Experimental Assessment of Crystal Collimation at the Large Hadron Collider

The crystal collimation of hadron beams relies on the usage of highly pure bent crystals to deflect halo particles coherently and steer them onto optimised beam absorber blocks. This concept is being studied as a possible upgrade of the present multi-stage collimation system at the Large Hadron Collider (LHC) for its High Luminosity upgrade (HL-LHC). Crystals might allow improved cleaning performance, in particular for ion beams. This concept requires, however, a demonstration of feasibility with the LHC beam conditions before being considered for collimation upgrades. While significant results were produced in other circular accelerators, the specific challenges of the LHC call for dedicated experiments in final configuration and a direct comparison against the present collimation system. A crystal collimation setup consisting of two crystals for horizontal and vertical halo channeling, has been designed and installed in the LHC betatron cleaning insertion, and was operational for beam tests starting in 2015. Two other crystals were installed on the counter–rotating Beam 2 at the end of 2016. So, the LHC features now a complete system for crystal collimation measurements on both beams and planes. In this Ph.D. work, the validation of crystal collimation is addressed experimentally for the first time with LHC beams and operational conditions. The results of LHC beam tests are analysed and interpreted by using detailed simulation tools developed for crystal collimation studies. The work also includes analysis of experimental data of LHC–relevant crystal tests which have been carried out at the Super Proton Synchrotron (SPS) where a crystal test stand is operational.