Abstract
For vacuum systems in high-power proton accelerators, compared with those in conventional particle accelerators, there are more challenging requirements in addition to their basic role owing to the existence of a large number of high-energy protons, rapid cycling of the magnetic field, and high radioactivation. In addition, it is necessary to promptly evacuate from the atmospheric pressure to ultra-high vacuum (UHV) and ensure sufficient pumping speed against an additional gas load because of the desorption of ion-induced molecules from the vacuum wall. The vacuum system of the 3 GeV Rapid Cycling Synchrotron (RCS) at the Japan Proton Accelerator Research Complex fulfills such unique requirements of high-power proton accelerators. Many vacuum devices such as turbo molecular pumps with radiation toughness, beam pipes made of alumina ceramics, and titanium beam pipes and bellows were developed in accordance with the design concept of the system. Treatments to minimize both static and dynamic outgassing were also performed, e.g., surface polishing, coating, and vacuum firing. With regard to the performance of the entire vacuum system, rapid evacuation from atmospheric pressure and assurance of UHV during beam operation have been achieved. Responding to the upgradation of the beam power, continuous improvements of the vacuum system have been performed, e.g., beam loss reduction by improving the beam line pressure, in-situ degassing of the kicker magnet, and magnetic shielding via beam pipes and bellows made of soft magnetic material. This report presents vacuum technologies typically used in high-power proton beam accelerators considering the design concept of the RCS vacuum system, developed components, vacuum performance, and recent upgrades.
