Numerical simulations of coaxial output cavity of S-band relativistic klystron amplifier

The calculation of coaxial output cavities, simulation of microwave extraction from a modulated intense relativistic electron beams, optimization on beams and output cavity geometry parameters, as well as the experiments of microwave extraction for an S-band long-pulse-intense-current relativistic klystron amplifier are described in this paper. Applying a three dimensional code, an output power of 500 MW is obtained. The efficiency is about 21.5%. In experiments, a hollow electron beam of 550 kV, 4 kA generates an electron beam with modulated current of 3.2 kA after idler cavity gap. About 500 MW RF power is obtained. The efficiency is about 22.7%.The results of simulation agree well with the experimental results.