250-MW X-band TE/sub 01/ ubitron using a coaxial PPM wiggler

A highly efficient 250-MW X-band ubitron amplifier to drive high gradient linear accelerators is described. The ubitron utilizes periodic permanent magnets with zero guide field and a coaxial circuit operating in the breakdown resistant TE/sub 01/ mode. Periodic wiggler focusing in a coaxial transmission line allows for stable transport of high-current annular electron beams while producing a strong quiver velocity to drive the ubitron. A large-signal self-consistent simulation code predicts that an efficiency of 37% and a gain of 53 dB can be achieved in a length of 100 cm with a 500-kV 1-kA electron beam, while a tapered wiggler will yield an efficiency as high as 56%.