Emission of electrode vapor resonance radiation at the onset of dc breakdown in vacuum

Simultaneous time-resolved spectroscopic and current measurements have been made during the early stages of current growth leading to dc breakdown in vacuum between plane-parallel electrodes of dissimilar material. These measurements show that resonance radiation characteristic of anode material is emitted prior to that of cathode material from all regions of the interelectrode gap. Further, the radiation is emitted first from the cathode region of the gap. The results indicate that the initial current growth occurs in anode vapor followed at later times by the appearance of cathode vapor in the gap.