Study of a High Order Mode Extended Interaction Oscillator at W-Band

A high-order mode operation is studied in a ladder cavity because it can support higher power capacity and larger size structure than the commonly used fundamental mode in millimeter-wave sources. The analysis of the field distribution shows the TM31-2 pi mode is more suitable for interaction when establishing fields with same frequency in using a large coupling cavity and a small one based on the same slow wave structure. The R/Q of the TM31 mode is optimized and proved to be higher than that of the fundamental mode in the identical ladder cavity, thus suppressing the potential mode competition. To demonstrate this capability, a W-band extended interaction oscillator (EIO) based on this cavity has been designed. A beam energy of 17.5 keV and current of 2 A was injected into the interaction circuit. Simulations via CST-PS predict an output power over 2.1kW with 93.4 GHz was obtained.