The Design and Investigation of Compact 648 MHz/1.2 MW Klystron With Loading Meta-Material for CSNS-II

China spallation neutron source second phase upgrade (CSNS-II) will require 26 sets of 648 MHz/ 1.2 MW klystrons to be applied to superconducting linear accelerators. In order to further reduce the area occupied by the klystron power source system, this article proposes a structural design and detailed simulation of a meta-material loaded klystron, in order to lay the foundation for the subsequent manufacturing and application. Due to the loading of such meta-material, the electromagnetic parameters inside the resonant cavity have been enhanced, allowing for greater power generation over shorter distances. The 3-D PIC simulation results show that 1.2 MW can be generated at 648 MHz, with the voltage and current is 100 kV and 20 A. In addition, in order to further reduce the complexity of the system, a diode-type electron gun structure is designed to remove the use of high-voltage divider fuel tank. This new compact klystron can not only be used in large particle accelerators but also in high-end medical devices such as proton/neutron cancer treatment.