Refurbishment of the ETDL Rep-Rate Pulse Generator at AFRL

The Air Force Research Laboratory is refurbishing a high-voltage rep-rate pulser that generates 550 kV output pulses with a nominal FWHM of 550 ns at pulse repetition rates of up to 5 Hz. This pulser was originally constructed for the Army Research Laboratory's Electronic Test Devices Laboratory (ETDL). The pulser can drive 20-, 10-, or 5-Omega loads when either one, two, or four 20-Omega PFN's, respectively, are installed. Among the major changes and upgrades that are being made to the pulser is the replacement of the output switch with a triggered cascade switch. Initially, a two-electrode self-breaking spark gap was used for the output switch, but this had jitter in pulse-to-pulse timing and waveshape due to variation in the self-break voltage. An earlier implementation of a triggered output switch was successful in reducing pulse-to-pulse jitter [1], but the spread still remained approximately 500 ns. A significant effort was directed during this present upgrade towards the development of an improved triggered output switch. The new switching system has a 10 ns total spread in breakdown time with respect to the initial trigger to the pulser system and provides reproducible waveshapes. The charging system has also been upgraded. The original system used a computer-controlled high-voltage DC power supply and a filter bank that pulse-charged the pulse generator's primary bank. This is being replaced with a commercially available, high-power (100 kV) DC charging supply to directly charge the primary bank. Eliminating the filter bank has led to a substantial reduction in size. Other modifications to the pulser include changes to the PFN design to allow greater ease and flexibility when tuning the pulse shape and to reduce the self-inductance of the PFN capacitors. This paper describes these modifications to the ETDL pulse generator in detail and presents data from initial tests following the upgrades.