High-power coaxial ubitron oscillator: theory and design

The theory and design of a high-power coaxial ubitron oscillator is discussed. The device utilizes a high-current annular electron beam interacting with the radio frequency (RF) breakdown-resistant TE₀₁ mode in a coaxial cavity. Stable and laminar flow of the electrons is achieved without a confining axial field by using periodic permanent magnets to form the wiggler. A linear theory is derived for the cavity´s start-oscillation condition using a Vlasov analysis and a nonlinear simulation code is described. Agreement is good between the linear theory, nonlinear code, and the 2-1/2-dimensional particle-in-cell code, MAGIC. A 1-GW, S-band oscillator design with 21% efficiency is presented. It was found that the interaction efficiency in the cavity could be increased to 46% using the technique of axial mode profiling