Influence of the Surface Structure on the Anode Boundary of High Current Moving Arcs in Atmosphere

Abstract

In this study the influence of the surface structure on the anode boundary of high intensity arcs in atmosphere is investigated. It was found that the surface structure of an anode has a significant influence on the anode fall voltage, which we claim can be caused by field enhancements. The tested anode material is copper. In order to produce different field enhancing surface structures induced by micro peaks, the samples are sandblasted with different grain sizes. For the determination of the field a new method is proposed and a field enhancement factor is defined. This is done by approximating the sample surfaces with ideal peaks, whose height is calculated using the roughness and whose base is calculated based on SEM-images. Knowing the geometry of the peaks it is possible to simulate the electric field and then calculate the field enhancement factor. The prepared samples are tested with TIG-like plasmas applying different parameters. While moving the arc across a prepared sample, voltage and current measurements take place with parallel high speed stereo image acquisition. Using the measured arc voltages, the calculated fields and a modified form of the Child-Langmuir law, it is possible to calculate the anode drop voltage. To verify the innovative method, Langmuir-probe measurements are performed. The results are in good agreement and are evidence that the method used for the determination of the field enhancement and the physical model based on the Child-Langmuir law are useful approximations.