Abstract: The power of the CSNS II accelerator beam is upgraded from 100 kW to 500 kW, requiring that the average beam power of the linear accelerator to be increased from 5 kW to 25 kW, and the pulsed beam current to be increased from 12.5 mA to greater than 40 mA. This inevitably leads to an increase in the pressure of the room-temperature cavities. The differential pumping system, as a crucial matching unit between the room-temperature and superconducting segments, can significantly reduce the pressure distribution in this range, and reduce the residual gas components at the end of the LEDP to effectively avoid the impact on the performance of the superconducting cavities from gas sources in the room-temperature cavities. Currently, the dynamic pressure at the end of the linear section (DTL cavity) is approximately 2.0×10^-6 Pa, while the low-energy differential pumping systems (LEDP) and high-energy differential pumping systems (HEDP) at the front and rear of CSNS II superconducting cavities, both require a dynamic pressure of ≤5.0×10^-8 Pa. This paper presented a systematic design of the vacuum systems for LEDP and HEDP, and simulation and experimental verification were carried out. The findings show that the experimental results are in basic agreement with the simulation results. The combination of ion pump and NEG pump can meet the vacuum requirements of LEDP and HEDP, and effectively reduce the residual gas composition at the end of LEDP.

Key words: LEDP, HEDP, Molflow simulation, experimental verification, RGA