3-D simulation of S-band wide-gap klystron amplifier output cavity

High frequency characteristics analysis is presented on a washer loaded wide-gap reentrant output cavity for the S-band relativistic wide-gap klystron amplifier(WKA). At resonant frequency points, the electric field modes of the wide-gap output cavity with large coupling hole are not TM011 anymore. To avoid these unwanted modes and their influences on cavity gap field distribution, a large enough distance between designed working frequency and resonant frequency is required. At the same time, an effort to reduce the output cavity external quality factor is also necessary. The output cavity power extraction effect was simulated by using a three-dimension fully electromagnetic particle-in-cell(PIC) code. At beam voltage of 600 kV, cathode current of 5 kA and current modulation dep