In the magnicon amplifier, a scanning electron beam drives a synchronous fast-wave interaction in a cylindrical output cavity. The output cavity is designed to support a synchronous transverse magnetic (TM) waveguide mode, usually the TM210 mode. However, a number of other transverse electric (TE) or TM modes can be excited in the cavity via a nonsynchronous, gyrotron-type interaction, To investigate the possibility of competition from these nonsynchronous modes, a multimode gyrotron simulation theory and code have been adapted to the magnicon configuration. The gyrotron theory and corresponding code have been generalized to include a synchronous TM mode as well as nonsynchronous TE modes. Proper phase averaging between the modes, and between the modes and the beam electrons, is critical to accurate mode competition calculations. In nonsynchronous interactions this is achieved by averaging with respect to electron entrance time and the orbit guiding center angle. The synchronous mode interaction is invariant with respect to these two averages; however, it is affected by the scanning angle spread, which is included via a third average over scanning angles. Calculations have been carried out to model a second-harmonic X-band magnicon experiment, which is currently underway at the Naval Research Laboratory (NRL). The output cavity has been optimized for the TM210 mode at 11.4 GHz or twice the drive frequency (ωd=5.7 GHz). The principal competing mode is the TE121 mode. The simulations show that nonsynchronous mode interactions are suppressed by the synchronous interaction if the scanning angle spread is sufficiently small (≤90° in the NRL configuration).
ASJC Scopus subject areas
- Condensed Matter Physics