A new method of effective current density determination in cold electrode arc spot

Abstract

Summary form only given. Cold cathode arc spots present a complex structure, consisting of many separate microspots. They are also unstationary, making difficult and ambiguous the meaning of spot current density. We overcame these difficulties by introducing the thermal concept of effective arc spot current density, by which we measure the spot macrofusion onset and not the spot diameter, as in conventional methods. This allows a straightforward calculation of erosion electrode regimes. In this report another approach for onset macrofusion time determination was applied. It consist in the using of real time observation of the electrode material spectral line intensity emitted by arc column (in our case, material is copper, observed spectral line wavelength is Cu I (5218 Aring)). The electrode spectral line intensity, radiated by arc from near cathode region, is proportional to erosion rate. This fact permits the application of the spectral line intensity like the indicator of the fusion process intensity on electrode surface. Measurements were carried out within the range of magnetic field B = 0.015-0.32 T and electric current I = 150-400 A, on a coaxial experimental setup with magnetically driven arc. The system was equipped with non-cooled commercial copper-ring electrodes. The outer electrode was the cathode, with 40-mm inner diameter and 3-mm width. It was isolated from the adjacent parts of the setup by thermal- and electro-insulating spacers. The working gas was an atmospheric air. The experimental setup had an optical system, collected the light from the arc and transmitted it by fiber line to spectrometer. The experimental setup was equipped by high-speed data acquisition system of National Instruments. The obtained results showed a nonlinearly character growth of the effective arc spot current density with magnetic field