Spark gap triggering with photoconductive switches
Photoconductive switches are well suited for triggering spark gaps since the triggering event is short and requires very little energy. Photoswitches offer fast-rising pulses of short duration with voltage levels of several tens of kV and tens of ps jitter and can be very simple in design, whereas typical trigger sources require multiple stages to generate tens of kV needed to effectively trigger a spark gap of the same potential and usually suffer from slow risetimes. This paper presents methods aimed at triggering spark gaps with photoswitches. Both linear and nonlinear photoswitches are discussed and their associated problems are presented.
A 3-MV Low-Jitter UV-Illumination Switch
In a wide variety of high-power pulsed devices, the megavolt switch plays a key role in the system performance. A capacitance-resistance coupling structure was designed to produce UV light which triggered the switch to decrease the breakdown jitter. High-speed electrical measurements with a circuit integrating probe in the nanosecond range were employed to measure the voltage before the switch. From the experimental results, the breakdown characteristic of a 3-MV UV-illumination switch was obtained in the range of 1.6-2.5 MV: The jitter of the breakdown voltage is lower than 25 kV, and the jitter of the breakdown time is shorter than 5 ns.
Optically-activated GaAs switches for compact accelerators and short pulse sensors
This paper describes research and development of high gain GaAs photoconductive semiconductor switches (PCSS) for two very different types of applications: compact, repetitive accelerators and short pulse, active optical sensors. The accelerator is being tested with a spark gap driven modulator. It is a short pulse, linear induction accelerator (LIA) with an electron diode. Its design goals are: 700 kV, 7 kA, 30 ns pulses at 50 Hz. After characterizing the accelerator with the spark gap modulator, it will be tested with a GaAs PCSS modulator, which is under construction. Forty-eight, 2 inch diameter PCSS will switch 70 kA in a 250 kV coaxial Blumlein to deliver 220 kV, 35 kA, 30 ns pulses to the LIA. One module (1/8/sup th/) of the PCSS modulator is being tested. Results from these tests and projections for the complete system are discussed. The short pulse sensors are for military and commercial applications in optical and electrical range sensing, 3D laser radar, and high speed photography. The highest optical power produced with PCSS-driven laser diode arrays is presently 50 kW in 75 ps wide pulses or 12 kW in 1 ns wide pulses. A variety of sizes of GaAs PCSS are being tested around voltage and current specifications of several applications. Voltages range from 2 to 100 kV, currents range from 10 to 500 A, and electrical pulse lengths range from 1 to 50 ns. This paper discusses developmental issues of GaAs PCSS, which are common to all: fundamental research in high gain GaAs, device longevity, optical triggering, circuit configuration, and switch performance.