RF design of a 1.3 GHz 3-cell superconducting cavity for high-current beam acceleration

Abstract Superconducting radio-frequency (SRF) cavities are widely used in particle accelerator facilities. The SRF-based energy recovery linac (ERL) equipped with special SRF cavities offers feasibility for application in high-power free electron lasers (FELs). This study aims to design and optimize a 3-cell cavity that serves as the accelerating structure for a 10 mA class injector of high-brightness ERL-FEL. We apply the middle-cell shape of the mature TESLA cavity, and the end-groups are optimized for high-current beam operation. The cavity is designed with two fundamental power coupler (FPC) ports, which enable high-power input by two FPCs. In addition, the beam pipe is enlarged to damp potentially strong higher-order modes (HOMs) induced by the high current beams. A multi-objective genetic algorithm is utilized to optimize the cavity geometry. The damping of HOMs, multipacting, and mechanical issues are also investigated to verify the rationality of the cavity design.