PSI, Villigen PSI, Switzerland
Diversified Technologies, Inc., Bedford, Massachusetts, USA
Semiconductor thyristers have long been used as a replacement for thyratrons, at least in low power or long pulse RF systems. To date, however, such thyristor assemblies have not demonstrated the reliability needed for installation in short pulse, high peak power RF stations used with many pulsed electron accelerators. The difficulty is that a fast rising current in a thyristor tends to be carried in a small region, rather than across the whole device, and this localized current concentration can cause a short circuit failure. It is not clear that this failure mode can be overcome with currently available device designs. An alternate solid-state device, the insulated-gate bipolar transistor (IGBT), can readily operate at the speed needed for the accelerator, but commercial IGBTs cannot handle the voltage and current required. Diversified Technologies, Inc. (DTI) has patented and refined the technology required to build these arrays of series-parallel connected switches. Under DOE contract, DTI is currently developing an affordable, reliable, form-fit-function replacement for the klystron modulator thyratrons at SLAC capable of pulsing at 360 kV, 420 A, 6 μs, and 120 Hz.
Diversified Technologies, Inc., Bedford, Massachusetts, USA
Rockfield Research Inc., Las Vegas, Nevada, USA
High voltage short-pulse klystron modulators are required for numerous X-Band accelerator designs. At the very high voltages required for these transmitters, all of the existing designs are based on pulse transformers, which significantly limits their performance and efficiency. There is not a fully optimized, transformer-less modulator design capable of meeting the demanding requirements of very peak power, short pulse RF stations. Under a U.S. Department of Energy grant, Diversified Technologies, Inc. (DTI) is developing a short pulse, solid-state Marx modulator. The modulator is designed for high efficiency in the 100 kV to 500 kV range, for currents up to 250 A, pulse lengths of 0.2 to 5.0 μs, and risetimes <300 ns. Key objectives of the development effort are modularity and scalability, combined with low cost and ease of manufacture. For short-pulse modulators, this Marx topology provides a means to achieve fast risetimes and flattop control that are not available with hard switch or transformer-coupled topologies. The system is in the final stages of testing prior to installation at Yale University.