Voltage Droop Compensation for High Power Marx Modulators

The International Linear Collider (ILC) will need hundreds of modulators to power the 10-MW, long pulse (1.4 ms) klystrons. A Marx modulator controlled by solid-state switches promises higher efficiency, longer lifetime, and reduced cost compared to existing hard tube modulator options. However, voltage droop is one of the critical challenges that limit the application of the Marx modulators. The current approach to minimizing this problem, using vernier cells, is unable to smooth the flat top of the voltage pulse output, requiring an additional high voltage charging source and a large number of cells, which complicate the design of the Marx circuit. This project will develop a new compensation scheme that exploits the high speed of solid-state switches and the circuit characteristics of additional inductance. Phase I demonstrated that simple compensation circuitry based on this scheme can be implemented on an existing Marx main cell structure. Simulations of the modified vernier cell showed compensation to within 1%. In Phase II, an 11 kV modified vernier cell will be designed and built. After initial high voltage laboratory testing, the modified cell will be integrated into SLAC¿s Marx modulator for a real-time application test. Commercial Applications and other Benefits as described by the awardee: The new compensation circuits should benefit the ILC project directly by meeting its stringent requirements for hundreds of modulators. It also would complement SLAC¿s Marx modulator program and other accelerator facilities that require long pulse modulators. Examples of such facilities include the TTF at DESY (hundreds of modulators, pulse width of 1.6 e ms) and the KEK in Japan (pulse width of 600 s)