Design of an Ultra-high Vacuum System for the XiPAF Heavy-ion Synchrotron

During the operation of a heavy-ion synchrotron, an ultra-high vacuum is required to reduce the likelihood of collisions between beam particles and residual gas molecules, increasing the beam’s lifetime. The specific requirement is for the average vacuum in the pipeline to reach an ultra-high vacuum (~10–10 Pa) and for the vacuum throughout the pipeline to exceed the designed value. This study investigates the implementation method of an ultra-high vacuum system for a heavy-ion synchrotron. The vacuum level throughout the pipeline can be achieved even if the vacuum pumps are not distributed uniformly. The main technical approaches are to reduce the pipe material’s outgassing rate and increase the pumping speed of the vacuum pump units. The outgassing rate of the pipe material is reduced by plating a non-evaporable getter (NEG) film on the inner surface of the vacuum pipe and baking the pipe at high temperatures. The pumping speed is increased using a high-pumping-speed titanium sublimation pump (TSP). The vacuum level throughout the pipeline is improved through NEG plating. This method is applied in the vacuum system design of the heavy-ion synchrotron for the upgrade project at the Xi’an 200 MeV Proton Application Facility (XiPAF). The baking solutions include heating jacket baking and high-temperature baking in vacuum ovens. The purpose of vacuum pipe baking is to reduce the specific outgassing rate of the inner surface of the vacuum pipe. The heating jacket is mounted on the outer surface of the vacuum piping, the titanium sublimation pump housing, and the vacuum chamber. This setup activates the NEG film and removes surface gas from the piping without NEG film coating. The inside surface of the vacuum piping is coated with a NEG film, which has a suction rate of 0.5 L/(s·cm–2) There are 36 titanium sublimation pumps installed in the heavy-ion synchrotron. At the primary vacuum pipe connection sites, a single titanium sublimation pump provides an effective pumping rate of 2200 L/s for hydrogen gas. The Molflow+ software is applied to simulate the vacuum distribution inside the XiPAF heavy-ion synchrotron vacuum piping. Through design optimization, calculations indicated that both the average vacuum degree and the vacuum degree along the annular pipe are expected to exceed 5×10–10 Pa, which meets the physical design requirements of the synchrotron. © 2025 Sichuan University. All rights reserved.