Vacuum Technologies in High-Power Proton Accelerators

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 magneticˆeld, and high radioactivation. In addition, it is necessary to promptly evacuate from the atmospheric pressure to ultra-high vacuum (UHV) and ensure su‹cient 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 fulˆlls 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 vacuumˆring. 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. 18 214-()-J. Vac. Soc. Jpn.

Evaluation of Vacuum Firing Effect on Stainless Steel from Vacuum and Surface Point of View

“…After the desorption of surface gas molecules 37 becomes sufficiently small by the long time evacuation or 38 baking, the pressure is considered to be dominated by the 39 desorbed molecules such as hydrogen, whose origin is the 40 atoms, which are dissolved in the bulk of the chamber mate-41 rial and diffused to the surface [1,2]. A vacuum firing, search [5,7,8]. The reduction of the gas desorption of the vacuum-fired materials in the thermal desorption spectra was also reported in the past [7−10].…”

Recent Status & Improvements of the RCS Vacuum System

“…The 3 GeV Rapid Cycling Synchrotron (RCS) in J-PARC aims to achieve the proton beam power of 1 MW, which corresponds to each cycle 8.3×10 13 protons accelerated up to 3 GeV at the repetition rate of 25 Hz. The design concept of the RCS vacuum system, the uniquely developed vacuum components, and the basic vacuum characteristics were reported in the previous articles [1,2]. The role of the vacuum system is obviously to maintain a sufficiently low pressure in the beam line to prevent the beam from being scattered by residual gas molecules; less than low 10 -6 Pa is required for the RCS beam line.…”