Fiber-Optic Controlled PCSS Triggers for High Voltage Pulsed Power Switches

Triggers for high voltage (HV) switches have always been critical components for reliable, efficient pulsed power systems because they control the timing synchronization and amplitude variation of multiple pulse forming lines that combine to produce the total system output pulse. In pulsed power systems of the future, the role of trigger systems are even more critical as they trigger more components and produce shaped-pulses by independent timing of individual switches or switch groups. Conventional trigger systems require high voltage trigger cables or line-of-sight optics that complicate design, demand space, and require extensive maintenance. With electrical triggers, large diameter, high voltage transmission line cables must be fed through high field regions. With optical triggers, line-of-sight optics must focus high energy laser beams to the interior of the switches with clean, rigidly-mounted, shock- withstanding optics. This paper reports on efforts to develop fiber- optically triggered photoconductive semiconductor switches (PCSS) to trigger high voltage switches with improved precision and eliminate the need for large- diameter trigger cables or line-of-sight optics. These triggers simplify design because their optical-isolation allows them to "float" with the switches that they trigger and have truly independent EMP-free timing control over 200 micron diameter optical fibers. They improve the performance of prime power switches, diverters, and diagnostics because their low-jitter sub-nanosecond rise times are more precise and more easily adjusted than conventional trigger sources. For pulse charged switches, the PCSS triggers can generally derive their trigger energy from the stray fields of the high voltage switch. Test results will be presented that have demonstrated 100 ps r-m-s jitter from a 40 kV, 500 ps rise time, PCSS- triggered 300 kV trigatron gas gap. PCSS design requirements, switching properties, and trade-offs for building high voltage trigger systems will also be described based on many previous experiments with PCSS technology. Results from PCSS Blumlein and PCSS capacitive discharge pulsers will be discussed along with the designs to use these pulsers to trigger both DC and pulse charged high voltage switches.