DESIGN AND PERFORMANCE OF THE UPGRADED LHC SYNCHROTRON LIGHT MONITOR

The LHC is equipped with two synchrotron radiation systems, one per beam, used to measure the transverse bunch distributions. The light emitted by a superconduct- ing undulator and/or by a dipole magnet (depending on beam energy) is intercepted by an extraction mirror in vac- uum and sent through a viewport to the imaging Beam Syn- chrotron Radiation Telescope (BSRT). The first version of the telescope, used from 2009 to mid 2012, was based on spherical focusing mirrors in order to minimize chromatic aberrations. However, this required a very complicated de- lay line in order to switch the focus between the two dif- ferent light sources as a function of beam energy. A new system based on optical lenses was designed and installed in mid 2012 in order to simplify the optical line and thus reduce misalignment and focusing errors. The first results with LHC beam using this new system showed a signifi- cant reduction in the correction factor required to match the emittance as measured by wire scanners. This contribution discusses the performance of the new optical system, pre- senting the LHC results and comparing simulations with measurement performed in the laboratory using a BSRT replica.