UV illumination switch is often utilized for pulse sharpening in large pulsed power devices. A lot of work has been done for UV illumination switch under nanosecond pulse 1 while the switch under microsecond pulse may show different performance 2 . The purpose of this study is to figure out the breakdown characteristics of UV illumination switch under microsecond pulse. To analyse the development of discharge channel, the switch with two spherical electrodes and a HV needle electrode inside was designed and ICCD with a minimum exposure time of 10 ns was used to capture images of the discharge. What's more, a similar higher voltage level switch was designed in this study. HV electrode of the switch was replaceable with three different types: the flat-head, the spherical-head and the saw-toothed. Factors which may influence the switch performance, including arrangement of electrodes, distance of main gap, current-limiting resistance of pre-ionizing gap, rise time of the pulse and gas type were experimentally studied. Jitter of discharge delay time and uncertainty of breakdown voltage were taken as two important properties to measure the performance of the switch. From ICCD photos, we can see that discharge in the preionizing gap first appears, and then is enhanced and results in the dispersive light spots along the main gap, and at last streamers are formed through the whole gap. As to the performance of the switch, experimental results indicate that the flat-head electrode extruding 1 mm out of the ambient electrode gains less jitter, more uniform discharge spots and less electrode erosion. When the resistance of pre-ionizing gap is selected to make sure that the peak current of presparking is about 1 A and N 2 is employed as the working medium, the switch reaches a lower jitter and uncertainty of breakdown voltage. The jitter scales approximately linearly with the increasing rise time of the applied voltage while the uncertainty shows inconspicuous change. The jitter and the uncertainty of breakdown voltage can achieve 11.8 ns and less than 0.2% respectively when the switch is performed at 6 microseconds rise time and 100 kV pulse.
