Extremely high power klystrons for particle accelerators

To make possible the realization of the different high-energy particle accelerator projects for physics researchers now in the design or planning stages, one fundamental necessity is the availability of extremely high power RF sources. Today, for such machines designed to operate beyond about 300 MHz, the only feasible candidate is the multicavity klystron amplifier. Furthermore, high conversion efficiency is essential, due to the high and ever-rising cost of electrical energy. Given here are the main considerations in improving klystron efficiency, emphasizing the role of computer-aided design (CAD), and a description of a 1 MW 352-MHz CW klystron from Thomson-CSF designed to meet the expressed requirements. Measured performances of this tube include 65 - 66 % efficiency, which may still be slightly improved. Also considered are the constraints of manufacturing and testing an electron tube of this size (over 4 meters long). Secondly, a pulsed klystron capable of delivering 35 MW peak at 3 GHz has also been developed by Thomson-CSF, for use in linear accelerators. This tube is also described and the considerations in maximizing its efficiency are discussed. Finally, mention is also made of a suitable driver for the latter tube.