Influence of the radial dimension on the high-frequency characteristics in the coaxial relativistic O-type Cherenkov oscillators

Coaxial slow wave structures have always been used to enhance the power handling capacity in the relativistic O-type Cherenkov oscillators generally. However, little attention has been paid to the regularity and the problem it may bring by using large average radius. The aim of this study was to investigate the high-frequency characteristics of coaxial slow wave structures in order to evaluate the influence of the radial dimension comprehensively. The results indicate that a large overmoded ratio can make the power handling capacity increase significantly, but as a result, it will bring some problems such as low efficiency, long starting time, and the difficulty in mode control. In addition, this paper also gives some suggestions and precautions for using large radial dimensions. The conclusion of this paper has strong applicability for the design of coaxial slow wave structures.