Design studies of high-power, two-cavity, second harmonic gyroklystrons

At the University of Maryland, the authors have produced 24 MW, 9.87 GHz microwave pulses with 33% efficiency and 34 dB gain in two-cavity, TE01, fundamental mode gyroklystrons. The nominal parameters include a 430 kV, 160-200 A beam with an average perpendicular to parallel velocity ratio near α = 1. In an effort to obtain higher beam power and thus high microwave output, the authors are exploring the use of second harmonic amplifiers with fundamental bunching. In this paper they describe their designs for two different experiments. The first utilizes the current beam parameters and input cavity/driver with a 19.7 GHz TE02 output cavity. This cavity is close to cutoff and has adiabatic wall variations to minimize mode conversion. Initial simulations have predicted saturated efficiencies near 25%. They will present simulations of the small and large-signal performance, cold test results of the microwave circuit, and designs of the output waveguide. The authors also present designs and cold test data of an overmoded 19.7 GHz TE02 directional coupler and other microwave diagnostics. To more closely approach the requirements of future linear colliders, the second experiment's design goals include 100 MW of power at 11.424 GHz. The authors also present simulation results for a 500 kV, 600 A, α = 1.5 double anode magnetron injection gun. The resultant beam is designed to interact with circular electric modes in coaxial cavities. They will present initial designs of a TE01 coaxial 5.712 GHz input cavity and a TE02 coaxial second harmonic output cavity. Finally, they will discuss initial simulations of small and large-signal performance