Three dimensional analysis and simulation of input cavity for S-band relativistic klystron amplifier

In this paper, high frequency characteristics analysis on an input cavity of an S-band relativistic klystron amplifier is presented. The influence of large coupling hole on symmetry and uniformity of the electric field in the gap region is discussed and a bias design in the input cavity is used to reduce the influence. The field in the gap region are sensitive to the coupling hole size and when the coupling hole is closer to the axis, the field in the gap region is more asymmetric. A three-dimension fully electromagnetic particle-in-cell(PIC) code is used to simulate the fundamental harmonic modulated current while the electron beam is propagating the input cavity gap. The simulation results show that the amplitude of the fundamental harmonic modulated current is relative to the gap voltag