Observation of the Plasma Plume at the Anode of High-Current Vacuum Arc

Stable and bright plumes with a distinct and bright shell are observed at the anode of the high-current vacuum arc burning during 10 ms at a current of up to 15 kA in peak. A plume is attached to a hot spot at the anode. The substance inside a plume is almost dark. Light from a plume shell is emitted mostly by neutral atoms. A distinct bright shell is surrounded by substances emitting light in ion lines. Appearance of plumes looks to be a result of the interaction between cathode and anode jets. Plume dimensions depend inversely on both arc current and arc voltage, which makes plumes small and inconvenient for observations except as near current zero. Anode plumes are recognized on copper-chromium electrodes to be a stable object. However, similar objects on pure copper are much less stable and appear only at heat-insulated liquid protrusions and droplets flying in a gap. This fact indicates the evaporation rate to play a key role in appearance of plumes. In addition, the evaporation rate of a plane copper-chromium surface under high-current vacuum arc is supposed to be as high as that of heat-insulated liquid copper protrusions and droplets.