Investigation of collimator materials for the High Luminosity Large Hadron Collider

This PhD thesis work has been carried out at the European Organisation for Nuclear Research (CERN), Geneva, Switzerland), in the framework of the High Luminosity (HL) upgrade of the Large Hadron Collider (LHC). The HL-LHC upgrade will bring the accelerator beyond the nominal performance: it is planning to reach higher stored beam energy up to 700 MJ, through more intense proton beams. The present multi-stage LHC collimation system was designed to handle 360 MJ stored beam energy and withstand realistic losses only for this nominal beam. Therefore, the challenging HL-LHC beam parameters pose strong concerns for beam collimation, which call for important upgrades of the present system. The objective of this thesis is to provide solid basis for optimum choices of materials for the different collimators that will be upgraded for the baseline layout of the HL-LHC collimation system. To achieve this goal, material-related limitations of the present system are identified and novel advanced composite materials are selected as candidates for the new collimators. A series of experimental activities are performed to characterise the material properties, both in normal operation or in conditions of extreme exposure to beam losses, in particular high irradiation doses similar to what could be induced by high intensity LHC operation. The results provided important feedback to the material production. Numerical simulations are also carried out to evaluate the achievable performance of the HL-LHC collimation system with new collimator materials. To this purpose, dedicated simulation tools are developed and successfully benchmarked to adequately simulate the new HL-LHC collimation layout. By means of these tools, cleaning performance of the upgraded system are assessed in standard operation and beam failure scenarios. Simulation results are being used to refine the material requirements needed to achieve the HL-LHC beam parameters.