Lattice design of the transport system for the bypass line in the storage ring based fully coherent light source

[Background]: The storage ring based coherent light source with the help of angular dispersion-induced microbunching (ADM) is introduced to obtain a high order harmonic radiation with a smaller energy modulation amplitude of electron beam. One design scheme of the storage ring based coherent light source is to kick the beam into a bypass line for energy modulation and energy demodulation, avoiding large impact on the storage ring. The electron beam in the storage ring is lead into the ADM modulation section by the beam transport line. The electron beam cancels most of the energy modulation through the demodulation section and returns to the storage ring passing through the beam transport line. [Purpose]: This study aims to design the lattice of the transport system for the bypass line in the storage ring based fully coherent light source. [Methods]: In this paper, the lattice of the beam transport line was designed, and the calculated beam optics satisfying the design requirements were described. Firstly, the geometric layout requirements were satisfied between the storage ring and the energy modulation section & energy demodulation section. Secondly, the beam optics functions were matched to ensure the high transport efficiency. Finally, the effect caused by the misalignment errors and magnet field errors were discussed. [Results]: Taking the dispersion introduced by the kicker and septum into account, the beam optics of the transport line is satisfied to the design requirements. Meanwhile, the orbit distortion caused by the misalignment errors and magnet field errors is reduced to approximately 4%~5% of that before correction within errors. [Conclusions]: Under the geometric layout condition, the beam optics of the transport system for the bypass line meet the specified design requirements. With considering of installation errors and magnet field errors, the orbit distortion after orbit correction can be limited in a small range, and the theoretical transport efficiency can reach 100%.