Fiber-Optically Controlled Pulsed Power Switches

The development and testing of fiber-optically controlled trigger generators (TGs) based on high gain photoconductive semiconductor switches (PCSSs), constructed from high resistivity GaAs, are described in this paper. The TGs are optimized to trigger the high voltage switches (HVSs) in pulsed power systems, where they control the timing synchronization and amplitude variation of multiple pulse forming lines that combine to produce the total system output. Future pulsed power systems are even more dependent on triggering, as they consist of many more HVS and, in some cases, produce shaped pulses by independent timing of the HVS. The goal of the PCSS TG is to improve timing precision and replace high voltage trigger cables or line-of-sight optics with fiber-optic trigger control. The PCSS trigger has independent EMP-free timing control via 200-mum-diameter optical fibers. This design is simpler than other TG because optical isolation allows PCSS triggers to be remotely located near the HVS at any voltage. PCSS can improve the performance of prime power HVS, diverters, and diagnostics by supplying trigger pulses with subnanosecond jitter and rise time that are more precise and easily adjusted than the conventional TG. For pulse-charged HVS, the PCSS TG can generally derive their trigger energy from the stray fields of the HVS. High gain PCSS capabilities for producing pulsed power TG have been demonstrated previously (not all simultaneously): 220 kV, 8 kA, 350-ps rise time, 100-ns pulsewidth, 50-ps rms jitter, and 10-kHz repetition rate. Furthermore, PCSS has previously triggered a 300-kV trigatron with 100-ps rms jitter.