Design studies on an s-band hybrid accelerating structure

Background In an electron linac, the standard bunching system is generally composed of a standing-wave (SW) pre-buncher (PB), a travelling-wave (TW) buncher and a standard TW accelerating structure. Purpose To keep the beam performance similar to the standard bunching system but reduce the cost as much as possible, the hybrid accelerating structure (HAS) was proposed by integrating the PB, the B and the accelerating structure together. Methods The RF design of the HAS was conducted by 2D code SUPERFISH, which is used to determine the dimensions of the SW and TW cells, and 3D code HFSS, which is used to optimize the input and output RF coupler cells. Results The on-axis electric field distribution simulated by HFSS can fully meet the dynamic requirement. The phase jump in SW section is 180 ^∘ while the phase advance in TW section is 120 ^∘ . Conclusion The RF design of the HAS is completed, and the engineering design of the prototype is being conducted.