Modulator for Short Pulse Switching

A fast-pulse modulator ¿ such as the 300 kV, 300 A, 1.3 µs modulator for Argonne National Laboratory¿s Short Pulse X-Ray Project, a DOE accelerator facility ¿ performs best when the speed of the current rise-time into the load (the modulator¿s dI/dt) is highest. In modern solid-state modulators, rise-time is limited by the intrinsic switching time of the solid state devices from which the modulator is built, and by the need to limit the current in the modulator when the RF amplifier tube experiences a fault. The rise-time for a conventional solid state modulator is limited to approximately 1 µs in order to allow it to be turned off before the peak current reaches damaging levels. This limitation in rise-time reduces the efficiency of the system and leads to a significant waste of available power. This project will develop an alternative method to actively limit the fault current through the modulator during an arc. This method will allow the system to operate at its peak current rise-time during normal operation, while preventing damaging current levels during an arc.Commercial Applications and other Benefits as described by the awardee: The active current-limiting approach should allow the Argonne modulator to operate with a faster risetime and higher frequency, as required by the DOE for future accelerator systems. The approach also should contribute to a wide range of potential applications: (1) modulators for systems that have a long output cable between the switch and the RF tube (as is the case in many accelerator designs); (2) tubes for high-PRF radar transmitters, which could be cathode-pulsed without the need for mod-anode or grid modulators; and (3) ion implantation and pulsed electric field treatment of food.