Study of the beam induced vacuum effects in the cryogenic beam vacuum chamber of the Future Circular Hadron Collider

The Future Circular Hadron Collider (FCC-hh) is a proposal for a 100 km long hadron collider conceived as the successor of the Large Hadron Collider (LHC). The FCC- hh is designed to reach 50 TeV of beam energy, greatly surpassing the current energy frontier set by the LHC at 7 TeV. Thus, it is expected to expand the current horizon of understanding of the Standard Model of particle physics. The beam vacuum chamber of the FCC-hh will have to cope with unprecedented levels of synchrotron radiation power for hadron colliders, around 160 times higher than its predecessor, dealing simultaneously with a tighter magnet aperture. Since the higher radiation power will result in a much higher gas load, the difficulty to achieve a good vacuum quality increases considerably compared with the LHC. This thesis presents a study of the so-called beam induced vacuum effects in the FCC-hh, meaning the different phenomena which, due to the presence of the particle beam, have a detrimental impact on the accelerator's vacuum level. These studied effects are the photon stimulated desorption (PSD), the electron stimulated desorption (ESD) and ion stimulated desorption (ISD). Each effect has been thoroughly studied, calculating analytically and with a series of Monte Carlo simulations the resulting gas density in the chamber for all the common gas species. Finally, the feasibility of the FCC-hh from the vacuum point of view has been assessed. To mitigate the beam induced effects and to improve the vacuum quality in the FCC-hh (essential for a proper machine operation) it was necessary to propose a new beam screen design. The new beam screen features new solutions to mitigate the e- cloud, to handle the synchrotron radiation and a much higher pumping speed, at the expense of a higher manufacturing complexity. A dedicated experimental setup was used by CERN during the design phase to measure the vacuum performance of the developed beam screen prototypes. Finally, the obtained experimental results were compared with the theoretical results to further enhance their validity. It is concluded that thanks to the new beam screen design, the vacuum level in the FCC-hh should be adequate. Using nominal beam parameters, the established FCC-hh vacuum specifications could be met within the first months of conditioning, a reason- able amount of time.