Ignition and instability of low-current DC vacuum arcs ignited by the opening of the electrodes

The ignition, lifetime, and instability of low-current de vacuum arcs, whic h were ignited by the opening of the electrodes, were investigated experime ntally. Copper electrodes were used and the are current was less than 50 A. Waveforms of the voltage and current between the electrodes at the moment of are ignition and during the are continuation were measured. It was confi rmed that, for the ignition of the are, a voltage which was larger than a c ritical value should appear between the electrodes at the moment of the ope ning of the electrodes. The lifetime of the arc is short, less than 1 s in the present condition, and increases with an increase in arc current and ou tput voltage of the current source. The arc voltage consists of a certain d c level, around 20 V, and an additive high-frequency component. The arc cur rent consists of a certain dc level and a subtractive high-frequency compon ent.