Investigation of Anode Plume in Vacuum Arcs Using Different Optical Diagnostic Methods

This paper presents the results of different optical diagnostic methods to investigate an anode plume which forms after the extinction of anode spot type 2. The formation of the anode plume is investigated by means of three high-speed cameras. Two high-speed cameras, positioned perpendicular to each other, are used to observe the general anode plume evolution. The third camera is connected to a spectrograph enabling the video spectroscopy. The arc is driven by a damped 50-Hz ac between Cu/Cr 75/25 butt contacts with a diameter of 10 mm. The emission coefficients for atomic and ionic Cu lines during anode plume formation are calculated. The inner part of the anode plume is dominated by atomic line radiation, whereas the outer part is dominated by the emission of singly charged ionic lines. The radiator density of the Cu I 510.55 nm is about 3x10(17) m(-3) compared with a radiator density of Cu II of 9 x 10(13) m(-3) at the same position inside the anode plume. A broadband absorption spectroscopy is used to determine the ground-state densities of Cu and Cr after the extinction of anode plume at current zero (CZ). The density of Cu I is about 1.5 times higher than Cr I at the same time around CZ. Moreover, near-infrared spectroscopy together with thermography is used to determine the anode surface temperature around CZ after the extinction of an anode plume. The central anode surface temperature varies from 1530 to 950 K within 20 ms after CZ.