see file “pap_crab_cavity.pdf” for more details

Motivation In baseline consider 3.9GHz crab cavity similar to CKM cavity built at Fermilab In the earlier study, evaluated losses of synchrotron radiation photons on the crab cavity versus its aperture: http://www-project.slac.stanford.edu/lc/bdir/Meetings/beamdelivery/2005-09-27/index.htm This cavity has LOM coupler at 11mm from the axis – there were photon loss on coupler In that study, did not use additional masks to protect crab cavity (only standard masks were used, the closest ~35m upstream of the crab cavity) In today’s study, include additional mask in front of crab cavity to eliminate the SR photon losses

Details of the Low order modes coupler (from Leo Bellantoni)

Position of synchrotron radiation photons from beam halo at the MSK1 (left) for collimation system with aperture of SPEX 1×0.8 mm2, PCs at 3×3 mm2 and aperture of absorbers to 2×2 mm2 (Tab. 4). Photons position at the Crab Cavity mask (right). Radius of Crab Cavity is 0.5 mm bigger than radius of mask. There is no direct photon loss on the Crab Cavity itself in this case.

Position of synchrotron radiation photons from beam core at the MSK1 (left) for collimation system with aperture of SPEX to 1×0.8 mm2, PCs at 3×3 mm2 and aperture of absorbers to 2×2 mm2 (Tab. 4). Photons position at the Crab Cavity mask (right). Radius of Crab Cavity is 0.5 mm bigger than radius of mask. There is no direct photon loss on the Crab Cavity itself in this case.

Conclusion With additional mask in front of 3.9GHz crab cavity, SR photon losses on the cavity itself and on LOM coupler can be eliminated Positioning the coupler in vertical plane helps