Liao, Y.C. Liu, X. Luo, R.Y. Qin, B. Wang, W. JACoW Publishing Geneva, Switzerland 978-3-95450-265-3 10.18429/JACoW-SAP2023-TUPB014 English 111-113 toolkit lattice simulation proton optics Contribution to a conference proceedings 2024 2024-11 https://doi.org/10.18429/JACoW-SAP2023-TUPB014 https://jacow.org/sap2023/papers/tupb014.pdf Superconducting (SC) gantry can be applied to proton therapy with significantly reduced footprint and weight. However, the relatively lower ramping limit of the SC magnetic field becomes a bottle-neck for fast energy change and beam delivery. The issue can be mitigated by designing a large momentum acceptance (LMA) beam optics. We present the design of an LMA gantry using AG-CCT SC magnets and symmetrical achromatic lattice. A fast degrader is combined in the design so that the gantry can rapidly switch energy during the treatment. The AG-CCT design process and beam transport simulation are all performed with our homemade integrated code CSPT, which has interfaces to Geant-4 and Opera, and can reach a maximum speed-up ratio of ~450 by applying parallel computation technique. The multi-particle simulation based on realistic field distribution proves that the gantry has a large momentum acceptance of ~20\%. Due to its large momentum acceptance, the dispersion effect caused by the scanning magnet is not neglectable. A dispersion compensation method, accompanied by a compact nozzle layout, is proposed to achieve a scanning field of 25×25 cm² with a maximum beam energy spread of 5.2\%.