Present status of a 17.1-GHz four-cavity frequency-doubling coaxialgyroklystron design

A design of a Ku-band 17.1-GHz four-cavity coaxial gyroklystron amplifier for driving future linear colliders is presented. The X-band input cavity operates in the TE_0.11 mode, whereas the remaining three cavities (buncher, penultimate, and output) operate in the TE₀₂₁ mode, doubling the frequency of the input signal. The electron beam parameters are the following: current of 540 A, voltage of 460 kV, perpendicular-to-parallel velocity ratio of 1.5, and a parallel velocity spread of 6.4%. The output cavity has been simulated as (1) zero-drive unstable with Q-factor of 320 and (2) zero-drive stable with Q-factor of 250. The simulations show that the maximum efficiency in the first case is 37.4%, and in the second one is 34.4%. In both cases, a high gain of 60 dB at a 100-MW output power level can be realized