August 5, 2005  
 

 

What is a Marx Modulator?

By Albe Larsen

Mechanical illustration of a 16-cell Marx Modulator for ILC.
 

The completely modular assembly is composed of cells shown above. Each cell is replaceable robotically or with a remotely operated hand manipulator.
(Images by Greg Leyh)

A Marx Modulator is an electrical circuit designed to generate a high voltage impulse. In accelerators, a modulator stores AC power and converts it to a DC pulse for klystrons. This is achieved by charging a stack with a number (N) of capacitors in parallel to a given voltage (V), then quickly switching to a series configuration, adding the voltages to generate an output (N times V).

For the SLAC ILC klystron modulator, 10 capacitors are charged to 12 (kV) in parallel, then switched using Integrated Gate Bipolar Transistors (IGBT) into a series stack to generate 120 kV peak voltage at 140 A. IGBTs are very fast solid state switches used first for switching trains. Key elements to success are the selection of capacitor type and droop compensation during discharge. The circuit shown here indicates the basic elements of the modulator.

For more information on Marx Bank, see: http://en.wikipedia.org/wiki/Marx_generator
NLC design: http://www-group.slac.stanford.edu/esd/PESC04_Paper.pdf
ILC design: http://www-group.slac.stanford.edu/esd/PPC2005Paper.pdf

 

 

 

 

The Stanford Linear Accelerator Center is managed by Stanford University for the US Department of Energy

Last update Friday August 05, 2005 by Topher White