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Prior to this research, we have developed high-gain GaAs photoconductive semiconductor switches (PCSSs) to trigger 50–300 kV high-voltage switches (HVSs). We have demonstrated that PCSSs can trigger a variety of pulsed-power switches operating at 50–300 kV by locating the trigger generator (TG) directly at the HVS. This was demonstrated for two types of dc-charged trigatrons and two types of field distortion midplane switches, including a \pm100 kVDC switch produced by the High Current Electronics Institute used in the linear transformer driver. The lowest rms jitter obtained from triggering an HVS with a PCSS was 100 ps from a 300 kV pulse-charged trigatron. PCSSs are the key component in these independently timed fiber-optically controlled low jitter TGs for HVSs. TGs are critical subsystems for reliable and efficient pulsed-power facilities because they control the timing synchronization and amplitude variation of multiple pulse-forming lines that combine to produce the total system output. Future facility-scale pulsed-power systems are even more dependent on triggering, as they are composed of many more triggered HVSs, and they produce shaped pulses by independent timing of the HVSs. As pulsed-power systems become more complex, the complexity of the associated trigger systems also increases. One of the means to reduce this complexity is to allow the trigger system to be charged directly from the voltage appearing across the HVS. However, for slow or dc-charged pulsed-power systems, this can be particularly challenging as the dc hold-off of the PCSS dramatically declines. This paper presents results that are seeking to address HVS performance requirements over large operating ranges by triggering using a pulsed-charged PCSS-based TG. Switch operating conditions that are as low as 45% of the self-break were achieved. A dc-charged PCSS-based TG is also introduced and demonstrated over a 39–61 kV operating range. DC-charged PCSS allows the TG to be directly charged from slow or dc-charged pulsed-power systems. GaAs and neutron-irradiated GaAs (n-GaAs) PCSSs were used to investigate the dc-charged operation. [ABSTRACT FROM PUBLISHER]

The demand for greater flexibility and increased energy density in pulsed-power systems is moving highly interactive components closer together. The development of compact technologies for less complex and more robust system designs is critical. A key system component that can impact these goals is the trigger generator (TG). Inexpensive, compact, and fiber-optically controlled TGs that deliver trigger pulses with subnanosecond jitter have been created with photoconductive semiconductor switches (PCSSs). However, high-voltage (HV) GaAs PCSSs are typically pulsed charged for less than 100 \mu\s so that they can hold off 60–100 kV/cm without self-triggering into high-gain (lock-on) switching or initiating surface flashover. Since many new pulsed-power system designs are based on dc-charged HV switches, pulse charging the trigger system is an additional complication requiring space, HV switching components, and HV cables. A further improvement in PCSS-based TG is to move from pulsed to dc-charged PCSSs. This paper reports results from dc-charged GaAs PCSSs with 0.25–1.0 cm gaps, extending previously reported results on smaller devices at 3 kV to a new regime of 100 kV. To hold off high fields for longer periods and to extend GaAs PCSSs to dc applications, we have utilized neutron-irradiated GaAs (n-GaAs). Neutron irradiation in GaAs increases the defect density, shortens the carrier recombination time, and (for devices with large insulating regions) reduces the dark current, which improves the dc hold-off strength. PCSS contacts in this research were created using rapid thermal annealing (RTA) to produce high adhesion and low contact resistance. However, this can reduce the defect density near the contacts by annealing some of the n-induced defects. Hence, a range of RTA temperatures and neutron doses was studied to understand the tradeoff space for contact adhesion and dc hold-off. This paper presents results from I–V characterization and dc hold-off on irradiated and nonirradiated GaAs PCSSs. These PCSS devices were demonstrated to hold off fields of 39–61 kVDC/cm, respectively. Irradiation doses over a range of \3 \times \10^13 - \1 \times \10^15 (1 MeV Si equivalent) were explored in search of the optimal performance. Additionally, the impact of the fabrication processes on the benefits of irradiation is explored, and the observation of unusual low-frequency oscillations during GaAs I–V testing is discussed. [ABSTRACT FROM PUBLISHER]

Pulsed-power systems traditionally have been designed to provide a pulse that is nonprogrammable 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. [ABSTRACT FROM AUTHOR]

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-μm-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-ky trigatron with 100-ps rms jitter. [ABSTRACT FROM AUTHOR]