Time- and Spatially Resolved Spectroscopy of the Plasma State Prior to and during Anode-Spot Formation in High-Current Vacuum Arcs

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Abstract
The emission of numerous lines was measured from a vacuum arc between an Al cathode and Cu anode in which the diffuse, anode-spot, and intense arc modes are observed during a single pulse. An increase in Cu emission and a decrease in Al emission are observed at the transition to the anode-spot mode, and increases in both Al and Cu emission are observed at the transition to the intense-arc mode. Spatial profiles of the excited-state density and Boltzmann-distribution temperatures could be obtained at several positions in the gap. The results show not only a clear correspondence between arc voltage and the arc appearance during different arc modes, but also distinctly different spectral emission properties and droplet behavior.