Development of a movable synchrotron-radiation mask for the Photon Factory Advanced Ring (PF-AR)

In order to protect 3.4-m-long rf cavities from impinging intense synchrotron radiation (SR), we developed a unique SR mask for use in the Photon Factory Advanced Ring (PF-AR). To obtain a wide aperture that is required for beam injection, we designed the mask so that the head of the mask can be moved over a horizontal range of 30 mm. To avoid the harmful excitation of resonance modes in this mask structure, a microwave absorber was built into it. Two of the designed masks were installed in the PF-AR, and they showed satisfactory performance during routine single-bunch operations under beam currents of up to 60 mA. We report the design of this movable mask and its performance during operations.