The LHC Synchrotron-Light Monitors

Synchrotron-light telescopes will measure the profiles of the two LHC beams of protons or lead ions, and verify that the abort gap is clear. At collision energy (7 TeV), each telescope will image visible light from a superconducting dipole used to widen beam separation at the RF cavities. At injection (0.45 TeV), this source must be supplemented by a 2-period superconducting undulator 1m from the dipole. An optical “trombone” delay line will provide the large shift in focus. We discuss the optical design, diffraction, depth of field, and the expected signals over the energy ramp, for emission from the centre and edge of the dipole and from the undulator.