Measurement of the neutral vapour density decay following the extinction of a high-current vacuum arc between copper electrodes

The decay of neutral copper vapour density which follows the extinction of a high current (2-11 kA) vacuum arc between copper electrodes has been measured. The results show that during the period 1-8 ms from current zero the vapour density decays at least an order of magnitude slower than expected on the assumption that vapour atoms generated by the arc move freely to the electrode and vacuum chamber surfaces where they condense. The results can be explained, however, if it is assumed that the vapour is produced by evaporation from molten droplets which are emitted from the cathode spots.