3-D design of output cavity post for wide-gap klystron

An output cavity with double-rows of metal posts for a wide-gap klystron amplifier (WKA) is built and simulated using the three-dimension fully electromagnetic particle-in-cell (PIC) code and high frequency analysis software. The results show that both the first row and the second row of posts affect the high frequency characteristics of the output cavity, thus the double-rows of posts must be designed together with the output cavity, and the design purpose is to obtain proper external quality factor and gap electric field through controlling the posts scattering characteristic. Under the electric power of 2.9 GW and the electron beam modulation depth of 90%, a microwave power of 1.06 GW with an average power efficiency of about 36.5% is obtained at 3.6 GHz from an output cavity with double rows of posts designed according to the rules mentioned above.