Upgrade of vacuum chamber at RCS beam injection area aimed at lower radiation and maintainability increase

Surround of the beam injection point in the J-PARC 3 GeV Rapid Cycling Synchrotron is the area where the residual radioactive dose is higher than other areas due to the beam scattering by the charge stripping foil. However, there is very little space to install radiation shields around the vacuum chamber in the beam injection point. Furthermore, the vacuum leak has often occurred due to the heat expansion of the chamber flange due to the induced current by the nearby pulse magnet. To solve such problems for minimizing the radiation exposure of maintenance workers, the vacuum chamber rin the beam injection point was newly designed. The space for the radiation shields was created by lengthening and the changing the cross-sectional shape. The titanium alloy with high mechanical strength was used for the flange material so that the flange was able to be fastened with higher tightening torque. (author)