Design of a 10-MW, 91.4-GHz frequency-doubling gyroklystron for advanced accelerator applications

A 10-MW, 91.4-GHz gyroklystron is under development for W-Band accelerator applications. The device is expected to generate 1-μs pulses at up to 120 Hz, with efficiencies near 38%, with a gain above 57 dB. A double-anode, magnetron injection gun operating at 500 kV will provide a 55-Ampere beam for interaction with a six-cavity circuit in a magnetic field of about 27.9 kG. The beam will have an average perpendicular-to-parallel velocity ratio of approximately 1.6 with a parallel velocity spread below 3.3%. The first two cavities will operate in the TE₀₁₁ mode at the drive frequency near 45.7 GHz, while the remaining cavities will operate in the TE₀₂₁ mode at twice the drive frequency. The output cavity will have smooth radial wall transitions to minimize mode conversion and pulse heating, the latter of which is shown via thermal modeling to be within acceptable limits. The output signal will be in a TE₀₁/TE₀₂ mode mixture for easier power handling and to facilitate possible depressed collector operation, which could result in wall plug efficiencies in excess of 50%. A complete description of the system design and modeling is presented