  An e+e- linear collider at 500-GeV C.M. (center of mass) has been proposed as
a future accelerator. The C-band linear collider has more than a thousand
klystrons and matching modulators. The linear colliders require smart
modulators with high reliability, compact and simple configuration, and good
power efficiency. This study suggests solutions to problems expected in the
future linear colliders. A C-band smart modulator has been developed using a
constant-current inverter power supply. The smart modulator provides 350-kV
pulses of the pulse-to-pulse stability of 0.35%, the pulse-width of 4.35
microseconds, and the repetition rate of 50 Hz. We also investigated the power
efficiency for the C-band scheme. A pulse efficiency of 75% can be achieved by
an optimized pulse transformer and the RF phase modulation. With pulsed
klystrons of 60% power efficiency, it is possible to achieve the RF system
efficiency of 32% with the wall-plug power of 170 MW.
