A compact, short pulse, repetitive accelerator has many useful military and commercial applications in biological counter-proliferation , materials processing, radiography, and sterilization (medical instruments, waste, and food). The goal of this project was to develop and demonstrate a small, 700 kV accelerator, which can produce 7 kA particle beams with pulse lengths of 10-30 ns at rates up to 50 Hz. At reduced power levels, longer pulses or higher repetition rates (up to 10 kHz) could be achieved. Two switching technologies were tested: (1) spark gaps, which have been used to build low repetition rate accelerators for many years; and (2) high gain photoconductive semiconductor switches (PCSS), a new solid state switching technology. This plan was economical, because it used existing hardware for the accelerator, and the PCSS material and fabrication for one module was relatively inexpensive. It was research oriented, because it provided a test bed to examine the utility of other emerging switching technologies, such as magnetic switches. At full power, the accelerator will produce 700 kV and 7 l~4 with either the spark gap or PCSS pulser.Mature spark gap technology was used to demonstrate operation of the accelerator. Later multiple PCSS were tested with a PFL, which could drive 1/8" of the accelerator. The spark gap based system is pulse charged with a low impedance pulse forming line (PFL) which is switched by a single high current spark gap. The PFL drives four small linear induction accelerator (LIA) cavities. In FY95 and 96, the spark gap system was assembled and tested. A field-enhanced diode was tested, and the LIA was analyzed for modifications to operate continuously at 50 Hz. Prolonged testing at 500 kV and 5.5 kA produced several cable breakdown problems, which were repaired, but eventually, the cables will have to be replaced with higher breakdown strength cables for continuous operation. The longest burst tested was 3000 pulses at 30 Hz.The main advantages of PCSS versus spark gaps for the LIA are lower inductance and greater design flexibility due to the distributed switching that is possible with precisely triggered PCSS. For the LIA and the diode, this translates to faster rise-times, more rectangular pulses, the capability of shorter pulses, and potentially higher diode efficiency. The PCSS-based pulser is composed of 8 identical modules. Each module is switched with six 2-inch diameter PCSS. In FY97, 30 simultaneous current filaments were initiated on a 3-cm wide section of a single switch to limit the current per filament to less than 50 A (500 Ncm) and improve switch lifetime. The first module was assembled and tested to 210 kV and 8 kA. Further optimization of the optical trigger delivery system is necessary to reach 250 kV and 10 kA (full power for 1 module) with reasonable PCSS lifetimes (>10,000 pulses). Improved PCSS contacts were developed which demonstrated switch lifetime greater than lo7 pulses.. However, further resources are necessary to incorporate the new switches, ...

Spark ignition engines of practically all types and sizes utilize ignition systems that can develop up to about 30 Kv for breakdown of the spark plug gap and typically deliver current levels in the range of 30 to 100 ma. Measurement and analysis of these systems show that the energy transfer efficiency is very low, typically in the order of one percent (1%) or less. Once the spark is formed, most of the energy is delivered to resistences in the transformer, spark plug wires and spark plugs. This operating level is adequate (but not necessarily optimum) for older and most modem engines, but will not meet the needs of future lean bum and some alternate fuel engines that require higher energy discharges to effectively ignite the adfuel mixtures 1.13* ' . To meet the requirements for increased ignition power and energy, ignition systems will have to be designed to operate at higher transfer efficiencies.There are two basic approaches to increasing the electrical eficiency of ignition systems. The f m t is to utilize peaking capacitors across the spark plug'. The second is to design and utilize a more efficient discharge circuit in combination with a low resistance spark coil'. A third alternative would be to u t i l k a combination of both. By the first method, transfer efficiency can be increased to nearly fifty percent (50%). By the third, transfer efficiency can be seventy-five percent (75%) or more. This paper summarizes the results of recent high power ignition experiments and related analyses, for socalled "breakdown ignition" conditions. The paper includes descriptions of both conventional system up-grades and a new higher energy system that features multiple drivers and an energy recovery circuit. It does not include analyses or experiments for arc or glow discharge conditions.

The SBS_1 experiment at Sandia National Laboratories is designed to demonstrate the feasibility of the Scanning Beam Switch for high-power RF generation. The primary application is to pulsed RF linacs and high-frequency induction accelerators. We expect that the apparatus will generate RF output power exceeding 100 MW at 50 MHz over a 5 p5 pulse. The device can operate as an oscillator or high gain amplifier. To achieve the capability for long-macropulse and high-duty-cycle operation, SBS_1 uses a large dispenser cathode and vacuum triode input driver.

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voltage is controlled by tile PFN charge voltage which, in a uni-polar PFN configuration, is 30 KV and, in a bipolar configuration, + 30 KV. Inputs to the generator include DC power, compressed air for the primary spark gap and a low voltage trigger pulse. The system can be A compact, easily transportable, pulse generator has been developed operated in a single pulse mode or repetitively in bursts to 50 H, or for a variety of applications that require a pulse duration in the range continuously at 10 H,. For the present pulser modules, pulse repetition rates and duty cycle are limited by the primary spark gap. With a of 11,t see., voltages from 150 to 300 KV and current levels from 2,000 to 3,000 amps. The generator has a simple cylindrical configuration heavier duty spark gap, continuous rep rates to at least 50 Hz would be and modularconstructionto facilitate assembly and service. The possible. generatormaybe operatedsihgle-pulseor repetitivelyat pulse repetitionratesto 50 Hz in a burstmode.