Photographic studies of the discharge development in a low-trigger-voltage vacuum switch

Transient voltage instabilities in the early discharge development phase of a triggered vacuum gap (TVG) have been investigated using high-speed photographic techniques. Luminosity was always detected first at the anode, corresponding (typically within 20 ns) to the main discharge current onset. Later when I>2 kA, somewhat less intense luminosity is detected at the cathode, apparently originating from several distinct sources. These results are shown to be consistent with a theoretical model which explains the discharge voltage excursions and the growth of the triggered vacuum discharge. A key factor in deciding the instability time is shown to be the emission-site formation time.