Matching Conditions of the RKA Input Cavity Based on the Cavity Absorbing Property Under Intense Beam Loading

Based on the equivalent circuit model, expressions for the power absorbed by an externally coupled input cavity of the relativistic klystron amplifier in both cold and hot cavities are derived. The matching conditions are clearly concluded from the expressions for the two cases. Under the guide of the matching conditions, the expressions are applied in the determination of the beam-loaded resonant frequency and the beam-loaded quality factor of the cavity loaded by the intense relativistic electron beam in a particle-in-cell simulation-aided approach presented in this paper.