Dynamics of vaporized electrode material during initiation of vacuum breakdown-laser-induced fluorescence

Results of laser-induced-fluorescence measurements of prebreakdown vapor concentration of electrode materials are reported. It is shown that the breakdown moment can be determined with an accuracy of 80 to 100 μs. At a laser pulse duration of 1 μs, the probability of coincidence of the pulse with the breakdown is only 2%, which strongly hinders the measurements. In addition, the technique allows the vapor concentration dynamics just before the breakdown to be measured only in a statistical sense. When the growth rate of the initiating voltage is increased, the time needed for experiments is reduced but it becomes doubtful whether the electrode processes remain similar to those taking place under constant voltage