The Shenzhen medium-energy high-repetition frequency X-ray Free Electron Laser (S3FEL) will become the first medium-energy X-ray free electron laser device operating at megahertz. We have designed a ferrite absorber for its 3.9GHz superconducting cavity. The coupling beam instability caused by the higher-order modes (HOMS) of the resonant cavity not only consumes RF power, increases the load on the cryogenic system, reduces the acceleration efficiency, but also causes beam instability, which can lead to beam break-up in severe cases. Therefore, the HOMS attenuation of the resonant cavity is an important issue. The HOMS absorber is an important component of a particle accelerator, and the attenuation of high-order modes is crucial to the performance of the accelerator. The material selection of absorbers is also crucial for attenuation effect. In this article, we designed a ferrite absorber for the S3FEL 3.9Hz TESLA superconducting cavity, which is placed at both ends of the beam tube. We evaluated the suppression characteristics of ferrite absorbers on HOMS and optimized the ferrite shape to determine the optimal ferrite size. Finally, on the basis of the above, the high-order mode suppression characteristics and high-order mode power losses of four 3.9GHz 9 unit cavities were calculated.

 

High-order Mode,3.9GHzTESLA Superconducting cavity,ferrite absorber