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Science Today: ILC's Marx Modulator

(Image - Marx Modulator)

The current design for the International Linear Collider (ILC) requires 576, 10-megawatt klystron tubes to supply microwave power along its 40 km linear accelerator. Each ILC klystron tube needs 120,000 volt, 140-ampere pulses, fired at a rate of five pulses per second. Each pulse delivers a total energy of more than 23 kilojoules—the kinetic energy of a 20 millimeter cannon shell.

The ILC Marx Modulator, a current R&D program at SLAC, eliminates the need for a massive transformer just before the klystron to raise the output voltage up to 100’s of kilovolts. However, the high pulse energy of the ILC klystron would require a truly massive (and expensive) transformer—upwards of 6.5 tons.

The ILC Marx Modulator eliminates the need for a massive transformer by using the relatively simple Marx concept: charge a number of capacitors in parallel, and then reconnect them in series to produce a higher voltage. Custom solid-state switches connected to each capacitor perform this function.

Construction of the first Marx prototype in Building 15 is nearly complete. Piotr Blum is the mechanical design lead for the Marx, and Alfred Viceral manages the construction and testing of the Marx cells and IGBT switches. Currently, eight completed Marx cells are in place, allowing the modulator to produce 70,000 volt pulses into a test load. Within the next eight weeks, enough cells will be completed to allow 120,000 volt operation.

Based upon further results from R&D, the Marx Modulator may become part of the final engineering design for the ILC.

—Greg Leyh, January 18, 2007

Above image: The prototype Marx modulator, designed and constructed at SLAC.