Design and Simulation of 1.2 MW Long Pulse Klystron for CSNS-II^*

A 1.2 MW long pulse klystron operating at 648 MHz has been designed and simulated for CSNS-II at Institute of High Energy Physics. In this paper, a triode thermionic electron gun with modulating anode has been designed. A beam current of 19.5 A is obtained at operating voltage of 97 kV with cathode current density of 0.5 A/cm ² . Then, the beam-wave interaction region that determines klystron characteristics has been designed and optimized. The full 3-dimensional particle-in-cell simulation of the whole klystron in CST indicates that the klystron efficiency is up to 67% using a second harmonic cavity. Finally, the microwave design of cavities for interaction section is described in detail. So far, the manufacturing of the klystron has been completed. The high-power test will be carried out in the first half of 2023.