Kim W. Reed

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.

Genetic Optimization for Pulsed Power System Configuration

Pulsed power systems traditionally have been designed to provide a pulse that is nonprogrammable or requires hardware modifications to adjust the output shape. Advancements in pulsed power technologies are enabling system designs that allow for greater flexibility such as programmable current shaping. Material science, which uses current pulse shaping to obtain data for Equation of State (EOS) analysis, is driving much of this work. Programming of pulsed power systems through the use of a simulation and a manual curve fitting approach can work well for systems that only have a few controllable parameters and simple spectral content. Complex systems with many controllable parameters become unmanageable from a manual trial-and-error perspective. This paper discusses an approach to the optimization of a current adder output using genetic algorithms. The approach to system programmability presented herein will allow for a more simplified user interface and system control as the requirements for flexibility and complexity in future systems increase.

Genesis: A 5-MA Programmable Pulsed-Power Driver for Isentropic Compression Experiments

Enabling technologies are being developed at Sandia National Laboratories to improve the performance and flexibility of compact pulsed power drivers for magnetically driven dynamic materials properties research. We have designed a modular system capable of precision current pulse shaping through the selective triggering of pulse forming components into a disk transmission line feeding a strip line load. The system is comprised of two hundred and forty 200 kV, 60 kA modules in a low inductance configuration capable of producing 250–350 kbar of magnetic pressure in a 1.75 nH, 20 mm wide strip line load. The system, called Genesis, measures approximately 5 meters in diameter and is capable of producing shaped currents greater than 5 MA. This performance is enabled through the use of a serviceable solid dielectric insulator system which minimizes the system inductance and reduces the stored energy and operating voltage requirements. Genesis can be programmed by the user to generate precision pulse shapes with rise times of 220–500 ns, allowing characterization of a range of materials from tungsten to polypropylene. This paper provides an overview of the Genesis design including the use of genetic optimization to shape currents through selective module triggering.

Genetic Optimization for Pulsed-Power System Configuration

Pulsed-power systems traditionally have been designed to provide a pulse that is non programmable or requires hardware modifications to adjust the output waveform shape. Advancements in pulsed-power technologies are enabling system designs that allow for greater flexibility such as programmable current shaping. Material science, which uses current pulse shaping to obtain data for the equation of state analysis, is driving much of this work. The programming of pulsed-power systems through the use of simulations and manual curve fitting techniques can work well for systems that only have a few controllable parameters and are generating waveforms with simple spectral content. Complex systems with many controllable parameters become unmanageable for manual trial and error to be effective. This paper discusses the characterization and modeling of a scaled down programmable current adder directed at investigating technical issues that will be encountered in full-scale drivers. A discussion of the procedure used to optimize the adder current output, using genetic algorithms, is presented. The approach to system programmability presented in this paper will allow for a more simplified user interface and system control, as the requirements for flexibility and complexity in future systems increase.

Status of repetitive pulsed power at Sandia National Laboratories

Multi-kilojoule repetitive pulsed power technology moved from a laboratory environment into its first commercial application in 1997 as a driver for ion beam surface treatment. Sandias RHEPP II (Repetitive High energy Pulsed Power), a repetitive 2.5 kJ/pulse electron beam accelerator, has supported the development of radiation treatment processes for polymers and elastomers, food products, and high dose-rate effects testing for defense programs since early 1996. Dos Lineas, an all solid-state testbed, has demonstrated synchronization techniques for parallel magnetic modulator systems and is continuing the development of design standards for long lifetime magnetic switches and voltage adders at a shot rate capability that exceeds 5/spl times/10/sup 6/ pulses per day. This paper describes progress in multi-kilojoule class repetitive pulsed power technology development, magnetic switching technology for modulator applications, and future research and development directions.

Magnetic modulator lifetime tests using the Sandia reliability test-bed

Experimental results are presented that provide design guidelines for high repetition rate, long-life pulsed power magnetic modulators. Fault mechanisms that occurred during a series of 32 million shots at 100 pps, with continuous runs of up to 5.7 million shots (/spl sim/16 hours) on the Dos Lineas magnetic modulator are described. An effort to explain the fault mechanisms and how to avoid them is made. Factors that limit the long life performance of a variety of components including switches, cables and oil are encountered. The high reliability of the magnetic switch technology is demonstrated.

Genesis: A 5 MA programmable pulsed power driver for Isentropic Compression Experiments

Enabling technologies are being developed at Sandia National Laboratories to improve the performance and flexibility of compact pulsed-power drivers for magnetically driven dynamic materials properties research. We have designed a modular system that is capable of precision current pulse shaping through the selective triggering of pulse-forming components into a disk transmission line feeding a strip line load. The system is composed of 240 200-kV 60-kA modules in a low-inductance configuration that is capable of producing 250-350 kbar of magnetic pressure in a 1.75-nH 20-mm-wide strip line load. The system, called Genesis , measures approximately 5 m in diameter and is capable of producing shaped currents that are greater than 5 MA. This performance is enabled through the use of a serviceable solid-dielectric insulator system which minimizes the system inductance and reduces the stored energy and operating voltage requirements. Genesis can be programmed by the user to generate precision pulse shapes with rise times of 220-500 ns, allowing characterization of a range of materials from tungsten to polypropylene. This paper provides an overview of the Genesis design, including the use of genetic optimization to shape currents through selective module triggering.

Status of genesis a 5 MA programmable pulsed power driver

Genesis is a compact pulsed power platform designed by Sandia National Laboratories to generate precision shaped multi-MA current waves with a rise time of 200–500 ns. In this system, two hundred and forty, 200 kV, 80 kA modules are selectively triggered to produce 280 kbar of magnetic pressure (>500 kbar pressure in high Z materials) in a stripline load for dynamic materials properties research. This new capability incorporates the use of solid dielectrics to reduce system inductance and size, programmable current shaping, and gas switches that must perform over a large range of operating conditions. Research has continued on this technology base with a focus on demonstrating the integrated performance of key concepts into a Genesis-like prototype called Protogen. Protogen measures approximately 1.4 m by 1.4 m and is designed to hold twelve Genesis modules. A fixed inductance load will allow rep-rate operation for component reliability and system lifetime experiments at the extreme electric field operating conditions expected in Genesis.

PCSS Lifetime Testing for Pulsed Power Applications

Trigger systems are becoming increasingly important in pulsed power systems with large numbers of high voltage switches (HVSs) or large numbers of different switching times. Performance can be critical with demands for fast rise-times, sub-nanosecond jitter, and long lifetimes. In particular component lifetimes affect maintenance costs and the available operational time of the system. High gain photoconductive semiconductor switches (PCSSs) deliver many of the desired properties including optical-isolation, 350 ps risetime, 100 ps rms jitter, scalability to high power (220 kV and 8 kA demonstrated), and device lifetimes up to 108 shots with 21 A per filament in 5 ns wide pulses [1], [2]. However, higher current and longer pulse applications can drastically reduce device lifetime. For typical single shot pulsed power applications, lifetimes of several thousand shots are required and much longer-lived HVSs are required for repetitive pulsed power applications.

PCSS Triggered Pulsed Power Switches

This paper describes results from a 3 year project to develop fiber-optically controlled trigger generators (TG) from high gain photoconductive semiconductor switches (PCSSs) for high voltage switches (HVSs) in pulsed power applications. Triggers for HVSs are 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 output. Proposed pulse power systems are even more dependent on triggering as they consist of many triggered HVSs and produce shaped-pulses by independent timing of the HVSs.