour has been found to be initiated by flow instabilities, which bring high electron temperature clouds into the extended anode boundary layer and encourage the electron overheating instabilities. Finally, together with the anode burn patterns, the experimental results are applied to plasma spray torches and a takeover mode is suggested as the favourable operation mode.