Selectivity Properties of Coaxial Gyrotron Cavities With Mode Converting Corrugations

Longitudinally corrugated inserts have been proposed as an additional mean to enhance the selectivity properties of coaxial gyrotron cavities. However, when increasing the frequency and the output power, the corrugated insert may not be sufficient to ensure mode stability. Vane loaded cavities with corrugated inserts seem to have the potential for superior mode selectivity and could be employed to facilitate the development of multimegawatt gyrotrons. In this paper, a numerical code based on the spatial harmonics method is used to study the spectrum rearrangement of a typical coaxial cavity with corrugated insert in which additional wedge-shaped corrugations are introduced on the outer wall. A general design procedure for the upgrade of the mode selectivity is presented. Its merits are demonstrated for a 140-GHz gyrotron cavity.