High power coaxial ubitron oscillator

Summary form only given. Previous work on the ubitron oscillator included the derivation of a linear theory for the cavity´s start of oscillation current, the development of a nonlinear simulation code, and the design of a compact 1 GW 21% effcient source for directed energy applications. Recent design efforts have increased the interaction efficiency to 46% using axial mode profiling in a TE/sub 011/ diffraction coupled cavity. In this technique, which is widely employed in gyrotrons, the radius of the cavity is tapered so that the peak of the wave´s field is displaced towards the output end. The beam then bunches more adiabatically in a lower rf field level while transferring its energy quickly in a higher field level. Additionally, the usage of diffraction coupling alleviates axial mode competition due to the decrease of cavity Q with axial mode number. A design for a 46% efficient S-band oscillator along with a 3.6 kA annular electron gun will be presented.