Video Spectroscopy of Vacuum Arcs During Transition Between Different High-Current Anode Modes

This paper presents spectroscopic results of high-current anode phenomena in a vacuum arc discharge between CuCr electrodes. AC (alternative current) 50-Hz and 10-ms pulsed dc (direct current) are applied as interrupting current. Time and space resolved optical emission spectroscopy (video spectroscopy) is used to examine the temporal and spatial distribution of different atomic and ionic copper lines. During the transition from low-current mode to different high-current modes, including footpoint, anode spot, and intense arc mode, the intensity of Cu I, Cu II, and Cu III line radiation is examined near the anode, the cathode, and in the interelectrode gap. The results show that during the formation of anode spot and intense mode the intensity and the distribution of all lines change noticeably in the different spectral regions. In fact, higher ionization states represent the arc dynamics behavior during transition to high-current anode modes. Significant differences have been found, for example, in the spatial structure of Cu II and Cu III lines in the anode spot mode. The results for Cu I lines indicate an active role of atoms together with the ions in different charge states in high-current anode modes. The impact of threshold current and transferred charge of the formation of high-current anode modes in case of ac and pulsed dc is also investigated regarding the intensity of copper lines near the anode.