The vacuum flashover of Dow-Corning type 704 diffusion-pump oil

Surface flashover characteristics of Dow-Corning type 704 diffusion-pump oil (DC-704) were measured to determine the suitability of this fluid as a vacuum barrier in pulse-power accelerators. These experiments were conducted on an Ion Physics Corporation FX-45 pulse generator, which provided 28-ns (FWHM) pulses in the 500- to 1000-kV range. These pulses went to either a resistive load or a field-emission diode via a vacuum-insulated coaxial transmission line partially filled with the oil. To date, almost 400 pulses have been fired and fields over 200-kV/cm have been sustained. For instances where the oil surface did flash over, open-shutter photographs recorded the spark channels. Since their probability did not show a strong field dependence, we believe that flashovers at these levels were due to spurious phenomena.